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Timing and coincidence circuitry for a time-sharing analog function generator Fiorentino, Joseph Samuel 1956

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TIMING AND COINCIDENCE CIRCUITRY FOR A TIME-SHARING ANALOG FUNCTION GENERATOR by Joseph Samuel F i o r e n t i n o B.A.Sc, U n i v e r s i t y of B r i t i s h Columbia, 1954 A t h e s i s submitted i n p a r t i a l f u l f i l m e n t of the requirements f o r the degree of Master of A p p l i e d Science i n the department of E l e c t r i c a l E n g i n e e r i n g We accept t h i s t h e s i s as conforming to the standard r e q u i r e d from candidates f o r the degree of Master of A p p l i e d Science. Members of the Department of E l e c t r i c a l E n g i n e e r i n g The U n i v e r s i t y of B r i t i s h Columbia A p r i l , 1956 Abstract This thesis i s concerned with the timing and coincidence c i r c u i t r y which controls the operation of a time-sharing function generator and four-quadrant analog m u l t i p l i e r . The functions to be generated are fed into the computer i n time sequence as v o l t -age waveforms of short duration, A waveform i s sampled at a p a r t i c u l a r value of the independent variable x and the resulting ordinate Ef i s normalized with respect to the maximum function ordinate Ej^ and multiplied by a reference voltage E r . The out-put of the m u l t i p l i e r i s then a voltage which represents the expression EfE r/E^ and t h i s voltage i s channeled through the computer. M u l t i p l i c a t i o n i s performed by the following method. Two voltages Ej and E 2 are simultaneously applied to two ident-i c a l l inear networks whose response to unit voltage i s N ( t ) . The outputs are then E^N(t) and Er>N(t). If, on comparing E^N(t) with a reference voltage E3, the second sweep E2N(t) i s clamped at the instant of equality, then N(t) = EQ/E^ and the output i s E = E 2N(t) = E ^ / E ^ The present proposal i s to generate the functions opt-i c a l l y . A function i s graphed, photographed on 35 millimeter f i l m , and mounted on the rim of a rotating d i s c . The o p t i c a l system projects a narrow segment of the function onto a photo-tube and i t s output, biased for the zero l e v e l , follows the function ordinate i n a s t r i c t voltage analog sense. The f u l l abscissa scale i s represented by a constant voltage and the i n -put specifying the sampling point i s some f r a c t i o n of t h i s f u l l -scale voltage. In order that the sampling point x be independent of the v e l o c i t y of the scanning disc the coincidence c i r c u i t r y eliminates v e l o c i t y as a variable i n the selection of x. I l l u s t r a t i o n s F i g . Page 1. C a l i b r a t i o n and f u n c t i o n frames on scanning d i s c . TO fOllOW e « o e « . o. 0 . . « « o « t t o « o « « . . 9 « o . o » . o . « o . . « 5 2. Symbols f o r computer u n i t s . To f o l l o w ....... 7 3. O p e r a t i o n a l A m p l i f i e r with negative feedback o o . o . e o o , . o o o o » . e . . . o e o . « « o . o . » « . 9 4. Negative feedback obtained by an adding network i n the g r i d c i r c u i t <> .. • 10 5. P r i n c i p l e of the Holding C i r c u i t .................. 13 6. B i d i r e c t i o n a l Holding C i r c u i t 14 7. Block diagram of the Holding C i r c u i t 15 8. Timing C i r c u i t s . To f o l l o w .... .. 17 9. Schematic of the M u l t i p l i e r 20 10. Sweep and Coincidence C i r c u i t s , To f o l l o w 21 11. Method f o r o b t a i n i n g two i d e n t i c a l sweeps ......... 25 12. F u n c t i o n Generator and M u l t i p l i e r Assembly. T O fOllOW e o o o « 9 « « « « « e e » e o o « o o o o o o « e o a o o « « « « o o 26 13. Counter and Fu n c t i o n Storage. To xollow 30 14. Diode Gate. T O follOW a o o e o o » o » o o e a « o e o e o o o o e o o « e o o o s ( » e « « o 32 15. Discharge of a condenser through a diode gate ..... 33 16. F l i p - F l o p . TO follOW O 9 o o « e e * o o o o o « » » o o 9 a « * e o o e 0 » o o o a « o a o 34 17. Delay F l i p - F l o p DFF1. T O follOW o o « « o « * 9 o e « o o o o o o a o O 0 « o o o o e a 0 « » « e o o 9 36 18. Delay F l i p - F l o p s DFF2a and DFF2b. T O follOW o » o o o o o « o o o o e o e o e o o o o D O o a o » o o o D O O 0 o o 37 19. Holding C i r c u i t . T O follOW o » o o o « e o e o 0 t o o e « o o o 0 O Q « o c e « « Q o a e o o o o 33 20. Schematic Holding C i r c u i t f o r s t a b i l i t y a n a l y s i s 9 « o o , a o o . o . « o o o . . . « o s o o o o o o o ° ° ° ° 40 21. I n v e r t e r f o r determining G ........................ 41 22. Measured frequency response and c a l c u l a t e d open-loop gain of the P h i l b r i c k and Storage A m p l i f i e r s . j?0 f o i l O W o o A o a o a o c o a o o o v e a o o o o a o o o e e a v a o a o o o a 41 i v I l l u s t r a t i o n s (cont'd,) P i g . Page 23. Pulse A m p l i f i e r . TO follOW o o e o « e o o e e « o o 0 « o « o « « « o « « e O 0 « o o o 0 » o f i o o 43 24. Comparator TO follOW • 0 0 0 9 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 46 25. B a s i c Phantastron and i t s waveforms 47 26. Blanking Phantastron. TO follOW g o o o o o o o o o o o o b o o e o o o o o o o a o o o o o o o o o o o o 48 27. P r e c i s i o n t e s t of the Phantastron. v s . 6t. TO follOW © o o o o o o o o o o o o o o o o o o o o o o o o o * • o o o o o o o o o 49 28. Test waveforms o c c u r r i n g i n the timing and coincidence c i r c u i t r y . TO follOW • o • o e o o « o o © o o o o o o ^ o o o o o o o c o o t o o o o o o o o 51 - Models K2-W and K2-X O p e r a t i o n a l A m p l i f i e r s . TO follOW o e o o e o o o e o e o o o e e e o o o o o o o o o o o o o o o o o o o o 55 v Contents Page Ab S t r& C t • • e o . . o . . . » . . . . . o o . . . . o o o . « o o . . . e « o o . « . . o XX XntZ*OCLU.CtiOn o o . . . o . o o . . . . o . o o . o . o o . . . o . . o . e o . o o o . 1 D e s c r i p t i o n of the F u n c t i o n G e n e r a t o r and M u l t i p l i e r . 0 0 0 . 0 0 0 0 0 0 0 0 . . 0 0 . 0 0 . 0 0 0 0 5 Requirements of t h e Timing and C o i n c i d e n c e C i r c u i t r y 7 Ge n e r a l D e s c r i p t i o n of t h e Components ......... 9 O p e r a t i o n a l A m p l i f i e r . o . o . . . . . . . . o . e . . . o o e o . 9 Dxode Gate . o o . . . . . « o o o . . . o . . . . o . . o o . . o . . . . o o 11 F l i p - F l o p and Delay F l i p - F l o p 12 Comparator . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 . 0 . . . . 12 H o l d i n g C i r c u i t . o o . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Pu l s e A m p l i f i e r . • • • o . . . ' . . . . . . . . . . . . • • « . . . . . . 15 B l a n k i n g P h a n t a s t r o n . . . . . . o . . . . . . . . . . 16 Timing C i r c u i t r y .........................oooooooo 17 Co i n c i d e n c e C i r c u i t r y . . o . o o o . . . 20 Timing of the F u n c t i o n G e n e r a t o r ................. 26 Storage C i r c u i t s and Counter 30 C i r c u i t D e t a i l s •..«*....>.«•«.*«....«>>..««*.*.•• 32 Diode Gate 00000.000.. . . o . 0 0 0 0 . . o . . . 0 0 0 32 F l i p — F l o p .................................... 34 Delay F l i p — F l o p . . . . . . . . . . o . o . . « o o . o o o . . o « . o . 36 Ho l d i n g C i r c u i t o o . . . . o o . . o o . e . . 0 0 0 0 . 0 0 . 0 0 0 0 0 38 Pu1se A m p l i f i e r o o o o o o o . . . . o o . . o o o o . . . . . o o o . o 43 Comparator o o o * . . o o o o o o o o . o . o e o o o o o o o o o o o . 0 0 0 46 B l a n k i n g Phant Testing the Timing and Coincidence C i r c u i t r y ooo©oooooooo©©©oeo*©©©o©o.oo 51 Reill£l .]?]£S ©©©©©©©©©©©•••oo©e©oo©©©o*©©©©o©o©*ooooooo 52 .References ©©•©©©©•©©•••o©©©©© ©A© ••••©•©©••©©oo©©©© 54 AppendXX o©ooo©©o©©o©©©©©©«©»©oooooeo»«oeoo©»o©ooo 55 S p e c i f i c a t i o n s f o r the P h i l b r i c k O p e r a t i o n a l A m p l i f i e r s o . . o . . . . . o o o 55 i i i Acknowledgement The work described i n t h i s t h e s i s i s part of a l a r g e r p r o j e c t sponsored by the Defence Research Board, Department of N a t i o n a l Defence, Canada, under Grant Number DRB C-9931-02(550-GC). Acknowledgement i s g r a t e f u l l y given to Dr. E. V. Bohn, under whose guidance t h i s work was performed, and to Dr. F. Noakes, grantee of the p r o j e c t . The author i s indebted to the N a t i o n a l Research Council of Canada f o r the as s i s t a n c e received through a post-graduate bursary granted i n 1954. v i TIMING AND COINCIDENCE CIRCUITRY FOR A TIME-SHARING ANALOG FUNCTION GENERATOR I n t r o d u c t i o n There i s an i n c r e a s i n g trend i n re s e a r c h e s t a b l i s h -ments and i n d u s t r y to solve problems u s i n g analog computers. As the name i m p l i e s such a machine i s a model of the p h y s i c a l system i n qu e s t i o n ( l l ) . Each b u i l d i n g block of an analog contains e l e c t r i c a l or el e c t r o - m e c h a n i c a l d e v i c e s designed to perform a c e r t a i n mathematical o p e r a t i o n o r t o generate a f u n c t i o n a l r e l a t i o n s h i p between two computer v a r i a b l e s . The in p u t s and outputs of these b l o c k s are measureable v o l t a g e s , s h a f t r o t a t i o n s or d i s t a n c e s . These q u a n t i t i e s correspond to the parameters i n the problem as a consequence of the mathe-m a t i c a l analogy which e x i s t s between the system performance and the computer performance 0 The s o l u t i o n , or any parameter, becomes d i r e c t l y observable i f i t s corresponding computer v a r i a b l e i s d i s p l a y e d on an o s c i l l o s c o p e or graphed by a re c o r d e r . E x i s t i n g analog computers completely formulate a problem with a set of c o n t i n u o u s l y o p e r a t i n g b l o c k s which are in t e r c o n n e c t e d by feedback loo p s . Thus, a l l measureable q u a n t i t i e s are a v a i l a b l e at any time. With such an arrange-ment i d e n t i c a l but independent operations must be performed simultaneously by the d u p l i c a t i o n of computing b l o c k s . In 2 comparison, d i g i t a l computers are t i m e - s e q u e n t i a l systems which compute a l l parameters f o r a d i s c r e t e value of the independent v a r i a b l e . The necessary operations are per-formed i n time sequence through one o p e r a t i o n a l u n i t . One i s u l t i m a t e l y l e d to conceive a computer i n c o r p o r a t i n g d e s i r e a b l e p r o p e r t i e s of both systems (12); namely, the ti m e - s e q u e n t i a l o p e r a t i o n of d i g i t a l computers which when a p p l i e d to analogs minimizes the c i r c u i t r y , and the analog approach to a problem which f a c i l i t a t e s i t s i n t e r p r e t a t i o n . The advantage of t i m e - s e q u e n t i a l o p e r a t i o n or time-s h a r i n g i s apparent when the computer i s s o l v i n g a set of simultaneous d i f f e r e n t i a l equations. Such a set might be the f l i g h t equations of an a i r c r a f t (7, p. 81). Here the computer must generate the c o e f f i c i e n t s of the d e r i v a t i v e terms where these c o e f f i c i e n t s , i n g e n e r a l , are. f u n c t i o n s of the independent computer v a r i a b l e . E x i s t i n g analogs generate each f u n c t i o n by a c o s t l y device such as the cathode-ray photoformer (7, p. 248) or the s e r v o - d r i v e n f u n c t i o n potentiometer (7, p. 251). Another method approximates a waveform by a s e r i e s of s t r a i g h t - l i n e or c u r v e d - l i n e segments us i n g a network of r e s i s t a n c e s and diodes ( l , p. 315). On the other hand, a computer designed on a t i m e - s e q u e n t i a l p r i n c i p l e can generate a l l the r e q u i r e d f u n c t i o n s w i t h the same b a s i c c i r c u i t . Time-sharing i s f u r t h e r a p p r e c i a t e d when an analog i s used f o r t r a i n i n g men i n s p e c i a l i z e d f i e l d s such as instrument f l y i n g and a e r i a l gunnery. In t h i s c a p a c i t y the inp u t s to the computer are manual d e f l e c t i o n s of d i a l s and c o n t r o l s . The r e s u l t i n g computer v a r i a b l e s ( u s u a l l y v o l t a g e s ) vary as the corresponding system parameters would i n a c t u a l o p e r a t i o n . Such s i m u l a t i o n under manual command r e q u i r e s " r e a l - t i m e " computing speeds and prolonged o p e r a t i o n Because the volt a g e outputs of d-c, i n t e g r a t o r s tend to d r i f t over long p e r i o d s of time these components are not used i n standard analogs intended f o r r e a l - t i m e s i m u l a t i o n . Instead i n t e g r a t i o n i s performed e l e c t r o - m e c h a n i c a l l y ( 5 ) , However, the r e l a t i v e accuracy, low co s t and f l e x i b i l i t y of d-c. components make these p r e f e r a b l e to the ele c t r o - m e c h a n i c a l d e v i c e s . F o r t u n a t e l y , the a f f e c t s of volt a g e d r i f t can be el i m i n a t e d i n time-sharing computers by automatic c a l i b r a t i o n hence, d-c, i n t e g r a t o r s can be used f o r r e a l - t i m e computation The analog computer now being developed i n the e l e c t r i c a l engineering department of the U n i v e r s i t y of B r i t i s Columbia has been designed on a time-sharing p r i n c i p l e . When completed i t w i l l have two d e s i r e a b l e f e a t u r e s . 1. The f u n c t i o n generator and m u l t i p l i e r w i l l accomodate a lar g e number of f u n c t i o n s . The f u n c t i o n sampling and m u l t i p l i c a t i o n processes occur i n one o p e r a t i o n and the f u n c t i o n s need be represented only by a vo l t a g e waveform of short d u r a t i o n . 2. A long i n t e g r a t i o n time w i l l be r e a l i z e d u sing d-c. i n t e g r a t o r s and a magnetic drum memory. This t h e s i s i s concerned with the timing and c o i n -cidence c i r c u i t r y of the f u n c t i o n generator and m u l t i p l i e r . D e t a i l s apart from the timing c i r c u i t r y appear i n a separate t h e s i s by B. P. Hildebrand (6); however, the author w i l l 4 borrow from t h i s work i n the i n t e r e s t of completeness. The i n t e g r a t o r w i l l be the su b j e c t of succeeding M. A. Sc, theses. To s i m p l i f y i n i t i a l design the prototype computer w i l l be r e l a t i v e l y "slow", hence the response time of v a r i o u s e l e c t r o n i c components w i l l not be c r i t i c a l . I t i s hoped t h a t t h i s machine w i l l s olve complex problems with a p r e c i s i o n of one or two per cent. 5 D e s c r i p t i o n of the Function Generator and M u l t i p l i e r A f u n c t i o n to be generated i s graphed on b l a c k paper which i s cut along the f u n c t i o n o u t l i n e and superimposed on p l a i n white paper. Thus, the area above the f u n c t i o n i s black and t h a t below i s white. The f u n c t i o n i s then photographed on 35 mm. f i l m and mounted on a s l i d e . Care i s taken to guarantee t h a t the absolute maxima of a l l f u n c t i o n s — — w i t h i n the ranges of i n t e r e s t of the independent v a r i a b l e s — h a v e equal height on the f i l m s . A l s o , the zero l e v e l of a l l f u n c t i o n s must be e q u i d i s t a n t from the lower f i l m boundary. F i g u r e 1 i l l u s t r a t e s a t y p i c a l f u n c t i o n as i t appears on the f i l m together with the c a l i b r a t i o n frame which w i l l be r e f e r r e d to l a t e r . A t r a n s i t i o n r e g i o n b precedes each f u n c t i o n to permit t r a n s i e n t decay i n the c i r c u i t r y . Each s l i d e r e p r e s e n t i n g a f u n c t i o n i s mounted i n a frame which i n t u r n i s f a s t e n e d to a r o t a t i n g d i s c . The number of f u n c t i o n s which the computer can handle thus depends i n p a r t upon the circumference of t h i s d i s c . The prototype computer accomodates 18. As the d i s c r o t a t e s , a f i x e d o p t i c a l system p r o j e c t s a narrow segment of the f i l m on to a photo-tube and scans each f u n c t i o n s u c c e s s i v e l y . Consequently, the output of the photo-tube i s a c o n t i n u o u s l y v a r y i n g p o s i t i v e v o l t a g e r e p r e s e n t i n g the " o r d i n a t e " of a l l f u n c t i o n s i n a t i m e - s e q u e n t i a l manner. This output i s f e d i n t o a d-c. a m p l i f i e r which i s b i a s e d by a v o l t a g e E m equal to the zero l e v e l d e f i n e d by the c a l i b r a t i o n frame. Thus, the p o s i t i v e r and negative excursions of the a m p l i f i e r output represent the P5 P6 P7 P8 P9 - m a r k e r p u l s e = t r i g g e r p u l s e s f r o m f u n c t i o n f r a m e s - d e l a y e d p u l s e d e r i v e d f r o m P I - c o m p a r a t o r p u l s e f r o m c o i n c i d e n c e c i r c u i t r y - s a m p l i n g p u l s e f r o m c o i n c i d e n c e c i r c u i t r y - c o m p a r a t o r p u l s e f r o m m u l t i p l i e r - d e l a y e d p u l s e d e r i v e d f r o m P8 F i g . 1 . C a l i b r a t i o n a n d f u n c t i o n f r a m e s o n s c a n n i n g d i s c . 6 graphed f u n c t i o n s i n a true v o l t a g e analog sense. By means of the timing and coincidence c i r c u i t r y (the subject of t h i s paper) each f u n c t i o n i s s u c c e s s i v e l y sampled at a p a r t i c u l a r value of the a b s c i s s a x, In p r a c t i c e , the f u l l a b s c i s s a s c a l e i s represented by 50 v o l t s and the i n p u t voltage s p e c i f y i n g th© sampling p o i n t i s some f r a c t i o n of the f u l l - s c a l e v o l t a g e . T h i s input voltage v a r i e s slowly r e l a t i v e to the scanning r a t e ; hence, i s considered constant over one r e v o l u t i o n of the d i s c . Immediately a f t e r sampling, the v o l t a g e Ef r e p r e s e n t -i n g a f u n c t i o n o r d i n a t e i s normalized with r e s p e c t to the maximum ordi n a t e v o l t a g e E ^ , then m u l t i p l i e d by a r e f e r e n c e v o l t a g e E r whose value i s d i c t a t e d by the computer programme and the l i m i t a t i o n s of the c i r c u i t r y . Thus, the output of the m u l t i p l i e r i s a v o l t a g e E f E r / E M whose s i g n i s t h a t of the product E f E r (E^ i s always p o s i t i v e ) . I f there are N f u n c t i o n s on the d i s c there w i l l be N such v o l t a g e s during each rev-o l u t i o n , and each vo l t a g e i s channeled to a storage u n i t where i t i s a v a i l a b l e f o r f u r t h e r o p e r a t i o n s . A l l v o l t a g e s c o r r e -sponding to the same f u n c t i o n frame go to on© storage u n i t . I t should be emphasized t h a t i f the o p t i c a l system d e s c r i b e d does not provide s u f f i c i e n t r e s o l u t i o n f o r engineer-i n g accuracy then the m u l t i p l i e r c i r c u i t r y i s not o b s o l e t e . The only requirement of the m u l t i p l i e r i s t h a t the f u n c t i o n be represented by a voltage waveform. Th© o p t i c a l method of gen e r a t i o n i s c e r t a i n l y the simplest but not the most p r e c i s e . 7 Requirements of the Timing and Coincidence C i r c u i t r y The operations of the t i m i n g and c o i n c i d e n c e c i r c u i t r y d i v i d e i n t o two main c a t e g o r i e s : the t r i g g e r i n g of the sampling c i r c u i t s at the d e s i r e d a b s c i s s a value, and the t i m i n g of the f o l l o w i n g m u l t i p l i e r o p e r a t i o n s ; b i a s i n g , n o r m a l i z a t i o n , m u l t i p l i c a t i o n and s i g n determination. Basic to these o p e r a t i o n s i s the c a l i b r a t i o n frame i l l u s t r a t e d i n F i g . 1. When t h i s frame i s scanned t r i g g e r pulses PI and P3 occur r e s p e c t i v e l y a t the beginning of the frame and a t the d i s c o n t i n u i t y . A l s o , a pulse P5 marks the beginning of each f u n c t i o n frame. The remaining pulses P2, P4, P6, P7, P8 and P9 are d e r i v e d w i t h i n the t i m i n g and m u l t i p l i e r c i r c u i t r y . Pulse P6 i s s i g n i f i c a n t i n t h a t i t t r i g g e r s the sampling c i r c u i t s a t the a b s c i s s a (b + x) where b i s the t r a n s i t i o n r e g i o n preceding the f u n c t i o n . The v o l t a g e E m f i x e s the zero l e v e l and E^ i s the n o r m a l i z -a t i o n v o l t a g e . The problem of sampling each f u n c t i o n at a d i s c r e t e a b s c i s s a value r e q u i r e s s p e c i a l treatment. As a l r e a d y p o i n t e d out the a b s c i s s a Is represented by a v o l t a g e which i s p r o p o r t i o n a l to (b + x ) ; but, how can a g i v e n v o l t a g e r e p r e s e n t the same a b s c i s s a f o r d i f f e r e n t scanning r a t e s ? I f one c o u l d guarantee a constant d i s c speed the problem would become t r i v i a l , but even a s l i g h t v a r i a t i o n i n l i n e v o l t a g e would change the speed of the d i s c s u f f i c i e n t l y to d e s t r o y any attempt to o b t a i n the r e q u i r e d p r e c i s i o n . The d i s t a n c e a, f i x e d i n time by the i n t e r v a l between the pulses P h i l b r i c k o p e r a t i o n a l d-Co a m p l i f i e r F l i p - F l o p Triode Gate P h i l b r i c k o p e r a t i o n a l d-c. a m p l i f i e r Delay F l i p - P l o p C - conducting N - non-conducting *~ Diode Gate I n v e r t e r Blanking Phantastron CF Cathode f o l l o w e r M u l t i a r Comparator In t e g r a t o r Pulse A m p l i f i e r Storage u n i t F i g . 2. Symbols f o r computer u n i t s . 8 PI and P3, i s used by the coincidence c i r c u i t r y to e l i m i n a t e d i s c v e l o c i t y v as a v a r i a b l e i n the s e l e c t i o n of the sampling p o i n t (b + x ) . The pulse c i r c u i t r y i s designed on the b a s i s of an average scanning time of two m i l l i s e c o n d s per f u n c t i o n frame and roughly the same time i n t e r v a l between succeeding frames. This c i r c u i t r y comprises a number of gates, f l i p - f l o p s , o p e r a t i o n a l a m p l i f i e r s , e t c . , whose assigned symbols are i l l u s t r a t e d i n F i g . 2. The c i r c u i t diagrams and s p e c i f i c a -t i o n s of the P h i l b r i c k o p e r a t i o n a l a m p l i f i e r s are i n c l u d e d i n the appendix. In keeping with t h e i r p l u g - i n design most c i r c u i t s represented i n F i g . 2 are c o n s t r u c t e d on small c h a s s i s which are plugged i n t o t h e i r assigned p o s i t i o n s on a master c h a s s i s . Sine® the l i n e a r o p e r a t i n g rang© of the P h i l b r i c k a m p l i f i e r s (model K2-W) i s from -50 to +50 v o l t s t h i s working rang© has been adopted as standard wherever a p p l i c a b l e . 9 G e n e r a l D e s c r i p t i o n o f t h o C o m p o n e n t s To f a c i l i t a t e u n d e r s t a n d i n g o f t h e o v e r a l l c i r c u i t o p e r a t i o n s a n d t h e d e s i g n p r o b l e m s e n c o u n t e r e d , a g e n e r a l d e s c r i p t i o n o f t h e c o m p o n e n t s i s p r e s e n t e d p r i o r t o e l a b o r -a t i o n o n t h e c i r c u i t d e t a i l s . O p e r a t i o n a l A m p l i f i e r H i g h g a i n d - c . a m p l i f i e r s w i t h n e g a t i v e f e e d b a c k a r e e x t e n s i v e l y e m p l o y e d i n o p e r a t i o n a l b l o c k s t o p r o v i d e g o o d l i n e a r i t y a n d t o m a t c h i m p e d a n c e s ( a w a v e f o r m f r o m a h i g h i m p e d a n c e s o u r c e i s f r e q u e n t l y r e q u i r e d t o s u p p l y a l o a d ) . T h e s a l i e n t p r o p e r t i e s w h i c h w a r r a n t t h e i r u s e a r e n o t e d h e r ® . I n F i g . 3 t h e o p e n - l o o p g a i n o f t h e o p e r a t i o n a l a m p l i f i e r i s A a n d t h e f r a c t i o n o f t h e o u t p u t v o l t a g e w h i c h i s s u b t r a c t e d f r o m t h e i n p u t v o l t a g e i s 8. The c l o s e d - l o o p g a i n i s o o A e >•»• E„ F i g . 3. O p e r a t i o n a l A m p -l i f i e r w i t h n e g a t i v e f e e d b a c k . G = Jo E i a n d i f 1 i s s u f f i c i e n t l y l a r g e a n d A8 much g r e a t e r t h a n u n i t y C o n s e q u e n t l y , t h e g a i n i s e s s e n t i a l l y i n d e p e n d e n t o f th© a m p l i f i e r p r o p e r t i e s a n d i s d e t e r m i n e d b y t h e p a s s i v e e l e m e n t s w h i c h d e t e r m i n e 8, 1 0 I t i s e a s i l y shown t h a t the output impedance of t h i s a m p l i f i e r can be made very s m a l l . Let Z be the output impedance of the open-loop a m p l i f i e r , then the a m p l i f i e r w i l l d e l i v e r A/Z amp. per input v o l t i n t o a short c i r c u i t across the output. I f u n i t voltage i s now a p p l i e d to the output of the c l o s e d - l o o p c i r c u i t by an e x t e r n a l source, the cu r r e n t I drawn from t h i s source i s equal to the c u r r e n t through Z plus the c u r r e n t s u p p l i e d by the a m p l i f i e r on being d r i v e n by the feedback voltage B. That i s , T i M 1 - A3 1 " z ~ z = z Thus, th© e f f e c t i v e output impedance i s Z / ( l - A£) and t h i s can be made small i f AB i s l a r g e . With a small output imped-ance the a m p l i f i e r a c t s as a constant v o l t a g e source. F r e q u e n t l y negative feedback i s obtained by an adding network i n the g r i d c i r c u i t ( F i g . 4). When the oper-a t i o n a l a m p l i f i e r i s ~\ u t i l i s e d t h i s way i t i s convenient to con-- o s i d e r i t s g a m and input impedance i n f i n -F i g . 4. Negative feedback obtained Because of f e e d -by an adding network i n the g r i d c i r c u i t . b a c k t h e g r i d v o i t a g © «g of the a m p l i f i e r i s h e l d v i r t u a l l y a t zero and the c u r r e n t through th© input impedance Z^ i s equal to the c u r r e n t through the loop impedance Z. That i s , 11 and E o = ~ f i E i I f Z = R and Z^ = R^  a phase i n v e r s i o n i s obtained and th© output i s a low impedance source s a t i s f y i n g E o = ~ J ^ i On the other hand, i f Z = l/pC and Zi = R± T? _ _1_ E i d t and the c i r c u i t a c t s as an i n t e g r a t o r . Two inputs are a v a i l a b l e with the o p e r a t i o n a l a m p l i f i e r s employed i n t h i s computer. I f phase i n v e r s i o n i s r e q u i r e d ( f o r negative feedback) one input i s used, i f no i n v e r s i o n i s r e q u i r e d the other i s used. The remaining i n p u t i s b i a s e d to provide zero output f o r zero i n p u t . Diods Gate A v o l t a g e s i g n a l i s e i t h e r passed or blocked by the diode gat© depending upon the p o l a r i t y of two c o n t r o l l i n g v o l t a g e s . In the conducting s t a t e one c o n t r o l v o l t a g e i s +60 v o l t s and the other i s -60 v o l t s , and i n the non-conduct-i n g s t a t e the p o l a r i t i e s are reversed. The gate i s a bridge type c o n t a i n i n g three double diodes and i s capable of a c c u r a t e l y passing a maximum of +50 or -50 v o l t s . This range i s determined by the magnitude of the c o n t r o l l i n g v o l t a g e s . 12 F l i p - F l o p and Delay F l i p - F l o p A b i s t a b l e m u l t i v i b r a t o r (denoted as a f l i p - f l o p i n t h i s t e x t ) i s used to generate a step f u n c t i o n . In t h i s a p p l i c a t i o n i t has two inputs which accept only negative t r i g g e r i n g v o l t a g e s and two outputs d e l i v e r i n g +60 and -60 v o l t s i n one s t a t e and -60 and +60 v o l t s r e s p e c t i v e l y i n th© other s t a t e . These output v o l t a g e s c o n t r o l the diode gates. A negative t r i g g e r i n g v o l t a g e a p p l i e d to a p a r t i c u l a r i nput w i l l always fore© th© c i r c u i t i n t o th® sam© s t a t e . I f th© c i r c u i t i s already i n t h i s s t a t e , t h i s and succeeding t r i g g e r s have no e f f e c t . Of course, th© other input i s a s s o c i a t e d with the opposite s t a t e . Th© monbstabl© m u l t i v i b r a t o r (delay f l i p - f l o p ) has only on© s t a b l e s t a t e and on© t r i g g e r i n p u t . In response to a negative t r i g g e r pulse the vol t a g e l©v@ls are f l i p p e d over i n t o an unstabl© s t a t e whoso d u r a t i o n i s f i x e d by the time constant of th© c i r c u i t . Here, a l s o , two outputs ar© provided, d e l i v e r i n g +60 or -60 v o l t s as d e s c r i b e d i n th© preceding paragraph. Comparator Th© two inputs to the comparator are a sweep voltag© waveform and a constant r e f e r e n c e v o l t a g e . At the i n s t a n t the sweep voltag© a t t a i n s ©quality with the r e f e r e n c e voltag© th© comparator generates a large negative pulse of very short d u r a t i o n . This pulse i s used to s t a r t c e r t a i n o p e r a t i o n s . In t h i s c i r c u i t th© referen c e v o l t a g e i s negative, henc© the sweep must a l s o b© neg a t i v e . 13 Holding C i r c u i t In order to store v o l t a g e s during on© r e v o l u t i o n of th© scanning d i s c a c i r c u i t was developed whose p r i n c i p l e of o p e r a t i o n i s i l l u s t r a t e d i n F i g . 5. When a step v o l t a g e -E F i g . 5 . P r i n c i p l e of the Holding C i r c u i t . i s a p p l i e d to the input the g r i d of the f i r s t a m p l i f i e r A-^  goes ne g a t i v e . Since there i s no phase i n v e r s i o n through t h i s a m p l i f i e r i t s output i s a l s o negative; consequently, th© diode conducts and a c u r r e n t i flows i n the i n d i c a t e d d i r e c t i o n . Because of the hig h g a i n of the second a m p l i f i e r &2 and th© negative feedback through C, th© input g r i d of t h i s a m p l i f i e r i s he l d at zero. To o f f s e t the tendency f o r t h i s input to go negative as c u r r e n t i s drawn out of C, the second a m p l i f i e r feeds an i d e n t i c a l c u r r e n t i i n t o th© opposite s i d e of th© condenser to b u i l d up a b a l a n c i n g pos-i t i v e charge. This o p e r a t i o n continues u n t i l the output of A2 reaches +E. At t h i s p o i n t th® i n p u t to A^ becomes zero du© to the equal voltage drops across the two i d e n t i c a l g r i d r e s i s t o r s B. Any tendency f o r the output to exceed +E imposes a p o s i t i v e d r i v i n g v o l t a g e on t h i s i n p u t . However, th© diod© blocks f o r a p o s i t i v e output from and no c u r r e n t can flow to in c r e a s e the p o s i t i v e charge on C. Tha h o l d i n g a c t i o n of t h i s c i r c u i t i s automatic. 14 As soon as th© input voltage i s removed the output of A^ i s d r i v e n p o s i t i v e by feedback from the output of A2 » conse-quently, th® diode blocks and the storage c i r c u i t i s i s o l a t e d . A small c u r r e n t leak from C through the g r i d r e s i s t o r r main-t a i n s the g r i d voltag® r e q u i r e d to hold the output at +E; but, because of t h i s leak the output decays with a time constant GrC. A reasonable value f o r t h i s time constant i s about ten minutes. I f the c i r c u i t i s r e q u i r e d to accept a p o s i t i v e i n put the diode must be i n v e r t e d so t h a t A^ feeds the p l a t e r a t h e r than the cathode. When the c i r c u i t i s used f o r s t o r i n g a f u n c t i o n o r d i n a t e Ef i t must be, capable of ac c e p t i n g both p o s i t i v e and negative v o l t a g e s . For t h i s reason the c i r c u i t f e a t u r e s b i d i r e c t i o n a l c o n t r o l . T h i s requirement was achieved without s a c r i f i c i n g th© h o l d i n g p r o p e r t i e s of the c i r c u i t by i n s e r t i n g a double t r i o d e gat© i n the p o s i t i o n occupied by th© diode as i n d i c a t e d i n F i g . 6. When a p o s i t i v e c o n t r o l v o l t a g e E c i s a p p l i e d to both g r i d s of the double t r i o d e conduction i s p o s s i b l e i n e i t h e r d i r e c t i o n and when a negative v o l t a g e - E Q i s a p p l i e d , both t r i o d e s are cut o f f and the h o l d i n g a c t i o n i s e f f e c t e d . Obviously, the automatic clamping a c t i o n of the F i g . 6, B i d i r e c t i o n a l Holding C i r c u i t . 15 diode has been s a c r i f i c e d and e x t e r n a l c o n t r o l i s now r e q u i r e d . I f the c o n t r o l v o l t a g e s ar© a p p l i e d only to on© t r i o d e and the second triod® i s connected as a diode ( g r i d connected to p l a t e ) a u n i d i r e c t i o n a l c i r c u i t i s achieved with the o p t i o n of b i d i r e c t i o n a l c o n t r o l . F i g u r e 7 represents th® h o l d i n g c i r c u i t as i t i s i l l u s t r a t e d i n the c i r c u i t diagrams which f o l l o w . I f th© c i r c u i t i s u n i d i r e c t i o n a l on© in p u t to the t r i o d e gate i s connected to the corresponding plat© and i f b i d i r e c t i o n a l , both inputs are connected together. * — * r +E ' F i g . 7. Block diagram of the Holding C i r c u i t . Pulse A m p l i f i e r As a l r e a d y s t a t e d pulses PI, P3 and P5 ar© r e q u i r e d at the d i s c o n t i n u i t i e s ' o f the c a l i b r a t i o n frame and at the beginning ( r i s i n g edge) of each f u n c t i o n frame. Sine© th© scanning beam has a f i n i t e width th® r i s i n g edges appear at th© output of th© photo-tub© a m p l i f i e r as volt a g e ramps. Th© puis© a m p l i f i e r was designed to guarantee that a pulse occurs w i t h i n a few microseconds aft«r a ramp i s i n i t i a t e d . T h i s c i r c u i t c o n s i s t s of an a m p l i f i e r which a m p l i f i e s th© ramp and whose output t r i g g e r s a b l o c k i n g o s c i l l a t o r w i t h i n th© r e q u i r e d time i n t e r v a l . When t r i g g e r e d th® b l o c k i n g o s c i l l a t o r emits a l a r g e negative pulse whose d u r a t i o n i s a f«w microseconds. 16 Blankin g Phantastron I f th© f u n c t i o n being scanned v a r i e s r a p i d l y i t i s capable of t r i g g e r i n g the pulse a m p l i f i e r and u n d e s i r a b l e pulses are emitted; consequently, a c i r c u i t i s r e q u i r e d to blank the input of th© pulse a m p l i f i e r , a f t e r P5 has occurred, f o r the d u r a t i o n of the f u n c t i o n frame. Since the scanning speed i s not constant t h i s blanking i n t e r v a l must be i n v e r s e l y p r o p o r t i o n a l to th© v e l o c i t y of the d i s c . The phantastron has the property t h a t on being t r i g g e r e d i t generates a square puis© whose d u r a t i o n i s i n v e r s e l y p r o p o r t i o n a l to an input r e f e r e n c e v o l t a g e . I f t h i s r e f e r e n c e voltage i s p r o p o r t i o n a l to the d i s c v e l o c i t y then the r e s u l t i n g pulse can be used to blank the pulse a m p l i f i e r . 17 Timing C i r c u i t r y The o p e r a t i o n of the coincidence c i r c u i t s and func-t i o n generator i s timed by an ordered sequence of " p u l s e - p a i r s 1 1 which t r i g g e r a number of f l i p - f l o p s . For example, i f PI t r i g g e r s a f l i p - f l o p and P3 r e t u r n s i t to i t s o r i g i n a l s t a t e then (PI, P3) i s a p u l s e - p a i r corresponding to the f l i p - f l o p which they actuate, and the two output s t a t e s of t h i s f l i p -f l o p are denoted PI and P3. The timing c i r c u i t r y i s i l l u s t r a t e d i n F i g . 8. In d e s c r i b i n g i t s o p e r a t i o n no attempt w i l l be made to j u s t i f y the choice of p u l s e - p a i r s f o r t h i s w i l l become obvious when the coincidence c i r c u i t r y and m u l t i p l i e r are d i s c u s s e d . The timing i s i n i t i a t e d by a pulse PO d e r i v e d from a refe r e n c e marker on the d i s c which precedes the c a l i b r a t i o n frame. This pulse sets f l i p - f l o p FF1 i n t o i t s PO s t a t e and the p o s i t i v e output i s f e d to the gate of pulse a m p l i f i e r PA.2 which now w i l l accept any r a p i d l y r i s i n g waveform a r r i v i n g from D, where D i s connected to the output of the photo-tube a m p l i f i e r . The f i r s t r i s i n g edge of the c a l i b r a t i o n frame t r i g g e r s pulse a m p l i f i e r PA2 which generates PI, T h i s pulse i s accepted by f l i p - f l o p s FF1, FF2, FF3 and delay f l i p - f l o p DFF1, and a l l are f o r c e d i n t o t h e i r PI s t a t e . Since PA2 i s now blocked by the negative output of FF1 no f u r t h e r pulses occur i n t h i s branch u n t i l PO, marking the s t a r t of the next r e v o l u t i o n of th© d i s c , i n i t i a t e s the next c y c l e . Delay f l i p - f l o p DFF1 remains i n i t s PI s t a t e f o r approximately F i g . 80 Timing C i r c u i t s 18 l/2 m i l l i s e c o n d then r e t u r n s to i t s s t a b l e P2 s t a t e . The d e r i v e d pulse P2 i s i n d i c a t e d i n F i g . 1. Since the p o s i t i v e output of f l i p - f l o p FF3 i s a p p l i e d to the gat© of puis® a m p l i f i e r PA3, t h i s c i r c u i t responds to the second r i s i n g edge of the c a l i b r a t i o n frame. The r e s u l t -i n g pulse P3 t r i g g e r s f l i p - f l o p FF8 and r e s e t s FF3. PA3 i s now blocked u n t i l PI occurs i n the next r e v o l u t i o n of the d i s c . Both f l i p - f l o p s FF2 and FF8 are r e s e t by pulse P4 o r i g i n a t i n g i n the coincidence c i r c u i t r y . Th© s i t u a t i o n i s s l i g h t l y d i f f e r e n t f o r th® branch f a d by PA1. T h i s pulse a m p l i f i e r responds to th© i n i t i a l r i s i n g «dg© of each f u n c t i o n fram«, f o r th© generated puis© t r i g g e r s the b l a n k i n g phantastron BPH which b l o c k s PA1 f o r the d u r a t i o n of the f u n c t i o n frame. Thus PA1 g«nerates PI and s u c c e s s i v e P5's which a l l t r i g g e r f l i p - f l o p s FF4 and FF5. These f l i p - f l o p s are r e t u r n e d to th©ir o r i g i n a l s t a t e s by pulses P6 and P8 before th© next p u l s e from PA1 a r r i v e s , P6 i s d a r i v e d i n the coincidence c i r c u i t r y and P8 i n th© m u l t i p l i e r . Th© pulse p a i r s (PI, P6) and (PI, P8) have not been i n d i c a t e d i n F i g . 8 sine® they are not e s s e n t i a l to th© o p e r a t i o n of the f u n c t i o n generator, A p o s s i b l e us© f o r them w i l l be discuss«d lat©r. The remaining pulse p a i r s are d e r i v e d from pulses P6 and P8. P6 t r i g g e r s delay f l i p - f l o p DFF2a i n t o i t s unstable s t a t e and when i t r e t u r n s to i t s normal s t a t e about 200 micro-seconds l a t e r the d e r i v e d pulse P7 t r i g g e r s f l i p - f l o p FF6. On a r r i v i n g from the m u l t i p l i e r , P8 t r i g g e r s f l i p - f l o p FF7 and delay , f l i p - f l o p DFF2b. About 200 microseconds l a t e r DFF2b 19 r e t u r n s to i t s s t a b l e s t a t e and the d e r i v e d pulse P9 r e s e t s both f l i p - f l o p s PF6 and FF7. I t should be s t r e s s e d t h a t the pulses generated by p u l s e a m p l i f i e r s PA2 and PA3 occur only when the c a l i b r a t i o n frame i s being scanned. A l l other pulses reoccur f o r each f u n c t i o n frame. 20 The Coincidence C i r c u i t r y The o p e r a t i o n of the coincidence c i r c u i t r y i s based on a m u l t i p l i c a t i o n system t e s t e d s u c c e s s f u l l y by Freeman and Parsons (3). I t s p r i n c i p l e i s i l l u s t r a t e d i n F i g , 9. Two v o l t a g e s and E 2 are simultaneously a p p l i e d to two i d e n t i c a l l i n e a r n et-works whose response to u n i t v o l t a g e i s N ( t ) . The E N ( t ) ETN( t ) E3 I Comparator t r i g g e r N(t) E 2 N ( t ) Clamping C i r c u i t E « , 1 • ^ ^, outputs are then E i N ( t ) F i g . 9. Schematic of the M u l t i p l i e r - a n d l 3 2 N ( t ) . I f on compar-i n g E i N ( t ) with a r e f e r e n c e v o l t a g e Eg, the second sweep E 2 N ( t ) i s clamped a t the i n s t a n t of e q u a l i t y , then, N(t) = E g / E i and the output i s E = E 2 N ( t ) = E 2 I3-The absence of s e t t l i n g time makes t h i s m u l t i p l i e r u s e f u l f o r t i m e - s h a r i n g a p p l i c a t i o n s . A product i s a v a i l a b l e at the i n s t a n t the comparator notes e q u a l i t y between one of the sweeps and the r e f e r e n c e v o l t a g e . Immediately a f t e r t h i s product has been store d the input v o l t a g e s can be changed, the sweeps regenerated, and a second product i s a v a i l a b l e . In comparison, m u l t i p l i e r s which generate a product propor-t i o n a l to-the average value of a c y c l i c waveform r e q u i r e low pass f i l t e r i n g over s e v e r a l c y c l e s (4, 8, 10). The output of these m u l t i p l i e r s i s not a v a i l a b l e u n t i l t h e i r t r a n s i e n t response has decayed, hence they are not s u i t a b l e f o r a p p l i -c a t i o n s r e q u i r i n g sudden changes of the input data. 21 As a l r e a d y mentioned the coincidence c i r c u i t r y e l i m i n a t e s the d i s c v e l o c i t y v as a parameter i n the s e l e c t i o n of the sampling p o i n t (b + x ) . In the d e s c r i p t i o n to f o l l o w i t i s assumed t h a t v i s constant f o r a t l e a s t one r e v o l u t i o n of the d i s c . Suppose E^ i n P i g . 9 i s a volt a g e p r o p o r t i o n a l to l / v and both E2 and E3 are constant r e f e r e n c e v o l t a g e s ; then, E = E2E3/E1 i s d i r e c t l y p r o p o r t i o n a l to v. I f now E i s s t o r e d i t can be used to d r i v e an i n t e g r a t o r whose output (-Et/RC) i s compared to a re f e r e n c e v o l t a g e -K(b + x ) , where K i s a constant. When e q u a l i t y i s reached the comparator t r i g g e r s the sampling c i r c u i t and r e s e t s the coinci d e n c e c i r c u i t r y f o r the next f u n c t i o n . The problem i s now solved, f o r i n the time t r e q u i r e d f o r the i n t e g r a t o r output to reach e q u a l i t y with -K(b + x) the f u n c t i o n frame has t r a v e l l e d a d i s t a n c e d = v t . S u b s t i t u t i n g t = d/v i n the expre s s i o n -Et/RC the v e l o c i t y terms cancel (a v e l o c i t y term i s i m p l i c i t i n E ) , and by a proper choice of time constants and c o e f f i c i e n t s i t can be arranged t h a t d = (b + x ) . In the block diagram of the coi n c i d e n c e c i r c u i t r y ( F i g . 10) the diode gates DG1, DG3 and DG5 are c o n t r o l l e d by f l i p - f l o p FF8, DG2 and DG4 by FF2 and DG6 by FF4. The l e t t e r s N and C imply non-conduction and conduction, r e s p e c t -i v e l y . E r i , -E r2 a n d -E r3 are constant r e f e r e n c e v o l t a g e s which have the i n d i c a t e d s i g n . A v o l t a g e E^ p r o p o r t i o n a l to l / v i s obtained by the i n t e g r a t o r i n the upper h a l f of F i g . 10. Th i s i n t e g r a t o r Pl-N P4-C JX32 V = v e l o c i t y of f u n c t i o n frame a = d i s t a n c e between PI and P3 on c a l i b r a t i o n frame - E r 3 (-25 v) Q a E a b s c i s s a i n p u t -K(b + x) -E ^ r ± ^ = -K(b + x) T"3 3 F i g . 10, Sweep and Coincidence C i r c u i t s . 22 i s o p e r a t i v e only when DG1 i s conducting and DG2 non-condcuting; consequently, a c o n s i d e r a t i o n of the s t a t e s of these gates w i l l show t h a t i n t e g r a t i o n i s i n i t i a t e d by PI and stopped by P3. But PI and P3 d e f i n e the time i n t e r v a l tj^ r e q u i r e d to scan the d i s t a n c e , a, on the c a l i b r a t i o n frame when the d i s c v e l o c i t y i s v. Thus, t ^ *?. a/v and the output of the i n t e g r a t o r a t the end of t h i s time i s a vo l t a g e E l = - B r i R ^ J = ~ E r l vR^Cg" The counterpart of the two i d e n t i c a l sweeps N(t) of F i g o 9 are the two expo n e n t i a l sweeps with time constant R l C i i n F i g . 10. Thus, - t N ( t) = (1 - e t ^ l ) Furthermore, i n the n o t a t i o n of F i g . 10 E 2 = ~ E r 2 E 3 = ~ E r 3 The two sweeps are simultaneously i n i t i a t e d by P3 (diode gates DG3 and DG5 are rendered non-conducting) and when the f i r s t sweep -EjNCt) reaches e q u a l i t y with -E r3 the comparator Ml emits pulse P4 which t r i g g e r s FF8 and stops both sweeps. Meanwhile, the h o l d i n g c i r c u i t has accepted the peak value of the second sweep and i t s output E i s clamped a t t h i s value when DG5 discharges C^, The magnitude of E i s f i x e d by the magnitude a t t a i n e d by N ( t ) . That i s , - E r l v ^ J N ( T ) = R E R 3 or 23 Hence, v R 2 C 2 E r 2 ^ r 3 E = E r 2 N ( t ) = a E r l T h i s v o l t a g e i s h e l d f o r the f u l l r e v o l u t i o n of the d i s c and i s Used to d r i v e the adjacent i n t e g r a t o r . Each pulse P5, which designates the beginning of a f u n c t i o n frame, s t a r t s the i n t e g r a t o r by throwing DG6 i n t o i t s non-conducting s t a t e . The output of t h i s i n t e g r a t o r i s f e d i n t o a second comparator M2 where i t i s compared with a v o l t a g e -K(b + x ) . A f t e r a time t 2 = (b + x)/y e q u a l i t y i s „ reached and the r e s u l t i n g pulse,P6 t r i g g e r s the sampling c i r c u i t r y . The h o l d i n g c i r c u i t , s t o r i n g v o l t a g e s of one sig n only, i s u n i d i r e c t i o n a l . In order t h a t i t s output be pro-p o r t i o n a l to v, the c i r c u i t must always accept the peak value of the sweep - E r 2 N ( t ) . I f t h i s peak decreases f a s t e r than the output of the h o l d i n g c i r c u i t , i t i s not accepted and c o n t r o l i s l o s t . Consequently, the output decay r a t e must be adjusted to accomodate any a n t i c i p a t e d r a t e of decrease i n v. In s e l e c t i n g time constants and v o l t a g e l e v e l s the p r o p e r t i e s of i n d i v i d u a l c i r c u i t s were considered. The r e f -erence v o l t a g e ETi was a r b i t r a r i l y chosen as 50 v o l t s . On the other hand, since the output a m p l i f i e r of the h o l d i n g c i r c u i t i s l i n e a r i n the range -50 to +50 v o l t s , - E r 2 was f i x e d a t -100 v o l t s to permit a w e l l d e f i n e d peak sweep v o l t -age of the order of -50 v o l t s . Por the same reason -?Er3 was f i x e d a t -25 v o l t s . I f i t i s l a r g e r the sweep waveform would 24 s t a r t to l e v e l o f f before e q u a l i t y with - E r g i s reached, thus the t r i g g e r p o i n t f o r Ml would be p o o r l y d e f i n e d . The ab-s c i s s a range i s 0 to -50 v o l t s . With t h i s i n f o r m a t i o n the r a t i o of the i n t e g r a t i o n time constants can be determined. R e c a l l t h a t P6 occurs when • ^ 3 or E r 2 E r 3 v R 2 C 2 < b + *>  E r l a v R 3 C 3 K(b + x) When (B + x) i s equal to the f u l l - s c a l e a b s c i s s a value s where s = 2a, the a b s c i s s a i n p u t i s 50 v o l t s . On s u b s t i t u t -i n g t h i s i n f o r m a t i o n and the values of the r e f e r e n c e voltages i n t o the above expression i t becomes (_100)(-25) R o C 2 2a = 5 0 or 50 R 3 C 3 a R 2 C 2 _ 1 R g C g 2 Furthermore, since Ks =50, K = 50/s. In f i x i n g the values of the components the f o l l o w i n g l i m i t a t i o n s of the c i r c u i t r y have to be c o n s i d e r e d . Diode gate DG6 must discharge Cg w i t h i n two b i l l i s e c o n d s , the approx-imate time i n t e r v a l between f u n c t i o n frames (the discharge a c t i o n of the diode gates w i l l be d i s c u s s e d l a t e r ) . In the one m i l l i s e c o n d i n t e r v a l between PI and P3 the output of the f i r s t i n t e g r a t o r should reach about 40 v o l t s ; t h i s permits a 20$ decrease i n the d i s c speed without exceeding the l i n e a r o p e r a t i n g l i m i t of the o p e r a t i o n a l a m p l i f i e r . The s i z e of 25 the sweep r e s i t o r Rj.must l i m i t the output current of the f i r s t i n t e g r a t o r to one milliamperec The sweep time con-stant RlC"i should be roughly l/2 m i l l i s e c o n d i f the pulse P4 i s to occur i n the second h a l f of the c a l i b r a t i o n frame. With these considerations the component values s e l e c t e d aret Rx 68 Ko Ci = 0.01 (if, R 2 = 500 K, C 2 = 0.002 [ito R 3 .= 1 Meg, C 3 m 0.002 | i f . I t i s i n t e r e s t i n g to note that p r e c i s i o n i s r e -qu i r e d only i n f i x i n g the values of the time constants; the values of the component R"s and C s need not be p r e c i s e . O s c i l l o s c o p e F i g . 11. Method f o r obt a i n i n g two i d e n t i c a l sweeps. The method used to obtain two i d e n t i c a l .RiOi sweeps i s i l -l u s t r a t e d i n F i g . 11. An a-c. s i g n a l was a p p l i e d to both i n t e g r a t o r s and the two outputs were connected across an o s c i l l o s c o p e . Since the gain of a K2-W i s high s l i g h t d i f -ferences between a m p l i f i e r s w i l l not a f f e c t the output of e i t h e r i n t e g r a t o r . Because the outputs are low impedance sources pickup i s not troublesome and a ground connection i s not required on the o s c i l l o s c o p e . The three components R j , C.j and C.iVwere select e d without regard to p r e c i s i o n and the r e s i s t o r Rj'was v a r i e d u n t i l the a-c. s i g n a l on the o s c i l l o -scope was n e g l i g i b l e , i n d i c a t i n g e q u a l i t y of the time constants. 26 Timing of the F u n c t i o n Generator The d e t a i l s of the f u n c t i o n generator and m u l t i p l i e r can be found i n P 0 Hildebrand's t h e s i s ( 6 ) 0 I t s o p e r a t i o n i s d e s c r i b e d here to j u s t i f y the c i r c u i t r y of Figo 8» The three channels of the assembly are i l l u s t r a t e d i n F i g . 12 0 A l l three channels and the ti m i n g c i r c u i t s are f e d by the photo-tube a m p l i f i e r which c o n s i s t s of two i n v e r t -ers i n cascade p r o v i d i n g a g a i n of 100» Since the output of the photo-tube v a r i e s from 0 to approximately 1 v o l t , the output of the a m p l i f i e r v a r i e s from -50 to +50 v o l t s a f t e r biasingo B i a s i n g , or the extablishment of the zero l e v e l , i s provided by the h o l d i n g c i r c u i t i n channel 3o Pulse PI, which i n t r o d u c e s the c a l i b r a t i o n frame, t r i g g e r s the delay f l i p - f l o p DFF1 which i n t u r n renders the t r i o d e gate TG2 conducting; thus, the h o l d i n g c i r c u i t charges up to a vo l t a g e -Em. When DFF1 r e t u r n s to i t s s t a b l e s t a t e l/2 m i l l i s e c o n d l a t e r , TG2 i s cut o f f and the s t o r e d v o l t a g e i s h e l d f o r the whole r e v o l u t i o n of the d i s c 0 At the same time DG15 becomes conductive and -1^ i s f e d back to the input of the photo-tube a m p l i f i e r S u i t a b l e s c a l i n g i s provided by the i n p u t g r i d r e s i s t o r s and the net e f f e c t i s t h a t the a m p l i f i e r d e l i v e r s zero v o l t s when the photo-tube output i s EJQO Besides estab-l i s h i n g a zero l e v e l , feedback a l s o e l i m i n a t e s the a f f e c t of d-c. d r i f t , f o r t h i s a f f e c t i s slow r e l a t i v e to the scanning r a t e and b i a s i n g , hence s e l f - c o r r e c t i o n , occurs once every r e v o l u t i o n D ( F i g . 8) 1 ( H W 4 - K2-W -M£Gl)- S2 * A A A T C X P3-C P4-N •>Vvf] K2-X photo-tube photo-tube a m p l i f i e r Pl-N P2-C 13 s i g n determination P9-^| FF9 \<-P7-N P9-C •VVNA-i P7-N AP9-C K2-MCF •AAA » K2-W B P(+)-C P(-)-N * E * f N ( t ) ^ K2-W S l -n Pl-C P2-N -EfN(t> E (Fig.13) P(+)-N P(-)-C F i g . 12. F u n c t i o n Generator and M u l t i p l i e r Assembly. 27 Channels 1 aad 2 perform a m u l t i p l i c a t i v e oper-a t i o n s i m i l a r to t h a t performed by the c o i n c i d e n c e c i r c u i t r y . The output of t h i s m u l t i p l i e r i s a v o l t a g e E f E r / E j ^ where Ef/Ej^ i s the normalized f u n c t i o n o r d i n a t e and E r i s a r e f -erence voltage which sets the v o l t a g e l e v e l of E^Ey/Ej^ i n s t o r a g e 0 The reason f o r n o r m a l i z i n g i s to provide a product which i s independent of the g a i n of the system, f o r there i s no assurance t h a t t h i s g a i n w i l l remain constant,^ The u n i d i r e c t i o n a l h o l d i n g c i r c u i t i n channel 1 charges up to the peak o r d i n a t e E ^ of the c a l i b r a t i o n frame and a u t o m a t i c a l l y holds t h i s v o l t a g e . I f the succeeding f u n c t i o n frames have p o s i t i v e maxima the h o l d i n g c i r c u i t accepts these peaks and the charge l o s t by the slow discharge of the storage c i r c u i t i s r e p l a c e d . I n i t i a l l y , however, t h i s c i r c u i t charges up to the zero l e v e l EJJJ, Since the g a i n of the photo-tube a m p l i f i e r i s l i k e l y changed by b i a s i n g , Ej^ w i l l d i f f e r s l i g h t l y from Eg,/ Consequently, to guarantee t h a t the h o l d i n g c i r c u i t w i l l accept the maximum or d i n a t e the t r i o d e gate TGI provides b i d i r e c t i o n a l c o n t r o l d u r i n g the charging i n t e r v a l from P3 to P4, In channel 2 the diode gates DG8, DG9, DG10 and DG11 are conducting on the a r r i v a l of a f u n c t i o n frame; thus the v o l t a g e across the condenser C 2 f o l l o w s the f u n c t i o n o r d i n a t e (with i n v e r s i o n ) . T h i s voltage i s clamped at the o r d i n a t e E^ corresponding to P6 when DG10 r e v e r t s to i t s non-conducting s t a t e . The v o l t a g e s Ej^ and Ef r e q u i r e d to d r i v e two i d e n t -i c a l sweeps are now a v a i l a b l e . One sweep i s the R^C^ c i r c u i t 28 i n channel 1; the other i s more d i f f i c u l t to o b t a i n si n c e a constant v o l t a g e source of E f i s not present. However, a simple a n a l y s i s of the i n t e g r a t o r i n channel 2 shows t h a t when t h i s i n t e g r a t o r i s f e d by a charge on C 2 i t s output i s E f p- (1 - e *592 ) e 3 I f C 2 B C3 = and B R ^ , two i d e n t i c a l sweeps are r e a l i z e d . These sweeps are i n i t i a t e d by F 7 which makes both DG7 and DG12 non-conducting. The system employed to e s t a b l i s h the c o r r e c t s i g n of the product E f E r / E ^ r e q u i r e s the genera t i o n of two sweeps i n channel 2; + E f N(t) and - E f N ( t ) , where E f may be p o s i t i v e or n e g a t i v e . The i n t e g r a t o r j u s t considered generates E f N(t) a t B. Since DG8, DG9 and DG10 are now non-conducting the output of t h i s i n t e g r a t o r i s f e d to the i n v e r t e r f o l l o w i n g DG8. I t s output, - E f N ( t ) , appears a t C. A t t h i s p o i n t three sweeps are i n progress; - E j^Nft) at A, E f N(t) at B and - E f N ( t ) at C, When -Ej^NCt) reaches e q u a l i t y with - E r the comparator M3 generates pulse F8 which blocks DG11 and clamps both sweeps i n channel 2. The sweep i n channel 1 i s terminated by P9. Thus, a v o l t a g e EfEp/Ej^j i s h e l d a t B and a v o l t a g e - E fE j - ZE j , ! a t C. Which v o l t a g e i s d i r e c t e d i n t o storage depends upon the sign of E f and E r . The s i g n of the product Is f i x e d by the s t a t e of f l i p - f l o p FF9. This st a t e determines which of the gates DG13 or DG14 i s conducting. Diode gates DG16 and DG17 a l s o are c o n t r o l l e d by t h i s f l i p - f l o p . Normally DG16 i s conduct-i n g and DG17 non-conducting; hence, i f E r i s negative the 29 comparator M4 i s not t r i g g e r e d since E r i s l e s s than ground potential,, F l i p - f l o p FF9 then remains i n i t s i n i t i a l state,, In t h i s state diode gate DG14 i s conducting and the sign of the product i s determined by the sign of -Ef. Furthermore, the voltage f e d to M3 i s of c o r r e c t sign f o r comparison w i t h - E J J N ( t ) . A l t e r n a t i v e l y , i f E r i s p o s i t i v e comparator M4 t r i g g e r s f l i p - f l o p FF9; diode gate DGrl3 conducts and the sign of the product i s that of Ef, Again the reference voltage f e d to M3 i s of c o r r e c t s i g n , f o r diode gate DG17 i s now con-ducting. Pulse P9 derived from P8 resets f l i p - f l o p FP9 f o r the next f u n c t i o n * 30 Storage C i r c u i t s and Counter The storage c i r c u i t s are i d e n t i c a l to the h o l d i n g c i r c u i t except t h a t the P h i l b r i c k a m p l i f i e r and the t r i o d e gate are common to a l l . The counter i l l u s t r a t e d i n F i g . 13 determines which storage c i r c u i t S n i s a c c e s s i b l e . I f there are N f u n c t i o n s being generated t h i s counter c o n t a i n s N f l i p -f l o p s . Each f l i p - f l o p c o n t r o l s the access gates corresponding to a p a r t i c u l a r storage c i r c u i t . The c o u n t i n g o p e r a t i o n i s i n i t i a t e d by the marker pulse PO which f o r c e s a l l f l i p - f l o p s i n t o the same s t a t e except FFSx« which takes on the opposite s t a t e . In t h i s o r i e n t a t i o n a i l storage c i r c u i t s are i n a c c e s s i b l e except the f i r s t . When P9 occurs a t the end of the f i r s t f u n c t i o n frame the only f l i p - f l o p which i s i n a s t a t e t h at w i l l accept i t i s F F S i o I t s output t r i g g e r s FFSg and the storage c i r c u i t S 2 i s now a c c e s s i b l e . At the end of the second f u n c t i o n frame P9 t r i g g e r s F F S 2 w n l c n i n t u r n f l i p s over FFSg. This process continues u n t i l P9 o c c u r r i n g a t the end of the Nth f u n c t i o n frame retu r n s FFSj} to i t s o r i g i n a l s t a t e . I t completes, the c y c l e by r e s e t t i n g F F S j . Suppose the storage c i r c u i t S n i s a c c e s s i b l e ; then the three gates i n t h i s c i r c u i t are conducting. Diode gate D G l n permits S n to charge up to - E f E r / E j ^ where Ef i s the ord i n a t e corresponding to the nth f u n c t i o n . DG2 n completes the feedback loop through R to the input g r i d of the P h i l b r i c k a m p l i f i e r and DG3 n permits the channeling of - E f E r / E j ^ to other p a r t s of the computer. I t was mentioned p r e v i o u s l y t h a t the B E O—*>=—AAA/—f (Fig.12) P9 o » PO o—> FFSi F u n c t i o n Storage F F S 2 n » U o PO to FF^3 Counter FFSjj H—^—o PO rr from F F S J J . . ! F i g . 13. Counter and F u n c t i o n Storage 31 circumference of the scanning d i s c was one f a c t o r which l i m i t e d the f u n c t i o n c a p a c i t y of the computer. Obviously, the remaining f a c t o r i s t h e number of st o r a g e elements pro v i d e d . However, s i n c e the c o s t of a storage c i r c u i t i s small t h i s i s not a s e r i o u s l i m i t a t i o n . 32 C i r c u i t D e t a i l s Diode Gate The b i d i r e c t i o n a l gates used i n t h i s p r o j e c t ( F i g . 14) were developed by J . Millman and T. H. Puckett (12), They are capable of a c c u r a t e l y p a s s i n g any vol t a g e l y i n g i n a range d e f i n e d by the c o n t r o l v o l t a g e s . Since the working v o l t a g e s i n the computer vary between +50 and -50 v o l t s the c o n t r o l v o l t a g e s f o r the gates were chosen as +60 and -60 v o l t s to accomodate v a r i a t i o n s i n the f l i p - f l o p outputs a r i s -i n g from the use of n o n - p r e c i s i o n r e s i s t o r s . The gates f e a t u r e s e v e r a l advantages, among which the f o l l o w i n g have been e x p l o i t e d : during conduction the gain through the gate i s very c l o s e to u n i t y , i n f a c t , only f o r small v o l t a g e s does the d e v i a t i o n from u n i t y exceed 0.5$ (7, p. 24); the ga i n dur i n g conduction i s i n s e n s i t i v e to unbalance i n the c o n t r o l v o l t a g e s ; leakage through the gate i s n e g l i g i b l e during non-conduction; and the gate r a p i d l y becomes non-conducting i f the c o n t r o l v o l t a g e s have i d e a l step waveforms. Fig u r e 14 shows t h a t both Via and Vlb are conducting when the gate i s non-conducting. Since there i s very l i t t l e v o l t a g e drop across these tubes the p l a t e of V3a i s at -60 v o l t s and the cathode of V3b a t +60 v o l t s . Consequently, both V3a and V3b are blocked and the output i s completely i s o l a t e d from the i n p u t . In the conducting s t a t e both V ia and Vlb are are blocked and c u r r e n t flows from +E to -E through both halves of V3. Depending upon the s i g n of the input, e i t h e r V2a or V2b s t a r t s to conduct and the bridge p r o p e r t i e s of the net-work come i n t o p l ay and f o r c e a balance between input and output. V3a 71 V2a L out (or i n ) V3b 4 > V2b Bi i n (or out) A W @ -E *2 VI b +N % - 1 K. Pot., M a l l o r y B 2 - 1 Meg.,10%, l/2 watt E C N 300 v o l t s 60 v o l t s 60 v o l t s VI, V2, V3 6AL5 F i g . 14. Diode Gate. 33 I t i s i n t e r e s t i n g to note that at balance a load on the output i s f e d by the +E and -E s u p p l i e s and not by the input; thus even d u r i n g conduction the output i s i s o -l a t e d from the i n p u t . This i s o l a t i o n i s apparent when a charged condenser C i s being discharged through the gate to ground. Suppose the output i s grounded, then both the p l a t e of V i a and the cathode of V3b t r y to a t t a i n ground p o t e n t i a l . I f the input v o l t a g e i s p o s i t i v e V2a blocks and the condenser can only discharge through V2b. T h i s , however, r a i s e s the p o t e n t i a l of the cathode of V3b to that of the input and t h i s tube a l s o b l o c k s . Consequently, the condenser d i s c h a r g e s through R2 to the -E supply and c o n t r o l i s obtained as soon as the input reaches ground p o t e n t i a l . The e f f e c t i v e time constant of t h i s d i s c harge to ground i s not R^C but something -*>t c o n s i d e r a b l y smaller as i m p l i e d by F i g . 15. F a s t d i s c h a r g e s can be obtained by decreasing the value of R*?? however, t h i s r e s u l t s i n an i n c r e a s e d c u r r e n t d r a i n from the r e g u l a t e d power s u p p l i e s E i n =300v F i g , 15, Discharge of a condenser through a diode gate ( s o l i d l i n e ) . which i s not d e s i r e a b l e . Operations r e q u i r i n g gates with h i g h back impedance and f a s t d ischarge a c t i o n could be ad-equately performed by a discharge t r i o d e r a t h e r than the diode gate. 34 F l i p - F l o p The o p e r a t i o n of the f l i p - f l o p ( F i g . 16) depends upon the f a c t t h a t a s t a b l e v o l t a g e c o n f i g u r a t i o n e x i s t s with V i a on and Vlb o f f , or v i c e v e r s a 0 Suppose V i a i s on and Vlb o f f ; then, the p l a t e voltage l e v e l of Vlb i s f i x e d e n t i r e l y by the c u r r e n t p a s s i n g through the r e s i s t o r s and R 2, while the p l a t e l e v e l of V i a i s lower s i n c e i t s p l a t e r e s i s t o r i s c a r r y i n g the a d d i t i o n a l tube c u r r e n t . The o p e r a t i n g p o i n t of e i t h e r V i a or Vlb and the values of the r e s i s t o r s R^, R2 and R3 are so chosen t h a t the p l a t e of the conducting tube i s a t -60 v o l t s and t h a t of the non-conducting tube at +60 v o l t s . I t i s apparent i n the c i r c u i t diagram t h a t the cathode f o l l o w e r outputs f o l l o w the p l a t e v o l t a g e s . The g r i d l e v e l s of V i a and Vlb are f i x e d by the v o l t a g e d i v i d e r i n e i t h e r cathode c i r c u i t of the output t r i o d e s . A g r i d may be a t -160 or -210 v o l t s depending upon the s t a t e of the c i r c u i t . Returning to the i n i t i a l s u p p o s i t i o n , i f V i a i s con-d u c t i n g then a negative t r i g g e r a p p l i e d a t the input ( p i n 4) passes through the diode V3a and cuts Via o f f . The r a p i d r i s e of the p l a t e of V i a i s t r a n s m i t t e d by C 2 to the g r i d of Vlb which s t a r t s to conduct, and i n t u r n , augments the a c t i o n of the t r i g g e r by f e e d i n g a negative r i s i n g edge from i t s p l a t e to the g r i d of Via through the second c o u p l i n g condenser, a l s o l a b e l e d C 2. Since the cathodes of V3a and V3b are at -150 v o l t s and t h e i r p l a t e s at -160 or -210 v o l t s these diodes conduct only when a negative pulse i s a p p l i e d to the i n p u t s . Thus, +300 C i r V2a out &6 ±60©-1>-P V3a 5R5 Re-Re: r -300 680 K., 5?6 C± ~ 0.01 | i f . R2 - 1 Meg., 5% C 2 - 50 uuf. R 3 - 480 K., 5% R 4 - 220 K., 5% (or 110 K.) R 5 - 140 E., (or 70 K.) VI, V2 - 12AX7 R 6 - 1 Meg., 10% V3 - 6AL5 i n — FF i n ±60 +60 Symbol F i g . 16. F l i p - F l o p ( B i s t a b l e M u l t i v i b r a t o r ) . 35 a diode c l i p s the t r a i l i n g edge of the input pulse and prevents t h i s p o s i t i v e p o r t i o n from t r i g g e r i n g the f l i p -f l o p back i n t o i t s o r i g i n a l s t a t e . Furthermore, a diode i s o l a t e s the f l i p - f l o p from the e x t e r n a l c i r c u i t r y ; a change of s t a t e i n i t i a t e d at one input cannot be t r a n s -m i t t e d through a diode to the opposite i n p u t . T h i s f l i p - f l o p d i f f e r s somewhat from conventional designs (13, p. 164) i n t h a t the discharge r e s i s t o r s normally i n p a r a l l e l with the c o u p l i n g condensers are now i n the cathode c i r c u i t s of the output tubes. Thus, the p l a t e of one f l i p - f l o p t r i o d e i s i s o l a t e d from the g r i d of the other as f a r as d-c. v o l t a g e l e v e l s are concerned. The advantage i s t h a t an a d d i t i o n a l degree of freedom i s obtained to f i x the two output l e v e l s at the d e s i r e d +60 and -60 v o l t s . F u l l load occurs f o r the f l i p - f l o p output which i s negative when a maximum number of d iode gates are non-conduct-i n g . Each gate then draws 0.36 ma. from t h i s output; hence, the r e s i s t o r s R4 and R§ must c a r r y s u f f i c i e n t c u r r e n t to sup-p l y both the f u l l l o a d and the tube requirement to maintain the cathode f o l l o w e r a c t i o n . As mentioned, the v o l t a g e s c o n t r o l l i n g the diode gates must exceed 50 v o l t s i n absolute value. In some cases 10$ v a r i a t i o n i n the values of the r e s i s t o r s used i n the f l i p - f l o p c o uld y i e l d outputs which do not s a t i s f y t h i s requirement. For t h i s reason the f o l l o w i n g p r e c a u t i o n s are necessary: 1. The r a t i o Rj/R^ = 240/360 must be s a t i s f i e d c l o s e l y i f the p o s i t i v e output i s to be +60 v o l t s . 36 2* The r a t i o R4/R5 = 220/140 (though not as c r i t i c a l as R1/R2) must be approximated to ensure the c o r r e c t oper-a t i n g p o i n t f o r the f l i p - f l o p . 3. The r e s i s t o r s R^ and Rg should be c l o s e to design value to guarantee an acceptable negative output. Delay F l i p - F l o p The b a s i c o p e r a t i o n of the delay f l i p - f l o p ( F i g . 17) i s embodied i n both the top and bottom h a l f of the c i r c u i t diagram. Consider the top h a l f . I n i t i a l l y V i a i s conducting and V2a non-conducting (the g r i d l e v e l of 72a i s about 25 v o l t s more negative than that of V i a ) . A negative t r i g g e r v o l t a g e a p p l i e d to the g r i d of Via cuts t h i s tube o f f and the r e s u l t i n g p o s i t i v e p l a t e r i s e i s f e d through C^ to the g r i d of V2a. This tube s t a r t s to conduct and continues to conduct as long as i t s cathode v o l t a g e l e v e l (which f o l l o w s the g r i d l e v e l ) i s s u f f i c i e n t l y high to cut o f f V i a . Since there i s no d-c. c o u p l i n g between the p l a t e of Via and the g r i d of V2a a p o s i t i v e r i s e on the p l a t e of V i a appears on the g r i d of V2a as a p o s i t i v e r i s e f o l l o w e d by an exponential decay. As soon as the g r i d l e v e l of V2a approaches t h a t of V i a , V i a conducts and the p l a t e - g r i d c o u p l i n g through C^ r a p i d l y f o r c e s V2a i n t o i t s normal non-conducting s t a t e . The output of the cathode f o l l o w e r V3a f o l l o w s the p l a t e of V2a. This output i s +60 v o l t s i n the s t a b l e s t a t e and -60 v o l t s while V2a i s conducting. The p l a t e of V i a cannot provide an output of oppo-s i t e p o l a r i t y because the waveform on t h i s p l a t e i s not square ® +300 2) -300 in ±60 +60 Symbol R l " *3 -R 4 " % " *7 " »8 " 680 K., 5% 480 K., 5% 1.0 Meg.,1% 1.3 Meg. , 1% 390 K., 10% 1 Meg., 10% 3.1 Meg.,1% 3.3 Meg.,1% C± - 470 uuf. Q 2 - O.Oi uf. VI, V2, V3 •- 12AX7 V4 - 6AL5 F i g . 17. Delay F l i p - F l o p (Monostable M u l t i v i b r a t o r ) . DFF1 - 500 microseconds delay. 37 but s i m i l a r to the i n v e r t e d cathode waveform,, For t h i s reason the second output i s obtained from the independent lower c i r c u i t . A l t e r n a t i v e l y , the output of V3a could have been i n v e r t e d using a d-c. a m p l i f i e r . In e i t h e r case the number of a d d i t i o n a l tubes r e q u i r e d i s equal; however, the use of two independent c i r c u i t s e l i m i n a t e s time delay between the l e a d i n g edges of both outputs, T h i s d e l a y i s unavoidable when using an i n v e r t e r . The o p e r a t i o n of the lower c i r u i t i s s i m i l a r to t h a t a l r e a d y d i s c u s s e d except t h a t Vlb i s normally conducting and V2b non-conducting. The negative t r i g g e r i n g voltage must now be a p p l i e d to the p l a t e of V2b r a t h e r than the g r i d since no i n v e r s i o n i s r e q u i r e d . The d u r a t i o n of the q u a s i - s t a b l e s t a t e i s determined by the time constant of the v o l t a g e exponential on the g r i d of e i t h e r V2a or Vlb (the charge on decays through Rg to ground and t h a t on C 2 through R^ to' ground). Of course, the amplitude of t h i s exponential must a l s o be c o n s i d e r e d . In the upper c i r c u i t the t r i g g e r pulse i s a m p l i f i e d hence t h i s c i r c u i t i s more e a s i l y t r i g g e r e d than the lower one; i n f a c t , to decrease i t s s e n s i t i v i t y to pick-up the r e s i s t o r s Rg and Rg were s e l e c t e d so t h a t only pulses exceeding -20 v o l t s can t r i g g e r the c i r c u i t , A l/2 m i l l i s e c o n d q u a s i - s t a b l e s t a t e f o r delay f l i p - f l o p DFF1 was achieved with C± =470 uuf. The delay f l i p - f l o p s DFF2a and DFF2b do not c o n t r o l any gates, hence there i s no need to provide them with, two outputs. The only requirement i s t h a t the t r a i l i n g edge of the output p u l s e be capable of t r i g g e r i n g a f l i p - f l o p . Since - 680 K., Eg - 470 K., Eg - 1.0 Meg., R 4 - 1.3 Meg., 5% B 5 -5% Be -1% E 7 .-1% B8 -270 K., 10% 100 K., 10% 4.7 K., 10% 390 K., 10% CT — 250 uuf. C 2 - 100 unf. C 3 - 0.01 uf. 18. Delay F l i p - F l o p s DFF2a and DFF2b 200 microseconds d e l a y . 38 t h i s pulse i s only about 200 microseconds wide, i t w i l l not t r i g g e r a f l i p - f l o p when a p p l i e d d i r e c t l y to the c i r c u i t . . The reason i s that the f l i p - f l o p i n p u t tends to d i f f e r e n t i a t e t h i s p u lse; but, because of the time constant of the input network, the i n i t i a l r i s e has i n s u f f i c i e n t time to decay before the t r a i l i n g edge of the pulse arrives., Consequently, the f u l l negative edge i s not passed by the in p u t diode and the c i r c u i t does not t r i g g e r . The d i f f i c u l t y was overcome by d i f f e r e n t i a t i n g the output pulse of the delay f l i p - f l o p , a m p l i f y i n g the d e r i v a -t i v e , and a p p l y i n g the r e s u l t i n g waveform to the f l i p - f l o p . The time constant of the input c i r c u i t of the f l i p - f l o p now i s not so c r i t i c a l s i n c e the incoming pulses are l a r g e r and have sharp t r i g g e r i n g edges. Both delay f l i p - f l o p s DFF2a and DFF2b are i d e n t i c a l and are contained i n the same c h a s s i s . T h e i r c i r c u i t diagram i s i l l u s t r a t e d i n F i g . 18. Holding C i r c u i t The o p e r a t i o n of t h i s c i r c u i t has been d i s c u s s e d a l r e a d y so the important d e t a i l s of F i g . 19 are now considered. Note that the f i r s t a m p l i f i e r i s a P h i l b r i c k K2-W. I t s high g a i n and r a p i d response are r e q u i r e d here to a c c u r a t e l y c o n t r o l the value of the stored v o l t a g e . This a m p l i f i e r responds to the e r r o r between the input and output v o l t a g e s ; hence, the smaller t h i s e r r o r need be to ensure c o n t r o l , the more p r e c i s e i s the output. The second a m p l i f i e r i s an ada p t a t i o n of the K2-W. Very high g a i n and high frequency response i s not a +300 Main Chassis Bus Rl - 1 Meg., 0,1$ B 2 - 10 K. Pot., Ma l l o r y R 3 - 1 Meg.j 10$ R 4 - 220 K., 10$ R 5 - 2.2 Meg.,10$ R 6 - 470 K., 10$ R 7 - 68 K., R 8 - 120 K., 10$, 1 watt R9 - 2.7 Meg.,10$ R 1 0 -R l l ~ R 1 2 -R 1 3 -c r -c 2 -C 3 -C 4 -c 5 -_E K2-f S I Symbol *-+E 4.7 Meg.,10$ • 1.5 K., 10$ • 33 K., 10$ • 15 L , 10$ • 0.5 uf. Polystyrene • 50 uuf. 10 uuf. f o r b i d i r e c t i o n a l c o n t r o l ( p o s i t i v e 470 uuf. a n £ negative v o l t a g e s t o r a g e ) both 0.01 uf. g r i d s of TG are connected i n s e r i e s . F i g . 19. Holding C i r c u i t . 3 9 requirement f o r t h i s a m p l i f i e r since i t s s o l e purpose i s to s t o r e a v o l t a g e . The value of t h i s voltage i s f i x e d e n t i r e l y by the adding network at the input of the K2-W and by the response of the K2-W. Since s e v e r a l storage c i r c u i t s are r e q u i r e d i n the computer an inexpensive h o l d i n g a m p l i f i e r i s d e s i r e a b l e . One input of both a m p l i f i e r s i s biased by a r e s i s -t i v e network between ground and e i t h e r power supply. I f the s i g n a l i s a p p l i e d to the ( + ) input the (-) i n p u t i s b i a s e d n e g a t i v e l y . A l t e r n a t i v e l y , i f the s i g n a l i s a p p l i e d to the (-) input the ( + ) input i s b i a s e d p o s i t i v e l y . Both methods are i l l u s t r a t e d i n F i g . 1 9 . Assuming that the two r e s i s t o r s BT_ i n the adding network are equal, the b i a s on the K2-W e s t a b l i s h e s e q u a l i t y between the absolute values of the i n p u t and s t o r e d v o l t a g e s . The 1 0 K. potentiometer i n t h i s b i a s c i r c u i t permits a 1.5 v o l t v a r i a t i o n i n the output. The b i a s on the second a m p l i f i e r f i x e s the h o l d i n g time constant of the storage c i r c u i t . The value of t h i s b i a s determines the v o l t a g e d i f f e r e n t i a l which must be maintained between the two i n p u t g r i d s to h o l d the output ( s t o r e d v o l t a g e ) a t i t s i n i t i a l l e v e l . This d i f f e r e n t i a l i s obtained by a c u r r e n t leak from the storage c a p a c i t o r through the g r i d r e s i s t o r Rg. I t i s p o s s i b l e to a d j u s t t h i s b i a s so t h a t no c u r r e n t leak i s r e q u i r e d . However, the a m p l i f i e r i n t h i s case tends to d r i f t ( s l i g h t v a r i a t i o n s i n ground l e v e l are i n t e g r a t e d and the output voltage wanders) and the r e q u i r e d d i f f e r e n t i a l i s not constant f o r a l l values of the s t o r e d v o l t a g e . I t i s import-a n t then that the b i a s be set t o guarantee an output decay 40 f o r any s t o r e d v o l t a g e . In order t h a t the h o l d i n g a m p l i f i e r never be d r i v e n beyond i t s l i n e a r o p e r a t i n g range a r e s i s t o r R^2 U n i t s the c u r r e n t i n t o the storage condenser to one milliampere at maximum output voltage of the K2-W. I f the l i n e a r range i s exceeded the output overshoots before c o n t r o l i s e s t a b l i s h e d . Thus, when a diode i s used f o r automatic c o n t r o l t h i s diode b l o c k s and c o n s i d e r a b l e time i s r e q u i r e d f o r the output to decay to i t s d e s i r e d l e v e l . A disadvantage of t h i s c i r c u i t i s i t s tendency to o s c i l l a t e during the charging process due to c o u p l i n g through the power s u p p l i e s . This o s c i l l a t i o n was reduced to a t o l e r -able minimum by the i n s e r t i o n of a small r e s i s t o r Rj_i i n the feedback loop of the h o l d i n g a m p l i f i e r . With R^g = 33 K., R ^ l = 1500 ohms and an input of 45 v o l t s the t o t a l f l u c t u -a t i o n i n output due to both overshoot and o s c i l l a t i o n was 0.025 v o l t (0.05% v a r i a t i o n ) . A s t a b l e , low impedance power supply should improve t h i s p r e c i s i o n . I t can be shown that the h o l d i n g c i r c u i t i s b a s i c -a l l y s t a b l e . In F i g . 20 the c u r r e n t through R i s equal, to the sum of the c u r r e n t s through r and C« Thus F i g . 20. Schematic Holding C i r c u i t f o r s t a b i l i t y a n a l y s i s 41 A l s o and 9 1 " C S = + ( e g - e 0 ) P C R r * «1 = 2 (®i + e o ) G • Combining equations e l • T f = * « ( 7 + I + p C ) ~ e ° p C -| (•! + e 0 ) G = -e 0jpRC + ± ( l + f + pRC)] pRC + i ( l + | + pRC)'] . «i = -•o| 1 + Q Por the system to o s c i l l a t e | [ p R C + J (1 + f + PBC)] = -1 where both G and A are f u n c t i o n s of p 0 Rewriting t h i s e x pression and s u b s t i t u t i n g p = jw CD j»(2BC + ^  ) + I (1 + I ) -G To determine i f a s o l u t i o n to t h i s equation e x i s t s the f u n c t i o n G(p) and A(p) should be known. These were ap-proximated from the response curves of both a m p l i f i e r s used as i n v e r t e r s . Each a m p l i f i e r i n t u r n was set up as i n F i g . R R VWA-G e ^ 21 and a 15 v o l t (peak-to-peak) a-c. s i g n a l was a p p l i e d a t the i n p u t . The i n p u t was compared F i g . 21. I n v e r t e r f o r determining G. to the output on an o s c i l l o -scope screen and the g a i n and Frequency (cps.) Frequency (cp.s.) F i g . 22. Measured frequency response and c a l c u l a t e d open-loop g a i n of the P h i l b r i c k and Storage A m p l i f i e r s . 42 phase r e l a t i o n s were measured over a f r e q u e n c y range from 20 to 300.000 c p . s . The db. g a i n and phase l a g over t h i s range are graphed f o r b o t h a m p l i f i e r s i n F i g . 22. The c u r v e s f o r open-loop g a i n were o b t a i n e d from the e x p r e s s i o n e i I f f Hence. ' o ^ i " e Q/e< + 1 S u b s t i t u t i n g the component v a l u e s R = 33 K., r = 1 Meg* and C == 0.5 ( i f . i n t o e q u a t i o n ( 1 ) , jw(0.033 + ^ ^ ) + i (2.066) = -G . A t f r e q u e n c i e s below lOOO c p . s . A i s l a r g e and t h i s e x p r e s -s i o n can be s i m p l i f i e d t o G = -jw(0.033) or iGl = 0 . 0 3 3 U ) ^G = -90° But G has a phase l a g of -90° a t some f r e q u e n c y beyond 200 K c , which i m p l i e s IGl - 0.033(200,000)(2w) =41,500 . S i n c e IGl does not exceed 15,000 t h e r e i s no s o l u t i o n a t low f r e q u e n c i e s . 5 A t f r e q u e n c i e s aboVe 10 c p . s . b o t h G and A a r e s m a l l . R e w r i t i n g e q u a t i o n ( l ) , GA = -(0.033JO) + 0.033AJU) + 2.066). T h i s e x p r e s s i o n cannot be s a t i s f i e d a t h i g h f r e q u e n c i e s s i n c e the p r o d u c t GA i s s m a l l and 0) i s v e r y l a r g e . 43 At an intermediate frequency o f roughly 4000 c.p.s. ( i n 4000 = 8*3) the magnitude of both sides of the preceding expression do correspond. However, the phase of GA i s about -12° (sum of the angles of 0 and A) and that of the l e f t s i d e i s c l o s e to -90°. Thus i t can be s a f e l y concluded t h a t the c i r c u i t i s b a s i c a l l y s t a b l e . Coupling through the power supply was d e f i n i t e l y confirmed by using both a m p l i f i e r s as i n v e r t e r s and connect-i n g both to the same power supply. When an a-c, s i g n a l was a p p l i e d t o the P h i l b r i c k a m p l i f i e r a v o l t a g e of comparable magnitude and same frequency was detected a t the output of the storage a m p l i f i e r even though there was no d i r e c t i n t e r -c onnection. A f i n a l c o n s i d e r a t i o n i n t h i s c i r c u i t i s t h e h o l d i n g condenser C^. A long time constant and accurate v o l t a g e storage can be a c h i e v e d only i f t h i s condenser i s ofgood q u a l i t y . I t must have n e g l i g i b l e c u r r e n t leakage and small charge a b s o r p t i o n . These p r o p e r t i e s are ob t a i n a b l e i n pol y s t y r e n e condensers. Pulse A m p l i f i e r I t i s assumed that the output of the photo-tube amp-l i f i e r corresponding to the r i s i n g edges of the c a l i b r a t i o n frame and f u n c t i o n frames i s a ramp r i s i n g to 50 v o l t s i n 1/10 m i l l i s e c o n d . Hence, the pulse a m p l i f i e r must respond r a p i d l y to a wave-form with a p o s i t i v e slope of 0.5 v o l t s per microsecond. Two a m p l i f y i n g stages are p r o v i d e d i n F i g . 23 to in c r e a s e the slope of the incoming waveform. The © +300 Westinghouse l / l / l 132AW2F -300 Input f o r PA2 and PA3 (gate c o n t r o l l e d by-f l i p - f l o p ) . - 220 K., 10$ - 470 uuf. *2 - 100 K.„ 10$ c 2 - 0.02 uf. *3 - 22 K., 10$ c 3 - 0.01 uf. - 1 Meg.. 10$ c 4 - .001 uf. % - 270 K., 5$ - 2.2 Meg., 5$ VI - 12AX7 - 150 K., 5$ V2 - 6AK5 % - 680 K., 5$ V3 - 6AQ5 i n {?) out 1 P A 1 (gate c o n t r o l l e d by p h a n t a s t r o n ) i 2) -300 PA out Symbol P i g . 23. Pulse A m p l i f i e r . 44 f i r s t stage i s the cathode-coupled amplifier VI and the sec-ond a pentode amplifier V2. The cathode-coupled amplifier has two inputs, one of which i s normally held at the fixed zero signal l e v e l . If a s u f f i c i e n t l y large negative voltage i s applied to thi s reference input (pin 3) the c i r c u i t w i l l not respond to a triggering waveform. Thus a convenient means i s available for blocking the c i r c u i t . This type of amplifier offers a further advantage. Its inherent low impedances reduce the effects of shunting capacitance and thus increase i t s frequency response. This i s desireable i f the delay through the pulse amplifier i s to be a minimum. •. The pentode V2 triggers the adjacent blocking o s c i l l a t o r by a current pulse through the plate c i r c u i t of V3. Since t h i s triggering operation i s i d e a l l y carried but by a constant current generator, the large rp (in the neigh-bourhood of zero bias) of a pentode makes thi s tube prefer-able to a triode. In the quiescent state the grid of V2 i s at ground level and the bias i s fixed by the voltage drop across the cathode r e s i s t o r R3 resulting from a small d-c. current drawn through one of the transformer windings. The operation of the c i r c u i t may be described as follows. I n i t i a l l y V3 i s cut off by a -50 vo l t bias on i t s control g r i d . A positive trigger applied to the input i s amplified by VI then applied to the control g r i d of V2. V2 conducts rapidly and a current surge results i n the plate winding of the transformer. This surge induces a positive voltage i n the grid winding which i s added to the grid bias. 4 5 When the grid cut-off voltage i s reached V3 starts t o conduct and the plate current and gr i d voltage increase more and more rapidly. This continues u n t i l the gain around the plate-grid loop equals unity. Regeneration then occurs and the trigger i s no longer needed to sustain the operation. As soon as the control grid becomes s l i g h t l y positive with respect to the cathode (which i s at ground potential) grid current starts to flow and the condenser Cg between the cathode and grid-bias network i s charged negatively. The voltage across Cg must be subtracted from the voltage across the grid winding to give the actual g r i d driving Voltage, A temporary equilibrium i s reached when the power dissipated i n the grid c i r c u i t becomes equal to that supplied by the plate c i r c u i t . However, this state i s terminated when the grid current becomes so large that the voltage across Cg i s changing more rapidly than the voltage supplied by the transformer. The gr i d then drops, plate current decreases, a further decrease i n g r i d potential results and regeneration again occurs u n t i l the grid i s driven beyond cutoff. When the tube cuts off, the plate voltage r i s e s above the positive supply voltage as the transformer core remagnetizes. This gives r i s e t o a positive overshoot of the output pulse. Be-fore the blocking o s c i l l a t o r can be reactuated the charge on C3 must be dissipated through the gr i d leak. A Westinghouse l / l / l transformer i s used (Rad. Lab, No.— 132AW2P). This transformer emits a very narrow pulse but requires a fast triggering waveform; consequently, the load to thi s c i r c u i t should offer low shunting capacitance 46 between the p l a t e output and ground. Notice t h a t the p l a t e winding c o n s i s t s of a s e r i e s connection of two transformer windings. T h i s arrangement steps down the v o l t a g e going to the g r i d thus p r o v i d i n g a l a r g e r p l a t e p u l s e . The c i r c u i t was t e s t e d with a sawtooth waveform with a r i s i n g edge of 0.5 v o l t s per microsecond and an amplitude of f i v e v o l t s . The output pulses had a 200 v o l t negative exc u r s i o n and a 70 v o l t p o s i t i v e overshoot. The width of the negative p o r t i o n was one microsecond. This pulse has a l a r g e peak power s i n c e a heavy p l a t e c u r r e n t flows i n V3 d u r i n g t h i s i n t e r v a l , thus a low r e s i s t i v e load can be d r i v e n without a p p r e c i a b l y a t t e n u a t i n g the p u l s e . The t o t a l d e lay through the c i r c u i t i s about 3.5 microseconds, of which one microsecond occurs across the double t r i o d e VI. A more complete d e s c r i p t i o n of b l o c k i n g o s c i l l a t o r s i s g i v e n i n Waveforms (13, p. 205). Comparator This c i r c u i t developed by P. Hildebrand f o r the m u l t i p l i e r (7, p. 27) i s used i n the coincidence c i r c u i t r y . In P i g , 24 the pentode V2 i s normally conducting ( c o n t r o l b i a s i s e s t a b l i s h e d by g r i d c u r r e n t through R 2) and the diode VI i s non-conducting. When a negative sweep voltage a p p l i e d a t the input reaches e q u a l i t y with the r e f e r e n c e v o l t a g e - E r the diode conducts and a negative pulse i s a p p l i e d to the c o n t r o l g r i d of V2, The cathode c u r r e n t through t h i s tube decreases and a negative v o l t a g e i s induced i n the input wind-i n g of the transformer. The diode then conducts more s t r o n g l y , in-(D+300 M Symbol out (§)out ® -300 Westinghouse 176AW2F or ... 134BW2F VI - 6AL5 V2, V3 ~ 6AK5 R l - 100 E., 10$ •- 4.7 Meg., 10$ R 3 33 .Ke Q 10$, 1 watt R 4 - 56 K., 10$, 1 watt R5 — 33 Ko o 10$ R6 - 1 Meg., 10$ Cl - 0.001 uf. c 2 - 0.1 uf. c 3 - 0.01 uf. Fig . 24. Multiar Comparator. 47 regeneration occurs and V2 i s rapidly cut o f f . When the charge on CJL discharges through Rg, V2 conducts, the regen-erative loop i s again closed and another cycle occurs, Thus, a t r a i n of positive pulses are generated at tie plate of V2, This t r a i n continues u n t i l the input sweep returns to a voltage level less negative than E r . The second pentode V3 i s used to invert the pulses appearing on the plate of V2. The r i s e time of a pulse i s approximately one micro-second, i t s width, two microseconds and i t s height, 230 v o l t s . Blanking Phanlastron Figure 25 i l l u s t r a t e s the basic phantastron (14). I n i t i a l l y grid current from V3 i s flowing through R and the g r i d i s held at ground. Also, the suppressor of V2 i s at -30 v o l t s — a s u f f i c i e n t l y negative bias on a 6AS6 to cut off plate current. Thus, the plate l e v e l of V2 i s held at Eg' ssor Fig . 25. Basic Phantastron and i t s waveforms. 48 and a l l cathode c u r r e n t except t h a t passing through R i t going to the screen, which i s a t about 65 v o l t s . Since both the p l a t e and g r i d of V2 are coupled through C, a neg-a t i v e t r i g g e r a p p l i e d to the p l a t e a l s o reaches the g r i d . Immediately the screen c u r r e n t i s s h a r p l y reduced and the r e s u l t i n g r i s e i n screen p o t e n t i a l i s r e s i s t i v e l y coupled to the suppressor. The suppressor r i s e s to s i x v o l t s and i s h e l d at t h i s l e v e l by i h e diode V3. P l a t e c u r r e n t now f l o w s j p l a t e v o l t a g e drops about seven v o l t s ; and the diode T l i s blocked. Meanwhile, the g r i d has s e t t l e d to -10 v o l t s , the b i a s r e q u i r e d f o r the small c u r r e n t permitted by the p l a t e r e s i s t o r . This i n i t i a l step i s f o l l o w e d by a M i l l e r sweep ge n e r a t i o n (13, p. 195). A c u r r e n t (E^' + 10)/R flows through C to the p l a t e . Since the g r i d s i d e of C i s h e l d at -10 v o l t s the p l a t e side drops at a r a t e (Ej_' + 10)/RC v o l t s per second. This process continues, the g r i d r i s i n g s l i g h t l y to permit the p l a t e to take the s l i g h t l y i n c r e a s i n g c u r r e n t needed by the p l a t e r e s i s t o r , u n t i l the p l a t e v o l t -age runs a g a i n s t the "knee" i n the p l a t e curve (bottoms). At about 15 v o l t s a t r a n s f e r of space c u r r e n t from the p l a t e to the screen begins. This e f f e c t coupled with bottoming prevents any f u r t h e r drop i n p l a t e voltage; hence, the g r i d s i d e of C r i s e s e x p o n e n t i a l l y towards E^' u n t i l g r i d c u r r e n t f l o w s . At t h i s p o i n t screen c u r r e n t i n c r e a s e s , the suppressor goes negative, and the c i r c u i t r e t u r n s to i t s o r i g i n a l s t a t e . The r a t e a t which the p l a t e r e t u r n s to Eg' i s determined by the time constant Rj_C where Rj_ i s the p l a t e r e s i s t o r . The P3>B6 V3b — 390 K., 10$ — 150 E., 10$ R3 — 1 M e g . , 10$ — 180 K., 10$, - 25 K. , 10$, - 100 K. , 10$ B7 — 50 K., 10$, Rs - 1 K., 10$ % — 270 K., 10$ *10 — 470 K., 5$ »11 — 3.3 Meg. , 10$ Bl2 12 E., 5$ R13 470 E., 10$ —• 1 Meg. P o t . — 940 uu f . — 0.01 o f . c 3 — 100 uu f . VI, V2, V5 - 12AX7 V3 - 6AL5 V4 6AS6 4 wat t out F i g . 26. B l a n k i n g Phan tas t ron 49 diode V4 i s not e s s e n t i a l but i t does prevent the suppressor from being c a r r i e d so f a r p o s i t i v e l y t h a t i t may " s t i c k " because of secondary e l e c t r o n emission,, For a l l p r a c t i c a l purposes the p l a t e rundown during the M i l l e r sweep ge n e r a t i o n can be considered l i n e a r . Hence, the time 6t r e q u i r e d f o r the p l a t e to reach 15 v o l t s i s ( 9 ) A + ( E2' - 1 5 ) R C (2) 6t = E i , + 1 Q sec. I f E 2 = E2* - 15 and E x = E ^ + 10 then 6t = RC 5s. sec. E n Furthermore, i f E 2 i s a constant and E]_ i s p r o p o r t i o n a l to the v e l o c i t y of the scanning d i s c then 6t i s i n v e r s e l y p r o p o r t i o n a l to v, as r e q u i r e d . In the d e t a i l e d c i r c u i t ( F i g . 26) E 2 i s f i x e d at approximately 150 v o l t s by the v o l t a g e d i v i d e r c i r c u i t f e e d i n g the cathode f ollower V2a. The v o l t a g e Ej_, p r o p o r t i o n -a l to v, i s obtained from the h o l d i n g c i r c u i t i n F i g . 10 and a p p l i e d to the g r i d of the cathode f o l l o w e r V i a . The arrange-ment of Via and Vlb i n c r e a s e s the l i n e a r i t y of the output Ei_' ; f o r a change i n the l e v e l of E^ r a i s e s the p l a t e of Vlb by an equal amount with a n e g l i g i b l e change i n the c u r r e n t p a s s i n g through both tubes. The o p e r a t i n g p o i n t s of Via and Vlb were chosen so t h a t t h i s c u r r e n t i s one m i l l i a m p e r e . The 12 K. r e s i s t o r R^2 provides a ten v o l t v a r i a t i o n between Ej_ and E]_' , thus s a t i s f y i n g the requirement that Ej_ = E^' + 10. The cathode f o l l o w e r V2b i s used to provide a low r e s i s t a n c e r e c h a r g i n g path f o r C. This r e s u l t s i n a s h o r t e r recovery 10 6t (milliseconds) F i g . 27. P r e c i s i o n Test of the Phantastron. C o n t r o l v o l t a g e Ei vs. blanking i n t e r v a l 6 t - — c a l c u l a t e d and measured. 50 time f o r the c i r c u i t . The only square waveforms which can be used f o r bl a n k i n g the pulse a m p l i f i e r are those of the screen and suppressor; however, e i t h e r waveform must be i n v e r t e d before i t is useful. The sharpest waveform—that of the suppressor-is inverted and a m p l i f i e d by VS. The r e s i s t o r s a s s o c i a t e d with this tube provide a zero output ( p i n 3) duri n g the quie s c e n t s t a t e . The r e s i s t a n c e R i s v a r i a b l e so t h a t the b l a n k i n g i n t e r v a l can be s e t f o r normal o p e r a t i o n of the scanning d i s c . Any departure from n o r m a l i t y i s then compensated f o r by changes i n E p This c i r c u i t was t e s t e d by a p p l y i n g Ej_, t r i g g e r i n g the c i r c u i t r e p e t e t i v e l y . and measuring the d u r a t i o n of the suppressor waveform on an o s c i l l o s c o p e . T h i s time was com-pared to the c a l c u l a t e d time using equation ( 2 ) . To avoid measuring R and E 2 i t was assumed t h a t the c a l c u l a t e d and measured values of 6t correspond when E^ = 40 v o l t s . Re-expressing equation (2), Constant and on e v a l u a t i n g the constant using the data corresponding to Ei = 40 v o l t s 6t = ^ Ei The measured and c a l c u l a t e d v a l u e s of 6t f o r v a r i o u s values of E^ are graphed i n P i g . 27. 51 T e s t i n g the Timing and Coincidence C i r c u i t r y The timing and c o i n c i d e n c e c i r c u i t r y assembly was t e s t e d independently of the f u n c t i o n generator and m u l t i p l i e r * The pulse sequence PI, P3, F5« F l , e t c , was su p p l i e d by a pulse generator at p o i n t D i n F i g . 8. The p e r i o d between pu l s e s was one m i l l i s e c o n d . For reasons which -become apparent a f t e r examining the waveforms i n F i g . 28 pulse a m p l i f i e r PA1 was permitted to generate only P5. This was accomplished by a d j u s t i n g the v a r i a b l e r e s i s t o r E i n the bl a n k i n g phantastron ( F i g . 26) u n t i l the bl a n k i n g p u l s e was somewhat g r e a t e r than two m i l l i -seconds wide. A l s o , so t h a t p u l s e P6 could be used as the marker pulse PO i t was necessary to a d j u s t the r e s i s t o r Rg i n F i g . 10 to guarantee t h a t P6 occurred roughly midway between P5 and PI. I f the i n t e r v a l between p u l s e s P6 and PI i s too small, f l i p - f l o p FF1 w i l l have i n s u f f i c i e n t time to respond to both p u l s e s . With these minor adjustments the whole o p e r a t i o n was p o s s i b l e . The important waveforms are i l l u s t r a t e d i n F i g . 27 with emphasis on t h e i r o r i e n t a t i o n w i t h r e s p e c t to the in p u t p u l s e s . P5 PI P3 P5 PI P3 P5 PI P3 IN BPH PAl P5 P5 P5 M2 SWEEP M2 PF1 (PA2 gate) PA2 P6 PO P I V P6 PO i l PI P6 PO P i FP3 (PA3 gate) FA3 P3 P3 P3 INPUT TO INTEGRATOR (R2C2) INTEGRATOR (R2C2) N(t) _/ P4 P4 Ml F i g . 28. Test waveforms o c c u r r i n g i n the tim i n g and coi n c i d e n c e c i r c u i t r y . 52 Remarks The o b j e c t of t h i s t h e s i s was t o design and c o n s t r u c t a number of elementary c i r c u i t s which can be stand-a r d i z e d f o r the whole computer. T h e i r a p p l i c a t i o n i n t h i s paper has been l i m i t e d t o the timing and c o i n c i d e n c e c i r c u i t r y c o n t r o l l i n g ' t h e f u n c t i o n generator and m u l t i p l i e r . No attempt has been made to conduct t e s t s which would i n d i c a t e the ac-curacy of the o v e r a l l o p e r a t i o n s i n c e such t e s t s w i l l have more meaning and w i l l be more e a s i l y c a r r i e d out when the c a l i b r a t i o n and f u n c t i o n waveforms are a v a i l a b l e . There w i l l be a constant delay a r i s i n g i n the s e l e c t i o n of the sampling p o i n t which i s independent of the a b s c i s s a x. However, the r e s u l t i n g e r r o r can be compensated e a s i l y by b i a s i n g the input v o l t a g e -K(b + x ) . The r e q u i r e d b i a s can be determined by u s i n g the c a l i b r a t i o n frame as a f u n c t i o n . The p u l s e p a i r s (PI, P6) and (PI, P8), which norm-a l l y do not c o n t r i b u t to the o v e r a l l o p e r a t i o n , now are use-f u l ( r e f e r to P. 18). I f the a b s c i s s a input v o l t a g e -K(b + x) v a r i e s s i n u s o i d a l l y with small amplitude about a -25 v o l t mean, the output of the m u l t i p l i e r E f E r / E ^ w i l l have a square waveform. Assuming E r i s constant E f o s c i l l a t e s between 0 and E ^ as (b + x) o s c i l l a t e s about the p o i n t a. I d e a l l y , no time delays occur through the system and the amplitude of the p o s i t i v e and negative e x c u r s i o n s 1 a b o u t the p o i n t a are equal. Consequently, the output waveform i s 0 or E r f o r equal time i n t e r v a l s . The presence of a c o n s t a n t time d e l a y through the system r e s u l t s i n an average value of (b + x ) which i s g r e a t e r t h a t the de-53 s i r e d value a, and the output waveform has an amplitude E r f o r an i n t e r v a l g r e a t e r than h a l f the p e r i o d . I f the time delay i s s u f f i c i e n t l y l a r g e the sampling p o i n t may never occur i n a r e g i o n where Ef = 0, and the output i s c o n s t a n t . I t f o l l o w s , then, t h a t the e f f e c t of constant time delay can be e l i m i n a t e d by v a r y i n g a v o l t a g e b i a s on the a b s c i s s a input u n t i l the output waveform, o s c i l l a t i n g between 0 and E r , assumes e i t h e r value f o r h a l f the p e r i o d . 5 4 References 1 . Chance, Hughes, MacNichol, Sayre and Wi l l i a m s , Waveforms, New York, Toronto and London, McGraw-Hill, 1 9 4 9 (Ridenour, L. N.. ed., M.I.T. Rad i a t i o n Laboratory  S e r i e s , v o l . 1 9 . ) 2 . P i n d l e y , L. D., "Phantastron Computes Pulse-Width R a t i o s ^ " E l e c t r o n i c s , v o l . 2 7 , no. 1 (January, 1 9 5 4 ) , pp. 1 6 4 r -1 6 7 . 3 . Freeman, H. and Parsons, E., "A Time-Sharing Analog Mult-i p l i e r , " Transactions of the I.R.E.. v o l . E C - 3 , no. 1 (March, 1 9 5 4 ) , pp. 1 1 - 1 7 . 4. Goldberg, Edwin A., "A High Accuracy Time D i v i s i o n Mult-i p l i e r , " Cyclone Symposium 1 9 5 2 , B.C.A. Review, v o l . X I I I (September, 1 9 5 2 ) , p. 2 6 5 . 5 . Greenwood, Holdam and MacRae, E l e c t r o n i c Instruments, New York, Toronto and London, McGraw-Hill, 1 9 4 8 , pp. 8 3 - 8 9 . (Ridenour, L. N., ed., M.I.T, Radiation  Laboratory S e r i e s , v o l . 2 1 . ) 6 . Hildebrand, B. P., "A Sampling-Type Function Generator and Four-Quadrant Analog M u l t i p l i e r , " M.A.Sc. Thesis, U n i v e r s i t y of B r i t i s h Columbia, 1 9 5 6 . 7 . Korn, G, A. and Korn, T. M,, E l e c t r o n i c Analog Computers, New York, McGraw-Hill, 1 9 5 2 , 8 . Lilamand, M,, " M u l t i p l i e u r s A D6coupage ^emporel," L'Onde E l e c t r i q u e . v o l . XXXV, no. 3 3 5 ( F e v r i e r , 1 9 5 5 " ^ pp. 1 4 2 - 1 5 0 . 9 . Millman, J . and Puckett, T. H., "Accurate Linear B i d i -r e c t i o n a l Gates," Proceedings of the I.R.E., v o l , 4 3 , no, 1 (January, 1 9 5 5 ) , pp. 2 9 - 3 7 . 1 0 . M o r r i l l , C. D. and Baum, R. V., " S t a b i l i z e d Time-Division M u l t i p l i e r , " E l e c t r o n i c s , v o l . 2 5 , no. 1 2 (December, 1 9 5 2 ) , pp. 1 3 9 - 1 4 1 . 1 1 . Paynter, H. M., ed., A Palimpsest on the E l e c t r o n i c Analog A r t , Boston, Mass., Geo. A. P h i l b r i c k Researches, Inc., 1 9 5 5 . 1 2 . Rubinoff, M o r r i s , "Analogue vs. D i g i t a l Computers—a Comparison," Proceedings of the I.R.E., v o l . 4 1 (October, 1 9 5 3 ) , pp. 1 2 5 4 - 1 2 6 2 . 55 Appendix The P h i l b r i c k o p e r a t i o n a l a m p l i f i e r s are compact p l u g - i n u n i t s p r i m a r i l y intended f o r feedback op e r a t i o n s * They f e a t u r e balanced d i f f e r e n t i a l i n p uts f o r v e r s a t i l i t y and minimum d r i f t . Model K2-W embodies bo t h high performance and economy of op e r a t i o n , whereas K2-X o f f e r s higher performance at t h e expense of g r e a t e r power consumption. The l a t t e r a m p l i f i e r i s not intended to r e p l a c e the K2-W, b u t serves f o r more demanding a p p l i c a t i o n s . F o l l o w i n g are the general spec-i f i c a t i o n s f o r both models and t h e i r c i r c u i t diagrams. Model K2-W O p e r a t i o n a l A m p l i f i e r GAIN 15,000 DC, open-loop POWER REQUIREMENTS 4.5 ma. at+300 VDC 4.5 ma. at-300 VDC 0.6 amp* a t 6.3 V INPUT IMPEDANCE Above 100 Megohms OUTPUT IMPEDANCE Less than IK open-loop, below 1 ohm f u l l y f e d back DRIFT RATE 5 m i l l i v o l t s per day, r e f e r r e d to the input VOLTAGE RANGE -50 to +50 VDC, a t output and inputs INPUT CURRENT Less than 0.1 micro-amp f o r e i t h e r i n p u t OUTPUT CURRENT -1 ma. to +1 ma.,driv-in g 50K loa d over f u l l v o l t a g e range Model K2-X O p e r a t i o n a l A m p l i f i e r GAIN 30,000 DC, open-loop POWER REQUIREMENTS 7.5 ma. a t +300 VDC 5.2 ma. a t -300' VDC 0.75 amp. a t 6.3 V INPUT IMPEDANCE Above 100 Megohms OUTPUT IMPEDANCE Below 300 ohms open-loop; l e s s than 0.2 ohms f u l l y f e d back DRIFT RATE 5 m i l l i v o l t s per day r e f e r r e d to the input VOLTAGE RANGE -50 to +50 VDC f o r inputs (together) -100 to +100 VDC f o r output (maximum) INPUT CURRENT Less than 0.1 micro-amp, f o r e i t h e r i n p u t OUTPUT CURRENT -2ma. to +2 ma., d r i v -i n g 25K load from -50 to +50 VDC INPUT BIAS P o s i t i v e i n p u t should operate 0.6 V high a t balance ( e x t e r n a l b i a s INPUT BIAS P o s i t i v e i nput should operate 1.5 V high a t b a l a n c e — a d j u s t -able e x t e r n a l b i a s required-RESPONSE 2 usee, r i s e time wi t h band width over 100 KC when used as an i n v e r t e r , RESPONSE 1 visec. r i s e time wi t h band width over 250 KC when used as an i n v e r t e r AUGMENTED POWER 50K 1W r e s i s t o r connected between output and -300 VDC supply. D r i v e s 33K l o a d over f u l l v o l t a g e range ) 220 K. 1 Meg. 2.2 Meg. 470 K. 10 K. 270 K. E 7 - 680 K. RQ - 4.7 Meg. Cx - 7.5 uuf. C 2 - 500 uuf. xn i n 1 K2-W Symbol R e s i s t o r t o l e r a n c e - 5$ Model K2-W O p e r a t i o n a l A m p l i f i e r . George A. P h i l b r i c k . Researches, Inc. heaters (7) cs: 6.3 »2 -@+300 3) ground <' ( § ) o u t • B 9 NE2 $ ) NE2 B 12 - ® -300 150 K. 150 K. , 470 K. 1 Meg. 1 180 K. 68 K. 2.2 K. 82 K. 1 watt Bg R 1 0 B l l B12 220 K. 10 Meg. 1.5 Meg. 4.7 Meg. 15 |4Uf< 5000 yuf, 7.5 uuf, i n i n + K2-X out Symbol B e s i s t o r t o l e r a n c e - 5% Model K2-X Op e r a t i o n a l A m p l i f i e r . George A. P h i l b r i c k Besearches, Inc. 

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