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A versatile digital-to-analog function generator and multiplier. Lovas, Laszlo Tamas


This work describes the design, construction, and testing of a digital-to-analog function generator and multiplier for analog computation and non-linear system simulation. The unit consists of two separate channels each of which is fed by a punched paper tape. Functions (of time) are represented on the tapes in binary code and are read into the machine photoelectrically. In one channel, voltage sources of constant value but of either polarity are switched into the parallel branches of a ladder network in accordance with the incoming digital information. As a result of the particular choice of resistor values in the ladder network the voltage at one end of the resistive network is proportional to the binary number signified by the polarity combination of the voltage sources. In the other channel the function represented on the tape controls the polarities of the voltage sources, and the magnitudes of the source voltages are changed according to a second function, which results in an output voltage proportional to the product of the two functions. This second function may be generated independently in the first channel, or it may be an external computer variable. One level on each tape is reserved for the generation of control pulses which can be used to de-energize the reset relay in the computer, i.e. to initiate the compute mode. The variable tape speed and gain controls greatly enhance the versatility of the device and render it very useful in analog computer simulation studies. Error analyses of two resistive decoding networks are outlined and their results are considered in the final choice of the decoding network. Complete circuit diagrams with short explanations of their operation are presented. Results of tests on accuracy, speed and general performance are summarized and illustrated.

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