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Design techniques for high-temperature analog and mixed-signal integrated circuits Sadeghi, Nima


Reliable high-temperature analog and mixed-signal CMOS circuits are required for several applications including aerospace, automotive control, oil field instrumentation, and pulp and paper digesters. In particular, in this work we focus on the design of key building blocks of a miniature sensor interface system that is intended to operate in a pulp and paper digester and collect and record sensory data such as pressure and temperature along its trajectory within the digester. The temperature inside the digester can be as high as 180℃. Design considerations and techniques for implementing these building blocks both at component- and circuit-levels are presented. At the component level, techniques for designing monolithic resistors with a desired temperature coefficient (TC) are proposed, and an analysis on the effects of design parameters such as resistor length, width and the number of fingers on the TC of such multi-finger resistor structures is presented. Furthermore, since the foundry-provided transistor models are typically valid up to 125℃, various NMOS and PMOS transistors with diff erent sizes are implemented to study their behaviour at high temperature. Based on our observations, a suitable sizing for transistors is suggested for circuits operating up to 200℃. At the circuit-level, several key building blocks such as bias circuits, voltage references and oscillators are designed and proof-of-concept prototypes are implemented in a standard 0.13 ㎛ CMOS process. The operation of the circuits is experimentally validated over the temperature range of interest, namely, 25 to 200℃. Also, a low-complexity resistive and capacitive temperature-compensation techniques for high-temperature relaxation oscillators is proposed. Although the temperature stability of the proposed oscillator (108 ppm/℃) compares favourably with that of state-of-the-art designs, it occupies 0.007 mm² which is 2.3 to 114 times smaller than other comparable designs. Also, the proposed circuit operates reliably up to 200℃ (as compared to 125℃ in other designs). Although the proposed techniques are only validated using proof-of-concept prototypes in a 0.13 ㎛ CMOS technology, they are general and our preliminary studies on several technologies indicate that the techniques can be implemented in other CMOS technologies as well.

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