A high temperature precision amplifier

A precision operational amplifier has been developed for instrumentation applications in which the circuitry must operate in ambient temperatures as high as 200°C. At 200°C the amplifier maintains an input offset voltage and current of less than 200 μV and 1 nA respectively, a gain bandwidth product of 2.2 MHz, and a slew rate of 5.4 V/μS. The amplifier is fabricated in a standard CMOS process and consumes 5.5 mW of power at a supply voltage of 5 V. A continuous time auto-zeroed amplifier topology is used to achieve the low offset voltage levels. At high temperatures the leakage currents of the sample and hold switches used to achieve auto-zeroing, degrading the offset correction voltages stored on the hold capacitors. This degradation is reduced by using large external hold capacitors and by minimizing the diffusion area of the switches through the use of a doughnut shaped layout. The effect of the voltage degradation is reduced by sensing the offset correction voltage with a low sensitivity differential auxiliary input stage. A new input switch topology is used to reduce the amplifier's input offset current at high temperatures