Abstract :
A single-chip (67/spl times/90 mil) integrated-circuit operational amplifier using thin-film resistors and super-gain transistors has been designed to achieve dc follower accuracies of 0.001 percent with 100-k/spl Omega/ source resistance. The circuit achieves gains of 140 dB using thermally balanced layout designs for both input and output stages, nulled drifts of 0.3 /spl mu/V//spl deg/C, and offset currents well under 1 nA. All other dc specifications including power-supply variation error (PSRR), common-mode gain error (CMRR), etc., are in the 1-10 ppm error range; and a procedure is given by which long-term drifts of less than 10 /spl mu/V/month can be assured. AC performance is comparable to general-purpose integrated-circuit operational amplifiers, i.e., f/SUB t/=300 kHz and slew rate of 1.2 V//spl mu/s at gain of ten. The circuit is externally compensated for unity gain with a single 390-pF capacitor and is fully input and output protected.
