A LOW-OUTPUT-IMPEDANCE FULLY DIFFERENTIAL OP AMP WITH LARGE OUTPUT SWING AND CONTINUOUS-TIME COMMON-MODE FEEDBACK

A fully differential (zero common-mode voltage) op amp has been developed 1 which has low output impedance, but unlike source-follower output stages, has a large output swing, namely, 8 V(p.p) for 1-k-OMEGA load and a 5-V supply. The output stage, which is a combination of common-source and source-follower stages, is driven by the two complementary outputs of the differential-output input stage. A continuous-time common-mode feedback circuit has been employed, which due to the op amp's low output impedance, causes negligible open-loop gain (95 dB) degradation. Floating compensation capacitors are used in order to reduce the capacitance value and hence area (490 mil2).