A CMOS differential-difference amplifier with class-AB input stages featuring wide differential-mode input range

In this paper, I present a CMOS differential-difference amplifier (DDA) circuit with a pair of matched class-AB input stages that each produce a differential output current that is an odd-symmetric, expansive nonlinear function of its differential-mode input voltage. In contrast to those of the usual differential pair, the nonlinear current-voltage characteristics of these class-AB transconductors do not saturate and allow the proposed DDA circuit to function properly with a differential-mode input voltage range that is comparable to the transconductor's common-mode input voltage range. I show experimental measurements from a proof-of-principle prototype circuit breadboarded from transistor arrays that were fabricated in a 500-nm CMOS process through MOSIS.