CMOS low-voltage operational amplifiers with constant-G/sub m/ rail-to-rail input stage

Abstract

Two 3-V CMOS low-voltage operational amplifiers (op-amps) with constant transconductance (g/sub m/) rail-to-rail input stages are presented. The constant g/sub m/ ensures a constant unity-gain frequency within the whole common-mode input range. Two new methods to control the g/sub m/ of the input stage are introduced. The op-amps contain the same class-AB output stage with rail-to-rail output swing. The common-mode input voltage swing extends the positive supply rail by 600 mV and the negative supply rail by 200 mV. The output voltage can reach the supply rails within 130 mV. The output current of the op-amps was limited to +or-2 mA, voltage gain was 85 dB, and the unity-gain frequency was 165 kHz. The op-amps were integrated in a semicustom CMOS process with transistor lengths of 10 mu m.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>