1.2 V constant-gm rail-to-rail CMOS Op-Amp input stage with new overlapped transition regions technique for ECG amplifier.

The conventional technique of overlapped transition regions for producing a constant transconductance rail to rail Op-Amp input stage can only tolerate a limited amount of voltage shifting. This is limited by the minimum Vgs required for active mode operation of transistors. In this paper, we present a novel overlapped transition regions technique that overcomes the limitation of the conventional technique. This new overlapped transition regions technique has no voltage shifting limit. For both N-type and P-type conventional complementary differential input pairs, one source follower and one MOSFET are added to control the saturation point of current of input pairs. For 1.2 V single supply voltage, simulation results demonstrate ±3.71% of overall transconductance variation. Cadence SPECTRE simulator and TSMC 0.25-µm CMOS technology are used to layout and simulate this work.