Two stage Class AB OpAmp principle M 6

Two stage – Class AB Op-Amp: principle M 6 M 5 Class - A Class - B ID 5 depends only on IB (bias current), while ID 6 depends also on VDD Paolo Bruschi 1 Very poor PSSR ! Progettazione Mixed Signa

Two stage – Class AB Op-Amp Solution 1: Bias Chain Bias chain By design: IB Solves: ID 5 and ID 6 matching is now VDD independent But: Limitations remain on the maximum output VGS Paolo Bruschi 2 Progettazione Mixed Signal

Solution 2: Floating battery Head–Tail Mesh (Monticelly Cell) The battery voltage decreases for large signals, allowing terminals A and B to swing across a full rail-to rail range Vbatt=VB-VA Paolo Bruschi 3 Progettazione Mixed Signal

First stage with folded cascode topology The floating battery class-AB control is often combined with a first stage with folded cascode structure. This stage provides increased gain and can be easily equipped with complementary input pairs to obtain rail-to-rail input range Wide swing output current mirror for improved lower output voltage limit. A complementary input pair can be added to obtain rail-torail input range Paolo Bruschi 4 Progettazione Mixed Signal

Two stage opamp with folded cascode input stage Output stage Paolo Bruschi 5 Progettazione Mixed Signal

Two stage opamp with folded cascode input stage and floating battery Miller compensation Ibias Floating battery with bias circuits Paolo Bruschi 6 Progettazione Mixed Signal