Progettazione Mixed Signa Paolo Bruschi1 Two stage – Class AB Op-Amp: principle Class - A Class - B M5 M6 I D5 depends only on I B (bias current), while I D6 depends also on V DD Very poor PSSR !

Progettazione Mixed Signal Paolo Bruschi2 Two stage – Class AB Op-Amp Solution 1: Bias Chain Solves: I D5 and I D6 matching is now V DD independent IBIB But: Limitations remain on the maximum output V GS Bias chain By design:

Progettazione Mixed Signal Paolo Bruschi3 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 V batt =V B -V A

Progettazione Mixed Signal Paolo Bruschi4 First stage with folded cascode topology Wide swing output current mirror for improved lower output voltage limit. A complementary input pair can be added to obtain rail-to- rail input range 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

Progettazione Mixed Signal Paolo Bruschi5 Two stage opamp with folded cascode input stage Output stage

Progettazione Mixed Signal Paolo Bruschi6 Two stage opamp with folded cascode input stage and floating battery Miller compensation Floating battery with bias circuits I bias