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Two stage – Class AB Op-Amp: principle

Two stage – Class AB Op-Amp: principle. M6. M5. Class - A. Class - B. Very poor PSSR !. I D5 depends only on I B (bias current), while I D6 depends also on V DD. Two stage – Class AB Op-Amp Solution 1: Bias Chain. Bias chain. By design:. I B.

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Two stage – Class AB Op-Amp: principle

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  1. Two stage – Class AB Op-Amp: principle M6 M5 Class - A Class - B Very poor PSSR ! ID5 depends only on IB (bias current), while ID6 depends also on VDD Paolo Bruschi

  2. Two stage – Class AB Op-Amp Solution 1: Bias Chain Bias chain By design: IB Solves: ID5 and ID6 matching is now VDD independent But: Limitations remain on the maximum output VGS Paolo Bruschi

  3. 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

  4. 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-to-rail input range Paolo Bruschi

  5. Two stage opamp with folded cascode input stage Output stage Paolo Bruschi

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

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