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AC Boosting Compensation Scheme for Low-Power Multistage Amplifier

AC Boosting Compensation Scheme for Low-Power Multistage Amplifier. 陳明軒 2005. 4. 20. Outline. Introduction to ACBC Pole-zero map and Bode Diagram of ACBC Performance Implementation. An Introduction to ACBC. 3-stage Amplifier  provides a high DC gain

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AC Boosting Compensation Scheme for Low-Power Multistage Amplifier

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  1. AC Boosting Compensation Scheme for Low-Power Multistage Amplifier 陳明軒 2005. 4. 20

  2. Outline • Introduction to ACBC • Pole-zero map and Bode Diagram of ACBC • Performance • Implementation

  3. An Introduction to ACBC • 3-stage Amplifier  provides a high DC gain • Miller capacitance  provides a pole-split to get a higher margin • Additional AC path  provides a better stability without additional power • Feedforward path  provides a high slew rate

  4. How does ACBC work? Push-pull output stage

  5. Pole-zero Map of ACBC (without AC Path) Unstable!

  6. Pole-zero Map of ACBC (with AC Path) LHPzero

  7. Bode Diagram of ACBC(without AC path) Unstable!!

  8. Bode Diagram of ACBC(with AC path) About A2h*p2 About A2h*z1

  9. Performance • Gain Bain Width Produce: GBW=gm1/Cm • Can use a lower Cm (because p2 is now at a higher frequency) or choose a lower gm1 to get a high GBW • Phase Margin：90-arctan(GBW/p2) • GBW is larger than original • However, p2 is (A2h+gmf/gm3) larger than original =>we can get a high Margin without losing GBW • Slew rate: SR=GBW(Vgs1-Vt1) • We can get a better SR by the higher GBW • Power： • We do not need to consume additional power, but get a higher performance • Usually we will choose a lower gm1 (0.1mS) ,gm2 and gma(60uS), but a lager gm3 and gmf (1mS)

  10. Implement

  11. Bode diagram of ACBC

  12. Time domain response

  13. Comparison

  14. Reference and Question • AC Boosting Compensation Scheme for Low-Power Multistage Amplifiers by Xiaohong Peng and Willy Sansen, Fellow, IEEE • Question： • How can the additional AC path split the pole p1 and p2? • Why won’t the feedforword path produce a Left-Half-Plane zero? • Why the rising edge will be different but the falling edge won’t be in time-domain response?

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