A High-Gain High-Speed Low-Power Class-AB Operational Amplifier Hassan Sarbishaei Tahereh Kahookar Toosi Ehsan Zhian Tabasy Reza Lotfi Integrated Systems Lab, Ferdowsi University of Mashhad, Iran

Integrated Systems Lab, Ferdowsi University of Mashhad Outline Introduction High-gain Opamps Positive Feedback Amplifier Current Driven Bulk Technique Single-Stage Class-AB Structure Proposed Opamp Simulation Results Conclusion

Integrated Systems Lab, Ferdowsi University of Mashhad Introduction Demand for portable equipments + Technology scaling => Low-power low-voltage circuit design. Design bottleneck in LP LV circuit design : Fast and accurate opamps. => Low-voltage high-gain opamp architecture is of much interest.

Integrated Systems Lab, Ferdowsi University of Mashhad Outline Introduction High-gain Opamps Positive Feedback Amplifier Current Driven Bulk Technique Single-Stage Class-AB Structure Proposed Opamp Simulation Results Conclusion

Integrated Systems Lab, Ferdowsi University of Mashhad High-gain Opamps Three common methods – Cascoding and gain boosting – Cascading – Positive feedback

Integrated Systems Lab, Ferdowsi University of Mashhad High-gain Opamps (Cont’d) Disadvantages – Cascoding : Not suitable for low-voltage applications. – Cascading : Frequency compensation complexity. – Positive Feedback : Nonlinearity issues, Sensitive to process variations.

Integrated Systems Lab, Ferdowsi University of Mashhad Outline Introduction High-gain Opamps Positive Feedback Amplifier Current Driven Bulk Technique Single-Stage Class-AB Structure Proposed Opamp Simulation Results Conclusion

Integrated Systems Lab, Ferdowsi University of Mashhad Positive Feedback Amplifier [Amourah et al. ISCAS2001]

Integrated Systems Lab, Ferdowsi University of Mashhad Positive Feedback Amplifier (Cont’d) Advantages – High DC-gain – No CMFB circuit is required. – High PSRR from negative rail. Disadvantages – Limited output voltage swing – Process variation dependency

Integrated Systems Lab, Ferdowsi University of Mashhad Outline Introduction High-gain Opamps Positive Feedback Amplifier Current Driven Bulk Technique Single-Stage Class-AB Structure Proposed Opamp Simulation Results Conclusion

Integrated Systems Lab, Ferdowsi University of Mashhad Current Driven Bulk Technique Based on equations above : Disadvantages : Lower output impedance and slew rate. Low frequency pole-zero pair. [Ardalan et al. ICECS2004 ]

Integrated Systems Lab, Ferdowsi University of Mashhad Outline Introduction High-gain Opamps Positive Feedback Amplifier Current Driven Bulk Technique Single-Stage Class-AB Structure Proposed Opamp Simulation Results Conclusion

Integrated Systems Lab, Ferdowsi University of Mashhad Single-Stage Class-AB Structure Flipped Voltage Follower (FVF) – Almost constant V GS(MFVF) – Low output impedance – High sinking capability [Ramirez-Angulo et al. ISCAS2004 ]

Integrated Systems Lab, Ferdowsi University of Mashhad Single-Stage Class-AB Structure (Cont’d) Low-Voltage Single-Stage Class-AB Amplifier using FVF block Advantage – Small, non slew rate limited settling time. [Baswa et al. ISCAS 2004 ]

Integrated Systems Lab, Ferdowsi University of Mashhad Outline Introduction High-gain Opamps Positive Feedback Amplifier Current Driven Bulk Technique Single-Stage Class-AB Structure Proposed Opamp Simulation Results Conclusion

Integrated Systems Lab, Ferdowsi University of Mashhad Proposed Opamp Combination of all three previous techniques => High gain, High slew-rate and high swing opamp.

Integrated Systems Lab, Ferdowsi University of Mashhad Outline Introduction High-gain Opamps Positive Feedback Amplifier Current Driven Bulk Technique Single-Stage Class-AB Structure Proposed Opamp Simulation Results Conclusion

Integrated Systems Lab, Ferdowsi University of Mashhad Simulation Results

Integrated Systems Lab, Ferdowsi University of Mashhad Simulation Results (Cont’d) DC-gain at all process and temperature corners :

Integrated Systems Lab, Ferdowsi University of Mashhad Outline Introduction High-gain Opamps Positive Feedback Amplifier Current Driven Bulk Technique Single-Stage Class-AB Structure Proposed Opamp Simulation Results Conclusion

Integrated Systems Lab, Ferdowsi University of Mashhad Conclusion A high-gain high-speed low-power class-AB operational amplifier was presented. Positive feedback gain enhancement technique was used to boost DC gain. Class-AB technique was employed to get a higher slew rate with lower power. And finally to overcome the swing limitation, CDB technique was applied to load transistors to decrease threshold voltage. The proposed opamp can be used as the first stage of a two stage operational amplifier with rail-to-rail output swing.