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
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[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
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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 VGS(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 (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.