Download A High-Gain High-Speed Low-Power Class

A High-Gain High-Speed Low-Power
Class-AB Operational Amplifier
Hassan Sarbishaei
Tahereh Kahookar Toosi
Ehsan Zhian Tabasy
Reza Lotfi
[email protected]
[email protected]
[email protected]
[email protected]
Integrated Systems Lab,
Ferdowsi University of
Mashhad, Iran
Outline
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
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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
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Three common methods
–
–
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Cascoding and gain boosting
Cascading
Positive feedback
Integrated Systems Lab, Ferdowsi University of Mashhad
High-gain Opamps (Cont’d)
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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
 vo

 vi
if

  g mi Aol (1   Aol )
 cl
Aol  1
 g m 2  g m1  g o1  g o 2  g oi

vo

vi
[Amourah et al. ISCAS2001]
Integrated Systems Lab, Ferdowsi University of Mashhad
Positive Feedback Amplifier (Cont’d)
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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
Vth0   ms  2 F 
QB 0 Qox Qi


Cox Cox Cox
QB 0  2 qN D si  F

Based on equations above :
I   N D   QB 0   Vth0 

[Ardalan et al. ICECS2004 ]
Disadvantages : Lower output impedance and
slew rate. Low frequency pole-zero pair.
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)
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Low-Voltage Single-Stage Class-AB Amplifier
using FVF block
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Advantage
–
Small, non slew rate
limited settling time.
Integrated Systems Lab, Ferdowsi University of Mashhad
[Baswa et al. ISCAS 2004 ]
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
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
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.
Integrated Systems Lab, Ferdowsi University of Mashhad