3. Multi-Stage OpAmps
Design of Analog and Mixed Integrated Circuits and Systems F. Serra Graells
1/27Two-Stage Compensation Miller Design
3. Multi-Stage OpAmps
Francesc Serra Graells
[email protected] de Microelectrònica i Sistemes Electrònics
Universitat Autònoma de Barcelona
[email protected] Circuits and Systems
IMB-CNM(CSIC)
3. Multi-Stage OpAmps
Design of Analog and Mixed Integrated Circuits and Systems F. Serra Graells
2/27Two-Stage Compensation Miller Design
Two-Stage Topologies1
Frequency Compensation2
Miller Effect3
Design Space4
3. Multi-Stage OpAmps
Design of Analog and Mixed Integrated Circuits and Systems F. Serra Graells
3/27Two-Stage Compensation Miller Design
Two-Stage Topologies1
Frequency Compensation2
Miller Effect3
Design Space4
3. Multi-Stage OpAmps
Design of Analog and Mixed Integrated Circuits and Systems F. Serra Graells
4/27Two-Stage Compensation Miller Design
Splitting Functions
Single stage CMOS OpAmp limitations:
High gain:
Largeoutputrange
cascoding
3. Multi-Stage OpAmps
Design of Analog and Mixed Integrated Circuits and Systems F. Serra Graells
5/27Two-Stage Compensation Miller Design
Splitting Functions
Single stage CMOS OpAmp limitations:
High gain:
Largeoutputrange
cascoding
Introducing two-stage architectures:
High gaininput stage
(low-noise amp,preamp)
Large full-scaleoutput stage(power amp,
output buffer)
Improved dynamicrange performance
Area and poweroverheads... Frequency compensation required!
3. Multi-Stage OpAmps
Design of Analog and Mixed Integrated Circuits and Systems F. Serra Graells
6/27Two-Stage Compensation Miller Design
Practical Example
Two-stage fully differential folded cascode OpAmp topology:
M1
M5
M2
M4M3
M9M8M7M6
M16M15M14
M13M12M11M10
M18
M20
M17
M19
3. Multi-Stage OpAmps
Design of Analog and Mixed Integrated Circuits and Systems F. Serra Graells
7/27Two-Stage Compensation Miller Design
Practical Example
Two-stage fully differential folded cascode OpAmp topology:
M1
M5
M2
M4M3
M9M8M7M6
M16M15M14
M13M12M11M10
high-impedancenodes with dynamicsignals
M18
M20
M17
M19
Frequency compensation strategy is neededunder feedback (closed loop) operation...
3. Multi-Stage OpAmps
Design of Analog and Mixed Integrated Circuits and Systems F. Serra Graells
8/27Two-Stage Compensation Miller Design
Two-Stage Topologies1
Frequency Compensation2
Miller Effect3
Design Space4
3. Multi-Stage OpAmps
Design of Analog and Mixed Integrated Circuits and Systems F. Serra Graells
9/27Two-Stage Compensation Miller Design
Single Stage OpAmp Case
Basic control theory:OpAmp
Passivenetwork
3. Multi-Stage OpAmps
Design of Analog and Mixed Integrated Circuits and Systems F. Serra Graells
10/27Two-Stage Compensation Miller Design
Single Stage OpAmp Case
Basic control theory:OpAmp
Passivenetwork
Single pole amplifier:
3. Multi-Stage OpAmps
Design of Analog and Mixed Integrated Circuits and Systems F. Serra Graells
11/27Two-Stage Compensation Miller Design
Single Stage OpAmp Case
Single pole amplifier:
-20dB/dec
openloop
follower
rootlocus
Barkhasuen criteria:
Intrinsically stable!
3. Multi-Stage OpAmps
Design of Analog and Mixed Integrated Circuits and Systems F. Serra Graells
12/27Two-Stage Compensation Miller Design
Two-Stage OpAmp Case
Double pole analysis:
3. Multi-Stage OpAmps
Design of Analog and Mixed Integrated Circuits and Systems F. Serra Graells
13/27Two-Stage Compensation Miller Design
Two-Stage OpAmp Case
Double pole analysis:
in order tocover up to H=1
rootlocus
dominantpole splittingis required!
3. Multi-Stage OpAmps
Design of Analog and Mixed Integrated Circuits and Systems F. Serra Graells
14/27Two-Stage Compensation Miller Design
Two-Stage OpAmp Case
Double pole analysis:
in order tocover up to H=1
rootlocus
dominantpole splittingis required!
-20dB/dec
openloop
follower -40dB/dec
Barkhasuencriteria:
Phasemargin
3. Multi-Stage OpAmps
Design of Analog and Mixed Integrated Circuits and Systems F. Serra Graells
15/27Two-Stage Compensation Miller Design
Two-Stage Topologies1
Frequency Compensation2
Miller Effect3
Design Space4
3. Multi-Stage OpAmps
Design of Analog and Mixed Integrated Circuits and Systems F. Serra Graells
16/27Two-Stage Compensation Miller Design
Principle of Operation
Transimpedance amplifier:
3. Multi-Stage OpAmps
Design of Analog and Mixed Integrated Circuits and Systems F. Serra Graells
17/27Two-Stage Compensation Miller Design
Principle of Operation
Transimpedance amplifier:
equivalent outputimpedance seenfrom amplifier
equivalent inputimpedance seen
from source
Miller effect:
3. Multi-Stage OpAmps
Design of Analog and Mixed Integrated Circuits and Systems F. Serra Graells
18/27Two-Stage Compensation Miller Design
Pole Adjustment
Transcapacitive impedance case:
two-stage OpAmpsmall signal
model
Millercompensation
dominantpole
secondpole
3. Multi-Stage OpAmps
Design of Analog and Mixed Integrated Circuits and Systems F. Serra Graells
19/27Two-Stage Compensation Miller Design
Practical Example
Two-stage single-ended Miller-compensated OpAmp topology:
M1
M5
M2
M8
M4
M7
M6M3
stage-1 stage-2
3. Multi-Stage OpAmps
Design of Analog and Mixed Integrated Circuits and Systems F. Serra Graells
20/27Two-Stage Compensation Miller Design
time
Practical Example
Two-stage single-ended Miller-compensated OpAmp topology:
M1
M5
M2
M8
M4
M7
M6M3
step response unstable
slow
stage-1 stage-2
3. Multi-Stage OpAmps
Design of Analog and Mixed Integrated Circuits and Systems F. Serra Graells
21/27Two-Stage Compensation Miller Design
Two-Stage Topologies1
Frequency Compensation2
Miller Effect3
Design Space4
3. Multi-Stage OpAmps
Design of Analog and Mixed Integrated Circuits and Systems F. Serra Graells
22/27Two-Stage Compensation Miller Design
Design Variables
Single-ended Miller OpAmp example:
M1
M7
M2
M8
M4
M5
M6M3
25 designvariables!
3. Multi-Stage OpAmps
Design of Analog and Mixed Integrated Circuits and Systems F. Serra Graells
23/27Two-Stage Compensation Miller Design
Design Variables
Single-ended Miller OpAmp example:
M1
M7
M2
M8
M4
M5
M6M3
25 designvariables!
Current biasing
Device matching groups:
3. Multi-Stage OpAmps
Design of Analog and Mixed Integrated Circuits and Systems F. Serra Graells
24/27Two-Stage Compensation Miller Design
Design Variables
Single-ended Miller OpAmp example:
M1 M2
M4 M6M3
25 designvariables!
Null systematic offset
Current biasing
Device matching groups:
8 designvariables!
M7M8 M5
3. Multi-Stage OpAmps
Design of Analog and Mixed Integrated Circuits and Systems F. Serra Graells
25/27Two-Stage Compensation Miller Design
Design Equations
Single-ended Miller OpAmp example:
M1
M7
M2
M8
M4
M5
M6M3
3. Multi-Stage OpAmps
Design of Analog and Mixed Integrated Circuits and Systems F. Serra Graells
26/27Two-Stage Compensation Miller Design
Design Equations
Single-ended Miller OpAmp example:
M1
M7
M2
M8
M4
M5
M6M3
3. Multi-Stage OpAmps
Design of Analog and Mixed Integrated Circuits and Systems F. Serra Graells
27/27Two-Stage Compensation Miller Design
Design Equations
Single-ended Miller OpAmp example:
strong inversionforward saturation
for all transistors
M1
M7
M2
M8
M4
M5
M6M3
performance
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