EE 435 Lecture 11 - Iowa State Universityclass.ece.iastate.edu/ee435/lectures/EE 435 Lect 10 Spring...

EE 435

Lecture 10

Laboratory Support

OTA circuits

Current Mirror Op Amps

-- Alternative perspective

-- Loop phase-shift concerns

Lab Support:

VDD

M1M2

VB2

M3 M4

VINVIN

CL

M5

VOUT

IT

VSS

4

Design space for single-stage op amp

EB131

0

V

2

λλ

1A

331 EBTTDDiC VVVVV

DD L EB1

P 1GB

V C V

Performance Parameters in Practical

Parameter Domain { VEB1 VEB3 VEB5 P}:

EB3DDOUT VVV

T2icOUT VVV

SSEB5EB1T1ic VVVVV

Simple Expressions (7) in Practical Parameter Domain

DD SS L

PSR

V V C

VDD

M1M2

VB2

M3 M4

VINVIN

CL

M5

VOUT

IT

VSS

Recall from Lecture 6

5

Design example for single-stage op amp

EB131

0

V

2

λλ

1A

331 EBTTDDiC VVVVV

DD L EB1

P 1GB

V C V

Performance Parameters in Practical


EB3DDOUT VVV

T2icOUT VVV

SSEB5EB1T1ic VVVVV

DD SS L

PSR

V V C

VDD

M1M2

VB2

M3 M4

VINVIN

CL

M5

VOUT

IT

VSS

1. Select Parameter Domain (will use practical parameter domain)

{ VEB1 VEB3 VEB5 P}

2. Pick VEB1 to meet gain requirement ) { VEB1 VEB3 VEB5 P}

3. Pick P to meet GB requirement

4. Pick VEB3 and VEB5 to meet signal swing requirements

5. Map back from the Practical Parameter Domain to the

Natural Parameter domain (next page)

EB1

1 3 0

1 2V

λ λ A

{ VEB1 VEB3 VEB5 P}

Assume design to meet A0, GB and signal swing specs.


6

Design example for single-stage op ampPerformance Parameters in Practical


VDD

M1M2

VB2

M3 M4

VINVIN

CL

M5

VOUT

IT

VSS

From expression it follows that 2k ox kDk EBk

k

C WI V

2L

1

2

1 n OX EB1 DD SS

3

2

3 p OX EB3 DD SS

5

2

5 n OX EB5 DD SS

T B2 EB5 ss THn

DD SS

W 1 P

L C V V V

W 1 P

L C V V V

W 2 P

L C V V V

PI or V V V V

V V

Mapping from Practical Parameter Domain { VEB1 VEB3 VEB5 P} to Natural

Parameter Domain { W1/L1 W3/L3 W5/L5 IT}


Design Space Exploration

Consider the 5T Op Amp with CM Biasing

5T Op Amp Design

Process Paramaters Fixed Contraints

μnCOX 350 uAV^2 VDD 2 V Input Quantities in

μpCOX 75 uAV^2 VSS -2 V

VTHn 0.4 V CL 10 pf

VTHp -0.4 VL1=L2=…=Lk 0.5 um

λ 0.01 V^-1 VB2 0.6 V

Op Amp Design Variables Performance Characteristics Practical Design Values in um Small Signal Parameters (if desired)

No VEB1 VEB3 VEB9 P (mw) A0 BW (MHz) GB (MHz) SR (V/uS) Vomax Vomin VCM IT (mA) W1 W2 W3 W4 W9 gm1 gm3 gm9 go1 go3 go9

1 0.1 -0.1 0.1 5 1000 0.20 199.04 0.125 1.9 0 0.1 1.25 357.1 357.1 1666.7 1666.7 714.3 0.0125 0.0125 0.025 6.25E-06 6.25E-06 1.3E-05

2 0.2 -0.2 0.1 5 500 0.20 99.52 0.125 1.8 -0.1 0.1 1.25 89.3 89.3 416.7 416.7 714.3 0.00625 0.00625 0.025 6.25E-06 6.25E-06 1.3E-05

3 0.4 -0.1 0.1 5 250 0.20 49.76 0.125 1.9 -0.3 0.1 1.25 22.3 22.3 1666.7 1666.7 714.3 0.003125 0.0125 0.025 6.25E-06 6.25E-06 1.3E-05

4 0.05 -0.1 0.1 5 2000 0.20 398.09 0.125 1.9 0.05 0.1 1.25 1428.6 1428.6 1666.7 1666.7 714.3 0.025 0.0125 0.025 6.25E-06 6.25E-06 1.3E-05

5 0.1 -0.1 0.1 1 1000 0.04 39.81 0.025 1.9 0 0.1 0.25 71.4 71.4 333.3 333.3 142.9 0.0025 0.0025 0.005 1.25E-06 1.25E-06 2.5E-06

6 0.1 -0.1 0.1 10 1000 0.40 398.09 0.25 1.9 0 0.1 2.5 714.3 714.3 3333.3 3333.3 1428.6 0.025 0.025 0.05 1.25E-05 1.25E-05 2.5E-05

7 0.1 -0.1 0.1 0.1 1000 0.00 3.98 0.0025 1.9 0 0.1 0.025 7.1 7.1 33.3 33.3 14.3 0.00025 0.00025 0.0005 1.25E-07 1.25E-07 2.5E-07

8 0.1 -0.1 0.1 20 1000 0.80 796.18 0.5 1.9 0 0.1 5 1428.6 1428.6 6666.7 6666.7 2857.1 0.05 0.05 0.1 0.000025 0.000025 0.00005

9 0.1 -0.1 0.2 1 1000 0.04 39.81 0.025 1.9 0 0.1 0.25 71.4 71.4 333.3 333.3 35.7 0.0025 0.0025 0.0025 1.25E-06 1.25E-06 2.5E-06

10 0.1 -0.2 0.1 0.1 1000 0.00 3.98 0.0025 1.8 0 0.1 0.025 7.1 7.1 8.3 8.3 14.3 0.00025 0.000125 0.0005 1.25E-07 1.25E-07 2.5E-07

Design Space Exploration

5T Op Amp Design

Process Paramaters Fixed Contraints

μnCOX 350 uAV^2 VDD 2 V Input Quantities in

μpCOX 75 uAV^2 VSS -2 V

VTHn 0.4 V CL 10 pf

VTHp -0.4 V L1=L2=…=Lk 0.5 um

λ 0.01 V^-1 VB2 0.6 V

Op Amp

No VEB1 VEB3 VEB9 P (mw) A0 BW (MHz) GB (MHz) SR (V/uS) Vomax Vomin VCM IT (mA) W1 W2 W3 W4 W9

1 0.1 -0.1 0.1 5 1000 0.20 199.04 0.125 1.9 0 0.1 1.25 357.1 357.1 1666.7 1666.7 714.3

2 0.2 -0.2 0.1 5 500 0.20 99.52 0.125 1.8 -0.1 0.1 1.25 89.3 89.3 416.7 416.7 714.3

3 0.4 -0.1 0.1 5 250 0.20 49.76 0.125 1.9 -0.3 0.1 1.25 22.3 22.3 1666.7 1666.7 714.3

4 0.05 -0.1 0.1 5 2000 0.20 398.09 0.125 1.9 0.05 0.1 1.25 1428.6 1428.6 1666.7 1666.7 714.3

5 0.1 -0.1 0.1 1 1000 0.04 39.81 0.025 1.9 0 0.1 0.25 71.4 71.4 333.3 333.3 142.9

6 0.1 -0.1 0.1 10 1000 0.40 398.09 0.25 1.9 0 0.1 2.5 714.3 714.3 3333.3 3333.3 1428.6

7 0.1 -0.1 0.1 0.1 1000 0.00 3.98 0.0025 1.9 0 0.1 0.025 7.1 7.1 33.3 33.3 14.3

8 0.1 -0.1 0.1 20 1000 0.80 796.18 0.5 1.9 0 0.1 5 1428.6 1428.6 6666.7 6666.7 2857.1

9 0.1 -0.1 0.2 1 1000 0.04 39.81 0.025 1.9 0 0.1 0.25 71.4 71.4 333.3 333.3 35.7

10 0.1 -0.2 0.1 0.1 1000 0.00 3.98 0.0025 1.8 0 0.1 0.025 7.1 7.1 8.3 8.3 14.3

Design Variables Performance Characteristics Practical Design Values in um

Embedded Spreadsheet

9

Other Methods of Gain Enhancement

OCCOQC

QCM

V

gg

gA

0

L

mQC

C

gGB

Two Strategies:

1. Decrease denominator of AV0

2. Increase numerator of AV0

Previous approaches focused on decreasing denominator

Consider now increasing numerator

Recall:

VIN

VDD

VSS

VOUT

Quarter

Circuit

Counterpart

Circuit

CL

VBB

Review from last lecture:

10

Differential input op amp directly from

quarter circuit

M1

OV

d L 1 2

GV 2AV sC G G

F

VIN

IXX

VOUT

VSS

CL GsC

GsA

L

MVQC

)(

F

P

VDD

VBB

OUTV

OUTV

d

2

V d

2

V

IBIAS

CLCL

or VSS

BB

M1

OV

d L 1 I

GV 2AV sC G G

F

VDD

IBB

OUTV

OUTV

d

2

V d

2

V CLCL

VSS

IBB

F

VDD

IBB

OUTV

OUTV

d

2

V d

2

V CLCL

IBB

IBIAS

BBIG is the output conductance of IBB


11

gmEQ Gain Enhancement Strategy

1 : M

VIN

IB

VOUT

M1

Redraw to absorb IB in the quarter circuit

BBOEQ OQC OIg g g

MQC M1g = g M


12


OEQ

mEQV0

g

gA

2

1m

mEQ

gMg Premise: Transconductance gain increased by mirror gain M

Premise: If output conductance is small, gain can be very high

Premise: GB very good as well

L

mEQ

C

gGB

Very Simple Structure!

M : 1

IB

M1

1 : M

IB

M2VIN

VOUT

VIN

VOUT

IT

CLCL

Still need to generate the bias current IB

BBOEQ OQC OIg g g

-

OUTV0 + +

IN IN

VA =

V - V

(for VIN+=Vd/2)


13


VDD

VSS

VINVIN

VOUT VOUT

M : 1 1 : M

IT

VSS VSS

M1M2

VDD

VSS

VINVIN

VOUT VOUT

IT

VB1

VSSVSS

VB2

M1 M2

M3 M4M5 M6

M7M8M9

Need CMFB to establish VB2

Can use higher output impedance current mirrors

Can use current mirror bias to eliminate CMFB but loose one output

Basic Current Mirror Op Amp


14

Basic Current Mirror Op Amp

86 OOOEQggg

VDD

VSS

VINVIN

VOUT VOUT

IT

VB1

VSSVSS

VB2

M1 M2

M3 M4M5 M6

M7M8M9

CL CL

2

1m

mEQ

gMg

O8O6

m1

VOgg2

gM

A

L

m

C

gMGB

2

1

CMFB not shown

L

T

C

IMSR

2


15

• Current-Mirror Op Amp offers strategy for

gm enhancement

• Very Simple Structure

• Has applications as an OTA

• Based upon small signal analysis,

performance appears to be very good !

• But – how good are the properties of the

CMOA?Is this a real clever solution?


16

Current Mirror Op Amp W/O CMFBV

DD

VSS

VIN

VIN

M : 1 1 : M

IT

VSS

1 : 1

VOUT

IOUT

VIN

gm

1mmEQMgg

Often termed an OTA

INmOUTVgI

Introduced by Wheatley and Whitlinger in 1969


17

OTA Circuits

• OTA often used open loop

• Excellent High Frequency Performance

• Gain can be made programmable with dc current

• Large or very large adjustment ranges possible

gm

IOUT

IABC

circuitsMOSforIK

circuitsBJTforIKg

ABC

ABC

m

2 to 3 decades of adjustment for MOS

5 to 6 decades of adjustment for BJT


18

OTA Applications

gm

VIN

VOUT

R

Voltage Controlled Amplifier

Note: Technically current-controlled, control variable

not shown here and on following slides

INmOUTVRgV

gm is controllable with IABC


19

OTA Applications

INmOUTVRgV

Voltage Controlled Inverting Amplifier

gm

VIN

VOUT

RL


20

OTA Applications

RIN

gm

RIN

gm

m

IN

gR

1

Voltage Controlled Resistances

m

IN

gR

1


21

OTA Applications

gm1

VIN

VOUT

gm2

gm1

VIN

VOUT

gm2

in

m

m

OUTV

g

gV

2

1

Voltage Controlled Resistorless Amplifiers

in

m

m

OUTV

g

gV

2

1

Noninverting Voltage Controlled Amplifier Inverting Voltage Controlled Amplifier

Extremely large gain adjustment is possible

22

OTA Applications

gm

VIN

VOUT

C

in

m

OUTV

sC

gV

in

m

OUTV

sC

gV

Voltage Controlled Integrators

Noninverting Voltage Controlled Integrator Inverting Voltage Controlled Integrator

gm

VIN

VOUT

C

23

Comparison with Op Amp Based Integrators

VIN

VOUT

CR

INOUTV

sRCV

1

VIN

VOUT

CR

R1

R1

INOUTV

sRCV

1

OTA-based integrators require less components and significantly

less for realizing the noninverting integration function !

24

Properties of OTA-Based Circuits

• Can realize arbitrarily complex functions

• Circuits are often simpler than what can be obtained with Op Amp counterparts

• Inherently offer excellent high frequency performance

• Can be controlled with a dc voltage or current

• Often used open-loop rather than in a feedback configuration (circuit properties depend directly on gm)

• Other high output impedance op amps can also serve as OTA

• Linearity is limited

• Signal swing may be limited but can be good too

• Circuit properties process and temperature dependent

25

• Current-Mirror Op Amp offers strategy for

gm enhancement

• Very Simple Structure

• Has applications as an OTA

• But – how good are the properties of the

CMOA?Is this a real clever solution?

26

Current Mirror Op Amp W/O CMFB

VDD

VSS

VIN

VIN

M : 1 1 : M

IT

VSS

1 : 1

VOUT

1mmEQMgg

86 OOOEQggg

86

1

OO

m

VO

gg

gMA

And can use higher output impedance

current mirrors to decrease gOEQ

VDD

VSS

VINVIN

IT

VB1

VSSVSS

M1 M2

M3 M4M5 M6

M7M8M9

VOUT

CL

L

T

C

MISR

27

SR of Current Mirror Op Amp VDD

VSS

VINVIN

IT

VB1

VSSVSS

M1 M2

M3 M4M5 M6

M7M8M9

VOUT

CL

L

T

C

MISR

VDD

VSS

VINVIN

VOUT VOUT

IT

VB1

VSSVSS

VB2

M1 M2

M3 M4M5 M6

M7M8M9

CLCL

T

L

MISR

2C

28

Fully Differential Current Mirror Op

Amp with Improved Slew Rate

1 : M MM M : 1

VSS

VIN VIN

IT

1 : 1 1 : 1

VOUT VOUT

VDD

VSS

CLCL

Need CMFB circuit and requires modest circuit

modification to provide CMFB insertion point

29

VDD

VSS

VINVIN

IT

VB1

VSSVSS

M1 M2

M3 M4

M5AM6A

M7M8AM9A

M6B

VOUT

M5B

M9B

M8B

VSSVSS

VOUT

Fully Differential Current Mirror Op Amp with

Improved Slew Rate



This circuit was published because of the claim for improved SR (Fig 6.15 MJ)

30

VDD

VSS

VINVIN

IT

VB1

VSSVSS

M1 M2

M3 M4

M5AM6A

M7M8AM9A

M6B

VOUT

M5B

M9B

M8B

VSSVSS

VOUT

TIMP

L

MISR

C


Improved Slew Rate



L

T

AmpOpCM

C

IMSR

2

Improved a factor of 2 !

but …

31

VDD

VSS

VINVIN

IT

VB1

VSSVSS

M1 M2

M3 M4

M5AM6A

M7M8AM9A

M6B

VOUT

M5B

M9B

M8B

VSSVSS

VOUT

TIMP

L

MISR

C

L

T

AmpOpCM

C

IMSR

2


Improved Slew Rate

Improved a factor of 2 !

but …

M1IVPTDD AmpOp CM

IMP DD TP V I 1 2M

M

M

CV

PSR

LDD

AmpOpCM

12

IMP

DD L

P MSR

V C 1 2M

SR actually about the same for “improved SR circuit”

and basic OTA

32

Comparison of Current-Mirror Op Amps

with Previous Structures

86

1

2

OO

m

VO

gg

gM

A

64

46

LW

LWM

Does the simple mirror gain

really provide an “almost free”

gain enhancement ?

VDD

VSS

VINVIN

VOUTVOUT

IT

VB1

VSSVSS

VB2

M1 M2

M3 M4M5 M6

M7M8M9

Ask the apple comparison question !

33



86

1

2

OO

m

VO

gg

gM

A

64

46

LW

LWM

Does the simple mirror gain really provide an “almost

free” really large gain enhancement ?VDD

VSS

VINVIN

VOUTVOUT

IT

VB1

VSSVSS

VB2

M1 M2

M3 M4M5 M6

M7M8M9

Are we comparing Apples with Apples?• In the small-signal parameter domain?

• In the practical parameter domain?

• Does it matter if we are making a comparison?

34

Reference Op Amp

VDD

VB1

M1M2

VB2

M3 M4

VINVIN

CL

M9

CL

VOUTVOUT

IT

L

T

C

ISR

2

31

1

2

OOL

m

ggsC

g

)s(A

31

1

2

1

OO

m

VO

gg

gA

L

m

C

gGB

2

1

EB131

V0

V

1

λλ

1A

EB1LDDV

1

C2V

PGB

LDDCV

PSR

2

Consider single-ended output performance :

35



86

1

2

OO

m

VO

gg

gM

A

4

6

m

m

g

gM

Does the simple mirror gain really provide an

“almost free” gain enhancement ?

86

1

4

6

2

OO

m

m

m

VO

gg

g

g

g

A

64

46

LW

LWMI

OUT

IIN

M6

M4

Gain Enhancement Potential Less Apparent but still

Improved by gm6/gm4 ratio

36



86

1

2

OO

m

VO

gg

gM

A

EB1MMEB1T

M8M6EB1

T

QDM8M6EB

T

V

V2λ

1

λλV

1

2

IMλλV

M2

I

IλλV

MI

A

8681

0

22

2

1

Does the simple mirror gain really provide an

“almost free” gain enhancement ?

VDD

VSS

VINVIN

VOUTVOUT

IT

VB1

VSSVSS

VB2

M1 M2

M3 M4M5 M6

M7M8M9

Consider how the gain appears in the practical parameter domain

This is exactly the same as was obtained for the simple differential amplifier!

For a given VEB1, there is NO gain enhancement !

37



LEB

T

L

m

L

mEQ

CV

MI

C

gM

C

gGB

1

1

22

M1IVPTDD

VDD

VSS

VINVIN

VOUT VOUT

M : 1 1 : M

IT

VSS VSS

M1M2

How does the GB power efficiency compare with

previous amplifiers ?

GB efficiency decreased for small M !!

M1

M

CV2V

P

C2V

MIGB

LDDEB1LEB1

T

GB for Telescopic Cascode and Ref Op Amp !

38



M1IVPTDD

VDD

VSS

VINVIN

VOUTVOUT

M : 1 1 : M

IT

VSS VSS

M1M2

M1

M

C2V

PSR

LDD

How does the SR compare with previous

amplifiers ?

L

T

C

IMSR

2

L

T

AmpOpfRe

C

ISR

2

SR Improved by factor of M !but …

LDD

OpAmpfRe

CV

PSR

2

SR Really Less than for Ref Op Amp !!

39



VDD

VSS

VINVIN

VOUT VOUT

M : 1 1 : M

IT

VSS VSS

M1M2

How does the Current Mirror Op Amp really

compare with previous amplifiers or with

reference amplifier?

Perceived improvements may

appear to be very significant

Actual performance is not as good in

almost every respect !

But performance is comparable to

other circuits and the circuit structure

is really simple

Widely used architecture as well but

maybe more for OTA applications

End of Lecture 10

EE 435 Lecture 11 - Iowa State Universityclass.ece.iastate.edu/ee435/lectures/EE 435 Lect 10 Spring...

Documents

Transcript of EE 435 Lecture 11 - Iowa State Universityclass.ece.iastate.edu/ee435/lectures/EE 435 Lect 10 Spring...