Edgar Sánchez-Sinencio TI J. Kilby Chair Professor Lect 1 part... · 2020. 10. 30. · Sta g e +-Second Sta e Output Stage Vin Vioio1in2 CRCRCRopoop11o2L23 v 1 2 3 L m p p p p V

Edgar Sánchez-Sinencio

TI J. Kilby Chair Professor

ECEN 607 (ESS)

Texas A&M University

1

2

Next we review the conventional Op Amp Design frequency response compensation techniques and also we introduced a simple LV Current-

Mode based Op Amp using resistors as

transconductors. Difference Differential

Amplifiers are also introduced.

M3 M4

M1 M2

M5

M6

M7

M8

M9

inV

bsV

inV

1pC

High

Impedance

1ov

2pC

ovLC

1

2

3

DDV

SSV 1~3VA

Node is a low impedance

M1=M2; M3=M4

Ignoring zeros we can model this topology as:

Input

Stage

+

-

Second

StageOutput

Stage

inV

inV

1oi 2oi

1oR 1pC 2oR 2pC 3o

RLC

ov1 2 3

Lm

p

ppp

VVVV

p

oop

p

op

oo

mV

oo

mV

C

g

sss

AAAsA

C

gg

C

gg

gg

gA

gg

gA

T8

3

321

76042

76

6

31

1

321

22

1121

;111

;;;

000

00

3

3

UNCOMPENSATED CMOS OPERATIONAL AMPLIFIER

3

UNCOMPENSATED CMOS OPERATIONAL AMPLIFIER STABILITY

ISSUES

• The low frequency voltage gain is high enough for a number of

applications.

• The open loop poles are far from the origin, this can cause stability

problems for closed loop applications.

• Closed loop poles might end very close to the jw axis and some in

the RHP.

• How to tackle this stability problem will be discussed next.

4

Two-Stage Uncompensated Amplifier

Uncompensated Operational Amplifier

problemsstability causing axis j the toclose are Poles

gg

g

gg

gAAA

0706

6m

0402

2m2V1VV

5

inv

VDD

M3 M4M6

M1 M22

I o2

I o

I6Ig

Vout

I7

M7M5

VSS

Io

inv

Large voltage gain

5

Employing a simple capacitor will split correctly the poles but will generate a

Zero in the RHP.

Using an RC compensation can eliminate the zero and split poles. The resistor

can be implemented with transistor in the ohmic region.

Improved internally compensated CMOS operational

amplifier. Better bias for the output stage (M8 and M9)

6

M1

M4

M2CC

Vout

M6

VDD

M8

B

A

M9

VSS

M7M5

inv

biasv

M1

0

M11

M3

Analog and Mixed Signal Center, TAMU (ESS)

6

A variation at the output stage with class – AB is shown below.

CMOS op-amp with class-AB output stage and RC pole splitting.

7

VDD

M3 M4

M9

M1 M2

2

I o2

I o

M5

VSS

Io

M10

in

v

4DS

v

+

6GSv

I6

-

+

M6

IL

CLCC

M8

I10

M7+

-biasV

inv

7GSv

9GSv

7

“Pole Splitting” can be carried out with a compensation capacitor

feedback and a voltage buffer as shown below

Two-Stage amplifier with source follower compensation scheme

• Without M12 and M11 a zero in the PRH

• With buffer (voltage follower), zero is eliminated and pole splitting

(due to CC ) is kept. 8

Ibias

M5

M3

M1

M4

M2

M6 M9

CC

M10 M12

M11

M8

Out

M7

inv

inv

8

An Improved Frequency Compensation

Technique for CMOS Operational Amplifiers

using Current Buffers

ECEN 607 (ESS)Courtesy of Hatem Osman

• The first stage is a differential-input/single-ended output stage, and

the second stage is a class A or class AB inverting output stage.

• Transfer Function

• Pole/zero locations

Background.-

Two-Stage Op-amp with Miller compensation

gm1gm2

Cc

CLro2ro1 Cp

VOUT

VIN,p

VIN,n

• DC Gain

RHP zero

Dominant Pole

Non-dominant Pole

• Pole Splitting

• Pole-zero position diagram

Increasing Cc achieves sufficient pole-splitting thus improving the PM. However, the

larger Cc shifts the RHP zero to lower frequencies thus ruining the PM.

Two-Stage Op-amp with Miller compensation

gm1gm2

Cc

CLro2ro1 Cp

VOUT

VIN,p

VIN,n

• Pole/zero locations

• Introducing a small series resistance in series with Cc may cancel the

RHP zero or shift it to the LHP.

• Disadvantages:

• To achieve a sufficient phase margin, second pole cross-over of the unity gain

frequency should be avoided.

Thus, the Op-amp stability is severely degraded for capacitive loads of the same

order as compensation capacitor.

Miller Op-amp with Nulling Resistance

gm1gm2

Cc

CLro2ro1 Cp

VOUT

VIN,p

VIN,n

Rc• Pole/zero locations

No zero

LHP zero – Can be used to cancel the

first non-dominant pole.

• The RHP zero is a result of the feed-forward path through Cc.

• The RHP zero can be eliminated if we cut the feed-forward path

and make the compensation capacitor unidirectional.

Improved compensation technique

gm1gm2

Cc

CLro2ro1 Cp

VOUT

VIN,p

VIN,n

V1

gm1gm2

Cc

CLro2ro1 Cp

VOUT

VIN,p

VIN,n

V1

Virtual Ground


• DC Gain

Dominant Pole

Non-dominant Pole

gm1gm2

Cc

CLro2ro1 Cp

VOUT

VIN,p

VIN,n

V1

Virtual Ground


Miller compensation with nulling

resistance


Dominant pole

Non-dominant pole

Gain-bandwidth product

Phase margin

Dominant pole

Non-dominant pole

Gain-bandwidth product

Phase margin

• Miller compensation with nulling resistance.

• Improved compensation technique.

Circuit Implementation

CcRc

CL

VOUT

VIN,pVIN,n

VDD

VSS

VB,pVB,p Mp,0

Mp,1 Mp,1

Mn,1 Mn,1 Mn,2

Mp,2

Cc

CL

VOUT

VIN,pVIN,n

VDD

VSS

VB,pVB,p Mp,0

Mp,1 Mp,1

Mn,1 Mn,1 Mn,2

Mp,2VB,p

Mn,3

Mp,3

VB,n

Mp,4

• Miller compensation with nulling resistance.

• Improved compensation technique.

Other performance parameters- PSR

CcRc

CL

VOUT

VIN,pVIN,n

VDD

VSS

VB,pVB,p Mp,0

Mp,1 Mp,1

Mn,1 Mn,1 Mn,2

Mp,2

Cc

CL

VOUT

VIN,pVIN,n

VDD

VSS

VB,pVB,p Mp,0

Mp,1 Mp,1

Mn,1 Mn,1 Mn,2

Mp,2VB,p

Mn,3

Mp,3

VB,n

Mp,4

VSS

PSR

-20log(Av,0)

freq

fp1

VSS

PSR

-20log(Av,0)

freq

fp1 1/ro1Cp GBW

• Better PSR at high

frequencies.

• Design an OTA with GBW > 5MHz, CL=10pF, PM>70, and SR> 2

V/µs.

Design Example – Miller Compensation

CcRc

CL

VOUT

VIN,pVIN,n

VDD

VSS

VB,pVB,p Mp,0

Mp,1 Mp,1

Mn,1 Mn,1 Mn,2

Mp,2

• Choose Cc=CL/2= 5 pF.

• GBW > 5MHz

• SR > 2 V/µS

• PM > 70°

Let

Then

• Choose Rc > 1/gm2

• Simulation results


OL Transfer function Negative supply rejection

Positive supply rejection Transient step response

• Capacitive load driving capability

• PM > 70° for CL < 15 pF.


• Design an OTA with GBW > 5MHz, CL=10pF, PM>70, and SR> 2

V/µs.

Design Example – Improved Compensation

• Choose Cc=CL/2= 5 pF.

• GBW > 5MHz

• SR > 2 V/µS

In order to make the current transformer

biased during slewing interval

• PM > 70°

Let

Then

Let’s use gm2=6gm1 like the miller Op-

amp to make a comparison between

the capacitive driving capability.

For the same capacitive load driving

capability, the second stage will

consume less current making it suitable

for low power applications

Cc

CL

VOUT

VIN,pVIN,n

VDD

VSS

VB,pVB,p Mp,0

Mp,1 Mp,1

Mn,1 Mn,1 Mn,2

Mp,2VB,p

Mn,3

Mp,3

VB,n

Mp,4

• Simulation results


OL Transfer function Negative supply rejection

Positive supply rejection Transient step response

• Capacitive load driving capability

• PM > 70° for CL < 100 pF.


• Summary of Simulation results


Parameter Spec Miller

Compensation

Improved

Compensation

GBW > 5MHz 5.5 MHz 6 MHz

PM > 70° 75° 87.6°

SR+ > 2 V/µs 2.75 V/µs 3 V/µs

SR- > 2 V/µs 3 V/µs 3.15 V/µs

PSR- - -65.6 dB

At (0-3.1 kHz)

-51.9 dB

At (0-245.4 kHz)

PSR+ - -97.2 dB

At (0-44 kHz)

-37.2 dB

At (0-538.9 kHz)

DC gain - 64.5 dB 51.3 dB

Current

consumption

- 80 µA 110 µA

Capacitive load

driving capability

- PM > 70° forCL < 15 pF

PM > 70° forCL < 100 pF

Using another current buffer Op Amp topology.

• Improve SR at the expense of power consumption.

Two-Stage amplifier with Current Buffer compensation scheme.

25

Ibias

M5

M3

M1

M4

M2

M6 M9

CC

M10

M12

M11

M8M7

Vout

inv

in

v

25

Differential Output Two Stage Amp with a capacitor compensationwith a current Buffer ( Common Gate)

26

Note that the current-mirror introduces an extra inversion which must be taken into consideration for the single ended version.P.J. Hurst, Lewis, S.H. ; Keane, J.P. ; Aram, F. ; Dyer, K.C. “ Miller compensation using current buffers in fully differential CMOS two-stage operational amplifiers” IEEE Transactions on Circuits and Systems I, Volume: 51 , Issue: 2, Feb. 2004

Note that this and previous structure are fully differential but this approachcould be used for single output topologies.

Compensation using a current buffer ( current gain)

28

29

Elements of Current-Mirror Cc compensated

Besides the above zero the

amp has three poles

Note that the common-gate and current mirror topologies under ideal case are

almost identical, however in practice the one using current-mirrors is more power hungry

and has a larger parasitic capacitance CB

Summary for Two Stage Op Amp Architecture Designs

inV

biasV5Q

ssI

inV

biasI

7Q

6Q

LC

• Roots close to the j axis for uncompensated

• Potentially unstable for some values of CLIbias = CLSR*2.5

• Improved output stage optimal bias of Q6 and Q7• No significant change of pole locations.

Av (0) -> +

Av () -> -

Pole splitting => one dominant pole

z1 Phase deteriorates phase marginThe good and the bad news

1ps

2ps

oVinV

biasV5Q

ssI

inV

biasI

10Q

9Q

7Q

6Q

oV

inV

biasV5Q

ssI

inV

biasI

10Q

9Q

7Q

6Q

CC

1ps

2ps

1z


30

Two possible solutions to cancel z1 and keeping sp2 > t =GBW and sp1 small

Internally Compensated

with RC CC

Internally Compensated

with unity gain buffer

(Q10, Q11)

biasV

ssI

oV

CC10Q

11Q

Operational Amplifier (conventional) Architectures.

biasV

ssI

oV

CC LCinV

inV


Reader.- See the internally Op Amp compensated with current gain buffer in previous pages

31

32

Compared to two-stage Op Amp, folded cascode Op Amp has:

• Improved input common-mode range (ICMR)

• Improved power supply rejection (PSR)

• Push-pull output stage

• Self compensation

Folded-cascode Op Amp broken into stages

[Allen]

The extended ICMR is achieved

The bias currents I4 and I5 should be designed such that I6 and I7 never

goes to zero (i.e. 𝐼4,5 = 1.2𝐼3 → 1.5𝐼3)

Poor noise performance: In addition to the input transistors, transistors M4,5and M10,11 generate significant current noise

Folded Cascode OpAmp

33

RA and RB are the resistances looking into the sources of M6 and M7

𝑅𝐴 =𝑟𝑑𝑠6+ 1 𝑔𝑚10

1+𝑔𝑚6𝑟𝑑𝑠6≈

1

𝑔𝑚6and 𝑅𝐵 =

𝑟𝑑𝑠7+𝑅𝐼𝐼

1+𝑔𝑚7𝑟𝑑𝑠7≈

𝑅𝐼𝐼

𝑔𝑚7𝑟𝑑𝑠7where 𝑅𝐼𝐼 = 𝑔𝑚9𝑟𝑑𝑠9𝑟𝑑𝑠11

The currents 𝑖7 and 𝑖10 is expressed as

𝑖7 =𝑔𝑚2(𝑟𝑑𝑠2 𝑟𝑑𝑠5)

𝑅𝐵+(𝑟𝑑𝑠2 𝑟𝑑𝑠5)

𝑣𝑖𝑛

2=

𝑔𝑚2

𝑘+1

𝑣𝑖𝑛

2where 𝑘 =

𝑅𝐵

𝑟𝑑𝑠2 𝑟𝑑𝑠5

𝑖10 = −𝑔𝑚1(𝑟𝑑𝑠1 𝑟𝑑𝑠4)

𝑅𝐴+(𝑟𝑑𝑠1 𝑟𝑑𝑠4)

𝑣𝑖𝑛

2≈ −𝑔𝑚1

𝑣𝑖𝑛

2

Thus, the transfer function can be found as follows

𝑣𝑜𝑢𝑡𝑣𝑖𝑛

=𝑔𝑚12

+𝑔𝑚2

2 𝑘 + 1𝑅𝑜𝑢𝑡 =

2 + 𝑘

2 + 2𝑘𝑔𝑚1𝑅𝑜𝑢𝑡

Where

𝑅𝑜𝑢𝑡 = 𝑔𝑚9𝑟𝑑𝑠9𝑟𝑑𝑠11 𝑔𝑚7𝑟𝑑𝑠7 𝑟𝑑𝑠2 𝑟𝑑𝑠5

Where 𝑘 is the low-frequency unbalance factor

Small Signal Analysis

34

The frequency response is dominated primarily by the output pole due to the high

output impedance

𝑃𝑜𝑢𝑡 =−1

𝑅𝑜𝑢𝑡𝐶𝑜𝑢𝑡 In order to have sufficient phase margin, all other pole should be located will above

the GBW

Pole at source of M6 (Folding node) 𝑃𝐴 = −1

𝑅𝐴 𝐶𝑔𝑠+2𝐶𝑏𝑑≈ −

𝑔𝑚6

𝐶𝑔𝑠+2𝐶𝑏𝑑

Pole at source of M7 (Folding node) 𝑃𝐵 = −1

𝑅𝐵 𝐶𝑔𝑠+2𝐶𝑏𝑑≈ −

𝑔𝑚7

𝐶𝑔𝑠+2𝐶𝑏𝑑

Pole at drain of M6 𝑃6 = −𝑔𝑚10

2𝐶𝑔𝑠+2𝐶𝑏𝑑

Pole at source of M8 𝑃8 = −𝑔𝑚8𝑟𝑑𝑠8𝑔𝑚10

𝐶𝑔𝑠+𝐶𝑏𝑑

Pole at source of M9 𝑃9 = −𝑔𝑚9

𝐶𝑔𝑠+𝐶𝑏𝑑

Remarks:

We assumed 𝑅𝐵 ≈ 1 𝑔𝑚7 because at high frequency, where this pole has influence, 𝐶𝑜𝑢𝑡 shunts the drain of 𝑀7 to ground.

Frequency Response

35

[Allen]

Output stage of folded cascode OpAmp

The following model is used to calculate the

negative PSR

• The gate, source and drain of M11 varies with VSS

• The gate, source of M9 varies with Vss

The transfer function 𝑉𝑜𝑢𝑡 𝑉𝑠𝑠 can be found as𝑉𝑜𝑢𝑡

𝑉𝑠𝑠=

𝑠𝐶𝑔𝑑9𝑅𝑜𝑢𝑡

𝑠𝐶𝑜𝑢𝑡𝑅𝑜𝑢𝑡+1

𝑃𝑆𝑅𝑅− can be calculated

𝑃𝑆𝑅𝑅− =𝐴𝑣 𝑉𝑜𝑢𝑡 𝑉𝑠𝑠

Power Supply Rejection

36

At low frequency, we assume that other source of 𝑉𝑠𝑠 injection becomes significant

Low frequency PSRR- is at least as large as the magnitude of the

differential voltage gain 𝐴𝑣 PSRR+ can be derived similarly: the primary source of injection is through

the gate-drain capacitor of M

Power Supply Rejection

37

[Allen]

Slew Rate

38

𝑆𝑅+ = 𝑆𝑅− =𝐼3𝐶𝐿

The bias currents 𝐼4,5 should be designed such that 𝐼6,7 never goes to zero

𝐼4,5 = 1.2𝐼3 → 1.5𝐼5

Maximum Available Output Swing

39

𝑉𝑜𝑢𝑡 𝑚𝑎𝑥 = 𝑉𝐷𝐷 − 𝑉𝑆𝐷5 − 𝑉𝑆𝐷7𝑉𝑜𝑢𝑡 𝑚𝑖𝑛 = 𝑉𝑠𝑠 + 𝑉𝐷𝑆9 + 𝑉𝐷𝑆11

The output common mode level 𝑉𝑜𝑐𝑚 is often dictated by the circuit that interface with the amplifier (e.g. 𝑉𝑜𝑐𝑚 = 𝑉𝐷𝐷 2)

Noise Analysis

40

The noise current of M1, M4 and M10 goes directly to the output

At low and medium frequencies, noise contribution of the cascode

transistors (M6 and M8) can be neglected

Total output noise current becomes

𝑖𝑜𝑢𝑡2 = 8𝐾𝑇𝛾 𝑔𝑚1 + 𝑔𝑚4 + 𝑔𝑚10

Input referred noise density

𝑣𝑛,𝑖𝑛2 =

8𝐾𝑇𝛾

𝑔𝑚11 +

𝑔𝑚4

𝑔𝑚1+

𝑔𝑚10

𝑔𝑚1

Half circuit model

Folded Cascode Op Amp Design Procedure

41

Design approach for the folded cascode Op Amp using long-channel model

[Allen]

Design Example

42

Design a folded cascode Op Amp to comply with the following

specifications using 0.18μm CMOS technology

Parameter Spec

Slew rate > 10 V μs

Load Capacitor 10pF

Power Supply ±1 V

Max/Min Output Voltage ±0.5 V

GBW > 10 MHz

Min Input CM Voltage −0.3 V

Max Input CM Voltage 1 V

Differential Voltage Gain > 60 dB

Power Dissipation < 2mW

Design Example (Cont.)

43

Solution:

From the value of the slew rate we can get I3I3 = SR × CL > 10 × 10

6 10 × 10−12 I3 ≥ 100μA

Select I3 = 120μA

𝐼4,5 will be designed such that 𝐼6,7 never goes to zero

I4 = I5 = 1.2I3 to 1.5I3Select I4 = I5 = 1.25I3 = 150μA

Knowing 𝐼4 and 𝐼3, we can get the quiescent, min, and max values of 𝐼6,7

𝐼6,𝑄 = 𝐼7,𝑄 = 𝐼4 − 0.5𝐼3 = 90𝜇𝐴

𝐼6 𝑚𝑖𝑛 = 𝐼7 𝑚𝑖𝑛 = 𝐼4 − 𝐼3 = 20𝜇𝐴

𝐼6 𝑚𝑎𝑥 = 𝐼7 𝑚𝑎𝑥 = 𝐼4 = 150𝜇𝐴

From the min and maximum output voltages we can get overdrive voltage of

transistors 𝑀4−11

𝑉𝑆𝐷𝑠𝑎𝑡 4−7 𝑚𝑎𝑥 = 0.5 𝑉𝐷𝐷 − 𝑉𝑜𝑢𝑡 𝑚𝑎𝑥 = 0.25 𝑉

𝑉𝐷𝑆𝑠𝑎𝑡 8−11 𝑚𝑎𝑥 = 0.5 𝑉𝑜𝑢𝑡 𝑚𝑖𝑛 − 𝑉𝑆𝑆 = 0.25 𝑉


44

The value of 𝐺𝐵 gives 𝑔𝑚1,2

𝑔𝑚1,2 = 𝐺𝐵 × 𝐶𝐿 ≥ 628.3 𝜇𝐴 𝑉

Thus, choose 𝑔𝑚1,2 = 700 𝜇𝐴 𝑉

From 𝑔𝑚1,2 and 𝐼1,2, we can obtain 𝑉𝐷𝑆𝑠𝑎𝑡(1,2)

𝑉𝐷𝑆𝑠𝑎𝑡 1,2 =2𝐼1

𝑔𝑚1=

𝐼3

𝑔𝑚1= 0.17 𝑉

The minimum input common mode voltage defines 𝑉𝐷𝑆𝑠𝑎𝑡3𝑉𝑖𝑐𝑚 𝑚𝑖𝑛 = 𝑉𝑆𝑆 + 𝑉𝐷𝑆𝑠𝑎𝑡(3) + 𝑉𝑇𝑛 + 𝑉𝐷𝑆𝑠𝑎𝑡 1

Thus, 𝑉𝐷𝑆𝑠𝑎𝑡 3 = 0.13𝜇𝐴 for 𝑉𝑇𝑛 = 0.4 𝑉

We need to check that the maximum input common mode voltage is satisfied

𝑉𝑖𝑐𝑚 𝑚𝑎𝑥 = 𝑉𝐷𝐷 − 𝑉𝑆𝐷𝑠𝑎𝑡 4 + 𝑉𝑇𝑛 = 1.15 𝑉Meets the spec


45

Now, we have the bias currents 𝐼𝐷 and overdrive voltage 𝑉𝐷𝑆𝑠𝑎𝑡 of all the transistors.Thus, we can obtain 𝑊 𝐿 of all the transistors from the ACM model or square-lawmodel if long-channel transistors are used.

The channel length of the transistors should be chosen to satisfy the specified

voltage gain.

The current flowing in transistors 𝑀6−11 can have any value from 20 𝜇𝐴 to150 𝜇𝐴 depending on the amplitude and polarity of the differential input voltage.Therefore, they should be sized such that the worst case 𝑉𝐷𝑆𝑠𝑎𝑡 of each transistormeets the specified limits on the output voltages.

Bias voltages of the cascode transistors 𝑉𝑃𝐵2 and 𝑉𝑁𝐵2 are chosen such that

𝑉𝑃𝐵2

Simulation Results

46

DC operating point

Transistor 𝑾 𝑳 𝑰𝑫 𝝁𝑨 𝑽𝑫𝑺𝒔𝒂𝒕

𝑀1,2 18 1 120 0.13

𝑀3 24 1 60 0.16

𝑀4,5 72 1 150 0.23

𝑀6,7 72 1 90 0.23

𝑀8,9 12 1 90 0.24

𝑀10,11 12 1 90 0.24

Simulation Results

47

Input common-mode range

Minimum input common mode voltage is 0.28 V

ICMR testbench

Simulation Results

48

Output Swing

The gain is perfectly linear for −0.5 ≤ 𝑉𝑜𝑢𝑡 ≤ 0.5

Output Swing Testbench

Simulation Results

49

Open loop response

𝐴𝑣 > 60 𝑑𝐵𝐺𝐵 > 10 𝑀𝐻𝑧

Open loop response testbench

Simulation Results

50

Slew Rate

𝑆𝑅+, 𝑆𝑅− > 10 𝑉 𝜇𝑠

Slew-rate testbench

Simulation Results

51

PSRR

PSRR+ testbench PSRR- testbench

Summary of Results

52

The following simulation results for 𝐶𝐿 = 10𝑝𝐹, 𝑉𝐷𝐷 = 1 𝑉 and 𝑉𝑆𝑆 = −1𝑉

Parameter Spec Simulation

SR+ > 10 V μs 11.3 V μs

SR- > 10 V μs 11.18 V μs

Max/Min Output Voltage ±0.5 V −0.65 → 0.61 𝑉

GBW > 10 MHz 10.7 𝑀𝐻𝑧

Min Input CM Voltage −0.3 V −0.28 𝑉

Max Input CM Voltage 1 V 1 𝑉

Differential Voltage Gain > 60 dB 62 𝑑𝐵

PSRR+ - 65.64 𝑑𝐵

PSRR- - 75.86 𝑑𝐵

Power Dissipation < 2 mW 840 𝜇𝑊

Techniques for Wideband Amplifiers

Focus the improvement in the load of the differential pair

Conventional

Current Mirror

at the output load

Wideband Alternative

R

CF

Frequency Dependent

Current Mirror (FDCM)

CF >> Cgs

0.1K < R < 1K

Low Frequency

Behavior

CFIb

High Frequency

Behavior

T. Itakura and T. Iida, “A Feedforward Technique with Frequency-Dependent Current Mirrors for a Low-Voltage

Wideband Amplifier,” IEEE J. Solid-State Circuits, Vol. 31, No.6, pp. 847-849, June 1996. 53

An example of its use:

Wideband Amplifier with Feedforward Technique

• What is the optimal value of R1 as a function og GmP3 ?

• CF1 by passes two current mirrors.

• CF2 is fed forward to the input of another FDCM and signal

is amplified.

3PM

3PM

3R

inv

1R

bI

1FC

1nM

1PM

2PM

2nM

2FC

2R

inv

4PM

DDV

ov

LC

4nM

SSV

54

Next, we discuss different families of wideband reported in the

literature.

F. Centurelli et al, “A Bootstrap Technique for Wideband Amplifiers,” IEEE Trans. on Circuits

And Systesm – I, Vol. 49, No. 10, pp. 1474-1480, October 2002

• An alternative is to

connect CF instead

to nodes B to nodes A

LR LR

4nM

3nM

1nM

ov

ov

B B

SSRFC FC

A A

inv

inv2nM

55

FOLDED-CASCODE WIDEBAND AMPLIFIER ( See page 11 for cascode)

OUTV

Conventional Folded-Cascode (FC)

4PM

2PM

3nM

3PM

1PM

5nM

4nM

LC

4bV

2bV

inv

tailI

inv

1bV

1bV

FC with Capacitive Feedforward

4bV

1FR

1bV

1FC

2FC

inv

inv

tailI

1bV

2bV LC

outV

Differential Wideband Amplifier

F. Opt Eynde, W. Sansen, “A CMOS Wideband Amplifier with 800MHz Bandwidth,” IEEE Custom Integrated Circuits Conf., pp. 9.1.1-9.1.4, 1991

3nM

4nM

biasI1b

V

oV

LC

1FR

1bV

2bV

oV

1FC

inV

1bV

2bVLC

DDV

SSV

oV

2FC

2FR

56

57

M4 M10

M12 M5 M6 M14

IB IB IB IB

ibM1 M3 M8

VDD

Vbias

B

A

R

iR

Xvin

ix

M13 M2 M9

VSS

M11

io- io+

ON OP

v+ Figure 1

io+

io-

Figure 1V- XOP

ON

X

OP

ON

Fig. 1 Transconductance Amp

Basic Structure based on current-mode

Fig 2

Pseudo Differential Op Amp

iR = Vin/R

iX = - iR

IB > iR

-

E.K.F. Lee, “ Low-Voltage Opamp Design and Differential Difference Amplifier Design Using Linear Transconductor with Resistor Input

, “ IEEE Trans. Circuits and Systems II,vol. 47, pp 776-778, Aug. 2000

58

v+

Figure 2

io+

io-v-

VSS

R1

VDD

CC

R1

vo

Vbias

Transimpedanceamplifier

v1+

Figure 2

io1+

io1-v1-

v2+

Figure 2

io2+

io2-v2-

Transimpedanceamplifier

vo

Fig 3 VCVS Amplifier: Op Amp

DDA

59

References

Analog & Mixed-Signal Center (AMSC)

SS Rajput, SS Jamuar, Low voltage analog circuit design techniques, IEEE Circuits and

Systems Magazine, pp. 24-42, 2002

S. Yan and E. Sánchez-Sinencio, Low Voltage Analog Circuit Design Techniques: A Tutorial,

IEICE Trans. Fundamentals, Vol. E83-A, No. 2, pp 179-196, February 2000

E. Sánchez-Sinencio and Andreas G. Andreou, Eds. “ Low-Voltage/Low-Power Integrated

Circuits and Systems “, IEEE Press, Piscataway, NJ 1999

X. Xie, M.C. Schneider, E. Sanchez-Sinencio and S.H.K. Embabi, “ Sound Design of Low

Power Nested Transconductance-Capacitance Compensation Amplifiers”, IEE

Electronics Letters, Vol. 35, pp.956-958, June 1999.

A. Rodriguez-Vazquez and E. Sánchez-Sinencio, Eds., Special Issue on Low-Voltage and

Low-Power Analog and Mixed-Signal Circuits and Systems, IEEE Trans. on Circuits

and Systems I, vol. 42, No. 11, November 1995

J. Crols, J.; Steyaert, M.; Switched-opamp: an approach to realize full CMOS switched capacitor circuits at very low power supply voltages” IEEE Journal of Solid-State Circuits,, Volume: 29 , Issue: 8 , Aug. 1994 Pages:936 - 942

60

References


Very low-voltage analog signal processing based quasi-floating gate transistors,J

Ramirez-Angulo, AJ Lopez-Martin, RG Carvajal, et all, IEEE J. Solid-State Circuits, pp

434- 442, March 2004

Low threshold CMOS circuits with low standby current

Stan, M.R. Low Power Electronics and Design, 1998. Proceedings. 1998 International Symposium

on , 10-12 Aug. 1998 Pages:97 - 99

A dynamic threshold voltage MOSFET (DTMOS) for ultra low voltage operation Assaderaghi, F.;

Sinitsky, D.; Parke, S.; Bokor, J.; Ko, P.K.; Chenming Hu;

Electron Devices Meeting, 1994. Technical Digest., International , 11-14 Dec. 1994 Pages:809 -

812

Resizing rules for MOS analog-design reuse

Galup-Montoro, C.; Schneider, M.C.; Coitinho, R.M.;

Design & Test of Computers, IEEE ,Volume: 19 , Issue: 2 , March-April 2002 Pages:50 - 58

An MOS transistor model for analog circuit design .Cunha, A.I.A.; Schneider, M.C.; Galup-

Montoro, C.; Solid-State Circuits, IEEE Journal of ,Volume: 33 , Issue: 10 , Oct. 1998

Pages:1510 – 151

Series-parallel association of FET's for high gain and high frequency applications

Galup-Montoro, C.; Schneider, M.C.; Loss, I.J.B.; Solid-State Circuits, IEEE Journal

of ,Volume: 29 , Issue: 9 , Sept. 1994 Pages:1094 - 1101

61

References


S. M. Mallya abd J. H. Nevin, “ Design Procedures for a Fully Differential Folded Cascode CMOS

Operational Amplifier”, IEEE J. of Solid-State Circuits, Vol 24, No. 6, pp1737-1740,

December 1989.

D. B. Ribner, M. A. Copeland. and M. Milkovic, “8OMHz low offsetfully-differential and single-

ended opamps,” in Proc. IEEE Custom Integruted Circuits Con/., 1983, pp. 74-75.

This reference discusses three different Op Amp topologies:

S. Rabii and B. A. Wooley, “ A 1.8V-V Digital Audio Sigma-Delta Modulator in 0.8-um CMOS”,

IEEE J. of Solid-State Circuits, Vol. 32, N0. 6, pp. 783-796, June 1997

CMOS Analog Circuit Design, P.E. Allen, D.R. Holberg, Oxford University Press, 3rd

Edition, 2012

Edgar Sánchez-Sinencio TI J. Kilby Chair Professor Lect 1 part... · 2020. 10. 30. · Sta g e +-Second Sta e Output Stage Vin Vioio1in2 CRCRCRopoop11o2L23 v 1 2 3 L m p p p p V

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