miller-ota opamp design in amis cmos 07 by roman prokop

Miller-OTA Opamp design

In AMIS CMOS 07

by Roman Prokop

Simple Miller-OTA Opampwith follower

).1.()(.2

. 20 DSTGS

pD VVV

L

WKI DSVLL

L

1][][

7

.

10

3 mcmALN

All MOSesAll MOSes should work in saturation region – then their parametersare following:

Dp

ThGS

DThGSp

IL

WK

VV

IVV

L

WK

2

)(

2)(mg

DIdsg

NA – substrate doping ~ X .1016 cm-3

Simple Miller-OTA OpampAC hand calculation

AC small signal linearized model


Redrawing - simplification

Simple Miller-OTA OpampAC hand calculation – A0=?

3898842261

494848382734765

9844383472722616511

.)().(.

0.).(

0)()(0).(.0).(.0..

VgmgogogmVVgogoVgm

VgoVgoVgmVgmVgmVgogogmgm

gogoVVVgmVgogoVgmVgogoVgmgmVVgm

NIN

NIN

988

8

3

403

47

7

2

302

26

1201 gogogm

gm

V

VA

gogo

gm

V

VA

gogo

gm

V

VA

NIN

)).().((

....

9884726

8710302010 gogogmgogogogo

gmgmgmAAAA

small~1

Simple Miller-OTA OpampAC hand calculation – fp1=?

We know, where it is

Follower neglected

INV

VA 3)(


INV

VA 3)(

0).(.)(

0)(

).(.

347271

23

1

232622

VgogoVgmR

VV

R

VVVgogoVgm

Cj

CjIN


0).(.)(

0)(

).(.

347271

23

1

232622

VgogoVgmR

VV

R

VVVgogoVgm

Cj

CjIN

CjRG

1

1

0)().(

0.).(.

0).(.).(

0).().(.

74372

36222

3472723

232622

gogoGVGgmV

GVgogoGVVgm

VgogoVgmGVV

GVVVgogoVgm

IN

IN

Ggm

gogoGVV

7

7432

)()).((

).(

)()).((.

0.)(.

76274

723

7

7627432

3627

7432

GgmGgogoGgogoG

Ggmgm

V

V

Ggm

GgmGgogoGgogoGVVgm

GVgogoGGgm

gogoGVVgm

IN

IN

IN


276,27,4

72

76274

723

.)).((

).()(

)()).((

).(

GgmGGGGG

GgmgmjA

GgmGgogoGgogoG

Ggmgm

V

V

IN

3 possibilities3 possibilities

a) No R, no C; G=0

)).((

.)(

6,27,4

72

GG

gmgmjA

Confirmation of the transfer function without R&C


b) No R, only C; G=jωC

).

.1.(.

)1.(.

)(

..).(

)1.(.

)(

.)).((

).()(

6,27,4

76,27,4

772

6,27,472

6,27,42

772

276,27,4

72

GG

gmCjGG

gmCj

gmgm

jA

GGgmGGGGGG

gmCj

gmgm

jA

GgmGGGGG

GgmgmjA

C

gmf z .2

7

7

6274

6,27,4

71 ..2

)).((

..2

1

gmC

gogogogo

GGgm

Cf p

A0


c) R & C (R added); G=(R+1/jωC)-1

).

(1

)1

(1

..

.)(

).

(1

)1

(1

..

.)(

..1

)1(

..

.)(

.)).((

).()(

6,27,4

7

7

6,27,4

72

6,27,4

7

7

6,27,4

72

6,27,4

7

7

6,27,4

72

276,27,4

72

GGgm

Cj

gmRCj

GG

gmgmjA

GG

gmRCj

gmRCj

GG

gmgmjA

GG

gmG

gmG

GG

gmgmjA

GgmGGGGG

GgmgmjA

A0

R - negligible

Pole without changes

Zero is movedif R=1/gm7 fZ=∞


GBW – Gain band width =?

7

4726

9884726

87110 .2

)).((.

)).().((

...

gmC

gogogogo

gogogmgogogogo

gmgmgmfpAGBW

CCgogogm

gmgmGBW

2).(

.

988

81

CC

gm

21


First non-dominant pole -> stability =?

1st non-dominant pole decides about stability. if fND1 > GBW stable

We have 3 ND poles. We are We are interested in the interested in the lowestlowest one. one.

net

nettotalfp g

C _

ad 1) C1 is small (high f)C1 shorts the V1 to the ground

Simple Miller-OTA OpampAC hand calculation First ND pole

744882 dbdbgdgdgb CCCCCC

ad 2) the most usual case At this frequency we expect CC is a short we get diode with gm7 >> other G

2

7

.2 C

gmfnd

Stability condition - approx.

3 <21

7 .C

C

gm

gm

GBW

f Cnd If there is no close other pole !!!estimate !!!

Simple Miller-OTA OpampAC hand calculation First ND pole

ad 3) caused by load capacitance It can appear if Cload is bigger capacitance

Then expecting Cload >> ΣCds,Cdg

loadNDp

loadloadload

load

C

gm

gmC

jCjgm

gm

Cjgogogm

gm

V

V

VCjVgogoVVgm

8

8

8

8

988

8

3

4

4498438

1

1

0.).().(

loadND C

gmf

.28

Simple Miller-OTA OpampAC hand calculation SR – Slew rate

[V]

[As]

[V/s]

[A]unitschecking

/

SR

IC

C

I

t

CQ

t

VSR CC

Input goes rail to rail all IB currentflows either through M1, M5, M6 or through M2

ICC:=min (IB,I4)

Usually I4 > IB

depends on IB

c

B

C

ISR

Simple Miller-OTA OpampDC hand calculation

DC input range

11

1

3

3max

11

1

3

3max

13max

.

.2

2.

.2.

.

.2

2.

.2.

TMp

D

p

Ddda

TMp

D

p

Ddda

GSMDSatMdda

VWK

LI

WK

LIVV

VWK

LI

WK

LIVV

VVVV

Simple Miller-OTA OpampDC hand calculation

DC input range

155

5min

11

1

5

15

5

5min

115min

.

.2

2

.

.2

2.

.2

2.

.2

2

TMTMp

D

TMp

D

p

DTM

p

D

GSMDSatMGSM

VVWK

LIV

VWK

LI

WK

LIV

WK

LIV

VVVV

Be careful for temperature and process worst case

Simple Miller-OTA Opamp

DC hand calculation – structure offset

76 gsds VV 55 gsds VV

This systematic offset usually appears when Vds5 ≠ Vds6

Vds6 depends on Vgs7

477

55 2/

/

/

I

I

LW

LW B75

65

buildtoneedwe

for

gsgs

dsds

VV

VV

To suppress the offsetTo suppress the offset

Simple Miller-OTA OpampDC hand calculation Matching offset

The first stage gives the most significant contributionfirst stage gives the most significant contribution to the offset. Contributionof the second stage is negligible because of the first stage gain.

Usually sufficient for hand calculationsufficient for hand calculation

2D

DB

II

2_

2_

2

2_

2_

2

2_0

2_

20

2_0

2_

20

/)/(

/)/(

/)(

/)(

NNNN

PPPP

NVTNNVTTN

PVTPPVTTP

CWLA

CWLA

CWLAV

CWLAV

2

22

02

22

2

222

02 .)(.)/(.)/()(

P

NTN

P

DBN

P

DBPTPoff gm

gmV

gm

I

gm

IVV

Result is valid for 1σ statistical result - use value (4σ ÷6σ) for offset calculation

Matching AMIS CMOS07 parameters - NMOS

Carefully: units mV, μm, %

Matching AMIS CMOS07 parameters - PMOS

Carefully: units mV, μm, %

Simple Miller-OTA OpampHand calculation - Conclusion - AC

)).().((

....

9884726

8710302010 gogogmgogogogo

gmgmgmAAAA

7

6274

6,27,4

71 ..2

)).((

..2

1

gmC

gogogogo

GG

gmC

f p

CC

gmGBW

.21

2

7

.2 C

gmfnd

Stability condition - approx.

3 <21

7 .C

C

gm

gm

GBW

f Cnd

c

B

C

ISR

Simple Miller-OTA OpampHand calculation - Conclusion - DC

1

1

1

3

3max .

.2

2.

.2.TM

p

D

p

Ddda V

WK

LI

WK

LIVV

155

5min .

.2

2 TMTMp

D VVWK

LIV

2

22

02

22

2

222

02 .)(.)/(.)/()(

P

NTN

P

DBN

P

DBPTPoff gm

gmV

gm

I

gm

IVV

DC input range

Matching offset

Simple Miller-OTA OpampSimulation - AC

Possible tested parameters: A0 - DC gainGBW – Gain bandwidthfp1 - The first pole frequency

~ fND1 - The first non-dominant pole frequencyAM, PM – Gain margin, Phase margin

Simple Miller-OTA OpampSimulation - DC

Possible tested parameters: OFFSET - Input asymmetry- systematic offset- matching offset

CM – DC input range

Simple Miller-OTA OpampSimulation – DC input range

Possible tested parameters: OFFSET - Input asymmetry- systematic offset- matching offset

CM – DC input range

Good luck !!!Good luck !!!

miller-ota opamp design in amis cmos 07 by roman prokop

Documents

hand calculationresult

c r c r

nondominant pole stability

stage gain

nd pole ad

nondominant pole frequencyam

pm gain margin

nd poles