INF 5460Electronic noise – estimates and countermeasures

Design of Analog CMOS integrated circuits, BahzadRazavi, Chapter 7 - Noise

• Thermic noise:– Represented as parallel current at the output.

Using γ=2/3. (For small linewidths, 250nm and below, γ may be 2-3.)

– Represented as voltage at output:

• Flicker noise:– Represented as serial voltage on gate:

mn gkTI 42

2222

3

24 OmOnn rgkTrIV

fWLC

KV

OX

n

12

Common-Source 1/2

• Vn: equivalent input noise on M1 gate.

• Vn,out: Integrated output noise with load capacitance CL

• SNR with Vm amplitude sinus input.

21

2

121

212

3

2

3

24

1

3

2

3

24

m

m

mm

mmng

g

gkT

gggkTV

02121222

21

2

21212

,, ||3

2

2||1||

3

2

3

24

L

OOmm

LOO

OOmmtotoutnC

kTrrgg

fCrr

dfrrggkTV

2

21

2121

2121

2

211 ||

4

3

||32

1

2

||m

mm

OOmL

LOOmm

mOOmOUT V

gg

rrg

kT

C

CkTrrgg

VrrgSNR

Common-Source 2/2

• Expands with resistance and flicker noise:

– First stage: Thermal noise,

– Second stage: Flicker noise,

– Last stage: RD

Dm

N

m

mP

oxmm

minn

Rg

kT

fWL

K

gWL

gK

Cgg

gkTV

211

212

22

121

22,

4111

3

24

Common-Gate

• Thermal noise

• Flicker noise:

2

2,

1324

mbm

Dminn

gg

RgkTV

D

innR

kTI

42,

211

312,

3

24

mbm

mminn

gg

ggkTV

322.

3

24 mminn ggkTI

2113

23

1

212

.

11

mbm

PmNm

ox

innggWL

Kg

WL

Kg

fCV

3

23

2

222

,

1

WL

Kg

WL

Kg

fCI PmNm

ox

inn

Total noise is Vn + In*Zs.

Source Follower (Common-Drain)

• When the gain is less than 1 the noise on the output will have more weight than noise on the input. Should be avoided when S/N is bad.

• Normally In can be ignored

21

2

12

22,2

12,

1

3

24

|

m

m

mv

Moutnninn

g

g

gkT

A

VVV