design of rf cmos low noise amplifiers using a current based mosfet model virgínia helena varotto...

Design of RF CMOS Low Design of RF CMOS Low Noise Amplifiers Using a Noise Amplifiers Using a Current Based MOSFET Current Based MOSFET

ModelModel

Virgínia Helena Varotto Baroncini

Oscar da Costa Gouveia Filho

OUTLINEOUTLINE

1. Introduction

2. MOSFET Model

3. High-Frequency Noise Model

4. LNA Analysis

5. LNA Design Example

6. Conclusion

IntroductionIntroduction

• Submicrometer CMOS technology allows the

integration of RF circuits.

• Low voltage and low power operation → moderate

inversion

• Model valid from weak to strong inversion

MOSFET MODEL MOSFET MODEL

S

D

B

G I(VG,VS)

I(VG,VD)

DGSGRFD V,VIV,VIIII

T'ox

'DIS

2

T'ox

'DIS

2T'

oxRF nC

Q2

nC

Q

L

W

2CμnI

IF= forward current

IR= reverse current

Normalized currentsNormalized currents

tox

DISrf Cn

Qi

)()( 11

S

Frf I

Ii )(where are the normalized currents

LW

CnI toxS 2

..2

' and is the normalization current

Operation Regions of the MOS transistorOperation Regions of the MOS transistor

ir

if 10-3 10-11 100 102 103

10-3

10-1

100

102

103

forward saturationif > 100 ir

reverse saturation ir > 100 if

stro

ng

wea

k

mod

erat

e

strong

moderate

weak

triode

Small signal parametersSmall signal parameters

112

ft

sms i

Ig

n

gg ms

m

211

2111

32

f

ffoxgs

i

iiCWLC

gsoxgb CCWLn

nC

1

Transconductances

Capacitances

High- Frequency Noise High- Frequency Noise ModelModel

SvRg Sig Sid

Rg

Cgb Cgs

gmsVsbgmVgb

B B

S S

GD

Channel Thermal NoiseChannel Thermal Noise

10-3 10-2 10-1 100 101 102 10310-29

10-28

10-27

10-26

10-25

10-24

10-23

if

Sid (

A2 /

Hz)

11i1

32

1i11

4kTgS ff

msid2I

id LQ4kTμ

S

Induced Gate NoiseInduced Gate Noise

ms

2gs

ig 5g

ωCδkTS 4

4

f

2

ff

T0

'ox

32

ig1i1

2i11i1

nμ

CLWωδkT

458

S

10-3

10-2

10-1

100

101

102

103

10-51

10-50

10-49

10-48

10-47

10-46

10-45

Sig

(A2/H

z)

inversion level

W /L=1000W /L=2000W /L=3000W /L=4000W /L=5000

LNA AnalysisLNA Analysis

LS

Lg

Ld

Vin

Vb

VDD

M1

M2

Cascode LNA with inductive source degeneration

Impedance MatchingImpedance Matching

Lg

Ls

Cgb Cgs

gmbVsb gmsVgs

Zin Z1

mgss

gsmgss

gCL

CjgCLZ

2

21

1

11

Z1 can be viewed as the parallel of a resistor R with the capacitance Cgs

gsgb20

g CCω1

L

gs

gbgs

T

ss C

CC

ω

RL

Simplified small signal model for the LNA

222

22

222 1

1

1 CR

CLCRLj

CRR

Z ggin

matching is achieved simply by making the real part of Zin equal to the source resistance and its imaginary part equal to zero.

Noise FigureNoise Figure

sourcethetoduenoiseoutputTotalnoiseoutputTotal

F

LNA small-signal model for noise calculations

Definition

The noise figure can be expressed as a function of if

500 1000 1500 2000 2500 3000 3500 4000 4500 50001

1.5

2

2.5

3

3.5

4N

oise

Fig

ure

(dB

)

W/L

if=15if=20if=25if=30if=35

Noise figure versus W/L for several inversion levels at 2.5 GHz

LNA Design ExampleLNA Design Example

Resonance frequency 2,5 GHz

Supply voltage 2,5 V

Length 0,35 m

Source resistance 50 Noise Figure < 2dB

LNA Design Parameters

1. Choice of the inversion level

if=35

ProcedureProcedure

2. Ls for impedance matching

2111

2111211143

2

22

ff

fff

TSs

ii

iiiLn

nRL

3. Transistor width for minimum noise figure

500 1000 1500 2000 2500 3000 3500 4000 4500 50001

1.5

2

2.5

3

3.5

4

Noi

se F

igur

e (d

B)

W/L

if=15if=20if=25if=30if=35

Noise figure versus W/L for several inversion levels at 2.5 GHz

4. Lg to satisfy the resonance frequency

2'2

0

2

111321112

113

fffox

fg

iniiWLC

inL

5. Ld to adjust the gain and the output resonance frequency

LNA Design ResultsLNA Design Results

W/L W ID Rs Ls Lg Ld

1500 525 m 4,1 mA 50 0,7 nH 7,6 nH 2,5 nH

Ls

Lg

Ld

RS CL

RLd

M1

M2

Vout

Vin +Vbias

VDD

Simulation resultsSimulation results

Input impedance

Noise Figure

ConclusionsConclusions

The main advantage of this methodology is that is valid in all regions of the operation of the MOS transistors;

It is possible to move the operation point of RF devices from strong inversion to moderate inversion taking advantage of higher gm/ID ratio, without degrading the noise figure;