Analog Lect 35-36-26042012 High Frequency Amplifiers

8/12/2019 Analog Lect 35-36-26042012 High Frequency Amplifiers

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Introduction

Cascode Amplifier

High Speed High Frequency Op-amps

Tuned Amplifiers

Single Tuned Amplifiers

Multiple Tuned Amplifiers

2


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Frequency Response of an Amplifier

3


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High Frequency hybrid -model

B

E

C

G

S

D

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High Frequency hybrid -model of BJT

jojeBE

T

C

F

CFdc

C2)/VV-(1

Cjo

ecapacitancjunctionemitter-baseCje

voltagethermalV

currentcollector-I

imetransit tbaseforward-

IecapacitancdiffusionC

m

T

jedc

Vwhere

CCC

0.5to0.2junctionbase-collector

theoftcoefficiengradingtheismwhere

)/VV-(1

oC

ecapacitancjunctionbase-collectorC

jcCB

m

5


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High Frequency hybrid -model of FET

gdgs

mT

oxovgdgs

oxovgdoxovoxgs

ox

ov

ox

oxovoxgdgs

CC

g

productbandwidthgain-Unity

CWL0CC

:regionoff-Cut

CWL0CandCWLWLC3

2C

ecapacitancoverlapWLC

layeroxideunder thedrainandsourcetheoflengthoverlaptheisL

ecapacitanclayeroxideisCwhere

CWLWLC21CC

:regionOhmic

:regionActive

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Comparison of three Amplifier configurations

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Cascode Amplifier

Bss'

B

B'

R||r||RR

R||

R||

s

s

s vrR

rV

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CR2

1f

bygiveniscircuitoutputtoduefrequencyoff-cutThe

C whereCR2

1f

bygiveniscircuitinputtoduefrequencyoff-cutThe

outL

2

T

TS'1

inCC

CAAC

CAC

v

vout

vin

1

)1(

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10


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LCL' R||RR

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11

-A

thenidentical,betorstransistowoconsider tweIf

1

rg

)v(1

rvg-A

v1

2

2m1

12

21m11v1

iv

v

2

'3

22e2

22

2

inT

T

'1

1in1

C2

1

fiscircuitoutputtoduefrequencycutoffThe

)/(1rr whereC2

1f

iscircuitinterfacetoduefrequencycutoffThe

CCC whereC2

1f

iscircuitinputtoduefrequencycutoffTheC2Cisinputat thereflectedCtheThus

L

e

S

R

r

R

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BS

BL'

m

s

ovs

2

2m2

s

Bs

Bs'

1

2

L'

21m1m2

s

L'

2m2

s

o

R||rR

)R||(rRg-

v

vA

rs,transistoidenticalFor

11

rg

vR||rR

R||rvv

)1(

R)vv(gg-

v

Rvg-

v

v

and

Now

vA

s

vs

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High-Speed High-frequency Op-amp

1. 50 MHz unity gain bandwidth

2. 350 V/s slew rate

3. Settling time 45 ns

4. Works with +5 V or 5 to 15 V

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Tuned Amplifiers

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Single Tuned Amplifiers

2

2

eq

2

eqeq

mv

eq

2

m

eq

eq

m

s

o

i

o

-LC

1

CRCeq

g|)(jA|

bygivenisgaintheofmagnitudeThe

filterpass-bandorder-secondaforexpressiontheisThis

L

1

R

s

g-

CssL

1

R

1

g-

v

v

v

v

eqeq

eq

v

CCsC

sA

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eqmv

eqmv

eq

0

0

Rg-A

Rg|)(jA|isgaintheofmagnitudetheandLC

1

,frequencycentreat themaximumisgaintheofmaginitudeThe

or

eqeq0

0

0

eqeq

LH

2

eq

2

eq

2

0

eqeq

L

2

eq

2

eq

2

0

eqeq

H

CRQ

isamplifiertunedtheoffactorqualityThe

CR

1-BWbandwidthThe

C4R

1

C2R

1-

C4R

1

C2R

1

bygivenaresfrequencieoff-cutThe

BW

and

LH

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0

0

0v

v

jQ1

1

)(A

)(jA

bygivenisgainnormalisedThe

j

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Inductor Losses

19

s

00

0

r

LQ

asdefinedisinductortheofQfrequency,resonantAt


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Tapped Coils

12

1

2

1

1

2 Nn

n

V

V

I

I

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Multiple Tuned Amplifiers

Synchronous-tuned amplifiers

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To find fL and fH, the square of the magnitude of the transfer

function of a single tuned circuit is set to one-halfN

oo

Q

2

21

1

2

1

12

4Q1112

2 1

21

N

No

H Q

12

4Q

11122 1

21

N

No

L Q

122

1

NoNQ

BW

121

N is called bandwidth

shrinkage factor 22


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N SN N SN

2 0.64 6 0.353 0.51 7 0.32

4 0.43 8 0.30

5 0.39 9 0.28

Bandwidth Shrinkage factor

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sss

s

m

mo

RVI

sLIv

vgv

sLvgv

'/'

||sC

1||R

)rvg-(

||sC

1||R

1

1

11

22m2112

2

2

222

2

2

22

222

'

212m10

2211

2

0

2211

N

11

g-Avisatgainvoltage

11

1

CR

1BW56.1

rg

rgwhere

R

RRThe

CLCL

CR

m

m

S

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Staggered-tuned Amplifier

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4

BW

2

11

4

BW

21

1

2

0

2

0

22

2

0

2

011

BW

CL

BW

CL

'

212m1

2

21

'

2m1v0

2

g

gAisatgainvoltageThe

S

S

R

RR

BWCCR

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Documents

Analog Lect 35-36-26042012 High Frequency Amplifiers