analog elctronics

8/14/2019 Analog Elctronics

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Presentation on HybridPresentation on HybridCommon Transistor ModelCommon Transistor Model

Amit GuptaAmit Gupta


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The hybrid commonThe hybrid common

emitter transistor modelemitter transistor model

The CE configuration is the most importantThe CE configuration is the most important

practical configuration.practical configuration.The analysis using the hybrid modelThe analysis using the hybrid model

is not very difficult and gives accurateis not very difficult and gives accurate

result at all the frequencyresult at all the frequency

The resistive components in this circuit canThe resistive components in this circuit can

be obtained from the low frequency h-be obtained from the low frequency h-

parameters.parameters.

All the components resistor andAll the components resistor and


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Components in the hybridComponents in the hybrid

modelmodel In the hybrid model there are 4In the hybrid model there are 4

terminals namely C,B,E and B out ofterminals namely C,B,E and B out of

which C, B and E have their normalwhich C, B and E have their normal

meaning and they are usermeaning and they are user

accessible terminalsaccessible terminals

B is not a user accessible terminalsB is not a user accessible terminals

it is called virtual base terminals.it is called virtual base terminals.


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Expression for TransistorExpression for Transistor

Transconductance (gTransconductance (gmm))

( )

)3......(

)1(.exp

)2.....(

tan

)1.....(tan

'

''

'

EEB

E

Em

EB

E

EB

ECO

m

ECOC

CE

EB

Cm

VSinceVV

Ig

V

I

V

II

g

eqntoinressionthisngSubstituti

III

transistorofregionactivetheIntconsVfor

V

IgcectransconduThe

othereachtoshortedareEmitterandcollectorThe

=

=

=

=

=

=

=


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)7........(

)6........(

tan

)5........(

)3(.

)4........(

tan

q

kTV

isetemperaturofequivalentvolt

thebutbiasedforwardisdiodeemittorthebecause

I

Vr

isetemperaturequivalentvoltinceresisemittorThe

rg

eqntoinvaluethisngSubstituti

IVr

isceresisemittertheBut

T

E

Te

e

m

E

Ee

=

=

=

=


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T

c

m

T

ccom

ccoE

T

Em

e

V

I

g

V

IIg

IIIBut

V

Ig

eqntoinrofvaluethengSubstituti

=

=

=

)5.(


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The Input Conductance (gThe Input Conductance (gbebe ))

fe

meb

eb

eb

ebm

b

cfe

ebbmebmc

ebbeb

ebb

h

ggso

Rgceconducputinbut

RgI

Ih

isgaincurrentcircuitshortthehenceRIgVgI

iscurrentcollectorcircuitshortthetherefore

RIV

isRthroughflowwillIcurrentbasethetherefore

=

=

==

==

=

>

'

'

'

'

''

''

'

cb'cb'

1tan

)*(

*

rr,valuecomponenttheFrom


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The feedback conductanceThe feedback conductance

(g(gbcbc ))

ebcbre

re

reebcbre

ebcbreebre

cbeb

eb

ce

ebre

cecbeb

eb

eb

cecbeb

b

ce

ebre

rrh

h

hrrh

rrhrh

rr

r

V

Vh

Vrr

rV

Vacrossdividerpotentialaformrandrthatevidentisit

IforV

Vh

''

''

'''

''

''

''

'

'

''

'

1)1(

)1(

*

0

=

=

=+

+==

+

=

==


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ebre

eb

eb

re

ce

eb

ebce

ebcb

eb

ebb

ce

bcb

ghceconducfeedback

g

r

andh

V

V

rVVg

r

VIbut

V

Ig

'

'

'

'

'

''

'

'

'

*tan

1

=

==

=

=

=


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Base spreading resistanceBase spreading resistance

(r(rbbbb ))

||||

)||(

)||(

)||(

.

'''

''

'''''

'''

'''

''

''

C

Tfe

C

Tfe

bbebbbie

ebiebb

ebbbcbebbbie

b

cbebbbbb

b

beie

ebcbeb

cbeb

ebcb

I

Vh

I

Vhrrrh

rhr

rrrrrh

I

rrIrI

I

Vhhence

rrrso

rr

butothereachwithparallelinappearrandr

+=+=

=

++=

+==


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The Output conductanceThe Output conductance

(g(gcece ))

( )

( )

( )

getweneglectingsorrBut

rrhg

rVI

rr

VVhg

r

VI

getwevaluestheallngSubstitutirrVIandVhgVgIrVI

IIIButI

IVIh

cbeb

cbeb

rem

ce

ceC

cbeb

cecerem

ce

ceC

cbebceceremebmcece

C

b

ce

Coe

,

11

,

0

''

''

''

''3'21

121


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19/20

cbremoece

cbremceoe

cbcbcece

cb

rem

cece

Coe

cb

rem

ce

ceC

ghghgghggh

grandgrsubstitutenow

rhg

rV

Ih

rhg

rVI

'

'

''

'

'

)/1()/1(

11

11

=++=

==

++==

++=


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