09 Voxiable tor:
MOSFE T
eSis
ressto nhn
A MOSFET Can operate as a vaxiable
reon. In ths vegi
t is used in the
ineasi
hat
Mos FET behewes Rke a Cottol esistante
the
voftage (Vas)
Jories Gote to Sourfe
deperding
to souree votaqe (Vs)
the dsoin
the linease Sreqíen, the
When Mos FET in
enough that the channt
to SoeXCe
doin s nof
blew the source and
behaves tike
steqlon the MOS FET
Jn -this
In de peods 0n both
sesistox the drain Current
is Contolled b.
Resistance Ros
The MosFET
the qate vo tag making it as uotaq
veSistoh.
Siete Vns is very
Small.
Rns =bs
Louw
frequence Model of JFET :
Lous moclel of JEET er) Sanall Slgnal tod
od JFET
has three terminals.
Drain
Jhe Congica in a sial enal ocda
paraeters
the droin Gurrent Io Gote Source votage Vos
(Ros)Drain source Resistornce,
The Drain cur rent I s
y
O1J Nas const
an oplifieation facto of JEET
amnpkfies:
is
drouw IFET ffers vey high inpt impedonte
Somall signal moclel of MOSFET -
charnel length Modulotton
;-
CoOo SouCe Annplilex :
NpD
R,
SRs
Make al the Capacites shoit Ciruit and Dc
Souree
qreunad. Ro
>Rs
Iin
As ts Zeso total total Custent f Los through
RllR
node Io t
Becanthey
e
tunents).
leauing
At octput
from the oput sectton
Vin =hs
Output Resistance ¿ - Qtpat impedne)
I
ojp
Source
e se Thevian's
As therets dependent vesistance
the equkualent
Model to find soures
the 2ode pencant
Rermove all
Pitcess,
-
CO3non
folouoe
Tt is also Called Squrce folloa (or) Bufex
as short
make all
Copacitotn
In Ac- onalysts
are qroundadl.
and DC Souces
Ro
D
qmgs
Zin 5 ilpv
The drainCusrent is Zero the
total Cu\ent flouw$ thregh
Nelltace qain -
rite the kv in Loop,
-Nin
+ Uo
Uin
Vin
output inpcdante
;
Vo = Vin Rs
Vo
Co)No is alteady calaalated
Comnon
Gate thyplfer
;
Vo
G
Tapt igedance
Zin = Vin
In
At node D
ine-Vqs
Tin
Vin
volage qoin -
At nsde 2 Vo =-gmm (Vin)Ro
Vin
atput
impedana
;
whtn Van is Zero then Vo becornes oper tirexit
the
Zex o And ongs also becenes Zero then
Csouit is open Cituit at the output impedonee is Ro
