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B.E.lB.Tech.

DEGREE

EXAMINATION,

APRIIIMAY

2008'

Third

Semester

(Regulation

2004)

Electronics

and

communication

Engineering

EC 1203

ELECTRONIC

CIRCUITS

I

(Common

o

B.E.

tPart-Timet

Second

Semester,

Regulation

2005)

fime

: Three

hours

Maximum

:

100

marks

Answer

ALL

questions.

PART

A

-

(10

x2

=

20

marks)

1.

Define

three

stabilitY

factors.

2. For the circuit shown in the figure, determine the operating point with

0

=L00

ls

93

ke

*i:.;

r_(

fr-

-:

3.

State

Millers

theorem.

4.

How

does

nput

impedance

ncrease

due

to

Darlington

connection?

5.

What

is meant

by Gain-Bandwidth

product?

6.

Give

the

equation

of

overall

upper

and

lower

cut

off

frequencies

of multistage

amplifier.

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9.

10.

t .

A class A CE amplifier operates

rom V..

=

20 V draws a

current

Iq

=

5

-\ a.nc

feeds a load of 40Q through

a step

up transformer of n, I

n,

=

3.16

Flnc

---:e

efficiency of

the ampiriier

rvhen

it

is

properly

matched for

maximum

1x

rer

supply.

Define Heat sink.

What is a

voltagemultiplier.

Find

the

ripple factor for a F\ lR

u'ith

capacitor

:lrer

r'.-ith

he output

rvaveform

as shown

n

the

figure. Assume Ez,

=

100Q

rrith

capacilorC

=

1000

,l

F.

e

PARTB- (5x16=80marks )

11.

(a) (i)

Draw and explain voltage divider bias using FET and derive

for its

stability factor.

(10 )

(ii)

Determine the bias resistor Rs for fixed bias and collector o base

bias and compare he stability factor S

for

both of them. Given

Vcc= 12V , RL =330Q, Io=0 .3mA, P =100 Vcrq=$ rg . ( 6 )

Or

A silicon transistor

uses voitage

divider

biasing

V , ,

=12V ,

Rr=10kQ,Rz=5hQ,

RL

=LkeL

and

Rn

=3kS) .

Determine

the

operating

point

using

Thevenin's

theorem.

(10)

Explain how FET acts

as

a variable resistor.

(6)

12.

(a)

Draw the hybrid model of CE

amplifier and obtain its

gain,

input

impedance and output impedance. Compare the performance of this CE

amplifier

with

CC and

CB configuration.

(16)

Or

(b) (i)

Explain the operation of basic

emitter coupled differential amplifier

and derive its CMRR.

(10 )

(ii)

How does the constant current source

increase the

gain

and hence

CMRR

in

a differential amplifier.

(6)

I

\lr

^

o , f

F -

t

( i)

(ii)

(b)

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13.

(a)

Derive

for

:he

"lpper

""d

iorer

cur-oii

frequencies

of

a

ampl:.ier.

RC

ccr:p-ed

3JT

i ' l

Or

,bt

Drarv

the high

frequency

equiraient

circuit

for a

FET

auip--::er

and

derive

the

values of

all the

parFmeters.

16 t

L4.

(a)

(i)

Discuss

the

complementar-v

slrnmetry

class

B arnplifier

and

obtain

its

efficiencv

10

(ii)

Describe

the operation

of

class

AB amplifier

to

avoid

cross

oler

distort ion.

(6)

Or

(b)

Explain

the operation

of Class

C amplifier

and

figure

of

merit.

derive

its efficiency

and

15.

(a)

(i)

Expiain

how

zener

diode

acts

as a

regulator'

(ii)

Derive

the ripple

factor

for

FWR

with capacitor

filter.

(16)

(6)

(10)

Or

(b)

Draw

and

explain

the

working

principle

of a

SMPS

circuit

with

its output

waveforms.

(16)

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