ELECTRONICS CIRCUITS II

DEEPAK.P

ECE

RC COUPLED AMPLIFIER

RC COUPLED AMPLIFIER

• RC coupled amplifier is a common emitter transistor amplifier configuration.

• RC coupled amplifier can be designed by using potential divider biasing circuit.

• RC coupled amplifier can be used as voltage amplifier.

• The o/p of RC coupled amplifier is simply taken from collector.

• The coupling used is RC coupling.

RC COUPLED AMPLIFIER (Cntd..)

• RC coupled amplifier is a medium frequency amplifier.

• R1,R2 combination provides the base current.

• RE is used for bias stabilization.

• CE is used to by pass the ac components developed across RE.

• RC is the collector resistor and it act as a load.

RC COUPLED AMPLIFIER (Cntd..) • Circuit Diagram

VCC

O/P

I/P

R1

R2

RC

RE

CC

CC

CE

RC COUPLED AMPLIFIER (Cntd..)

• The voltage gain of RC coupled amplifier is grater than unity.

• The Q point of the transistor must fix in the centre of the active region/Load line.

• For that ,fix VCEQ=50% VCC and

• IERE= 10% VCC ICRC= 40% VCC

•

RC COUPLED AMPLIFIER (Cntd..)

• LOAD LINE

VCC

VCC/(RC+RE)

Q POINT

VCEQ

ICQ

RC COUPLED AMPLIFIER (Cntd..)

• h parameter equivalent circuit

• To draw the h parameter equivalent circuit,

• Draw the AC behavior of the circuit

• AC behavior of a circuit

• Open circuit all capacitors.• Short circuit all DC power supply.

RC COUPLED AMPLIFIER (Cntd..)

VCC

O/PI/P

RC COUPLED AMPLIFIER (Cntd..)

• AC behavior of a circuit

RC

R2R1

RC COUPLED AMPLIFIER (Cntd..)

• h parameter equivalent circuit

hie

R2R1

+

-hre vce

hfe ib

RC 1/hoe

RC COUPLED AMPLIFIER (Cntd..)

• Simplified h parameter equivalent circuit

• R1,R2>>hie so R1//R2//hie=hie

• hre Vce is a very small voltage , so it is neglected.

• 1/hoe//RC=RC

• Now ckt becomes

RC COUPLED AMPLIFIER (Cntd..)

hie

hfe ib

RCI/P

Simplified h parameter equivalent circuit

RC COUPLED AMPLIFIER (Cntd..)

Gain

Frequencyf1 f1

BW

Frequency Response

RC COUPLED AMPLIFIER (Cntd..)

Max Gain in db

Frequency

f1 f1

BW

If we express gain in db, frequency response will be

3db Gain

RC COUPLED AMPLIFIER (Cntd..)

Design

• Assume VCC,IC,β

• O/P Loop equation

• VCC=ICRC +VCE+IERE VCE=50% VCC, ICRC=40% VCC

• Assume that Ic=IE IERE=10% VCC

• I/P Loop equation

• IC= β IB

• VCC=10 IB R1+VBE+IERE ; 9IB R2=VBE+IERE

• R1=VCC –VBE - IERE/ 10 IB ; R2=VBE+IERE/ 9IB

END