ELECTRONICS CIRCUITS II DEEPAK.P ECE
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