written 7.3 years ago by | modified 3.1 years ago by |
Mumbai University > Electronics Engineering > Sem 4 > Discrete Electronic Circuits
Marks: 10M
written 7.3 years ago by | modified 3.1 years ago by |
Mumbai University > Electronics Engineering > Sem 4 > Discrete Electronic Circuits
Marks: 10M
written 7.3 years ago by | • modified 7.3 years ago |
Hence Hybrid π equivalent circuit becomes,
Av(Voltage Gain) :
The output voltage is,
VO=−(ro||Rc||RL)gmVbe…………………..(1)
The base emitter voltage Vbe, which controls the collector current, Vbe is voltage across Zi, Applying voltage divider rule,
Vbe=R1||R2||rπRs+R1||R2||rπVs
Substituting value of Vbe in equation (1),
Vo=−(ro||Rc||RL)gmR1||R2||rπRs+(R1||R2||rπ)Vs
This gives voltage gain Rs,
Av=VoVs=−(R1||R2||rπ)(ro||Rc||RL)gmRs+(R1|R2||rπ)
Av=−(R1||R2||rπ)×(ro||Rc||RL)gmRs+(R1||R2||rπ)
Ai( Current Gain) :
Current Io flows through load resistance RL. Hence applying current divider rule at C,
Io=−gmVbe×(ro||Rc)(ro||Rc)+RL----------------------------(2)
From Figure 2,
Vbe=Ibrπ
Apply current divider rule at b,
Ib=R1||R2rπ+(R1||R2)Ii
Vbe=(R1||R2)rπrπ+(R1||R2)Ii
Vbe=(R1||R2||rπ)Ii
Substitute Vbe in equation (2),
Ai=IoIi=−gm(R1||R2||rπ)×(ro||Rc)(ro||Rc)+RL
Ai=−gm(R1||R2||rπ)×(ro||Rc)(ro||Rc)+RL
Zi (Input Resistance):
Zi'=Vb/Ib
But
Vb=Ibrπ
Hence,
Zi′=rπ
Zi = R1||R2||Zi’
Zi=R1||R2||rπ
Zo (Output Resistance):
For Output Resistance:
Step 1: Set Vs=0V
Step 2: Open the load.
Step 3: Connect an imaginary voltage source Vs at output terminal
Hence an imaginary voltage source delivers current through parallel combination ro and Rc. Where,ro=VA/ICQ