written 7.3 years ago by |

Since β is mentioned use re-model. First carry out dc analysis for Ie1 and Ie2, so all connected capacitors acts as open circuit. Hence circuit becomes,

As β1=β2=220, then Ie1 will be equal to Ie2
By Voltage divider rule,
VR2=R2R1+R2Vcc
VR2=2.2K22K+2.2K×15
VR2=1.36V
By KVL,
VR2−VBE=VE1
1.36V−0.7V=VE1
Let,VBE=0.7V
VE1=0.663V
Ie1=VE1Re1=0.663V150Ω
Ie1=4.424mA
As stage 1 and stage 2 are identical & value ofβ1=β2=220
Ie1=Ie2=4.424mA
AC equivalent of the circuit becomes,

Rin (Input Resistance):
Rin=R1||R2||βre
re=26mVIe1=26mV4.424mA
re=5.87Ω
Hence, Rin becomes
Rin=22k||2.2k||220×5.87
Rin=0.784kΩ
Ro(Output Resistance):
Ro=Rc2s=1kΩ
Av (Voltage Gain):
Av2=VoVo1=−Rc2re
Av2=−1kΩ5.87Ω
Av2=-170.35
Av1=−(Rc1||Rin2)re
But, Rin2=R3||R4||βre=0.784kΩ
Av1=(−1kΩ||0.784kΩ)5.87Ω
Av1=-74.865
So Av is obtained by multiplying Av1 and Av2,
Av=Av1×Av2
Av=(−170.35×−74.865)
Av=12753.25