common emmiter-feedback resistor small signal analysis

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mohammad.khatib

Joined Aug 2, 2010
1
hey all please help me with the (common emmiter-feedback resistor small signal analysis) i need the derivation of Rin and Ro and the gain pleasee
 

Jony130

Joined Feb 17, 2009
5,244
You need to create small signal model of a amplifier and then find the unknown.
2.PNG

For example voltage gain is equal :
Au = Vout/Vin
Vin = Ib*H11 + Ie *Re
Ie = Ic + Ib = (hfe+1)*Ib
Vin = Ib*H11 + (hfe+1)*Ib *Re = Ib*(h11 + (hfe + 1)*Re)
Vout = -Ic*Rc = -Ib*hfe*Rc

Au = - ( Ib*hfe*Rc ) / ( Ib*(h11 + (hfe + 1)*Re) = - ( hfe*Rc ) / (h11 + (hfe + 1)*Re)
And h11 = (Hfe +1) * re = (Hfe +1) * 26mV/Ic

To find Rin you need to find
Rin = Vin /Iin
Rout = Vout/Iout
 
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