# Input and Output Impedance of the Common Emitter Amplifier

I just have solved one of the bjt common emitter question below. However, I'm curious that how can I additionally find those things below:

1) Input and Output Impedance

2) AC Gain

Here is the example and my hand draw solution. However, the question only asked to find Vout/Vin...

Also, my 3rd question is, Does Vout/Vin (I calculated as -3) mean voltage gain?

Another my 4th question is Does voltage gain mean mean AC gain? Or, what is AC gain exaclty? I am not sure

I will be enormously happy if you satisfy my curiosity and show me the right way...

Also, if you have suggestions to solve this question in a more usable way, I am open to listen your suggestions.

I'm just secondary class student, that is why I try to figure out with questioning...

• For input impedance: electronics.stackexchange.com/questions/159140/… Commented Jun 3, 2021 at 16:50
• Thank you Erik for that. Also do you know how can I calculate output impedance please? Commented Jun 3, 2021 at 16:53
• Yes, - 3 is an AC signal voltage gain. $A_V = - \frac{\beta R_C}{R_B + r_\pi} \approx \frac{\beta R_C}{R_B} \approx -3 V/V$ And can be calauclate using this : Rin = Vi/Ii Can you do it? As for the Rout see this electronics.stackexchange.com/questions/464496/… or this
– G36
Commented Jun 3, 2021 at 18:46
• And I highly recommend you to read this pdf ittc.ku.edu/~jstiles/412/handouts/…
– G36
Commented Jun 3, 2021 at 18:50
• @G36 I am really sorry but still I could not figure out the technique which you used for calculating Rin and Rout. I really want to understand the logic of this calculation. Commented Jun 4, 2021 at 3:40