# Gain of a transistor

I am studying the design of an amplifier in common emitter configuration. I am studying from microelectronic circuits by sedra and smith. the author has described two terms for gain of a amplifier. one is the represented by Av and is called the voltage gain of that amplifier and the other is Gv called the overall gain of amplifier. I m not able to understand the difference between the two. can anybody help me out with this confusion?

## Answers and Replies

sophiecentaur
Gold Member
2020 Award
Voltage gain just says what it says. It is the ratio of the volts out over the volts in.
'Overall gain' will be referring to the gain in actual Power, that is achieved. After all, a transformer can give you a voltage gain of 100, but the power transferred can't be greater than unity.
It's a matter of input impedance and output impedance. For instance, if you want to feed 100V into 50Ω you need 200W. To feed 100V into 1kΩ you only need 10W.

Dear I was not able to grasp on your answer. would you please explain it in terms of transistor itself

Depending on the edition that you have, in the fifth edition Sedra/Smith on page 463 the quantities G_v and A_v are clearly defined.

G_v is the ratio of v_out to the open voltage of the source generator (it's not the input voltage of the amplifier).

A_v is the ratio of v_out to the input voltage of the amplifier.

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sophiecentaur