Gain of an Amplifier: Av & Gv Explained

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Discussion Overview

The discussion revolves around the concepts of voltage gain (Av) and overall gain (Gv) in the context of amplifier design, specifically in a common emitter configuration. Participants seek clarification on the definitions and implications of these terms as described in a textbook.

Discussion Character

  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • One participant expresses confusion about the difference between voltage gain (Av) and overall gain (Gv) as defined in the textbook.
  • Another participant explains that voltage gain is the ratio of output voltage to input voltage, while overall gain refers to the power gain, emphasizing the importance of input and output impedance.
  • A participant requests further clarification specifically in terms of the transistor itself, indicating a need for a more detailed explanation related to the common emitter circuit.
  • It is noted that Gv is the ratio of output voltage to the open voltage of the source generator, whereas Av is the ratio of output voltage to the amplifier's input voltage.
  • One participant highlights that a transistor does not have inherent voltage gain without being part of a circuit, reiterating the context of the common emitter configuration.
  • A later reply indicates that the original questioner found understanding after revisiting the textbook material.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the definitions and implications of Av and Gv, as some express confusion while others provide explanations that may not fully address the initial inquiry.

Contextual Notes

There are limitations in the explanations provided, particularly regarding the dependence on circuit context and the definitions of input and output voltages, which may vary based on specific configurations and assumptions.

Danish_Khatri
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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?
 
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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.
 
Last edited:
Danish_Khatri said:
Dear I was not able to grasp on your answer. would you please explain it in terms of transistor itself

A fair enough question but you need to realize that a transistor never operates in isolation. It is part of an amplifying circuit and it has no inherent Voltage Gain without being in a circuit - you actually state your question in the context of a common emitter circuit so you appreciate what I have just said.
 
Thanks for your help dear. I understood this concept when I repeated the paragraph.
 

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