question of design - RF Cafe Forums

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knightoftheparadise
Post subject: question of design Posted: Tue May 02, 2006 2:45 pm

Lieutenant

Joined: Tue May 02, 2006 2:26 pm
Posts: 1
how can we design a automatic gain control circuit for amplifier?

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fred47
Post subject: AGC amplifierPosted: Tue May 02, 2006 6:26 pm

General

Joined: Wed Feb 22, 2006 3:51 pm
Posts: 104
Hi!
You need two things for an AGC amplifier:
1. A way to measure the signal strength, and
2. A way to vary the gain based on that measurement.

AGC amplifiers come in two varieties, feedback (closed-loop, more common) and feedforward (open-loop, less common).

Signal strength measurement is often done by rectification followed by low-pass filtering.

There are two major ways to vary amplifier gains:
1. Varying the operating parameters of a BJT or FET
2. Using a FET or a PIN diode as a controllable impedance

Within those two major ways are a large number of specific approaches, depending on frequency, dynamic range, etc.

I hope this helps.

Good Luck,
Fred

Posted 11/12/2012