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