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Question of Design - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement

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


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


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


Joined: Wed Feb 22, 2006 3:51 pm
Posts: 104
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,

Posted  11/12/2012

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