Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would
be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate
that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views.
It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if
you would like to post something on RF Cafe's
page, please do.
Below are all of the forum threads, including all
the responses to the original posts.
Post subject: question of design Posted: Tue May 02, 2006 2:45 pm
Joined: Tue May 02, 2006 2:26 pm
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
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.