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variable gain amplifier

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kazim

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can one provide some literature regarding variable gain amplifier. or simple shematic on how would we achieve variable gain.
 

It should include a detector to detect power, then the detector voltage compare to the power setting signal to produce a differential voltage to control the VGA.
 

There are several ways how to control a RF amplifier gain.
One is to use a variable (controllable) attenuator with a stable-gain amplifier.
Another is to use an integrated VGA like RF2637 from RF MicroDevices. There are now many VGAs from various IC Manufacturers.
Recently, digitally-controlled gain RF amplifiers have been introduced as receivers became fully controlled by a computer or micro-controller.

In RF amplifiers the exactly sinusoidal signal is not too important as each resonant circuit restores the signal shape. Therefore you can achieve a wide range of gain by simply varying transistor bias (if you know what it is).
 

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