Hi all,


I want to design a variable-gain common-source amplifier with a resistive load. The gain step should be of discrete values (6 dB for example), and the gain should be controllable by the bias voltage of the amplifier. Rather than inputting a reference signal into a matched amplifier and recording the gain step, is there a way to set the gain?


thanks,
Aaron

Hi pancho_hideboo,


at the moment I'm just looking for conceptual ideas. Suppose for arguments sake however, that i would need a dynamic range of 24 dB with 6 dB steps. The VGA would be differential. It actually occurred to me that I can use a peak detector to detect the gain change, but i'm still kind of playing the idea around in my head. The actual situation is somewhat more complicated than what I described.

Most of the AGCs I've seen change a control voltage until the output level is within certain limits. My goal however is to change the control voltage until the gain drops by a desired amount (for example6dB).

I'm merely curious about whether it can be done without the use of a peak detector.

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The first idea that came to me was to design a matched amplifier and inject a reference signal into the amplifier. Then compare the input and output to get the gain you want. However, the absolute value of the gain is not that important to me, so the method I described above (peak detector) is probably better...

cheers,
Aaron

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Yes

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thanks. I'll have a look.