Simple AGC amplifier

[Fei]

I need a simple AGC circuit, either digital or analogue, consisting easy-to-find chips/components, with 50-60dB range. Frequency range is around 100kHz to 400kHz. Is there any already existing ones that I can grab and use? Thank you very much!

 

[melone]

Where have you looked?

 

[Warpspeed]

For a suitable gain control block, what you require is an analog multiplier chip.

Your signal goes into one input, and your gain control voltage into the other input. The output will be input times gain.

There are many chips available, the choice really comes down to required accuracy and bandwidth, and how much you are prepared to pay.

 

[m3]

Fei,

Try national agc amplifier CLC520,

http://cache.national.com/ds/CL/CLC520.pdf

Regards,

M3

 

[nbucska]

buy a cheap AM radio and replace the two inductors in
the input circuit.



<nbucska@pcperipherals.com>

 

[hacksaw]

sounds like you need to rephrase the question, agc designs have been part of electronic design for at least 60 years.

 

[Fei]

Thanks for the suggestions!

I actually tried to use PSpice to simulate a simple circuit with transistors and diodes from 'Modern Electronic Circuits Reference Manual' but it didn't work. I wonder how practical such circuits (built with discrete transistors and diodes and R's and C's) would be? Do they tend to have problems in reliability etc in practice? If so, I will look harder for (cheap) IC chips.

Suggestions welcome! Cheers!

 

[Warpspeed]

It is difficult to suggest something because I have no clue as to what it is you are doing, or what factors are most important to you.

There are two simple possibilities, one is to use the drain source resistance of a FET in a voltage divider scheme. This works reasonably well in audio applications where the actual gain figure is not critical, you just want more/less over a decent control range.

Another way is the three transistor &quot;gilbert cell&quot; configuration, which is a two quadrant analog current multiplier circuit. This is the basis of most gain control integrated circuits.

Thirdly, just buy a gain control integrated circuit, or analog multiplier suitable for your needs.