agc loop design

[cimbom]

i need information about agc loop design in receiver.

thanks

 

[melone]

What specific questions do you have?

 

[cimbom]

I need information about designing AGC(automatic gain control) circuit for VGAs (Variable Gain Amplifiers). How can I design an AGC circuit by using OP-Amps in the loop after detector? (Receiver, IF section)

 

[eztech]

The V-G amplifier loop is essentially two op-amps; i-f amp, DC amp and a detector. (some i-f use more than one op-amp)
A control voltage is center of this circuit it varies the i-f amplifier in an even linear fashion. AGC detection uses two types; audio derived and i-f signal derived. This detected signal is detected by a diode and stored on a capacitor with a bleed resistor, C stores the detected input as a voltage .The DC amp takes the detected voltage on the capacitor and buffers it and sends it back to the i-f amp. This control voltage acts so that an increase on C will decrease the V-G amp or a decrease on C will increase the V-G amp.

As designs can start simple and grow an audio derived AGC might be a good place start. If you sample the audio so that it can be seen on an anolog meter then consider how to keep the meter within the bounds of normal modulation.

 

[jbartos]

Suggestion: Visit

http://www.eecg.toronto.edu/~kphang/ece1352f/papers/martin_AGC.pdf

etc. for more info