Gain settling requirement for the FM system

[sunnybear]

Hello

I have one question about VGLNA with AGC in FM receiver front-end design. I made one VGLNA with analog AGC for the PhD research work, if possible, could you please let me know what's the gain settling requirement for the FM system and how fast should this AGC loop achieved?

Thank you very much

 

[jiripolivka]

In a FM receiver there should be a limiter. AGC is used rather to reduce limiter overload.
The AGC speed response depend on conditions the receiver is to be used (fixed, mobile), and naturally on the minimum FM modulation frequency. A faster AGC may distort the low-frequency response of the receiver.

If you drive your car in a town, you may hear the effect of multipath too. Mostly in bass response- this shows a poor AGC design, or, do not drive fast in a town!

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I find a curious detail in your "VGLNA" definition. I would not include the LNA in the AGC loop. Rather design a better limiter before FM demodulator.

 

[chuckey]

Putting AGC on the RF stage is OK, providing it is delayed, so it only acts when there is an extremely strong signal in an attempt to stop the RF stage cross modulating the strong signal's modulation on to every weak station in the band.
Frank