FM band filter and amplifier

[XRISTOS]

I believe too that not using a IF stage and tune inside the fpga is more challenging and modern approach. Do you have an idea on how i can achieve this AGC?

 

[RadioRon]

AGC is an amplitude driven feedback loop. You will have to measure the amplitude of the signal in your DSP, and derive a DC value that represents that amplitude. This DC value would be output through a D/A and then fed to a hardware gain-control line in your front end amplifier. So we have to choose an amplifier that has an analog gain control input.

The bandwidth of the feedback loop needs to be large enough to deal with slow multipath and fading due to walking. I would think that 50Hz might be OK. This means that the amplitude sampling and resulting D/A update has to be done fast enough to suit this. The translation from input amplitude measurement to output DC value should be done using a table of values. The values in this table can be tuned by manual calibration once everything else is working.

Unfortunately, requiring gain control in the front end restricts out choice of parts but there are amplifiers with such a feature. Another approach is to insert a variable attenuator after the first amplifier.

Here is an amp with variable gain control (below). I see the noise figure is not as good as we like, but otherwise it has 40 dB of adjustment range which is pretty good. The amount of adjustment range depends on the dynamic range of your A/D. How many bits of A/D are you planning?

https://www.electro-tech-online.com/custompdfs/2009/03/upc3217-18gv.pdf
**broken link removed**
**broken link removed**
https://www.electro-tech-online.com/custompdfs/2009/03/ZFL-1000G.pdf