Hi,
Almost scary - for me is:
My input signal is a frequency it's about 1k Hz
Firstly i'm converting the signal from Frequency to Volt using LM331
Here I expect the major of errors. All noise, distortion, drift errors caused by the AAF are negligible....in my opinion.
Why not simply ADconvert the original 1kHz signal?
You don't loose information, but avoid any additional errors.
Any simple microcontroller will work more accurate and precise than the LM331.
Btw: You say you convert f-->V ... then you are not interested in amplitude and waveform. Why an ADC then?
It's more simple to:
1kHz input signal --> simple signal conditioning --> zero cross comparator --> microcontroller_capture_periferal.
And using suitable software (which is more flexible) will result in much more precise values than the ADC solution.
Cost, hardware effort, ammount of data....will be greatly reduced...while still getting better results.
I really recommend to specify your needs ... then find a solution
...not the other way round.
*****
i need to make an AAF just to make sure that my signal is pure and stable
This requirement rather sounds like for a "sample and hold" circuit, rather than for an AAF.
The AAF will (should) only have influence on input frequencies above f_sample/2 which is 125kHz in your case.
Because alias frequencies happen only at input frequencies higher than f_sample/2.
Klaus