**DanielLam wrote on Oct 10**^{th}, 2017, 12:52pm:Just to double check, your Fin has as many digit precision as possible right? For example, for Fin = 7/64 * Fs. That is the Fin input, and you are not using 0.11 * Fs as your Fin.

Yes exactly, for instance when using N=64 and cycles=7 for Fs=200K, I choose Fin to be => 200k*7/64=21.875K

**DanielLam wrote on Oct 10**^{th}, 2017, 12:52pm:Otherwise, I am a little stumped. Best advice I can give is to make an ideal ADC in matlab, and make sure that works. If that works fine, I'd suspect a rounding issue somewhere.

I have simulated an ideal sine (only including quantization noise) and this SNR decline didn't happen at all(with and without a window).

**DanielLam wrote on Oct 10**^{th}, 2017, 12:52pm:I'm assuming these measurements were from a Cadence sim?

Yes, I have imported data from Cadence to Matlab.

Sounds that RobG is totally right, the first samples are corrupted, I will post the results below. Thanks so much for your help.