DanielLam wrote on Apr 2nd, 2018, 1:42pm:Ok, if you're unit caps are 10 fF, and you're bottom sampling, and the comparator input is normal, I don't think the ideal buffer (vcvs element in cadence) will do anything. Note, the ideal buffer has no capacitance.
Thanks Daniel. Yes the structure is as you said. Inputs to the comparator are Vcm being sampled via two switches. I know that ideal buffer doesn't have capacitors, I thought that after using a real buffer the parasitic capacitors will cause problem.
DanielLam wrote on Apr 2nd, 2018, 1:42pm:If those are your harmonics (and they are odd), and they seem to be a function of frequency, then I might guess they are coming from your sampling switches. If you used ideal sampling switches, do the harmonics go away?
If they are harmonics, they are even harmonics surprisingly(the output is approximately symmetric around the X axis), since I have calculated the frequencies. I will use ideal switches and inform you with the results (It might take a while, I am sorry).