Hi,
Kindly, let me know what you think about my last reply.
According to the above condition, I would have expected that ENOB of the output signal (S/H signal) to match the ENOB of the input sinusoidal input because all included circuit elements are ideal and linear so it seems that incomplete settling of every input sample is the cause of this linearity degradation.
For reference, ENOB of an ideal sinusoidal input was about 44 bits
After S/H, ENOB becomes about 14 bits (conservative settings)
You don´t show your math ... thus we are in a guessing show.
I can only guess that your math is not correct.
It seems you just calculated the worst case error of a sample and calculated ENOB from this.
But ENOB isn´t a measure of a single sample. ENOB is a measure of a lot of samples.
In more detail:
I guess you used a sine as input, then performed the acquisition and referred this to the expected value.
Now at the TOP and BOTTOM of a sine the error will be vary small (down to zero at the horizontal parts of sine)
(given your info that the capacitor has the charge of the previous acquisition)
At zero cross you have the highest errors. But this is not an error at all. It´s basically just a tiny phase shift.
So if you compare your ideal values and the holding values ... and perform an FFT on it ... you see about no distortion, about no amplitude reduction, sine shape stays sine shape.
The only "effect" you see is the phase shift. And phase shift has no impact on ENOB at all.
Again: all this is just guessing.
Another question, when I take FFT of a S/H output, should I take my FFT samples at the end of the track phase or at the end of the hold phase? and why?
Good question.
In best case it should not matter. That´s basically the idea of a holding circuit.
Indeed what doe s "at the end of the hold phase mean"? Imortant is the time from beginning to the end of a ADConversion.
After the conversion is finished .. the hold voltage may do any crazy stuff .. it won´t matter at all.
Also, should I choose my strobeperiod as my sampling period or an integer factor less than it?
I can answer after you provided a timing diagram (sketch, hand drawn...)
Klaus