yvkrishna
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hi all,
This is regarding fft,snr calculations in spice for T/H circuit of an ADC. For finding the fft of a sine wave we choose freq of input (fin) such that there are prime number of cycles of input in N clock cycles(which is 2^n, n is integer). So strobing one point per each clock cycle would be sufficient for fft . however tstep of .TRAN need to be lesser than that. (correct me if i am wrong)
my doubt is how to choose tstep , how small should it be compared to fin or fs(clock freq) ?
also I have seen people(in some of matlab scripts) taking some 256 points per clock cycle for both tstep and tstrobe .
So should the tstep and tstrobe always be that small, that too a multiple of 2^x ?? some one please help me out in understanding this ..
ex: fs=80e6 , nfft=2^14 , and here fin =5.219726563e6 ( when 1069 cycles of input is chosen for 2^14 cycles of clock) and the tstep,tstrobe here was 48.828125ps . this number(which is 1/(256*fs) ) made me to raise this doubt.
thanks for the replies..
regards, yvkrishna
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