I have two questions about PSD calculation of phase noise in LISTING-17 at page-46 in the following.
http://www.designers-guide.org/Analysis/PLLnoise+jitter.pdf Quote:% output estimates of period and jitter
T=mean(periods);
% compute the cumulative phase of each transition
phases=2*pi*cumsum(periods)/T;
% compute power spectral density of phase
[Sphi, f] = psd(phases, nfft, 1/T, winLength, overlap, "linear");
(1) Why do you apply above
"phases" for evaluating PSD of phase noise ?
http://www.designers-guide.org/Forum/YaBB.pl?num=1066269978/1#1If we use the above
"phases", result of phase noise can not be consistent for completely clean signal.
For evaluating phase noise, I think phases has to be :
phases=2*pi*cumsum(periods-T) / T;The following is same as my opinion.
http://www.designers-guide.org/Forum/YaBB.pl?num=1196964298/6#6 Quote:% correct for scaling in PSD due to FFT and window
Sphi = winNBW*Sphi / nfft;
% plot the results (except at DC)
K = length(f);
semilogx( f(2:K), 10*log10(Sphi(2:K)) );
title("Power Spectral Density of VCO Phase");
xlabel("Frequency (Hz)");
ylabel("S phi (dB/Hz)");
rbw = winNBW/(T*nfft);
(2) Why is a unit of Sphi
(dB/Hz) ?
Has it to be
(dB/nbw) ?
Here
"nbw" is a normalized Noise Bandwidth defined as following.
nbw = rbw * T