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