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Simulators >> Circuit Simulators >> [q] PSD in calculator
https://designers-guide.org/forum/YaBB.pl?num=1201878601

Message started by kidhyun on Feb 1^st, 2008, 7:10am

Title: [q] PSD in calculator
Post by kidhyun on Feb 1^st, 2008, 7:10am

Dear,

I plotted the psd of ideal sine wave using psd function in the calculator. (in log scale)
There seems to be noise floor and the difference between the peak signal frequency and the noise floor is less than 70dB. I don't know why I got this high noise floor even when I used ideal sine wave.
Is it because the psd function uses interpolated points when they do fourier transform? (I am thinking the normal spectre simulation time step might not be evenly spaced. So I guess in this case to get evenly spaced points, psd function might do some interpolation to the waveform.)

Thank You

Title: Re: [q] PSD in calculator
Post by ACWWong on Feb 1^st, 2008, 7:35am

try looking at this previous relevant thread

http://www.designers-guide.org/Forum/YaBB.pl?num=1143819227/5#5

basically if you want "accurate" (i mean lower numerical noise) results its best to coincide the simulated points, with those used as sample points for any post processed transform by setting the strobe period correctly.

also of interest to you would be the fourier analysis available in spectre (using fourier component in netlist). its akin to pss analyses. try spectre -h fourier