The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Simulators >> Circuit Simulators >> pac/pnosie simulation
https://designers-guide.org/forum/YaBB.pl?num=1571655874

Message started by NvR on Oct 21^st, 2019, 4:04am

Title: pac/pnosie simulation
Post by NvR on Oct 21^st, 2019, 4:04am

I have a question regarding the pnoise and pac simulations in sc-filters.pdf. The first null in the pnoise simulation is at 666.7kHz (figure 4) but where is the first null in the pac simulation (figure 6, continuous output)?

Thanks,
Nico

Title: Re: pac/pnosie simulation
Post by Ken Kundert on Jan 16^th, 2020, 11:37am

SpectreRF is often creating little puzzles like this. It always takes some deep thought to come up with possible explanations and then some experimentation to verify them.

My theory is that width of the sin(x)/x curve in the noise results is set by the pulse width (1.5μs -> 666kHz), whereas the in the PAC results of figure 6 the output is resampled with a 2.5μs period and so has width of the sin(x)/x is 400kHz. I am not sure why the unsampled PAC output also seems to have a 400kHz width.

Unfortunately, I do not have the time to explore this question to the depth it would require to completely explain the results.

-Ken