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Design >> RF Design >> FFT Plot for Injection Locked PLL output
https://designers-guide.org/forum/YaBB.pl?num=1524916543

Message started by sarthak on Apr 28^th, 2018, 4:55am

Title: FFT Plot for Injection Locked PLL output
Post by sarthak on Apr 28^th, 2018, 4:55am

Hello,
I am trying to calculate the phase noise of an injection locked PLL by calculating the DFT of the oscillator output waveform. In the DFT plot I see a lot of spurs appearing due to injection locking. But the amplitude level of spurs follows a sinc type distribution. Can someone explain where this sinc response comes from?
Simulation parameters:
Osc. Freq = 2.56GHz
Ref. Freq = 64MHz
Sinc zero crossing = 16.512GHz

Title: Re: FFT Plot for Injection Locked PLL output
Post by sheldon on Apr 28^th, 2018, 10:44am

Try using either the direct plot of phase noise or he phase noise calculator function.

Title: Re: FFT Plot for Injection Locked PLL output
Post by sarthak on Apr 28^th, 2018, 12:37pm

I thought that the phase noise function works only on the PSS result data but I am using transient noise simulation. Is there a way to use phase noise function on transient simulation data as well?

Title: Re: FFT Plot for Injection Locked PLL output
Post by Andrew Beckett on Apr 29^th, 2018, 12:43am

No.

Title: Re: FFT Plot for Injection Locked PLL output
Post by deba on Apr 30^th, 2018, 12:47am

That Sinc probably appears to be the artifact of windowing the data. Does it change with the window length you have for the FFT?

By the way, if you want phase noise you can directly run the driven PSS/PNOISE simulation to check phase noise.