Hi all,


I want to simulate my PLL using transient noise analysis and then calculate the jitter. However, I'm having trouble deciding the Fmin and Fmax parameters for the transient noise analysis.

I am simulating my circuit for 20us and taking the dft over the last 5 us. I set my strobe period = 5u/65536. Therefore, I'm thinking my transient noise Fmax should be 65536/(2*5u) to prevent aliasing, which is 6.5536 GHz. My thinking is that strobing the data is essentially the same concept as sampling.

For the Fmin, I was thinking that in 5us I need to make sure the low frequency transient noise is able to complete multiple cycles (say 10) for accuracy. Which means that my Fmin should be 10/5u = 2 MHz. Or is one full cycle enough (200 kHz)? Actually 2 MHz is not accurate enough for my circuit, so if I need 10 cycles, I'm worried I need at least 50 us of data. I can go on holiday while I wait. BTW, I guess for Fmin it isn't as critical as I can simply change my limits of integration when I integrate the phase noise to find the jitter.

Is my thinking correct? Any help is appreciated.


thanks,
Aaron

EDIT: For Fmax, seems that people are saying you should set it to 50x the oscillation frequency. In that case it will alias, but maybe it is a more accurate result for the purposes of jitter calculation since it should be integrated anyway. So does that mena that the DFT will be less accurate, but the jitter will be more accurate?