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How many sample points are enough ? (Read 3094 times)

tumeda

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How many sample points are enough ?
Sep 09^th, 2005, 7:14am

Hello Experts,
Thanks for your answer to my previous questions! It is a new question. :P

According to the paper of Ken, to fast simulation, the VCO and divider(DF) are writte in a behavioral block. So I can get the "Jdf=std(DF_Output_periods)". With different numbers of the sample points, the "Jdf" are also different. How many samples could be enough to let the "Jdf" stable for a PLL Circuit?

In addition to, I also use the VCO and Divider in individual Blcok, the I can directly get the "Jvco=std(VCO_ouptu_periods)". But I can not get the right relationship between the "Jvco" and "Jdf", which should satisify the form "Jvco=Jdf/sqrt(N)" (Table in page42).

How many sample points are enough to calculate the jitter performance of the whole PLL circuit? 1000, or 10000, or even more? ???

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boa

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Re: How many sample points are enough ?
Reply #1 - Sep 10^th, 2005, 10:41pm

Citing Ken (p.43):

"The simulation should cover an interval long enough to allow accurate Fourier analysis at the lowest frequency of interest (Fmin). With deterministic signals, it is sufficient to simulate for K cycles after the PLL settles if Fmin = 1/(TK). However, for these signals, which are stochastic, it is best to simulate for 10K to 100K cycles to allow for enough averaging to reduce the uncertainty in the result."

Is that what you want?

Btw, what do you mean by "Jdf"? Period jitter at the output (J_FD)?

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tumeda Community Member Offline Posts: 37	Re: How many sample points are enough ? Reply #2 - Sep 14^th, 2005, 4:08am Hi boa Thanks for your answer! Have your tried to make a long simulation to get these 10k/100k sample points, and have you got a stable value of J_FD? and the right relationship between J_vcoand J_FD? BTW. Jdf is J_FD. Thanks a lot!
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