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Design >> Mixed-Signal Design >> eye diagram of VCO
https://designers-guide.org/forum/YaBB.pl?num=1214911699

Message started by analog_cha on Jul 1^st, 2008, 4:28am

Title: eye diagram of VCO
Post by analog_cha on Jul 1^st, 2008, 4:28am

How many cycles of the VCO output one can take to plot the eye diagram to find the peak to peak jitter??
Because as the number of cycles increase the pk to pk jitter also increases.

Thanks.

Title: Re: eye diagram of VCO
Post by Frank Wiedmann on Jul 1^st, 2008, 6:38am

The jitter of a free-running VCO with white noise sources is proportional to the square root of the time between the two observed transitions. See section 10 of http://www.designers-guide.org/Analysis/PLLnoise+jitter.pdf for details. So, it does not make much sense to talk about the peak-to-peak jitter of a free-running VCO because it is infinite if you observe it for an infinite time.

Title: Re: eye diagram of VCO
Post by loose-electron on Jul 3^rd, 2008, 12:19pm

for a closed loop system its a different story.

You are seeing the additive data points in a Gaussian distribution when you run over multiple cycles. So, how well do you want to define the distribution?

Title: Re: eye diagram of VCO
Post by thechopper on Jul 3^rd, 2008, 7:17pm

Based on what loose-electron suggested, I would wait for a "representative" number of cycles for guaranteeing 6 sigma distribution. I´m assuming the pk2pk jitter to be six sigma provided we see the cumulative Gaussian distribution.
Such number for me would be about 1000 cycles, since that should be the min # of cycles in order to see 1 event outside the six sigma population.

Rgds
Tosei

Title: Re: eye diagram of VCO
Post by analog_cha on Jul 4^th, 2008, 1:34am

Thank you very much to all.