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Simulators >> Circuit Simulators >> PLL period and phase jitter estimation using spectre
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Message started by xaxanitsa on Feb 19^th, 2015, 1:19am

Title: PLL period and phase jitter estimation using spectre
Post by xaxanitsa on Feb 19^th, 2015, 1:19am

Hello,

I’m trying to estimate the period jitter of a PLL using the period_jitter function from the waveform calculator (Cadence, Virtuoso 6.1.5) while running a transient noise simulation.

I suppose that:

The result obtained using the "sd" output type and binsize=0 is not correct because the average period is calculated taking into account the initial unlocked state. Could you please confirm that?

The result obtained using the "sd" output type and binsize=500 is again not correct because the average period is calculated taking into account the last 500 periods but the sd is calculated taking into account all the periods. Could you please confirm that?

So probably I have to export the results obtained using "plot" output type and binsize=500 to a .csv file and use MATLAB to calculate the stddev over a sample size of 10,000 periods (as specified by the JEDEC standard). Do you agree?

Finally, is it appropriate to use the eye diagram to estimate the phase jitter using samples obtained once the PLL is in lock state?

Best Regards,
xaxanitsa

Title: Re: PLL period and phase jitter estimation using spectre
Post by sheldon on Feb 19^th, 2015, 4:21pm

Xaxanitsa,

You can use the clip() function to choose data from a time window
and eliminate the unwanted data. Dug this up from an old presentation
on the topic.
To calculate jitter:
1. Use the period_jitter function to measure the variation in the zero
crossing point from cycle to cycle --> period_jitter( …)
2. Use the rms function to measure the standard deviation of the jitter
--> rms(period_jitter( …))-avg(period_jitter))

Sheldon

Title: Re: PLL period and phase jitter estimation using spectre
Post by xaxanitsa on Feb 25^th, 2015, 10:10am

Hi Sheldon,

Thanks for your answer.

According to Cadence, period_jitter returns a waveform or a value representing deviation from the average period.

In that case (period_jitter( …))-avg(period_jitter)) is somehow already calculated, right?

xaxanitsa