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Measurements >> Phase Noise and Jitter Measurements >> sidebands and frequencies for Jittercalculation
https://designers-guide.org/forum/YaBB.pl?num=1171633634

Message started by JitterGeorge on Feb 16^th, 2007, 5:47am

Title: sidebands and frequencies for Jittercalculation
Post by JitterGeorge on Feb 16^th, 2007, 5:47am

Dear all,

I want to calculate the jitter of a kind of Delay Locked Loop (DLL). The design is driven by a 5MHz clock and is locked after about 7 us (tstab=20us for some safety). So, after reading some papers, I assume, that I have to set the Frequency Range in pnoise (and also within the Jee-Dialog) from about 1Hz to 2.5MHz. Is this assumption correct?

In some cadence-Handbook i read that the default number of sidebands is about 7. This number should be increased, until the calculated Jittervalues get constant. And here my problems begin:
I first set the sidebands in pnoise and the harmonics in pss to the same value. But than the Jittervalues are nearly chaotic within a range from 7 to 300 sidebands (=harmonics). I got the hint, that the harmonics influence the maxtimesteps and by this the accuracy of the whole design. So I set them to a fixed value of 150 and only vary the number of sidebands. Now the Jitter looks a bit like it could be assymptotic but a small positive gradient is left. So I have no idea of how to determine the jitter.

I would be thankful for every hint on this.

Greetings,
JitterGeorge

Title: Re: sidebands and frequencies for Jittercalculatio
Post by Ken Kundert on Feb 16^th, 2007, 6:47am

I recommend that you read the section on sidebands in the paper on simulating SC-filters with SpectreRF, which can be found at www.designers-guide.org/Analysis.

-Ken

Title: Re: sidebands and frequencies for Jittercalculatio
Post by JitterGeorge on Feb 19^th, 2007, 1:58am

Thank you.
This paper gave me a very good insight into the theory.
The calculated jittervalues now seem to be suitable and nearly stable, after i calculated the desired sidebands to be nearly 1k.

So nice greetings till my next question ;)

JitterGeorge

Title: Re: sidebands and frequencies for Jittercalculatio
Post by Visjnoe on Feb 19^th, 2007, 2:42am

Dear George,

just out of curiosity: what was the impact on your simulation time?
Is the simulation time still acceptable to allow corner analysis?

Regards

Peter

Title: Re: sidebands and frequencies for Jittercalculatio
Post by JitterGeorge on Feb 22^nd, 2007, 6:53am

This depends on how much time you have ;)

For 1k sidebands our sim-machine took about 9h. So for 8 corners you will need some time.
But I did some simulations with less sidebands and as it is written in Ken's Paper the error is quiet low even for only 100 sidebands (about 3%). So you will save 8 hours wich can be used for the corners.

Greetings,
George