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Design >> Mixed-Signal Design >> supply noise
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Message started by sure on Jan 31^st, 2010, 10:07pm

Title: supply noise
Post by sure on Jan 31^st, 2010, 10:07pm

hi,
i am designing charge pump in pll, so in that how to apply supply noise. I heard through some one that supply noise has white PSD, is it true?

Thanks,
sure.

Title: Re: supply noise
Post by loose-electron on Feb 1^st, 2010, 6:03pm

very dependent on what else is connected to the supply, because it creates the noise.

Title: Re: supply noise
Post by raja.cedt on Feb 1^st, 2010, 7:43pm

hi sure,
as loose electron said it is very depends on how other's are working manily on what freuqency digital end works and how good your power grid. But i think supply noise not that random as you said it is having white psd...up to my knowledge it's quite deterministic (i saw one kind of psd for 4.8GBPS serial link..there it is having some peaks rather flat). May be some exp person can give more abut how a typical supply noise specturm.

Thanks,
Rajasekhar.

Title: Re: supply noise
Post by Mayank on Feb 1^st, 2010, 8:47pm

Hi sure,
Supply noise is rarely white.....
It does have a broadband noise floor like any other noise, which can be called white....
but depending on your Mixed Signal cktry, you are bound to observe some peaks.
Also the PMU is a known source for supply noise spurs owing to PWM pulses used inside.
Exact derivation of supply noise profile can only be obtained by full chip simulation.
--
Mayank.

Title: Re: supply noise
Post by raja.cedt on Feb 2^nd, 2010, 3:46am

hi,
probably this paper may help ...
http://www-vlsi.stanford.edu/papers/ea_jssc_05.pdf

Thanks,
rajasekhar.

Title: Re: supply noise
Post by love_analog on Apr 7^th, 2010, 2:27pm

why are you planning to apply supply noise to CP.

In a typical PLL, its the VCO (and also the post VCO buffer) which will cause the most supply induced jitter on the output.

If you just want to get a feel, apply a sinewave at a frequency which is a non-integer of the reference clock but I suspect you need to answer the why question first.