[SI-LIST] Re: PCIe DCD / Jitter simulation
- From: steve weir <weirsi@xxxxxxxxxx>
- To: Hermann Ruckerbauer <hermann.ruckerbauer@xxxxxxxxxxxxx>
- Date: Mon, 26 Oct 2009 05:44:36 -0700
Hermann, frequency dependent loss in the signal band will give you
pattern dependent distortion, IE DCD.
Steve
Hermann Ruckerbauer wrote:
> Hello,
>
> I'm just looking in PCI express gen2 simulations, but do not fully
> understand the Spec regarding DCD and Jitter (low and high frequency)
> for worst case simulations.
>
> There is mentioned, that the simulation should be done with 0.1 DCD.
> Additionally there are 78ps Dj and 28ps for slewing the eye.
>
> 0.15UI is the max. High Frequency TX jitter. From this 30ps (0.15UI)
> one should include 0.1UI (20ps) as DCD in the simulation.
> ==> What is the Jitter distribution, that should be assumed here?
> I guess a fixed 0.1UI DCD is not correct. Personally I would use +-
> 0.05UI with some gaussian distribution, but I'm not sure if this is the
> intension there.
> This would reduce the eye size, but still results in a nice symmetric eye.
> So in my understanding this is not really a Duty cylce distortion with
> e.g. each even bit short and each odd bit long, but high frequency
> jitter e. g. introduced by SSO noise and package x-talk.
> ==> Is my understanding correct ?
>
> Additionally there is a value of 78ps Dj mentioned. not sure if I need
> to add this in simulation or data evaluation, or if this is accounted
> for by the DCD already.
> ==> My understanding is, that this is the max value of the sum of the
> 0.1DCD + the Jitter introduced by the channel.
> Is this correct, or do I need to add this DJ in addition (in simulation
> or data evaluation)?
> I can evaluate this, but if I place a Receiver eye mask it should be
> enough not to violate the mask, correct ?
>
>
> Finally there is there is the jitter that I need to add in the
> dataevaluation by slewing the eye (e. g. 28.9ps for common clock
> architecture.
> ==> is it OK to expand the eye mask by this number (+-15ps from the
> center) ?
>
> So far i have not seen any documents that describe it in a way that I
> would understand it (guess I'm just to stupid). Maybe somebody can
> enlighten me here, or point me to some description.
>
> Thanks and regards
>
> Hermann
>
>
>
>
> EKH - EyeKnowHow
> Hermann Ruckerbauer
> www.eyeknowhow.de
> hermann.ruckerbauer@xxxxxxxxxxxxx
> Veilchenstrasse 1
> 94554 Moos
> Tel.: +49 (0)9938 / 902 083
> Mobile: +49 (0)176 / 787 787 77
> Fax: +49 (0)3212 / 121 9008
>
>
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