[SI-LIST] Re: Clock Jitter

Power supply noise can be correlated or uncorrelated to the oscillator.  
If the problem is self impedance at the clock gen the noise and jitter 
will correlate.  If the problem is noise from other devices propagating 
through the PDN to the clock chip, the jitter will not correlate.  
Outside disturbances may or may not be effectively random.  Usually they 
are deterministic.

At least three posts have mentioned various ways that changes to the fab 
could impair the clock generator power.  There are others.


Richard Jungert wrote:
>  
> No one has yet said how the changes in the fabrication of the pcb adds 
> random noise to the clock circuit. Yes noise can be added from clock 
> to reciever but it seems to me that the oscillator has to work right 
> first.
>  
> One can realistically only fix one problem at a time.
>  
> Richard Jungert
>  
> > Date: Tue, 30 Jun 2009 10:13:39 -0700
> > From: weirsi@xxxxxxxxxx
> > To: r_jungert@xxxxxxxxxxx
> > CC: hermann.ruckerbauer@xxxxxxxxxxxxx; greg.pietz@xxxxxx; 
> si-list@xxxxxxxxxxxxx
> > Subject: [SI-LIST] Re: Clock Jitter
> >
> > The problem can be anywhere from the oscillator to the receiver.
> >
> > Richard Jungert wrote:
> > > Random voltage changes on the switching threshold is done in the 
> oscillator right? How is that done, with random variations on power or 
> ground in the oscillator.
> > >
> > >
> > >
> > > That is why I am promoting good filtering on the oscillator. Lets 
> say the changes to the impedance will cause changes and create new 
> fixed variables in impedances. Now we have a new set of fixed variables.
> > >
> > >
> > >
> > > I would recommend blocking the source of random energy. Isolate it 
> if you will so that the problem sources can't change it. Its nice to 
> know too what frequencies that are causing the modulation.
> > >
> > >
> > >
> > > Richard Jungert
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >> Date: Tue, 30 Jun 2009 08:13:35 -0700
> > >> From: weirsi@xxxxxxxxxx
> > >> To: r_jungert@xxxxxxxxxxx
> > >> CC: hermann.ruckerbauer@xxxxxxxxxxxxx; greg.pietz@xxxxxx; 
> si-list@xxxxxxxxxxxxx
> > >> Subject: Re: [SI-LIST] Re: Clock Jitter
> > >>
> > >> Jitter is any variation in the time the signal ( pair ) crosses the
> > >> switching threshold. It has both random and deterministic sources.
> > >> Richard Jungert wrote:
> > >>
> > >>> I don't quite get how small changes in board construction can 
> increase
> > >>> jitter.
> > >>> If one isolates the oscillator with good power filters and good 
> ground
> > >>> plane splits then how can the noise get in to modulate the 
> oscillator?
> > >>>
> > >>> Jitter is all about randomness right?
> > >>>
> > >>> Richard Jungert
> > >>>
> > >>>
> > >>>
> > >>>> Date: Tue, 30 Jun 2009 16:48:00 +0200
> > >>>> From: hermann.ruckerbauer@xxxxxxxxxxxxx
> > >>>> To: r_jungert@xxxxxxxxxxx
> > >>>> CC: greg.pietz@xxxxxx; si-list@xxxxxxxxxxxxx
> > >>>> Subject: [SI-LIST] Re: Clock Jitter
> > >>>>
> > >>>> Content-Type: text/plain; charset=ISO-8859-1
> > >>>> Content-Transfer-Encoding: quoted-printable
> > >>>> Hi,
> > >>>>
> > >>>> although some explantions came back I guess the orignal 
> question was not
> > >>>> really answered. What can be the difference in PCB manufacuring to
> > >>>> increase jitter ?
> > >>>>
> > >>>> I think the hint to power/ground noise is quite good. We have 
> seen, that
> > >>>> the Copper thickness is varying quite a bit with different 
> vendors, what
> > >>>> might cause a difference in power noise between the different 
> boards.
> > >>>> But what would worry me is, that such a small change should 
> change your
> > >>>> design from pass to fail. If your design is that critical it is not
> > >>>> stable enough for HVM (high volumen manufacturing). In a volume
> > >>>> production you will see a certain distribution of the Power plane
> > >>>> thickness what could be a big problem for sutch a design.
> > >>>>
> > >>>> As you measured your impdance and confirmed the same value I 
> would not
> > >>>> really expect the issue to come from the dielectric properties. 
> If they
> > >>>> would change too much this would influence er and therefore the
> > >>>> impedance. Overall I would not really see this to cause a 
> bigger change
> > >>>> for the Jitter (but is 20ps really a bigger change ??)
> > >>>>
> > >>>> What I would see as another possiblilty is e.g. the size of 
> Anti-pads.
> > >>>> If there are some Anti-pads along the current return they might 
> even
> > >>>> create a cut in the Ground plane when the PCB manufacterer does 
> some
> > >>>> overetch. Basically it might be possible to see such things in 
> the TDR,
> > >>>> but maybe the effect is big enough to shift a reflection a bit, 
> but not
> > >>>> easily see it as difference in the TDR.
> > >>>>
> > >>>> regards
> > >>>>
> > >>>> Hermann
> > >>>>
> > >>>>
> > >>>>
> > >>>>
> > >>>> EKH - EyeKnowHow
> > >>>> Hermann Ruckerbauer
> > >>>> www.eyeknowhow.de
> > >>>> hermann.ruckerbauer@xxxxxxxxxxxxx
> > >>>> Veilchenstrasse 1
> > >>>> 94554 Moos
> > >>>> Tel.: +49 (0)9938 / 902083
> > >>>> Mobile: +49 (0)176 / 787 787 77
> > >>>> Fax: +49 (0)721 / 151 258 230
> > >>>>
> > >>>>
> > >>>>
> > >>>> Richard Jungert schrieb:
> > >>>>
> > >>>>> Greg.
> > >>>>>
> > >>>>>
> > >>>>>
> > >>>>> Its more than likely power noise or noise from the ground plane
> > >>>>>
> > >>> getting> > > into the oscillator.
> > >>>
> > >>>>> You might need to put a moat in the ground plane and power plane
> > >>>>>
> > >>> on the> > > oscillator to cut the jitter cuz noise can sneak in 
> any connection
> > >>> thru > > > the ground or the power.
> > >>>
> > >>>>>
> > >>>>>
> > >>>>> I was suprized how much the noise on the ground can sneak into an
> > >>>>>
> > >>> oscil> > > lator when we had to fix this probklem type years ago 
> on a video
> > >>> graphics> > > board. Originally I thought it was power noise but 
> turned out to be
> > >>> grou> > > nd noise causing the problem.
> > >>>
> > >>>>>
> > >>>>>
> > >>>>> Are the any splits in your ground plane around the oscillator? Is
> > >>>>>
> > >>> the o> > > scillator in the middle of the board is another issue 
> that can make
> > >>> it wo> > > rse.
> > >>>
> > >>>>>
> > >>>>>
> > >>>>> If you free run the oscillator with a battery how much jitter is
> > >>>>>
> > >>> presen> > > t? Getting the jitter within spec is hard work! Try 
> free running it
> > >>> by i> > > tself totally away from the circuit board to see what 
> stand alone
> > >>> best ca> > > se jitter can be.
> > >>>
> > >>>>>
> > >>>>>
> > >>>>> Richard Jungert
> > >>>>>
> > >>>>>
> > >>>>>
> > >>>>>
> > >>>>>
> > >>>>>
> > >>>>>
> > >>>>>> Subject: [SI-LIST] Re: Clock Jitter
> > >>>>>> Date: Tue, 30 Jun 2009 10:06:28 -0400
> > >>>>>> From: mrose@xxxxxxxxxxxx
> > >>>>>> To: greg.pietz@xxxxxx; si-list@xxxxxxxxxxxxx
> > >>>>>>
> > >>>>>> Greg,
> > >>>>>>
> > >>>>>> Is the additional jitter DJ or RJ? If it's uncorrelated, you
> > >>>>>>
> > >>> could loo> > > k
> > >>>
> > >>>>>> at power noise. If it's DJ, you may want to look at the relative
> > >>>>>> magnitude of the impedance discontinuities (traces, vias,
> > >>>>>>
> > >>> connectors).> > >
> > >>>
> > >>>>>> Did you check trace coupons? Also, you might check if there 
> is any
> > >>>>>> additional duty cycle distortion from the oscillator.
> > >>>>>>
> > >>>>>> Good luck
> > >>>>>>
> > >>>>>> -----Original Message-----
> > >>>>>> From: si-list-bounce@xxxxxxxxxxxxx
> > >>>>>>
> > >>> [mailto:si-list-bounce@xxxxxxxxxxxx> > > g]
> > >>>
> > >>>>>> On Behalf Of Pietz, Greg P
> > >>>>>> Sent: Tuesday, June 30, 2009 9:55 AM
> > >>>>>> To: si-list@xxxxxxxxxxxxx
> > >>>>>> Subject: [SI-LIST] Clock Jitter
> > >>>>>>
> > >>>>>> We have a board design using PCIe. The PCIe reference clock 
> for each
> > >>>>>> ASIC comes from a clock generator IC. On initial proto boards,
> > >>>>>>
> > >>> build i> > > n
> > >>>
> > >>>>>> the USA, the clock jitter was about 78ps or less on all boards
> > >>>>>>
> > >>> tested.> > >
> > >>>
> > >>>>>> We then had boards built overseas and are seeing jitter of 90 to
> > >>>>>>
> > >>> 100ps> > > .
> > >>>
> > >>>>>> This is greater then the spec allows and is causing problems 
> with the
> > >>>>>> link. I did a TDR of the clock traces and they are 100 ohms
> > >>>>>> differential.
> > >>>>>>
> > >>>>>> For two of the board vendors I was able to make some changes 
> to the
> > >>>>>> design to get their jitter in spec. For the third vendor I 
> have been
> > >>>>>> unable to fix the jitter problem.
> > >>>>>>
> > >>>>>> The board stackup is the standard 6 layer design. The clocks all
> > >>>>>> reference the ground plan.
> > >>>>>> My question is what can a board vendor do to increase clock 
> jitter.
> > >>>>>>
> > >>>>>> Thanks,
> > >>>>>> Greg
> > >>>>>>
> > >>>>>>
> > >>>>>>
> > >>>>>> 
> ------------------------------------------------------------------
> > >>>>>> To unsubscribe from si-list:
> > >>>>>> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the 
> Subject field
> > >>>>>>
> > >>>>>> or to administer your membership from a web page, go to:
> > >>>>>> http://www.freelists.org/webpage/si-list
> > >>>>>>
> > >>>>>> For help:
> > >>>>>> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
> > >>>>>>
> > >>>>>>
> > >>>>>> List technical documents are available at:
> > >>>>>> http://www.si-list.net
> > >>>>>>
> > >>>>>> List archives are viewable at:
> > >>>>>> http://www.freelists.org/archives/si-list
> > >>>>>> or at our remote archives:
> > >>>>>> http://groups.yahoo.com/group/si-list/messages
> > >>>>>> Old (prior to June 6, 2001) list archives are viewable at:
> > >>>>>> http://www.qsl.net/wb6tpu
> > >>>>>>
> > >>>>>>
> > >>>>>> 
> ------------------------------------------------------------------
> > >>>>>> To unsubscribe from si-list:
> > >>>>>> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the 
> Subject field
> > >>>>>>
> > >>>>>> or to administer your membership from a web page, go to:
> > >>>>>> http://www.freelists.org/webpage/si-list
> > >>>>>>
> > >>>>>> For help:
> > >>>>>> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
> > >>>>>>
> > >>>>>>
> > >>>>>> List technical documents are available at:
> > >>>>>> http://www.si-list.net
> > >>>>>>
> > >>>>>> List archives are viewable at:
> > >>>>>> http://www.freelists.org/archives/si-list
> > >>>>>> or at our remote archives:
> > >>>>>> http://groups.yahoo.com/group/si-list/messages
> > >>>>>> Old (prior to June 6, 2001) list archives are viewable at:
> > >>>>>> http://www.qsl.net/wb6tpu
> > >>>>>>
> > >>>>>>
> > >>>>>>
> > >>>>>>
> > >>>>> _________________________________________________________________
> > >>>>> Insert movie times and more without leaving Hotmail®.
> > >>>>>
> > >>>>>
> > >>> 
> http://windowslive.com/Tutorial/Hotmail/QuickAdd?ocid=TXT_TAGLM_WL_HM> 
> > > _Tutorial_QuickAdd_062009
> > >>>
> > >>>>> ------------------------------------------------------------------
> > >>>>> To unsubscribe from si-list:
> > >>>>> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the 
> Subject field
> > >>>>>
> > >>>>> or to administer your membership from a web page, go to:
> > >>>>> http://www.freelists.org/webpage/si-list
> > >>>>>
> > >>>>> For help:
> > >>>>> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
> > >>>>>
> > >>>>>
> > >>>>> List technical documents are available at:
> > >>>>> http://www.si-list.net
> > >>>>>
> > >>>>> List archives are viewable at:
> > >>>>> http://www.freelists.org/archives/si-list
> > >>>>> or at our remote archives:
> > >>>>> http://groups.yahoo.com/group/si-list/messages
> > >>>>> Old (prior to June 6, 2001) list archives are viewable at:
> > >>>>> http://www.qsl.net/wb6tpu
> > >>>>>
> > >>>>>
> > >>>>>
> > >>>>>
> > >>> 
> -----------------------------------------------------------------------> 
> > > -
> > >>>
> > >>>>> Eingehende eMail ist virenfrei.
> > >>>>> Von AVG überprüft - www.avg.de
> > >>>>> Version: 8.5.375 / Virendatenbank: 270.13.0/2209 - Ausgabedatum:
> > >>>>>
> > >>> 06/29/> > > 09 14:43:00
> > >>>
> > >>>>>
> > >>>>>
> > >>>>
> > >>>> ------------------------------------------------------------------
> > >>>> To unsubscribe from si-list:
> > >>>> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject 
> field
> > >>>>
> > >>>> or to administer your membership from a web page, go to:
> > >>>> http://www.freelists.org/webpage/si-list
> > >>>>
> > >>>> For help:
> > >>>> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
> > >>>>
> > >>>>
> > >>>> List technical documents are available at:
> > >>>> http://www.si-list.net
> > >>>>
> > >>>> List archives are viewable at:
> > >>>> http://www.freelists.org/archives/si-list
> > >>>> or at our remote archives:
> > >>>> http://groups.yahoo.com/group/si-list/messages
> > >>>> Old (prior to June 6, 2001) list archives are viewable at:
> > >>>> http://www.qsl.net/wb6tpu
> > >>>>
> > >>>>
> > >>>>
> > >>> 
> ------------------------------------------------------------------------
> > >>> Hotmail® has ever-growing storage! Don’t worry about storage 
> limits.
> > >>> Check it out.
> > >>> 
> <http://windowslive.com/Tutorial/Hotmail/Storage?ocid=TXT_TAGLM_WL_HM_Tutorial_Storage_062009>
> > >>>
> > >> --
> > >> Steve Weir
> > >> Teraspeed Consulting Group LLC
> > >> 121 North River Drive
> > >> Narragansett, RI 02882
> > >>
> > >> California office
> > >> (866) 675-4630 Business
> > >> (707) 780-1951 Fax
> > >>
> > >> Main office
> > >> (401) 284-1827 Business
> > >> (401) 284-1840 Fax
> > >>
> > >> Oregon office
> > >> (503) 430-1065 Business
> > >> (503) 430-1285 Fax
> > >>
> > >> http://www.teraspeed.com
> > >> This e-mail contains proprietary and confidential intellectual 
> property of Teraspeed Consulting Group LLC
> > >> 
> ------------------------------------------------------------------------------------------------------
> > >> Teraspeed(R) is the registered service mark of Teraspeed 
> Consulting Group LLC
> > >>
> > >>
> > >
> > > _________________________________________________________________
> > > Windows Live™ SkyDrive™: Get 25 GB of free online storage.
> > > 
> http://windowslive.com/online/skydrive?ocid=TXT_TAGLM_WL_SD_25GB_062009
> > > ------------------------------------------------------------------
> > > To unsubscribe from si-list:
> > > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
> > >
> > > or to administer your membership from a web page, go to:
> > > http://www.freelists.org/webpage/si-list
> > >
> > > For help:
> > > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
> > >
> > >
> > > List technical documents are available at:
> > > http://www.si-list.net
> > >
> > > List archives are viewable at:
> > > http://www.freelists.org/archives/si-list
> > > or at our remote archives:
> > > http://groups.yahoo.com/group/si-list/messages
> > > Old (prior to June 6, 2001) list archives are viewable at:
> > > http://www.qsl.net/wb6tpu
> > >
> > >
> > >
> > >
> >
> >
> > --
> > Steve Weir
> > Teraspeed Consulting Group LLC
> > 121 North River Drive
> > Narragansett, RI 02882
> >
> > California office
> > (866) 675-4630 Business
> > (707) 780-1951 Fax
> >
> > Main office
> > (401) 284-1827 Business
> > (401) 284-1840 Fax
> >
> > Oregon office
> > (503) 430-1065 Business
> > (503) 430-1285 Fax
> >
> > http://www.teraspeed.com
> > This e-mail contains proprietary and confidential intellectual 
> property of Teraspeed Consulting Group LLC
> > 
> ------------------------------------------------------------------------------------------------------
> > Teraspeed(R) is the registered service mark of Teraspeed Consulting 
> Group LLC
> >
> > ------------------------------------------------------------------
> > To unsubscribe from si-list:
> > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
> >
> > or to administer your membership from a web page, go to:
> > http://www.freelists.org/webpage/si-list
> >
> > For help:
> > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
> >
> >
> > List technical documents are available at:
> > http://www.si-list.net
> >
> > List archives are viewable at:
> > http://www.freelists.org/archives/si-list
> > or at our remote archives:
> > http://groups.yahoo.com/group/si-list/messages
> > Old (prior to June 6, 2001) list archives are viewable at:
> > http://www.qsl.net/wb6tpu
> >
> >
>
> ------------------------------------------------------------------------
> Windows Live™: Keep your life in sync. Check it out. 
> <http://windowslive.com/explore?ocid=TXT_TAGLM_WL_BR_life_in_synch_062009>


-- 
Steve Weir
Teraspeed Consulting Group LLC 
121 North River Drive 
Narragansett, RI 02882 

California office
(866) 675-4630 Business
(707) 780-1951 Fax

Main office
(401) 284-1827 Business 
(401) 284-1840 Fax 

Oregon office
(503) 430-1065 Business
(503) 430-1285 Fax

http://www.teraspeed.com
This e-mail contains proprietary and confidential intellectual property of 
Teraspeed Consulting Group LLC
------------------------------------------------------------------------------------------------------
Teraspeed(R) is the registered service mark of Teraspeed Consulting Group LLC

------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field


List technical documents are available at:
                http://www.si-list.net

List archives are viewable at:     
                http://www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu

Other related posts: