[SI-LIST] Re: Decoupling for PLL
- From: "Neves, AlfredX" <alfredx.neves@xxxxxxxxx>
- To: <weirsp@xxxxxxxxxx>, <tom@xxxxxxxxxxxxx>, <cgrassosprint1@xxxxxxxxxxxxx>, <zhang_kun@xxxxxxxxxx>, <a.ingraham@xxxxxxxx>
- Date: Mon, 30 Aug 2004 16:45:12 -0700
How about a strategy of relating the spurious sideband energy from the
PLL carrier to the PSD of noise generated on the supply as a way of
getting a parameterized handle on the problem? Another way of doing
this is to use FFT of autocorrelation of the accumulated jitter of the
clock output. Acquainted with Wavecrest (Tektronix and Agilent also
have hardware/algorithms to check out), they use this type of algorithm
which provides measures of periodic jitter in the frequency domain in
psecs peak-peak. The clock output periodic jitter can be related to PDN
so that PDN jitter to clock output jitter transfer function in Unit
Interval or psec peak-peak can be made.
Also have used the Wavecrest instruments/algorithms to separate the
jitter into random and deterministic components and generate a
statistically significant failure rate based on number of clocks cycles
and peak-peak jitter. These peak-peak numbers can be used in
conjunction with skew to get insight into the overall skew+jitter system
budget.
Peaking in the PLL loop response, jitter transferred from the PDN to
clock output, allowable jitter input tolerance, etc., should all be
characterized and not just simply fixed or made to work. =20
Al Neves
503 679 2429
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of steve weir
Sent: Sunday, August 29, 2004 8:09 PM
To: tom@xxxxxxxxxxxxx; cgrassosprint1@xxxxxxxxxxxxx;
zhang_kun@xxxxxxxxxx; a.ingraham@xxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Decoupling for PLL
Tom, given Zhangkun's observation that substitution of an R for the L in
the power feed "fixes" the PLL, I think it is safe to say that the
problem=20
is power related.
Regards,
Steve.
At 03:09 PM 8/29/2004 -0700, Tom Dagostino wrote:
>No where in this discussion has anybody said, "this PLL is failing
because".
>Until we know why the PLL is failing nobody can fix it, no matter how
clean
>the power supply is.
>
>Tom Dagostino
>Teraspeed Consulting Group LLC
>503-430-1065
>tom@xxxxxxxxxxxxx
>www.teraspeed.com
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx
>[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Charles Grasso
>Sent: Sunday, August 29, 2004 4:03 PM
>To: weirsp@xxxxxxxxxx; zhang_kun@xxxxxxxxxx; a.ingraham@xxxxxxxx
>Cc: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Re: Decoupling for PLL
>
>
>Steve - I completley agree. I have tried to measure a power bus with a
SA -
>only to find that the 50 ohm termination swamped the reading. (This was
on a
>two layer board where the Power impedance is pretty high to begin with)
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx
>[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of steve weir
>Sent: Sunday, August 29, 2004 3:21 AM
>To: zhang_kun@xxxxxxxxxx; a.ingraham@xxxxxxxx
>Cc: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Re: Decoupling for PLL
>
>
>Zhangkun, if I understand correctly, you said that you have a bead and
a
>big electrolytic capacitor and two or three ceramic capacitors. If you
are
>looking at this with a 50ohm spectrum analyzer load, you are very
likely
>damping the network. Try a 50 ohm resistor across the network without
the
>spectrum analyzer and see if it works as it does with the series
>resistor. You should make up an attenuator so that the spectrum
analyzer
>does not load the filter.
>
>Steve.
>At 05:34 PM 8/29/2004 +0800, zhangkun 29902 wrote:
> >Andy
> >
> >I use spectrum analyzer to measure the power ground noise in
frequency
> >domain. At almost all the harmonic frequency, the amplitude with 0
ohm
> >resistor is less of 3db than that with bead.
> >
> >The pre-filter power is of plane pair.
> >
> >Best Regards
> >
> >Zhangkun
> >2004.8.29
> >
> >----- Original Message -----
> >From: Andrew Ingraham <a.ingraham@xxxxxxxx>
> >Date: Saturday, August 28, 2004 9:48 pm
> >Subject: [SI-LIST] Re: Decoupling for PLL
> >
> > > Zhangkun,
> > >
> > > Some PLLs can be very sensitive to tiny amounts of noise. They
> > > are, after
> > > all, analog devices.
> > >
> > > When you say the noise difference is only 3dB, (1) that might be
> > > just enough
> > > of a difference to cause a problem, if your circuits were just on
> > > the edge
> > > of misbehaving; and (2) if you are measuring and comparing
> > > broadband noise,
> > > it is a meaningless comparison. The PLL is particularly sensitive
> > > to noise
> > > at particular frequencies, and you may need to look specifically
> > > for those
> > > frequencies. A broadband noise measurement could mask the
> > > frequencies that
> > > are causing the problem. Even a spectrum analyzer might, if you
> > > don't know
> > > what frequencies to look for.
> > >
> > > Another thought: does connecting the instruments to measure the
noise,
> > > significantly affect the circuit? Maybe simply connecting probes
> > > reducesthe noise enough to stop that PLL from misbehaving (while
> > > the other two PLLs
> > > continue to misbehave).
> > >
> > > How clean is the pre-filtered power? Is it a plane?
> > >
> > > Is there anything else of an analog nature on this board?
> > >
> > > Regards,
> > > Andy
> > >
> > >
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