[SI-LIST] Re: Power plane noise measurement
- From: "istvan novak" <istvan.novak@xxxxxxxxxxxxxxxx>
- To: <zhang_kun@xxxxxxxxxx>, <vishrampandit@xxxxxxxxxxx>,<si-list@xxxxxxxxxxxxx>
- Date: Wed, 21 May 2003 08:38:50 -0400
Dear Zangkun and Vishram,
The proper connection depends on what we want to measure.
1., Connecting to pads of different caps, which are 'far' from
each other in terms of wavelength of the highest frequency of
interest, what we get is transfer impedance between the two
connection points. The transfer impedance is more 'low-pass'
in nature due to series lossesand possibly due to caps and
other components on the board.
2., Connecting to pads of the same capacitor, or to power/ground
vias from the same side will give the self impedance of that point,
which in this case is the self impedance of the power planes PLUS
the via impedance in series. The series via impedance may mask
out the details of the power/ground plane network.
3., Connecting to the same via pair from the opposite sides will
give the self impedance of the power-ground plane pairs alone by
virtually eliminating the impedance of series via connections on
either side. We can come close to this by connecting to pads of
different capacitors, which are 'close'. If the highest frequency of
interest is 1GHz, on an FR4 PCB 'close' could be 1cm or closer.
Connecting to vias or pads of different 'close' capacitors on the
same side of the PCB carries the additional risk of having so
much coupling between the two connecting loops to the pads
or vias that it again may mask out the impedance we want to
measure. Connecting from opposite sides is a little bit trickier
to make, but it gives the true self impedance of the structure
without the added via impedance.
Regards,
Istvan Novak
SUN Microsystems
----- Original Message -----
From: "Zhangkun" <zhang_kun@xxxxxxxxxx>
To: <istvan.novak@xxxxxxxxxxxxxxxx>; <vishrampandit@xxxxxxxxxxx>;
<Larry.Smith@xxxxxxx>; <si-list@xxxxxxxxxxxxx>; <adsurevv@xxxxxxxxx>
Sent: Tuesday, May 20, 2003 11:20 PM
Subject: [SI-LIST] Re: Power plane noise measurement
>
> Dear Vishram
>
> The two ports of VNA should connect to pads of different cap. Otherwise,
the inductance of via and leading will overshadow the impedance of PDS. This
is my experience:)
>
> Best Regards
>
> Zhangkun
> 2003.05.21
> ----- Original Message -----
> From: "istvan novak" <istvan.novak@xxxxxxxxxxxxxxxx>
> To: <vishrampandit@xxxxxxxxxxx>; <Larry.Smith@xxxxxxx>;
<si-list@xxxxxxxxxxxxx>; <adsurevv@xxxxxxxxx>
> Sent: Wednesday, May 21, 2003 9:02 AM
> Subject: [SI-LIST] Re: Power plane noise measurement
>
>
> >
> > Vishram,
> >
> > Converting S11 values into impedance does work as long as you
> > dont want to measure impedances below about 0.1 ohms. For
> > low impedance values you still can use a network analyzer, but
> > you have to connect both ports. You can search the archives of
> > the si-list for past threads on the topic. Also, there was a half-day
> > TecForum at DesignCon 2003 in Santa Clara earlier this year,
> > where five companies presented power-distribution measurement
> > techniques. Parts of it are available online, and an updated version
> > of the TecForum will be presented late June in Boston, at
> > DesignCon East 2003.
> >
> > regards,
> >
> > Istvan Novak
> > SUN Microsystems
> >
> >
> > ----- Original Message -----
> > From: "Vishram Pandit" <vishrampandit@xxxxxxxxxxx>
> > To: <Larry.Smith@xxxxxxx>; <si-list@xxxxxxxxxxxxx>; <adsurevv@xxxxxxxxx>
> > Sent: Tuesday, May 20, 2003 3:54 PM
> > Subject: [SI-LIST] Re: Power plane noise measurement
> >
> >
> > >
> > >
> > > Can anyone of you please elaborate about the measurement techniques?
If I
> > > want to measure
> > >
> > > 1] Time domain noise between power and ground,
> > >
> > > 2] Frequency domain Impedance between power and ground,
> > >
> > > what are the best ways of doing that?
> > >
> > > If I have a special SMA connector at the point of interest (between
power
> > > andground), I can use a network analyzer, to measure S11. Will this be
of
> > > anyuse? Also, if I want to measure the impedance at different points
> > > including the BGA pads, where it is very difficult to have special
> > > connector,what is the best approach?
> > >
> > > Thanks for your reply,
> > >
> > > Vishram PanditSenior Member Technical Staff SI/EMC Engineering Hughes
> > > NetworkSystems (301)428-5725
> > >
> > >
> > >
> > > >Virendra - To get a clean measurement of your power distribution
>system,
> > > you will want to remove the decoupling capacitor from it's pads
>before
> > > probing them. >>If the capacitor is left in place, it will "color" the
> > > measurement. The >decoupling capacitor mounted on the pads has a
resonant
> > > frequency. The >inductance for this resonant circuit is in the vias
and
> > > mounting pads >and in the height of the capacitor if you attach probes
to
> > > thetop of >it. You will be measuring across the inductance which is
highly
> > > >involved in the resonant circuit and will measure mostly noise at the
> > > >"selfresonant frequency". >>Usually, there are many small capacitors
on a
> > > product. Pick one out of >a common value. For example, if there are 10
x
> > .01
> > > uF caps, remove one >out of the 10. It will not have a large effect on
the
> > > PDS that you are >measuring. >>regards, >Larry Smith >Sun Microsystems
> > > >>>Delivered-To: si-list@xxxxxxxxxxxxx >>Date: Tue, 20 May 2003
10:28:36
> > > -0700 (PDT) >>From: Virendra >>Subject: [SI-LIST] Power plane noise
> > > measurement >>To: si-list@xxxxxxxxxxxxx >>MIME-Version: 1.0
> > > >>Content-Transfer-Encoding: 8bit >>X-archive-position: 6885
> > > >>X-ecartis-version: Ecartis v1.0.0 >>X-original-sender:
> > adsurevv@xxxxxxxxx
> > > >>X-list: si-list >>>>>>Hi all, >>>>i am trying to measure noise on a
PCB
> > > directly across a decoupling capacitor. >The PCB has buried/ blind
vias
> > and
> > > has no specific power noise test points. My >question is, will there
be a
> > > difference in the measured noise if i measure noise >across the
capacitor
> > > andif i remove the capacitor and probe at the pads? I >cannot remove
the
> > > capacitor to do a what-if as i have only one board. >>>>thanks in
advance,
> > > >>>>Virendra Adsure >>>>>>>>--------------------------------- >>Do you
> > > Yahoo!? >>The New Yahoo! Search - Faster. Easier. Bingo.
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