[SI-LIST] Re: Power plane noise measurement
- From: "Vishram Pandit" <vishrampandit@xxxxxxxxxxx>
- To: istvan.novak@xxxxxxxxxxxxxxxx, zhang_kun@xxxxxxxxxx,si-list@xxxxxxxxxxxxx
- Date: Wed, 21 May 2003 18:01:07 +0000
Dear Dr. Novak and Zangkun,
1] I can put an SMA connector (on a test board) at a less dense area of the
board. Typically there is a ground fill on the upper layer of the board, I
can connect the ground of the SMA connector to this ground fill. The center
pin of the SMA will go directly to the power plane through a via. Will this
be okay? Does it have to be at the capacitor pads?
2] Secondly, there may be different impedance response for power and ground
plane at different points on the board. If I am interested in measuring the
power/ground impedance at BGA pins, I may not be able to put an SMA
connectorthere. In this case, how to measure the impedance?
3] What are the typical values of the measured impedances? In my
simulations,I have got the following results:
* Best case board: from low frequency to 2GHz, power and ground impedance is
linearly rising up to 6 Ohms
* Worst case board: As high as 100 Ohms resonating at 800 MHz or beyond.
In simulations, I try to reduce it. What should be my criteria? Let us take
an example. The highest frequency on the board is 480MHz. I will try to
reduce the impedance upto 480MHz as far as possible. What should be my
targetimpedance at 480MHz? How far beyond 480MHz I can tolerate the
resonances?
Any leads will be appreciated.
Regards,
Vishram Pandit
Senior Member Technical Staff
SI/EMC Engineering
Hughes Network Systems
Phone: (301)428-5725
>From: "istvan novak" >To: ,, >Subject: Re: [SI-LIST] Re: Power plane noise
measurement >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
impedanceis 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
ofthe 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
orcloser. >>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
impedanceof the structure >without the added via impedance. >>Regards,
>>Istvan Novak >SUN Microsystems >>>>----- Original Message ----- >From:
"Zhangkun" >To: ; ; >; ; >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" >>To: ; ; >; >>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
haveto 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
presentedlate June in Boston, at >>>DesignCon East 2003. >>>>>>regards,
>>>>>>Istvan Novak >>>SUN Microsystems >>>>>>>>>----- Original Message -----
>>>From: "Vishram Pandit" >>>To: ; ; >>>Sent: Tuesday, May 20, 2003 3:54 PM
>>>Subject: [SI-LIST] Re: Power plane noise measurement
>>>>>>>>>>>>>>>>>>Cananyone 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
>ona >>>>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
largeeffect 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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