[SI-LIST] Re: Power Integrity Measurments - on-die impedance
- From: Cosmin Iorga <ci249534@xxxxxxxxx>
- To: Frank_Paglia@xxxxxxxx, rula.bakleh@xxxxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Thu, 6 Aug 2009 13:21:45 -0700 (PDT)
Rula,
I would like to add one comment about evaluating the accuracy of your
measurement: if your PCB measurement shows the high frequency impedance lower
than the target impedance this does not always mean that the on-die circuits
will see that low impedance. Additional power distribution loops form on the
path between PCB and package, mounting interfaces, and on-die impedance and
capacitance. Many times the high frequency transient currents flow mainly
through the package capacitance, on-die power grid capacitance, and on-chip
diffusion capacitance, so they do not actually reach to the PCB impedance. To
be more accurate you would want to have access to the power distribution
impedance as seen by the on-die circuits, which is a lot harder to measure but
still possible.
Cosmin Iorga
NoiseCoupling.com
http://www.noisecoupling.com
________________________________
From: "Frank_Paglia@xxxxxxxx" <Frank_Paglia@xxxxxxxx>
To: rula.bakleh@xxxxxxxxxx; si-list@xxxxxxxxxxxxx
Sent: Thursday, August 6, 2009 12:41:14 PM
Subject: [SI-LIST] Re: Power Integrity Measurments
Rula,
The way to measure the power planes is with a VNA using what is called
the two port method.
What you do is basically put 2 probes in parallel. This is similar to a
4 point Kelvin measurement.
The plane impedance is calculated using S21. This method can be used to
make measurements in the milliohms over a range of a few GHz.
Check out the paper "Frequency Domain Power Distribution Measurements -
An Overview" by Istvan Novak. It was given at DesignCom East 2003 goes
into the details. Agilent also has some app notes. Search on their site.
I've used this method myself and have got very good correlation to
simulations.
Frank
Frank Paglia
Enterprise Engineering Signal Integrity Team
Dell, Inc.
Frank_Paglia@xxxxxxxx
512 724-8520 Office
512 283-3988 Fax
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of rula.bakleh@xxxxxxxxxx
Sent: Thursday, August 06, 2009 1:53 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Power Integrity Measurments
Hi Everyone,
I'm trying to validate our power integrity tools/simulations and I would
like to make some power integrity measurements of our planes.
With respect to performing these measurements, I plan to use a Vector
Network Analyzer (VNA) to measure the plane impedances of a bare PWB and
a PWB with a voltage plane that is populated with only caps in order to
correlate these measurements to the simulations. I also plan to measure
the plane impedance of a fully populated PWB, just to see the effects
that other parts' impedance/mounting would have on the plane impedance.
I also plan to use a spectrum analyzer to measure the plane noise
spectrum of a powered up module and use an oscilloscope to measure
absolute levels of this noise. The purpose of using a spectrum
analyzer/oscilloscope is to measure the simultaneous switching effects
on the plane, hoping to isolate the PWB effects from internal SSO
effects of a component.
My dilemma is the following:
The VNAs are optimized for 50 ohms and plane impedances of PWBs are
designed for very low impedance (most of the time much <1.0 ohm).
1) Due to the impedance discontinuities, what is the expected accuracy
of such a measurement?
All the research I have conducted concerning PWB impedance measurements
points to using a VNA. During my discussions with an Agilent FAE, he
recommended using an Impedance Analyzer vs. VNA to measure the PDS of a
plane. He also recommended using a high impedance active solderable
probe with the impedance analyzer with it being calibrated out to make
this measurement.
2) What is the best equipment to use to measure the PDS of a PWB (VNA or
Impedance Analyzer)?
3) If the answer is an Impedance Analyzer, is the approach described
above correct?
4) Can somebody validated my approach for this type of
analysis/measurements?
Thank You,
Rula
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