[SI-LIST] Re: Measuring PDN impedance with a VNA?
- From: Istvan Novak <istvan.novak@xxxxxxxxxxx>
- To: tom_cip_11551@xxxxxxxxxxx
- Date: Thu, 13 Sep 2012 21:54:40 -0400
Hi,
The type of probe needed depends on the highest frequency you need to
cover. For low-frequency measurements, say up to 10MHz, you dont even
need any probes, just two coax cables, and you can use quite long
pigtails in soldering and the data is still good. With the semirigid
probes shown in the paper you cite, you can do reasonably good
measurements up to about a gigahertz. For even higher frequencies you
need wafer probes.
To measure low impedances with a VNA, you have to make a two-port
shunt-through connection, which requires two probes and you have to make
sure that the two probes close through the DUT, not before. If you
connect the two probes together and then you connect the DUT, will
introduce series resistance and inductance, which will raise the error
floor.
You can find more details in a later paper:
"Frequency Domain Power Distribution Measurements - An Overview",
DesignCon 2003 East, High-Performance System Design Conference, Boston,
MA, June 23-25, 2003, which is posted on the same site, or even more
details in the book Frequency Domain Characterization of Power
Distribution Networks.
Regards,
Istvan Novak
Oracle
On 9/13/2012 8:03 PM, miner_tom Cipollone wrote:
> I have read several references about how to measure the impedance of a PCB
> PDN (power to ground).
> A VNA can be used to measure these very low impedances but there is usually a
> catch in terms of the probes that should be used. Agilent says that in order
> to measure very low impedances "microprobes" should be used. I do not have
> microprobes.
> As an alternative, I have considered building a "Dual Semi-rigid" probe as
> outlined in
> http://www.electrical-integrity.com/Paper_download_files/DC99_ProbesAndSetup.pdf.
> With respect to the semi rigid probe made from coax, I have two questions:
> In the diagram shown in the referenced article on page 8, slide 18, the tips
> of the probes are not shorted together. I would have thought that for this
> measurement they would be.Up to what frequency is this home made apparatus
> good? Are there alternative methods?
> Thank You
>
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