[SI-LIST] Re: Measuring PDN impedance with a VNA?
- From: DAVID CUTHBERT <telegrapher9@xxxxxxxxx>
- To: olaney@xxxxxxxxx
- Date: Fri, 14 Sep 2012 13:03:59 -0600
VNA ports have 50 ohm ports and no matching resistors are needed.
Example: set the VNA amplitude to 1/2 volt. It is actually a 1 volt source
with a 50 ohm series R. Into a low Z PDN it will drive 1V/50 ohms or 20 mA
into the PDN.
Connect the other probe nearby on the PDN and measure the amplitude.
Calculate the PDN impedance.
Dave Cuthbert
On Sep 13, 2012 8:46 PM, "O. Laney" <olaney@xxxxxxxxx> wrote:
> Since PDN impedances are usually really low compared to 50 ohms,
> practical measurements often require Kelvin probe arrangements. Yes,
> that implies the need for 4 VNA ports.
>
> Orin
>
> ------ Original Message ------
> From: "Istvan Novak" <istvan.novak@xxxxxxxxxxx>
> To: tom_cip_11551@xxxxxxxxxxx
> Cc: si-list@xxxxxxxxxxxxx
> Sent: 9/13/2012 6:54:40 PM
> Subject: [SI-LIST] Re: Measuring PDN impedance with a VNA?
> >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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