[SI-LIST] Re: Measuring PDN impedance with a VNA?
- From: Randy Dawson <rdawson16@xxxxxxxxxxx>
- To: <istvan.novak@xxxxxxxxxxx>, <olaney@xxxxxxxxx>
- Date: Thu, 13 Sep 2012 23:14:40 -0500
A min loss pad solves the match problem, and with 0402 resistors (or smaller)
at the probe tip solves the reflection issue.
Randy Dawson
Sencore
> Date: Thu, 13 Sep 2012 23:52:00 -0400
> From: istvan.novak@xxxxxxxxxxx
> To: olaney@xxxxxxxxx
> CC: tom_cip_11551@xxxxxxxxxxx; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Measuring PDN impedance with a VNA?
>
> Orin,
>
> I know that you know, but just to clarify for those who are not familiar
> with these concepts:
> the AC Kelvin-probe arrangements need four connections, which means
> two-port VNAs.
>
> Regards,
>
> Istvan Novak
> Oracle
>
>
> On 9/13/2012 10:43 PM, O. Laney 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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