[SI-LIST] Re: Re[2]: Re: Measuring PDN impedance with a VNA?
- From: DAVID CUTHBERT <telegrapher9@xxxxxxxxx>
- To: "O. Laney" <olaney@xxxxxxxxx>
- Date: Fri, 14 Sep 2012 15:02:02 -0600
And the vias down to the PDN can present a higher Z than the PDN. I tried
an S11 once and ended up measuring only the via.
Dave Cuthbert
On Sep 14, 2012 1:41 PM, "O. Laney" <olaney@xxxxxxxxx> wrote:
> Correct, and thanks for pointing that out. Two ports for Z alone, four
> if you need full S-parameters. You just can't get meaningful results from a
> single port reflection measurement due to the extreme impedance mismatch
> e.g. 50 ohms into 50 milliohms.
>
> ------ Original Message ------
> From: "DAVID CUTHBERT" <telegrapher9@xxxxxxxxx>
> To: olaney@xxxxxxxxx
> Cc: tom_cip_11551@xxxxxxxxxxx;istvan.novak@xxxxxxxxxxx;
> si-list@xxxxxxxxxxxxx
> Sent: 9/14/2012 12:03:59 PM
> Subject: Re: [SI-LIST] Re: Measuring PDN impedance with a VNA?
>
> 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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