[SI-LIST] Re: Measuring PDN impedance with a VNA?
- From: Istvan Novak <istvan.novak@xxxxxxxxxxx>
- To: "O. Laney" <olaney@xxxxxxxxx>
- Date: Thu, 13 Sep 2012 23:52:00 -0400
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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