[SI-LIST] Re: To measure impedance of a capacitor using VNA
- From: "Ken Cantrell" <ken@xxxxxxxxxxxxxxxx>
- To: <eric@xxxxxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Mon, 28 Jul 2014 09:17:39 -0600
Eric,
Heck of a freebie! 806 pages. Once again, thanks for all of your input and
advice.
Ken
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Eric Bogatin
Sent: Monday, July 28, 2014 7:24 AM
To: si-list@xxxxxxxxxxxxx
Cc: antokdavis@xxxxxxxxx
Subject: [SI-LIST] To measure impedance of a capacitor using VNA
Anto-
If you are trying to measure the impedance of a capacitor, you should read
the chapter in the book Mike and I wrote on measuring low impedance with
2-ports. This is the same approach that Istvan advocates in his book.
As we show in the book, using Z_dut = 25 x S21/(1-S21), this works for hi
and low impedances.
For those of you who want a free copy of the book, "Signal Integrity
Characterization Techniques" by Resso and Bogatin, you can download it for
free from:
http://www.bethesignal.com/bogatin/product_info.php?cPath=88&products_id=843
then click on the SPSI-03-03 lesson.
No registration required.
--eric
*******************************************************
Dr. Eric Bogatin, Dean
Teledyne LeCroy Signal Integrity Academy www.beTheSignal.com Adjunct Prof,
ECEE Univ of Coloroado, Boulder
105 S Sunset St, Suite J
Longmont, CO 80501 USA
Twitter @beTheSignal
e: eric@xxxxxxxxxxxxxxx
cell: 913-424-4333
******************************************************
-----Original Message-----
From: FreeLists Mailing List Manager [mailto:ecartis@xxxxxxxxxxxxx]
Sent: Friday, July 25, 2014 11:08 PM
To: si-list digest users
Subject: si-list Digest V14 #169
si-list Digest Fri, 25 Jul 2014 Volume: 14 Issue: 169
In This Issue:
#1: From: Anto Davis <antokdavis@xxxxxxxxx>
Subject: [SI-LIST] Re: To measure impedance of a capacitor
using VNA
----------------------------------------------------------------------
Msg: #1 in digest
Date: Fri, 25 Jul 2014 11:07:30 +0530
Subject: [SI-LIST] Re: To measure impedance of a capacitor using VNA
From: Anto Davis <antokdavis@xxxxxxxxx>
Thanks for the replies,
I am going through the book, Signal Integrity Characterization Techniques by
Mike Resso and Eric Bogatin Ch.9, It is explaining the method of
de-embedding for two port n/w.
I am doing a one port measurement; the impedance of a single loop
(inductance), using VNA.
VNA is calibrated at the plane of VNA port, and using 50 ohm coaxial cable
(which is not included in the calibration process), connected to the DUT
(single loop).
1) Instead of using De-embedding, can I directly use the method explained in
Section 9 of the paper "Inductance Calculations in a Complex Integrated
Circuit Environment" by A. E. Ruehli?
Or when we talk about one port measurement, does de-embedding and the method
explained in that paper become same?
2) With De-embedding can I avoid buying the calibration kit, if the VNA is
already calibrated at the connnection ports? (Say, I am ok with slight
variations due to time) Basically, can I de-embed the coaxial cable
connectors also with the fixtures?
Anto
On Thu, Mar 13, 2014 at 6:13 PM, Istvan Novak <istvan.novak@xxxxxxxxxxx>
wrote:
> Hi Anto,
>
> 1) If you have a large-size DUT with low capacitance, it means that in
> addition to the impedance of the DUT we may also have a lot of stray
> capacitance from the large DUT body to ground, which distorts the
> results if we wanted to measure the DUT in the series connection
> scheme. Typical such scenario: measuring the power/ground plane
> capacitance of an unpopulated board at low frequencies.
>
> 2) Each instrument has finite resolution, repeatability, noise floor
> and accuracy.
> If we connect the DUT in shunt-through connection, the conversion
> formula giving you impedance from S21 becomes very sensitive to small
> data errors when the DUT impedance is large. There are low-frequency
> VNAs, such as the Agilent E5061B, which can work down to a few hertz
> quite accurately. And cable length actually matters much less as
> frequency goes down.
>
> Regards,
>
> Istvan Novak
> Oracle
>
>
> On 3/13/2014 1:51 AM, Anto Davis wrote:
>
>> Dr. Istvan,
>> 1) From your book, why series through connection for higher impedances?
>> Why
>> do you suggest size of DUT to choose between series through and shunt
>> through? Shouldn't it be based on the impedance only?
>>
>> 2) VNA measurement for lower frequencies is a challenge; they
>> extrapolate for lower frequencies?
>> They rely on reflection coefficients for measuring impedance. So if I
>> connect longer cable, will it give better results for lower frequencies?
>> For eg, if have 1m (=0.5m+0.5m) total cable length and the DUT is
>> very small, v = 2e8 m/s taking wavelength/4 for distinguishing
>> between lumped equivalent and Transmission line, below 50MHz, will it
>> be treated as a lumped equivalent? And in this case anything less
>> than 50MHz will be extrapolated by VNA?
>> Basically, is there a minimum length for connection cable for a
>> minimum frequency?
>>
>> Thanks,
>> Anto
>>
>>
>> On Wed, Mar 12, 2014 at 6:23 PM, Istvan Novak
>> <istvan.novak@xxxxxxxxxxx>
>> wrote:
>>
>> Hi Anto,
>>>
>>> Fair question, but for most practical situations, you dont need to
worry.
>>> Even with very simple instrumentation, like a VNA created around a
>>> little USB-powered oscilloscope with an arbitrary waveform
>>> analyzer), the Two-port shunt-through measurement will be reasonably
>>> good up to at least a kohm impedance magnitude. Professional
>>> network analyzers have better resolution and you get reasonable
>>> result at least up to ten kohms. For a 0.1uF capacitor this means
>>> you dont need to worry about this potential problem unless you want
>>> to measure the impedance at frequencies with single digits or below.
>>> If that was the case, you can use either traditional impedance
>>> bridges or just use the same two-port setup but switch to
>>> series-through
connection.
>>>
>>> Best regards,
>>> Istvan Novak
>>> Oracle
>>>
>>>
>>>
>>> On 3/12/2014 7:12 AM, Anto Davis wrote:
>>>
>>> Hi,
>>>> I am trying to get the impedance plot of a 0.1uF capacitor (using
>>>> VNA), which has ESL and ESR associated with it. The frequeuncy
>>>> response should be a V curve. From the book, Frequency Domain
>>>> Characterization of PDN by Istvan Novak (ch-5) I realized that two
>>>> port measurements are better (measuring Z12 or S12) when Z << 50
>>>> ohms.
>>>> But for a single capacitor, how to get the V curve? If I connect it
>>>> to measure as Z12, I can measure it correctly for frequencies where
>>>> Z<<50 ohms only?
>>>>
>>>> Thanks,
>>>> Anto
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
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