[SI-LIST] Re: passive but not reciprocal network
- From: "Alfred P. Neves" <al@xxxxxxxxxxxxxxxxx>
- To: balaseven@xxxxxxxxx
- Date: Mon, 25 Nov 2013 07:37:46 -0800
We dealt with VNA measurement validation in DesignCon 2013 tutorial Methods of
Improving 3D EM Model Development and Associated Time/Frequency Domain
Measurements , authors were from Anritsu, Tektronix, and Wild River Technology.
The measurements are not necessarily reciprocal even if the device is passive
and of course reciprocal. Also, ALL of your measurements will have some
residual causality error based on windowing and limited BW of a finite Fstop in
your measurement. We do a simple time domain transform and expect to see a
small level of sinx/x ringing since I only use rectangular window. Usually
we set a small threshold at 100psec before t=0. BTW, we also showed all the
tools on the market dont fix causality without breaking the S-parameter.
Measure it right, dont fix it later. We made some really good measurements on
our last Channel Modeling platform that we will report, describe what we did in
Design paper on Managing S-parameters in Designcon in Jan 2014. We nailed
M1800 BERT eye diagram and VectorStar VNA S-parameter measurements from 10 to
28G from 3 to 40inches of trace in simulation-measurement and got good
measurement metrics using Simbeor. We run all of our S-parameters through
Simbeor as a standard measurement work flow.
Our approach for low-loss, short, low reflectance interconnect measurements is
to check forward transmission using a mating adapter like KF-KF if your
measurement is non-insertable (both ends of VNA cables are male, for example)
for Etf in both directions. Secondly, we check directivity of each port with
an airline and a good terminator (Anritsu 28K50 are very good wide-band
terminators). This is described in the tutorial. If your making a multiple
port measurement make sure you also make a good calibration of the relevant
THRU paths using SOLR or a good THRU cal. The VectorStar VNA allows you to
rehydrate any THRU path which I find helpful also if the THRU measurements are
not up to our standard.
We also discuss in DesignCon 2012 Tutorial High-confidence S-parameter
Measurement Methodologies for 15-28 Gbps a simple measurement validation suite
using a metrology grade. We still use Matlab for checking causality using
polar plots, but now as I stated before use Simbeor tools for quality metrics.
Both tutorials are available on our website.
Products for the Signal Integrity Practitioner
Alfred P. Neves
Chief Technologist
Office: 503-679-2429
www.wildrivertech.com
On Nov 25, 2013, at 3:11 AM, bala <balaseven@xxxxxxxxx> wrote:
> Hi,
> While checking the integrity of s-parameter data, we do check passivity to
> ensure no gain and casulaity to guarantee there is no impulse response
> before T=0 (when freq domain data converted into time domain) and
> reciprocity.
>
> Some theorem says passive network always reciprocal. If a particular
> network is passive, then loss in both directions should be same.
>
> Do we really need to check reciprocity of a passive matrix?
>
>
> Regards
> bala
>
>
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