[SI-LIST] Re: NETWORK MODELS ADJUSTED TO MEASURED TDR DATA.

Hey, Ron

Thanks.

I noticed a paragraph in your conclusions, here I quoted, that is,
"Measurements of differential S-Parameters are difficult to get
because of the single-ended nature of the Vector Network Analyzers."

I knew that, in order to get more accurate differential S-parameters for
active balanced DUTs, R&S, you know, a VNA instruments vendor,
pushed ZVA series VNA into the market, which used a so-called technique
true differential, not a virtual differential for traditional
VNA instruments, for example, ZVA24.

But, for passive balanced DUTs, for example, S-parameters from PCB traces,
cables, or others and so on, no matter what instrument is used,
they told me, we will also get the same measurement data.

I want to know, how do you think about these? Have you ever compared and
measured about these?



-----
Best Regards.
Shiang Yao

Email: syao@xxxxxxx
Website: www.3m.com/electronics
              www.3m.com/interconnect



                                                                           
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                                                                   Subject 
             2008-10-15 05:11          [SI-LIST] NETWORK MODELS ADJUSTED   
                                       TO  MEASURED TDR DATA.              
                                                                           
                                                                           
                                                                           
                                                                           
                                                                           
                                                                           




Hi Guys
I was an RF engineer for many years, and was totally committed to the
use of S-Parameters
as an accurate model of a passive network.

When I became an SI Engineer I tried for several years to use
S-Parameters as models of the
source, interconnect and destination of Digital signals.  Because I was
using ADS which had a
frequency domain engine together with time domain simulators including
SPICE and harmonic
balance, and the convolution to make the frequency domain models work in
the time domain I was
confident that all would work well, using S-Parameters as models.

However, several problems emerged:
1.     Some vendors were supplying S-Parameters without Phase
data(magnitude only)
         Such data is unusable.
2.     Measured S-Parameters contain noise which result in spikes going
above "1" resulting
        in gain for a passive network which causes non-convergence.
The data has to be massaged
       to remove the >1 values, which is time consuming.
3.    Measurements of differential S-Parameters are difficult to get
because of the single-ended nature
       of the Vector Network Analyzers.
4.     Calibration of the VNA is very hard to perform out to the end of
the adapters used.
5.    Measured S-Parameters must also have a DC line added in order for
the convolution to work.

It was very time consuming, tedious and gave questionable data.

So, in 2006 I was finally successful in adapting frequency domain
transmission models (which generate
S-Parameters durring simulation)  to measured TDR data.

THIS WAS VERY SUCCESSFUL FOR SEVERAL REASONS:

   1. TDR measurements with differential head SD-24, so the data was in
      differential form.
   2. TDR data in simple tabular form - time vs magnitude
   3. Approximate models are assumed from mechanical data as ADS models.
   4. ADS models for transmission lines are simple - trace width,
      thicknes, dielectric thickness, dieliectric
      constant, length etc.
   5. ADS adjustments of length, width and thickness as first cut to
      meet approximaely the TDR data.
   6. ADS model for frequency dependent (loss and dielectric constant)
      uses only 3 adjustable parameters.
   7. ADS has Optimization  model for final adjustments of network
      models to match measured data.
   8. Simulation results from adjusting these models in the time domain
      is inherently accurate for time domain
      simulations such as EYE-Patterns and BER simulation.

In the above I have given away a lot of what took me years to perfect.
However, because I am semi-retired
perhaps some of you can carry on.

Good luck.

Ron Miller


--
Ronald B. Miller, Microwave/SI Engineer  RAIL = NOISE + REFLECTIONS
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