[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
Gigahertz Data Div of MI Corp.              \\  //         \\  // 
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Newark,  CA  94560                      ->JITTER<-   EYE   ->JITTER<-
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fax 510-742-6686                            //  \\         //  \\
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