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Mixed Mode S-parameters

Both SPview and Autolab include the full mixed mode S-parameters transform tool.

Mixed mode S-parameters are commonly used in signal integrity applications especially in the latest high speed digital systems and microprocessor-PCB interfaces. This analysis mode can be used to highlight such problems as crosstalk between interconnects.

Because of the difficulty in making high frequency differential measurements on signal paths, measurements are usually made using single-ended Vector Network Analyzers (referenced to ground). The overall system performance measurements are stored as an n-port S-parameter matrix.

With mixed mode S-parameters, the multi-port single ended ports are paired to form differential +/- ports which can be excited differentially or in common mode.

Single ended to Differential port mapping

SPview’s data extraction facility enables a standard Single-ended Transmission-Reflection analyzer, 2-port or n-port S-parameter Vector Network Analyser to generate multi-port data. The data is then transformed using a software algorithm to produce the mixed mode S-parameters.

Vector Network analyzers invariable have a limited number of measurement ports so SPview's capture facilities can generate the data directly from VNA's with an internal algorithm which prompts the user to change ports so that large systems S-matrix can be built sequentially.

SPview works with standard Touchstone format files with data for up to 98 ports. The data can be generated by SPview or existing touchstone files can be imported.

4 modes can be generated using the data as follows

  • cc denotes Common mode input and output.
  • cd denotes Differential input to Common mode output.
  • dc denotes Common mode input to Differential output.
  • dd denotes Differential input and output.

SPview/Autolab Mixed mode control panel

The control panel allows any single ended ports to be paired and mapped to differential ports and the curves to be plotted can be selected.

Data can be plotted on Grid or Vector charts

Typical Mixed mode plot


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