Touchstone file

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A Touchstone file was originally a proprietary file format for the eponymous frequency-domain linear circuit simulator[1] from EEsof, launched in 1984 and acquired by HP. The simulator has been called HP/EEsof, then its engine has been successively included in the jOmega and ADS software suites and it is now owned by Keysight.

The Touchstone simulator has long since been superseded,[2] but its file format lives on.

A Touchstone file (also known as an SnP file after its set of file extensions[3]) is an ASCII text file used for documenting the n-port network parameter data and noise data of linear active devices, passive filters, passive devices, or interconnect networks. An example of the format of the S-parameter section is given in the article about S-parameters. In addition to S-parameters, other representations such as Y-parameters and Z-parameters can be recorded.

It later became a de facto industry-standard file format not only for circuit simulators but also for measurement equipment (e.g. vector network analyzers, or VNAs), then later still an EIA standard as part of the Input/output Buffer Information Specification (IBIS) project.[4] On April 24, 2009, the IBIS Open Forum ratified version 2.0,[5] superseding Version 1.1.[6] Version 2.0 adds IBIS-style keywords such as [Reference], which permits per-port definition of the reference environment.

Several further enhancements to the file format that allow description of the non-linear behavior of the component have been developed under the P2D and S2D pair of formats,[7] but these two have been superseded by the X-parameters functionality.


  1. ^ "History of EEsof and Touchstone at Microwaves 101".
  2. ^ "W2200 Advanced Design System (ADS) Core".
  3. ^ .S1P for one-port (e.g. termination), .S2P for two-port (e.g. transmission line), .S3P for three-port (e.g. a balun), .S4P for four-port (e.g. a differential transmission line) and so on.
  4. ^ "IBIS (I/O Buffer Information Specification)".
  5. ^ "Touchstone File Format Specification Version 2.0" (PDF).
  6. ^ "Touchstone File Format Specification Rev 1.1" (PDF).
  7. ^ "E8854A RF System, now part of W2200 Advanced Design System (ADS) Core".