Using the Save and Recall Measurements Feature - SPARQ and SI Studio

Summary

Version 6.8.0.3 of the SPARQ software includes new features for saving and recalling measurements taken with your LeCroy SPARQ series Signal Integrity Network Analyzer. These features allow users to easily reconstruct results previously taken, and then to generate updated S-parameters results – all without needing to re-run the measurement. When saving a measurement, the source TDR and TDT waveforms are saved to a “zip” file, along with everything required to reconstruct the results, including the complete instrument setup and files used for de-embedding. A screenshot is also saved.

When should I use the Save Measurement feature?

For best results, use the Save Measurement feature after every measurement, and certainly when also saving Touchstone files that you plan on sharing with others. Future versions of the SPARQ software may include an “Autosave Measurement” feature as well. Additionally, LeCroy application engineers can recall your measurement file to help answer questions about your measurements.

How to Save Measurements

To save the measurement, select File → Save Measurement… to open a “Save file” dialog. Select a name for the zip file that will contain the measurement. By default, the zip file is saved in the path C:\LeCroy\SPARQ\SPARQ\Measurements.

What Gets Saved

The zip file that is created after saving measurements includes:

• Measurement data (e.g. MeasurementFile_LCRY2401N12345.cal). This file includes all of the TDR and TDT waveforms (after averaging) taken during both the calibration and DUT measurement phase of the acquisition. The filename includes the serial number of the SPARQ that took the measurements.
• Instrument Setup file (Setup.lss). This file includes all instrument settings except for cable, adapter and fixture de-embedding settings.
• De-embedding Setup file (e.g. 4004E_LCRY2401N1234.lss). This file includes the path to the Touchstone files used for de-embedding cables, adapters and fixture, and whether de-embedding of these structures is enabled ordisabled.
• Screenshot (ScreenDump.png)
• Any de-embedding files used in the calculation (cable s2p files, adapter s2p files, user 2nd-tier L12T file, etc.)

When would I need (or want) to recall a measurement?

Recalling a measurement is very useful when wanting or needing to re-calculate S-parameters, especially when there is a need to have the S-parameters calculated with different settings. Some scenarios include:

1. Wanting S-parameters with a different end frequency, number of points or frequency spacing.
2. Wanting S-parameters with different settings for enforcement of passivity, reciprocity or causality. (The default setting is to not enforce these properties)
3. Wanting S-parameters with different de-embedding settings. For example, if the user forgets to enable time-domain gating and wants to recalculate with gating enabled.
4. Wanting different port assignments. For example, if the user realizes that the port assignments were accidentally reversed when initially making the S-parameter measurement.

How to Recall Measurements

To recall a measurement, select File → Recall Measurement… and measurement ZIP file to recall. After clicking “Open”, the SPARQ application will 1) load the instrument and de-embedding setup files, 2) load the measurement_[serialnumber].cal file, and 3) invoke a “recalculation”. After the recalculation is complete, the results are displayed. At this point you can change settings (see further discussion below), and recalculate the results.

What can be changed prior to recalculating after recalling a measurement?

The following settings can be changed after recalling a measurement zip file (or after taking a measurement.) After changing one or more of these settings, click Recalculate at the top of the application to calculate revised results. If you wish to also save the revised setup, you can choose to Save Measurement after the recalculation.

What cannot be changed prior to recalculating?

There are three settings to consider: Num Ports: This setting should not be changed after recalling a measurement. Doing so “invalidates” the recalled measurement, since it initializes the SPARQ for a new measurement.
DUT Length Mode: This setting is only applicable to the acquisition of the TDR and TDT waveforms when taking a measurement, and is not involved with the recalculation procedure.
Accuracy Mode: This setting controls the amount of averaging performed when acquiring TDR and TDT waveforms, and is not involved with the recalculation procedure.

Example Use-Case #1: Changing Frequency Spacing

Suppose that you saved S-parameters with 30GHz end frequency, and 500 points, but realized the next day that you should have used 1000 points in order to have sufficient frequency resolution. (This is not an uncommon scenario!) If the Save Measurement... feature was used after taking the measurement, then you can:

1. Use the Recall Measurement… feature to load in the measurement data.
2. Change the Num Points setting to 1000 via the main Setup dialog.
3. Recalculate the S-parameters by clicking the Recalculate at the top of the application window.
4. Use the Save Touchstone… menu option to save the new results as a Touchstone format.

Example Use-Case #2: Changing Passivity and Reciprocity Enforcement

Suppose that you saved S-parameters with passivity and reciprocity enforcement turned off, but realized then next day that your simulator requires strictly passive and reciprocal S-parameters. If the Save Measurement... feature was used after taking the measurement, then you can:

1. Use the Recall Measurement… feature to load in the measurement data
2. Change the settings for Enforce Passivity and Enforce Causality via the main Setup dialog.
3. Recalculate the S-parameters by clicking the Recalculate at the top of the application window.
4. Use the Save Touchstone… menu option to save the new results as a Touchstone format. The resulting S-parameters now are strictly passive and reciprocal.