Short-Open-Load-Reciprocal (SOLR) Calibration

Short-Open-Load-Reciprocal (SOLR) calibration is a combination between the Short-Open-Load-Through (SOLT) and the Through-Reflect-Line (TRL) family of calibrations. SOLR uses the SOLT short, open, and load standards and requires the same characterization knowledge. The difference between SOLR and SOLT calibration is that SOLR does not require an electrical model of the through standard. However, SOLR calibration does require that the through standard be reciprocal, such that S₂₁ equals S₁₂. As with TRL calibrations, the most accurate implementation of this calibration method requires a four-receiver hardware configuration, where SOLT calibration could be performed with a three- or four-receiver design.

The TRL calibration assumption of the ideal switch, which is inaccurate, is overcome using extra measurements made during the through portion of the calibration. These measurements, and the reciprocity of the through standard, allow the through standard to be characterized and corrected for during the calibration. You need to know the approximate electrical phase of the through to allow a root choice during the characterization and correction of the through standard.

The limited knowledge requirement on the through standard makes SOLR calibration ideally suited for situations where a non-ideal through standard is desired, such as with on-wafer probing where the probes are positioned 90 degrees from each other (orthogonally) during the desired measurement. If this measurement configuration is necessary, there are two options for making calibrated measurements. One option is to move the measurement probes away from their desired calibration measurement positions using a straight through standard, which introduces errors in the final measurements. The errors are caused by the necessary cable movements when repositioning the ports for the final measurements. You also can calibrate using a through standard with a 90-degree bend. A bend makes the through behave non-ideal and therefore creates errors or degradation in those calibration models relying on the ideal characteristics. SOLR calibration does not have this limitation since it does not rely on an ideal through model and thus does not introduce this degradation during the measurement. The use of the SOLR algorithm with a 90-degree through standard simplifies both the calibration and the measurement, which provides the best calibration for these less ideal measurement configurations.

Note  SOLR calibration is compatible with only the NI 5632.