Extraction System: Measurement Caching

During association, and when a physical netlist is being created, measurements may be performed on devices in the layout to extract parameter values associated with the device. This may, for example, be the resistance of a resistor device, or geometrical factors associated with a MOS transistor device.

The measurement may be rather compute intensive and time consuming, thus Xic supports a means for caching measurement results. The caching can radically reduce the time required to associate the circuit, but it requires that the user intervene to update the cached values if the underlying geometry changes. This does not happen automatically. Thus, measurement caching is disabled by default. The caching is enabled by setting the UseMeasurePrpty variable, or equivalent checking the Use Measurement results cache property check box in the Device Config page of the Extraction Setup panel from the Extract Menu.

Every device can have a ``data box''. This is created automatically in Xic on a layer-purpose pair named ``device:xicdata''. The box coordinates are set to the extracted body bounding box of the device.

The measurement results are saved to a measures property that is applied to the data box. This is property number 7106. The property string is set to a space-separated list of numbers, or colon-separated pairs of numbers, representing measurement results, or non-permuted and permuted measurement results if the device has permutable contacts and the measurement result changes on permutation. The ordering is the same as the order of measurement requests in the device definition block.

When a cell is read, by default the data box and measures property, if present, are ignored. If the UseMeasurePrpty variable is set, and the NoReadMeasurePrpty variable is not set, the values from the measures property will be used when parameters are needed, and no values will be computed if the measures property is found. The NoReadMeasurePrpty variable tracks the state of the Don't read measurement results from property check box in the Device Config page of the Extraction Setup panel from the Extract Menu.

After association, if the UseMeasurePrpty variable is set, the data boxes and measures properties will be created if necessary, and updated with the current measurement values.

Thus, to globally update the cached measurement values, one can use the following procedure.

1. Press the Clear Extraction button in the Extraction Setup panel. This will invalidate the present extraction state.

2. Make sure that the Use measurement results cache property check box in the Device Config page of the Extraction Setup panel is checked.

3. Make sure that the Don't read measurement results from property check box on the same page is also checked.

4. Press the Do Extraction button in the same panel. This will run grouping, extraction and association operations. Measured values will be computed, since any cached values are ignored due to NoReadMeasurePrpty being set. After association, the measures properties are updated to the newly computed values.

5. Un-check the Don't read measurement results from property check box. Save the cell hierarchy.