When running resistance extraction using xRC and xACT-3D some differences might be noticed, this is mainly because, in general xRC and xACT-3D use different fracturing methodology.
While xRC and xACT-3D uses the same R engine, they have different resistance fracturing mechanisms.
In Particular; xRC fractures (cuts) metal segments into smaller segments when they exceed a certain length for a certain technology. As for xACT-3D, it uses a more refined length/width ratio that results in more resistance fracturing for longer wires.
To have both xRC and xACT-3D work the same way in terms of resistance calculation, Resistance fracturing must be set for xRC. This is done by adjusting the MAXLENGTH for PEX RESISTNCE PARAMTER.
The value to be used to match the one used in xACT-3D is: 100*MINWIDTH for a given layer, where MINWIDTH is the minimum width parameter defined for each layer in the PEX PROFILE statements.
For example, if a resistor layer (met1 for ex.) has a minimum width of 0.1microns, then the MAXLENGTH parameter for this layer should be adjusted to be 10microns. This is done by the following PEX statement.
PEX RESISTANCE PARAMETER layer [layer] [MAXLENGTH length]
So for the previous example it would be :
PEX RESISTANCE PARAMETER layer met1 MAXLENGTH 10
This statement can be defined multiple times per layer in the rule file, it may produce a different number of resistance count than the default for xRC.
And to have exact matching results, it should be adjusted for all resistance layers in the technology.