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How do I use the Impedance Rule DRC to check different target impedances?

Question asked by cathy_terwedow on Dec 1, 2017

Most nets are designed with 55 Ohm with a tolerance of +/- 10% of the target impedance. DDR3 has 45 Ohm target impedance +/- 10%. So, a common question is whether to run the Impedance Rule with 55 Ohms and then change the parameter in the ‘Settings’ Window before executing the DRC a second time.


Here's how to handle the situation. First create separate Object Lists for each collection of signal nets that require different differential impedances. Select the DRC >> Select the Spreadsheet >> Select the Parameters tab >> Change the Target impedance.


Do the same for the DDR Differential Pair Rule Group. Notice they can have different parameters. It may be useful to put the target impedance in the name of the rule group as well.

Note that this works with the Impedance rule for single-ended nets and that in the parameters window of each specific DRC, there is a tolerance parameter (+/- 10% that can also be edited for each specific net target value).