Saturday, 17 October 2015

Non Default Rules (NDR)

NDR are mainly used in place & routing section of design flow. when they actually route the design.

The Default routing guideline for the router would be provided by tech Lef (incase of Encounter) or techfile (incase of ICC). However when we are routing special nets especially CLOCK, we would like provide more width & more spacing for them. Instead of default 1unit width & 1 unit spacing specified in tech LEF, NDR will have double width , double spacing or triple width double spacing rules coded in them. when the CLOCK net is routed using NDR , they would have better Signal Integrity, lesser cross talk, lesser Noise. but we cannot increase the width & spacing to some large value as it will affect the area of chip. hence backend designer needs to make a call on timing VS noise VS Area on finalizing about NDR rules.

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