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Is it possible that lvs passes but ERC/Softcheck fails

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joharali

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Is it possible that lvs passes but ERC/Softcheck fails. If yes in what type of cases this happens ?


Thanks in Advance ,
Johar.
 

Yes. LVS/ERC are only as good as how the rules are written. In the case of a softcheck, the rules have to define all possible conductors and how they interconnect. If the a possible conductor is not defined then it will pass the softcheck check but in reality you may have a soft connect.

Build some test cases of possible violations and then run LVS/DRC.

Hope this helps.
 

Is it possible that lvs passes but ERC/Softcheck fails. If yes in what type of cases this happens ?


Thanks in Advance ,
Johar.

Build some test cases of possible violations and then run LVS/DRC.

Hope this helps.

Hi,

Can you help me out with what type of possible violation test cases I can create to examine this type of scenarios ?
 

What's the error message of your ERC/Softcheck?

For instance: This check can't know when more than one tristate outputs connected to the same net are active at the same time. Depending on the rules this may generate a warning or an error message.
 

Not sure about "softcheck" but electrical rules checks are checking not
connectivity match, but connectivity against other constraints (fanout
maybe, shorted outputs probably, polarity perhaps...). Just because
you drew it (layout) the way you said you were going to draw it
(schematic) has only some bearing on whether you did the right thing,
entirely right.

And of course if you leave things like placement, addition of buffer
stages and branches and so on up to the computer, it might very
well make sub-ideal decisions, maybe even violations - especially
if there is not "closure" between ERCs and constraints (or whatever
the cool kids call what direction you give the auto-layout, these days).

Reading the rules deck, or maybe just its inline comments, ought to
tell you what's possible to fail; your judgment and understanding
of the design and your methods then ought to suggest likely violations.
 

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