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How to fix the floating gate errors in IBM assura checks?

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helenpenghan

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Antenna check errors in IBM. Need help!

I am using IBM cmrf6sf 3 metal technology for the layout. When doing assura floating gate check for my complete circuit, there are lots of errors as:
GR908, There are floating AM//ML/MA of pads.
GR131: There are metal/(gate+15*tie-down)>200 areas at AM/ML level.
GR131: There are metal/(gate+15*tie-down)>200 areas at MT level.
GR131a:There are floating gates to MT touching (AV/FT/FTbar) not tie down.
GR131: There are floating ANALOGgates not tied down at first metal level.

And I also checked floating gate for my individual cells. There are still erros of:
GR131: There are floating ANALOGgates not tied down at first metal level.
pointing to most of transistor gates, but not all of them. I do not know what cause the problem and even a basic inverter layout has such errors.
Could anyone tell me how to solve them? Thanks a lot.
 
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Hi helenpenghan,

Have you put tie down diodes to the gates of your transistors?If not,do it and then come back to report the remaining errors of the floating gate check.You could also check the pdk manuals for further error explanation with the search criterion to be the error code.

Regards,

Jimito13
 
I added tiedown cells. it works and most of the errors are gone. Thanks
 

If it is your top level, you can have these errors when your transistors are NOT connected to bond pads. If they connect to bond pads i would not put tie down cells, it could effect your circuit. For example, if you have an diff amp you have to input transistors vinp, vinm, vdd, vss and output, you would then have two floating gate errors ( or more if your input transistors are fingered or multiples) Then all inputs and outputs go to bond pads, This would then remove your floating gate errors. If you have tie down on your inputs, your amplifier will not work!

When building up in hierarchy you would of course have these dumb floating gate errors, just ignore them! When you are all done and at top level connected to bond pads, then you have to make sure you don't have any errors left!!

Jgk
 
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