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Tie or float spare cells?

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jelydonut

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When adding extra std cells to a layout, do i need to tie the inputs high or low, or can i let them float?

jelydonut
 

It wont hurt to tie them high to avoid some noise.

Also, if you have spare registers you may connect them to the clock which should create a clock tree, so if you use the register it will have the right insertion delay
 

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    jelydonut

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Hi,

You need tie the input to 0/1 to avoid the warning and if you use the FF, you must connect the FF ck/rst pin with the correctly clock and reset tree.

Thanks.

Lsong
 

You can not leave an input pin floating. You have to tie it to hi or low or a known
signal such as clock. Otherwise short circuit current through PMOS & NMOS could happen and waste power consumption.
 

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