creating filler cells in virtuoso

[serhannn]

Hi. I need to use filler cells in a design and in specifications it is told that there should be only a capacitor between Vdd and Gnd rails. I didn't really get it. Should I connect capacitor to Vdd and Gnd rails? What kind of capacitor should I use? Also, what is the use of the capacitor?
Thanks a lot.

 

[erikl]

... what is the use of the capacitor?

Decoupling (decrease noise) of the power supply.

If you need filler cells in order to comply with the necessary layer coverage, you could use standard (or any other) cells, which you possibly could use in a redesign. In this case make sure you can access their I/Os by top metal (or at least by the 2 topmost metal layers) only.

 

[eklikeroomys]

Its not necessary to connect caps between your vdd and gnd rails in a filler cell. It is, however, advantageous because it helps eliminate noise caused by fast switching digital circuitry.