Tap Cells (Well Taps) : These library cells
connect the power and ground connections to the substrate and nwells,
respectively.
By placing well taps at regular
intervals throughout the design, the nwell potential is held constant for
proper electrical functioning. The placer places the cells in accordance with
the specified distances and automatically snaps them to legal positions (which
are the core sites).
- Floating nets or unused nets need to be tied with some constant value (0 or 1), can be achieved using Tie cells
- Using connect_tie_cells command, we can inser a tie cell in the design during the PNR
- To Protect the gate of a standard cell placed near the boundary from damage during manufacturing
- To Avoid the base layer DRC(Nwell and Implant Layer) at the boundary
- To make the proper alignment with other block
- Some standard cell library has END CAP cell which serve as Decap cell as well