DIFFERENT KIND OF CELLS

What are end cap cells ?

End caps are the physical only cells which are used to identify the end of the standard cell rows and used to identify the blocks in the chip. During fabrication process etching occurs and because of that cells present towards the end of the chip are etched. As the functional cells are etched during fabrication it may hamper the functionality of the standard cells. So generally we place end cap cells towards the boundary so that etching will not impact the functional cells.

What are De-cap cells ?

Decap cells are normal capacitors added in the design between the power and ground rails to overcome the effect of dynamic IR drop. At the active edge of the clock most of the sequential cells starts switching simultaneously and consumes huge current for small interval of time. If the flop is placed away from the power source then there is a chance that flop will not get the required voltage and goes to the metastable state. To overcome this effect we add decap cells over there.

What are filler cells ?

Filler cells are non functional cells used to maintain the n-well and p-well continuity also the power continuity. 

What are tie high and tie low cells ?

For the floating input pins of the standard cells we need to connect it to either VDD or GND, so insted of connecting them directly to VDD and GND power rings we use special kind of cells, those cells are called tie high and tie low cells. 

What are pad cells ?

In PCB the wire lengths are very large in mm and within the chip net lengths are very small which are in microns. So normal buffers cannot withstand huge loads, to overcome that a special kind of cells are used those we call it as padcells. Padcells are the combination of large buffers and level shifters.

What is pitch ?

When two metal routes are routed parallely following minimum spacing and minimum width rule, than the distance between the center of one route to another route is called as the pitch.

What is SITE?

One SITE is the smallest width standard cell and it is equal to the metal2 pitch.