I/O ring (pad ring)
Beginner
The ring of connection points around the edge of a chip, where it plugs into the outside world.
Novice
A ring of special cells around the edge of the chip, each with a pad where a bond wire attaches. Signal cells contain drivers strong enough for the outside world and protection against static electricity; others bring in power and ground. Corner and filler cells close the ring.
Expert
Built from I/O cells in dedicated I/O rows, joined end to end so their supply rails connect, with corner and filler cells closing gaps. The ring is then wire-bonded or connected to flip-chip bumps through a redistribution layer. Multiple I/O voltage groups, multi-row rings and pad spacing drive die size when the design is pad-limited.
Explained in Floorplanning (Design Flow).
See also: Pad-limited vs. core-limited, Flip-chip bumps.