If the size of the core is a factor responsible for determining the size of the whole chip, then we say that our design is core limited.
But if the core is too small, and the number of pads are too much to the extent that the size of the chip is determined by the space required to place all the pads, then it is called pad limited.
Ideally speaking, a design should be core limited.
1. Pad Limited Design :
A design is called Pad limited design when there are large number of pad cells determining the die size .
In a Pad limited design the core placement area uses less real state that available .
2. Core Limited Design :
A design is called Core limited design when the large number of standard cells and macros determine the die size .
In core limited design the pads use less than available periphery area .