2.5 Sequential Logic Cells
There are two main approaches to clocking in VLSI design: multiphase clocks or a single clock and synchronous design . The second approach has the following key advantages: (1) it allows automated design, (2) it is safe, and (3) it permits vendor signoff (a guarantee that the ASIC will work as simulated). These advantages of synchronous design (especially the last one) usually outweigh every other consideration in the choice of a clocking scheme. The vast majority of ASICs use a rigid synchronous design style.