why synchronous ckts?

Synchronous designs eliminate the problems associated with speed variations

through different paths of logic. By sampling signals at well-defined

time intervals, fast paths and slow paths can be handled in a simple manner.

•

Synchronous designs work well under variations of temperature, voltage and

process. This stability is key for high-volume manufacturing.

•

Many designs must be portable—that is, they must be easy to migrate to a

new and improved technology (say, moving from .6 micron to .35 micron).

The deterministic behavior of synchronous designs makes them much more

straightforward to move to a new technology.

•

Interfacing between two blocks of logic is simplified by defining standardized

synchronous behavior. Asynchronous interfaces demand elaborate handshaking

or token passing to ensure integrity of information; synchronous

designs with known timing characteristics can guarantee correct reception of
data.

Reference:

The Ten Commandments of Excellent Design

Peter Chambers

Engineering Fellow

VLSI Technology