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An asynchronous circuit is one in which synchronization is performed with-out a global clock. Asynchronous circuits have several advantages over their synchronous counterparts, including:
1.
Elimination of clock skeul problems. As systems become larger, increas-
ing amounts of design effort is necessary to guarantee minimal skew in
the arrival time of the clock signal at different parts of the chip. In an
asynchronous circuit, skew in synchronization signals can be tolerated.
2.
Average-case performance. In synchronous systems, the performance
is dictated by worst-case conditions. The clock period must be set to
be long enough to accommodate the slowest operation even though the
average delay of the operation is often much shorter. In asynchronous
circuits, the speed of the circuit is allowed to change dynamically, so the
performance is governed by the average-case delay.
3.
Adaptivity to processing and environmental variations. The delay of a
VLSI circuit can vary significantly over different processing runs, supply
voltages, and operating temperatures. Synchronous designs have their
clock rate set to allow correct operation under some allowed variations.
Due to their adaptive nature, asynchronous circuits operate correctly
under all variations and simply speed up or slow down as necessary.
4.
Component modularity and reuse. In an asynchronous system, compo-
nents can be interfaced without the difficulties associated with synchro-
nizing clocks in a synchronous system.
5.
Lower system power requirements. Asynchronous circuits reduce syn-
chronization power by not requiring additional clock drivers and buffers
to limit clock skew. They also automatically power-down unused compo-
nents. Finally, asynchronous circuits do not waste power due to spurious
transitions.
6.
Reduced noise. In a synchronous design, all activity is locked into a very
precise frequency. The result is nearly all the energy is concentrated
in very narrow spectral bands at the clock frequency and its harmon-
ics. Therefore, there is substantial electrical noise at these frequencies.
Activity in an asynchronous circuit is uncorrelated, resulting in a more
distributed noise spectrum and a lower peak noise value.
copywrights- Chris J. Myers
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