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An asynchronous (ripple) counter is a "chain" of toggle (T) flip-flops in which the least-significant flip-flop (bit 0) is clocked by an external signal (the counter input clock), and all other flip-flops are clocked by the output of the nearest, less significant flip-flop (e.g., bit 0 clocks the bit 1 flip-flop, bit 1 clocks the bit 2 flip ...
Clock gating in more conventional synchronous designs is an approximation of the asynchronous ideal, and in some cases, its simplicity may outweigh the advantages of a fully asynchronous design. Performance (speed) of asynchronous circuits may be reduced in architectures that require input-completeness (more complex data path). [34] Lack of ...
Synchronizer circuits are used to reduce the likelihood of metastability when receiving an asynchronous input or when transferring signals between different clock domains. Synchronizers may take the form of a cascade of D flip-flops (e.g. the shift register in Figure 3). [ 7 ]
For power-of-2 integer division, a simple binary counter can be used, clocked by the input signal. The least-significant output bit alternates at 1/2 the rate of the input clock, the next bit at 1/4 the rate, the third bit at 1/8 the rate, etc. An arrangement of flipflops is a classic method for integer-n division. Such division is frequency ...
Asynchronous logic components can be hard to design because all possible states, in all possible timings must be considered. The usual method is to construct a table of the minimum and maximum time that each such state can exist and then adjust the circuit to minimize the number of such states.
The basic idea has some complications: the start and stop events are asynchronous, and one or both might happen close to a clock pulse. The counter and interpolators must agree on matching the start and end clock events. To accomplish that goal, synchronizers are used. The common hybrid approach is the Nutt method. [20]
Furthermore, several asynchronous styles have been shown to accommodate clocked interfaces, and thereby support mixed-timing design. Hence, asynchronous systems match well the need for correct-by-construction methodologies in assembling large-scale heterogeneous and scalable systems.
A quasi-delay-insensitive circuit (QDI circuit) is an asynchronous circuit design methodology employed in digital logic design.Developed in response to the performance challenges of building sub-micron, multi-core architectures with conventional synchronous designs, QDI circuits exhibit lower power consumption, extremely fine-grain pipelining, high circuit robustness against process–voltage ...