Asynchronous counters have a disadvantage. They need time to provide the final result. Especially for long flip-flop chains, the execution time becomes large.
For a flip-flop to compute the result, a propagation delay time of typically 300-500 ns is needed before the result is shown. In an asynchronous counter, the next flip-flop can only to start compute its result after the previous flip-flop has finished computing the resultat. It is said that the result "ripples" through the counter.
Design of an asynchronous counter. |
Design of a synchronous counter. |
With the synchronous design you shorten the execution time. In a synchronous counter, the input signal is directly connected to all flip-flops and compute the result in parallel...
However, synchronous counter are more complex, as you can see in the next experiments...
