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Synchronous Counter

Synchronous Counters are so called because the clock input of all the individual flip-flops within the counter are all clocked together at the same time by the same clock signal

Unlike asynchronous counters whose output of one stage is connected directly to the clock input of the next counter stage in the chain. The synchronous counter has its stages all clocked together at the same time.

The problem with Asynchronous counters is that they suffer from what is known as “Propagation Delay” in which the timing signal is delayed a fraction through each flip-flop.

However, with the Synchronous Counter, the external clock signal is connected to the clock input of EVERY individual flip-flop within the counter so that all of the flip-flops are clocked together simultaneously (in parallel) at the same time giving a fixed time relationship. In other words, changes in the output occur in “synchronisation” with the clock signal.

The result of this synchronisation is that all the individual output bits changing state at exactly the same time in response to the common clock signal with no ripple effect and therefore, no propagation delay.

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