A 4-bit synchronous counter uses flip-flops with propagation delay of 20 ms each. The maximum possible time required to change of state will be:

Concept:

The maximum propagation delay (tpd) for the synchronous counter is given by:

tpd = td

td = Propagation delay of 1 Flip flop.

Calculation:

Given is a 4-bit synchronous counter for which the maximum possible time needed for the change of state will be the maximum possible propagation delay:

tpd = Delay of 1 flip-flop only

tpd = 20 ms

Important Points

• In synchronous counters, all flip-flops change simultaneously and in asynchronous counters, the propagation delay of the flip-flops add up to produce the overall delay.
• Although synchronous counters usually have more combinational logic, the propagation delay through these gates is small compared to the propagation delay through many stages of flip-flops.
• So the Synchronous counter will provide the least delay compared to Asynchronous counters.

The maximum propagation delay for an n-bit asynchronous counter is given by:

tpd = n × td