GATE Overflow Test Series | Mock GATE | Test 5 | Question: 18

Question

A $8$-bit ripple counter consists of flip-flops, which each have a propagation delay from clock to $Q$ output of $19\;\text{ns}.$ For the counter to recycle from $11111111$ to $00000000,$ it takes a total of ________ (nanoseconds).

Answer 1

Since a counter is constructed using flip-flops, therefore, the propagation delay in the counter occurs only due to the flip-flops. One bit change is $19\;\text{ns}\;,$ so $8$-bit change $= 19\;\text{ns} \times 8 = 152\;\text{ns}.$

Comments

Shouldn’t the question specify Up or Down counter? Answer will vary based on the same.

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@gatecse can you please confirm that if nothing is mentioned about the counter(up or down) in the question,then we have to consider it as a up counter?

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delay in ripple counter does not depends on number of state changes. Think like a square phase shifted some time (propagation delay) by each stage, but total shift does not depend on high and low of the square wave.