Concept & Reasoning

Unlike a synchronous counter, a ripple counter does not switch every flip-flop from a common clock edge. One stage's output triggers the next, so delays accumulate. The 1111→0000 recycle can require the change to ripple through all four stages, giving the worst-case propagation delay.

How to Solve It in the Exam

Ripple counter worst-case delay = number of stages × delay per stage.

Important Exam Point

This cumulative delay limits the maximum reliable clock frequency.

Quick Trick

Ripple counter worst-case delay = number of stages × delay per stage.

Common Mistake

Using only one flip-flop's 15 ns delay as the counter settling time.

Concept & Reasoning

Unlike a synchronous counter, a ripple counter does not switch every flip-flop from a common clock edge. One stage's output triggers the next, so delays accumulate. The 1111→0000 recycle can require the change to ripple through all four stages, giving the worst-case propagation delay.

How to Solve It in the Exam

Ripple counter worst-case delay = number of stages × delay per stage.

Important Exam Point

This cumulative delay limits the maximum reliable clock frequency.

Quick Trick

Ripple counter worst-case delay = number of stages × delay per stage.

Common Mistake

Using only one flip-flop's 15 ns delay as the counter settling time.

Concept & Reasoning

Unlike a synchronous counter, a ripple counter does not switch every flip-flop from a common clock edge. One stage's output triggers the next, so delays accumulate. The 1111→0000 recycle can require the change to ripple through all four stages, giving the worst-case propagation delay.

How to Solve It in the Exam

Ripple counter worst-case delay = number of stages × delay per stage.

Important Exam Point

This cumulative delay limits the maximum reliable clock frequency.

Quick Trick

Ripple counter worst-case delay = number of stages × delay per stage.

Common Mistake

Using only one flip-flop's 15 ns delay as the counter settling time.