Synchronous vs. ripple counters — speed advantage Why can a synchronous (parallel-clocked) counter operate at a higher maximum clock frequency than a ripple (asynchronous) counter?

Introduction / Context:
Counter speed is limited by how state changes propagate. Ripple counters clock each flip-flop from the previous stage's output, introducing cumulative delays. Synchronous counters apply the same clock to all stages, so outputs settle simultaneously after one stage of combinational logic. Recognizing this difference explains why synchronous counters achieve higher clock rates.

Given Data / Assumptions:

• Synchronous counters share a common clock (parallel clocking).
• Ripple counters chain the clock through toggling outputs.
• Propagation delay through flip-flops and logic limits f_max.

Concept / Approach:

In ripple counters, a transition must ripple through N flip-flops, so worst-case settling time ≈ N * t_pd_ff. In synchronous counters, all flip-flops sample together, and delay is dominated by logic depth + one flip-flop t_pd, typically far smaller than N * t_pd_ff.

Step-by-Step Solution:

Verification / Alternative check:

Timing diagrams show ripple outputs changing at staggered times, whereas synchronous outputs change nearly together after the same edge, enabling tighter timing closure.

Why Other Options Are Wrong:

“One after the other” describes ripple, which is slower.

Claiming synchronous cannot be faster contradicts practice.

“Ripple is faster” is false for typical technologies.

Common Pitfalls:

Ignoring combinational decode delay in synchronous designs; reading counter outputs during ripple transitions causing glitches.

Final Answer:

The flip-flops change at the same time.