Ripple counter speed — The maximum counting speed of a ripple counter is limited primarily by the propagation delay of which elements?

Introduction:
Ripple (asynchronous) counters propagate toggles from one stage to the next, so their speed is constrained by cumulative delays. Identifying the limiting element helps estimate maximum clock rates and choose suitable architectures.

Given Data / Assumptions:

• N flip-flop stages, cascaded in ripple fashion.
• Nonzero propagation delay for each flip-flop (t_pd).
• Negligible extra logic between stages for the basic counter.

Concept / Approach:

The worst-case settling time after a clock edge is approximately the sum of flip-flop delays along the ripple path. Thus, each flip-flop’s delay contributes directly to the maximum frequency limit. External gates may affect decoded outputs, but the inherent limit comes from the flip-flops themselves in the counting chain.

Step-by-Step Solution:

Verification / Alternative check:

Datasheets for ripple counters specify maximum toggle frequency decreasing as bit-width increases, reflecting cumulative flip-flop delays rather than external gate delays.

Why Other Options Are Wrong:

• All flip-flops and gates / flip-flops with gates / only gates: Gates impact decoded outputs but not the fundamental counting path delay in the simplest ripple counter.
• Clock source only: Clock quality matters, but does not set the internal combinational delay limit.

Common Pitfalls:

• Using asynchronous decoded outputs without registering; glitches may be captured.
• Ignoring temperature and supply variation that increases t_pd at extremes.

Final Answer:

each flip-flop