Question

What is the maximum delay that can occur if four flip-flops are connected as a ripple counter and each flip-flop has propagation delays of tPHL = 22 ns and tPLH = 15 ns?

(a) 15 ns

(b) 22 ns

(c) 60 ns

(d) 88 ns

The question was asked during an online interview.

I want to ask this question from Counter Implementation and Applications topic in chapter Counters of Digital Circuits

Answer 1

The correct choice is (d) 88 ns

To explain: Maximum propagation delay is the longest delay between an input changing value and the output changing value. Hence, 22 * n = 22*4 (Since there are 4 FFs) = 88ns.