Question

A certain JK flip-flop has $t_{pd}=8ns$. The largest modulus of ripple counter that can be constructed from such flip-flops and still operate upto 16 MHz is

• A. 6
• B. 32
• C. 64
• D. 128

Answer 1

The correct option is D 128

For ripple counter:
Maximum frequency of operation,
$f\le \frac{1}{n{t}_{pd}}$
n $\to$ no. of flip-flops
$t_{pd}$ $\to$propagation delay of flip-flop

$16\times {10}^6\le \frac{1}{n(8\times {10}^{-9})}$

$n\le \frac{1000}{16\times 8}$

$n\le 7.8125$

$\therefore$ n = 7

With n = 7, the modulus of counter
$=2^7=128$