Sequential Circuits

Ripple counter

We can attach more flip-flops to make larger counter. We just use more flip-flops in cascade and give output of first to the clock of 2nd and output of 2nd to clock of 3rd and so on. This way every flip-flop would divide frequency of the clock by 2 and hence we can obtain a divide by larger value circuit. Let’s see how we can make larger counters:

And following waveforms would illustrate how the above circuit does counting. It is actually a MOD-8 counter so it would count from 0 to 7 and then again reset itself as shown:

With every negative edge, count is incremented and when the count reaches 7, next edge would reset the value to 0.

These waveforms represent count as (Q3 Q2 Q1) 2.

Hence we can design a MOD-2n counter using n flip-lops in cascade

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