In a 4-bit ripple counter, if the period of the waveform at the last flip-flop is 64 microseconds, then the frequency of the ripple counter in kHz is ________ . (Answer in integer)

A 4-bit ripple counter uses 4 flip-flops connected in series, dividing the input clock frequency by $2^4 = 16$.

Let:

• $T_{\text{in}}$ be the time period of the input clock

• $T_{\text{out}}$ be the time period of the waveform at the last (4th) flip-flop

Since frequency is divided by $16$, the time period is multiplied by $16$:

Given $T_{\text{out}} = 64\ \mu\text{s}$:

The frequency of the ripple counter (input clock frequency $f_{\text{in}}$) is:

Thus, the answer is 250.