Output frequency of Binary counters


Q1.Two binary counters are cascaded, where first counter has n flipflop and second counter has mflipflop.If the input signal has frequency of 30 MHz and n = 6, m =4, then the output frequency of output signal will be _______ kHz.

Q.2 The lowest frequency in kHz, if a 6 MHz clock frequency is applied to a cascaded counter of modulus-2 counter and modulus-3 counter are ________.

for 1st Q ans is 29.29KHz
and for Q 2 i got 187.5 KHz but second is wrong plz explain


Good question this time.

Here the first assumption that you should make is “counters are asynchronous”. In synchronous counters all the flipflops are applied with same clock pulse, so the output signal constantly varies with input signal.

Just as a general formula, you can remember it as

Fout = Fin / ( Total No of States ) ----> { For a single counter }

Now in 1st question there are 2 counter (say counter1 & counter2)
counter1 has n flipflops. Number of states = 2^n
counter2 has m flipflops. Number of states = 2^m

After passing through counter1,
fout1 = fin/2^n = 30MHz/2^6

Now fout1 will be the input frequency for counter2.
fout2 = fout1/2^m = (30MHz/2^6)/2^4 = 29.29KHz

Coming to 2nd question,

In 2nd question,
there are 2 counters( say counter1 and counter2)

counter1 is modulus-2 counter. so no of states = 2
counter1 is modulus-3 counter. so no of states = 3

apply same formula,

fout1 = fin/2 = 6MHz/2 = 3MHz

fout2 = fout1/3 = 3MHz/3 = 1MHz



Please clear my doubt…

Since we are said to use mod-2 and mod-3 counters so we are directly using 2 and 3 states in this question, whereas in the 1st question we are only said about the number of flip-flops so we use them to find the states ?

Am I right?


yes absolutely…