Sequential Circuits

USING K-MAPS to design counter

Q- Design MOD-3 ripple counter using (a) Observing outputs (b) K-maps to design the circuit.

Ans: (a)We can design the MOD 3 counter using 2 FFs as 3 is less than 4 i.e. 22 and greater than 2. We can see directly that as we have to reset the counter only after 2 i.e. when output is 3 we reset the counter and hence we need to reset only when we have Q0= 1 & Q1=1. Now firstly design MOD-4 counter using 2 FFs and then take NAND of Q0 & Q1 and feed the output to CLEAR of both FFs.

(b) We firstly draw state diagram of the counter required as:

And we have the general circuit to design the other than MOD 2 n then we have the general circuit as

And now we draw a table to list the different input combinations to Combinational circuit and their corresponding output as:

Q1          Q0                          OUTPUT of reset logic

0              0                              1

0              1                              1

1              0                              1

1              1                              0

And using K-map as

And hence we get the whole circuit for MOD-3 counter as

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