GATE 2025 CS (CS1) – Question 60

Digital Logic · Sequential Circuits · 2 marks · Numerical answer

Consider the given sequential circuit designed using D-Flip-flops. The circuit is initialized with some value (initial state). The number of distinct states the circuit will go through before returning back to the initial state is _________ . (Answer in integer)

four D flip-flops D0-D3 on a common clock, with Q0→D1, Q1→D2, Q2→D3 and the complement output $\overline{Q_3}$ fed back to D0.

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Correct answer: 8

Explanation

Feeding the complemented last output back to the first input makes a 4-bit twisted-ring (Johnson) counter. It cycles through 2n = 8 distinct states.