The GATE Grind

GATE 2023 IN – Question 41

Digital Electronics · Number systems and combinational logic · 2 marks · Multiple choice

For the given digital circuit, A = B = 1. Assume that AND, OR, and NOT gates have propagation delays of 10 ns, 10 ns, and 5 ns respectively. All lines have zero propagation delay. Given that C = 1 when the circuit is turned on, the frequency of steady-state oscillation of the output Y is ______.

Diagram for GATE 2023 IN question 41
  1. 20 MHz
  2. 15 MHz
  3. 40 MHz
  4. 50 MHz

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Correct answer: (A) 20 MHz

Explanation

With A = B = 1, the feedback implements $Y=(\bar C+0)(1)=\bar C$. One transition takes $5+10+10=25$ ns through NOT, OR, AND. Two transitions form a full cycle, so $f=1/(50\ \mathrm{ns})=20$ MHz, **A**.