If the data input (D) of a positive edge-triggered D flip-flop changes from 0…
2025
If the data input (D) of a positive edge-triggered D flip-flop changes from 0 to 1 right during the rising edge of the clock signal, what will the resulting output Q be?
Answer: C. Q may be unpredictable due to timing violation — For any sequential logic circuit like a D flip-flop to operate reliably, its input signals must adhere to strict timing requirements relative to the clock…
- A.
Q will become 0
- B.
Q will become 1
- C.
Q may be unpredictable due to timing violation
- D.
Q will not change
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Correct answer: C
For any sequential logic circuit like a D flip-flop to operate reliably, its input signals must adhere to strict timing requirements relative to the clock edge. These are known as setup time and hold time .
Setup Time: The minimum time the data input (D) must remain stable before the active clock edge.
Hold Time: The minimum time the data input (D) must remain stable after the active clock edge.
If the data input changes right during the rising edge of the clock signal, both setup and hold times are violated. When this happens, the internal master-slave latches fail to settle cleanly into a logic 0 or logic 1 state. Instead, the flip-flop enters a highly unstable state called metastability, where the output Q can oscillate or get stuck at an intermediate voltage level before eventually settling arbitrarily.
Therefore, the output becomes completely unstable and unpredictable.