Why a monostable multivibrator is not an oscillator Select the primary reason a monostable does not self-oscillate.

Introduction / Context:
Oscillators generate periodic waveforms autonomously, without external timing triggers. A monostable multivibrator (one-shot) produces a single pulse of a defined width only when triggered. The question probes this fundamental difference.

Given Data / Assumptions:

• Circuit under discussion is a monostable (one-shot).
• Pulse width set by R*C or an equivalent timing network.
• No free-running feedback loop that sustains oscillation.

Concept / Approach:

Oscillation requires positive feedback and a loop gain/phase condition that sustains periodic transitions. Monostables lack this continuous condition; they return to a stable state after each pulse unless a new trigger is applied.

Step-by-Step Solution:

Verification / Alternative check:

Timing diagrams and truth tables show output transitions only following triggers; there is no periodic activity in the absence of input stimuli.

Why Other Options Are Wrong:

“its output switches between two states”: true for many multivibrators, including astable oscillators; not the decisive reason.
“it requires a sine wave input signal”: monostables are typically edge-triggered; a sine is not required.
“the circuit does not require a dc power supply”: incorrect; it does require DC power like most logic/timer ICs.

Common Pitfalls:

Confusing mono- and astable behavior; assuming any switching implies oscillation; overlooking the role of an external trigger.

Final Answer:

it requires a trigger to obtain an output signal