Why a monostable multivibrator is not an oscillator Select the primary reason a monostable does not self-oscillate.
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Aits output switches between two states
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Bit requires a trigger to obtain an output signal
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Cit requires a sine wave input signal
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Dthe circuit does not require a dc power supply
Answer
Correct Answer: it requires a trigger to obtain an output signal
Explanation
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:
Identify device class: monostable → one stable state, one quasi-stable state.Operation: a trigger moves the circuit into the quasi-stable state for a duration set by timing components.After the timing interval, it returns to the stable state and remains there until the next trigger.No self-sustaining mechanism exists to repeat pulses without triggers.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