Multivibrator taxonomy: among the listed choices, identify which device is <em>not</em> classified as a multivibrator (i.e., not inherently an astable, monostable, or bistable timing circuit).

Introduction / Context:
Multivibrators are fundamental timing circuits that generate or condition digital-like signals: astable (free-running), monostable (one-shot), and bistable (flip-flop). Knowing which circuits fall under this umbrella helps in selecting proper blocks for pulse generation, timing, and storage. This classification question distinguishes true multivibrators from other oscillatory elements.

Given Data / Assumptions:

• “One-shot” is a common name for a monostable multivibrator.
• “Flip-flop” denotes a bistable multivibrator.
• “Astable” denotes free-running multivibrators.
• VCO is a voltage-controlled oscillator.

Concept / Approach:
Multivibrators are defined by their stable states: astable has no stable state, monostable has one stable state, and bistable has two stable states. A VCO is an oscillator whose frequency is tuned by a control voltage; it is not categorized by stable states in the same way and is typically a continuous-time oscillator (often LC, RC, or ring-based) rather than a discrete stable-state timing circuit.

Step-by-Step Solution:

Verification / Alternative check:
Textbooks place multivibrators under pulse/timing circuits, whereas oscillators (including VCOs) are in the sinusoidal or relaxation oscillator chapter. A VCO may internally use a Schmitt trigger or comparator, but its defining feature is voltage-controlled frequency, not its number of stable states.

Why Other Options Are Wrong:

• One-shot: classic monostable multivibrator.
• Flip-flop: classic bistable multivibrator.
• Bistable: by definition a multivibrator type.
• Astable: by definition a multivibrator type.

Common Pitfalls:
Assuming any oscillator is a multivibrator; conflating relaxation oscillators with the multivibrator classification without considering stable states.

Final Answer:
VCO