Astable multivibrator definition and behavior: An astable multivibrator is a circuit that exhibits which set of properties?

Introduction / Context:
Multivibrators are foundational timing circuits categorized into astable, monostable, and bistable types. Each has distinct stability and triggering characteristics. The astable form is widely used for clock generation, LED blinking, tone production, and general waveform synthesis without an external trigger.

Given Data / Assumptions:

• No external clock or trigger is applied for normal operation.
• Standard implementations include transistor pairs, op-amp comparators with hysteresis, or the 555 timer.
• Idealized switching between two quasi-stable voltage levels is considered.

Concept / Approach:
An astable circuit has no stable resting state. Once powered, it continually transitions between two states, producing a periodic output—hence it is “free-running.” In contrast, a monostable has one stable state and requires a trigger to produce a single pulse, and a bistable has two stable states, requiring inputs to switch between them with no inherent oscillation.

Step-by-Step Solution:

Verification / Alternative check:
Prototype a 555 astable with two resistors and one capacitor; measure continuous oscillation on an oscilloscope without providing any trigger. The same observation holds for transistor-based astables and Schmitt-trigger RC oscillators.

Why Other Options Are Wrong:

• Two stable states: That is a bistable multivibrator (flip-flop).
• Free-running only or continuous output only: Each is partially correct; both properties together define astable behavior succinctly.
• Requires an external clock: This contradicts the “free-running” nature of astables.

Common Pitfalls:
Confusing astable with monostable (one-shot) due to similar component counts; assuming a perfect 50% duty cycle without additional circuitry; neglecting supply and component tolerances that affect frequency and duty cycle stability.

Final Answer:
is free-running and produces a continuous output signal