Explain the terms-monostable, bistable and astable multivibrator.

Monostable Multivibrator:

A monostable multivibrator, also known as a one-shot multivibrator, is a type of electronic circuit that generates a single, fixed-duration output pulse in response to a trigger input. It is characterized by its ability to stay in a stable state (usually a low or high voltage level) until triggered, at which point it transitions to an unstable state and generates an output pulse before returning to the stable state.

Operation:

• Stable State: In the stable state, the monostable multivibrator's output remains at a constant voltage level, typically high or low. This state is maintained by the feedback loop formed by the resistors and capacitors in the circuit.
• Triggering: When a trigger signal is applied to the circuit, it causes a rapid change in the voltage across the timing capacitor. This triggers the multivibrator to transition into the unstable state.
• Unstable State: In the unstable state, the voltage across the timing capacitor changes rapidly due to the feedback loop. This causes the output voltage to change from its stable state value to the opposite value (i.e., from high to low or vice versa).
• Timing: The duration of the output pulse is determined by the values of the resistors and capacitors in the circuit. The pulse width remains constant regardless of the duration of the trigger signal.
• Return to Stable State: After the timing period has elapsed, the monostable multivibrator returns to its stable state. This happens when the voltage across the timing capacitor reaches a predetermined value, which is determined by the circuit design.

Bistable Multivibrator:

A bistable multivibrator, also known as a flip-flop, is a type of electronic circuit that has two stable states and can be switched between these states by applying input signals. It is characterized by its ability to maintain its current state indefinitely, even in the absence of an input signal.

Operation:

• Stable States: A bistable multivibrator has two distinct stable states, usually represented by high and low voltage levels. The circuit remains in one of these states until it is triggered to switch to the other state.
• Triggering: To switch between stable states, a trigger signal is applied to the circuit. The trigger signal causes a rapid change in the voltage across the timing capacitors, triggering the multivibrator to transition from one stable state to the other.
• Memory: A bistable multivibrator has memory because it can retain its current state even after the trigger signal is removed. This allows it to be used as a storage element in digital circuits.
• Switching Thresholds: Bistable multivibrators have two switching thresholds, one for each stable state. When the input voltage exceeds one threshold, the circuit switches to the corresponding stable state and remains there until the input voltage falls below the other threshold.

Astable Multivibrator:

An astable multivibrator, also known as a free-running multivibrator, is a type of electronic circuit that generates a continuous train of rectangular pulses without the need for an external trigger signal. It is characterized by its ability to oscillate between two unstable states, producing a continuous output waveform.

Operation:

• Unstable States: An astable multivibrator has two unstable states, with the circuit continuously switching between these states. The output voltage oscillates between high and low values as the circuit alternates between the two unstable states.
• Timing: The frequency and duty cycle of the output waveform are determined by the values of the resistors and capacitors in the circuit. The frequency of the waveform is inversely proportional to the RC time constant, while the duty cycle is determined by the ratio of the resistor values.
• Continuous Oscillation: Astable multivibrators are designed to oscillate continuously without the need for external triggering. This is achieved by the positive feedback loop formed by the resistors and capacitors, which ensures that the circuit transitions from one unstable state to the other indefinitely.

In summary, monostable, bistable, and astable multivibrators are electronic circuits with distinct characteristics and applications. Monostable multivibrators generate a single, fixed-duration output pulse in response to a trigger signal, bistable multivibrators have two stable states and can be switched between them using input signals, and astable multivibrators generate a continuous train of rectangular pulses without the need for external triggering.