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Subelement E
Digital Logic
Section 37
Multivibrators
The frequency of an AC signal can be divided electronically by what type of digital circuit?
• Free-running multivibrator.
Bistable multivibrator.
• OR gate.
• Astable multivibrator.

The frequency of an AC signal can be divided electronically by what type of digital circuit?

Bistable multivibrator.

As the name implies, it can be in one of two states, switching upon the introduction of a current signal, and remaining stable in the switched to state, being either high or low voltage. Because of remaining stable in one state, it can be used to store data and in executing computer logic.

See Wikipedia's article Multivibrator

Also, see the Electronics Coach site for the article Bistable Multivibrator

And, see the Tutorials Point site for the article Pulse Circuits - Bistable Multivibrator

For practical explanation, please see the Circuit Digest site for the article Design and Build a Simple Bistable Multivibrator Circuit Using Op-amp

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What is an astable multivibrator?
• A circuit that alternates between two stable states.
• A circuit that alternates between a stable state and an unstable state.
• A circuit set to block either a 0 pulse or a 1 pulse and pass the other.
A circuit that alternates between two unstable states.

What is an astable multivibrator?

A circuit that alternates between two unstable states.

When you connect two capacitive or resistive coupling networks with two amplifying stages, in a positive feedback loop, you end up with an astable multivibrator. Why astable? Because this system is never stable, and flips between states.

From ffleming:

An astable multivibrator consists of two amplifying stages connected in a positive feedback loop by two capacitive-resistive coupling networks. It continually switches from one state to the other.

Multivibrator circuits are frequently used in two-state devices. The question asks about a circuit that continuously alternates without an external clock.

We can immediately eliminate both flip-flop answers because flip-flops change state on input, and the question specifies no external clock. Flip-flops are bistable multivibrators.

We can eliminate "monostable multivibrator" because these circuits are stable in one state: they change state on input and then return to their stable state.

It's enough to simply examine the words used. The question asks for a circuit that continuously changes. This means that it has zero stable states. "Astable" means "no stable", "monostable" means "single stable", and flip-flops are "bistable", or "two-stable."

See Wikipedia's article on Multivibrator

Also, see the Electronics Tutorials site for the article on Astable Multivibrator

And, see the Tutorials Point site for the article on Pulse Circuits - Astable Multivibrator

For practical well-illustrated information, please see the Build Electronics Circuits site for the article on How Astable Multivibrator Circuits Work

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What is a monostable multivibrator?
A circuit that can be switched momentarily to the opposite binary state and then returns after a set time to its original state.
• A “clock” circuit that produces a continuous square wave oscillating between 1 and 0.
• A circuit designed to store one bit of data in either the 0 or the 1 configuration.
• A circuit that maintains a constant output voltage, regardless of variations in the input voltage.

What is a monostable multivibrator?

From Wikipedia - Multivibrator

A circuit that can be switched momentarily to the opposite binary state and then returns after a set time to its original state.

A Multivibrator is an electronic circuit used to implement a variety of simple two-state systems such as oscillators, timers and flip-flops. There are three types, astable, monostable and bistable.

A Monostable Multivibrator is an electronic circuit in which one of the states is stable, but the other state is unstable (transient). A trigger pulse causes the circuit to enter the unstable state. After entering the unstable state, the circuit will return to the stable state after a set time. Such a circuit is useful for creating a timing period of fixed duration in response to some external event. This circuit is also known as a one shot.

From kj6prf:

A monostable multivibrator only has one stable state. If it leaves this state, it will fall back to its stable state. Hence, it is monostable.

See Wikipedia's article on Multivibrator

Also, see the Tutorials Point site for the article Pulse Circuits - Monostable Multivibrator

And, see the All About Circuits site for the article Monostable Multivibrators

For practical information, please see the Circuit Digest for the article How to Design and Build a Simple Monostable Multivibrator Circuit using Op-amp

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What is a bistable multivibrator circuit commonly named?
• AND gate.
• OR gate.
• Clock.
Flip-flop.

What is a bistable multivibrator circuit commonly named?

Flip-flop.

From kj6prf:

A flip-flop can vary between two values and stay at either of those states indefinitely. This makes it bistable.

From kv0a:

"A clock is a device that is periodically switching states, and so is not stable because its output does not remain in a particular state.

The outputs of AND and OR gates immediately reflect the inputs of their corresponding circuits, and so are not considered stable circuits.

A flip-flop can retain its output state(s) after one or more of its inputs have changed, and so is stable in either of its binary states, making it a bistable circuit."

To help you remember: a flip-flop is stable in two (bi-) different states.

See Wikipedia's article Flip-flop (electronics)

Also, see the Geeks for Geeks site for the article Flip-flop types, their Conversion and Applications

And, see the Electronics Tutorials site for the article Sequential Logic Circuits

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What is a bistable multivibrator circuit?
Flip-flop.
• AND gate.
• OR gate.
• Clock.

What is a bistable multivibrator circuit?

Flip-flop.

From kj6prf:

A flip-flop can vary between two values and stay at either of those states indefinitely. This makes it bistable.

From kv0a:

"A clock is a device that is periodically switching states, and so is not stable because its output does not remain in a particular state.

The outputs of AND and OR gates immediately reflect the inputs of their corresponding circuits, and so are not considered stable circuits.

A flip-flop can retain its output state(s) after one or more of its inputs have changed, and so is stable in either of its binary states, making it a bistable circuit."

To help you remember: a flip-flop is stable in two (bi-) different states.

See Wikipedia's article Flip-flop (electronics)

Also, see the Geeks for Geeks site for the article Flip-flop types, their Conversion and Applications

And, see the Electronics Tutorials site for the article Sequential Logic Circuits

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What wave form would appear on the voltage outputs at the collectors of an astable, multivibrator, common-emitter stage?
• Sine wave.
• Sawtooth wave.
Square wave.
• Half-wave pulses.

What waveform would appear on the voltage outputs at the collectors of an astable, multivibrator, common-emitter stage?

Square wave.

Square wave switches instantly between two states in the same amount, so it looks like a bar graph. These two states can be 0 and 1.

See Wikipedia's article on Square wave

Also, see the Electronics Notes site for the article What is a Square Wave & Rectangular Waveform

And, see the Learn About Electronics site for the article Module 4.0 CR Relaxation (Square Wave) Oscillators

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