Voltage Follower Using Op Amp

In this lecture, we are going to discuss the Inverting Operational Amplifier. We will discuss the operation of inverting Op Amp, derivation of the closed-loop voltage gain of inverting operational amplifier, and input and output resistance.

There are three basic op-amp configurations:

1. Inverting operational amplifier
2. Non-inverting operational amplifier
3. Buffer amplifier or Voltage follower

Note that the Voltage follower configuration discussed in this section, we assume that the used operational amplifier in this section is ideal.

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Voltage Follower Using Op Amp

Letting the R₁ = ∞ and R_F = 0 the non-inverting amplifier gets converted into a voltage follower or a unity gain amplifier.

When the non-inverting amplifier is configured so as to obtain a gain of 1, it is called as a voltage follower or unity gain non-inverting amplifier.

The voltage follower circuit diagram is shown in the below figure.

The voltage follower configuration is obtained by a short-circuiting R_F and open-circuiting R₁ connected in the usual non-inverting amplifier configuration.

Thus all the output is fed back to the inverting input of op-amp. Therefore the gain of the feedback circuit i.e. β = 1.

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Closed Loop Voltage gain of Voltage follower

Consider the expression for the closed-loop gain of the non-inverting operational amplifier, that is,

\mathbf{A_{VF} = 1 + \frac{R_F}{R_1}}

In this equation, substitute the values of R_F = 0 and R₁ = ∞ to get the closed loop gain of the voltage follower as:

A_VF = 1

Therefore the output voltage will be equal to and in phase with the input voltage as shown in the above figure. Thus voltage follower is a non-inverting amplifier with a voltage gain of unity.

The unity gain amplifier does not behave like a conventional voltage amplifier but it will be acts as a Resistance Transformer.

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Features of Voltage Follower Op Amp

The important features of the voltage follower are as follows:

1. Closed loop voltage gain equal to 1 i.e. output is equal to input with no phase shift.
2. Very high input impedance
3. Very low output impedance
4. Large bandwidth

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Application of Voltage follower

The voltage follower, also known as a unity gain amplifier, is a basic op-amp circuit with the output voltage equal to the input voltage. While it might seem simple, this circuit finds applications in various areas due to its unique characteristics. Here are some common applications of the voltage follower using an op-amp:

Applications	Description
Impedance Matching	The voltage follower is often used to match the impedance between a high-impedance source and a low-impedance load. It prevents loading effects by presenting a high input impedance and a low output impedance.
Buffer Amplifier	Voltage followers act as buffer amplifiers by isolating the input from the output. They are used to prevent the circuit connected to the output from affecting the circuit connected to the input.
Isolation	When you need to isolate one part of a circuit from another, a voltage follower can be used to provide isolation, ensuring that changes in one part of the circuit do not affect the other.
Level Shifting	The voltage follower is often employed for level-shifting purposes, where the output voltage needs to be the same as the input but referenced to a different voltage level.
Active Filters	The voltage follower is often employed for level-shifting purposes, where the output voltage needs to be the same as the input but referenced to a different voltage level.
Sensor Interface	Voltage followers are commonly used in sensor interface circuits where the sensor output needs to be buffered before being sent to the next stage.
Feedback Applications	Voltage followers are used in feedback applications where a high-input impedance and low-output impedance are required.
Pulse Amplification	In applications where fast pulse signals are involved, a voltage follower can be used to provide a low-impedance output without affecting the signal shape.

Remember, the voltage follower is a versatile circuit due to its ability to replicate the input voltage at the output while providing benefits such as high input impedance and low output impedance in various applications.

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Advantages of Voltage Follower

• Unity Gain: Output matches input voltage.
• High Input Impedance: Utilizes op-amp’s high input impedance.
• Low Output Impedance: Achieves low output impedance with negative feedback.
• Isolation: Acts as a buffer, separating input and output circuits.
• No Signal Inversion: Maintains input signal phase without inversion.
• Stability: Benefits from negative feedback for improved stability.
• Simple Implementation: Easy design with minimal external components.
• Improved Linearity: Enhances linearity for applications requiring a linear relationship.
• Signal Integrity: Preserves input signal quality, crucial for applications like audio systems.
• Sensor Interfaces: Commonly used for high input and low output impedance in sensor interfaces.

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FAQs on Voltage Follower using Op Amp

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