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:
- Inverting operational amplifier
- Non-inverting operational amplifier
- 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.
Voltage Follower Using Op Amp
Letting the R1 = ∞ and RF = 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 RF 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.
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 RF = 0 and R1 = ∞ to get the closed loop gain of the voltage follower as:
AVF = 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.
Features of Voltage Follower Op Amp
The important features of the voltage follower are as follows:
- Closed loop voltage gain equal to 1 i.e. output is equal to input with no phase shift.
- Very high input impedance
- Very low output impedance
- Large bandwidth
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.
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.
FAQs on Voltage Follower using Op Amp
What is a voltage follower circuit, and how does it work?
A voltage follower, also known as a unity gain buffer, uses an operational amplifier to produce an output voltage that closely follows the input voltage. It works by providing unity gain, meaning the output voltage equals the input voltage.
What is the equation for the voltage follower gain?
The gain of a voltage follower is unity, so the equation is simply Vout = Vin
Why is a high input impedance important in a voltage follower?
A high input impedance prevents loading of the source, ensuring minimal impact on the signal. The input impedance of a voltage follower is effectively the input impedance of the op-amp, which is typically very high.
How does the voltage follower improve signal integrity?
The voltage follower preserves the quality of the input signal by maintaining its amplitude and phase. This is crucial in applications like audio systems where signal fidelity is important.
How does the voltage follower contribute to stability in a circuit?
The negative feedback in the voltage follower configuration improves stability by minimizing distortion and reducing sensitivity to variations in op-amp parameters.
Disadvantages to using a voltage follower?
They do not provide voltage gain. If voltage amplification is required, other amplifier configurations might be more suitable.
Applications of voltage followers in electronic circuits?
Used in sensor interfaces, audio pre-amplifiers, impedance matching, and any application requiring high input impedance and low output impedance.
