What is the Difference Between Inverting and Non-Inverting Amplifier? . In electronic circuits, we use an electronic device called operational amplifier (Op-Amp). The operational amplifier is a high-gain multistage differential amplifier. It has two inputs and one output, where the input terminals are named as inverting terminal and non-inverting terminal. The inverting terminal of the Op-Amp is marked with positive (+) polarity, whereas the noninverting represents the negative (-) polarity terminal.
Depending on the circuit configuration, the operational amplifier is classified into two types namely,
- Inverting Amplifier
- Non-Inverting Amplifier
This article is meant for explaining the differences between an inverting amplifier and a noninverting amplifier. But before that, let’s understand the basics of inverting amplifier and noninverting amplifier so that it becomes easy to the differences between them.
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What is Op-Amp
An op-amp or operational amplifier is a device that is used for the amplification of signals. It uses external components such as resistors and capacitors to perform various operations on signals. It has certain ideal characteristics such as infinite input resistance, zero output resistance, infinite open-loop gain, high bandwidth.
It has three terminals including two inputs and one output terminal. One of the two input terminals is a positive (Non-Inverting) terminal and the other is a negative (inverting) terminal. It is used for mathematical operations on signals such as amplification, addition, subtraction, comparison, integration, filtering, etc.
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What is Inverting Amplifier?
An inverting amplifier is a type of amplifier that is designed to produce output that is 180 degrees out of phase with the input signal. As its name suggests, it inverts the phase of the input signal. For example, if we apply a positive voltage signal at its input, its output will be a negative voltage signal.
Here is the design of an inverting amplifier. The input signal is applied at the inverting (negative) terminal while the non-inverting terminal is grounded. The feedback signal is applied at the inverting terminal. The feedback signal feeds part of the output signal back at the input through resistors to form a closed-loop circuit. Since the open-loop gain is very high, it helps reduce and accurately control the gain of the amplifier.
The voltage at both input terminals of an ideal op-amp is equal to each other; this is also known as the virtual short concept. To find the gain of this amplifier, apply KCL at the inverting node.
(0 – Vi) / Rin + (0 – Vo) / Rf = 0
-Vi / Rin – Vo / Rf = 0
Vo / Vi = – (Rf / Rin)
Voltage gain, Av = Vo / Vi = – (Rf / Rin)
Since the amplifier is in inverting configuration, its voltage gain is negative.
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Features of Inverting Amplifier
- It amplifies and also inverts the phase of the input signal.
- The output is 180 degrees out of phase with the input signal.
- The input signal is applied at its inverting (Negative) terminal.
- The non-inverting terminal is grounded.
- Its voltage gain is given Av = -(Rf/ Rin)
- Its voltage gain is negative.
- Its gain can be designed to have less than, greater than, and equal to 1.
- Its input impedance is Rin.
Advantages of Inverting Amplifiers
- Flexibility in Gain Control: Adjusting resistors easily modifies gain.
- Wide Range of Applications: Commonly used in signal mixing and filtering.
- Improved Linearity: Provides excellent linearity in many scenarios.
What is Non-Inverting Amplifier?
The type of amplifier that is designed to amplify the input signal without changing its phase is called a non-inverting amplifier. Its output is in-phase with the input signal. It does not change the phase of the signal but only amplifies it. As its name suggests, it does not invert the phase of the signal.
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The given figure shows a non-inverting amplifier configuration. Here the input is applied to the non-inverting (positive) terminal of the op-amp. While the inverting terminal is grounded through a resistor. Also, the feedback is applied to its inverting terminal, also called negative feedback, for better control of the gain.
Using the virtual short concept of an ideal op-amp, the voltage at both input terminals is equal i.e. both terminals have Vi. Applying KCL at the inverting node of the op-amp.
(Vi-0) / R + (Vi-V0) / Rf = 0
Vi/R + Vi / Rf – V0 / Rf = 0
Vi (R + Rf) / RRf = V0/Rf
V0 / Vi = (R + Rf) / R
Voltage gain, Av= V0 / Vi = 1 + Rf / R
Since the amplifier is in a non-inverting configuration, the gain is also positive and it is greater than inverting amplifier by 1.
Features of Non-Inverting Amplifier
- It amplifies and does not change the phase of the signal.
- Its output is in-phase with the input signal.
- The input is applied at its non-inverting terminal.
- The inverting terminal is grounded through a resistor.
- Its voltage gain is given by Av = 1 + Rf / R
- It gain is always greater than 1.
- Its voltage gain positive.
- Its input impedance is infinite.
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Advantages of Non-Inverting Amplifiers
- High Input Impedance: Ideal for interfacing with sensors and high-impedance sources.
- Positive Gain: Ensures consistent signal polarity.
- Ease of Use: Straightforward design with minimal signal distortion.
Difference between Inverting Amplifier and Non-Inverting Amplifier
The following table shows the major differences between an inverting amplifier and a non-inverting amplifier
| Basis of Difference | Inverting Amplifier | Non-Inverting Amplifier |
|---|---|---|
| Definition | A type of operational amplifier which generates an amplified output signal that is 180° out of phase with the input signal is called an inverting amplifier. | A type of operational amplifier which generates an amplified output signal that is in phase with the applied input signal is called a non-inverting operational amplifier. |
| Input | In case of an inverting amplifier, the input signal is applied at the negative (called inverting) terminal of the amplifier. | In a non-inverting amplifier, the input signal is applied at the positive (called non-inverting) terminal. |
| Phase difference between input & output signals | In the inverting amplifier, there is a phase difference of 180° between the input signal and output signal. Hence, the input and output signals are out of phase in case of an inverting amplifier. | The non-inverting amplifier has a phase difference of 0° between the input and output signals. Therefore, the input and output signals are in-phase with each other in case of a noninverting amplifier. |
| Feedback | In the inverting amplifier, the feedback is provided at the same terminal at which the input signal is applied. | In the non-inverting amplifier, the feedback signal (negative terminal) and input signal (positive terminal) are connected to different terminals. |
| Ground terminal | The positive terminal of the inverting amplifier is connected to the ground. | The negative terminal of the noninverting amplifier is connected to the ground. |
| Feedback ground | In the inverting amplifier, the feedback is not connected to ground. | In the non-inverting amplifier, the feedback is connected to ground through a resistance (in our case R1). |
| Nature of output | The inverting amplifier produces an inverted output which is expressed with negative polarity. | The output produced by a noninverting amplifier is non-inverted in nature and expressed with positive polarity. |
| Expression of closed loop gain | The closed loop gain of an inverting amplifier is
Av = Vo / Vi = – (Rf / Rin)
Thus, the gain of the inverting amplifier is just a ratio of resistances. |
The closed loop gain of a non-inverting amplifier is
Av= V0 / Vi = 1 + Rf / R
Hence, the gain of the non-inverting amplifier is the sum of 1 and the ratio of resistances. |
| Gain polarity | The polarity of gain of an inverting amplifier is negative. | The polarity of gain of a non-inverting amplifier is positive. |
| Gain value | The gain of an inverting amplifier may be less than, more than or equal to unity (1). | The gain of a non-inverting amplifier is always more than 1. |
| Input impedance | The input impedance of an inverting amplifier is equal to R1 (refer Figure-1). | The input impedance of a noninverting amplifier is extremely high. |
| Applications | The applications of inverting amplifiers are: in trans-resistance amplifiers, at the output stage in the circuits designed with different types of sensors, integrator circuits, phase shifter, etc. | The applications of the non-inverting amplifiers are: in the circuits that require high input impedance, isolation of cascaded circuits, changing gain considerations, voltage followers, etc. |
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Comparison between Inverting and Non-Inverting Amplifier
- The inverting amplifier inverts the phase of the signal while the non-inverting amplifier does not change the phase of the signal.
- The gain of inverting amplifier is 1 less than the non-inverting amplifier.
- The gain of inverting amplifier can be less than, greater than, or equal to 1 but the non-inverting amplifier gain is always greater than 1.
- The gain of inverting amplifier is negative while the gain of the non-inverting amplifier is positive.
- In inverting amplifier, the input signal is applied at inverting terminal while in a non-inverting amplifier, the input signal is applied at its non-inverting terminal.
- The input impedance of inverting amplifier is Rin while it is infinite in a non-inverting amplifier.
Choosing Between Inverting vs. Non-Inverting Amplifiers
The choice depends on the application requirements:
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FAQs
What is the inverting and non-inverting amplifier?
The amplifier which has 180 degrees out of phase output with respect to input is known as an inverted amplifier, whereas the amplifier which has the o/p in phase with respect to i/p is known as a non-inverting amplifier.
What are noninverting amplifiers used for?
Non-inverting amplifiers mainly used where high i/p impedance is needed.
What is the function of the non-inverting amplifier?
It is used to provide a high input impedance
- Choose Inverting Amplifiers if:
- Signal inversion is acceptable or required.
- Precise gain control is crucial.
- Low input impedance suits the source.
- Choose Non-Inverting Amplifiers if:
- High input impedance is necessary.
- Signal phase integrity is critical.
- Voltage gain greater than unity is needed.
