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Inverting vs Non-Inverting Op-Amp: A Comparison

Published Date
Author Cadence PCB Solutions

Key Takeaways

  • An operational amplifier (op-amp) is a high-gain voltage amplifier with two inputs, inverting (-) and non-inverting (+), and a single output.

  • Choosing between inverting and non-inverting op-amp configurations depends on the application’s requirements, taking into consideration phase requirements, gain, input and output impedance, common-mode rejection, and other factors.

  • The most distinctive feature of an inverting op-amp is its input configuration, where the signal is applied to the inverting input terminal, while the non-inverting op-amp features the input signal applied to the non-inverting input terminal.

Operational amplifier (op-amp) schematic symbol

Operational amplifier (op-amp) schematic symbol

An operational amplifier (op-amp) is a high-gain voltage amplifier with two inputs, inverting (-) and non-inverting (+), and a single output. The op-amp's key features include a high input impedance, low output impedance, and a differential input that amplifies the voltage difference between the inverting and non-inverting inputs. The high gain of op-amps allows them to amplify very small input signals to larger output voltages. Because of their versatility and reliability, op-amps are fundamental building blocks in electronic circuits.

There are two op-amp configurations: inverting vs non-inverting op-amps. With an inverting op-amp, the input signal is applied to the inverting (-) terminal, and the output is inverted relative to the input signal. On the other hand, with a non-inverting op-amp, the input signal is connected to the non-inverting (+) terminal, resulting in an output that is in phase with the input. These configurations enable designers to tailor the amplification characteristics of op-amp circuits to suit specific application requirements.

Inverting vs Non-Inverting Op-Amp: Pros and Cons

Below is a table summarizing the pros and cons of inverting and non-inverting op-amp configurations:

Inverting vs Non-Inverting Op-Amp: Pros and Cons

Feature

Inverting Op-Amp

Non-inverting Op-Amp

Voltage Inversion

Pro: Useful for inverting signals or phase-shifting applications

Pro: Useful for amplifying and buffering signals without phase inversion

Input Impedance

Pro: Input impedance is determined by the input resistor, making it easier to control

Pro: Very high input impedance, minimizing the loading effect on the source

Common Mode Rejection Ratio (CMRR)

Con: Lower CMRR compared to non-inverting configurations, making it less capable of distinguishing between the desired signal and common-mode noise.

Pro: Higher CMRR, making it more suitable for applications where common-mode noise rejection is crucial

Negative Gain

Con: Can introduce negative gain, which may not be suitable for all applications

Con: Always provides positive gain, limiting its use in applications where inversion is required

Feedback Configuration

Con: Feedback resistor is connected between the inverting input and the output, leading to increased noise

Pro: Feedback resistor is connected between the non-inverting input and the output, leading to lower noise compared to inverting configurations

Voltage Follower Capability

Con: Lacks the capability to act as a voltage follower directly

Pro: Can be configured easily as a voltage follower

Phase Shift

Con: Introduces a 180-degree phase shift, which may not be desirable in some applications

Con: Provides a 0-degree phase shift, which might not be suitable for applications requiring phase inversion

Applications

Pro: Well-suited for inverting amplifier circuits, summing amplifiers, and differential amplifiers

Pro: Well-suited for voltage followers, non-inverting amplifier circuits, and buffer amplifiers

Choosing between inverting and non-inverting op-amp configurations depends on the application’s requirements, taking into consideration phase requirements, gain, input and output impedance, common-mode rejection, and other factors.

Deeper Dive Into Inverting and Non-inverting Op-Amps

Let’s a closer look at these two op-amp configurations:

Inverting Op-Amp Explained

Inverting op-amp diagram

Inverting op-amp diagram

Source:  Wikipedia user Alejo2083

The most distinctive feature of an inverting op-amp is its input configuration, where the signal is applied to the inverting (-) input terminal. The output voltage is therefore inverted with respect to the input signal. The gain is given by the formula:

Vout = −Rf/Rin x Vin

Where:

Rf is the feedback resistor
Rin is the input resistor
Vout is the output voltage
Vin is the input signal

Inverting op-amps are used in numerous applications, including inverting amplifier circuits, summing amplifiers, and differential amplifiers. Unfortunately, the inverting configuration may introduce a 180-degree phase shift, and careful consideration is needed to manage potential noise and maintain signal integrity.

Non-Inverting Op-Amp Explained

Non-inverting op-amp diagram (R1 = Rin and R2 = Rf)

Non-inverting op-amp diagram (R1 = Rin and R2 = Rf) 

Source:  Wikipedia user Ramjar

The non-inverting op-amp configuration features the input signal applied to the non-inverting (+) input terminal. In this case, the output voltage maintains the same phase as the input signal, and the gain is given by the formula:

Vout = (1 + Rf/Rin) x Vin

Non-inverting op-amps are used in applications where maintaining signal phase is critical, such as voltage followers, non-inverting amplifier circuits, and buffer amplifiers. It offers high input impedance, reducing the loading effect on the source, and is generally associated with a 0-degree phase shift. The non-inverting configuration is advantageous for applications that require signal amplification without introducing phase inversion.

Cadence Has the Tools to Incorporate Op-Amps Into Your Design

Whatever design you plan on using op-amps for, it’s important to have a strong fundamental understanding of the features of inverting vs non-inverting op-amp configurations. To create a schematic and layout for your electronic design, you’ll need robust PCB design and analysis software to help you out. Consider Cadence’s suite of tools, including OrCAD PCB Designer, for your next project.

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