What Is the Difference Between an Inverting & Non-Inverting Amplifier?

Written by j.t. barett
  • Share
  • Tweet
  • Share
  • Pin
  • Email
What Is the Difference Between an Inverting & Non-Inverting Amplifier?
An operational amplifier has both inverting and non-inverting modes. (Stockbyte/Stockbyte/Getty Images)

The job of an electronic amplifier is to boost the current or voltage of an incoming signal. Amplifiers come in inverting and noninverting types. A non-inverting amplifier's output follows the input exactly. An inverting amplifier shifts the input 180 degrees, so positive voltages become negative and vice versa. An operational amplifier contains both types in a single convenient package.

Other People Are Reading

Operational Amplifier

Electronic engineers created a packaged circuit called the operational amplifier, or op-amp. It performs many basic amplification tasks in a format having only three connections: an inverting input, a non-inverting input and an output. Electronic designers treat the op-amp integrated circuit, or IC, as a "black box," needing to know only its general behaviour, not the details of its internal parts. Designers can use either the inverting or non-inverting inputs, or both together, depending on their design goals.

Inverting Input

The inverting input reverses the sign of the input voltage, so a positive voltage at the input appears as a negative one at the output. For some applications, the sign of the output voltage does not matter, so the engineer may choose to use the inverting input if it simplifies a circuit design. For other uses, such as cancelling a positive voltage with a negative one, the inverting input allows a circuit to selectively remove signals.

The inverting input also accepts feedback from the amplifier's output. With no feedback, an op-amp has infinite gain, so any positive signal drives the output to the amplifier's positive supply voltage. This is useful but produces severe distortion. Feeding back a portion of the signal to the inverting input reduces gain to a reasonable figure, allowing accurate signal reproduction.

Non-Inverting Input

Whereas the inverting input produces a "mirror image" of the voltage at the output, the non-inverting input produces a copy, though amplified, at the output. A designer uses the non-inverting input for signals that must be reproduced as closely as possible. A direct current, or DC, signal, for example, is more sensitive to a reversed sign than an audio signal, so a designer will likely choose the non-inverting input for DC. Unlike the inverting input, the non-inverting input does not normally accept feedback, as it would only increase a gain factor that is already infinite.

Adding and Subtracting

One of an op-amp's many tricks is its ability to combine signals. An audio engineer, for example, uses a multichannel console to mix the microphone signals from vocalists and instruments. At the heart of the mixer is an op-amp that adds the signal from each of the mixer's microphone inputs to produce the song with all its parts properly balanced.

The op-amp can add signals from either of its two inputs. Multiple sources that arrive at the inverting input are first added together, then inverted. Those that arrive at the non-inverting input simply add together. The op-amp then subtracts the total of the inverted inputs from the total of the non-inverting inputs. The combinations of different inputs give the designer flexibility in creating circuits.

Don't Miss

  • All types
  • Articles
  • Slideshows
  • Videos
  • Most relevant
  • Most popular
  • Most recent

No articles available

No slideshows available

No videos available

By using the eHow.co.uk site, you consent to the use of cookies. For more information, please see our Cookie policy.