Editing Operational amplifier (section)

==== Inverting amplifier ====
[[Image:Op-Amp Inverting Amplifier.svg|frame|right|An op amp connected in the inverting amplifier configuration]]

In an inverting amplifier, the output voltage changes in an opposite direction to the input voltage.

As with the non-inverting amplifier, we start with the gain equation of the op amp:

:<math>V_\text{out} = A_\text{OL} (V_+ - V_-).</math>

This time, ''V''<sub>−</sub> is a function of both ''V''<sub>out</sub> and ''V''<sub>in</sub> due to the voltage divider formed by ''R''<sub>f</sub> and ''R''<sub>in</sub>. Again, the op-amp input does not apply an appreciable load, so

:<math>V_- = \frac{1}{R_\text{f} + R_\text{in}} \left( R_\text{f} V_\text{in} + R_\text{in} V_\text{out} \right).</math>

Substituting this into the gain equation and solving for <math>V_\text{out}</math>:

:<math>V_\text{out} = - V_\text{in} \frac{A_\text{OL} R_\text{f}}{R_\text{f} + R_\text{in} + A_\text{OL} R_\text{in}}.</math>

If <math>A_\text{OL}</math> is very large, this simplifies to

:<math>V_\text{out} \approx -V_\text{in} \frac{R_\text{f}}{R_\text{in}}.</math>

A resistor is often inserted between the non-inverting input and ground (so both inputs see similar resistances), reducing the [[input offset voltage]] due to different voltage drops due to [[bias current]], and may reduce distortion in some op amps.

A [[Capacitive coupling|DC-blocking]] [[capacitor]] may be inserted in series with the input resistor when a [[frequency response]] down to DC is not needed and any DC voltage on the input is unwanted. That is, the capacitive component of the input impedance inserts a DC [[complex zero|zero]] and a low-frequency [[complex pole|pole]] that gives the circuit a [[bandpass]] or [[high-pass]] characteristic.

The potentials at the operational amplifier inputs remain virtually constant (near ground) in the inverting configuration. The constant operating potential typically results in distortion levels that are lower than those attainable with the non-inverting topology.{{cn|date=January 2025}}