Common op-amp configurations

When negative feedback is removed, an operational amplifier can function as a comparator, shown in Figure 7. In this configuration, the output switches between its positive and negative saturation limits depending on which input voltage is greater.

Because the open-loop gain is extremely high, even a small difference between the input voltages causes the output to rapidly transition to one of the supply rails. This makes comparator operation nonlinear and effectively digital in behavior despite that op-amps are analog devices. Overall, comparators show how op-amps can be used to compare two different signals.

Comparators are widely used in measurement circuits and display systems, such as LED level indicators, where voltage thresholds must be detected and represented visually (Electronics Notes).

One of the most widely used operational amplifier configurations is the inverting amplifier, shown in Figure 8. In this configuration, the input signal is applied to the inverting terminal through a resistor, while the non-inverting terminal is connected to ground. A feedback resistor connects the output terminal back to the inverting input, forming a closed-loop system.

The output voltage is proportional to the input voltage and is determined by the ratio of the two resistors in the circuit. Figure 8 shows that the output voltage is related to the input voltage scaled by −R₂/R₁, meaning the output signal is inverted and amplified by this factor.

Negative feedback sets the closed-loop gain of the circuit. This resistor ratio allows engineers to precisely control the level of amplification in practical applications. Overall, inverting amplifiers show how op-amps are used to amplify signals (Next Electronics).

The complement to the inverting amplifier is the non-inverting amplifier, shown in Figure 9. In this configuration, the input signal is applied to the non-inverting terminal, while the inverting terminal is connected to a resistor to ground. Like in the inverting amplifier, the feedback resistor connects the output terminal back to the inverting input.

This figure shows that the output voltage is related to the input voltage scaled by 1 + R₂/R₁, meaning the output signal is not inverted and larger than the input signal.

A summing amplifier, shown in Figure 10, allows multiple input signals to be combined into a single output signal. Each input contributes to the output based on the resistor through which it is applied. As shown in Figure 10, the output voltage is determined by scaling each input voltage by the ratio of the feedback resistor to its respective input resistor, summing the results, and then inverting the final output.

This configuration is widely used in audio systems to combine left and right channels into a single signal. Summing amplifiers demonstrate how operational amplifiers can perform mathematical operations such as addition (Electronics101).