1. What is an op-amp?

Op-amp stands for “operational amplifier.” An op-amp is so called because it is used for various computational operations such as comparison, addition, subtraction, differentiation, and integral.
Figure 1-1 shows the electronic symbol for op-amps. An op-amp has five terminals: 1) noninverting input, 2) inverting input, 3) output, 4) positive power supply, and 5) negative power supply. Here, “inverting” and “noninverting” indicate the polarity with respect to the output.
The voltage applied to the noninverting input is amplified by a factor of A_V with respect to the inverting input potential. The output has the same phase as the noninverting input.
The voltage applied to the inverting input is also amplified by a factor of A_V with respect to the noninverting input potential. The output has the opposite phase to the inverting input.
As a result, the output provides a voltage equal to a difference in voltage between the inverting and noninverting inputs multiplied by A_V. Therefore, when the inverting and noninverting inputs have the same voltage and phase, the output voltage becomes zero. When the inverting and noninverting inputs have the same voltage and opposite phases, the output has the same phase as the noninverting input and provides a voltage equal to twice the difference between their voltages multiplied by A_V.
Despite a simple configuration, op-amps provide close-to-ideal characteristics as amplifiers. Therefore, they are widely used for various purposes in a wide range of IoT home appliance and other electronic applications. For example, op-amps are used to amplify analog signals from sensors and measuring instruments.