1 Basics of Operational Amplifiers

Operational amplifiers are a common building block in analog designs due to their low cost and high performance. The goal of the operational amplifier circuit is to match the voltage on the inverting (negative) input with the voltage on the non-inverting (positive) input. If the voltage on the inverting input is less than the non-inverting input, then the operational amplifier increases the output voltage to try and compensate for the error through the feedback in circuit.

This behavior is useful for circuit analysis, as the voltage applied to one input normally is matched on the other input. Another useful behavior of operational amplifiers is their extremely high input impedance. (Some specialized types of operational amplifiers may break this rule, but these are outside of the scope of this document.) The high input impedance keeps the input bias current of the operational amplifier inputs to a minimum, making it negligible in many general-purpose applications.

There are many different types and architectures of operational amplifiers, which vary in performance and characteristics. For example, a zero-drift operational amplifier is designed such that the voltage offset is very small and extremely stable across temperature. (See Voltage Offset for more information.) Unless otherwise stated, this document will focus on general-purpose operational amplifiers that are embedded in a microcontroller.