Operational amplifier applications
（重定向自Zero crossing detector）
A non-ideal op amp's equivalent circuit, showing a finite input impedance, non-zero output impedance, and a finite gain. This article illustrates some typical applications of operational amplifiers. A real op amp has a number of non-ideal features as shown in the diagram, but here a simplified schematic notation is used, and the reader is reminded that many details such as device selection and power supply connections are not shown. Operational amplifiers are optimised for use with negative feedback, and this article discusses only negative-feedback applications. When positive feedback is required, a comparator is usually more appropriate. See Comparator applications for further information.