Introduction

Abstract

The signals of interest in control systems—command inputs, tracking errors, actuator outputs, etc.—are usually continuous-time signals and the performance specifications—bandwidth, overshoot, risetime, etc.—are formulated in continuous time. But since digital technology offers many benefits, modern control systems usually employ digital technology for controllers and sometimes sensors. A digital controller performs three functions: It samples and quantizes a continuous-time signal (such as a tracking error) to produce a digital signal; it processes this digital signal using a digital computer; and then it converts the resulting digital signal back into a continuous-time signal. Such a control system thus involves both continuous-time and discrete-time signals, in a continuous-time framework.