Sampled Data Systems

Consider the basic laws of Physics that describe the behavior of physical objects: Newton’s laws, Lagrange’s equations, the Navier-Stokes equations, Maxwell’s equations, Kirchhoff’s laws etc. Each of these laws describe continuous-time phenomena. At present it is cost effective to manipulate signals in digital form: for this purpose, signals are sampled by an A/D (analog-to-digital) converter, the resulting sequence of numbers is operated on by a digital computer (a controller) and the resulting sequence of numbers must be restored to analog form (i.e. to a continuous-time form) by a D/A (digital-to-analog) converter. Indeed, the analog form is required to actuate the physical devices that are to achieve the engineering goals.