1 Analogue systems and concepts
Analogue systems are characterised by electrical signals that vary continuously between two extreme amplitude levels. There is thus an infinity of actual levels that such signals can assume. Compared with other forms, analogue signals usually occupy minimum bandwidth.
Amplifiers can be sub-divided into many different types, each designed for some specific purpose. But depending upon the time period for which the output current flows with respect to a changing input signal, they can be assigned to one of the classifications shown in Fig 1.1.