Electronic circuits can be divided into two categories, analogue or digital. Analogue systems are also sometimes referred to as linear systems and are designed to amplify or process signals whose amplitude is smaller than the supply voltage. Logic or digital circuits as they are more commonly called have only two states:

(i) when the device is fully conducting and therefore has a very low voltage drop across it;

(ii) when the device is non-conducting and turned off completely. The advantage of operating in either of these two conditions is that very little power is dissipated in the device because the current is small or the voltage drop is low.