Analog vs. Digital Signals

The information carrying signals are divided into two broad classes;

Analog Signals

Analog signals are continuous electrical signals that vary in time as shown in figure 4a. Most of the time, the variations follow that of the non-electric (original) signal. Therefore, the two are analogous hence the name analog.

Figure 4a: Analog Signal

Not all analog signals vary as smoothly as the waveform shown in Figure 4a. Analog signals represent some physical quantity and they are a ‘MODEL’ of the real quantity.

Example:

Telephone voice signal is analog. The intensity of the voice causes electric current variations. At the receiving end, the signal is reproduced in the same proportion. Hence the electric current is a ‘MODEL’ but not one’s voice since it is an electrical representation or analog of one’s voice.

Digital Signals

Digital signals are non-continuous, they change in individual steps. They consist of pulses or digits with discrete levels or values. The value of each pulse is constant, but there is an abrupt change from one digit to the next. Digital signals have two amplitude levels called nodes. The value of which are specified as one of two possibilities such as 1 or 0, HIGH or LOW, TRUE or FALSE and so on. In reality, the values are anywhere within specific ranges and we define values within a given range.

Figure 4b: Digital Signal