14.7 - Analogue & Digital Signals

Analogue and digital signals

Analogue signals

• An analogue signal can take any value within a continuous range.
• Its value varies smoothly and continuously, producing a smooth curve on a trace.

Digital signals

• A digital signal can only take certain fixed values.
• It jumps between these allowed values in discrete steps, often switching between just two states (on and off).

Sound as an analogue or digital signal

• The amplitude and frequency of a sound wave vary continuously, so sound can be carried directly as an analogue signal (e.g. AM and FM radio).
• Sound can also be converted into a digital signal through a process called digitising (e.g. DAB radio).

How digitising works

1. Sampling - The value of the analogue signal is measured at regular time intervals.
2. Each measured value is rounded to the nearest allowed digital value.
3. The result is a digital approximation of the original analogue wave.

Benefits of digital signals

• Faster data transmission - Digital signals can carry more information per second than analogue signals.
• Easier processing - Digital signals can be processed directly by computers and digital circuits.
• Better signal regeneration - Digital signals can be cleaned up and restored much more accurately than analogue signals, so they can be sent over a greater range without losing quality.

Regeneration and noise

• As any signal travels, it weakens and picks up noise (unwanted electrical interference).
• Amplifying an analogue signal amplifies the noise along with the signal, permanently distorting it.
• A digital signal only uses fixed, discrete values (such as 1s and 0s). A regenerator can easily determine whether a noisy pulse was meant to be a high or low value and reconstruct the original, noise-free signal.