Know the difference between a digital and analogue signal

Published by Patrick Mutisya · 14 days ago

Cambridge IGCSE Physics 0625 – 3.3 Electromagnetic Spectrum

Cambridge IGCSE Physics 0625 – Topic 3.3 Electromagnetic Spectrum

Objective

Know the difference between a digital and analogue signal.

1. What is an Analogue Signal?

An analogue signal is a continuous wave that varies smoothly over time. Its amplitude, frequency or phase can take any value within a given range.

  • Represented mathematically as a function, e.g. \$v(t)=A\sin(2\pi ft)\$.

  • Typical examples: sound waves, radio waves, television broadcast signals.

  • Can be described by parameters such as amplitude, frequency and phase.

2. What is a Digital Signal?

A digital signal consists of discrete steps or levels, usually representing binary values (0 and 1). The signal changes abruptly from one level to another.

  • Represented as a series of pulses or square waves.

  • Typical examples: computer data, digital audio (CDs, MP3), digital television.

  • Information is encoded in the presence or absence of a pulse, or in the timing of pulses.

3. Key Differences

The table below summarises the main contrasts between analogue and digital signals.

FeatureAnalogue SignalDigital Signal
DefinitionContinuous variation of amplitude, frequency or phase.Discrete levels, usually binary (0 or 1).
RepresentationWaveforms such as sine or cosine functions.Square pulses or stepwise levels.
Typical ExamplesAudio from a microphone, AM/FM radio, analogue TV.Computer data, digital audio files, digital TV.
BandwidthOften requires a broader continuous spectrum.Can be more efficiently packed using modulation techniques.
Noise SensitivityNoise adds directly to the signal, degrading quality.Noise can be filtered; errors are detected and corrected.
TransmissionSusceptible to attenuation and distortion over long distances.Regenerates clean pulses at repeaters; less distortion.
StorageRequires continuous recording (e.g., magnetic tape).Stored as discrete bits; easy to copy without loss.
Typical UsesMusic broadcasting, analog sensors, traditional telephony.Computing, digital communications, modern audio/video.

4. Advantages and Disadvantages

Analogue Signals

  • Simple to generate and process with basic electronics.

  • Can represent an infinite range of values, useful for high‑resolution measurements.

  • More vulnerable to noise and signal degradation.

Digital Signals

  • Robust against noise; errors can be detected and corrected.

  • Easy to store, copy, and transmit over long distances.

  • Requires conversion (ADC/DAC) when interfacing with the real world.

5. Practical Applications in the Electromagnetic Spectrum

  1. Radio broadcasting: traditionally analogue (AM/FM), now often digital (DAB).

  2. Television: analogue T \cdot replaced by digital terrestrial television (DTT).

  3. Mobile communications: digital modulation schemes (e.g., QAM, OFDM) dominate.

  4. Data transmission over fibre optics: digital light pulses encode binary data.

6. Summary

Understanding whether a signal is analogue or digital is fundamental for interpreting how information is carried across the electromagnetic spectrum. Analogue signals vary continuously, while digital signals consist of discrete steps. The choice between them depends on factors such as noise tolerance, bandwidth, and the need for processing or storage.

Suggested diagram: Analogue waveform (smooth sine wave) versus Digital waveform (square wave) illustrating continuous versus discrete values.