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3.3.5Waves

Digital and Analogue Signals — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions

5 min read 9 parts Lesson 30 of 35 1 quiz

📚 Cambridge IGCSE Physics 0625 Hub / Topical Revision
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Lesson summary

3.3.5 Digital and Analogue Signals — IGCSE PHYSICS notes: Distinguish analogue and digital signals and state the advantages of digital transmission.Analogue signal — varies continuously and can take any valueExample — a sound wave drawn as a smooth, continuously varying lineProbl…

  • Speech and music
  • Digital sampling
  • Before transmission
  • After reception
  • Digital regeneration
  • Analogue amplification

Part 1 of 7Analogue signals

Analogue signal
  • Analogue signal varies continuously and can take any value
Example
  • Example a sound wave drawn as a smooth, continuously varying line
Problem
  • Problem any noise picked up in transmission becomes part of the signal

Part 2 of 7Digital signals

Digital signal
  • Digital signal can take only one of two discrete states
Names
  • 1s and 0s, highs and lows, ons and offs
Graph
  • Graph a signal that jumps between two levels

Part 3 of 7Transmitting sound

Speech and music
  • Speech and music made up of varying frequencies, so the signal needs as little interference as possible
Digital sampling
  • Digital sampling an analogue signal is converted to digital by recording the sound at set time intervals
Before transmission
  • Before transmission the signal is converted from analogue to digital
After reception
  • After reception the signal is converted back from digital to analogue

Part 4 of 7Noise and regeneration

Noise
  • Noise random interference that weakens and distorts signals over distance
Digital regeneration
  • Digital regeneration a digital signal can be recreated cleanly because the receiver only has to decide between two levels
Analogue amplification
  • Analogue amplification amplifies the noise along with the signal

Part 5 of 7Advantages of digital signals

Little noise
  • Little noise the signal can be regenerated so there is minimal noise
Longer range
  • Longer range accurate regeneration lets digital signals cover larger distances than analogue
Higher data rate
  • Higher data rate digital enables an increased rate of data transmission
Error checking
  • Error checking extra data can be added so the signal can be checked for errors

Part 6 of 7Where each is used

Telephones and broadband
  • Telephones and broadband landline calls convert sound to digital pulses sent along optical fibres
Television and radio
  • Television and radio many broadcasts are now digital
Reproduction
  • Reproduction digital copies are identical to the original, unlike analogue copies

Part 7 of 7More from the specification

1High energy x-rays and photo cells
  • High energy x-rays and photo cells penetrating x-rays carry high photon energy propagating at light speed to activate detector cells.
2Artificial satellite
  • A man-made object orbiting a body in space.
3Microwaves
  • Electromagnetic waves with wavelengths of millimetres to centimetres.
4Satellite
  • A body that orbits a larger one; the Moon is the Earth's natural satellite.
5Infrared
  • The part of the electromagnetic spectrum emitted by warm objects.
6Ultraviolet
  • Radiation of shorter wavelength than visible light that can damage skin.
7Spectrum
  • Range of colours in white light.
8Radiation
  • Transfer by electromagnetic waves, requiring no medium
9X-ray
  • A high-frequency electromagnetic wave produced when fast electrons are stopped by a metal target.
10Geostationary
  • Orbiting with a period of 24 h above the equator, so staying above one point.

Key terms

TermMeaning
Analogue signalSignal that varies continuously and can take any value
Digital signalSignal that has only two states, 1 and 0
Digital samplingRecording an analogue signal at set time intervals to convert it to digital
NoiseUnwanted random interference added to a signal
RegenerationRecreating a clean signal from a weakened digital one

Avoid these mistakes

1
Saying a digital signal can take any value — it has only two states.
2
Saying digital sampling happens at the receiver only — conversion is done before and after transmission.
3
Saying noise is removed from analogue signals by amplifying — amplification boosts the noise too.
4
Confusing analogue and digital on a graph — analogue is continuous and digital jumps between two levels.

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