What is meant by sampling a signal?

Measuring the value of the analogue signal at regular intervals and recording each measurement as a number.

Explain how an analogue signal is turned into a string of binary numbers.

The signal is sampled at regular intervals and each sample is rounded to the nearest of the 2ᵇ available levels, whose number is then written in binary.

What is meant by the resolution of a digitisation?

It is the size of the voltage step between adjacent levels, equal to the total range divided by the number of levels.

A range of 5.0 V is digitised using 8 bits. Calculate the resolution.

There are 256 levels, so the resolution is 5.0/256 = 0.020 V, about 20 mV.

OCR A-Level Physics B H557

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Imaging and Signalling

Sampling and digitising an analogue signal

3 things to know
Components 01, 02 and 03

Overview

Recall questions on analogue and digital signals, sampling and turning samples into binary numbers, the resolution of a digitisation, the minimum sampling rate and what goes wrong below it, filtering before digitising, the staircase shape and how bits and sampling rate change it, sampling music 44 100 times per second, and quantisation error.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What is an analogue signal?

Key term

What is a digital signal?

Key term

State the minimum rate at which a signal must be sampled.

Questions from this subtopic

Each one with the model answer underneath.

1
What is an analogue signal?
Model answer
One whose value varies continuously with time and can take any level within its range.
2
What is a digital signal?
Model answer
One that carries information as a sequence of discrete values, normally represented by only two voltage levels.
3
What is meant by sampling a signal?
Model answer
Measuring the value of the analogue signal at regular intervals and recording each measurement as a number.
4
Explain how an analogue signal is turned into a string of binary numbers.
Model answer
The signal is sampled at regular intervals and each sample is rounded to the nearest of the 2ᵇ available levels, whose number is then written in binary.
5
What is meant by the resolution of a digitisation?
Model answer
It is the size of the voltage step between adjacent levels, equal to the total range divided by the number of levels.
6
A range of 5.0 V is digitised using 8 bits. Calculate the resolution.
Model answer
There are 256 levels, so the resolution is 5.0/256 = 0.020 V, about 20 mV.

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