Analogue systems process analogue signals which can take any value within a range, for example the
output from an LDR (light sensor) or a microphone.
An audio amplifier is an example of an analogue system.
The amplifier produces an output voltage which can be any value within the range of its power supply.
An analogue meter can display any value within the range
available on its scale. However, the precision of readings is limited by our ability to read
them. For example the meter scale shows 1.25V because the pointer is estimated to be
half way between 1.2 and 1.3. The analogue meter can show any value between 1.2 and 1.3 but
we are unable to read the scale more precisely than about half a division.
Analogue meter display
All electronic circuits suffer from 'noise' which is unwanted signal mixed in with the desired
signal, for example an audio amplifier may pick up some mains 'hum' (the 50Hz frequency of the UK
mains electricity supply). Noise can be difficult to eliminate from analogue signals because it
may be hard to distinguish from the desired signal.
Digital systems process digital signals which can take only a limited number of values
(discrete steps), usually just two values are used: the positive supply voltage (+Vs) and zero volts (0V).
Digital systems contain devices such as logic gates, flip-flops,
shift registers and counters. A computer is an example of a digital system.
Digital (logic) signal
A digital meter can display many values, but not every
value within its range. For example the display can show 6.25 and 6.26 but not
a value between them. This is not a problem because digital meters normally have sufficient
digits to show values more precisely than it is possible to read on an analogue display.
Digital meter display
Most digital systems use the simplest possible type of signal which has just two values.
This type of signal is called a logic signal because the two values (or states) can be called
true and false. Normally the positive supply voltage +Vs represents true and 0V represents false.
Other labels for the true and false states are shown in the table.
Noise is relatively easy to eliminate from digital signals because it is easy to distinguish from
the desired signal which can only have particular values. For example: if the signal is meant to be
+5V (true) or 0V (false), noise of up to 2.5V can be eliminated by treating all voltages greater
than 2.5V as true and all voltages less than 2.5V as false.
This website does not collect personal information.
If you send an email your email address and any personal information will be
used only to respond to your message, it will not be given to anyone else.
This website displays advertisements. If you click on
these the advertiser may know that you came from this site and I may be rewarded.
No personal information is passed to advertisers.
(including this one) as explained by Google.
To learn how to delete and control cookies from your browser please