Home > What is a digital circuit? > What is the difference between an analog circuit and a digital one?

What is the difference between an analog circuit and a digital one?

Basically, Analog signals operate on a  continuous range of  voltage levels, where as a digital circuit can be looked at as a string of data 0 and 1 (binary numbers) or off and on.  The key difference is that analog technologies register and use waveforms as they are, whereas digital technologies will convert the analog waveforms into a binary set of numbers.

Digital has only two states, on or off or 1 and 0 whereas analog is not going on for on or off it is in order of the actual level.

For instance an audio signal may range  anywhere from 0V to 1000 mV and an infinite number of places in between.  A digital circuit will operate on only one of it’s two states which are typically represented as 0 and 1 and these on/ off states can be represented by different voltages in different systems.  But any given digital signal will only have two distinct values.  A typical digital signal will dictate that anything below 1.0V its considered off and anything above 4.5 V is on .

Since most physical quantities such as velocity, temperature and audio will vary constantly, an analog circuit provides the best means of representing them.   However  digital circuits can often be preferred because of the ease in which their outputs can be manipulated by computers and they are considered more robust and less subject to transmission errors.   For example an audio signal that is represented digitally can be transmitted as a sequence of 1s and 0’s and can be reconstructed without error providing the noise picked up is not too great to prevent the identification of the 1’s and 0’s.  A more precise signal can be obtained by using these binary numbers to represent it. 

This information storage can be easier in digital circuits compared to analog.  The noise immunity of a digital system will allow the data to be stored and retrieved without degradation, whereas an analog circuit can be affected by things such as noise, age and wearing that can alternate the information it is trying to store.  As long as the noise is below a certain level, a digital circuit will be able to recover the information without error.

One disadvantage of a digital circuit is that it can use more energy than an analog circuit to complete the same task.  This in turn would produce more heat and so in the case of a portable or battery-powered unit such as a mobile phone the use of a digital system may be limited and they would instead use a low power analog circuit to amplify and tune the radio signals it receives.  Digital circuits can often be more expensive particularly in lower quantities.

In this graphic it appears to give the impression that an analog signal is better than the digital one due to its smooth continuous flow, however this is not necessarily the case.  By increasing the number and decreasing the size of the time divisions in the digital circuit it would be possible to make it nearly as smooth as the analog. 

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