Electronic devices represent and manipulate real-world phenomena through the use of electrical signals. Electronic circuits are designed to perform a wide array of manipulations. Analog representations are continuous. Some aspect of an electric signal is modified proportionally to the real-world item that is being represented.
For example, a microphone has electricity flowing through it that is altered when sound is applied. The type and strength of the modification to the electric signal is characteristic of the sound that is made into the microphone. The result is that sound, a real-world phenomenon, is represented electronically. It can then be moved, amplified, and reconverted from an electrical signal back into sound and broadcast from a speaker across the room or across the globe.
Since the flow of electricity through the microphone is continuous, the sound continuously modifies the electrical signal. On an oscilloscope, an analog signal is a continuous curve. [Figure 1] An analog electric signal can be modified by changing the signal’s amplitude, frequency, or phase.
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| Figure 1. An analog signal displayed on an oscilloscope is a continuous curve |
A digital electronic representation of a real-world event is discontinuous. The essential characteristics of the continuous event are captured as a series of discrete incremental values. Electronically, these representative samplings are successive sequences of voltage and no-voltage signals.
They can be transported and manipulated in electronic circuits. When the samples are sufficiently small and occur with high frequency, real-world phenomena can be represented in a way that appears continuous.
Noise
A significant advantage of digital electronics over analog electronics is the control of noise. Noise is any alteration of the represented real-world phenomena that is not intended or desired. Consider the operation of a microphone when understanding noise. A continuous analog voltage is modified by a voice signal that results in the continuous voltage varying in proportion to the volume and tone of the input sound.
However, the voltage responds and modifies to any input. Thus, background sounds also modify the continuous voltage as will electrostatic activity and circuitry imperfections. This alteration by phenomena that are not the intended modifier is noise.
During the processing of digitized data, there is little or no signal degradation. The real-world phenomenon is represented in a string of binary code. A series of ones and zeros are electronically created as a sequence of voltage or no voltage and carried through processing stages. It is relatively immune to outside alteration once established.
If a signal is close to the specified voltage level, it is interpreted as that voltage. If the signal is close to zero, it is considered to be no voltage. Small variations or modifications from undesired phenomena are ignored.
Figure 2 illustrates an analog sine wave and a digital sine wave. Any unwanted voltage will modify the analog curve. The digital steps are not modified by small unwanted inputs. There is either voltage or no-voltage conditions.
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| Figure 2. Analog signals are continuous voltage modified by all external events including those that are not desired called noise. Digital signals are a series of voltage or no voltage that represent a desired event |
What is the fundamental difference between analog and digital signals?
Why is digital electronics better at controlling signal noise?
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