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Difference between Analog Signal & Digital Signal

By September 12, 2017 No Comments
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Do you know the difference between analog signal and digital signal? Before we know the difference, we have to know what analog signal is and what digital signal is.

What is analog signal?

Analog signal is a kind of signal with information expressed by constantly changing physic quantities. For example, sound signal of a radio, or pattern signal, etc.. Analog signal is continuous. If we set information parameter within a certain range, then we can get analog signal. In a period of continuous time, the characteristic quantity of the information it represented can be suddenly transformed into signals with any value at will.

The advantage of analog communication is intuitive and easy to implement. But it has two major shortcomings. Analog communication, especially microwave communication and wired communication, is easy to be eavesdropped. Once analog signal is received, it is easy to obtain the communication messages. When signal is transmitting along the cable road, it will suffer all kinds of noise interruptions from its internal communication system or external space. These noise interruptions mixed with signal are very difficult to separate so that the quality of communication is declined. Longer cable road, more noise accumulation.

Let’s take a look at the following analog signal chart.


We can see this signal is changing continuously. Each moment in a cycle has different voltage value corresponded? In our life, earphone is work on analog signal.


What is digital signal?

Digital signal is a kind of signal with both independent variable and dependent variable dispersed. Its independent variable usually represented by integers, while dependent variable represented by a number of limited numerals.

Digital signal is discrete. Its amplitude is limited within a definite value. Binary code is a kind of digital signal. Binary code has small influence of noise. It is easy to be handled by digital circuit. So binary code is widely used.

Because of “0” and “1” are represented by two kinds of physic status in digital signal, so its resistance material has stronger ability of anti-interruption than analog signal. In present signal process technology, digital signal become more and more important. Almost all of complex signal process cannot be done without digital signal. Or it can be said only if we can use mathematical formulas to represent method of solving problems, we can use computers to deal with digital signals which stand for physic quantities.

Let’s take a look at the following digital signal chart.


We can see from the chart that digital signal is represented by “0” and “1” only. For example, mobiles in our daily life use digital signal to do communication.


Inter-conversion of analog signal and digital signal

Analog signal and digital signal can realize mutual transform. Analog signal usually use PCM (Pulse Code Modulation) method to quantify and transform to digital signal. PCM method is to make different range of analog signal correspond to different binary value. For example, if we use 8-bit code, we can quantify analog signal to 2^8=256 quantity level. In practice, we often use 24-bit or 30-bit code. Normally digital signal transform to analog signal through phase shift of carrier wave. Computers, LAN, MAN all use binary digital signal. At present, the real transmission of WAN has both binary digital signal and analog signal conversed from digital signal. But digital signal is more frequently used due to its wider application future.

Control boards (like Micro:bit, Arduino) have specified ADC interface, which is used to converse analog quantities into digital quantities. Potentiometer and photocell use analog signal too. They realize digital signal transformation by ADC port too. So it is very convenient to handle.

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