Digital signal means that the value of amplitude is discrete, and the amplitude representation is limited to a limited number of values. A binary code is a digital signal. Binary coding is less affected by noise and easy to be processed by digital circuits, so it has been widely used. Independent variables are discrete, so are dependent variables. The independent variable of this signal is represented by an integer, and the dependent variable is represented by one of the finite numbers. In a computer, the size of a digital signal is usually represented by the finite bits of a binary number. For example, a binary number with a word length of 2 bits can represent four digital signals, namely 00, 0 1, 10 and11; If the signal changes in the range of-1~ 1, these four binary numbers can represent four numerical ranges, namely [- 1, -0.5], [-0.5, 0], [0.5, 1.

Analog signal (English) refers to a signal whose mathematical form is a time-domain continuous function. Corresponding to analog signals are digital signals, which take discrete logical values, while the former can get continuous values. The concept of analog signal is often used in the field of electricity, but it is sometimes used in classical mechanics, aerodynamics, hydraulics and other disciplines.

The main differences between them are as follows:

1. Analog signal and digital signal

Different data must be converted into corresponding signals before transmission: analog data (analog quantity) is generally represented by analog signals, such as a series of continuously changing electromagnetic waves (such as electromagnetic waves in radio and television broadcasting) or voltage signals (such as audio voltage signals in telephone transmission); Digital data (digital quantity) is represented by digital signals, such as a series of intermittent voltage pulses (for example, we can use a constant positive voltage to represent binary number 1 and a constant negative voltage to represent binary number 0) or optical pulses. When analog signals are represented by continuously changing electromagnetic waves, the electromagnetic waves themselves are both signal carriers and transmission media. When analog signals are represented by continuously changing signal voltages, they are generally transmitted through traditional analog signal transmission lines (such as telephone networks and cable television networks). When digital signals are expressed by intermittent voltages or optical pulses, twisted pair, cable or optical fiber media are generally needed to connect the two communication parties and transmit signals from one node to another.

2. Mutual conversion between analog signals and digital signals

Analog signals and digital signals can be converted to each other: analog signals are generally quantized into digital signals by PCM pulse code modulation, that is, different amplitudes of analog signals correspond to different binary values. For example, analog signals can be quantized into 2 8 = 256 orders of magnitude by 8-bit coding, and in practice, 24-bit or 30-bit coding is often used; Digital signals are usually converted into analog signals by phase shifting a carrier wave. Binary digital signals are used in computers, computer local area networks and metropolitan area networks. At present, both binary digital signals and analog signals converted from digital signals are actually transmitted in computer WAN. But the more promising application is digital signal.