Digital signal means that the independent variable is discrete and the dependent variable is discrete. 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 a finite bit binary number.
Because digital signals represent 0 and 1 respectively in two physical states, their ability to resist material interference and environmental interference is much stronger than that of analog signals. In the signal processing of modern technology, digital signal plays an increasingly important role, and almost complex signal processing can not be separated from digital signal; In other words, as long as the solution of the problem can be expressed by mathematical formulas, digital signals representing physical quantities can be processed by computers.
Analog signal definition
Analog signal refers to the information expressed by continuously changing physical quantities. Analog signals are characterized by continuous amplitude (continuous means that an infinite number of values can be taken within a certain value range). Analog signal, its signal waveform is also continuous in time, so it is a continuous signal. Analog signal A sampled signal sampled at a certain time interval t is still an analog signal, because its waveform is discrete in time, but its amplitude is still continuous. Telephone, fax and TV signals are all analog signals.
After sampling, the signal is discrete in time, but the amplitude is not discrete. Common sampling signals are periodic rectangular pulse and periodic pulse sampling. Analog signals are defined on the whole time axis, and the meaning of "no amplitude" zone is that the amplitude is zero. Discrete-time signals are defined only at discrete moments, but not elsewhere. They are different concepts from zero amplitude. These two signals look very similar on the time axis, but they are actually two fundamentally different signals based on different types of systems. Intuitively, the horizontal axis of discrete time signal can be considered as no longer representing time.
The difference between the two
Different data must be converted into corresponding signals before transmission: analog data is generally represented by analog signals, such as a series of continuously changing electromagnetic waves (such as electromagnetic waves in radio and television) 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 represent binary number 1 with a constant positive voltage and binary number 0 with a constant negative voltage) 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 usually 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.
The connection between the two.
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. 2 1 century, both binary digital signals and analog signals converted from digital signals are actually transmitted in computer wide area networks. But the more promising application is digital signal.
The main difference is that analog signals are pulse-controlled, while digital signals are phase (parity)-controlled.
1. Analog signal
The advantages of analog signals are intuitive and easy to realize, but there are two main disadvantages.
(1) has poor security.
Analog signals, especially microwave communication and wired communication, are easily eavesdropped. As long as the analog signal is received, it is easy to get the communication content.
(2) Weak anti-interference ability
In the process of electric signal transmission along the line, it will be interfered by various noises inside and outside the communication system, and it is difficult to separate the noise from the signal after mixing, thus reducing the communication quality. The longer the line, the more noise is accumulated.
2. Digital signal
Advantages of (1) digital transmission and exchange
(1) Strengthen the confidentiality of communication.
② Anti-interference ability is improved. Digital signals will be mixed with noise during transmission. The input signal voltage can be measured by mosfet (called threshold) composed of electronic circuit. Only when the voltage reaches a certain amplitude, the circuit will have an output value and automatically generate neat pulses (called shaping or regeneration). When the small noise voltage comes, it will be filtered out because it is lower than the threshold value, and it will not cause circuit action. Therefore, the regenerated signal is exactly the same as the original signal, and unless the interference signal is greater than the original signal, an error code will be generated. In order to prevent the error code, the method of error detection and correction is set in the circuit, that is, when the error code occurs, the opposite party can be retransmitted by using the reverse signal. Therefore, digital transmission is suitable for long-distance transmission, and can also be applied to lines with poor efficiency.
③ A complete digital communication network can be built. After adopting time division switching, transmission and switching are unified, and a complete digital communication network can be formed.
(2) Disadvantages of digital signals
(1) occupies a wide frequency band. Because the line transmits pulse signals, it takes 20? The bandwidth is 64kHz, while an analog channel only occupies 4kHz, that is, a PCM signal occupies several analog channels. For a certain telephone line, its utilization rate has decreased, or its requirements for the line have increased in detail.
② The technical requirements are complex, especially the synchronization technology requires high precision. If the receiver can correctly understand the meaning of the sender, it must correctly distinguish each symbol and find the beginning of each block, which requires strict synchronization between the sender and the receiver. If a digital network is formed, it will be more difficult to solve the synchronization problem.
③ The analog-to-digital conversion will bring quantization error. With the use of large-scale integrated circuits and the popularization of broadband transmission media such as optical fiber, more and more digital signals are used for information storage and transmission, so analog signals must be converted from analog to digital, and quantization errors will inevitably occur in the conversion.
Specifically, digital signals have the following advantages: "First, the anti-interference ability is relatively strong, and the quality of transmitted signals is relatively high;" Second, the image clarity is high and the sound changing effect is good. Third, channel resources can be used more effectively, and hundreds of programs can be transmitted. In analog TV signals, only dozens can be transmitted.
Fourth, it can provide various information services, such as stock market information and e-commerce information.
The difference between digital signal and analog signal is that the answer is B.
Analog signal refers to the continuous value of amplitude (amplitude can be expressed by infinite value). Continuous analog signals and continuously changing video (TV, fax) signals, etc. As shown in figure 1- 1(a). A discrete analog signal in time is a sampling signal, as shown in figure 1- 1(b). It is a signal obtained by sampling the analog signal in figure 1- 1(a) every t. Although its waveform is discontinuous in time, its amplitude is continuous, so it is still an analog signal.
Digital signal refers to the discrete value of amplitude, and the amplitude representation is limited to a limited number of values. A binary code is a digital signal.
What's the difference between analog signals and digital signals? Analog signal and digital signal
(1) analog signal and digital signal
Different data must be converted into corresponding signals before transmission: analog data are generally represented by analog signals, such as a series of continuously changing electromagnetic waves (such as electromagnetic waves in radio and television) or voltage signals (such as audio voltage signals in telephone transmission); Digital data 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 usually 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, 8-bit coding can quantize analog signals into 2 8 = 256 orders of magnitude, 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.
Analog signal refers to the continuous value of amplitude (amplitude can be expressed by infinite value). Continuous analog signals and continuously changing video (TV, fax) signals, etc. As shown in figure 1- 1(a). A discrete analog signal in time is a sampling signal, as shown in figure 1- 1(b). It is a signal obtained by sampling the analog signal in figure 1- 1(a) every t. Although its waveform is discontinuous in time, its amplitude is continuous, so it is still an analog signal.
Digital signal refers to the discrete value of amplitude, 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.
The difference between digital signal and analog signal analog signal is represented by a series of continuously changing electromagnetic waves or voltage signals; Digital signals are represented by a series of voltage pulses that change intermittently (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 usually 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.
What is the difference between digital signal and analog signal in WEDM? The pulse width error of analog signal is large. The pulse width signal of digital signal is accurate. The pulse width and pulse matching of the last power amplifier circuit in the same cabinet are the same, and the cutting is the same.
The difference between digital signal and analog signal data can be used to represent any information, such as symbols, characters, sounds, images and so on. , from the form of expression can be divided into two types: analog signals and digital signals. The difference between analog signal and digital signal can be determined according to whether the amplitude is discrete or not.
Analog signal refers to the continuous value of amplitude (amplitude can be expressed by infinite value). Continuous analog signals and continuously changing video (TV, fax) signals, etc. As shown in figure 1- 1(a). A discrete analog signal in time is a sampling signal, as shown in figure 1- 1(b). It is a signal obtained by sampling the analog signal in figure 1- 1(a) every t. Although its waveform is discontinuous in time, its amplitude is continuous, so it is still an analog signal.
Digital signal refers to the discrete value of amplitude, 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.
1. Analog communication
The advantages of analog communication are intuitive and easy to realize, but there are two main disadvantages.
(1) has poor security.
Analog communication, especially microwave communication and wired communication, is easily eavesdropped. As long as the analog signal is received, it is easy to get the communication content.
(2) Weak anti-interference ability
In the process of electric signal transmission along the line, it will be interfered by various noises inside and outside the communication system, and it is difficult to separate the noise from the signal after mixing, thus reducing the communication quality. The longer the line, the more noise is accumulated.
2. Digital communication system
Advantages of (1) digital transmission and exchange
(1) Strengthen the confidentiality of communication. After A/D conversion, the voice signal can be encrypted first, then transmitted, decrypted at the receiving end, and then restored to analog signal through D/A conversion.
The digital encryption process can be simply described as: Y 1 digital signal y1=1011100001,with 8-bit cipher C. Before sending it to the transmission line, the password is "added" to the voice code, X = Y 1+C (password c is repeated constantly), so the transmitted digital signal is
x = y 1+C = 10 1 10 1 10000 1y 1
+100011kloc-0/10001celsius.
—————————————
00 1 10 1 10 10000 X
Obviously, X≠Y 1, even if someone eavesdrops on the X code, it is impossible to get the Y1code immediately. At the receiving end, as long as the same password C is added to the number X, the original phonetic symbol number Y 1 can be erected, that is
y 1 = X+C = 00 1 10 1 10 10000 X
+100011kloc-0/10001celsius.
—————————————
10 1 1 10 10000 1y 1
It can be seen that the digitization of speech provides a very favorable condition for encryption processing, and the more password digits, the more difficult it is to decipher the password.
② Anti-interference ability is improved. Digital signals will be mixed with noise during transmission. The input signal voltage can be measured by mosfet (called threshold) composed of electronic circuit. Only when the voltage reaches a certain amplitude, the circuit will have an output value and automatically generate neat pulses (called shaping or regeneration). When the small noise voltage comes, it will be filtered out because it is lower than the threshold value, and it will not cause circuit action. Therefore, the regenerated signal is exactly the same as the original signal, and unless the interference signal is greater than the original signal, an error code will be generated. In order to prevent the error code, the method of error detection and correction is set in the circuit, that is, when the error code occurs, the opposite party can be retransmitted by using the reverse signal. Therefore, digital transmission is suitable for long-distance transmission, and can also be applied to lines with poor efficiency.
③ A complete digital communication network can be built. After adopting time division switching, transmission and switching are unified, and a complete digital communication network can be formed.
(2) Disadvantages of digital communication
(1) occupies a wide frequency band. Because the line transmits pulse signals, it takes 20? 64kHz bandwidth, while an analog channel only occupies 4kHz bandwidth, that is, a PCM signal occupies several analog channels. For a certain telephone line, its utilization rate has decreased, or its requirements for the line have increased in detail.
② The technical requirements are complex, especially the synchronization technology requires high precision. If the receiver can correctly understand the meaning of the sender, it must correctly distinguish each symbol and find the beginning of each block, which requires strict synchronization between the sender and the receiver. If a digital network is formed, it will be more difficult to solve the synchronization problem.
③ The analog-to-digital conversion will bring quantization error. With the use of large-scale integrated circuits and the popularization of broadband transmission media such as optical fiber, more and more digital signals are used for information storage and transmission, so analog signals must be converted from analog to digital, and quantization errors will inevitably occur in the conversion.
What is the difference between digital signal and analog signal in junior middle school physics? Numbers are information recorded by symbols, and simulations are not recorded by symbols. They can be found in junior high school physics textbook, 8th grade Volume II.
What's the difference between analog signals and digital signals? Analog signal: it is a time-related waveform, continuous information, and its value is continuous.
Digital signal: represents the stored binary discrete state information, and takes discrete values.