"Conversion" analog and digital signals

From: http://www.elecfans.com/article/88/171/2008/2008082211604.html

 

 

What is analog signal?

Signals that change continuously in time and value are called analog signals. A simulated signal is information expressed by a continuously changing physical quantity. The amplitude, frequency, or phase of the signal changes continuously at any time, such as the current broadcast sound signal or image signal.

What is a digital signal?

Digital signals indicate that the value of the amplitude is discrete, and the value of the amplitude is limited to a finite number. Binary Code is a digital signal. Binary codes are less affected by noise and easy to process with digital circuits. Therefore, binary codes are widely used.

Digital Signal Features

(1) strong anti-interference ability and no noise accumulation. In analog communication, in order to improve the signal-to-noise ratio, the attenuation transmission signal must be amplified in a timely manner during signal transmission, the noise superimposed on the signal during transmission is also magnified at the same time. As the transmission distance increases, the noise accumulation increases, causing serious deterioration of transmission quality.

For digital communication, because the amplitude of a digital signal is a finite discrete value (usually two amplitude values), although it is also subject to noise interference during transmission, however, when the signal-to-noise ratio deteriorates to a certain degree, that is, the method of decision regeneration is adopted at an appropriate distance, and then the same digital signal as the original sending end without noise interference is generated, therefore, long-distance high-quality transmission can be achieved.

(2) Easy to encrypt. The security and confidentiality of information transmission are becoming more and more important. digital communication encryption is much easier to process than analog communication. Taking voice signals as an example, after digital transformation, the signal can be encrypted and decrypted using simple digital logic operations.

(3) easy to store, process, and exchange. The signal format of digital communication is the same as that used by computers. It is binary code. Therefore, it is easy to connect to computers and to store, process, and exchange digital signals, the management and maintenance of communication networks can be automated and intelligent.

(4) devices facilitate integration and miniaturization. Digital Communication uses time-division multiplexing and does not require a large filter. Most of the circuits in the device are digital circuits, which can be implemented by large-scale and ultra-large-scale integrated circuits, so they are small in size and low in power consumption.

(5) easy to form a comprehensive digital network and a comprehensive business digital network. Using digital transmission, you can use a programmable digital exchange device for digital exchange to achieve the integration of transmission and exchange. In addition, telephone services and various non-telephone services can be digitalized to form a comprehensive business digital network.

(6) The occupied channel bandwidth is wider. The bandwidth of one analog phone is 4 kHz, and the bandwidth of one digital phone is about 64 kHz, which is the main reason why analog communication is still active. With the extensive use of broadband channels (optical cable and digital microwave) (thousands of telephones can be activated for one pair of optical cables) and the development of digital signal processing technology (the digital rate of a digital phone can be reduced from 64 KB/s to 32 kb/s or even lower digital rate ), the bandwidth of digital phones is no longer a major problem.

According to the above introduction, digital communication has many advantages, so all countries are actively developing digital communication. In recent years, China's digital communication has developed rapidly and is moving towards high-speed, intelligent, broadband and integration.

Differences between analog and digital signals:

Analog and digital signals

Different data must be converted to corresponding signals for transmission: analog data generally uses analog signals (analog signal), 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 uses digital signals ), for example, we use a series of intermittent voltage pulses (for example, we can use a constant positive voltage to represent the binary number 1, and a constant negative voltage to represent the binary number 0), or optical pulse to represent. When the analog signal is represented by a continuously changing electromagnetic wave, the electromagnetic wave itself is both a signal carrier and a transmission medium. When the analog signal is represented by a continuously changing signal voltage, it is generally transmitted through traditional analog signal transmission lines (such as telephone networks and cable television networks. When the digital signal is expressed by intermittent voltage or optical pulse, it is generally necessary to connect the communication parties with twisted pair wires, cables or optical fiber cables to transmit the signal from one node to another.