Television was first developed bybritainengineerJohn Logie Baird Invented in 1925, the working process of the television system is that the sending end converts the various fine parts of the scene into electrical signals according to brightness and chroma, and then transmits them sequentially.Display the brightness and chroma of each micro part at the receiving end according to the corresponding geometric position to reproduce the whole pictureoriginalImage.[1]
November 2023，SARFT issued three notices on the industry standards of radio and television and network audiovisual, including the Technical Requirements for Cable TV Business, requiring cable TV terminals to provide two "power on mode" options: "power on to full screen live broadcast" and "power on to interactive home page highlighting live broadcast channels". The default setting of the system should be "power on to full screen live broadcast".[6]
By the end of 2023, after more than four months of promotion, the first phase of work has achieved the goal of "starting to watch live broadcast, reducing the toll package by 50%, and improving the transparency of consumption".Cable TV and IPTV boot advertisements were completely canceled, and the boot time was reduced from 118 seconds at most before governance to no more than 35 seconds.[8]
TV sets are mainly composed ofTuner, audio head, audio channelPublic access, synchronous scanning channel, color control display and power supply.Its working principle is as follows.
fromantennaThe signals received from the TV receiver are selected by the tuner, amplified and processed, and then a fixed IF TV signal is sent.
Public access is provided byIF amplifier, video detector, video amplifier and picture tube.The IF amplifier amplifies the IF signal from the tuner to a sufficient amplitude, detects it by the video detector, removes the IF carrier, restores the image signal, and converts the second audio IF signal.The image signal is sent to the electron emitting cathode of the picture tube after being amplified by video to control the emphasis of the electron beam emitted by the picture tube, and the image can be displayed on the fluorescent screen.
The second audio IF signal enters the audio channel for amplification and processing, and the loudspeaker emits the audio synchronous scanning channel, which mainly generates field scanning and line scanning signals.The line scanning signal enables the magnetic field generated by the deflection coil sheathed on the picture tube to control the electrons emitted by the picture tube cathode. The first line is scanned on the fluorescent screen from the upper left corner to the upper right corner, and then the next line is scanned (625 lines of the whole fluorescent screen are scanned). The field scanning signal controls the deflection coil, so that the picture has 25 fields per second (because of interlaced scanning, there are actually 2 × 25=50 pictures per second).Since the scanning position of the line and field light points is the same as the scanning position of the scene light points when the television camera tube is facing the sceneFluorescent screenIt can show the outline of the scene and the light and dark degree of each part of the scene
The power supply part is to complete the conversion from AC to DC, and the DC voltage obtained will supply power to all parts of the TV.[3]
development history
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John Logie Baird
（1) Electromechanical television:
The first television set was introduced in 1925 bybritainWas invented by John Baird, an electronic engineer in 1928,U.S.AThe RCA TV station of "The Cat" took the lead in broadcasting the first TV series Felix The Cat. Since then, television has begun to change the way of life, information dissemination and thinking of human beings.Since then,human beingsIt began to enter the era of television.From black and white to color, from analog to digital, fromsphereTo plane.In 1929, Baird's company produced Baird C-type television, which was the first mass production television in the world.[1-2]
（2) Cathode ray tube (CRT) television:
In 1933, Zvorikin, a Russian born American scientist, successfully developed a camera tube and picture tube that can be used for TV camera, and completed the process of making TV camera and picture completely electronic.Later, RCA spent four million dollars to improve and perfect the TV, which became a practical household appliance.
（3) Color Picture Tube (CPT) TV:
In 1951, H. Lo of the United States invented the three gun shadow mask color picture tube. The principle of the color picture tube is shown in the figure.Lawrence invented the single gun color picture tube.The early color picture tube television is shown in the figure.
In 1954, the United States Dexaci Instrument Company developed the first all transistor television receiver.In 1966, Radio Corporation of America developed the integrated circuit television.
Schematic diagram of color picture tube
Early Color Picture Tube Television
(4) Plasma Display Panel TV:
The first plasma display screen was born in 1964, which was invented by Professor Donald Bitzer, Professor H. Gene Slottow and graduate Robert Wilson of the University of Illinois in the United States on the basis of predecessors.They inject inert gas into the sealed space of matrix mode between two ultra-thin glass plates, and apply high voltage to make the gas produce plasma discharge to generate ultraviolet light, which excites R, G and B primary phosphors to emit light.Each pixel is an active light emitting unit. After 256 gray levels are achieved in the light emitting unit, color mixing is carried out to finally display rich colors.
(5) Liquid Crystal Display TV:
In 1981, Sony Corporation of Japan developed a pocket black and white TV set.Sharp SHARP's pioneering and innovation in the field of liquid crystal has earned it the reputation of "the father of liquid crystal".Add a substance called liquid crystal between the solid and liquid in the middle of the two glasses. After the voltage is applied between the glasses, the arrangement and zigzag changes of molecules can be controlled, so as to control the amount of light passing through the glass and achieve the purpose of reproducing the picture.
(6) Organic Light Emitting Diode TV:
OLED display schematic diagram
Ching W. Tang, a Chinese American professor born in Hong Kong, found this organic polymer in the laboratory and used it as a semiconductor material in light-emitting diodes, thus carrying out research on OLED. The display principle of OLED is shown in the figure.Each OLED display unit corresponds to a thin film transistor (TFT).The organic material sandwiched in the middle can be controlled to emit light under the drive of TFT.The unit selected by the row and column address will actively emit three different colors of light to display the image.
classification
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1. Classification according to main components used
(1) Tube TV.The main circuit of this kind of TV sets consists of 18~20 setsElectronic tube（Vacuum tube）Composition.Because the cathode of the electron tube needs to be heated to a certain extent to emit electrons and enter the working state.Therefore, electronic tube televisions consume a lot of power. The fluorescent screen is generally small and the whole machine is heavy. Most of them are early products of televisions and have been eliminated.
(2) Transistor TV.Transistor TV is also called discrete component TV. The main circuit of the whole machine is composed of more than 50 transistors and diodes.The circuit structure is complex and the failure rate is high.Maintenance and debugging are quite troublesome.With the progress of electronic technology and the updating of products, such televisions have also been eliminated.
(3) Integrated circuit television.The main circuits in the machine are integrated in one or several pieceslarge-scale integrated circuitThe functions are more and more perfect to meet the needs of users in many aspects.Integrated circuit television can be divided into four pieces, two pieces and one piece.
2. Classification by function
(1) Remote control color TV.All color TV sets produced today have remote control function.Compared with the old manual and mechanical tuning, it is more convenient to use and has more complete functions.It can enable the viewer to operate the TV while keeping a certain distance from the TV, including power on, power off, selecting program channels, adjusting volume, brightness, color saturation, etc.In addition, it can also automatically retrieve selected stations, store and memorize multiple preselected channels (30~100 programs), and regularly start and shut down.
(2) Color TV with karaoke function.The color TV with karaoke function can be matched with ordinary video recorders for karaoke singing.
(3) Video and color TV combination machine.In order to facilitate the recording, playing and karaoke singing of TV programs, some manufacturers have also produced video and color TV sets, making them a whole.
3. Classification according to the characteristics of fluorescent screen
The picture tube is the heart of the TV set and the most important device in the TV set. The fluorescent screen is the part of the picture tube that displays images. It is directly exposed to the outside of the TV set. It is simple, convenient and intuitive to classify by the characteristics of the fluorescent screen.
(1) Classification by screen reproduction color
1) Black and white TV.The fluorescent screen of this type of TV can only reproduce the brightness difference of the subject, presenting a black and white image.
2) Color TV.The fluorescent screen of such TV can not only reproduce the brightness difference of the subject, but also restore the hue and color saturation of the subject, presenting a color image.
From the perspective of image information transmission, color TV can transmit more information than black and white TV. It can reflect the actual situation of the original scenery more realistically and vividly, and has more colorful expressive force.
(2) Classified by screen size.Television screens vary in size, and people are used to using inches (diagonal size) to reflect this difference.However, the inch representation method is sometimes not accurate. For a 14 inch TV, the diagonal size of the screen may be 35cm or 37cm, so cm is directly used to represent the diagonal size in some new standard technical data.According to the size of the diagonal of the fluorescent screen, televisions can be roughly divided into three categories: medium screen, large screen and super large screen.
(3) Classified according to the flatness of the fluorescent screen.TV sets produced in the past mostly used ordinary spherical picture tubes. Due to the bending of the fluorescent screen, there was a certain degree of distortion of the picture, and the viewing angle range was relatively small.The new generation of large screen color TV sets mostly use fluorescent screens such as "right angle plane" and "super plane", which increases the viewing angle and avoids distortion of the picture.As a result, "right angle plane color TV", "super plane color TV" and "plain color TV" have appeared, mainly emphasizing the characteristics of these color TV sets in terms of the flatness of the fluorescent screen.
(4) Classified according to the width and height ratio of the fluorescent screen.Generally, the width height ratio of TV screen is 4:3 or 5:4HDTVWith the successful development of HDTV, wide screen televisions have developed rapidly, and the aspect ratio of its fluorescent screen is 16:9.
4. Classification according to signal processing mode
According to the signal processing mode, it can be divided into analog TV and digital TV.If analog TV signals (including image and audio signals) are converted into digital signals and then processed and transmitted in digital form, they must be received by digital TV.
After the TV signal is encoded with binary digital code, it has a strong anti-interference ability than the original analog signal. Even after long distance transmission and repeated recording, it can be restored almost without distortion through balanced regeneration.Digital TV is easier to adjust than analog TV, with higher reliability and stability.in especialvlsiWith the application of microprocessors and software, the production process of digital TV in the future will be simplified, the cost will be low, and the volume will be small. It can be used as a computer terminal to join the modern information network.Therefore, digital TV will eventually replace analog TV, which is the inevitable trend of TV technology development.[2]
structure
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1. Front, rear and remote control of the whole machine
Since the TV can be turned on, off, program selection, volume adjustment and various function settings with a remote control, the remote control has become an indispensable part of the TV.There are fewer and fewer control keys on the front panel of the TV, and only the power switch is necessary, because only when the power switch is turned on, the TV can enter the standby state, and the remote control can control the TV.When operating the remote control, you must aim the remote control at the "infrared receiving window" on the front panel, and various control information will be transmitted to the TV through infrared.
The rear cover of the chassis is reserved with power lines, lead-in holes for receiving antennas, and video and audio input terminals.
2. Main parts of TV
Whether it is a color TV or a black and white TV, its chassis is generally composed of three parts: front panel (front frame), middle frame and back cover.In the routine maintenance work, the front panel and the middle frame do not need to be removed, but only the back cover can be removed for general maintenance operations, so the front panel and the middle frame of some TVs are made into a whole.Remove the back cover to see the main components in the TV. They can be divided into three parts: the back cover of the chassis, the front panel, the middle frame, the picture tube, etc., the main printed board (center), and various components.[2]
Routine maintenance
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If the TV is used improperly, its life will be affected.
be carefulGeomagnetismImpact.Large screen color TVThe fluorescent screen should be placed facing south or north, so that the direction of the earth's magnetic field is consistent with the direction of the electron beam rays in the picture tube, to prevent the geomagnetism from affecting the color purity.
Pay attention to ventilation and heat dissipation.in useLarge screen color TVDo not cover plastic cloth, cloth cover, etc., and do not pad foam plastic at the bottom to avoid affecting the ventilation and heat dissipation of color TV.
Pay attention to color and volume.The color, volume, contrast, etc. of the large screen color TV should be appropriate, so that not only the viewing effect is good, but also the power is saved, and the life of the TV can be prolonged.
TV brightness should not be too large.On the premise that the image is clear, it is better to dim the brightness.If the brightness is turned on too much, first, it will accelerate the aging of the fluorescent materials of the TV, promote their premature depletion, and shorten the life of the TV;Second, it will increase power consumption, cause waste, and stimulate the eyes, resulting in decreased vision.
Pay attention to protectionKinescope。Do not move or vibrate the TV when watching programs or just shutting down, to prevent damage to the picture tube.The picture tube shall be protected from direct sunlight.[4]
Development trend
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It will become a smart home entrance similar to mobile phones and smart speakers, not only a home video entertainment center, but also an information sharing center, control management center and multi device interaction center.Communication brands led by Huawei and Glory entered the home appliance market with smart screens,[5]"Smart screen" is not only a home video entertainment center, but also an information sharing center, control management center and multi device interaction center.
With the increasing size of the screen, high-definition picture quality is an important goal of television.Both LCD and OLED are developing towards high definition 4K and 8K.In 2018, the global shipments of 4K LCD TV panels reached 110 million, accounting for just over half of the market.It is estimated that the global 8K TV shipments will reach 1.89 million by 2020 and 5.41 million by 2022.
In 2013, the sales volume of smart TV in the Chinese market exceeded the market share of non smart TV.With the acceleration of broadband and the popularization of network, the penetration rate of smart TV market will reach more than 90% by 2020.With the deep application of artificial intelligence and machine learning, TV sets will understand users better.
In January 2024, the Report on the New Trends of China's Smart TV Interaction in 2024 released by the Prospective Industry Research Institute showed that since 2016, China's TV power on rate has dropped precipitously from 70% to less than 30% in 2022[7]。
Relevant regulations
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November 2023，SARFT issued three notices on the industry standards of radio and television and network audiovisual, including the Technical Requirements for Cable TV Business, requiring cable TV terminals to provide two "power on mode" options: "power on to full screen live broadcast" and "power on to interactive home page highlighting live broadcast channels". The default setting of the system should be "power on to full screen live broadcast".According to the relevant notice, the time required for the startup of the cable TV intelligent set-top box should not be more than 35s.When providing cable TV services such as live broadcast channel, time shifted TV, channel review, video on demand, etc., cable TV operating agencies shall ensure simple and friendly interface, convenient and fast operation, and high-quality transmission of programs.The relevant notice stipulates the response time of program broadcast when the normal bandwidth available for Internet TV terminal access is not less than 100Mbps.It is required that the response time of on-demand programs from clicking the program to the first frame should be less than 2s and not more than 3.5s;The response time of program pause/play, fast forward, fast backward and other operations should be less than 2s and not more than 3.5s;The response time of the page before exiting the program and returning to play should be less than 1s.[6]
