Broadband coaxial cable
Coaxial cable systems that use limited television cables for analog signal transmission are called broadband coaxial cables. The term "broadband" comes from the telephone industry and refers to a frequency band wider than 4kHz. However, in computer networks, "broadband cable" refers to any cable network that uses analog signals for transmission.
Because the broadband network uses standard cable TV technology, the usable frequency band is up to 300MHz (often to 450MHz); due to the use of analog signals, an electronic device needs to be placed at the interface to convert the bit stream entering the network into analog signals, and Convert the signal output by the network into a bit stream.
Broadband systems are divided into multiple channels, and TV broadcasting usually occupies a 6MHz channel. Each channel can be used for analog TV, CD quality sound (1.4Mb / s) or 3Mb / s digital bitstream. TV and data can be mixed and transmitted on one cable.
One of the main differences between wideband systems and baseband systems is that wideband systems cover a wide area, so analog amplifiers are required to periodically strengthen the signal. These amplifiers can only transmit signals in one direction. Therefore, if there is an amplifier between computers, the packet packets cannot be reversed between computers. To solve this problem, people have developed two types of broadband systems: dual-cable systems and single-cable systems.
1) Double cable system The double cable system has two identical cables laid side by side. In order to transmit data, the computer transmits the data to several devices at the root of the cable through the cable 1, namely the head-end, and then the top-end device transmits the signal along the cable down through the cable 2. All computers are sent via cable 1 and received via cable 2.
2) Another solution for the single-cable system is to allocate different frequency bands for internal and external communications on each cable. The low frequency band is used for communication from the computer to the top device. The signal received by the top device is moved to the high frequency band and broadcast to the computer. In subsplit systems, the 5MHz ~ 30MHz frequency band is used for inbound communication, and the 40MHz ~ 300MHz frequency band is used for outbound communication. In the midsplit system, the inward frequency band is 5MHz ~ 116MHz, while the outward frequency band is 168MHz ~ 300MHz. This choice is caused by historical reasons.
3) There are many ways to use the broadband system. A dedicated permanent channel can be allocated between a pair of computers; other computers can apply to establish a temporary channel through the control channel, and then switch to the applied channel frequency; you can also make all Computers share one or a group of channels. Technically speaking, broadband cable is worse than baseband (ie single channel) cable in transmitting digital data, but its advantage is that it has been widely installed.
With the maturity of TFT technology in the early 1990s, color LCD flat-panel displays developed rapidly. In less than 10 years, TFT-LCD has rapidly grown into a mainstream display, which is inseparable from its advantages. The main features are:
(1) Good use characteristics: low-voltage applications, low driving voltage, and improved safety and reliability of solid use; flat panel, light and thin, saving a lot of raw materials and use space; low power consumption, its power consumption is about CRT display One-tenth of that, reflective TFT-LCD is even only about one-hundredth of CRT, saving a lot of energy; TFT-LCD products also have specifications, models, and sizes in series, with various varieties, convenient and flexible use, maintenance, and update , Easy to upgrade, long service life and many other features. The display range covers the application range of all displays from 1 inch to 40 inches and large projection planes. It is a full-size display terminal; the display quality ranges from the simplest monochrome character graphics to high resolution and high color fidelity. Various specifications and models of video displays with high brightness, high contrast and high response speed; display methods include direct view, projection, see-through, and reflective.
(2) Good environmental protection characteristics: no radiation, no flicker, no harm to the user's health. In particular, the emergence of TFT-LCD e-books will bring mankind into the era of paperless office and paperless printing, triggering a revolution in human learning, dissemination, and recording of civilization.
(3) The application range is wide, and it can be used normally in the temperature range from -20°C to +50°C. The low temperature working temperature of the TFT-LCD after temperature reinforcement can reach minus 80°C. It can be used as a mobile terminal display, a desktop terminal display, and a large-screen projection TV. It is a full-size video display terminal with excellent performance.
(4) The degree of automation of manufacturing technology is high, and the characteristics of large-scale industrial production are good. The TFT-LCD industry technology is mature, and the mass production yield rate has reached more than 90%.
(5) TFT-LCD is easy to integrate and upgrade. It is a perfect combination of large-scale semiconductor integrated circuit technology and light source technology, and has great potential for continued development. At present, there are amorphous, polycrystalline and monocrystalline silicon TFT-LCDs. In the future, there will be TFTs of other materials, including glass substrates and plastic substrates.
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