《电子信息类专业英语 教学课件 ppt 作者 温丹丽unit 4 Reading Material 》由会员分享，可在线阅读，更多相关《电子信息类专业英语 教学课件 ppt 作者 温丹丽unit 4 Reading Material （9页珍藏版）》请在金锄头文库上搜索。
1、电子信息类专业英语,http:/,机械工业出版社同名教材配套电子教案,温丹丽 高源 制作,Reading Material Digital Displays,Text The first digital display devices were mechanical, made up of numbered wheels and driven by servo-controlled motors（伺服控制电机）. Next on the scene were various formats consisting of miniature（微型的）incandescent（白炽的）lamps.
2、These devices evolved to a surprisingly satisfactory state of the art and gave rise to control techniques that now enable the popular light emitting diodes (LED)（发光二级管）and liquid-crystal displays (LCD)（液晶显示屏）to dominate（支配）instrumentation readouts.,机械工业出版社 http:/,Reading Material Digital Displays,Th
3、e weak link in the incandescent lamp display is the fragile（易脆的） filament. Even when operated at low current, the incandescent bulb had life expectancy that is measured in hours. Short life notwithstanding, the thermal（热的）response time of the filament（灯丝）also poses a problem in instrument readouts w
4、ith a relatively long lag time（延迟时间）. Although lamps are little used now, they established the popular seven-segment display format that is used by all digital readouts today.,机械工业出版社 http:/,Reading Material Digital Displays,Gas-discharge plasma（等离子体）readouts emit light via the ionization（离子化）of neo
5、n-argon（氩氖）, and other noble gases（惰性气体）. A small amount of mercury（汞）is often used to manipulate the ionization potential and to modify the spectrum（光谱）. These displays have been made into many forms, some of which have external electrodes. Light output is very good and the definite on-off characte
6、ristics of plasma devices allow for convenient multiplexing（多路技术）. A long-enduring and very satisfactory gas-discharge readout was the Nixie tube（阴极管） made by Burroughs. These neon display tubes had nine internal cathodes, each shaped as a digit. The cathodes were stacked one behind the other in a l
7、ine perpendicular（垂直的，正交的） to the line of sight. When a cathode was selected for excitement, it would glow in the shape of the number it represented. The fact that the nine digits were each in a different plane was somewhat disconcerting（令人不安的）, but acceptable. A disadvantage of plasma displays is t
8、he high ionization potential required to ignite（点燃）the lamp. It is on the order of 150 to 200 volts, which creates interfacing problems with todays low-voltage, solid-state circuitry. While no longer the dominant readout, plasma displays continue to find applications. The truth table of seven-segmen
9、t display module is shown in Fig.4-2.,机械工业出版社 http:/,Reading Material Digital Displays,Display Format of Segmented module,Fig.4-2 Seven-segment display,机械工业出版社 http:/,Reading Material Digital Displays,Vacuum fluorescent（荧光的）readouts were also a product of vacuum-tube technology. The fluorescent read
10、out had a multiplicity（多样性）of anodes（阳极，正极）that were coated（涂上一层）with a light-emitting phosphor（磷）similar to the material found inside fluorescent lamps. While blue-green was the most popular color, others existed. The anode would fluoresce when bombarded（轰击）by electrons from the cathode emitter. In
11、 most cases, the digit was formed using the seven-segment format described above. While these readout devices had the shortcomings inherent to vacuum tubes, including their fragile, short-lived filaments and high voltage requirements, they nevertheless had considerable aesthetic（有审美观的）appeal and sti
12、ll find their way into modern application, such was automotive and compute displays.,机械工业出版社 http:/,Reading Material Digital Displays,Electro luminescent（发光的）display also makes use of a light-emitting phosphor. Instead of the electron tube structure, though, these displays are essentially capacitors
13、. A phosphor-rich film is sandwiched between two transparent, conductive plates. When a voltage is applied to the plates, the capacitance（电量，电容） displacement current excites the phosphor and caused it to glow. Light emitting diode devices, developed as a result of continued advancement with semicond
14、uctor materials and fabrication（制作）, are the workhorses of digital display. They are bright, cost-effective, compatible with solid-state voltage and current levels, and long lasting. Originally available only in red, LEDs now come in a wide range of colors, including red, orange, yellow, green, and
15、blue.,机械工业出版社 http:/,Reading Material Digital Displays,Liquid crystal displays (LCDs) do not emit light, but instead alter the characteristics of the crystal material to reflect incident（易于发生的） light. Optically, LCDs shine where LEDs fail; the brighter the ambient（周围的）light, the brighter the LED dis
16、play. Conversely, LEDs wash out with increasing ambient light levels, and can scarcely be seen. On the other hand, the LCD display becomes shadowy at the low light levels at which the LED offers maximum readability. Because they are not light emitters, LCD displays offer the lowest power consumption of any electrical
