电子与通信工程专业英语 教学课件 ppt 作者 徐存善 Unit 21

Unit 21,Digital Television & Liquid Crystal Display,Digital Television & Liquid Crystal Display,Digital Television & Liquid Crystal Display,1. Digital TV The horizontal resolution is something like 500 dots for a color analog TV set. This level of resolution was amazing 50 years ago, but today it is rather passe. The lowest resolution computer monitor that anyone uses today has 640×480 pixels, and most people use a resolution like 800×600 or 1024×768. We have grown comfortable with the great clarity and solidity of a computer display, and analog TV technology pales by comparison.,1.数字电视 一个模拟彩电的水平分辨率约500点，这个分辨率在50年前是很高的，但今天却过时了。现在所用的计算机显示器最低分辨率为640×480像素，很多人用的是分辨率为800×600或1024×768像素的显示器。计算机的显示器正在变得更加清晰和可靠，相比之下，模拟电视技术就比较逊色了。,许多新的卫星(电视)系统以及DVD，是采用可以提供十分清晰图像的数字编码机制。这种系统中，数字信息被转换成模拟格式，以便显示在模拟电视机上。与VHS式图像相比，这种图像很清晰，但如果不把这些图像转换成模拟格式，图像将会更加清晰。,Many of the new satellite systems，as well as DVDs, use a digital encoding scheme that provides a much clearer picture. In these systems, the digital information is converted to the analog format to display it on your analog TV. The image looks great compared to a VHS tape, but it would be twice as good if the conversion to analog didnt happen.,现在，正逐渐把所有模拟电视机转换成数字电视机，这样数字信号就可以直接驱动我们的电视机。 当提到数字电视时，指的是纯数字电视信号传输以及用数字电视机接收并播放这些数字信号。数字信号可以无线传播，也可以通过有线及卫星传播，在家中通过一个解调器以数字形式接收数字信号并直接在数字电视机上播放。,There is now a big push underway to convert all TV sets from analog to digital, so that digital signals drive your TV set directly. When you read and hear people talking about digital television (DTV), what they are talking about is the transmission of pure digital television signals, along with the reception and display of those signals on a digital TV set. The digital signals might be broadcast over the air or transmitted by a cable or satellite system to your home. In your home, a decoder receives the signal and uses it, in digital form, to directly drive your digital TV set.,There is a class of digital television that is getting a lot of press right now. It is called highdefinition television, or HDTV. HDTV is highresolution digital television combined with Dolby Digital surround sound(AC-3). This combination creates a stunning image with stunning sound. HDTV requires new production and transmission equipment at the HDTV stations, as well as new equipment for reception by the consumer. The higher resolution picture is the main selling point for HDTV. Imagine 720 or 1080 lines of resolution compared to the 525 lines people are used to in the United States (or the 625 lines in Europe)it ' s a huge difference !,现在有一种很吸引人的数字电视，称为高清晰度电视(HDTV)，它是高分辨率数字电视与杜比环绕数字立体声(Ac3)的结合，这个结合创造了最好的图像和最好的声音。HDTV要求HDTV电视台有新的制作和传输设备，还要求用户有新的接收设备。高分辨率图像是HDTV主要卖点。720或1080线分辨率的图像与如今美国525线分辨率(或欧洲625线分辨率)的图像相比，图像绝对要清晰得多。,2. LCD(液晶显示器) 在便携式电脑、数字钟表、微波炉、CD播放器和许多其他日用电子产品中都含有液晶显示器(LCD)。LCD之所以如此普及是因为与其他显示技术相比它确实有优点。它比CRT薄、轻且功耗小。,2. Liquid Crystal Display (LCD) You probably use items containing an LCD (1iquid crystal display) every day. They are all around us in laptop computers, digital clocks and watches, microwave ovens, CD players and many other electronic devices. LCDs are common because they offer some real advantages over other display technologies. They are thinner and lighter and draw much less power than cathode ray tubes (CRTs).,One feature of liquid crystals is that theyre affected by electric current. A particular sort of nematic liquid crystal, called twisted nematics (TN), is naturally twisted. Applying an electric current to these liquid crystals will untwist them to varying degrees, depending on the currents voltage. Theres far more to building an LCD than simply creating a sheet of liquid crystals. The combination of four facts makes LCD possible:,液晶的一个特点是液晶易受电流影响，一种特殊的被称为扭曲向列液晶的向列液晶本身是扭曲的，在这种液晶中有电流流过时，液晶根据所加的电压，向不同的角度解开扭曲。 并不是简单地铺一层液晶就可以做成LCD，做成一个LCD要结合以下四点：,Light can be polarized. Liquid crystals can transmit and change polarized light. The structure of liquid crystals can be changed by electric current. There are transparent substances that can conduct electricity. An LCD is a device that uses these four facts in a surprising way! There are two main types of LCDs used in computers, passive matrix and active matrix.,偏振光的产生 液晶可以传输和改变偏振光 液晶的结构可以用电流来改变 有可以导电的透明物质 LCD就是奇妙地结合了这四种技术的产品。 电脑所用的LCD主要有两种类型：被动矩阵式和主动矩阵式。,大部分LCD显示器采用主动矩阵技术，在显示器的玻璃上，薄膜晶体管 (TFT) 以矩阵形式排列小晶体管和电容。为定位某个像素，相应行的开关合上，然后把电荷送到相应的列上。因为该列上其他点的行开关都断开，只有指定像素点的电容接收电荷。电容可以保持这个电荷直到下一次刷新周期。,Most LCD displays use active matrix technology. A thin film transistor (TFT) arranges tiny transistors and capacitors in a matrix on the glass of the display. To address a particular pixel, the proper row is switched on, and then a charge is sent down the correct column. Since all of the other rows that the column intersects are turned off, only the capacitor at the designated pixel receives a charge. The capacitor is able to hold the charge until the next refresh cycle.,另一种LCD技术是被动矩阵技术，这种LCD显示器用一个导电金属栅格给各像素点充电，虽然制造成本比较低，但现在被动矩阵显示器很少用，因为与主动矩阵技术相比这种技术响应速度慢，且电