电子与通信技术专业英语Unit 2 Reading Material

1、PART17. Digital Voltmeter A voltmeter is used to measure the voltage in volts. A voltmeter is always connected across the two point of the device under test. Since voltmeters are always connected in parallel with the component or components under test, any current through the voltmeter will contribu

2、te to the overall current in the tested circuit, potentially affecting the voltage being measured. An electronic digital voltmeter gives a reading on a numerical display (e.g. LED). It eliminates errors due to parallax that can arise in instruments requiring the position of a pointer on a scale to b

3、e estimated and also has a very high input resistance (e.g.l0 M). The simplified block diagram and the waveforms is shown in Fig.R7-1, it help us to follow the action. The D.C. voltage to be measured is fed to one input of a voltage comparator. The other input of the comparator is supplied by a ramp

4、 generator which produces a repeating sawtooth waveform. The output from the comparator is high (1) until the ramp voltage equals the input voltage when it goes low (0). PART17. Digital VoltmeterFig.R7-1 Block Diagram and the Waveforms of Digital VoltmetePART17. Digital Voltmeter The comparator outp

5、ut is applied to one input of an AND gate, the other input of the gate being fed by a generator. When both these inputs are high, the gate opensand gives a high output, i.e. a pulse. The number of steady train of pulses from a pulse output pulses so obtained from the AND gate depends on the length o

6、f the comparator output pulse, i.e. on the time taken by the ramp voltage to reach the value of the input voltage. If the ramp is linear, this time is proportional to the input voltage. The output pulses from the AND gate are recorded by a binary counter and then converted into decimal form by a dec

7、oder before being passed on to the display. The whole process commences when the voltmeter is switched on and a pulse from a trigger circuit starts the ramp generator and sets the counter to zero. When the input voltage is of the order of millivolts, it is amplified before being measured. With some

8、additional circuitry the voltmeter can be adapted for use as a multimeter to measure A.C. voltages, current and also resistance.PART28. Touchsreen A touchscreen is an intuitive computer input device that works by simply touching the display screen, either by a finger, or with a stylus, rather than t

9、yping on a keyboard or pointing with a mouse (Fig.R8-1). The touchscreen interface whereby users navigate a computer system by touching icons or links on the screen itself is the most simple, intuitive, and easiest to learn of all PC input devices and is fast becoming the interface of choice for a w

10、ide variety of applications, such as:Fig.R8-1 TouchscreenFig.R8-2 Public Information SystemsPART2 Public Information Systems (as Fig.R8-2): Information kiosks, tourism displays, and other electronic displays are used by many people that have little or no computing experience. The user friendly touch

11、sreen interface can be less intimidating and easier to use than other input devices, especially for novice users, making information accessible to the widest possible audience. Restaurant/POS Systems: Time is money, especially in a fast paced restaurant or retail environment. Because touchsreen syst

12、ems are easy to use, overall training time for new employees can be reduced. And work can get done faster, because employees can simply touch the screen to perform tasks, rather than entering complex key strokes or commands. Customer Self-Service: In todays fast pace world, waiting in line is one of

13、 the things that have yet to speed up. Self-service touchscreen terminals can be used to improve customer service at busy stores, fast service restaurants, transportation hubs, and more. Control/Automation Systems: The touchsreen interface is useful in systems ranging from industrial process control

14、 to home automation. By integrating the input device with the display, valuable workspace can be saved. And with a graphical interface, operators can monitor and control complex operations in real-time by simply touching the screen.8. TouchsreenPART2 Any touchscreen system comprises the following th

15、ree basic components(as Fig.R8-3). A touchscreen sensor panel, that sits above the display and which generates appropriate voltages according to where, precisely, it is touched. A touchsreen controller, that processes the signals received from the sensor and translates there into touch event data wh

16、ich is passed to the PCs processor, usually via a serial or USB interface. A software driver provides an interface to the PCs operating system and which translates the touch event data into mouse events, essentially enabling the sensor panel to emulate a mouse. There are several types of touchscreen

17、s. Here we discuss the infrared touchscreens. Infrared touchscreens are based on light-beam interruption technology. Instead of placing a layer on the display surface, a frame surrounds it. The frame assembly is8. TouchsreenFig.R8-3 Components of Touchscreen SystemPART2comprised of printed wiring bo

18、ards on which the opto-electronics are mounted and is concealed behind an IR-transparent bezel. The frame contains light sources or light-emitting diodeson one side, and light detectors-or photosensors on the opposite side. The effect of this is to create an optical grid across the screen. When any

19、object touches the screen, the invisible light beam is interrupted, causing a drop in the signal received by the photosensors. Based on which photosensors stop receiving the light signals, it is easy to isolate a screen coordinate. Infrared touch systems are solid state technology and have no moving

20、 mechanical parts. As such, they have no physical sensor that can be abraded or worn out with heavy use over time. Furthermore, since they do not require an overlaywhich can be brokenthey are less vulnerable to vandalism and also extremely tolerant of shock and vibration.8. TouchsreenPART3 HDTV or H

21、igh Definition TV (as shown in Fig.R9-1) refers to those amazingly realistic audio and video signals received via cable or satellite. Your decoder receives these signals and converts them to high quality audio/video. HDTV implies a larger aspect ratio wide screen TV in your home theater system, the

22、way movies were always meant to be viewed. HDTV resolution is far superior compared to traditional TV, which is why it is preferred. A conventional, analog TV uses a cathode ray tube to deliver images to you, which limits the quality of the image. The screen resolution of an analog TV is about 512x4

23、00 pixels. HDTV uses a digital display, like your computer monitor, and the screen resolution is at least 1280 x720 pixels, which is comparable to a high-end computer display. A higher screen resolution means a crisper, clearer picture. In addition to dramatically improved picture quality, HDTV also

24、 offers a wider format. This makes an HDTV image more like a movie-screen image. The width-to-height ratio called the aspect ratio of HDTV is 16:9. Analog TV has an aspect ratio of only 4:3. The difference in aspect ratio is most noticeable when watching theatrical movies on TV. For analog TV, the m

25、ovie must be cut down in a process called pan and scan, in which a part of every scene is deleted to fit the lower aspect ratio. The only way to see the entire movie scene on an analog 9. High Definition TV (HDTV)PART3TV is to letterbox the movie. In letterboxing, the full movie is shown in the midd

26、le of the screen with black bars at the top and bottom. HDTV eliminates letterboxing and allows you to see the complete movie on the whole TV screen. The Federal Communications Commission (FCC) agrees with TV networks and manufacturers that digital television, including HDTV, should be the new stand

27、ard for broadcasting. As of May 1999, the FCC requires the top TV networks to broadcast a digital signal in the 10 biggest markets, which represent 30 percent of TV households in the U.S. The networks plan to expand digital coverage and phase out analog TV broadcasts entirely by the end of 2006. 9.

28、High Definition TV (HDTV)Fig.R9-1 High Definition TVPART4 Digital audio is the representation of audio information in digital (discrete level) formats. The use of digital audio allows for simple transmission, storage, and processing of audio signals. Audio Digitization Audio digitization is the conv

29、ersion of analog audio sounds into digital form. To convert an analog audio signal to digital form, the analog signal is digitized by using an analog-to-digital (pronounced A to D) converter. The A/D converter periodically senses (samples) the level of the analog signal and creates a binary number o

30、r series of digital pulses that represent the level of the signal (as shown in Fig.R10-1). The typical sampling rate for the conversion of analog audio ranges from 8,000 samples per second (for telephone quality) to 44,000 samples per second (for music quality).10. Digital AudiFig.R10-1 A/D converte

31、r and D/A converterPART410. Digital Audi Audio Compression Audio compression is the analysis and processing of digital sound to a form that reduces the space required for transmission or storage. Audio compression coders and decoders (codecs) analyze digital audio signals to remove signal redundanci

32、es and sounds that cannot be heard by humans. Digital audio data is random in nature unlike digital video which has repetitive information that occurs on adjacent image frames. This means that audio signals do not have a high amount of redundancy, making traditional data compression and prediction p

33、rocesses ineffective at compressing digital audio. It is possible to highly compress digital audio by removing sounds that can be heard or perceived by listeners through the process of perceptual coding. Audio Coding The type of coder (type of analysis and compression) can dramatically vary and diff

34、erent types of coders may perform better for different types of audio sounds (e.g. speech audio as compared to music). The MPEG system allows for the use different types of audio coders. The type of coder that is selected can vary based on the application (such as playing music or speech) and the ty

35、pe of device the audio is being played through (such as a television or a battery operated portable media player). ThePART410. Digital AudiMPEG speech coders range from low complexity (layer 1) to high complexity (layer 3). A new version of audio coder has been created (advanced audio codec-AAC) tha

36、t offers better audio quality at lower bit rates. The AAC coder also has several variations that are used in different types of applications (e.g. broadcast radio -vs.- real time telephony). Multichannel Audio Multichannel audio is the use of multiple sound channels to produce an enhanced listening

37、experience. Examples of multichannel audio include stereo, surround sound and low frequency enhancement (LFE). The MPEG system was designed to allow the combination of multiple audio channels (such as stereo). Many types of audio applications can benefit from the high quality, power efficiency, spac

38、e savings and ease of use in TIs all-digital audio solution. These include consumer entertainment such as HTIB, DVD receivers and mini/micro systems, PC gaming and entertainment applications, business applications, such as speakerphones and multimedia conferencing systems, and digital headsets for a

39、ll application areas. In addition, TIs all-digital audio solution will enhance automotive entertainment, reducing space and heat dissipation for manufacturers while allowing consumers to enjoy the experience of high-quality multichannel digital audio in their vehicles (as shown in Fig.R10-2).PART410

40、. Digital AudiFig.R10-2 Digital Audio SystemPART511. Home Theatre System A home theater consists of audio and video equipment that transforms your home into a movie theater. Your home theater system could comprise of a large screen TV, a DVD player an AV receiver or stereo and speakers (as shown in

41、Fig.R11-1). Anything else is optional and will enhance your enjoyment. Home theater design is fundamentally based on how easy it is to use and set up, easy maintenance, good performance and looks, of course. Your home theater system can be located anywhere in your home convenient to you.Fig.R11-1 Ho

42、me Theatre SystemPART511. Home Theatre System Home theater systems are designed to provide the real theater like environment. Besides the visual effects, sound is very crucial to creating the real theater like environment. You must have watched movies in a theater. One thing that always captivates t

43、he audience is the sound the Dolby Surround sound, which makes you feel like you are in middle of the action. So what is Dolby surround sound? The Dolby Surround process involves encoding four channels of information into a two-channel signal. A decoder then decodes the signal and sends it to approp

44、riate destinationLeft, Right, Rear, and Phantom Center. In Dolby Surround, the main sounds come from the left and right channels, the vocal or dialog come from the center Phantom channel, and finally the ambience effect is generated from the rear channel. Dolby surround system was the first to intro

45、duce surround sound in home theater system. It evolved into Dolby Surround Pro Logic, Dolby Digital EX, and THX Surround EX. Presently the current standard in surround sound is Dolby Digital 5.1 channel. Dolby Digital is widely used in laser discs, satellite programming, and DVDs. To get Dolby Digit

46、al surround sound you should have a discrete Dolby surround sound decoder in the DVD player and Dolby surround sound preamplifier or Dolby digital surround sound receiver.PART511. Home Theatre System If you have always coveted a particular type of home theatre system, you can take those home theater

47、 pictures when you go shopping for your system. It will also help if you have a professional helping you with the home theater design. If you enjoy do it yourself projects, you can check around and get information on different types of systems. Home theater magazines and home theater system reviews

48、online can help a great deal. After making your plan for how exactly you would like to set up your home theater, next comes creating the atmosphere with home theater furniture, setting up speakers, wiring, lighting, storage cabinets, etc. Seating is an important aspect of your home theaters. You can

49、 have recliners, couches, or just regular chairs. Both type of seating and locating them is an important decision. Depending on how much space you have, you can decide how many seats to install, as you will have to maintain the right angle and distance from the screen.PART612. Set-top Box(STB) ASet-

50、top Box(STB) is aninformation appliancedevice that generally contains atunerand connects to a television setand an external source ofsignal, turning the source signal intocontentin a form that can then be displayed on the television screenor otherdisplay device. Set-top boxes can also enhance source

51、 signal quality. They are used incable television (as Fig.R12-1)and satellite televisionsystems, as well as other uses.Fig.R12-1 A Set-top Box(STBPART612. Set-top Box(STB) Set-top boxes were also made to enableclosed captioningon older sets in North America, before this became a mandated inclusion i

52、n newTV sets. Some have also been produced to mute theaudio(or replace it with noise) whenprofanityis detected in the captioning, where the offensive word is also blocked. Some also include a V-chip that allows only programs of some television content ratings. A function that limits childrens time watching TV or playing video gamesmay also be built in, though some of these work on main electricity rather than the video signal. Hybrid set-top boxes, such as those used forSmart TVprogramming, enable viewers to