Điện tử - Viễn thông chuyên ngành Tiếng Anh: Phần 2

Phần 2 của Tài liệu Tiếng Anh chuyên ngành Điện tử - Viễn thông gồm các nội dung từ unit 14 đến unit 20. Ngoài ra trong phần này còn cung cấp các bài kiểm tra giữa và cuối khoá học, các bài dịch mẫu cũng như phần giải đáp các bài tập của từng bài trong phần phụ lục giúp cho sinh viên tự đánh giá kết quả học tập của mình và tra cứu những đoạn dịch mẫu khi cần. Mời các bạn cùng tham khảo.
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Điện tử - Viễn thông chuyên ngành Tiếng Anh: Phần 2 Unit 14 COMPACT DISC A digital recording system, kn ow n as a co mpact disc (CD) system, wasintroduced in 1982. This uses a laser optical m e c h a n is m in w h ich a laser beam readsmarks on the surface o f a specially prepared perspex disk. It gives near-perfectreproduction o f sound and the sound quality does not deteriorate with use. Thisbreakthrough co mpletely replaced the grooved phono grap h record by the end o f the 20century. The C D differs from the standard phonograph record in two principal ways. Therecorded signal on it is in PCM digital format and it is a grooveless, co ntactless system.Instead of a groove, a C D has a spiral track ma de o f a series o f pits o f differentlengths. These pits represent the pulse code. The master disc for a C D is an optically flat glass disc co ated with a resist. Theresist is a chemi cal that is impervious to an other chemical, called an etchant, whichdissolves glass. The mast er is placed on a turntable. Abo ve it is a re co rdi ng headcontaining a laser. The digital signal to be recorded is fed to the laser, turning the laseron and off in respond to the binary on-o ff signal. W h e n the laser is on. it b u m s away asmall am ount o f the resist on the disc. While the disc turns, the recording head movesacross the disc, leaving a spiral track of elongated burns in the resist surface. After the recording is complete, the glass m a st er is placed in the c h e m i c a l etchantbath. This developing re moves glass only where the resist is burned away. The spiraltrack now contains a series o f small pits o f varying length and con stan t depth. The c om m e rc ia l C D ma ss produced from the m a st er is m a de from a clear plastic.It is about 0.05 inch (1.3 millimeters) thick. The spiral track of pits is on its top surface.This surface has a coating of al u m in u m so that it reflects light. In playing a CD, an e xtr e m el y fine laser b e am is focused on the spiral track frombeneath the disc. As the disc turns in the C D player, the laser beam is focused on thepits (seen from below the disc as bumps). At the same time, the be am m ov e s from thecenter of the disc outward, following the spiral. Since there is no m e ch a ni c al contactwith the disc, a C D player must keep the be am focused and follow the spiral bywatching how the light is reflected from the C D and correcting its position as needed.Unit 14 99 The laser beam is reflected from the bumps onto a photo detector. The photodetector sends out a signal whenever light hits it and remains off when there is notenough light. These ons and offs produce a digital signal that is the same as the originaldigital signal recorded on the CD. This signal is then decoded by a D/A converter intothe original analogue signal. The analogue signal is amplified and converted to soundby loudspeakers. (Text taken from The N e w book o f p o p u la r s cience by Grolier International. Inc.)Words and expressions coat (v) phu, trang (len) depth (n) do sau elongate (v) keo dai, lam dai etchant (n) chat khac 3n mon extremely (adv) ci/c ky, het sire focus (v) lam hoi tu, dieu tieu groove (n/v) ranh, xe ranh imperious (adj) khong tham (nirdc), khong lot (qua) introduce (v) gidi thieu, dua vao sir dung perspex (n) nhiia pech-pech pit (n) vet ro principal (adj) chinh, chu yeu spiral (adj) (thuoc, co hinh) tron oc turntable (n) ban quay, ban xoay1. M ain idea W hich sta tem en t best expresses the m ain idea o f the text? 1. Compact disk is a plastic disc for the reproduction of recorded sound. 2. The C D represents a technological advancement over the groove-and-stvlus m e ch a nis m o f the phonograph in that nothing actually touches the surface of the disc. 3. The CD is a digital recording system where data writing and reading is done using a laser beam.2. Q u estion s A n sw e r th e fo llo w in g questions. 1. What is the recording me ch a nis m o f the compact disk? 2_____________________________ Tieng A nh chuyen nganh Dien ttf - Vien thong 2. How does the C D represent the audio pattern? 3. What is special about the material with which the master disc is coated ? 4. A compact disk system called a con ...