第一篇：北華大學(xué)電子信息工程專業(yè)英語(yǔ)期末翻譯(The Application of DSP in medicine)

原文：信息26

The problem of overlapping structures was solved in 1971 with the introduction of the first computed tomography scanner(formerly called computed axial tomography,or CAT scanner).Computed tomography(CT)is a classic example of Digital Signal Processing.X-rays from many direction are passed through the section of the patient's body being examined.Instead of simply forming images with the detected X-ray, the signals are converted into digital data and stored in a computer.The information is then used to calculate images that appear to be slices through the body.These images show much greater detail than conventional techniques, allowing significantly better diagnosis and treatment.The impact of CT was nearly as large as the original introduction of X-ray imaging itself.Within only a few years, every major hospital in the world had access to a CT scanner.In 1979, two of CT's principle contributors, Godfrey N.Hounsfield and Allan M.Cormack, shared the Nobel Prize in Medicine.That's good DSP!

The last three X-ray problems have been solved by using penetrating energy other than X-rays, such as radio and sound waves.DSP plays a key role in all these techniques.For example, Magnetic Resonance Imaging(MRI)uses magnetic fields in conjunction with radio waves to probe the interior of the human body.Properly adjusting the strength and frequency of the fields cause the atomic nuclei in a localized region of the body to resonate between quantum energy states.This resonance results in the emission of a secondary radio 10 The Scientist and Engineer's Guide to Digital Signal Processing wave, detected with an antenna placed near the body.The strength and other characteristics of this detected signal provide information about the localized region in resonance.Adjustment of the magnetic field allows the resonance region to be scanned throughout the body, mapping the internal structure.This information is usually presented as images, just as in computed tomography.Besides providing excellent discrimination between different types of soft tissue, MRI can provide information about physiology, such as blood flow through arteries.MRI relies totally on Digital Signal Processing techniques, and could not be implemented without them.Space

Sometimes, you just have to make the most out of a bad picture.This is frequently the case with images taken from unmanned satellites and space exploration vehicles.No one is going to send a repairman to Mars just to tweak the knobs on a camera!DSP can improve the quality of images taken under extremely unfavorable conditions in several ways: brightness and contrast adjustment, edge detection, noise reduction, focus adjustment, motion blur reduction, etc.Images that have spatial distortion, such as encountered when a flat image is taken of a spherical planet, can also be warped into a correct representation.Many individual images can also be combined into a single database, allowing the information to be displayed in unique ways.Forexample, a video sequence simulating an aerial flight over the surface of a distant planet.信息26

Commercial Imaging Products

The large information content in images is a problem for systems sold in massquantity to the general public.Commercial systems must be cheap, and this doesn't mesh well with large memories and high data transfer rates.One answer to this dilemma is image compression.Just as with voice signals, images contain a tremendous amount of redundant information, and can be run through algorithms that reduce the number of bits needed to represent them.Television and other moving pictures are especially suitable for compression, since most of the image remain the same from frame-to-frame.Commercial imaging products that take advantage of this technology include: video telephones, computer programs that display moving pictures, and digital television.譯文：

1971年，隨著第一臺(tái)計(jì)算機(jī)斷層掃描儀的發(fā)明，重疊結(jié)構(gòu)的問(wèn)題解決了。（計(jì)算機(jī)斷層掃描儀之前叫做計(jì)算機(jī)X射線軸向分層造影掃描儀，也就是CAT 掃描儀）。計(jì)算機(jī)斷層掃描儀是數(shù)字信號(hào)處理比較典型的例子。我們用各個(gè)方向的X射線掃描病人身體來(lái)查出病理。信號(hào)轉(zhuǎn)變?yōu)閿?shù)字化數(shù)據(jù)并存儲(chǔ)在電腦中，而不是用檢測(cè)到的信號(hào)簡(jiǎn)單成像.之后用這些信息計(jì)算出似乎是通過(guò)身體切片的圖像。這些圖像比傳統(tǒng)的技術(shù)顯示的圖像更加清晰，這就使診斷和治療更有效。CT的影響幾乎和X射線成像本身的發(fā)明的影響是一樣重要。在短短幾年里，世界上所有大醫(yī)院都引進(jìn)了CT掃描儀。1971年科馬克和亨斯菲爾德因發(fā)明CT掃描儀獲得諾貝爾醫(yī)學(xué)獎(jiǎng)。DSP真好。

通過(guò)使用穿透能量比如無(wú)線電波和聲波解決了最后三個(gè)X射線問(wèn)題，而不是用X射線。DSP在所有這些技術(shù)里發(fā)揮著至關(guān)重要的作用。比如說(shuō)，核磁共振成像（MRI）使用磁場(chǎng)結(jié)合無(wú)線電波探測(cè)人體的內(nèi)部。適當(dāng)?shù)卣{(diào)整磁場(chǎng)的頻率和強(qiáng)度就會(huì)引起身體特定部位原子的共振，共振在原子能量級(jí)之間進(jìn)行。這種共振會(huì)發(fā)射出另一種無(wú)線電信號(hào)，科學(xué)家和工程師用DSP技術(shù)來(lái)處理放在人體周圍天線檢測(cè)到的這種信號(hào)。這種檢測(cè)到的信號(hào)的波長(zhǎng)和其他特性決定了共振的區(qū)域。電磁場(chǎng)的變化使得通過(guò)身體的共振區(qū)域能夠被掃描并成像。就像在CT中那樣，這種信息以圖像的形式呈現(xiàn)出來(lái)。MRI不僅能精確的區(qū)分不同的軟組織，還能提供生理機(jī)能的信息，比如血液在動(dòng)脈的流動(dòng)。MRI完全依賴于DSP技術(shù)，沒(méi)有DSP，就沒(méi)有MRI。

太空

有時(shí)，你必須把一張損壞的圖片還原。從無(wú)人操縱的衛(wèi)星和太空探測(cè)器中提取圖像是很頻繁的事情。我們總不可能把修理工人帶上火星去控制照相機(jī)的把手吧！DSP能用很多方法提高在極其不利的條件下拍的圖像的質(zhì)量，例如：調(diào)整亮度和對(duì)比度，檢測(cè)銳度，降低噪聲，調(diào)整焦距，減少移動(dòng)的污跡等等?？臻g變形的圖像可能扭曲成一個(gè)正確的表示，例如遇見(jiàn)拍攝球形行星的平面圖。許多獨(dú)特的圖像也可以結(jié)合為一個(gè)單獨(dú)的數(shù)據(jù)庫(kù)，并以一種獨(dú)特的方式來(lái)展示信息。例如，視頻演示在遙遠(yuǎn)的行星表面模擬飛行。

信息26

商業(yè)化圖像產(chǎn)品

對(duì)于大量賣給一般大眾的商業(yè)系統(tǒng)來(lái)說(shuō)，大信息量的圖像還是一個(gè)問(wèn)題。商業(yè)系統(tǒng)必須便宜，這一點(diǎn)和大存儲(chǔ)量、傳輸數(shù)據(jù)速率高相矛盾。壓縮圖像解決了這個(gè)進(jìn)退兩難的問(wèn)題。和聲音信號(hào)一樣，圖像也包含大量多余的信息，這些圖像經(jīng)過(guò)算法處理可以減低其容量。電視和其他能動(dòng)的圖片很適合壓縮，因?yàn)閺目驅(qū)騺?lái)看，大部分圖像保持一樣。商業(yè)化圖像產(chǎn)品利用了這個(gè)技術(shù)，例如視頻電話、演示動(dòng)畫的計(jì)算機(jī)程序、和數(shù)字電視。

第二篇：電子信息工程專業(yè)英語(yǔ)總結(jié)

Actuator 致動(dòng)器，執(zhí)行器 acquisition time采樣時(shí)間 address從事，忙于 address pointer地址指針 adjustment 調(diào)整，調(diào)節(jié) adverse 不利的，相反的 aliasing混疊現(xiàn)象 all in all總而言之 alter 改變 alternative選擇 aluminium 鋁 analogous 類似的 anguish 痛苦，苦惱 antenna 觸角，天線 anti-aliasing filter 抗混疊濾波器 appliance用具，器具 approach 方法 arena競(jìng)技場(chǎng)，舞臺(tái) array 陣列，數(shù)組 asynchronous 異步的 as a consequence因此 as opposed to...與...相反 baseband基帶 base station基站 be encumbered with為...所累 behavioral synthesis行為綜合 be referred to as...被稱作...bipolar 雙極性的 boast 夸耀 Boolean variable布爾變量 budget預(yù)算 buffer緩沖器，緩沖區(qū) building block構(gòu)件，模塊 bulky 容量大的，體積大的 bus interface總線接口 cache 高速緩存 capacitor 電容器 capacity 容量，電容 capture 記錄，輸入 carrier wave載波 cell 細(xì)胞，蜂房，電池 cellular 蜂窩狀的 chrominance 色度 circular 圓形的，循環(huán)的 commute 通勤 comparator 比較器 compatibility兼容性 component 組件 conditioning 調(diào)節(jié)，調(diào)整 conduct 傳導(dǎo) configure 配置，設(shè)定 consequently 從而，因此 consumption 消耗 consolidated加固的，整理過(guò)的，統(tǒng)一的 context上下文，背景，環(huán)境 cordless 不用電線的 cordless phone無(wú)繩電話 corresponding 相應(yīng)的 cost-effective 合算的 couple連接，結(jié)合 cubic 立方體的，立方的 current source電流源 cryptography密碼系統(tǒng)，密碼術(shù) daunting 使人畏縮的 data processing數(shù)據(jù)處理 data sheet數(shù)據(jù)手冊(cè) deceptive欺騙性的 dedicate專用，致力于 deduce推導(dǎo)，演繹 deflection偏轉(zhuǎn) descendant 后裔，后代 design flow設(shè)計(jì)流程 device 器件 diagram 圖表 dial tone撥號(hào)音 digitisation 數(shù)字化 disadvantage缺點(diǎn)，劣勢(shì) discrete 離散的 drawback 缺點(diǎn)，障礙 drift 漂移 drive 驅(qū)動(dòng)器 dynamic 動(dòng)態(tài)的 dynamic range動(dòng)態(tài)范圍 educated受過(guò)教育的，有教養(yǎng)的，有根據(jù)的embedded system嵌入式系統(tǒng) embrace擁抱，包含 emulation仿真 encompass包含 encumber阻礙 end office端局 end product最終產(chǎn)品 ensue跟著發(fā)生 erasable 可擦寫的 erroneous錯(cuò)誤的 even field偶數(shù)場(chǎng) facilitate使容易，使便利 ferroelectric 鐵電的 fiasco 慘敗，大失敗 field-programmable現(xiàn)場(chǎng)可編程的 flicker閃爍，顫動(dòng) flip flop觸發(fā)器 floppy disk軟盤 for the nonce目前，暫且 for fear of為了避免 formality 手續(xù)，禮節(jié)，儀式 format 格式 foundry半導(dǎo)體制造商 frame 幀 frame grabber 幀采集器 frequency reuse頻率重用 full-custom全定制的 full scale range滿量程范圍 functional accelerator性能加速器 glue logic膠連邏輯 graphical 圖形的 guesstimate估計(jì)，猜測(cè) hand-held手持的，手持式的 handset 電話聽(tīng)筒，手持機(jī) handy 手邊的，容易取得的 henceforth自此以后，今后 hexagon 六邊形

high-powered 大功率的 humble 級(jí)別低的，位置低的 humongous極大的 hybrid 混合的

impediment妨礙，阻礙 implement 實(shí)現(xiàn)；器具 in any event無(wú)論如何 inbound 輸入的 incoming 輸入的

incoming inspection入廠檢查；輸入檢驗(yàn) inconsistent不一致的，矛盾的 incorporate 一體化

incredibly難以置信地，驚人地 incur招致

in conjunction with與...協(xié)力 in detail詳細(xì)地 inevitably 不可避免 infinite無(wú)限的

in motion在運(yùn)轉(zhuǎn)，處于活躍狀態(tài) innovative創(chuàng)新的

in one’s own right依靠自身的本領(lǐng)或素質(zhì) in parallel并行的，平行的 in practical terms實(shí)際上 install 安裝

insulate 絕緣；隔離 integrated 集成的

in terms of根據(jù)，在...方面 interface capacitor溝道電容器 interference 干擾，干涉 interlace交織，交錯(cuò)

interpretation解釋，闡明 in the field在現(xiàn)場(chǎng)

iterative重復(fù)的，迭代的 jargon行話

laborious 艱苦的，費(fèi)力的 leakage 泄露

lessen 減少，減輕

level shifter電平移動(dòng)器 lifetime 壽命

line driver線路驅(qū)動(dòng)器 lithographic平版印刷的 luminance亮度

macrofunction宏功能 magnetic 磁的

manageable 易處理的 mandate 委任

manipulate 操作，處理 market時(shí)常，銷路，行情 mask 掩模，掩碼，掩蔽 mass-produced 大量生產(chǎn)的 mechanical 機(jī)械的 memory 存儲(chǔ)器，內(nèi)存

metal interconnect金屬互聯(lián) metalization 金屬化 methodology 方法學(xué) microcell 微蜂窩

miniaturization 細(xì)微化 mixed-signal混合信號(hào) more often than not時(shí)常 next state次態(tài)

nonrecurring一次性的，不重視的 numerical數(shù)值的

Nyquist theorem奈奎斯特定理 octal八管腳的，八進(jìn)制的 odd field奇數(shù)場(chǎng)

of age成熟；發(fā)達(dá)；充分發(fā)展 offset彌補(bǔ)，抵消 optical 光學(xué)的

order of magnitude數(shù)量級(jí) oscillator 振蕩器 outbound 輸出的

overload使超載，超過(guò)負(fù)荷；超載，過(guò)載 over（a/the）period（of）在某段時(shí)間內(nèi) packet 封包，分組

packet switching分組交換 parallelism并行度 partition 分割，劃分 passive 無(wú)源的 pattern 模式，圖案

pay off帶來(lái)利益；償清債務(wù)

perceptive 有知覺(jué)的，有理解力的 placement 布置，安排 power dissipation功耗 precede領(lǐng)先于

predominant 卓越的，支配的，主要的 present state現(xiàn)態(tài)

price/performance ratio性能價(jià)格比 prior to先于，在...之前 profession 職業(yè)，專業(yè) proportion比例

proposition主張，建議 prototype原型，樣機(jī)

put out放出，產(chǎn)生；消除；熄滅 quantization level量化電平rating 等級(jí)，級(jí)別 real time實(shí)時(shí) reciprocal倒數(shù)

reconfigurable可重新配置的 refresh 刷新 register 寄存器 routing 布線

run up升起；積欠；匆匆制成

sample and hold circuit采樣保持電路 sampling interval采樣間隔 schematic 原理圖，示意圖 second-level二級(jí)的 self-destruction 自毀 semiconductor 半導(dǎo)體 semi-custom半定制的 sequential 時(shí)序的 shed棚，小屋

signal conditioner信號(hào)調(diào)節(jié)器 signal-to-noise ratio信噪比 silicon 硅

simultaneously 同時(shí)

simulation 模擬，仿真 simulator 模擬器，仿真器 simultaneously同時(shí)地 smoothing平滑 solid state固態(tài) sourcing 供貨

specialized 專門的，專用的

specification 技術(shù)要求，規(guī)格明細(xì) spectral inversion頻譜反轉(zhuǎn) spectrum光譜，頻譜，范圍 spurt噴射，迸發(fā)，沖刺 squash擠進(jìn)，擠壓 squeal 長(zhǎng)聲尖叫 stability 穩(wěn)定性 state machine狀態(tài)機(jī) static 靜態(tài)的

successor 繼承者，接任者；后續(xù)的事物 synchronous 同步的 synthesis 綜合

tailor剪裁，修改，調(diào)整 textural 文本的

time to market上市時(shí)間 transducer 傳感器，變換器 transfer function傳輸函數(shù) transistor 晶體管 trick竅門，訣竅 trigger 觸發(fā)

ultimate 最終的，根本的 uncommitted 未確定用途的 underlying根本的，潛在的 undependable 不可靠的 undersampling 欠采樣 vendor 廠商 viable可行的 volatile 易失的

voltage source電壓源 watt 瓦特

well-paid 收入高的 whereas 然而

wireless infrastructure無(wú)線基礎(chǔ)設(shè)施 wrapp包裹，覆蓋，纏繞 zero order hold零階保持

AMPS.advanced mobile phone system.先進(jìn)移動(dòng)電話系統(tǒng)

ASIC.application specific integrated circuit.專用集成電路 ASSP.application-specific standard parts.專用標(biāo)準(zhǔn)器件 CAD.computer aided design.計(jì)算機(jī)輔助設(shè)計(jì)

CAM.content addressable memory.內(nèi)容尋址存儲(chǔ)器 CB.citizen' band.民用波段

CCD.charge-coupled device.電荷耦合器件 CD.compact disc.光盤

CMOS.complementary metal-oxide-semiconductor.互補(bǔ)金屬氧化物半導(dǎo)體 CPLD.complex programmable logic device.復(fù)雜可編程邏輯器件 DA.desigh automation設(shè)計(jì)自動(dòng)化

DRAM.dynamic random access memory動(dòng)態(tài)隨機(jī)存儲(chǔ)器 DSP.digital signal processor數(shù)字信號(hào)處理器 ECL.emitter coupled logic射極耦合邏輯

EDA.electronic design automation電子設(shè)計(jì)自動(dòng)化

EEPROM.electrically erasable programmable rom電可擦除可編程只讀存儲(chǔ)器FCC.federal communications commission聯(lián)邦通信委員會(huì) FPGA.field programmable gate array現(xiàn)場(chǎng)可編程門陣列 GBW.gain×bandwidth增益帶寬積

GPP.general-purpose microprocessor通用微處理器

GSM.global system for mobile communication全球移動(dòng)通信系統(tǒng) HDL.hardware description language硬件描述語(yǔ)言 IC.intergrated circuit.集成電路

IMTS.improved mobile phone system 改進(jìn)移動(dòng)電話系統(tǒng) ISP.in-system programmable在系統(tǒng)可編程 LP.long playing（record）慢轉(zhuǎn)密紋唱片 LSI.large-scale integration.大規(guī)模集成

MOS.metal-oxide-semiconductor互補(bǔ)金屬氧化物半導(dǎo)體 MTSO.mobile telephone switching office移動(dòng)電話交換局 MSC.mobile switching center移動(dòng)交換中心 NRE.nonrecurring engineering一次性工程 ns.nanosecond納秒

NTSC.national television systems committee國(guó)家電視系統(tǒng)委員會(huì) OTP.one-time programmable一次可編程 PAL.phase alternation by line逐行倒相

PAL.programmable array logic可編程陣列邏輯 PLA.programmable logic array可編程邏輯陣列 PLD.programmable logic device可編程邏輯器件

PTT.post telephone and telegraph administration郵電管理局 PSTN.public switched telephone network公共交換電話網(wǎng) RC.reconfigurable computing可重配計(jì)算 ROM.read only memory只讀存儲(chǔ)器

RTL.register transfer level寄存器傳輸級(jí) SDR.software-defined radios軟件無(wú)線電

SECAM.sequential couleur avec memoire順序與存儲(chǔ)彩色電視系統(tǒng) SoC.system-on-chip片上系統(tǒng)

SPLD.simple programmable logic devices簡(jiǎn)單可編程邏輯器件 SRAM.static random access memory.靜態(tài)隨機(jī)存取存儲(chǔ)器 UV.ultraviolet紫外線

VHDL.very high speed integrated-circuit hardware-description language 超高速集成電路硬件描述語(yǔ)言

VHSIC.very high speed integrated circuit超高速集成電路 VLSI.very large-scale integration.超大規(guī)模集成 μP.microprocessor微處理器

第三篇：電子信息工程專業(yè)英語(yǔ) 課文翻譯 Unit 11 譯文

Unit 11 數(shù)字圖像處理

Unit 11-1 第一部分：二維數(shù)字圖像

圖像是表示一些物理參數(shù)空間分布的二維信號(hào)，典型的物理參數(shù)是光強(qiáng)，而更普通的是能量的任一種形式。例如，運(yùn)動(dòng)圖像以及多光譜的遙感圖像是三維或者是更高維的信號(hào)。現(xiàn)代數(shù)字技術(shù)使得處理多維信號(hào)成為可能，所使用的系統(tǒng)可從簡(jiǎn)單的數(shù)字電路到先進(jìn)的并行計(jì)算機(jī)。這種處理的目的可以分為3類：

-圖像處理：輸入圖像?輸出圖像用相機(jī)拍攝和沖洗照片

-大自然的例子：水面上景色的反射，水霧中景色的失真，等等。高級(jí)圖像處理的應(yīng)用例子包括：

-司法科學(xué)：視頻監(jiān)控?cái)z像機(jī)圖像的增強(qiáng)，圖像中的臉，指紋，DNA碼等的自動(dòng)識(shí)別和分類?？梢暬?。例如：在我們制作一個(gè)三維物體的三維可視化之前，我們首先需要從二維圖像中提取物體的信息。圖像增強(qiáng)，例如，減少噪聲或圖像銳化。

-模式識(shí)別，例如，圖像中某種形狀或紋理的自動(dòng)檢測(cè)。

-將數(shù)據(jù)量減少為更容易處置或解釋的信息，例如將圖像減小為一幅較簡(jiǎn)單的圖像、一組對(duì)象或特征、或者一組測(cè)量結(jié)果。

-圖像合成，如由二維照片重建三維場(chǎng)景。

-圖像拼接。當(dāng)從同一個(gè)場(chǎng)景獲取兩種不同形態(tài)（類型）的圖像時(shí)，將它們拼接起來(lái)涉及配準(zhǔn)，其后是數(shù)據(jù)減少和圖像合成。

-數(shù)據(jù)壓縮。為了縮小包含圖像的計(jì)算機(jī)文件的大小，以及加快網(wǎng)絡(luò)中圖像傳輸?shù)乃俣?，?shù)據(jù)壓縮常常是必需的。

我們關(guān)心的只是數(shù)字圖像處理，而不是模擬處理，理由是，模擬處理需要專用的硬件，這使得建立一個(gè)特殊的圖像處理應(yīng)用成為一項(xiàng)艱巨的任務(wù)。此外，在許多圖像處理領(lǐng)域中模擬硬件的使用正在迅速地成為過(guò)去，因?yàn)樗３Ｄ鼙桓哽`活性的數(shù)字硬件（計(jì)算機(jī)）所取代。

但究竟什么是數(shù)字圖像呢？數(shù)字圖像獲取與處理的示意圖如圖11.2所示。頂部有某個(gè)成像設(shè)備，如攝像機(jī)，醫(yī)療掃描儀，或其它任何可將物理現(xiàn)實(shí)的量度轉(zhuǎn)換為電信號(hào)的設(shè)備。成像設(shè)備產(chǎn)生一個(gè)連續(xù)的電信號(hào)。因?yàn)檫@種模擬信號(hào)不能直接用計(jì)算機(jī)處理，信號(hào)通過(guò)數(shù)字化儀轉(zhuǎn)換為離散形式。最后產(chǎn)生的圖像便可直接用于數(shù)字圖像處理應(yīng)用。

數(shù)字化儀完成兩個(gè)任務(wù)：采樣和量化（見(jiàn)圖11.3）。在采樣過(guò)程中，圖像中連續(xù)信號(hào)的值在特定位置被采樣。在量化過(guò)程中，真實(shí)值被離散化為數(shù)字?jǐn)?shù)值。量化后的圖像我們稱為數(shù)字圖像。這樣就回答了本節(jié)開(kāi)頭的問(wèn)題：數(shù)字圖像只不過(guò)是一個(gè)數(shù)值的矩陣。每個(gè)矩陣元素，即已量化樣本，被稱為圖像元素或像素。對(duì)于三維圖像則稱為體積元素或體素。

我們可以用兩個(gè)坐標(biāo)(x;y)表示圖像中每個(gè)像素的位置。按照慣例，(0;0)像素，即原點(diǎn)，是在圖像的左上角，X軸是從左向右，Y軸自上而下（見(jiàn)圖11.4）。這可能要用一點(diǎn)功夫去習(xí)慣它，因?yàn)樗煌诔Ｒ?guī)的二元函數(shù)的數(shù)學(xué)表示法，也不同于常規(guī)的矩陣坐標(biāo)。如果一幅數(shù)字圖像僅僅是一個(gè)數(shù)值矩陣，有人可能會(huì)說(shuō)：數(shù)字圖像處理只不過(guò)是一種對(duì)矩陣進(jìn)行運(yùn)算的數(shù)學(xué)算法的集合。幸運(yùn)的是，現(xiàn)實(shí)情況遠(yuǎn)非所說(shuō)的那么枯燥乏味，因?yàn)樵趯?shí)際中，我們很少使用圖11.3所示的矩陣表示，而是對(duì)圖11.3的中間圖像進(jìn)行處理，實(shí)際上是同一幅圖像，但將光強(qiáng)度賦予每一個(gè)數(shù)，對(duì)人而言它通常更有意義。你會(huì)發(fā)現(xiàn)圖像處理算法將被描述為數(shù)學(xué)算子作用于像素值或像素矩陣，這些算法的運(yùn)算結(jié)果也將被用圖像形式顯示出來(lái)。

Unit 11-3 第三部分：圖像處理引言

圖像由各種物理設(shè)備產(chǎn)生，包括照相機(jī)和攝像機(jī)、X光設(shè)備、電子顯微鏡、雷達(dá)、超聲設(shè)備等，并用于各種目的，包括娛樂(lè)、醫(yī)療、商務(wù)、工業(yè)、軍事、民用、安全、科學(xué)。各種應(yīng)用的目的都是使觀察者（人或機(jī)器）提取被成像的場(chǎng)景中的有用信息。

原始圖像通常并不直接適合于這一目的，必須以某種方式進(jìn)行處理。這種處理稱為圖像增強(qiáng)；而觀察者從圖像 中提取信息的處理則稱為圖像分析。增強(qiáng)和分析根據(jù)其輸出性質(zhì)即輸出的是圖像還是關(guān)于場(chǎng)景的信息來(lái)區(qū)分，也根據(jù)所面臨的挑戰(zhàn)和所使用的方法來(lái)區(qū)分。

圖像增強(qiáng)通過(guò)化學(xué)、光學(xué)、電子方法實(shí)現(xiàn)，而分析則主要由人工和電子方法實(shí)現(xiàn)。用于觀察者的（視覺(jué)）增強(qiáng)方法或用于（計(jì)算機(jī)）自主分析的數(shù)字圖像處理技術(shù)在成本、速度、靈活性方面具有優(yōu)越性，隨著個(gè)人計(jì)算機(jī)價(jià)格的急劇下降和功能的快速提升而成了實(shí)用的主要方法。

挑戰(zhàn)

圖像并不是被觀察的物理對(duì)象性質(zhì)的直接測(cè)量，而是諸多物理因素相互作用的結(jié)果：光照強(qiáng)度及其分布、光照與構(gòu)成景物的物質(zhì)之間的相互作用、反射光或透射光從三維空間到二維圖像平面的投影幾何關(guān)系、以及傳感器的電子特性。不像某些其它工作例如編寫編譯程序那樣有正式理論為基礎(chǔ)的算法，可將高級(jí)計(jì)算機(jī)語(yǔ)言翻譯成機(jī)器語(yǔ)言，不存在從圖像中提取感興趣的景物信息如位置或某一制成品質(zhì)量的算法和可比的理論。

這種困難常被初學(xué)者低估，因?yàn)槿说囊曈X(jué)系統(tǒng)似乎可輕而易舉地從景物中提取信息。人的視覺(jué)通常比我們目前乃至可預(yù)見(jiàn)的未來(lái)能夠設(shè)計(jì)制造的任何東西復(fù)雜得多。于是我們必須注意，不要根據(jù)人們對(duì)某一數(shù)字圖像處理應(yīng)用的印象來(lái)評(píng)估其難易程度。

一個(gè)首要的指導(dǎo)原則也許是人類更擅長(zhǎng)于判斷而機(jī)器更擅長(zhǎng)于測(cè)量。因此，比方說(shuō)在傳輸帶上確定一個(gè)汽車零件的確切位置和大小很適合于數(shù)字圖像處理，而要對(duì)蘋果或木材的質(zhì)量定級(jí)卻更具挑戰(zhàn)性，盡管不是不可能的。按照這些原則，需進(jìn)行大量計(jì)算而極少需要判斷的圖像增強(qiáng)就是很適合于數(shù)字處理的。

對(duì)處理時(shí)間的嚴(yán)格要求常使問(wèn)題變得更復(fù)雜。很少用戶在意電子表格的數(shù)據(jù)刷新時(shí)間是300毫秒而不是200毫秒；但是，譬如說(shuō)大部分工業(yè)應(yīng)用卻必須在機(jī)器周期所要求的嚴(yán)格限制以內(nèi)完成操作。還有許多應(yīng)用如超聲圖像增強(qiáng)、交通監(jiān)控、攝像機(jī)防抖動(dòng)等要求對(duì)視頻流進(jìn)行實(shí)時(shí)處理。

為了具體了解對(duì)處理速度的挑戰(zhàn)，設(shè)想一下，一臺(tái)標(biāo)準(zhǔn)黑白攝像機(jī)的視頻流每秒有1000萬(wàn)個(gè)像素。在撰寫本文時(shí)，一臺(tái)典型臺(tái)式PC也許可在處理每個(gè)像素所允許的100ns時(shí)間內(nèi)執(zhí)行50條機(jī)器指令，而能用區(qū)區(qū)50條指令完成的處理十分有限。

此外，許多圖像處理應(yīng)用還受到成本的嚴(yán)格限制，因此我們經(jīng)常面臨工程師們望而生畏的三重難題：要求設(shè)計(jì)的產(chǎn)品同時(shí)具備性能優(yōu)良、運(yùn)行快捷、價(jià)格便宜的優(yōu)點(diǎn)。

圖像獲取

所有圖像處理應(yīng)用始于某種形式的照射，典型的是光線但廣義的是某種能量。有時(shí)必須使用環(huán)境光線，但更為典型的是根據(jù)具體應(yīng)用設(shè)計(jì)照明。在這些情況下事情的成敗往往就在于此：任何高明的軟件都無(wú)法將因?yàn)檎彰鞑涣级鴣G失的信息恢復(fù)出來(lái)。

照相機(jī)就是一個(gè)能將輻射能量分布轉(zhuǎn)換為存放在RAM中的數(shù)字圖像的裝置。過(guò)去這一過(guò)程分成兩步：將能量轉(zhuǎn)換為電信號(hào)即照相機(jī)的功能；用數(shù)字化設(shè)備將信號(hào)轉(zhuǎn)換成數(shù)字形式并存儲(chǔ)?，F(xiàn)在兩者之間的界線正在變得模糊，照相機(jī)將通過(guò)USB、以太網(wǎng)、IEEE 1394接口直接將圖像送入計(jì)算機(jī)。

照相機(jī)技術(shù)以及所產(chǎn)生的圖像特性幾乎無(wú)例外地受到最大實(shí)際應(yīng)用量的驅(qū)動(dòng)，其中之一是消費(fèi)電視。因此大多數(shù)的攝像機(jī)具有半個(gè)多世紀(jì)以前電視廣播標(biāo)準(zhǔn)所制定的分辨率和速度特性。

典型的可見(jiàn)光單色攝像機(jī)的分辨率為640?480，每秒輸出30幀圖像，并支持電子快門和快速?gòu)?fù)位（任意時(shí)刻回復(fù)到一幀初始狀態(tài)的能力，從而可避免在開(kāi)始捕獲一幀新圖像前的等待）。這種攝像機(jī)是基于CCD傳感器技術(shù)的，能產(chǎn)生優(yōu)良的圖像，但相對(duì)于其它具有同樣數(shù)量晶體管的多數(shù)芯片而言其價(jià)格很高。

隨著大容量個(gè)人計(jì)算機(jī)多媒體應(yīng)用的激增情況首次發(fā)生了變化。首先影響到的是顯示器，它已有相當(dāng)一段時(shí)間給我們提供了比廣播更高的速度和分辨率。人們可期待照相機(jī)/攝像機(jī)也隨之跟上，包括由民用數(shù)字照相機(jī)所推動(dòng)的高速度、高分辨率器件，娛樂(lè)業(yè)、互聯(lián)網(wǎng)遠(yuǎn)程會(huì)議和用戶視覺(jué)界面應(yīng)用所推動(dòng)的低分辨率和極低價(jià)格的設(shè)備。

廉價(jià)器件可能會(huì)產(chǎn)生更大的影響。這些是基于新出現(xiàn)的CMOS傳感器技術(shù)的，其生產(chǎn)工藝與大多數(shù)計(jì)算機(jī)芯片相同，因而得益于生產(chǎn)批量大而價(jià)格低廉。目前它的圖象質(zhì)量還達(dá)不到CCD標(biāo)準(zhǔn)，但隨著技術(shù)的成熟是注定會(huì)改進(jìn)的。

圖像增強(qiáng)

數(shù)字圖像增強(qiáng)算法大致分為兩類：點(diǎn)變換（像素映射）和鄰域運(yùn)算。

1.點(diǎn)變換

點(diǎn)變換產(chǎn)生的輸出圖像中每個(gè)像素都是一個(gè)相應(yīng)輸入像素的某種函數(shù)。這一函數(shù)對(duì)于每個(gè)像素都相同，通常是由圖像的全局統(tǒng)計(jì)特性導(dǎo)出的。點(diǎn)變換一般運(yùn)行很快，但僅限于進(jìn)行全局變換，例如調(diào)整整幅圖像的對(duì)比度。

點(diǎn)變換包括許多可用于分等級(jí)值像素的圖像增強(qiáng)。這些算法常由基于查找表的單一軟件程序或硬件模塊實(shí)現(xiàn)。查找表的運(yùn)行速度快，可以編程用于實(shí)現(xiàn)任何功能，以合理的速度提供最終的普適性。而MMX以及類似的處理器則能以比查找表快得多的速度通過(guò)直接計(jì)算來(lái)執(zhí)行各種功能，其代價(jià)是軟件復(fù)雜性的提高。當(dāng)某種功能是通過(guò)圖像全局統(tǒng)計(jì)特性來(lái)計(jì)算時(shí)，像素映射是最為有用。例如人們可以處理一幅圖像，在輸入信號(hào)的均值和標(biāo)準(zhǔn)偏差，或者最小值和最大值的基礎(chǔ)上，獲得所要求的增益和補(bǔ)償（偏移）。

直方圖指標(biāo)是一種有效的像素映射點(diǎn)變換，對(duì)輸入圖像進(jìn)行處理使之具有與某一參考圖像同樣的像素值分布。其像素映射關(guān)系很容易從輸入圖像和參考圖像的直方圖得到。直方圖指標(biāo)是進(jìn)行圖像分析前的一種有用的增強(qiáng)技 術(shù)，這種分析的目的是對(duì)輸入圖像和參考圖像進(jìn)行某種比較。

閾值分割是一種常用增強(qiáng)技術(shù)，其目的是將圖像分割成目標(biāo)和背景。計(jì)算閾值，大于（或小于）閾值的就當(dāng)作對(duì)象，否則就是背景。有時(shí)用兩個(gè)閾值來(lái)確定對(duì)應(yīng)于目標(biāo)像素的一個(gè)范圍。閾值可以是固定的，但最好是根據(jù)圖像的統(tǒng)計(jì)特性計(jì)算得到。也可以用鄰域處理進(jìn)行閾值分割。在所有這些情況下得到的結(jié)果都是一幅二值圖像，即只有黑白兩色而沒(méi)有灰階。

顏色空間轉(zhuǎn)換用于轉(zhuǎn)換不同的顏色表示方法，例如將照相機(jī)提供的RGB空間轉(zhuǎn)換成圖像分析算法所要求的HIS（色調(diào)，亮度，飽和度）空間。由于精確的顏色空間轉(zhuǎn)換涉及的計(jì)算量很大，在對(duì)時(shí)間有嚴(yán)格要求的應(yīng)用中常采用粗略的近似。這些近似方法十分有效，但在選擇一種算法以前應(yīng)該對(duì)速度和精度間的權(quán)衡有所了解。

時(shí)間平均是處理反差極低圖像最有效的方法。像素灰度映射對(duì)信號(hào)和噪聲的作用相同，因此對(duì)于提高圖像增益的作用很有限。鄰域運(yùn)算可以降低噪聲，卻會(huì)損失圖像的保真度。降低噪聲而不影響信號(hào)的唯一方法是對(duì)不同時(shí)間的多幅圖像求平均。不相關(guān)噪聲的幅度以參與平均的圖像數(shù)目的平方根被衰減。將時(shí)間平均與擴(kuò)大增益的像素映射法相結(jié)合可處理反差極低的圖像。時(shí)間平均的主要缺點(diǎn)是用照相機(jī)獲取多幅圖像需要花費(fèi)較長(zhǎng)的時(shí)間。

2.鄰域運(yùn)算

在鄰域運(yùn)算中，每一個(gè)輸出像素都是一組輸入像素的函數(shù)。這組像素通常圍繞一個(gè)對(duì)應(yīng)的中心像素的某個(gè)區(qū)域，因此稱為鄰域，例如3?3鄰域。鄰域運(yùn)算可實(shí)現(xiàn)頻率濾波和形狀濾波，以及其他復(fù)雜的增強(qiáng)操作，但是運(yùn)行起來(lái)較慢，因?yàn)閷?duì)于每個(gè)輸出像素而言，鄰域內(nèi)的像素必須重復(fù)計(jì)算。

由于有了可追溯到200年前Fourier信號(hào)理論的廣泛數(shù)學(xué)框架，線性濾波器是鄰域處理中最容易理解的。線性濾波器有選擇地放大或衰減空間頻率成分，可達(dá)到平滑和銳化等效果，通常是重采樣和邊緣檢測(cè)算法的基礎(chǔ)。

線性濾波器可用卷積運(yùn)算定義，其輸出像素由鄰域內(nèi)各像素乘以叫做“核”的同樣形狀區(qū)域內(nèi)的相應(yīng)值，然后將乘積相加得到。線性濾波器可直接由卷積實(shí)現(xiàn)，也可以利用FFT在頻域?qū)崿F(xiàn)。盡管頻域?yàn)V波在理論上更為有效，實(shí)際上幾乎總是用直接卷積的方法。由于使用小的整數(shù)運(yùn)算和時(shí)序存儲(chǔ)器尋址，卷積比起FFT來(lái)與數(shù)字硬件更加匹配，更容易實(shí)現(xiàn)，在邊界條件的處理方面幾乎沒(méi)有問(wèn)題。

邊界檢測(cè)有相當(dāng)長(zhǎng)的歷史和大量的文獻(xiàn)資料，從簡(jiǎn)單的邊緣檢測(cè)到更適合于圖像分析中考慮采用的復(fù)雜算法。我們可以有點(diǎn)隨意地將邊緣檢測(cè)看成是一種圖像增強(qiáng)，因?yàn)槠淠康氖峭怀龈信d趣的邊緣特征，而將其他一切都衰減掉。

圖像中由目標(biāo)產(chǎn)生的陰影是目標(biāo)特性中最不可靠的因素，因?yàn)殛幱笆怯烧彰?、表面特性、投影幾何學(xué)、感光器件特性這些因素復(fù)雜地結(jié)合而成的。而另一方面，圖像中的不連續(xù)區(qū)通常直接對(duì)應(yīng)于目標(biāo)表面的不連續(xù)性（例如邊緣），因?yàn)槠渌蛩夭灰讓?dǎo)致不連續(xù)性。圖像中的不連續(xù)性即使在光度學(xué)方面不一致，在幾何即形狀方面通常卻是一致的。因此作為邊緣檢測(cè)目的，不連續(xù)部位的確定和定位是數(shù)字圖像處理中最重要的任務(wù)之一。

粗糙的邊緣檢測(cè)器只是標(biāo)出相應(yīng)于梯度大小的峰值或二階微商過(guò)零點(diǎn)處的像素。精密復(fù)雜的邊界檢測(cè)器則給出有序的一串邊界點(diǎn)，以及亞像素位置和各像素處的邊界方向。最商用的邊緣檢測(cè)器還可以在一個(gè)很寬的范圍內(nèi)調(diào)節(jié)空間頻率響應(yīng)，并以高速運(yùn)行。

設(shè)計(jì)成可以通過(guò)或阻止指定形狀而不是空間頻率的非線性濾波器在數(shù)字圖像增強(qiáng)中十分有用。我們首先考慮的是中值濾波器，它在每個(gè)像素位置的輸出是相應(yīng)輸入鄰域的中值。粗略地講，中值濾波器的作用是將小于鄰域尺寸的圖像內(nèi)容衰減掉，讓大于鄰域范圍的圖像內(nèi)容通過(guò)。

數(shù)字重采樣是指照射到傳感器上的能量連續(xù)分布被重新采樣的情況下估計(jì)圖像的過(guò)程。不同方式采樣，用不同的分辨率或以不同方向采樣常常是有用的。

另一類重采樣算法是坐標(biāo)變換，能產(chǎn)生亞像素?cái)?shù)量的偏移、旋轉(zhuǎn)和改變圖像尺寸、在直角坐標(biāo)系和極坐標(biāo)系之間相互轉(zhuǎn)換。輸出像素的值由輸入值的鄰域內(nèi)插得到。三種常用方法是：速度最快的最近鄰法，更精確但速度較慢而且會(huì)損失一些高頻分量的雙線性法，非常精確但是最慢的三次卷積法。

第四篇：電子信息工程專業(yè)英語(yǔ)導(dǎo)論考試資料

DCDirect Current直流電AC alternating current交流電IC integrated circuit 集成電路

DRAMDynamic Random Access Memory動(dòng)態(tài)隨機(jī)存儲(chǔ)器CPUCentral Processing Unit中央處理器RAMrandom access memory隨機(jī)存儲(chǔ)器SOCSystem-on-Chip片上系統(tǒng)OS operating system操作系統(tǒng)IPintellectual property知識(shí)產(chǎn)權(quán)DSPDigital Signal Processing數(shù)字信號(hào)處理RTLregister transfer level寄存器傳輸級(jí)

DACDigital toanalog converter 數(shù)模轉(zhuǎn)換器VLSIVery Large Scale Integration超大規(guī)模集成電路PLDprogrammable logic device可編程邏輯電路FPGAField Programmable Gate Array場(chǎng)可編程門陣列CPLD Complex Programmable Logic Device復(fù)雜可編程邏輯器件

SRAMstatic random Access Memory靜態(tài)存儲(chǔ)器ASICApplication Specific Integrated Circuit專用集成電路

LUTLook-Up-Table查找表

TDMA Time-Division Multiple Access時(shí)分多址

FIRFinite Impulse Response無(wú)限脈沖相應(yīng)數(shù)字濾波器CDMAcode-division multiple access碼分多址IIRInfinite Impulse Response有限脈沖相應(yīng)數(shù)字濾波器ADCAnalog to Digital Converter模數(shù)轉(zhuǎn)換器

1、We are so used to electric lights, radio, televisions, and telephone that it is hard to imagine what life would be like without that..我們對(duì)電燈，無(wú)線電廣播，電視和電話是如此的熟悉，所以很難想象離開(kāi)啦他們，我們的生活將會(huì)是什么樣子。

2、When large numbers of electrons break away from their atoms and move through a wire, we describe this action by saying that electricity is “flowing” through the wire.當(dāng)大量的電子脫離原子的束縛并通過(guò)導(dǎo)線運(yùn)動(dòng)迪，這時(shí)我們就說(shuō)電通過(guò)導(dǎo)線在流動(dòng)。

3、A resistor has two terminals across which electricity must pass, and is designed to dropthe voltage of the current as it flows from one terminal to the next.電阻有兩端，并且電流都必須通過(guò)。當(dāng)電流從一端流道另一端是，電阻上就有電壓降。

4、The unit of resistance is ohm.In a direct-current circuit, the current through a resistor is inversely proportional to its resistance, and directly proportional to the voltage across it.電阻的單位是歐姆。在直流電路中，通過(guò)電阻的電流與它的阻抗成反比，與加在其上的電壓成正比。

5、Large capacitors are used in the power supplies of electronic of all types, including computers and their

peripherals.In these systems, the capacitors smooth out the rectified utility AC, providing pure, battery-like DC.所有型號(hào)的電子設(shè)備，包括計(jì)算機(jī)及其外圍GSMglobal system for mobile全球移動(dòng)通信系統(tǒng)FDMAFrequency Division Multiple Access頻分多址

設(shè)備的電源儲(chǔ)備系統(tǒng)，都使用了大電容器。

在這些系統(tǒng)中，電容器能進(jìn)一步平滑經(jīng)整流過(guò)的公用交電流，是其提供如電流產(chǎn)生的純直流電一樣。

6、This does not affect performance in DC circuits, but can have an adverse effect in AC circuit because inductance renders the device sensitive to change in frequency.在直流電路中這并沒(méi)有影響，但是對(duì)交流電路卻有反作用，因?yàn)殡姼行?yīng)系數(shù)使該器件對(duì)頻率的變化很敏感。

7、Transistor have three leads which must be connected the correct way around;thecommon-base, the common-emitter and the common-collector.晶體管在電路中有三種正確的連接方式，共基極，共發(fā)射極，共集電極法。

8、By licensing, rather than

manufacturing and selling its chip technology, the Company established a new business model that has redefined the way microprocessors are designed, produced and sold.通過(guò)許可，而不是制造和出售的芯片技術(shù)，公司重新定義了微處理器設(shè)計(jì)，生產(chǎn)與銷售的方式，從而建立了一種新的商業(yè)模式。

9、The single-processor solution offers higher performance, lower system cost and lower power than coprocessors and dual-processor solutions.與協(xié)處理器和雙處理器解決方案相比，單處理器解決方案提供了更高的性能，更低的系統(tǒng)和能耗。

10、Since many signal processing applications process millions of samples of data for every second of operation, the minimum sample period is

usually more important than the

computationa latency of the processor.由于許多信號(hào)處理應(yīng)用過(guò)程中每秒處理的樣本數(shù)據(jù)數(shù)以百萬(wàn)計(jì)，因此，最低采樣周期通常比處理器的計(jì)算時(shí)延更為重要。

11、For example, a speech signal can be represented mathematically by acoustic pressure as a function of time, and a picture can be represented by brightness as a function of two spatial variables.在一個(gè)連續(xù)時(shí)間信號(hào)x（t），數(shù)字處理的第一步是選擇一個(gè)采樣周期T，然后對(duì)樣本x（t）產(chǎn)生x（nT）。

18、Under certain conditions, a continuous signal can be completely represented by and recoverable from a sequence of its values, or samples, at points equally spaced in time.在一定的條件下，一個(gè)連續(xù)信號(hào)可以完全由可以由該信號(hào)在時(shí)間等間隔點(diǎn)上的瞬時(shí)值例如，一個(gè)語(yǔ)音信號(hào)在數(shù)學(xué)上可以用聲壓隨時(shí)間變化的函數(shù)來(lái)表示，而一張照片可以表示亮度隨二維空間變量變化的函數(shù)。

12、To distinguish between continuous-time signals and

discrete-time signals, we will use the symbol t to denote the continuous-time independent variable and n to denote the discrete-time independent variable.區(qū)分連續(xù)時(shí)間信號(hào)和離散時(shí)間信號(hào)之間，我們將使用符號(hào)T表示連續(xù)時(shí)間的獨(dú)立變量，用n來(lái)表示離散的獨(dú)立變量。

13、FPGAs are a form of programmable logic devices which permits the design of many different complex digital circuits.現(xiàn)場(chǎng)可編程門陣列（FPGAs）是可編程邏輯器件的一種形式，它允許設(shè)計(jì)許多不同的復(fù)雜數(shù)字電路。

14、A continuous-time system is a system in which continuous-time input signals are applied and result in

continuous-time output signals.一個(gè)連續(xù)時(shí)間系統(tǒng)是施加連續(xù)時(shí)間輸入信號(hào)，而產(chǎn)生連續(xù)時(shí)間輸出信號(hào)的系統(tǒng)。

15、Signals encountered in practice are mostly continuous-time signals and can be denoted as x(t), where t is a continuum.實(shí)際遇到的信號(hào)大多是連續(xù)時(shí)間信號(hào)，這類信號(hào)可以用x（t）表示，其中t是連續(xù)變量。

16、most discrete-time signals are obtained from continuous-time signals by sampling and can be denoted as x[n]:=x(nT).大多數(shù)離散時(shí)間信號(hào)，是從連續(xù)時(shí)間信號(hào)的采樣得到的，可以表示為X[n]：=x（nT）。

17、In digital processing of a

continuous-time signal x(t), the first step is to select a sampling period T and then to sample x(t)to yield x(nT).或樣本值來(lái)表示，并且能用這些樣本值恢復(fù)出原信號(hào)來(lái)。

19、Much of the importance of the

sampling theorem also lies in its role as a bridge between continuous-time signals and discrete-time signals.抽樣理論的重要性還在于它在連續(xù)時(shí)間信號(hào)和離散時(shí)間信號(hào)之間起了橋梁作用。20、In many contexts, processing

discrete-time signals is more flexible and is often preferable to processing continuous-time signals.在許多方面，處理離散時(shí)間信號(hào)要更加靈活些，因此往往比處理連續(xù)時(shí)間更為可取。

21、In actuality, each cellconsists of a base station and an antenna that supports operations over a wide range of frequencies.在現(xiàn)實(shí)中，每個(gè)小區(qū)由一個(gè)基站和天線，支持業(yè)務(wù)在很寬的頻率范圍內(nèi)。

22、Those access methods are referred to as time-division multiple access(TDMA)and code-division multiple access(CDMA).那些訪問(wèn)方法都被稱為time-division多址(TDMA)和code-division多址(CDMA)。

23、As the satellite received a signal from a ground or earth station, a communications complex that transmitted and/or received satellite signals, it relayed its own signal to earth.當(dāng)衛(wèi)星收了從地面或地球站發(fā)來(lái)的信號(hào)后，衛(wèi)星上的通信設(shè)備將要發(fā)送的和已接受的衛(wèi)星信號(hào)復(fù)合起來(lái)后在發(fā)往地球。

24、The primary value of satellite in a geostationary orbit is its ability to communicate with ground stations in its coverage area 24 hours a day.對(duì)地靜止軌道上的衛(wèi)星的主要作用是，一天二十四小時(shí)和覆蓋區(qū)域中的地面站進(jìn)行通信。

漢譯英：

1、可以這么說(shuō)，沒(méi)有晶體管的發(fā)明，今天我們所知的計(jì)算是完全不可能的。It is safe to say that without the invention of transistors, computing as we know it today wuld not be possible.2、可編程邏輯區(qū)別于傳統(tǒng)硬件的關(guān)鍵特性是它們可以重新配置。The key property of programmable logics that differentiates

9、如果你是電子的初學(xué)者，最好現(xiàn)在就開(kāi)始學(xué)習(xí)如何使用NPN晶體管。If you are new to electronics it is best to start by learning how to use NPN transistors.10、在晶體管發(fā)明之前，數(shù)字電路是由真空管（vacuum tubes）組成，這有很多不足。Prior to the invention of

transistors,digital circuits werecomposed of vacuum tubes, which had many them from custom hardware is their reconfigurability.3、在許多方面，處理離散時(shí)間信號(hào)要更加靈活些，因此比處理連續(xù)時(shí)間信號(hào)更為可取。In many contexts , processing discrete-time signal is more flexible and is often preferable to processing continuous-time signals.4、時(shí)間上離散，幅值上量化的信號(hào)稱之為數(shù)字信號(hào)。Time is discrete, the

amplitude quantization signal called digital signal5、實(shí)際遇到的信號(hào)大多是連續(xù)時(shí)間信號(hào)，這類信號(hào)可以用x(t)表示，t是連續(xù)變量。Signals encountered in practice are mostly continuous-time signals and can be denoted as x(t),where t is a continuum.6、反過(guò)來(lái)，這種設(shè)計(jì)的改進(jìn)又可引導(dǎo)研制新一代的衛(wèi)星，這些衛(wèi)星能夠通過(guò)其他轉(zhuǎn)發(fā)器及其相關(guān)電子系統(tǒng)處理大量的信息。This design evolution has led,in turn ,to the development of a new generation of satellites that can handle an enormous volume of information via their

transponders and relatedelectronic sysrems.7、地面站是傳送/接收衛(wèi)星信號(hào)的通信設(shè)備，衛(wèi)星接收來(lái)自地面站發(fā)送的信號(hào)后，再將其信號(hào)傳送給地球。As the satellite received a signl from a ground or earth station , a communications complex that transmitted and received satellite signals,it telayed its own signal to earth.8、在直流電路中這并沒(méi)有影響，但對(duì)交流電路卻有反作用，因?yàn)楦袘?yīng)系數(shù)使該器件對(duì)頻率的變化很敏感。This does not affect performance in DC circuits ,but can have an adverse effect in AC circuits because inductance renders the device sensitive to changes in frequency.disadvantages.11、電阻的阻抗是由它的物理結(jié)構(gòu)決定的The amount of resistance offered by a resistor is determined by its physical construction.。

12、控制總線是控制處理器與系統(tǒng)其他部分通信的信號(hào)樞紐。Thecontrol bus is a collection of signals that controls how the processor communicates with the test of the system.13、正是由于這一特性，在發(fā)明DSP處理器時(shí)采用了一種與傳統(tǒng)的微處理器不同的結(jié)構(gòu)。It is because of this very nature that DSP processors are created with an architecture unlike those of conventional micropprocessors.段落英譯漢：

1.The control bus is a collection of signals that controls how the processor communicates with the rest of the system.Consider the data bus for a moment.The CPU sends data to memory and receives data from memory on the data bus.This prompts the question.“Is it sending or receiving?” There are two lines on the control bus, read line and write line, which specify the direction of data flow.Other signals include system clocks, interrupt lines, status lines, and so on.The exact structure of control bus varies among processors in the 80x86 family.However, some control lines are common to all processors and are worthy a brief mention 控制總線是控制處理器與系統(tǒng)其它部件如何通信的信號(hào)樞紐。考慮數(shù)據(jù)總線，CPU通過(guò)數(shù)據(jù)總線向存儲(chǔ)器發(fā)送數(shù)據(jù)或從存儲(chǔ)器接受數(shù)據(jù)，這就產(chǎn)生了一個(gè)疑問(wèn)：“他是在發(fā)送還是在接受呢？”在控制總線上有兩條線，即讀線和寫線，他們指明了數(shù)據(jù)流的方向。其他信號(hào)包括系統(tǒng)時(shí)鐘、中斷信號(hào)、狀態(tài)信號(hào)等。80X86系列控制總線的具體結(jié)構(gòu)因處理器的不同而不同，但一

些控制線對(duì)所有的處理器是共同的。2，In digital processing of a

continuous-time signal x(t), the first step is to select a sampling period T and then to sample x(t)to yield x(nT).It is clear that the smaller T is, the closer x(nT)is to x(t).However, a smaller T also requires more computation.Thus an important task in DSP is to find 有人也提出了少數(shù)的非商業(yè)FPGAs結(jié)構(gòu)，其

設(shè)計(jì)細(xì)節(jié)更易獲得?？删幊踢壿媴^(qū)別于傳統(tǒng)硬件的關(guān)鍵特性在于他的可重構(gòu)行。從執(zhí)行的強(qiáng)度和速度看，這種裝置不能與傳統(tǒng)硬件相比，但他們的可重構(gòu)性能的開(kāi)發(fā)和硬件設(shè)計(jì)改變的迅速性，縮短了產(chǎn)品上市的時(shí)間，降低了成本。

5.第五代計(jì)算機(jī)大力發(fā)展計(jì)算機(jī)可以解決問(wèn)題最終可能是被稱為創(chuàng)造性的方式是另一the largest possible T so that all information(if not possible, all essential information)of x(t)is retained in x(nT).Without the

frequency-domain description, it is not possible to find such a sampling period.Thus computing the frequency content of signals is a first step in digital signal processing.連續(xù)時(shí)間信號(hào)的數(shù)字處理，第一步是選擇一個(gè)采樣周期T，然后采樣x(t)產(chǎn)生x(nT).。很明顯，周期T越小，x(nT)越接近x(t)。然而，T越小計(jì)算量越大。因此，數(shù)字信號(hào)處理的一項(xiàng)重要任務(wù)，是要找出最大可能T，使x(t)的所有信息（如果不能，那么信號(hào)的所有基本信息）仍然保留在x(nT)中。沒(méi)有頻域描述，就不可能找到采樣周期。因此數(shù)字信號(hào)處理的第一步是計(jì)算信號(hào)的頻譜。3，F(xiàn)PGAs are a form of programmable logic devices which permits the design of many different complex digital circuits.FPGAs were first introduced in 1986 by Xilinx using a memory-based programming technology.Since then there have been many new commercial architectures.A new non-commercial FPGA architecture have been proposed for which the design details are more readily available.The key property of programmable logics that differentiates them from custom

hardware is their reconfigurability.such device cannot compete with a custom hardware implementation in terms of density or speed, but their

reconfigurability allows hardware designs to be created and changed rapidly, thus reducing time-to-market and costs over custom hardware.現(xiàn)場(chǎng)可編程門陣列是可編程邏輯器件的一種形式，它允許設(shè)計(jì)許多不同的復(fù)雜數(shù)字電路。1986年，Xilinx首次把基于內(nèi)存的編程技術(shù)引入了FPGAs。此后還有許多新的商業(yè)結(jié)構(gòu)出現(xiàn)，個(gè)趨勢(shì)在計(jì)算機(jī)的發(fā)展，理想的目標(biāo)是真正的人工智能。正在積極探索的一個(gè)路徑是并行處理計(jì)算機(jī)，它使用許多芯片在同一時(shí)間執(zhí)行多個(gè)不同的任務(wù)。并行處理可能最終能在一定程度上重復(fù)了復(fù)雜的反饋，近似于人類思想的評(píng)估能力。另一種形式正在研究并行處理是分子計(jì)算機(jī)的使用。在這些計(jì)算機(jī)，邏輯符號(hào)用DNA的化學(xué)單元表達(dá)，而不是通過(guò)常規(guī)的電子流問(wèn)題，比目前的超級(jí)計(jì)算機(jī)速度快，將使用更少的能源。

第五篇：電子信息英語(yǔ)專業(yè)英語(yǔ)詞組專業(yè)英語(yǔ)b篇翻譯

Translated by何瑩婷，版權(quán)沒(méi)有，翻印不究。有錯(cuò)誤歡迎指正:)Unit3 27-2In the binary system of representation the base is 2, and only two numerals 0 and 1 are required to represent a number.The numerals 0 and 1 have the same meaning as in the decimal system, but a different interpretation is placed on the position occupied by a digit.In the binary system the individual digits represent the coefficients of powers of two rather than ten as in the decimal system.For example, the decimal number 19 is written in the binary representation as 10011 since

10011=1×24+0×23+0×22+1×21+1×20=16+0+0+2+1=19

A short list of equivalent numbers in decimal and binary notation is given in Table 3.2.

二進(jìn)制示數(shù)系統(tǒng)中的基數(shù)是二，且只有0和1兩個(gè)數(shù)被用以示數(shù)。0和1在這里與在十進(jìn)制中具有一樣的意義，但每個(gè)數(shù)位表示的不一樣。二進(jìn)制系統(tǒng)中每個(gè)數(shù)字表示二的冪系數(shù)，而十進(jìn)制中表示十的冪系數(shù)。例如，十進(jìn)制數(shù)19在二進(jìn)制中表示為10011因?yàn)?10011=1×24+0×23+0×22+1×21+1×20=16+0+0+2+1=19 二進(jìn)制和十進(jìn)制數(shù)相等數(shù)字見(jiàn)表3.2.27-3A general method for converting from a decimal to a binary number is indicated in Table 3.3.The procedure is the following.Place the decimal number(in this illustration, 19)on the extreme right.Next divide by 2 and place the quotient(9)to the left and indicate the remainder(1)directly below it.Repeat this process(for the next column 9÷2 =4 and a remainder of 1)until a quotient of 0 is obtained.The array of 1’s and 0’s in the second row is the binary representation of the origin decimal number.In this example, decimal 19=10011 binary.

十進(jìn)制轉(zhuǎn)換成二進(jìn)制的一般方法如圖3.3。過(guò)程如下：把十進(jìn)制數(shù)（圖中的19）放在最右端，接下來(lái)除以2，把商（9）放在左邊并直接在其下方標(biāo)明余數(shù)（1）。重復(fù)這個(gè)步驟（下一列為9÷2=4余1），直到商為0截止。第二行中的1和0就是原始十進(jìn)制數(shù)的二進(jìn)制表示。此例中，十進(jìn)制19=二進(jìn)制10011.28-1A binary digit(a 1 or a 0)is called a bit.A group of bits that has the same significance is called a byte, word, or code.For example, to represent the 10 numerals(0, 1, 2, …, 9)and the 26 letters of the English alphabet would require 36 different combinations of 1’s and 0’s.Since 25<36<26, then a minimum of 6 bits per bite are required in order to accommodate all the alphanumeric characters.In this sense a bite is sometimes referred to as a character and a group of one or more characters as a word.

一位二進(jìn)制數(shù)（一個(gè)1或0)叫做比特。一組具有相同意義的比特叫做字節(jié)，詞，或代碼。例如，表示10個(gè)數(shù)字（0,1,2，...9）和26個(gè)英文字母要用到36種不同的1和0的組合。因?yàn)?5<36<26，那么表示所有這些字母數(shù)字字符組最少需要6比特每字節(jié)。這種情況下一字節(jié)有時(shí)候被稱為一個(gè)字符和一個(gè)或多個(gè)字符組成的字符串。

29-1The parameters of a physical device(for example, VCE·sat of a transistor)are not identical from sample to sample, and they also vary with temperature.Furthermore, ripple or voltage spikes may exist in the power supply or ground leads, and other sources of unwanted signals, called noise, may be present in the circuit.For these reasons the digital levels are not specified precisely, but as indicated by the shaded region in Figure 3.6, each state is defined by a voltage range about a designated level, such as 4±1 V and 0.2±0.2 V.

每個(gè)實(shí)體器件樣本的參數(shù)(如晶體管的VCE·sat)是不完全相同的，它們還會(huì)隨溫度變化。而且，電源或地線可能存在電壓脈動(dòng)或電壓峰值，其他干擾信號(hào)——噪聲也可能出現(xiàn)在電路中。由于這些原因，數(shù)字電平?jīng)]有明確的規(guī)定，但如圖3.6中陰影所示，將每個(gè)狀態(tài)定義為指定電平的電壓范圍，例如4±1 V 和 0.2±0.2 V。

Unit4 37-1The materials that make up our universe are composed of over one hundred basic and individual types of matter called elements.Ninety-two of these elements occur naturally and the remainders are man-made.Each element has a separate identify of its own, that is, no two elements have the same physical and chemical properties, nor can an element be subdivided by ordinary physical and chemical means into simple elements.[1] Examples of elements are gold, mercury and oxygen.構(gòu)成宇宙的物質(zhì)是由一百多種基本的不同類型的物質(zhì)——元素組成的。其中92種元素是天然形成的，其他的則是人造的。每種元素都各有其自己的標(biāo)識(shí)，也就是說(shuō)，元素的物理和化學(xué)特性是獨(dú)一無(wú)二的，一種元素也不可以用物理和化學(xué)手段再分成簡(jiǎn)單的元素。例如金，汞和氧元素。

37-3Electrons whirl around nuclei in much the same manner that the planets of our solar system travel around the sun.The difference between an atom of one element and that of another is in the number of protons and neutrons contained in the nucleus.[2] All the elements in the universe, and therefore all matter, is composed of protons, neutrons, and electrons.電子圍繞原子核旋轉(zhuǎn)，其方式類似于太陽(yáng)系中行星圍繞太陽(yáng)旋轉(zhuǎn)。一種元素的原子和另一種元素的原子的差別在于其原子核中的質(zhì)子數(shù)和中子數(shù)。宇宙中的所有元素，也就是說(shuō)所有的物質(zhì)，都是由質(zhì)子，中子和電子組成的。

37-4There must be force of attraction between a nucleus and the electrons surrounding it, otherwise the electrons would fly off into space, in order to understand its nature, we find it helpful to call this force a charge.The charge of the nucleus is defined as positive, and the opposite charge of the electron, negative.In view of the fact that opposites attract, the force between the nucleus and the rotating electron around it prevents the electron from flying off into space.在原子核與其周圍的電子間必然存在著吸引力，否則電子將會(huì)飛離原子核，為了理解它的性質(zhì)，我們把這種力稱為電荷。原子核電荷定義為正電荷，電子的電荷則相反，為負(fù)電荷。鑒于異性相吸，原子核和圍繞其旋轉(zhuǎn)的電子間的力阻止了電子飛離到空間中。

38-last para Impurities may be added to pure semiconductors.This results in semiconductor materials, which may either have an excess of free electrons or a deficiency of orbital electrons.When an excess of electrons is present we call the material N-type;when lack of orbital electrons occurs, we call the material P-type.Both N-type and P-type semiconductors are made by treated materials.such as germanium and silicon with impurities，such as arsenic and indium.The addition of impurities to semiconductors is called doping.雜質(zhì)被加入到純的半導(dǎo)體中。這會(huì)導(dǎo)致半導(dǎo)體材料中有過(guò)剩的自由電子或軌道電子缺失。有過(guò)剩電子時(shí)材料被稱為n型；缺失軌道電子時(shí)材料被稱為p型。N型和P型半導(dǎo)體都由加工材料制成。例如有雜質(zhì)的鍺和硅，砷和銦。往半導(dǎo)體中加入的雜質(zhì)添加物叫摻雜質(zhì)。

Unit5 50-2At first, these disk drives used 14 inch disks, but now they use 5 1/4 inch, 3 1/2 inch,2 1/2 inch, and 1 4/5 inch diameters.In contrast to the floppy disk drive, hard disk drives hold from 80 megabytes to gigabytes and terabytes of information.When purchasing a hard disk, consider storage capacity and seek time, a measure of a hard disk’s access speed.The smaller the numbers, the faster the disk.In the past, 65 milliseconds was the standard access time, but today the standard is less than 7 milliseconds.起初，這些磁盤驅(qū)動(dòng)采用14英寸磁盤，但現(xiàn)在采用的是5 1/4英寸，2 1/2英寸和1 4/5直徑的磁盤。與軟盤驅(qū)動(dòng)截然不同的是，硬盤驅(qū)動(dòng)保存著兆字節(jié)到千兆字節(jié)、萬(wàn)兆字節(jié)的信息。購(gòu)買硬盤時(shí)要考慮存儲(chǔ)容量和尋道時(shí)間及存取速度。這些數(shù)字越小，磁盤就運(yùn)行得越快。在過(guò)去，標(biāo)準(zhǔn)存取時(shí)間為65毫秒，而現(xiàn)在的標(biāo)準(zhǔn)為低于7毫秒。

50-3Storing data on hard disks is similar to storing data on diskettes.In order to read or write data on the surface of the spinning disk platter, the disk drives are designed with access arms, or actuators.[1] The access arms, or actuators, contain one or more read/write heads per disk surface.As the disk rotates at a high rate of speed, usually 3,600 revolution per minute, the read/write heads move across its surface.These read/write heads float on a cushion of air and do not actually touch the surface of the disk.[2] The distance between the head and the surface varies from approximately ten to twenty millionths of an inch.If some form of contamination is introduced or if the alignment of the read/write heads is altered by something accidentally jarring the computer, the disk head can collide and damage the disk surface, causing a loss of data.This event is known as a head crash.Because of the time needed to repair the disk and to reconstruct the data that was lost, head crashes can be extremely costly to users in terms of both time and money.硬盤上的數(shù)據(jù)存儲(chǔ)與軟盤上的類似。為了在旋轉(zhuǎn)的磁盤盤片表面讀寫數(shù)據(jù)，磁盤驅(qū)動(dòng)器被設(shè)計(jì)成具有存取和傳動(dòng)裝置。存取和傳動(dòng)裝置由每個(gè)盤片表面的一個(gè)或多個(gè)讀寫頭構(gòu)成。當(dāng)盤片以通常為3600轉(zhuǎn)每分的速度高速旋轉(zhuǎn)時(shí)，讀寫頭移過(guò)盤片表面。這些讀寫頭在高壓氣流上漂浮，移動(dòng)時(shí)并不與盤片表面真正接觸。讀寫頭與盤片表面的距離約為一萬(wàn)到兩千萬(wàn)分之一英寸。如果有污染物介入，或讀寫頭隊(duì)列被電腦的意外震動(dòng)改變，讀寫頭會(huì)碰撞并損壞盤片表面，引起數(shù)據(jù)丟失。這種情況叫做磁頭碰撞。由于修復(fù)磁盤并重建數(shù)據(jù)需要一定的時(shí)間，磁頭碰撞會(huì)花費(fèi)用戶相當(dāng)多的金錢和時(shí)間。

50-5The sector method for physically organizing data on disks divides each track on the disk surface into individual storage areas called sectors.Each sectors can contain a specified number of bytes.Data is referenced by indicating the surface, track, and sector where the data is stored.用扇區(qū)方式物理地在磁盤上組織數(shù)據(jù)是將盤片表面分成獨(dú)立的存儲(chǔ)區(qū)域，稱之為扇區(qū)。每個(gè)扇區(qū)能包含特定字節(jié)數(shù)。數(shù)據(jù)通過(guò)指示存儲(chǔ)著數(shù)據(jù)的盤片表面，軌道和扇區(qū)來(lái)引用。

51-6Most optical disks are prerecorded and cannot be modified by the user.These disks are used for applications such as an auto parts catalog where the information is changed only occasionally, such as once a year, and a new updated optical disk is created.[3] Optical disk devices that provide for one-time recording are called WORM devices, an acronym for write once, read many.Erasable optical disk drives are just starting to be used.The most common erasable optical drives use magneto-optical technology, in which a magnetic field changes the polarity of a spot on the disk that has been heated by a laser.[4] 大多數(shù)光盤是事先錄好的，且不能被用戶修改。這種光盤用于信息量大，不需要經(jīng)常更改信息內(nèi)容的場(chǎng)合。例如，一個(gè)汽車零件目錄，其中的信息是經(jīng)過(guò)一段時(shí)間（比如一年）才更新一次，需要更新時(shí)再制作一張新的光盤就可以了。只能刻錄一次的光盤設(shè)備叫WORM設(shè)備，是write once, read many的縮寫。可擦寫光盤設(shè)備剛開(kāi)始被使用。最常見(jiàn)的可擦寫光盤驅(qū)動(dòng)采用磁光技術(shù)，在這種技術(shù)中，磁場(chǎng)改變了磁盤上被激光加熱的點(diǎn)的極性。

Unite6 65-1 PCM is dependent on three separate operations: sampling, quantizing, and coding.Many different schemes for performing these three functions have evolved during recent years, and we shall describe the main ones.[1] In these descriptions we shall see how a speech channel of telephone quality maybe conveyed as a series of amplitude values, each value being represented, that is, coded, as a sequence of 8 binary digits.[2] Furthermore, we shall prove that a minimum theoretical sampling frequency of order 6.8 kilohertz(kHz)is required to convey a voice channel occupying the range 300 Hz to 3.4 kHz.[3] Practical equipments, however, normally use a sampling rate of 8 kHz, and if 8-digits per sample value are used, the voice channel becomes represented by a stream of pulses with a repetition rate of 64 kHz.Figure 6.2 illustrates the sampling, quantizing, and coding processes.

脈沖編碼調(diào)制依靠三個(gè)獨(dú)立的運(yùn)作：采樣，量化，編碼。近年來(lái)，人們對(duì)這三個(gè)環(huán)節(jié)的實(shí)現(xiàn)提出了許多不同的方案，我們將對(duì)其中一些主要的方案進(jìn)行討論。在這些討論中，我們會(huì)看到話路中的語(yǔ)音信號(hào)是如何轉(zhuǎn)換成一個(gè)幅值序列的，而每個(gè)幅值又被編碼，即以8位二進(jìn)制數(shù)的序列表示。而且我們將證明，為了變換頻率范圍為300hz-3.4khz的話路信號(hào)，理論上的最小采樣頻率為6.8khz。但實(shí)際的設(shè)備通常采用8 kHz的采樣速度，而如果采用8位每樣本的值，則會(huì)出現(xiàn)重復(fù)速率為64 kHz的脈沖流。采樣，量化和編碼過(guò)程如圖6.2所示。

67-2Digital transmission provides a powerful method for overcoming noisy environments.Noise can be introduced into transmission path in many different ways;perhaps via a nearby lightning strike, the sparking of a car ignition system, or the thermal low-level noise within the communication equipment itself.It is the relationship of the true signal to the noise signal, known as the signal-to-noise ratio, which is of most interest to the communication engineer.Basically, if the signal is very large compared to the noise level, then a perfect message can take place;however, this is not always the case.For example, the signal received from a satellite, located in far outer space, is very weak and is at a level only slightly above that of the noise.[4]

Alternative examples may be found within terrestrial systems where, although the message signal is strong, so is the noise power.數(shù)字傳輸是克服噪聲環(huán)境的一種有力方式。噪聲會(huì)以多種不同方式引入傳輸路徑。也許是附近的閃電，汽車點(diǎn)火裝置的火花，或者是通信設(shè)備中熱的低電平噪聲。確實(shí)信號(hào)與噪聲信號(hào)間的關(guān)系稱為信噪比，這是通信工程師最感興趣的問(wèn)題。基本上說(shuō)，若信號(hào)相對(duì)噪聲占的比重很大，這條信息將得到完美傳輸。但事實(shí)并不總是這樣。比如，從位于遙遠(yuǎn)太空中的衛(wèi)星接收到的信號(hào)極其微弱，其電平僅比噪聲稍高一點(diǎn)。另一個(gè)例子是地面系統(tǒng)，盡管信息信號(hào)強(qiáng)，但噪聲功率也強(qiáng)。

67-3If we consider binary transmission, the complete information about a particular message will always be obtained by simply detecting the presence or absence of the pulse.By comparison, most other forms of transmission systems convey the message information using the shape, or level of the transmitted signal;parameters that are most easily affected by the noise and attenuation introduced by the transmission path.[5] Consequently there is an inherent advantage for overcoming noisy environments by choosing digita1 transmission.

要是我們考慮二進(jìn)制傳輸，完整的信息總會(huì)通過(guò)簡(jiǎn)單地檢測(cè)脈沖的有無(wú)獲得。相比之下，許多其他形式的傳輸系統(tǒng)利用被傳信號(hào)的波形或電平高低來(lái)傳送信息，而這些參數(shù)又極易受到傳輸路徑中噪聲和衰耗的影響。因此選擇數(shù)字傳輸對(duì)克服噪聲環(huán)境有固有的優(yōu)勢(shì)。

67-4So far in this discussion we have assumed that each voice channel has a separate coder, the unit that converts sampled amplitude values to a set of pulses;and decoder, the unit that performs the reverse operation.This need not be so, and systems are in operation where a single codec(i.e., coder and its associated decoder)is shared between 24, 30, or even 120 separate channels.A high-speed electronic switch is used to present the analog information signal of each channel, taken in turn, to the codec.The codec is then arranged to sequentially sample the amplitude value, and code this value into the 8-digit sequence.Thus the output to the codec may be seen as a sequence of 8 pulses relating to channel 1, then channel 2, and so on.This unit is called a time division multiplexer(TDM), and 15 illustrated in Figure 6.3.The multiplexing principle that is used is known as word interleaving.Since the words, or 8-digit sequences, are interleaved in time.目前我們?cè)谶@個(gè)討論中假定每個(gè)話路有單獨(dú)的編碼器，也就是將采樣幅值轉(zhuǎn)換成脈沖序列的單元；并有單獨(dú)的解碼器，也就是執(zhí)行相反操作的單元。其實(shí)并不需要這樣，系統(tǒng)靠單一的編譯碼器（編碼器和其關(guān)聯(lián)的解碼器）運(yùn)行，它有24，30,甚至120個(gè)單獨(dú)的信道。高速電子開(kāi)關(guān)用以表示每個(gè)信道的模擬信息信號(hào)，并把信號(hào)依次送入編譯碼器。而后編譯碼器順序地進(jìn)行幅值采樣，并把幅值編排成8位碼序列。這樣編譯碼器的輸出看起來(lái)就像一串關(guān)于信道1，信道2等的8位脈沖序列。這個(gè)單元叫做時(shí)分多路器。圖6.3說(shuō)明了15個(gè)信道的時(shí)分多路器工作原理。采用的分路原理叫字交叉。因?yàn)槊總€(gè)字或8位碼序列是在一段時(shí)間內(nèi)交叉存取的。