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Unit 3 电磁场，天线和微波Unit 3-1第一部分：电磁场电磁场是由带电物体产生的物理场。
它会影响场附近的带电物体的行为。
电磁场在空间无限延伸，描述电磁相互作用。
它是自然界中四个基本作用力之一（其余为万有引力，弱相互作用，强相互作用）。
电磁场可以看成是电场和磁场的结合。
电场是由静止电荷产生的，磁场由运动电荷（电流）产生；这两种（电荷）通常被描述为电磁场的源。
电荷和电流与电磁场相互作用的方式由麦克斯韦方程组和洛伦兹力定律所描述。
从经典的角度，电磁场可认为使平滑、连续的场，以波动方式传播；而从量子力学的角度，场可看作是由光子组成的。
电磁场的结构电磁场可用两种截然不同的观点来看。
连续结构：经典地，电场和磁场被认为是由带电物体的平滑运动产生的。
例如，振荡电荷产生电场和磁场，可看成光滑的、连续的波动方式。
这时，能量可以看成是在任意两个位置之间通过电磁场连续地传递。
例如，在无线电发射机中的金属原子（看来是）连续地传递能量。
这个观点在一定程度上（低频辐射）是有用的，但是高频时就有问题（如紫外灾难）。
由此产生了另一种观点。
离散结构：电磁场可以一种比较“粗略”的方式来考虑。
实验表明：电磁场的能量传递可以更好地描述为用固定频率的光子来传递。
普朗克的关系式将光子的能量E及其频率ν通过下式联系起来E = h ν ，其中h是为纪念马克斯普朗克而命名的普朗克常量。
ν是光子的频率。
例如在光电效应中，即因电磁辐射而从金属表面发射电子的现象，我们发现增加入射辐射的强度并无影响，只有辐射频率与发射的电子有关。
已经证明电磁场的量子描述是非常成功的，引出了量子电动力学。
量子电动力学是一种描述电磁辐射与带电物体之间相互作用的量子场理论。
电磁场的动力学过去，认为带电物体会产生与它们电荷性质有关的两种场。
相对于测量电荷性质的观察者，电荷静止时产生电场，电荷运动（产生电流）时产生磁场（和电场）。
随着时间的推移，人们认识到电场和磁场是电磁场这一整体的两个部分。
1 The transistor is what started the evolution of the modern computer industry in motion.晶体管开启了现代电脑工业的革命2 The storage cell only requires one capacitor and one transistor, whereas a flip-flop connected in an array requires 6 transistors.存储单元仅需要一个电容和晶体管，并而不像触发器整列那样需要6个晶体管3 There has been a never ending series of new op amps released each year since then, and their performance and reliability has improved to the point where present day op amps can be used for analog applications by anybody.从此以后每年都有新系列的运放发布，他们的性能和可靠性得到了提升，如今任何人都能用运放来设计模拟电路。
4 This is capable of very high speed conversion and thus can accommodate high sampling rates, but in its basic form is very power hungry.它具有高速转换能力，从而能适应高速采样速率，但它的基本形式非常耗电。
5 During the “on” period , energy is being stored within the core material of the inductor in the form of flux.在”on”阶段，能量以涌浪形式存储在电感的核芯材料里面6 The design goal of frequency synthesizers is to replace multiple oscillators in a system, and hence reduce board space and cost.频率合成器的设计目标是取代系统中多个振荡器，从而减小板卡面积和成本。
a portion of 一部分a variety of各种各样的a mass of 大量的AC abbr. Alternating Current 交流电accide ntal adj.意外的accumulator n.累加器acquisiti on n.获取，采集acquisition time 采集时间acquisition time 采集时间activate vt .激活active adj.有源的actuator n 致动器，执行器add-o n n.附件administration邮电管理局address vt.从事，忙于address gen erator 地址产生器address poin ter 地址指针addressing mode 寻址模式adjustme nt n 调整，调节ADSL abbr. Asymmetrical Digital Subscriber Loo非对称数字用户线adverse adj不利的，相反的AFG Arbitrary Function Generator 任意函数发生器aggregate v.聚集，合计AGP Accelerated Graphic Port 加速图形接口akin adj.同族的，类似的algorithm n.算法alias ing n.混叠现象alkali ne adj.碱性的all in all 总而言之all of a sudde n 突然allocate vt.分配allocate vt.分配allow for 虑及，体谅allow for 虑及，酌留alpha nu mericadj.包括文字与数字的alter v.改变alter native n .选择 ALU abbr Arithmetic Logic Unit 算术逻辑单元alumi nium n 岭铝ambie ntadj.周围的 n.周围环境an alogous adj.类似的 an cillary adj.辅助的，副的an guish n 痛苦，苦恼analogyn.类似，类推an gular freque ncy 角频率anno tati on n.标注，注角军antenna n.触角，天线anti-aliasing filter抗亍昆叠滤波器anti-aliasing filter 抗混叠滤波器applia nee n.用具，器具applia nee n.用具，器县applicati on in terface 应用程序接口approach n.方法appropriate adj.适当的approximati on n.近似（值）approximati on n.逼近，近似值archive vt.存档n.档案文件arena n.竞技场，舞台arena n.竞技场舞台arise from 由…引起；从…中产生arithmetic n算数array n.阵列，数组array n.数组，阵列artificial adj.不自然的as a consequenee 因此匕as always 照常as opposed to ..与...相反as yet到目前为止ASIC abbr. Application Specific Integrated Circuit专用集成电路ASIC Applicati on Specific In tegrated CircuitASIC Applicatio n-Specific I ntegrated Circuit^ 用集成电路assembler n 汇编器assembly Ian guage 汇编语言assig nment n.赋值ASSP abbr. Application Specific Standard Product专用标准器件ASSP Applicatio n-Specific Sta ndard Part专用标准器件assume vt 假定asynchronous adj.异步的asynchronous adj.异步的atte nu ator n.衰减器audiophile n.高保真音响爱好者auditorium n.会堂，礼堂auditory system 听觉系统automatic variable 自动变量automotive adj.汽车的AWG Arbitrary Waveform Ge nerator 任意波形发生器B(be) known as …称作......(be) capable of具备••…的能力(be) equivalerit to 相当于... ,等价于 ...(be) proportional to 与•…成比例back bias 反向偏压backplane n.背叛backside n.背部，后方bar graph条形图bargai n n.交易，协议，廉价品barrier n.隔板，势垒，阻挡层base station 基站base stati on 基站baseba nd n.基带baud n 波特be concerned with •对•…关心be encumbered with 为…•所累be mad e up of由…•组成be referred to as.... 被称作...be thought of as 被认为....beam splitter 分光镜behavioral syn thesis 行为综合ben eficial adj.有益的，受益的Bessel filter贝塞耳滤波器biased adj.加偏压的，有偏向的bill of materials 材料单BIOS abbr. Basic Input Output System基本输入输出系统bipolar adj.双极性的bit vector位向量bland adj.平淡的block diagram 方框图blow up 爆炸，放大blur v使…•模糊BNC bayo net neill-co ncelman 同轴电缆卡环形接头boast v.夸耀Bode plot伯德图bond n.接头Boolean variable 布尔变量boost n.升压，放大bootn.启动，引导，自举boot sector弓丨导扇区bootstran.引导程序pbootstraloader引导装入程序pbrake n.刹车branch instruction分支指令brief adj.短暂的bring up 捉出，引出browse v.浏览budget n.预算budget n.预算budgetary adj.预算的buffer n 缓冲器buffer r 1.缓冲器，缓冲区buildi ng block构件，模块built-in adj.内置的bulky adj.体积大的bulky adj谷量大的，体积大的bun chin.聚束ngbus in terface 总线接口bus in terface 总线接口by one ' s(own) bootstraps 通过自己的努力by way of 经由；作为Ccable n.电缆cable modem 线缆调制解调器cable TV 有线电视cache n.高速缓存CAD Computer Aided Desig n 计算机辅助设计calculable adj.可计算的，能预测的calculation-intensive algorithm 运算密集型算法camcorder n.便携式摄像机can did adj.非排演的，偷拍的capacitive adj.电容性的capacitor n.电容器capacity n.容量，电容capture v .记录，输入carrier wave 载波cascade n 级联cathode n.阴极cauldr on n.大锅炉CB citizens'band 民用波段CCD Charge Coupled Device 电荷耦合器件CD Compact Disc 光盘cell n.细胞，蜂房，电池cellular adj.蜂窝状的characterizati on n.描述，表征charge pump 电荷泵chat n.聊天Chebyshev Type l filter切比雪夫1型滤波器chip rate码片速率chro minance n.色度circular adj.圆形的，循环的circular adj.循环的，环形的circular buffer循环缓冲区class n.类clear-cut adj .界限分明的clever adj.精巧的，灵巧的，巧妙的clich e n空话，套话，废话clock jitter 时钟抖动clump n.块，团CMOS abbr. Compleme ntary Metal-Oxide-Semico nducto互补金属氧化物半导体vi.碰撞，抵触concerned adj.有关的adj.并发的con curre nt process 并发进程con diti onal adj.条件的con diti oning n 调节，调整con duct v 传导con ductivity n.传导性，传导率con figure vt.配置，设定con flict n .冲突，抵触con forma nee n.顺应，一致conjugate adj .共轭的con seque ntly adv.从而，因此con sist of...由…•组成con solidated adj 。
电子信息工程专业英语教程第三版译者：唐亦林p32In 1945 H. W. Bode presented a system for analyzing the stability of feedback systems by using graphical methods. Until this time, feedback analysis was done by multiplication and division, so calculation of transfer functions was a time consuming and laborious task. Remember, engineers did not have calculators or computers until the '70s. Bode presented a log technique that transformed the intensely mathematical process of calculating a feedback system's stability into graphical analysis that was simple and perceptive. Feedback system design was still complicated, but it no longer was an art dominated by a few electrical engineers kept in a small dark room. Any electrical engineer could use Bode's methods find the stability of a feedback circuit, so the application of feedback to machines began to grow. There really wasn't much call for electronic feedback design until computers and transducers become of age.1945年HW伯德提出了一套系统方法，用图形化方法来分析反馈系统的稳定性。
Unit3 computer architecture and microprocessors3--1 Computer Architecture1) Computer architecture , in computer science , is a general term referring to the structure of all or part of computer system . The term also covers the design of system software , such as the operating system (the program that controls the computer) , as well as referring to the combination of hardware and basic software that links the machines on a computer network . Computer architecture refers to an entire structure and to the details needed to make it functional . Thus , computer architecture covers computer systems , microprocessors , circuits , and system programs . Typically the term does not refer to application programs , such as spreadsheets or word processing , which are required to perform a task but not to make the system run .2)1.Design Elements3) In designing a computer system , architects consider five major elements that make up the system's hardware : the arithmetic /logic unit , control unit , memory , input , and output . The arithmetic /logic unit performs arithmetic and compares numerical values . The control unit directs the operation of the computer by taking the user instructions andtransforming them into electrical signals that the computer 's circuitry can understand . The combination of the arithmetic /logic unit and the control unit is called the central processing unit (CPU) . The memory stores instructions and data . The input input and output sections allow the computer to receive and send data , respectively .4) Different hardware architectures are required because of the specialized needs of systems and users . One user may need a system to display graphics extremely fast , while another system may have to be optimized for searching a database or conserving battery power in a laptop computer .5) In addition to the hardware design , the architects must consider what software programs will operate the system . Software , such as programming languages and operating systems , makes the details of the hardware architecture invisible to the user . For example , computers that use the C programming language or a UNIT operating system may appear the same from the user's viewpoint , although they use different hardware architectures .6)2.Processing Architecture7) When a computer carries out an instruction , it proceeds through five steps . First ,the control unit retrieves theinstruction from memory , for example , an instruction to add two numbers . Second , the control unit decodes the instruction into electronic signals that control the computer . Third , the control unit fetches the data (the two numbers) . Fourth , the arithmetic/logic unit performs the specific operation ( the addition of the two numbers ) . Fifth , the control unit saves the result ( the sum of the two numbers ) .8) Early computers used only simple instructions because the cost of electronic capable of carrying out complex instructions was high . As this cost decreased in the 1960s , more complicated instructions became possible . Complex instructions ( single instructions that specify multiple operations ) can save time because they make it unnecessary for the computer to retrieve additional instructions . For example , if seven operations are combined in one instruction , then six of the steps that fetch instructions are eliminated and the computer spends less time processing that operation . Computers that combine several instructions into a single operation are called complex instruction set computers ( CISC ) .9) However , most programs do not often use complexinstructions , but consist mostly of simple instructions . When these simple instructions are run on CISC architectures , they slow down processing because each instruction--whether simple or complex --takes longer to decode in a CISC design . An alternative strategy is to return to designs that use only simple , single--operation instruction sets and make the most frequently used operations faster in order to increase overall performance . Computers that follow this design are called reduced instruction set computers ( RISC ) .10) RISC designs are especially fast at the numerical computations required in science , graphics , and engineering applications . CISC designs are commonly used for non-numerical computations because they provide special instruction sets for handling character data , such as text in a word processing program . Specialized CISC architectures , called digital signal processors , exist to accelerate processing of digitized audio and video signals .11)3.Open and Closed Architectures12) The CPU of a computer is connected to memory and to the outside world by means of either an open or a closed architecture . An open architecture can be expanded after the system has been built , usually by adding extra circuitry ,such as a new microprocessor computer chip connected to the main system . The specifications of the circuitry are made public , allowing other companies to manufacture these expansion products .13) Closed architectures are usually employed in specialized computers that will not require expansion , for example , computers that control microwave ovens . Some computer manufacturers have used closed architectures so that their customers can purchase expansion circuitry only from them . This allows the manufacture to charge more and reduces the options for the consumer .14)work Architecture15) Computers communicate with other computers via networks . The simplest network is a direct connection between two computers . However , computers can also be connected over large networks , allowing users to exchange data , communicate via electronic mail , and share resources such as printers .16) Computers can be connected in several ways . In a ring configuration , data are transmitted along the ring and each computer in the ring examines this data to determine if it is the intended recipient . If the data are not intended fora particular computer , the computer passes the data to the next computer in the ring . This process is repeated until the data arrive at their intended destination . A ring network allows multiple messages to be carried simultaneously , but since each message is checked by each computer , data transmission is slowed .17) In a bus configuration , computers are connected througha single set of wires , called a bus . One computer sends data to another by broadcasting the address of the receive and the data over the bus . All the computers in the network look at the address simultaneously , and the intended recipient accepts the data . A bus network , unlike a ring network , allows data to be sent directly from one computer to another . However , only one computer at a time can transmit data . The others must wait to send their messages .18) In a star configuration , computers are linked to a central computer called a hub . A computer sends the address of the receiver and the data to the hub , which then links the sending and receiving computers directly . A star network allows multiple messages to be sent simultaneously , but it is more costly because it uses an additional computer , the hub , to direct the data .19)5.Recent Advances20) One problem in computer architecture is caused by the difference between the speed of the CPU and the speed at which memory supplies instructions and data . Modern CPUs can process instructions in 3 nanoseconds ( 3 billionths of a second ) . A typical memory access , however , takes 100 nanoseconds and each instruction may require multiple accesses . To compensate for this disparity , new computer chips have been designed that contain small memories , called caches , located near the CPU . Because of their proximity to the CPU and their small size , caches can supply instructions and data faster than normal memory . Cache memory stores the most frequently used instructions and data and can greatly increase efficiency .21) Although a large cache memory can hold more data , it also becomes slower .To compensate , computer architects employ designs with multiple caches . The design places the smallest and fastest cache nearest the CPU and locates a second large and slower cache farther away . This arrangement allows the CPU to operate on the most frequently accessed instructions and data at top speed and to slow down only slightly when accessing the secondary cache . Using separatecaches for instructions and data also allows the CPU to retrieve an instruction and data simultaneously .22) Anther strategy to increase speed and efficiency is the use of multiple arithmetic/logic units for simultaneous operations , called super scalar execution . In this design , instructions are acquired in groups . The control unit examines each group to see if it contains instructions that can be performed together . Some designs execute as many as six operations simultaneously . It is rare , however , to have this many instructions run together ,so on average the CPU does not achieve a six-fold increase in performance . 23) Multiple computers are sometimes combined into single systems called parallel processors . When a machine has more than one thousand arithmetic/logic units , it is said to be massively parallel . Such machines are used primarily for numerically intensive scientific and engineering computation .Parallel machines containing as many as sixteen thousand computers have been constructed .3-3 VLIW Microprocessors24) When Transmeta Corp. revealed its new Crusoe of processors last month ,experts weren’t surprised to learn that the chips are based on Very Long Instruction Word(VLIW)technology .VLIW has become the prevailing philosophy of microprocessor design , eclipsing older approaches such as RISC and complex instruction set computing(CISC) .25) All microprocessor designs seek better performance within the limitations of their contemporary technology. In the 70s of 20th century ,for example ,memory was measured in kilobytes and very expensive .CISC was the dominant approach because it conserved memory .26) In the CISC architecture . there can be hundreds of program instructions-simple commands that tell the system to add numbers, store values and display results. If all instructions were the same length , the simple ones would waste memory .Simple instructions require as little as 8 bits of storage space , while the most complex consume 120 bits .27) Variable-length instructions are more difficult for a chip to process, though, and the longer CISC instructions are especially complex. nonetheless ,to maintain software compatibility, modern chips such as Intel’s Pentium III and Advanced Micro Devices Inc.’s Athlon must still work with all troublesome CISC instructions that were designed in the 1980s , even though their original advantage-memory conservation-isn’t as important .28) In the 1980s , RAM chips got bigger and bigger in capacity while their prices dropped . The emphasis in CPU design shifted to relatively simple , fixed-length instructions , always 32 bits long .Although this wastes some memory by making programs bigger ,the instructions are easier and faster to execute .29) The simplicity of RISC also makes it easier to design superscalar processors-chips that can execute more than one instruction at a time .This is called instruction-level parallelism. Almost all modern RISC and CISC processors are superscalar. But achieving this capability introduced significant new levels of design complexity.30) VLIW chips can cost less , burn less power and achieve significantly higher performance than comparable RISC and CISC chips But there are always trade-offs. One is code expansion-programs grow larger , requiring more memory. Far more important , though , is that compilers must get smarter .A poor VLIW complier will have a much greater negative impact on performance than would a poor RISC or CISC compiler .31) VLIW isn’t a magic bullet , but it’s the new wave in microprocessor design .Within a few years , it’s certain that at least some of your software will be running on VLIW chips .单元3 电脑体系和微处理器3-1 电脑体系电脑体系，在电脑科技中，是一个依据整个或部分电脑结构的通用术语，这个术语也包含软件系统的设计，例如这个操作系统（控制电脑的程序），以及依据这个在电脑网络中连接主机的硬件和基本的软件的结合体。
