Translated by何莹婷，版权没有，翻印不究。有错误欢迎指正:)
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.
二进制示数系统中的基数是二，且只有0和1两个数被用以示数。0和1在这里与在十进制中具有一样的意义，但每个数位表示的不一样。二进制系统中每个数字表示二的幂系数，而十进制中表示十的幂系数。例如，十进制数19在二进制中表示为10011因为 10011=1×24+0×23+0×22+1×21+1×20=16+0+0+2+1=19 二进制和十进制数相等数字见表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.
十进制转换成二进制的一般方法如图3.3。过程如下：把十进制数（图中的19）放在最右端，接下来除以2，把商（9）放在左边并直接在其下方标明余数（1）。重复这个步骤（下一列为9÷2=4余1），直到商为0截止。第二行中的1和0就是原始十进制数的二进制表示。此例中，十进制19=二进制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.
一位二进制数（一个1或0)叫做比特。一组具有相同意义的比特叫做字节，词，或代码。例如，表示10个数字（0,1,2，...9）和26个英文字母要用到36种不同的1和0的组合。因为25<36<26，那么表示所有这些字母数字字符组最少需要6比特每字节。这种情况下一字节有时候被称为一个字符和一个或多个字符组成的字符串。
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.
每个实体器件样本的参数(如晶体管的VCE·sat )是不完全相同的，它们还会随温度变化。而且，电源或地线可能存在电压脉动或电压峰值，其他干扰信号——噪声也可能出现在电路
中。由于这些原因，数字电平没有明确的规定，但如图3.6中阴影所示，将每个状态定义为指定电平的电压范围，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.
构成宇宙的物质是由一百多种基本的不同类型的物质——元素组成的。其中92种元素是天然形成的，其他的则是人造的。每种元素都各有其自己的标识，也就是说，元素的物理和化学特性是独一无二的，一种元素也不可以用物理和化学手段再分成简单的元素。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. 电子围绕原子核旋转，其方式类似于太阳系中行星围绕太阳旋转。一种元素的原子和另一种元素的原子的差别在于其原子核中的质子数和中子数。宇宙中的所有元素，也就是说所有的物质，都是由质子，中子和电子组成的。
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.
在原子核与其周围的电子间必然存在着吸引力，否则电子将会飞离原子核，为了理解它的性质，我们把这种力称为电荷。原子核电荷定义为正电荷，电子的电荷则相反，为负电荷。鉴于异性相吸，原子核和围绕其旋转的电子间的力阻止了电子飞离到空间中。
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. 杂质被加入到纯的半导体中。这会导致半导体材料中有过剩的自由电子或轨道电子缺失。有过剩电子时材料被称为n型；缺失轨道电子时材料被称为p型。N型和P型半导体都由加工材料制成。例如有杂质的锗和硅，砷和铟。往半导体中加入的杂质添加物叫掺杂质。
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，这些磁盘驱动采用14英寸磁盘，但现在采用的是5 1/4英寸，2 1/2英寸和1 4/5直径的磁盘。与软盘驱动截然不同的是，硬盘驱动保存着兆字节到千兆字节、万兆字节的信息。购买硬盘时要考虑存储容量和寻道时间及存取速度。这些数字越小，磁盘就运行得越快。在过去，标准存取时间为65毫秒，而现在的标准为低于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. 硬盘上的数据存储与软盘上的类似。为了在旋转的磁盘盘片表面读写数据，磁盘驱动器被设计成具有存取和传动装置。存取和传动装置由每个盘片表面的一个或多个读写头构成。当盘片以通常为3600转每分的速度高速旋转时，读写头移过盘片表面。这些读写头在高压气流上漂浮，移动时并不与盘片表面真正接触。读写头与盘片表面的距离约为一万到两千万分之一英寸。如果有污染物介入，或读写头队列被电脑的意外震动改变，读写头会碰撞并损坏盘片表面，引起数据丢失。这种情况叫做磁头碰撞。由于修复磁盘并重建数据需要一定的时间，磁头碰撞会花费用户相当多的金钱和时间。
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. 用扇区方式物理地在磁盘上组织数据是将盘片表面分成独立的存储区域，称之为扇区。每个扇区能包含特定字节数。数据通过指示存储着数据的盘片表面，轨道和扇区来引用。
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]
大多数光盘是事先录好的，且不能被用户修改。这种光盘用于信息量大，不需要经常更改信息内容的场合。例如，一个汽车零件目录，其中的信息是经过一段时间（比如一年）才更新一次，需要更新时再制作一张新的光盘就可以了。只能刻录一次的光盘设备叫WORM设备，是write once, read many的缩写。可擦写光盘设备刚开始被使用。最常见的可擦写光盘驱动采用磁光技术，在这种技术中，磁场改变了磁盘上被激光加热的点的极性。
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.
脉冲编码调制依靠三个独立的运作：采样，量化，编码。近年来，人们对这三个环节的实现提出了许多不同的方案，我们将对其中一些主要的方案进行讨论。在这些讨论中，我们会看到话路中的语音信号是如何转换成一个幅值序列的，而每个幅值又被编码，即以8位二进制数的序列表示。而且我们将证明，为了变换频率范围为300hz-3.4khz的话路信号，理论上的最小采样频率为6.8khz。但实际的设备通常采用8 kHz的采样速度，而如果采用8位每样本的值，则会出现重复速率为64 kHz的脉冲流。采样，量化和编码过程如图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.
数字传输是克服噪声环境的一种有力方式。噪声会以多种不同方式引入传输路径。也许是附近的闪电，汽车点火装置的火花，或者是通信设备中热的低电平噪声。确实信号与噪声信号间的关系称为信噪比，这是通信工程师最感兴趣的问题。基本上说，若信号相对噪声占的比重很大，这条信息将得到完美传输。但事实并不总是这样。比如，从位于遥远太空中的卫星接收到的信号极其微弱，其电平仅比噪声稍高一点。另一个例子是地面系统，尽管信息信号强，但噪声功率也强。
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.
要是我们考虑二进制传输，完整的信息总会通过简单地检测脉冲的有无获得。相比之下，许多其他形式的传输系统利用被传信号的波形或电平高低来传送信息，而这些参数又极易受到
传输路径中噪声和衰耗的影响。因此选择数字传输对克服噪声环境有固有的优势。
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.目前我们在这个讨论中假定每个话路有单独的编码器，也就是将采样幅值转换成脉冲序列的单元；并有单独的解码器，也就是执行相反操作的单元。其实并不需要这样，系统靠单一的编译码器（编码器和其关联的解码器）运行，它有24，30,甚至120个单独的信道。高速电子开关用以表示每个信道的模拟信息信号，并把信号依次送入编译码器。而后编译码器顺序地进行幅值采样，并把幅值编排成8位码序列。这样编译码器的输出看起来就像一串关于信道1，信道2等的8位脉冲序列。这个单元叫做时分多路器。图6.3说明了15个信道的时分多路器工作原理。采用的分路原理叫字交叉。因为每个字或8位码序列是在一段时间内交叉存取的。
电子信息英语专业英语词组专业英语b篇翻译
