【正文】 lity 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 kilohertz(kHz)is required to convey a voice channel occupying the range 300 Hz to kHz.[3] Practical equipments, however, normally use a sampling rate of 8 kHz, and if 8digits per sample value are used, the voice channel bees represented by a stream of pulses with a repetition rate of 64 illustrates the sampling, quantizing, and coding processes.脈沖編碼調(diào)制依靠三個獨立的運作：采樣，量化，編碼。例如，一個汽車零件目錄，其中的信息是經(jīng)過一段時間（比如一年）才更新一次，需要更新時再制作一張新的光盤就可以了。每個扇區(qū)能包含特定字節(jié)數(shù)。如果有污染物介入，或讀寫頭隊列被電腦的意外震動改變，讀寫頭會碰撞并損壞盤片表面，引起數(shù)據(jù)丟失。存取和傳動裝置由每個盤片表面的一個或多個讀寫頭構(gòu)成。這些數(shù)字越小，磁盤就運行得越快。往半導(dǎo)體中加入的雜質(zhì)添加物叫摻雜質(zhì)。這會導(dǎo)致半導(dǎo)體材料中有過剩的自由電子或軌道電子缺失。原子核電荷定義為正電荷，電子的電荷則相反，為負(fù)電荷。373Electrons whirl around nuclei in much the same manner that the planets of our solar system travel around 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 posed of protons, neutrons, and ，其方式類似于太陽系中行星圍繞太陽旋轉(zhuǎn)。Unit4 371The materials that make up our universe are posed of over one hundred basic and individual types of matter called of these elements occur naturally and the remainders are 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 ——元素組成的。而且，電源或地線可能存在電壓脈動或電壓峰值，其他干擾信號——噪聲也可能出現(xiàn)在電路中。sat of a transistor)are not identical from sample to sample, and they also vary with , 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 these reasons the digital levels are not specified precisely, but as indicated by the shaded region in Figure , each state is defined by a voltage range about a designated level, such as 4177。此例中，十進制19= binary digit(a 1 or a 0)is called a group of bits that has the same significance is called a byte, word, or example, to represent the 10 numerals(0, 1, 2, …, 9)and the 26 letters of the English alphabet would require 36 different binations of 1’s and 0’ 25一位二進制數(shù)（一個1或0)叫做比特。過程如下：把十進制數(shù)（圖中的19）放在最右端，接下來除以2，把商（9）放在左邊并直接在其下方標(biāo)明余數(shù)（1）。0和1在這里與在十進制中具有一樣的意義，但每個數(shù)位表示的不一樣。有錯誤歡迎指正:)Unit3 272In the binary system of representation the base is 2, and only two numerals 0 and 1 are required to represent a 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 the binary system the individual digits represent the coefficients of powers of two rather than ten as in the decimal example, the decimal number 19 is written in the binary representation as 10011 since10011=124+023+022+121+120=16+0+0+2+1=19A short list of equivalent numbers in decimal and binary notation is given in Table .二進制示數(shù)系統(tǒng)中的基數(shù)是二，且只有0和1兩個數(shù)被用以示數(shù)。2 =4 and a remainder of 1)until a quotient of 0 is array of 1’s and 0’s in the second row is the binary representation of the origin decimal this example, decimal 19=10011 binary.。第二行中的1和0就是原始十進制數(shù)的二進制表示。因為25291The parameters of a physical device(for example, VCEsat)是不完全相同的，它們還會隨溫度變化。 V。例如金，汞和氧元素。374There 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 of the nucleus is defined as positive, and the opposite charge of the electron, 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 ，否則電子將會飛離原子核，為了理解它的性質(zhì)，我們把這種力稱為電荷。when lack of orbital electrons occurs, we call the material Ntype and Ptype semiconductors are made by treated as germanium and silicon with impurities，such as arsenic and addition of impurities to semiconductors is called 。例如有雜質(zhì)的鍺和硅，砷和銦。購買硬盤時要考慮存儲容量和尋道時間及存取速度。為了在旋轉(zhuǎn)的磁盤盤片表面讀寫數(shù)據(jù)，磁盤驅(qū)動器被設(shè)計成具有存取和傳動裝置。讀寫頭與盤片表面的距離約為一萬到兩千萬分之一英寸。505The sector method for physically organizing data on disks divides each track on the disk surface into individual storage areas called sectors can contain a specified number of is referenced by indicating the surface, track, and sector where the data is ，稱之為扇區(qū)。這種光盤用于信息量大，不需要經(jīng)常更改信息內(nèi)容的場合。最常見的可擦寫光盤驅(qū)動采用磁光技術(shù)，在這種技術(shù)中，磁場改變了磁盤上被激光加熱的點的極性。而且我們將證明。perhaps via a nearby lightning strike, the sparking of a car ignition system, or the thermal lowlevel noise within the munication equipment is the relationship of the true signal to the noise signal, known as the signaltonoise ratio, which is of most interest to the munication , if the signal is very large pared to the noise level, then a perfect message can take place。確實信號與噪聲信號間的關(guān)系稱為信噪比，這是通信工程師最感興趣的問題。另一個例子是地面系統(tǒng)，盡管信息信號強，但噪聲功率也強。因此選擇數(shù)字傳輸對克服噪聲環(huán)境有固有的優(yōu)勢。高速電子開關(guān)用以表示每個信道的模擬信息信號，并把信號依次送入編譯碼器。采用的分路原理叫字交叉。Design is the area of human experience, skill and knowled