電氣工程及其自動化專業(yè)英語第二章課文翻譯(共5頁)

1、精選優(yōu)質(zhì)文檔-傾情為你奉上第二章第一篇To say that we live in an age of electronics is an understatement. From the omnipresent integrated circuit to the equally omnipresent digital computer, we encounter electronic devices and systems on a daily basis. In every aspect of our increasingly technological society whether i

2、t is science, engineering, medicine, music, maintenance, or even espionagethe role of electronics is large, and it is growing.談?wù)撽P(guān)于我們生活在一個電子學(xué)時代的論調(diào)是一種空泛的論調(diào)。從無處不在的集成電路到同樣無處不在的數(shù)字計算機(jī)，我們在日?；顒又锌倳龅诫娮釉O(shè)備和電子系統(tǒng)。在我們?nèi)找姘l(fā)展的科技社會的方方面面無論是在科學(xué)、工程、醫(yī)藥、音樂、維修方面甚至是在諜報方面電子學(xué)的作用是巨大的，而且還將不斷增強(qiáng)。 In general, all of the tasks with

3、which we shall be concerned can be classified as "signal-processing“tasks. Let us explore the meaning of this term一般說來，我們將要涉及到的工作被歸結(jié)為“信號處理”工作，讓我們來探究這個術(shù)語的含義吧。A signal is any physical variable whose magnitude or variation with time contains information. This information might involve speech and m

4、usic, as in radio broadcasting, a physical quantity such as the temperature of the air in a room, or numerical data, such as the record of stock market transactions. The physical variables that can carry information in an electrical system are voltage and current. When we speak of "signals"

5、;, therefore, we refer implicitly to voltages or currents. However, most of the concepts we discuss can be applied directly to systems with different information-carrying variables. Thus, the behavior of a mechanical system (in which force and velocity are the variables) or a hydraulic system (in wh

6、ich pressure and flow rate are the variables) can often be modeled or represented by an equivalent electrical system. An understanding of the behavior of electrical systems, therefore, provides a basis for understanding a much broader range of phenomena. 信號就是其與時間有關(guān)的量值或變化包含信息的任何物理變量。這種信息或許像無線電廣播的演講和音

7、樂，或許是像室內(nèi)溫度的物理量，或許像股市交易記錄的數(shù)字?jǐn)?shù)據(jù)。在電氣系統(tǒng)中能夠載有信息的物理變量是電壓和電流。因此當(dāng)我們談到“信號”，我們不言而喻指的是電壓和電流，然而，我們要討論的大多數(shù)概念是可以被直接應(yīng)用于載有不同信息的變量的系統(tǒng)，因此，一個機(jī)械系統(tǒng)（在這個系統(tǒng)中力和速度是其變量）或者液壓系統(tǒng)（在這個系統(tǒng)中壓力和流速是其變量）的性能通?？梢杂靡粋€等效的電氣系統(tǒng)來模擬或表示。因此，我們對于電氣系統(tǒng)性能的理解為理解更寬領(lǐng)域的現(xiàn)象打下了一個基礎(chǔ)。A signal can carry information in two different forms. In an analog signal th

8、e continuous variation of the voltage or current with time carries the information. An example, in Fig.2-l, is the voltage produced by a thermocouple pair when the two junctions are at different temperatures. As the temperature difference between the two junctions varies, the magnitude of the voltag

9、e across the thermocouple pair also varies. The voltage thus provides an analog representation of the temperature difference. 一個信號可以以兩種形式來承載信息。在一個模擬信號中電壓或電流隨時間而產(chǎn)生的連續(xù)變化載有信息。在圖2-1中，當(dāng)一對熱電偶的接頭處于不同的溫度時由熱電偶所產(chǎn)生的電壓就是一個例子。當(dāng)兩個接頭之間的溫度差改變時，一對熱電偶兩端的電壓也將改變。于是電壓就提供了溫度差的模擬表現(xiàn)形式The other kind of signal is a digital s

10、ignal. A digital signal is one that can take on values within two discrete ranges. Such signals are used to represent ON-OFF or YES-NO information. An ordinary household thermostat delivers a digital signal tocontrol the furnace. When the room temperature drops below a preset value, the thermostat s

11、witch closes turning on the furnace. Once the room temperature rises high enough, the switch opens turning off the furnace. The current through the switch provides a digital representation of the temperature variation: ON equals "too cold" while OFF equals "not too cold". 另一種的信號是

12、數(shù)字信號。數(shù)字信號是在兩個離散的范圍內(nèi)能夠呈現(xiàn)一定數(shù)值的信號。這種信號常用以表示“開關(guān)”或“是不是”信息。一個普通的家用恒溫器傳遞一種數(shù)字信號來控制爐子當(dāng)房間的溫度下降到預(yù)定溫度以下時，恒溫器的開關(guān)合上使?fàn)t子開始加熱；一旦房間的溫度上升到足夠高，開關(guān)就斷開使?fàn)t子關(guān)閉。流過開關(guān)的電流提供了溫度變化的數(shù)字表示：ON即為“太冷”而OFF即為“不太冷”A signal-processing system is an interconnection of components and devices that can accept an input signal or a group of input

13、signals, operate on the signals in some fashion either to extract or improve the quality of the information, and present the information as an output in the proper form at the proper time. 一個信號處理系統(tǒng)是某些元件或設(shè)備之間的相互連接，這些元件和設(shè)備能夠接收一個輸入信號或一組輸入信號，信號處理系統(tǒng)以某種方式來處理這些信號即提取這些信號或提高這些信號的品質(zhì)，然后在適當(dāng)?shù)臅r間以適當(dāng)?shù)男问桨堰@個信號表示為輸出量。

14、Fig.2-2 illustrates the components in such a system. The central circles represent the two types of signal processing (digital and analog), while theblock between the two signal- processing blocks represents the conversion of an analog signal to equivalent digital form (A/D=Analog-to-Digital) and th

15、e reverse conversion of a digital signal to the corresponding analog form (D/A=Digital-to-Analog). The remaining blocks involve inputs and outputs getting signals into and out of the processing system. 圖2-2顯示了這樣一個系統(tǒng)的組成部分。中間的圓圈代表了兩種類型的信號處理（數(shù)字和模擬），而處于信號處理框之間的方框表示模擬信號向等效數(shù)字形式（A/D即模擬到數(shù)字）的轉(zhuǎn)換，以及從數(shù)字信號向相應(yīng)的模擬

16、形式（D/A即數(shù)字到模擬）的逆轉(zhuǎn)換。剩下的方框涉及輸入和輸出取得信號以及從處理系統(tǒng)輸出信號。Many electrical signals derived from physical systems are obtained from devices called transducers. We have already encountered an example of an analog transducer, the thermocouple pair. It converts temperature difference (the physical variable) to a vol

17、tage (the electrical variable). Generally, a transducer is a device that converts a physical or mechanical variable to an equivalent voltage or current signal. Unlike the thermocouple example, however, most transducers require some form of electrical excitation to operate從物理系統(tǒng)獲得的很多電氣信號是從被稱為傳感器的器件中輸入

18、的。我們已經(jīng)碰到了一個模擬傳感器的例子。即熱電偶。它把溫度的變化（物理變量）轉(zhuǎn)換成電壓（電氣變量）。通常，傳感器是一種將物理或機(jī)械變量轉(zhuǎn)換成等效電壓或電流信號的器件。然而，不同于熱電偶例子，大多數(shù)傳感器需要一些形式的電激勵以驅(qū)動傳感器The output from a system can be in many forms, depending on the use to be made of the information contained in the input signals. One can seek to display the information, either in an

19、alog form (using a meter, for example, in which the needle position indicates the size of the variable of interest) or in digital form (using a set of digital display elements that are lit up with a number corresponding to the variable of interest). Other possibilities are to convert the output to s

20、ound energy (with a loudspeaker), or to use the output asan input signal to another system, or to use the output as a control signal to initiate some action. 個系統(tǒng)的輸出可以有多種形式，這取決于包含在輸入信號中的信息所起的作用。我們可以選擇何種方式顯示這些信息，無論是以模擬形式（例如，使用一種儀表，儀表的指針的位置指明我們所感興趣的變量的大?。┗蚴且詳?shù)字形式（使用一套數(shù)字顯示元件，顯示對應(yīng)于我們所感興趣的變量的數(shù)字）。其它的可能的情況下是

21、將輸出轉(zhuǎn)換成聲能（利用揚(yáng)聲器），或是將輸出作為另一個系統(tǒng)的輸入，或是利用輸出作為控制信號來產(chǎn)生某個動作第二篇The mathematics of computers and other digital electronic devices have been developed from the decisive work of George Boole (l815l864) and many others, who expanded and improved on his work. The body of thought that is known collectively as symb

22、olic logic established the principles for deriving mathematical proofs and singularly modified our understanding and the scope of mathematics. 布爾代數(shù)也稱為邏輯代數(shù)。它是英國數(shù)學(xué)家喬治布爾（18151864）于1849年創(chuàng)立的。在當(dāng)時，這種代數(shù)純粹是一種數(shù)學(xué)游戲。在布爾代數(shù)里，布爾構(gòu)思出一種關(guān)于0和1的代數(shù)系數(shù)，用基礎(chǔ)的邏輯符號系統(tǒng)描述物體和概念。這種代數(shù)不僅廣泛于概率和統(tǒng)計等領(lǐng)域，更為重要的是，它為數(shù)字計算機(jī)開關(guān)電路設(shè)計提供了最重要的數(shù)學(xué)方法。Onl

23、y a portion of this powerful system is required for our use. Boole and others were interested in developing a systematic means of deciding whether a proposition in logic or mathematics was true or false, but we shall be concerned only with the validity of the output of digital devices. True and fals

24、e can be equated with one and zero, high and low, or on and off. These are the only two states of electrical voltage from a digital element. Thus, in this remarkable algebra performed by logic gates, there are only two values, one and zero; anyalgebraic combination or manipulation can yield only the

25、se two values. Zero and one are the only symbols in binary arithmetic這種很有用的系統(tǒng)中只有一部分內(nèi)容為我們所應(yīng)用。布爾等人感興趣的是推導(dǎo)出一種用來判斷某個命題在邏輯上或在數(shù)學(xué)上是真還是假的系統(tǒng)性的方法，但我們要關(guān)注的僅僅是數(shù)字設(shè)備的輸出的正確與否。真或假可以等同于一和零 ，或者等同于開和關(guān)。這是電子元件中電壓的兩種唯一的狀態(tài)。因此，由邏輯門所完成的這個奇異的代數(shù)中，只有兩種值，一和零，任何代數(shù)組合或者計算只能產(chǎn)生這兩種值。零和一是二進(jìn)制運(yùn)算中唯一的符號The various logic gates and their int

26、erconnections can be made to perform all the essential functions required for computing and decision-making. In developing digital systems the easiest procedure is to put together conceptually the gates and connections to perform the assigned task in the most direct way. Boolean algebra is then used

27、 to reduce the complexity of the system, if possibl，ewhile retaining the same function. The equivalent simplified combination of gates will probably be much less expensive and less difficult to assemble不同的邏輯門和它們之間的相互連接可以用來完成計算以及判斷所要求的必要的功能。在開發(fā)數(shù)字系統(tǒng)時最簡單的做法是把邏輯門以及它們之間的連接根據(jù)概念排放在一起 以最直接的方式完成 設(shè)定的任務(wù)。于是我們采用

28、布爾代數(shù)來減小系統(tǒng)的復(fù)雜程度，如果可能的話，與此同時應(yīng)保留其相同的功能。邏輯門之間等效的簡單的組合可能使得費(fèi)用更加便宜而在裝配上更加容易。Boolean algebra has three rules of combination, as any algebra must have: the associative, the commutative, and the distributive rules. To show the features of the algebra we use the variables A, B, C, and so on. To write relations

29、 between variables each one of which may take the value 0 or l, we use to mean “not A,” so if A = l , then = 0. Thecomplement of every variable is expressed by placing a bar over the variable; the complement of = "not B". Two fixed quantities also exist. The first is identity, I = l; the o

30、ther is null, null = 0布爾代數(shù)與任何代數(shù)一樣具有結(jié)合律、交換律和分配律。為了表示代數(shù)的特性我們使用變量A,B和C以及諸如此類的變量。為了寫出這些可能取值為0或1的各個變量之間的相互關(guān)系，我們采用來表示“非A”，因此如果A1，那么0。每個變量的補(bǔ)碼用每個變量上方加一橫線來表示，B的補(bǔ)碼就是也即“非B”。同時還存在兩個固定的量。第一個量是單位量，即I1，另外一個量是零，即null0。Boolean algebra applies to the arithmetic of three basic types of gates: an OR-gate, an AND-gate a

31、nd the inverter. The symbol and the truth tables for the logic gates are shown in Fig.2-3, the truth table illustrate that the AND-gate corresponds to multiplication, the OR-gate corresponds to addition, and the inverter yield the complement of its input variable. 布爾代數(shù)應(yīng)用于三種基本類型的邏輯門的運(yùn)算：一種是或門，一種是與門，還有

32、一種是反相器（非門）。邏輯門的符號和真值表如圖23所示，真值表顯示與門對應(yīng)于乘，或門對應(yīng)于加，而反相器產(chǎn)生其輸入變量的補(bǔ)碼We have already found that AB = "A AND B" for the AND-gate and A + B = "A OR B"for the OR-gate我們已經(jīng)算出對于與門來說 AB=“A AND B”而對與或門來說 A+B=“A OR B”The AND, or conjunctive, algebraic form and the OR, or disjunctive, algebraic fo

33、rm must each obey the three rules of algebraic combination. In the equations that follow, the reader may use the two possible values 0 and l for the variables A, B, and Cto verify the correctness of each expression. Use A = 0, B = 0, C = 0; A = l, B = 0, C = 0; and so on, in each expression. The ass

34、ociative rules state how variables may be grouped.對于“與”，即邏輯乘，以及“或”，即析取，它們的代數(shù)形式必須遵循代數(shù)組合的三個法則。在接下來的等式中，讀者可以把變量A,B,C設(shè)為兩個可能的值0和1來證明每個表達(dá)式的正確性。例如采用A=0,B=0,C=0，或A=1, B=0,C=0等等，在每個表達(dá)式中，結(jié)合律表明如何把變量進(jìn)行重組For AND (AB)C = A(BC) = (AC)B,and for OR (A + B) + C = A + (B + C) = (A + C) + B對于“與”有（AB）CA（BC）（AC）B而對于“或”有（

35、AB）CA（BC）（AC）Bthe rules indicate that different groupings of variables may be used without altering the validity of the algebraic expression這個法則表明我們可以采用變量的不同組合而不改變代數(shù)表達(dá)式的正確性。交換率表明了變量的順序The commutative rules state the order of variables. For AND AB = BA and for OR A+B = B+A the rules indicate that the

36、 operations can be grouped and expanded as shown對于“與”有ABBA，而對于“或”有ABBA。這個法則表明了可以如上式所示進(jìn)行運(yùn)算的組合和展開Before we show the remaining rules of Boolean algebra for digital devices, let us confirm the distributive rule for AND by writing the truth table, Table 2-l. We will discover soon how we knew that we coul

37、d write AB + C = (A + C)(B + C), which is proved by the truth table to be a proper expansion. 在我們展示數(shù)字設(shè)備布爾代數(shù)的剩下的那個法則之前，讓我們通過寫出真值表的方式即真值表21來驗證對于“與”的分配律。我們將很快發(fā)現(xiàn)如何寫出等式ABC（AC）（BC），這一等式由真值表證明了是一個正確的展開式。The more complex expression and its simpler form yield identical values. Because binary logic is dominat

38、ed by an algebra in which a sum of ones equals one, the truth table permits us to identify the equivalence among algebraic expressions. A truth table may be used to find a simpler equivalent to a more complex relation among variables, if such an equivalent exists. We will see shortly how the reduction of complexity may be achieved in a systematic manner with truth tables and other techniques更為復(fù)雜的表達(dá)式和它的一次式產(chǎn)生了相等的值。由于二進(jìn)制邏輯取決于某一代數(shù)，其單個變量之和等于一個變量，所以真值表允許我們在代數(shù)表達(dá)式中找出等效值，我們可以使用真值表來求出一個等效于變量之間較復(fù)雜的關(guān)系式的一次表達(dá)式。如果這樣的等效關(guān)系存在，我們將很快看到利用真值表以及其它方法以一種系統(tǒng)性的方式如何完成這樣一個復(fù)雜步驟的簡化工作。Some additional relations in the algeb