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单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,Chapter 2,Electronics,Section 1 Introduction,Text,New Words and Expressions,Exercises,End,Vocabulary Characteristic III,Section 1,Introduction,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 it is science, engineering, medicine, music, maintenance, or even espionagethe role of electronics is large, and it is growing.,In general, all of the tasks with which we shall be concerned can be classified as signal-processing,Section 1,Introduction,tasks. Let us explore the meaning of this term.,Signal,A signal is any physical variable whose magnitude or variation with time contains information. This information might involve speech and music, 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, therefore,Section 1,Introduction,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 which 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.,Section 1,Introduction,Analog and Digital signals,A signal can carry information in two different forms. In an analog signal the 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 voltage across the thermocouple pair also varies. The voltage thus provides an analog representation of the temperature difference.,Section 1,Introduction,The other kind of signal is a digital signal. 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 to,Fig.2-1,(a) An example of an analog signal; (b) Voltage-time characteristic,Section 1,Introduction,control the furnace. When the room temperature drops below a preset value, the thermostat switch 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.,Section 1,Introduction,Signal-Processing Systems,A signal-processing system is an interconnection of components and devices that can accept an input signal or a group of input 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.,Fig.2-2 illustrates the components in such a system. The central circles represent the two types of signal processing (digital and analog), while the,Section 1,Introduction,block between the two signal- processing blocks represents the conversion of an analog signal to equivalent digital form (A,/,D=Analog-to-Digital) and the 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.,Section 1,Introduction,Fig.2-2 Components of a signal system,Section 1,Introduction,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 voltage (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.,Section 1,Introduction,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 analog 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 sound energy (with a loudspeaker), or to use the output as,Section 1,Introduction,an input signal to another system, or to use the output as a control signal to initiate some action.,Return,New Words and Expressions,electronics,n.,电子学，电子仪器，电子设备，电子线路,u,nderstatement,n.,轻描淡写，有节制的表达,omnipresent,a.,无处不在的，普遍存在的,electronic,a.,电子（学）的,transaction,n. ,交易，业务 办理，处理，执行，记录,digital,a.,数字的，数字式的，计数的,espionage,n.,谍报，间谍活动，密探，监视,New Words and Expressions,signal-processing,a.,信号处理的,analog,n. ,模拟（量，装置，设备，系统） 类似，类比，比拟,velocity,n.,速度，速率,thermocouple,n.,热电偶,discrete,a.,离散的，不连续的，分散的,household,a.; n.,家用的，普通的，一般用途的，家庭，家，户,thermostat,n.,恒温器，定温器，温度自动调节器,New Words and Expressions,preset,v.; a. ,预定，预置，（预先）调整 安装程序，给定程序的,switch,n.,开关；,v.,接通或关断，转变，换接,A/D = Analog-to-Digital,模数转换，模数变换,D/A = Digital-to-Analog,数模转换，数模变换,transducer,n.,传感器，变送器，发射器，换能器，换流器,excitation,n. ,激励，激发，激磁 刺激，干扰,display,v.,显示，显像，表现，陈列，,展览；,n.,显示，指示，表现,Return,Vocabulary Characteristic III,除加词根和词缀外，其它构词法有：,合成法,两个或两个以上的词结合成一个新词。专业英语中的合成词有合写式（无连字符）和分写式（有连字符）两种。,hardware,硬件；,software,软件；,pulse-,scaler,脉冲标定器。,混成法,两个词中在拼写或读音上比较适合的部分以“前一词去尾、后一词去首”的方式，加以叠合混成新词，而混成的新词兼具有两个旧词的形和义。,telex =,teleprinter,+ exchange,电传；,transistor = transfer + resistor,晶体管。,Vocabulary Characteristic III,截短法,删除某一词中的一个或多个音节形成新词，其词义不变。,auto = automobile,汽车；,lab = laboratory,实验室；,amp = ampere,安培。,缩略法,将某一词组中主要的词的第一个字母组成新词。,radar = radio detecting and ranging,雷达；,UPS = uninterrupted power supply,不间断电源；,DC = direct current,直流电；,AC,交流电；,CAD = computer assisted design,计算机辅助设计。,Vocabulary Characteristic III,转化法,不通过任何词形上变化，直接转化为另一个词。在转化过程中，词性有所改变而词义则与转化前的原义仍保留若干联系。,xerox,用静电复印法复印。,Return,Exercises,I. Choose the best answer into the blank,1. The voltage produced by a thermocouple pair is,signal.,A. a digital B. an analog,C. a discrete D. a control,2. ON-OFF information can be represented by,signal.,A. a digital B. an analog,C. a continuous D. a control,Exercises,I. Choose the best answer into the blank,3. A device that can convert an analog signal to the corresponding digital form is called,for short.,A. A/DB. D/A C. D/DD. A/A,4. The thermocouple pair converts temperature difference to a,.,A. current B. voltage,C. power D. energy,Exercises,I. Choose the best answer into the blank,5. A D/A is a device that can convert a digital signal to the equivalent,.,A. digital formB. numerical form,C. binary form D. analog form,Exercises,II. Answer the following questions according to the text,1. What is a signal?,2. Which forms can a signal carry information in?,3. What basic components does a signal-processing system consist of ?,4. What role does a transducer play in a signal-processing system?,5. What does the output form of a system depend on?,Exercises,III. Translate the following into Chinese,Analog electronics pertains to those systems in which the electrical voltage and electrical current are analogous to physical quantities and vary continuously. Electronic circuits that reproduce music must have voltages and currents that are proportional to the sound. A high fidelity amplifying system attempts to keep the analogy as true as possible. Analog electronic circuits are carefully designed to make the electrical voltages and currents follow the input signal. If an input signal,Exercises,III. Translate the following into Chinese,doubles in amplitude, the output voltage or current also should double; this is possible because the circuit elements are made to operate within limits that preserve the linearity.,Return,Chapter 2,Section 1,End,Section 2 Boolean Algebra for Digital Systems,Text,New Words and Expressions,Exercises,End,Selection of Word Meaning,Section 2,Boolean Algebra for Digital Systems,Introduction,The mathematics of computers and other digital electronic devices have been developed from the decisive work of George,Boole,(l815,l864) and many others, who expanded and improved on his work. The body of thought that is known collectively as symbolic logic established the principles for deriving mathematical proofs and singularly modified our understanding and the scope of mathematics.,Section 2,Boolean Algebra for Digital Systems,Only 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 false 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; any,Section 2,Boolean Algebra for Digital Systems,algebraic combination or manipulation can yield only these two values. Zero and one are the only symbols in binary arithmetic.,The various logic gates and their interconnections 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 to reduce the complexity of the system, if possible,Section 2,Boolean Algebra for Digital Systems,while retaining the same function. The equivalent simplified combination of gates will probably be much less expensive and less difficult to assemble.,Rules of Boolean algebra for digital devices,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 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. The,Section 2,Boolean Algebra for Digital Systems,complement 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 other is null, null = 0.,Boolean algebra applies to the arithmetic of three basic types of gates: an OR-gate, an AND-gate and 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.,Section 2,Boolean Algebra for Digital Systems,Fig.2-3 Logic symbols and truth tables for AND, OR, NOT,(a) AND,；,(b) OR,；,(c) NOT,Section 2,Boolean Algebra for Digital Systems,We have already found that,AB = A AND B,for the AND-gate and,A + B = A OR B,for the OR-gate.,The AND, or conjunctive, algebraic form and the OR, or disjunctive, algebraic form 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 C,Section 2,Boolean Algebra for Digital Systems,to 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 associative rules state how variables may be grouped.,For AND,(AB)C,=,A(BC),=,(AC)B,and for OR,(A,+,B),+,C,=,A,+,(B,+,C),=,(A,+,C),+,B,the rules indicate that different groupings of variables may be used without altering the validity of the algebraic expression.,The commutative rules state the order of variables.,For AND,AB,=,BA,Section 2,Boolean Algebra for Digital Systems,and for OR,A,+,B,=,B,+,A,the rules indicate that the operations can be grouped and expanded as shown.,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 could write AB,+,C,=,(A,+,C)(B,+,C), which is proved by the truth table to be a proper expansion.,Section 2,Boolean Algebra for Digital Systems,Table 2-1 Truth table for the AND-distribution rule,A,B,C,AB + C =Value,(A + C)(B + C) = Value,0,0,0,0 + 0 0,0 0 0,0,0,1,0 + 1 1,1 1 1,0,1,0,0 + 0 0,0 1 0,0,1,1,0 + 1 1,1 1 1,1,0,0,0 + 0 0,1 0 0,1,0,1,0 + 1 1,1 1 1,1,1,0,1 + 0 1,1 1 1,1,1,1,1 + 1 1,1 1 1,Section 2,Boolean Algebra for Digital Systems,The more complex expression and its simpler form yield identical values. Because binary logic is dominated 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.,Section 2,Boolean Algebra for Digital Systems,Some additional relations in the algebra, which use identity and null, are worth nothing. Here we illustrate properties of the AND,and,OR operations that use the distributive rules and the fact that I is always l and null is always 0.,ANDAI,=,A,or A1,=,A,ORA+ null =,A,A,+ 0 = A,ANDA = null A = 0,OR A + = I A + =1,ANDA,null =,null,A0 = 0,ORA,+,I = I,A,+,1,=,1,ANDAA,=,A,ORA,+,A,=,A,Section 2,Boolean Algebra for Digital Systems,The relation points out an important fact, that is, that,I, the identity, is the universal set. Null is called the empty set.,We have considered several logical relations. For the two-value Boolean algebra of digital electronics, the choice of the technique depends upon the nature of the function whose reduction is desired. Some simple functions may be easily reduced by examining their truth table; others require the manipulation of Boolean algebra to reveal the relationship . When we consider the circuit for,Section 2,Boolean Algebra for Digital Systems,adding binary numbers, we see that Boolean algebra is required to discover a simplification in that particular application.,Return,New Words and Expressions,Boolean,布尔的,symbolic,a.,符号的，记号的，象征（性）的,proof,n.,证明，证实，证据；,v.,检验，试验；,a.,试验过的，合乎标准的，防,的,singularly,ad.,非凡地，特殊地，奇异地，单独地,logic gate,逻辑门,Manipulation,n.,处理，计算，操作，控制，管理,binary,n.; a.,二进制的，二进位的，二元的，二成分的 二，双，复,New Words and Expressions,arithmetic,n.,算术，计算，运算；,a.,算术的，计算的，运算的,associative,a.,结合的，联合的，相关的，,commutative,a.,交换的，换向的，代替的，相互的,distributive,a.,分配的，分布的，个别的,truth table,真值表,multiplication,n. ,乘法，相乘 增加，增多，增殖，倍增,addition,n. ,加法 增加，附加，相加,New Words and Expressions,conjunctive,a. ,合取的，逻辑乘的 连接的，连系的,disjunctive,a.,析取的，分离的，转折的,identity,n.,单位，同一，完全相同，一致，恒等，身份,null,n. ; a. ,零的，空的，无 不存在的，没有的,complement,n.; a. ,补码，补数，余的，补的 补充，互补,Return,Selection of Word Meaning,一词多类，一词多意，需词义的选择和引申,根据专业选择词义,例：,power,（,1,）,Knowledge is,power,. (,力量）,（,2,）,Assume that the input voltage from the,power,supply remains constant.,（译成“电源”）,（,3,）,The third,power,of 2 is 8.,（译成“方”）,（,4,）,By,power,we mean the rate of doing work.,（译成“功率”）,（,5,）,The combining,power,of one element in the compound must equal the combining power of the other element.,（译成“化合价”）,Selection of Word Meaning,根据专业选择词义,例：,power,（,6,）,Energy is the,power,to do work.,（译成“能力”）,（,7,）,Electric,power,can be transmitted over long distance to users.,（译成“电力”）,（,8,）,Basically, all,power,is with the people. (,译成“权力”,),Selection of Word Meaning,根据词类选择词,例：,like,（,1,）,Like,charges repel, unlike charges attract.,（形容词，作“相同的”解）,（,2,）,He,likes,power electronics. (,动词,作“喜欢”解）,（,3,）,In the sunbeam passing through the window there are fine grains of dust shining,like,gold.,（介词，作“像”解）,（,4,）,It is the atoms that make up iron, water, oxygen and the,like,.,（名词，做“相同之物”解）,（,5,）,Waves in water move,like,the waveform moves along a rope.,（连词，作“像、如”解）,Selection of Word Meaning,根据上下文选择词义,例：,（,1,）,The transformer,works,properly.,这台变压器,运转,正常。,（,2,）,The motor is,not working,.,电动机,故障,了。,（,3,）,The threads of the screw,work,hard,.,这螺丝的螺纹,太涩,了。,(4)In order to meet the,critical,service requirements, scientists are still looking for better materials.,为满足使用的,紧迫,要求，科学家们仍在寻找更好的材料。,Selection of Word Meaning,根据上下文选择词义,例：,（,5,）,We can heat the steel again to a temperature below the,critical,temperature, then cool it slowly.,我们可以把钢材再次加热到,临界,温度以下的某一温度，然后再让它慢慢地冷却。,Selection of Word Meaning,根据搭配习惯选择词义,例：,heavy,(1),heavy current,强大电流；,(2),heavy industry,重工业；,(3),heavy line,粗线；,(4),heavy traffic,交通拥挤。,Return,Exercises,I. Choose the best answer into the blank,1. Any algebraic combination or manipulation can yield only,values in Boolean algebra.,A. one B. two C. three D. four,2. According to the text, the AND-gate corresponds to, the OR-gate corresponds to,.,A. multiplication, subtraction,B. multiplication, division,C. multiplication, addition,D. addition, subtraction,Exercises,I. Choose the best answer into the blank,3. The commutative rule is used for the AND algebraic operation to alter,of variables.,A. the orderB. the valueC. the validityD. the result,4. The associative rule indicates that different groupings of variables do not alter,of the algebraic expression.,A. the orderB. the operational orderC. the validityD. the form,Exercises,I. Choose the best answer into the blank,5. The relation results in,.,A. null B. identity,C. indefinite value D. zero,Exercises,II. Answer the following questions according to the text,1. Which symbols are there in binary arithmetic? What are they?,2. What are the rules of combination about Boolean algebra?,3. What are the three basic gates in digital circuits?,4. What functions does a truth table have?,5. How many rules of Boolean algebra do you know? Say out these rules as many as possible.,Exercises,III. Translate the following into Chinese,There are many different ways to build electronic circuits with input-output characteristics that correspond to the various digital operations. Several of these circuit types are manufactured in integrated circuit form. The collection of integrated circuit logic functions that share a common circuit type is called a logic family. Within each family, the wiring diagram for the logic inputs and outputs is identical to the logic flow diagram (only the power supply and ground connections must be added). Therefore,Exercises,III. Translate the following into Chinese,one generally selects a single logic famil
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