电子信息类专业英语(西电第二版)Unit-3--Electrical-Technique课件.ppt

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1、Unit 3 Electrical TechniqueUnit 3 Electrical TechniquePassage A Analog Circuit Passage B Binary System and Logic Systems Passage C Magnitude Locked Loop Unit 3 Electrical TechniquePassage A Analog Circuit1.Principles of Common Emitter CircuitAn NPN transistor is shown in Figure 3.1 with a load resis

2、tor(RL=10 k)in series with the collector terminal.A collector supply voltage(VCC=20 V)is provided with a polarity that reverse biases the collector base junction.A base current IB is also provided via RB,and this is results in a forward bias(VBE)at the base emitter junction.Unit 3 Electrical Techniq

3、ueFigure 3.1 Common Emitter CircuitUnit 3 Electrical TechniqueA signal voltage VS having a source resistance RS is capacitor coupled via C1 to the transistor base.The output is derived via another capacitor C2 connected to the transistor collector.Both capacitors are open circuit to direct currents,

4、but offer very low impedance to AC signals.If the signal source were direct connected instead of capacitor coupled,there would be a low resistance path from the base to the negative supply line,and this would affect the circuit bias conditions.Similarly,an external load directly connected to the tra

5、nsistor collector might alter the collector voltage.Unit 3 Electrical TechniqueUnit 3 Electrical TechniqueWhen IB is 20 A,VCE=10 V,and when IB is 25 A,VCE=7.5 V.Hence,for an increase in IB of 5 A,VCE decreased by 2.5V(i.e.,VCE changed by the same amount as the voltage change across RL).Similarly,if

6、VBE is decreased until IB is 15 A,IC becomes 501510-6=0.75 mA and ICRL=0.75 mA10 k=7.5 V.Thus,VCE=20 V-7.5 V=12.5 V.Therefore,for a 5 A decrease in IB,VCE increases by 2.5 V.Unit 3 Electrical TechniqueThe variation in base emitter voltage could be produced by the AC signal VS.This might require sign

7、al amplitude of perhaps 10 mV.If VS=10 mV produces VO=2.5 V,the signal may be said to be amplified by a factor of VO/VS=2.5 V/10 mV=250,or circuit amplification is 250.The transistor current and voltage variations have no effect on the supply voltage(VCC).So,when assessing the AC performance of the

8、circuit;VCC can be treated as a short circuit.The coupling capacitor C1 also becomes a short circuit to AC signals.Redrawing the circuit of Figure 3.1 with VCC and C1 shorted gives the AC equivalent circuit shown in Figure 3.2.Unit 3 Electrical TechniqueFigure 3.2 Common Emitter AC Equivalent Circui

9、tUnit 3 Electrical TechniqueUnit 3 Electrical Technique2.Basic Op-ampsA conventional operational amplifier(op-amps)can be simply described as a high-gain direct-coupled voltage amplifier that has a single output terminal,and because it has both inverting and non-inverting input terminals,the device

10、can function as an inverting,non-inverting,or differential amplifiers,filters,oscillators,level switches,comparators,etc.Three basic types of operational amplifiers are currently available.We are going to take an in-depth look at the operating principles and practical application of the most common

11、type,the conventional“voltage-in voltage-out”op-amp(typified by the LM741 and CA3140).The other two basic types of op-amps are the current-differencing or Norton op-amp,and the operational transconductance amplifier or OTA.Unit 3 Electrical Technique Op-amp BasicsIn its simplest form,a conventional

12、op-amp consists of a differential amplifier(bipolar or FFT)followed by offset compensation and output stages,as shown in Figure 3.3.All of those elements are integrated on a single chip and housed in an IC package.The differential amplifier has a high-impedance(constant-current)“tail”to give it a hi

13、gh input impedance and a high degree of common-mode signal rejection.It also has a high-impedance collector(or drain)load,to give it a large amount of signal-voltage gain(typicallyabout 100 dB).Unit 3 Electrical TechniqueUnit 3 Electrical TechniqueThe output of the differential amplifier is fed to t

14、he circuits output stage via an offset-compensation network,which causes the op-amps output to center at zero volts.The output stage takes the form of a complementary emitter follower,and provides a low-impedance output.1Op-amps are normally powered from a split supply providing+V,-V,and a common gr

15、ound,enabling the op-amps output to swing to either side of ground and take on a value of zero volts when the differential input voltage is zero.Unit 3 Electrical TechniqueUnit 3 Electrical TechniqueOne useful application for an op-amp is as a linear amplifier in the closed-loop mode,as shown in Fig

16、ure 3.4.The circuits have negative feedback applied from the output to the inverting input.That technique enables the overall gain of those circuits to be precisely controlled by the values of the external-feedback components,regardless of the open-loop characteristics of the particular op-amps that

17、 are used.Figure 3.4(a)shows an op-amp can be used as an inverting amplifier by grounding the non-inverting terminal and feeding the input signal to the inverting terminal,or as a non-inverting amplifier by transposing the two input connections,as shown in Figure 3.4(b).It can also be used as a diff

18、erential amplifier by feeding a separate input signal to each input,in which case the op-amp will amplify voltage difference between the two inputs,as shown in Figure 3.4(c).Note that if identical signals are fed to both inputs of the op-amp,ideally the output should be zero.Unit 3 Electrical Techni

19、queFigure 3.4 Closed-loop Amplifier Circuit(An inverting DC amplifier is shown in(a),a non-inverting DC amplifier is shown in(b),and a differential amplifier is shown in(c).)Unit 3 Electrical TechniqueUnit 3 Electrical TechniqueFigure 3.5(b)shows the circuits transfer characteristics.Note that it is

20、 the magnitude of the differential voltage at the inputs that determines the output voltage,and that the absolute values of the input voltages are of little importance.For example,if a 2 volts reference is applied,a differential voltage of only 200 V is needed to swing the output from negative satur

21、ation to positive saturation.Unit 3 Electrical TechniqueFigure 3.5 A Simple Voltage Comparator and Its Transfer CharacteristicsUnit 3 Electrical TechniqueNotes1.The output of the differential amplifier is fed to the circuits output stage via an offset-compensation network,which causes the op-amps ou

22、tput to center at zero volts.The output stage takes the form of a complementary emitter follower,and provides a low-impedance output.差动放大级的输出通过一个失调补偿网络与输出级相连,目的是使运放的输出以0 V为中心。输出级采用互补的射极跟随器的形式以使输出阻抗很低。which引导非限制性定语从句。Unit 3 Electrical Technique2.Because of the very high open-loop voltage gain of the

23、op-amp,the output is driven into positive saturation(close to+V)when the sample voltage goes slightly above the reference voltage,and driven into negative saturation(close to-V)when the sample voltage goes slightly below the reference voltage.由于运放的开环电压增益很高,当取样电压略高于参考电压时,输出趋向于正向饱和状态(接近+V)。当取样电压低于参考电压

24、时,输出趋向于负向饱和状态(接近-V)。“because of”短语意为“因为,由于”。when引导时间状语从句。Unit 3 Electrical TechniqueExercises1.Please translate the following phrases into English.(1)模拟电路 (2)集成电路(3)共射极电路 (4)负载电阻 (5)短路 (6)运算放大器 (7)差分放大器 (8)同相输入端电压(9)反相输入端电压 Unit 3 Electrical TechniqueUnit 3 Electrical Technique(3)The differential am

25、plifier has a high-impedance(constant-current)“tail”to give it a high input impedance and a high degree of common-mode signal rejection.It also has a high-impedance collector(or drain)load,to give it a large amount of signal-voltage gain(typically about 100 dB).(4)In that circuit,a fixed reference v

26、oltage is fed to the non-inverting terminal.Because of the very high open-loop voltage gain of the op-amp,the output is driven into positive saturation(close to+V)when the sample voltage goes slightly above the reference voltage,and driven into negative saturation(close to-V)when the sample voltage

27、goes slightly below the reference voltage.Unit 3 Electrical Technique3.Fill in the blanks.(1)In Figure 3.2 the circuit input terminals are ,and the output terminals are .(2)A conventional operational amplifier(op-amps)can be simply described as .(3)The variation in could be produced by the AC signal

28、 VS.This might require signal amplitude of perhaps 10mV.(4)The output of the differential amplifier is fed to the circuits output stage via，which causes the op-amps output to center at zero volts.Unit 3 Electrical Technique(5)Another way of using an op-amp is as ,such as the one shown in Figure 3.5(

29、a).(6)For example,if a 2 volts reference is applied,a differential voltage of only 200 V is needed to swing the output from .Unit 3 Electrical TechniqueUnit 3 Electrical TechniquePassage B Binary System and Logic Systems1.Binary SystemA digital system functions in a binary manner.It employs devices

30、which exist only in two possible states.A transistor is allowed to operate at cutoff or in saturation,but not in its active region.A node may be at a high voltage of,say,41 V or at a low voltage of,say,0.20.2 V,but no values are allowed.Various designations are used for these two quantized states,an

31、d the most common are listed in Table 3.1.In logic,a statement is characterized as true or false,and this is the first binary classification listed in the table.A switch may be closed or open,which is the notation under 9,etc.Binary arithmetic and mathematical manipulation of switching or logic func

32、tions are best carried out with classification 3,which involves two symbols,0(zero)and 1(one).Unit 3 Electrical TechniqueUnit 3 Electrical TechniqueUnit 3 Electrical TechniqueIn the binary system of representation the base is 2,and only two numerals 0 and 1 are required to represent a number.The num

33、erals 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

34、is written in the binary representation as 10011 since10011=124+023+022+121+120=16+0+0+2+1=19A short list of equivalent numbers in decimal and binary notation is given in Table 3.2.Unit 3 Electrical TechniqueUnit 3 Electrical TechniqueA general method for converting from a decimal to a binary number

35、 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 92=4 and a remainder of 1)until

36、 a quotient of 0 is obtained.The array of 1s and 0s in the second row is the binary representation of the origin decimal number.In this example,decimal 19=10011 binary.Unit 3 Electrical TechniqueUnit 3 Electrical TechniqueA binary digit(a 1 or a 0)is called a bit.A group of bits that has the same si

37、gnificance 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 1s and 0s.Since 253626,then a minimum of 6 bits per bite are required in order to accommodate all the alphanumeric character

38、s.In this sense a bite is sometimes referred to as a character and a group of one or more characters as a word.Unit 3 Electrical Technique2.Logic SystemsIn a DC,or level-logic,system a bit is implemented as one of two voltage levels.If,as in Figure 3.6(a),the more positive voltage is the 1 level and

39、 the other is the 0 level,the system is said to employ DC positive logic.On the other hand,a DC negative-logic system,as in Figure 3.6(b),is one which designates the more negative voltage state of the bit as the 1 level and the more positive as the 0 level.1 It should be emphasized that the absolute

40、 values of the two voltages are of no significance in these definitions.In particular,the 0 state need not represent a zero voltage level(although in some systems it might).Unit 3 Electrical TechniqueFigure 3.6 Illustrating the definition of(a)positive and(b)negative logic.A transition from one stat

41、e to the other occurs at t=tUnit 3 Electrical TechniqueThe parameters of a physical device(for example,VCEsat 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 sourc

42、es 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 41 V and 0.20.2 V.Unit 3 Electrical Techniq

43、ueIn a dynamic,or pulse-logic,system a bit is recognized by the presence or absence of a pulse.At 1 signifies the existence of a positive pulse in a dynamic positive-logic system;a negative pulse denotes a 1 in a dynamic negative-logic system a 0 at a particular input(or output)at a given instant of

44、 time designates that no pulse is present at that particular moment.Unit 3 Electrical TechniqueNotes1 On the other hand,a DC negative-logic system,as in Figure 3.6(b),is one which designates the more negative voltage state of the bit as the 1 level and the more positive as the 0 level.另一方面,如图3.6(b)所

45、示,把比特的较低的电压状态记为1电平,较高的电压状态记为0电平,这样的系统称为直流负逻辑系统。“on the other hand”意为“另一方面”。which引导限制性定语从句,修饰one。Unit 3 Electrical TechniqueExercises1.Please translate the following phrases into English.(1)二进制方式 (2)低电压 (3)数字系统 (4)逻辑功能(5)十进制 (6)直流负逻辑系统 (7)脉冲逻辑 (8)动态正逻辑系统 Unit 3 Electrical Technique2.Please translate

46、the following sentences into Chinese.(1)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 1s and 0s.Since 253626,then a minimum of 6 bits per bite are required in order to accommodate all the alphanumeric characters

47、.(2)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.Unit 3 Electrical Technique(3)For these reasons the digital levels are not specified precisely,but as indicated by the shaded region

48、 in Figure 3.6,each state is defined by a voltage range about a designated level,such as 41 V and 0.20.2 V.(4)At 1 signifies the existence of a positive pulse in a dynamic positive-logic system;a negative pulse denotes a 1 in a dynamic negative-logic system a 0 at a particular input(or output)at a g

49、iven instant of time designates that no pulse is present at that particular moment.Unit 3 Electrical Technique3.Fill in the blanks.(1)are used for these two quantized states,and the most common are listed in Table 3.1.(2)In the latter the base is 10(ten),and ten numerals,0,1,2,3,9,are required to ex

50、press .(3)The numerals 0 and 1 have the same meaning as in .(4)In particular,the 0 state need not represent (although in some systems it might).(5)For these reasons the digital levels are not specified precisely,but as indicated by in Figure 3.6,each state is defined by a voltage range about a desig