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1、精选优质文档-倾情为你奉上An electric circuit (or network) is an interconnection of physical electrical device. The purpose of electric circuits is to distribute and convert energy into some other forms. Accordingly, the basic circuit components are an energy source (or sources), an energy converter (or converte
2、rs) and conductors connecting them. 电路（或者网络）是物理电气设备的一种互相连接。电路的目的是为了将能量分配和转换到另外一种形式中。因此，基本的电路元件包括电源、电能转换器以及连接它们的导体。An energy source (a primary or secondary cell, a generator and the like) converts chemical, mechanical, thermal or some other forms of energy into electric energy. An energy converter, a
3、lso called load (such as a lamp, heating appliance or electric motor), converts electric energy into light, heat, mechanical work and so on. 电源（原生电池或者再生电池、发电机等类似装备）将化学能量、机械能量，热能或者其他形式的能量转换成电能。电能转换器（也称为负载，如灯泡、电热器或者电动机）将电能转换成光、热、机械运动等等。 Events in a circuit can be defined in terms of e.m.f. (or voltage
4、) and current. When electric energy is generated, transmitted and converted under conditions such that the currents and voltages involved remain constant with time, one usually speaks of direct-current (D.C.) circuits. 电路属性可以根据电动势和电流来定义。当电能在产生、传输和变换时，若电路中相关的电流和电压不随时间而变化，我们便称其为直流电路With time-invariant
5、 currents and voltages, the magnetic and electric fields of the associated electric plant are also time-invariant. This is the reason why no e.m.f.s of self-(or mutual-)induction appear in D.C. circuits, nor are there any displacement currents in the dielectric surrounding the conductors. 在电流和电压时不变的
6、情况下，相关电气设备的电磁场也是时不变的。这就是为什么直流电路中没有自（互）感电动势、以及围绕在导体附近的电介质没有位移电流。Fig.1.1 shows in simplified form a hypothetical circuit with a storage battery as the source and a lamp as the load. The terminals of the source and load are interconnected by conductors (generally but not always wires). 图1.1给出了一个假设电路的简单
7、形式：一个蓄电池作为电源、以及一个灯泡作为负载。电源和负载的终端用导体互相连接，通常这种导体是导线，但少数情况下也有例外。As is seen, the source, load and conductors form a closed conducting path. The e.m.f. of the source causes a continuous and unidirectional current to circulate round this closed path.如图所示，电源、负载和导体构成了一个闭合导电回路。电源的电动势产生一个连续的单方向电流在闭合回路中流通。The
8、simple circuit made up of a source, a load and two wires is seldom, if ever, met with in practice. Practical circuits may contain a large number of sources and loads interconnected in a variety of ways. 这种由一个电源、一个负载和两根导线组成的简单电路在实践中即使有时能遇到，也是很少见的。实际的电路包括很多用不同方法连接起来的电源和负载。 To simplify analysis of actu
9、al circuits, it is usual to show them symbolically in a diagram called a circuit diagram, which is in fact a fictitious or, rather, idealized model of an actual circuit of network. Such a diagram consists of interconnected symbols called circuit elements or circuit parameters. 为了简化分析，通常用电路图来象征性地表示实际
10、的电路。实际上，电路图是实际电路的一个假设模型，或相当于一个理想模型。这样的电路图包括电路元件或者电路参数等互联符号。Two elements are necessary to represent processes in a D.C. circuit. These are a source of e.m.f. E and of internal (or “source”) resistance RS, and the load resistance (which includes the resistance of the conductors) R (Fig.1.2). 在直流电路中，有两
11、个元件是有必要描绘出来处理的。这就是电源的电动势E、内阻RS，以及负载电阻R（其中包含了导体电阻）。Whatever its origin (thermal, contact, etc.), the source e.m.f. E(Fig.1.2(a) is numerically equal to the potential difference between terminals 1 and 2 with the external circuit open, that is, when there is no current flowing through the source.无论图1.
12、2(a)中的电动势E的原动力是什么（即不论是热的、机械的还是其它什么形式），其大小就等于1、2两端之间的开路电压，也就是电源没有电流通过的情况。 The source e.m.f. is directed from the terminal at a lower potential to that at a higher one. On diagram, this is shown by arrows. 电动势从较低电压端指向较高电压端，这在图表中用箭头表示。 When a load is connected to the source terminals (the circuit is th
13、en said to be loaded) and the circuit is closed, a current begins to flow round it. Now the voltage between source terminals 1 and 2 (called the terminal voltage) is not equal to its e.m.f. because of the voltage drop VS inside the source, that across the source resistance RS . 当一个负载加在电源两端（也就是说电路被加上
14、负载），同时电路闭合，就有电流开始流通。这时在电源1、2两端之间的电压（称为端电压）不等同于电源的电动势，因为这时电源内阻RS两端将产生电压降VS。 Fig.1.3 shows a typical so-called external characteristic of a loaded source (hence another name is the load characteristic of a source). As is seen, increase of current from zero to II1 causes the terminal voltage of the sou
15、rce to decrease linearly 图1.3表示带负载电源的一个典型的外特性（由于电源带负载，所以也称为电源的负载特性）。如图所示，当电流从0增加到I1时，引起电源端电压的线性减小。In other words, the voltage drop VS across the source resistance rises in proportion to the current. This goes on until a certain limit is reached. Then as the current keeps rising, the proportionality
16、between its value and the voltage drop across the source is upset, and the external characteristic ceases to be linear. 换句话说，横跨电源内阻的电压降与电流成比例的增长，这种增长趋势一直持续到一个特定的限值。然后当电流继续增加时，电流值与横过电源的电压降之间的比例关系被扰乱，使得外特性终止线性关系。This decrease in voltage may be caused by a reduction in the source voltage, by an increas
17、e in the internal resistance, or both. The power delivered by a source is given by the equality PS=EI, where PS is the power of the source.电源1、2两端电压的减小可能是由于电源电压的减小或电源内阻的增加引起的，也可能是两种情况共同引起的。电源提供的功率由等式PS=EI表示，其中PS是电源的功率。It seems relevant at this point to dispel a common misconception about power. Thus
18、 one may hear that power is generated, delivered, consumed, transmitted, lost, etc. In point of fact, however, it is energy that can be generated, delivered, consumed, transmitted or lost. 这个公式恰当地消除了对功率的一个普遍的误解。例如有人可能听过功率被产生、释放、消耗、传输、损耗等等。然而，实际上是能量才能够被产生、释放、消耗、传输或损耗。Power is just the rate of energy
19、input or conversion, that is, the quantity of energy generated, delivered, transmitted etc per unit time. So, it would be more correct to use the term energy instead of power in the above context. Yet, we would rather fall in with the tradition.功率只是能量输入或者转换的比率，也就是说，单位时间内产生能量、释放能量、传输能量的数量。因此，在上文中用能量这
20、个术语代替功率会更准确些。但是，我们一般采用传统的说法。The load resistance R(Fig.1.2(b), as a generalized circuit element, gives an idea about the consumption of energy, that is, the conversion of electric energy into heat, and is defined as P=I2R.In the general case, the load resistance depends solely on the current through
21、the load, which in fact is symbolized by the function R(I).负载电阻R作为一个普遍的电路元件，给出了能量消耗的概念，也就是电能转化成热能，定义为P=I2R。一般情况下，负载电阻只由流过负载的电流决定，用方程R(I)表示。By Ohms law, the voltage across a resistance is V=RI.In circuit analysis, use is often made of the reciprocal of the resistance, termed the conductance, which is
22、 defined as g=1/R.从欧姆定律可知，电阻两端的电压表示为V=RI。在电路分析中，经常使用电阻的倒数，称为电导，定义为g=1/R.In practical problems, one often specifies the voltage across a resistance as a function of current V(I),or the inverse relation I(V) have come to be known as volt-ampere characteristics.在实际问题中，通常规定横跨电阻的电压为关于电流的方程V(I),或者是反比关系I(V
23、)，这就是众所周知的伏安特性。Fig.1.4 shows volt-ampere curves for a metal-filament lamp V1(I), and for a carbon-filament lamp V2(I). As is seen, the relation between the voltage and the current in each lamp is other than linear （nonlinear）. The resistance of the metal-filament lamp increases (with increase of cur
24、rent), and that of the carbon-filament lamp decreases with increase of current.图1.4给出了金属丝灯泡和碳丝灯泡的伏安曲线。如图所示，每个灯泡的电压和电流关系并不是线性的，当电流升高时，金属丝灯泡的电阻增大，碳丝灯泡的内阻减小。Electric circuits containing components with non-linear characteristic are called non-linear. If the e.m.f and internal resistances of sources and
25、 associated load resistances are assumed to be independent of the current and voltage, respectively, the external characteristic V(I) of the sources and the volt-ampere characteristic V1(I) of the loads will be linear(Fig.1.5). 包含非线性特性元件的电路称为非线性电路。如果假定电源的电动势和内阻以及相连的负载电阻分别与电流和电压无关，那么电源的外特性V(I)和负载的伏安特
26、性V1(I)将是线性的（如图1.5所示）。Electric circuits containing only elements with linear characteristic are called linear.Most practical circuits may be classed as linear. Therefore, a study into the properties and analysis of linear circuits is of both theoretical and applied interest. 只包含具有线性特性的元件的电路称为线性电路。很多应
27、用电路都归类为线性电路，因此，对线性电路的特性和分析的学习具有理论和实际应用的双重意义。An operational amplifier may be treated as a single electronic component with input and output terminals, rather as transistor is. The amplifier itself consists of a number of transistor stages such as those described in other lesson, fabricated and interc
28、onnected on a single substrate, and the user has access to a limited number of terminal points. Thus, of most interest from the applications point of view are the terminal characteristics.运算放大器可以看做一个具有输入端口和输出端口的单个电子元件，就像晶体管那样。放大其本身由多级晶体管组成，这样的多极晶体管在前述课程中已经介绍，他们制作和连接在一块基板上，有几个引出端可供客户使用。从使用的角度看，人们感兴趣的
29、是端口特性。The name operational amplifier came about from the use to which early versions of the amplifiers were put, which was to provide electronic analogs of mathematical operations such as addition, Subtraction, Multiplication, Integration etc. Present-day usage is very much wider scope but the popul
30、ar name “op-amp” persists.运算放大器这个名字起源于早期放大器的用途，他被用来进行一些电子模拟数学运算，例如，加减乘积分等，如今它的使用范围已大大扩展，但运算放大器这个通用名字却流传下来。The operational voltage amplifier is represented schematically by the triangular symbol. A0 is the voltage gain from differential input to single-ended output and is always a positive number. Ph
31、ase reversals are taken into account at the input terminals, which is the reason why these are labeled + and -. The voltage at each terminal, including the output, may be referred to common reference, usually ground, and unless otherwise stated, this common reference will be assumed. Thus, letting V
32、(+) represent the voltage of the positive input terminal, we may define the differential input voltage as Vid=V(+)-V(-), and the output voltage is V0=A0Vid. If, however, the differential input voltage is defined as Vid=V(-)-V(+), the output voltage is V0=-A0Vid.电压运算放大器可用三角形符号来表示。A0表示从差动输入端到单一输出端的电压增
33、益，并恒为正值，考虑到在输入端可能会有反向输入的情况，所以要标上+号与-号。每个端口包括输出端口的电压，都可以选一个共同的参考点，通常选大地。除非另有说明，否则所假定的参考点就是地。这样用V+代表正相输入端对参考点的电压，而V则代表负相输入点对参考点的电压，我们可以将差动电压定义为Vid=V(+)+V(-),输出电压V0=A0Vid。然而，如果差动输入电压定为Vid=V(-)-V(+);则输出电压V0=-A0Vid。Because no phase reversal takes place in the circuit, the positive input terminal is terme
34、d the noninverting terminal, and because a phase reversal dose take place in the circuit, the negative input terminal is termed the inverting terminal. These terminals will always be specified in the manufacturers data sheet for an amplifier. One or other of the input terminals may be connected to t
35、he common line, and the phase relationships still hold as shown. Note that the inverting terminal convention does not mean that the positive input must be connected to the noninverting and the negative input to the inverting; the amplifier may be used either way up, so to speak.因为当信号从正输入端输入时电路不发生反相，
36、所以称之为同相端，而从负输入端输入时，电路发生反相，因此称之为反相端。这些端口在放大器的铭牌上已注明。输入端口的一端或其他的端都可连到参考点，可以看出其他相位关系仍保持不变。注意，称反相端和同相端的惯例，并不意味着正信号输入一定要与同相端相连，而负信号输入一定要与反相端相连，可以说放大器可以采取其中任何一种使用方式。The basic equivalent circuit for the operational voltage amplifier is shown in fig. Ri is the differential input resistance, and will always
37、be high, usually in the megohm range. High input resistance may be achieved through the use of Darlington connected pairs in the input stage , or by using an FET differential input pair, as described in other lesson. R0 is the output resistance, and always be low, usually less then 100, for the oper
38、ational voltage amplifier. A0 is the voltage gain as defined in the previous section, and this will always be large, of the order of 106:1. For many applications, the amplifier may be represented by an voltage amplifier, for which 电压放大器的基本等值电路如图所示。Ri为差动输入电阻，切总是很大，经常在兆欧级范围内。高输入电阻可以通过在输入端使用达林顿连接对来实现，或
39、如前所述，通过使用一个FET差动输入对来实现。R0为输出电阻，并且总是很小。对电压运算放大器来说，通常不到100欧。A0为前几节所定义的电压放大倍数，他总是很大。大约属于106:1的数量级。在许多实际应用中，放大器可用一理想放大器来代表，这时：The concept of infinite voltage gain, or , for that matter, a very high but finite voltage gain, requires some explanation,. A voltage gain of 106:1 does not mean that a one-volt
40、 input signal would be amplified up to one million volts at the out put! In fact, the maximum out put voltage is limited by the bias supply voltage, typically 15V. However, an input signal of one microvolt will be amplified up to one volt at the output, and, because the amplifier is always used in c
41、ircuits in which a large fraction of the output voltage is fed back to the input, the differential input voltage may be assumed negligible in comparison with the feedback component, or in other words, Vid is assumed zero. This gives rise to the odd situation in which a zero input voltage, multiplied
42、 by an infinite voltage gain, results in a finite and very ordinary level output. The technique for analyzing this situation is illustrated in the next section.对无穷大电压增益（此处即指非常大却有限的电压增益的概念）在此需要一些解释。106:1的电压增益并不代表将1V的电压输入信号放大成106V的输出信号，实际上最大输出信号电压由偏置电源电压所限制，典型值为正负15V。然而，一个微伏级输入信号在输出端将放大到1V，同时因为放大器一般用于
43、输出电压有一大部分反馈到输入端的电路中，所以差动输入电压与反馈部分比可忽略不计，或者换句话说，Vid假定为0。这样就产生一个奇特的现象，输入电压为0，乘以一个无穷大的电压增益，得到一个有限的常规输出电压，这种情况的分析技巧将在下一节中阐述。The basic inverting amplifier circuit is shown in fig, in which ideal operational voltage amplifier is assumed. The input voltage Vi is fed to the inverting terminal through a resi
44、stor R1, and the noninverting terminal is connected to ground (or the common reference line). Feedback from output to input occurs through resistor R2. Now, because Vid=0 for the ideal amplifier, the inverting terminal is at the same potential as the noninverting terminal, and is termed a virtual gr
45、ound. Because of the virtual ground, the input loop voltage equation may be written as Vid=i1R1. For the same reason, the output voltage loop equation may be written as V0=i2R2. Because Ri is assumed infinite, the input current ii is zero, and, therefore i1=-i2. Collecting and rearranging gives for
46、the terminal voltage gain:基本反向放大器的电路如图所示，其中假设了一个理想的电压运算放大器，输入电压Vi通过一电阻R1输到反相端，并且同相端直接接地（或者接到公共参考线上）。输出端到输入端的反馈电压出现在电阻R2上。因为对理想放大器来说，Vid=0，因此其反相端与同相端电势相等，并称为虚地。因为是虚地，输入回路电压方程便可写成同样输出电压方程可写成。因为已经令r1无限大输入电流为0，所以整理后得端口电压增益The significance of this result is that the terminal voltage gain, which is the us
47、able voltage gain, is independent of the parameters of the amplifier, and depends only on the external components R1 and R2. Had A0 been assumed large but finite, the terminal gain would be reduced approximately by a factor(1-1/A0), and it can be seen that with A0 of the order of 106:1 this factor i
48、s very close to unity. It is also assumed in the ideal amplifier that the output resistance is zero so that zero voltage drop results, internal to the amplifier. A0 is known as the open loop gain because it is the voltage gain which would result with the feedback loop open; the results of feedback w
49、ith amplifiers of finite A0 are described in other lesson.这个结论的意义在于端电压增益（这是很有用的电压增益）与放大器的参数无关，而只取决于外部元件R1和R2.若A0真的假定为很大但有限，端口电压增益就会大致下降一个系数（1-1/A0）。可以看出，由于A0属于106:1数量级，因此这个系数非常接近于1.在理想放大器中，假定输出电阻为0，这样在放大器内部电压将为0.因为A0是在反馈回路开路时得出的电压增益，所以他定义为开环增益。对于A0为有限的放大器反馈结果将在其他课中讲述。 Practical comstraints limit the ration of R2/R1 to about 106:1 maximum. Offset problems, discussed in section 2