Unit 6,Linear Circuit Analysis,Linear Circuit Analysis,电子与通信工程专业英语,电子与通信工程专业英语,Linear Circuit Analysis,Gustav Robert Kirchhoff,1Ohms Law Suppose that some material is connected to the terminals of an ideal voltage source u(t) as shown in Fig 6-1Suppose that u(t)=1 V , then the electric potential at the top of the material is 1 V above the potential at the bottomSince an electron has a negative charge, electrons in the material will tend to flow from bottom to topTherefore，we say that a current tends to go from top to bottom through the material. Hence, for the given polarity, when u(t) is a positive number, i(t) will be a positive number with the direction indicated in Fig 6-1.,第6单元 线性电路分析 1欧姆定律 假若把某种材料连接到一个理想电压源u(t) 的两端(如图6-1所示)，设u(t)=1V，则材料顶部的电势(电位)比材料底部的电势高出1V，由于电子是携带负电荷的，在材料中的电子将从材料的底部流向顶部，即有电流i(t)从材料的顶部通过材料流向底部。因此，当电源极性给定时，当u(t)为正时，电流正方向如图6-1所示。,电子与通信工程专业英语,If u(t) =2V, again the potential at the top is greater 2V than at the bottom，so i(t) will again be positive. However，because the potential is now twice as large as before，the current i(t) be greater (If the material is a “linear” element，the current will be twice as great)If the resulting current i(t) is always directly proportional to the voltage for any function u(t)，the material is called a linear resistor To a linear resistor，we have： R= and i(t)= The unit of resistance (volts per ampere) is referred to as Ohms and is denoted by the capital Greek letter omega Both equations above are also referred to as Ohms law,假若u(t) =2V，同理，材料顶部的电势(电位)比材料底部的电势高出2V，所以电流i(t)仍为正的(当材料为“线性”材料时，电流是原来的两倍)。对任意给定的电压函数u(t)，假若产生的电流总是与给定的电压函数u(t)成正比，则该材料被称为线性电阻。 一个线性电阻有：R= 和 i(t)= 电阻的单位(伏特每安培)叫欧姆，且用大写希腊字母“ ”表示，上面的两个方程均称为欧姆定律。,电子与通信工程专业英语,2Kirchhoffs Current Law It is a consequence of the work of the German physicist (1824-1887) that enables us to analyze an interconnection of any number of elements (voltage sources，current sources，and resistors), as well as other electronic devicesWe will refer to any such interconnection as a circuit or a network For a given circuit a connection of two or more elements shall be called a node. We now present the first of Kirchhoffs two laws，his current law (KCL)，which is essentially the law of conservation of electric charge：,2基尔霍夫电流定律 德国物理学家Gustav Kirchhoff (18241887)得出了基尔霍夫定律，我们可以用它来分析任何电路元件(电压源、电流源和电阻)以及其它电子器件构成的相互连接。我们把这种相互连接称为一个电路或一个网络。 对一个给定的电路，两个或更多的元件的连接点叫结点。现在我们介绍两个基尔霍夫定律中的第一个基尔霍夫电流定律，它是根据电荷守恒定律得到的：,电子与通信工程专业英语,At any node of a circuit，at every instant of time, the sum of the currents into the node is equal to the sum of the currents out of the node. = An alternative, but equivalent，form of KCL can be obtained by considering currents directed into a node to be positive in sense and currents directed out of a node to be negative in sense. Under this circumstance，the alternative form of KCL can be stated as follows： = 0 At any node of a circuit，the currents algebraically sum to zero.,= 。 对电路的任何一个结点，在每一瞬时流入结点的电流和总是等于流出结点的电流和。 假若考虑电流的方向，取流入结点为正，流出结点为负，则基尔霍夫电流定律也可以表示为： =0 对电路中的任一结点，电流的代数和为O。,电子与通信工程专业英语,3. Kirchhoffs Voltage Law (KVL) We now present the second of Kirchhoffs lawsthe voltage law. To do this，we must introduce the concept of a “loop”. Starting at any node n in a circuit, we form a loop by traversing through elements and returning to the starting node n，and never encountering any other node more than once. Kirchhoffs voltage law (KVL) is： + = - In traversing any loop in any circuit，at every instant of time，the sum of the voltages having one polarity equals the sum of the voltages having the opposite polarity.,3基尔霍夫电压定律 现在介绍基尔霍夫第二定律电压定律。我们先引入“闭合回路”的概念。从电路的任一结点开始，通过电路中每一个元件且每个结点只能通过一次，再回到电路的出发结点构成一个闭合回路。基尔霍夫电压定律为： = 沿着电路的任一闭合回路，每一瞬时的正电压和等于负电压和。,电子与通信工程专业英语,An alternative statement of KVL can be obtained by considering voltages across elements that are traversed from plus to minus to be positive in sense and voltages across elements that are traversed from minus to plus to be negative in sense (or vice versa). Under this circumstance，KVL has the following alternative form. Around any loop in a circuit，the voltages algebraically sum to zero.,假定元件两端的电压是从正到负为正电压，从负到正为负电压，基尔霍夫电压定律也可以表述成下列形式： = 0 环绕电路中的任一闭合回路，电压的代数和等于O。,电子与通信工程专业英语,4. Circuit Analysis Techniques The process by which we determine a variable (either voltage or current) of a circuit is called analysis. Though：some simple single-stage amplifier circuits can be quite useful. We have already come across some simple single-stage amplifier circuits whose analysis was accomplished by applying the basic principles converted to data-Ohms law, KCL and KVL. Nonetheless, we must also be able to analyze more complicated circuitsthose in which it is simply not possible to conveniently write and solve a set of linear algebraic equations.,4电路分析方法 求出一个电路的变量(无论是电压还是电流)的过程叫电路分析。虽然一些简单的单级放大电路就十分有用了，对这些简单的单级放大电路，只要直接运用欧姆定律、KCL和KVL就能够求解。但是我们必须学会分析比较复杂的电路，在复杂电路中直接列出并求解线性代数方程组并不容易。,电子与通信工程专业英语,There are several distin