1、2020/7/25,通信與信息工程專業(yè)英語教程,1,Chapter 2 Circuit System and Design 第二章 電路系統(tǒng)與設(shè)計(jì),Outline 大綱 2.1 Circuit and System 電路與系統(tǒng) 2.2 Analog and Digital Circuits Design 模擬與數(shù)字電路設(shè)計(jì) 2.3 Radio Receiver Circuit 無線電接收機(jī)電路,2020/7/25,通信與信息工程專業(yè)英語教程,2,2.1 Circuit and System,Outline 大綱 Basic concepts 基本概念 Circuit and System 電路

2、與系統(tǒng),2020/7/25,通信與信息工程專業(yè)英語教程,3,Terminology 術(shù)語,charge n.負(fù)荷, 電荷, 費(fèi)用, 主管, 充電, 充氣, 裝料 conductivity n.傳導(dǎo)性, 傳導(dǎo)率 insulator n.絕緣體, 絕熱器 gravitational adj.重力的 voltage n.電工電壓, 伏特?cái)?shù) volts n.直流電壓 ampere n.安培 ohm n.物歐姆 coulomb n.電庫侖(電量單位) diameter n.直徑 inductance n.感應(yīng)系數(shù), 自感應(yīng),2020/7/25,通信與信息工程專業(yè)英語教程,4,dielectric n.電

3、介質(zhì), 絕緣體 adj.非傳導(dǎo)性的 farad n.電法拉(電容單位) polarity n.極性 potential difference 電電位差，電勢(shì)差 equivalent resistance 等效電阻 Superposition Theorem 疊加定理 Thevenins Theorem 戴維南定理 Norton s Theorem 諾頓定理,2020/7/25,通信與信息工程專業(yè)英語教程,5,In the Bohr theory of the atom (named after Niels Bohr, 18851962), electrons orbit a nucleus c

4、ontaining neutrons and protons. Electric charge is measured in coulombs.,Introduction,Text tour 文本瀏覽,Basic concepts Charge and conductivity,2020/7/25,通信與信息工程專業(yè)英語教程,6,This relative mobility of electrons within a material is known as electric conductivity. Conductivity is determined by the types of at

5、oms in a material (the number of protons in each atoms nucleus, determining its chemical identity) and how the atoms are linked together with one another.,2020/7/25,通信與信息工程專業(yè)英語教程,7,It should also be understood that some materials experience changes in their electrical properties under different cond

6、itions. While the normal motion of free electrons in a conductor is random, with no particular direction or speed, electrons can be influenced to move in a coordinated fashion through a conductive material. This uniform motion of electrons is what we call electricity, or electric current.,2020/7/25,

7、通信與信息工程專業(yè)英語教程,8,There can be electric current only where there exists a continuous path of conductive material providing a conduit for electrons to travel through. If the path is blocked, the flow will not occur.,2020/7/25,通信與信息工程專業(yè)英語教程,9,Electric circuits, voltage and current,An electric circuit is

8、 formed when a conductive path is created to allow free electrons to continuously move. This continuous movement of free electrons through the conductors of a circuit is called a current, and it is often referred to in terms of flow, just like the flow of a liquid through a hollow pipe. The force mo

9、tivating electrons to flow in a circuit is called voltage, which technically is a measure of potential energy per unit charge of electrons. The more mass something has and the higher we lift it, the more potential energy it has.,2020/7/25,通信與信息工程專業(yè)英語教程,10,One volt is defined as that magnitude of ele

10、ctromotive force required cause a current of one ampere to pass through a conductor having a resistance of one ohm. Current flow is represented by the letter symbol I. The basic unit in which current is measured is the ampere (amp). One ampere of current is defined as the movement of one coulomb pas

11、t any point of a conductor during one second of time.,2020/7/25,通信與信息工程專業(yè)英語教程,11,Free electrons tend to move through conductors with some degree of friction, or opposition to motion. This opposition to motion is more properly called resistance. The resistance of a material that follows Ohms law is c

12、onstant, or independent of voltage or current, and the relationship between current and voltage is linear. Whenever an electric voltage exists between two separated conductors, an electric field is present within the space between those conductors. Electrical energy can be stored in an electric fiel

13、d. The device to be capable of doing this is called a capacitor or a condenser.,Resistance, capacitance and inductance,2020/7/25,通信與信息工程專業(yè)英語教程,12,If a condenser is connected to a battery, the electrons will flow out of the negative terminal of the battery and accumulate on the condenser plate connec

14、ted to that side. Thus the condenser is said to be charged. The capacitance is directly proportional to the dielectric constant of the material and to the area of the plates and inversely to the distance of the plates. The larger the plate area, the smaller the space between them, the greater the ca

15、pacitance. Whenever electrons flow through a conductor, a magnetic field will develop around that conductor. This effect is called electromagnetism. Magnetic energy can be stored in a magnetic field. The device to be capable of doing this is called an inductor.,2020/7/25,通信與信息工程專業(yè)英語教程,13,To store mo

16、re energy in an inductor, the current through it must be increased. This means that its magnetic field must increase in strength, and that change in field strength produces the corresponding voltage according to the principle of electromagnetic self-induction. When the current through an inductor is

17、 increased, it drops a voltage opposing the direction of electron flow, acting as a power load. In this condition the inductor is said to be charging, because there is an increasing amount of energy being stored in its magnetic field. Note the polarity of the voltage with regard to the direction of

18、current.,2020/7/25,通信與信息工程專業(yè)英語教程,14,2. Circuit and System,Ohms Law The first, and perhaps most important, relationship between current, voltage, and resistance is called Ohms Law, discovered by Georg Simon Ohm in 1827. Ohms principal discovery was that the amount a circuit is directly proportional t

19、o the voltage of electric current through a metal conductor in impressed across it, for any given temperature. If we know the values of any two of the three quantities (voltage, current, and resistance) in a circuit, we can use Ohms Law to determine the third.,2020/7/25,通信與信息工程專業(yè)英語教程,15,Kirchoffs Cu

20、rrent Law and Kirchoffs Voltage Law Kirchoffs Current Law is the total charge flowing into a node must be the same as the total charge flowing out of the node. Kirchhoffs Voltage Law (or Kirchhoffs Loop Rule) is a result of the electrostatic field being conservative. It states that the total voltage

21、 around a closed loop must be zero. If this were not the case, then when we travel around a closed loop, the voltages would be indefinite.,2020/7/25,通信與信息工程專業(yè)英語教程,16,Introduction to network theorems In electric network analysis, the fundamental rules are Ohms Law and Kirchhoffs Laws. While these hum

22、ble laws may be applied to analyze just about any circuit configuration (even if we have to resort to complex algebra to handle multiple unknowns), there are some “shortcut” methods of analysis to make the math easier.,2020/7/25,通信與信息工程專業(yè)英語教程,17,Superposition Theorem The strategy used in the Superpo

23、sition Theorem is to eliminate all but one source of power within a network at a time, using series/parallel analysis to determine voltage drops (and/or currents) within the modified network for each power source separately. Then, once voltage drops and/or currents have been determined for each powe

24、r source working separately, the values are all “superimposed” on top of each other (added algebraically) to find the actual voltage dropscurrents with all sources active.,2020/7/25,通信與信息工程專業(yè)英語教程,18,Thevenins Theorem Thevenins Theorem states that it is possible to simplify any linear circuit, no matter how complex, to an equivalent circuit with just a single voltage source and series resistance connected to a load. Thevenins Theorem is especia