专业外语大作业.doc

专业英语大作业专业：电子信息工程班级：学号：姓名： 20112012（2）晶体管的工作原理晶体管的设计使它的功能相当于一个放大器或一个开关。它的作用是实现用少量的电能去控制大量的电源供应，就像转阀控制水的供应一样。晶体管是由三个部分组成基极、集电极和发射极。基极是大供电的门控制器部分，集电极是提供更大的电力的部分，,发射极供电的输出部分。通过发送不同范围的基极电流,从而调节流经集电极的电流。这样，就像放大器一样，一个非常小的电流就可以用来控制较大的电流。这个过程被用来为数字处理器创建二进制代码,但需5伏特的门槛电压才能正常工作。因此，晶体管常被用作门限开关：开关闭合；不超过5伏特时，开关断开。半导体材料的应用使晶体管的制作成为可能。人们习惯把材料分为导电和绝缘两种。金属通常被认为是良导体，而木材、塑料、玻璃、陶瓷等材料通常被认为是不导电的，即绝缘体。19世纪40年代末，一组在新泽西州的贝尔实验室工作的科学家在研究半导体的特性时，发现了如何制作某些类型的晶体，并把它们作为电子控制装置。大多数非金属晶体都会被视为绝缘体。但通过迫使在锗或硅晶体中掺杂硼或磷等杂质，会使晶体获得完全不同的导电性能。通过在两个导电板(发射极和集电极) 间加入这种材料，晶体管就做好了。利用基极电流来控制电流的流向。约翰。巴丁,沃尔特。布拉顿和威廉萧克利对晶体管的发明做出了卓越的贡献，他们的专利被称为:“利用半导体材料三电极电路元件。”现在主要有两种类型的晶体管双极结型晶体管（BJT）和场效应晶体管。它们以不同的方式进行工作。但任何晶体管的用处都在于它能用较弱的电压去控制很大的电流。例如, 在公共广播系统利用电晶体放大(即加强)人的声音经麦克风形成的弱电压，经晶体管放大后的电源已足够操作扩音器，使之产生比人声响亮的多的声音。双极结型晶体管双极结型晶体管是在两层厚介质间填充一种稍薄的半导体材料的晶体管类型。例如,若中间的介质为P型，那么外边的两层介质必须为N型，这样就构成了一个NPN晶体管。外层介质中的一端被称为发射极，另一端被称为集电极，中间层被称为基极。发射极和基极、基极和集电极的接触部分称为连接。NPN晶体管的层与层之间必须要有适当的电压连接着：基极电压要大于发射极电压，而且和，基极电压要小于集电极电压。电压均来自电池或其他来源的直流电。发射器发射电子，基极吸收这些电子（也可译作：电子从发射极运动到基极），因为它的电压比发射极大。电子的运动创造了一个流经晶体管的电流。电流经由基极从发射极流向集电极，通过改变基极电子的数目来控制基极的电压以达到改变基极电流的作用。这样就能通过基极电压的微小变化来实现集电极电流的较大输出变化。另一种双极结型晶体管是PNP晶体管。在这种设备中,发射极和集电极都是p型半导体材料，而基极是n型半导体材料。该双结型晶体管的工作原理与NPN晶体管大体上都是相同的，不同之外体现在一个方面：电流变化的控制是通过一个PNP晶体管改变的孔数而不是电子在基极的数量来实现的。同时，这类晶体管只有在正极和负极连接反向的NPN晶体管时才能正常工作。场效应晶体管场效应晶体管是由两个相互叠加层次的半导体材料构成。电流流经其中一个被频道的层，电压连接到另外一个叫做门限的层，该电压对流经通道电流形成干扰。以这种方式，通过控制连接到门限层电压来达到影响渠道层电流强度的效果。有两个基本的场效应晶体管交界处场效应晶体管(JFET)和金属氧化物半导体场效应晶体管(MOSFET)。现在，嵌套在集成电路的大部分晶体管是MOSFETS型的。晶体管的底部是U型部分,是n型半导体，存储大量的自由电子。它的中心部分是一段称为“基极”是由p型(带正电)半导体，只存储少量电子。(其实,N 型和P型结构可以相互替换,构成的装置仍然会以同样的方式工作。在该装置中，产生电流的不是电子的运动，而是漏极电流。)半导体晶体管由三个电极相连构成：一个中间节正面,一只胳膊夹着一只美国施加的电压电极进行U、电流流过它。那边的电子进来是众所周知的来源,并且要把那边的电子被称为排泄出来。场效应晶体管理正常工作时，,电流就从一侧流到另。电子运动的交汇处形成N - p型半导体结面。,需要注意的是，,当前的电流不会流经基极，它只通过场效应晶体管的窄通道中间。场效应晶体管是如此命名的原因是：微弱的电子信号在剩余的晶体管内通过一个电极来创建磁场。当有信号输入时，磁场由正极向负极转换，从而控制二级电流穿越其余的晶体管。电磁场调整二级电流模仿原始电流但二级电流可以得到充分地放大。今天大多数的晶体管是“MOS-FETs”,或金属氧化物半导体场效应晶体管，它们主要由贝尔实验室,供应商、半导体以及数以百计的硅谷高新园区,以及日本公司和其他电子公司联合开发的。附：英文原文/education/askexperts/ae430.cfm （文章网址）How does a transistor work?The design of a transistor allows it to function as an amplifier or a switch. This is accomplished by using a small amount of electricity to control a gate on a much larger supply of electricity, much like turning a valve to control a supply of water. Transistors are composed of three parts a base, a collector, and an emitter. The base is the gate controller device for the larger electrical supply. The collector is the larger electrical supply, and the emitter is the outlet for that supply. By sending varying levels of current from the base, the amount of current flowing through the gate from the collector may be regulated. In this way, a very small amount of current may be used to control a large amount of current, as in an amplifier. The same process is used to create the binary code for the digital processors but in this case a voltage threshold of five volts is needed to open the collector gate. In this way, the transistor is being used as a switch with a binary function: five volts ON, less than five volts OFF. Semi-conductive materials are what make the transistor possible. Most people are familiar with electrically conductive and non-conductive materials. Metals are typically thought of as being conductive. Materials such as wood, plastics, glass and ceramics are non-conductive, or insulators. In the late 1940s a team of scientists working at Bell Labs in New Jersey, discovered how to take certain types of crystals and use them as electronic control devices by exploiting their semi-conductive properties.Most non-metallic crystalline structures would typically be considered insulators. But by forcing crystals of germanium or silicon to grow with impurities such as boron or phosphorus, the crystals gain entirely different electrical conductive properties. By sandwiching this material between two conductive plates (the emitter and the collector), a transistor is made. By applying current to the semi-conductive material (base), electrons gather until an effectual conduit is formed allowing electricity to pass The scientists that were responsible for the invention of the transistor were John Bardeen, Walter Brattain, and William Shockley. Their Patent was called: “Three Electrode Circuit Element Utilizing Semiconductive Materials.”There are two main types of transistors-junction transistors and field effect transistors. Each works in a different way. But the usefulness of any transistor comes from its ability to control a strong current with a weak voltage. For example, transistors in a public address system amplify (strengthen) the weak voltage produced when a person speaks into a microphone. The electricity coming from the transistors is strong enough to operate a loudspeaker, which produces sounds much louder than the persons voice. JUNCTION TRANSISTORS A junction transistor consists of a thin piece of one type of semiconductor material between two thicker layers of the opposite type. For example, if the middle layer is p-type, the outside layers must be n-type. Such a transistor is an NPN transistor. One of the outside layers is called the emitter, and the other is known as the collector. The middle layer is the base. The places where the emitter joins the base and the base joins the collector are called junctions. The layers of an NPN transistor must have the proper voltage connected across them. The voltage of the base must be more positive than that of the emitter. The voltage of the collector, in turn, must be more positive than that of the base. The voltages are supplied by a battery or some other source of direct current. The emitter supplies electrons. The base pulls these electrons from the emitter because it has a more positive voltage than does the emitter. This movement of electrons creates a flow of electricity through the transistor. The current passes from the emitter to the collector through the base. Changes in the voltage connected to the base modify the flow of the current by changing the number of electrons in the base. In this way, small changes in the base voltage can cause large changes in the current flowing out of the collector. Manufacturers also make PNP junction transistors. In these devices, the emitter and collector are both a p-type semiconductor material and the base is n-type. A PNP junction transistor works on the same principle as an NPN transistor. But it differs in one respect. The main flow of current in a PNP transistor is controlled by altering the number of holes rather than the number of electrons in the base. Also, this type of transistor works properly only if the negative and positive connections to it are the reverse of those of the NPN transistor. FIELD EFFECT TRANSISTORS A field effect transistor has only two layers of semiconductor material, one on top of the other. Electricity flows through one of the layers, called the channel. A voltage connected to the other layer, called the gate, interferes with the current flowing in the channel. Thus, the voltage connected to the gate controls the strength of the current in the channel. There are two basic varieties of field effect transistors-the junction field effect transistor(JFET) and the metal oxide semiconductor field effect transistor (MOSFET). Most of the transistors contained in todays integrated circuits are MOSFETSs.On the bottom of the transistor is a U-shaped section (though its flatter than a true U) of N-type semiconductor with an excess of electrons. In the center of the U is a section known as the base made of P-type (positively charged) semiconductor with too few electrons. (Actually, the N- and P-types can be reversed and the device will work in exactly the same way, except that holes, not electrons, would cause the current.) Three electrodes are attached to the top of this semiconductor crystal: one to the middle positive section and one to each arm of the U. By applying a voltage to the electrodes on the U, current will flow through it. The side where the electrons come in is known as the source, and the side where the electrons come out is called the drain. If nothing else happens, cur