Resistor

A resistor is a two-terminal electronic component that opposes an electric current by producing a voltage drop between its terminals in proportion to the current, that is ,in accordance with Ohm’s law :V=IR .The electrical resistance R is equal to the voltage drop V across the resistor divided by the current I through the resistor. Resistors are used as part of electrical networks and electronic circuits.

译：电阻器是一个二端口电子元件,电阻是阻止电流流动，通过按比例产生其端子之间的电压降的电流,也就是说,根据欧姆定律:V = IR。电阻R等于电压降V除以通过电阻的电流I。电阻作为电子网络和电子电路的一部分。

Transistor

In electronics, a transistor is a semiconductor device commonly used to amplify or switch electronic signals . A transistor is made of a solid piece of a semiconductor material , with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor’s terminals changes the current flowing through another pair of terminals. Because the controlled current can be much larger than the controlling current, the transistor provides amplification of a signal. The transistor is the fundamental building block of modern electronic devices, and is used in radio, telephone, computer and other electronic systems. Some transistors are packaged individually but most are found in integrated circuits.

译：在电子技术中，晶体管是一种，常用来放大或进行开关控制电子信号的半导体器。晶体管是由一块固体半导体材料制成的，且至少有三个终端与外部电路连接。电压或电流适用于一双晶体管的终端改变目前流经的另一对终端。因为受控电流可以远大于控制电流，晶体管提供信号的放大。晶体管是构建现代电子设备的基本单元，并在收音机，电话，计算机和其它电子系统被使用。一些晶体管被单独包装，但大多数都在集成电路中。

Transformer

A transformer is a device that transfers electrical energy from one circuit to anther through inductively coupled electrical conductors . A changing current in the first circuit creates a changing magnetic field; in turn, this magnetic field induces a changing voltage in the second circuit. By adding a load to the secondary circuit, one can make current flow in the transformer, thus transferring energy from one circuit to the other.

译：变压器是一种通过感应耦合将电能从一个电路传输到另一个电路的装置。在第一电路中的一个变化的电流创建一个不断变化的磁场；反过来，这个磁场诱导第二个电路中的电压变化。通过向二次回路中增加负载，使电流在变压器中流动，从而将能量从一个电路传递到另一个电路中。

Relay

A relay is an electrical switch that opens and closes under the control of another electrical circuit . In the original form ,the switch is operated by an electromagnet to open or close one or many sets of contacts. It was invented by Joseph Henry in 1835. Because a relay is able to control an output circuit of higher power than the input circuit ,it can be considered to be, in a broad sense, a form of an electrical amplifier.

译：继电器是一种电子开关,控制另一个电路的打开和关闭。在原始形式中，该开关是由一个电磁铁操作，打开或关闭一个或多个触点。它是由约瑟夫亨利在1835年发明的。由于继电器能够控制比输入电路功率更高的输出电路，广义上说, 它可以被认为是电子放大器的一种形式。

Types of circuits

In any circuit where the only opposition to the flow of electrons is resistance , there is a definite relationship between the values of voltage , current, and resistance. This relationship was discovered by George Simon Ohm in 1827. It is known as Ohm’s law.

译：任何电路中电阻仅仅阻止电子的流动, 电压，电流和电阻的值之间有一个明确关系。这种关系在1827年由格奥尔格·西蒙·欧姆发现。它被称为欧姆定律。

Duality

Because of the strong similarity between the Fourier analysis and synthesis equations in continuous time , there is a duality between the time domain and frequency domain . However , for the discrete-time Fourier transforms of aperiodic signals , no similar duality exists , since aperiodic signals and their Fourier transforms are very different kinds of functions : Aperiodic discrete-time signals are , of course, aperiodic sequences , while their Fourier transforms are always periodic functions of a continuous frequency variable .

译：由于傅里叶分析和合成方程在在连续时间上有很大的相似性,有一个时域和频域之间的二元性。然而,对于非周期信号的离散傅里叶变换,没有类似的二元性存在, 由于非周期信号和它们的傅立叶变换有着迥然不同的功能: 当然,非周期离散时间信号,非周期序列,然而他们的傅里叶变换总是周期性的频率连续变化的函数。

Network Configuration

Broadly speaking , there are two types of network configuration based on their layout ,peer-to-peer networks and client/server network.

Peer-to-peer networks are more commonly implemented where less than ten computers are involved and where strict security is not necessary. All computers have the same status , hence the term ”peer” , and they communicate with each other on an equal footing .Files , such as word processing or spreadsheet documents ,can be shared across the network and all the computers on the network can share devices ,such as printers or scanners ,which are connected to any one computer.

译：广义地说，有基于两种类型网络配置的的布局，对等网络和客户机/服务器网络。

对等网络较为普遍实现，其中不到10台计算机参与并且不需要很严格的安全性。所有计算机都具有相同的地位，因此被称为“对等”，而且他们平起平坐相互通信。文件，例如文字处理或电子表格文档，可以通过网络共享来和所有的网络上的计算机进行设备共享，打印机或者扫描仪，可以连接到任何一台计算机。

Signals

A signal , as the term implies , is a set of information or data . Examples include a telephone or a television signal , monthly sales of a corporation , or the daily closing prices of a stock market . In all these examples , the signals are functions of the independent variable time . This is not always the case , however ,when an electrical charge is distributed over a body , for instance , the signal is the charge density , a function of space rather than time . In this book we deal almost exclusively with signals that are functions of time . The discussion , however , applies equally well to other independent variables .

译：信号，正如这个术语所暗示的，是一组信息或数据。例子包括电话或电视信号，一个公司的月销售，或股票市场的每日收盘价。在所有这些例子中，信号是独立的时变函数。这并非总是如此，然而，当电荷分布在一个物体上时，例如，该信号是电荷密度，它是空间而不是时间的函数。在这本书中，我们处理的信号几乎完全是时间的函数。然而，讨论，同样适用于其他独立的变量。

In 1876 Alexander Graham Bell took the telegraph one step further . Rather than converting a message into a sequence of dots and dashes , he showed that a voice could be converted directly to electrical energy and transmitted over a wire using continuously varying voltages . At the wire’s other end the electrical signals were converted back to sound . The result was that a person’s voice could be transmitted electronically between two points as long as a physical connection existed between them . To most people whose lives were based on only what they could see and hear , this invention was absolutely incredible and seemed magical.

译：在1876年亚历山大·格雷厄姆·贝尔促进了电报进一步的发展。而不是将消息转换为一系列的点和破折号,他表明,声音可以直接转化成电能,通过使用电线传输连续不同的电压。线的另一端的电信号被转换回的声音。结果是,一个人的声音可以在两点之间传播，只要它们之间存在一个物理连接。对大多数人来说,他们的生活是基于只有他们能看到和听到的,这项发明绝对是令人难以置信的，似乎是不可思议的。

An operational amplifier , often called an op-amp , is a DC-coupled high-gain electronic voltage amplifier with differential inputs and , usually , a single output . Typically the output of the op-amp is controlled either by negative feedback , which largely determines the magnitude of its output voltage gain , or by positive feedback , which facilitates regenerative gain and oscillation .High input impedance at the input terminals and low output impedance are important typical characteristics .

译：一个运算放大器，通常被简称为op-amp，是一个直流耦合、差分输入、高增益的电压放大器，通常，有一个单一的输出。典型的运算放大器的输出是由负反馈控制，这在很大程度上决定了其输出电压增益的幅度，或者通过正反馈，这有利于增加增益和振荡。输入端输入阻抗高和输出端输出阻抗低是重要的典型特征。

With email , it is possible to send a message to remote locations from the privacy of your own home . A person with a PC and modem at home can access his or her company’s or Internet Service Provider’s computer . This computer is connected to local area network that allows a message to be sent to any person connected to it . The local area network also connects to a wide area network that allows message to be sent across the country or to other countries . Local area networks at the other end can route a transmitted message to any connected PC . An individual on that end with a PC and modem can receive the message at home .

译：电子邮件，使你在家里可以向偏远地区发送私密信息成为了可能。一个人在家里用电脑和调制解调器可以访问他或她的公司或互联网服务商提供的计算机。该计算机被连接到局域网，允许一个消息被发送到连接到它的任何人。局域网还连接到一个广域网，它允许在全国或到其他国家要发送的消息。在另一端发送的消息可以通过路由局域网与任何计算机连接。个人可以用个人电脑和调制解调器在家里接收到信息。

Multimedia is a computer technology . Its applications involve the integrated processing of various types of data, like sound , images , full motion video , graphics , character data , and etc . Now , multimedia applications have ben developed for traditional uses like customer service , office automation , and computer-aided instruction . In the multimedia environment , we have graphics and text at the same time , we can also add photograph , animation , good-quality sound , and full motion video , all of the technologies make computers much more powerful and much easier to use .

译：多媒体是计算机技术。它的应用涉及到各种类型的数据的综合处理，如声音，图像，完整的动态视频，图形，字符数据等。现在，传统的多媒体应用已经成熟，如客户服务，办公自动化，计算机辅助教学。在多媒体环境中，我们同时对图形和文字进行处理，我们还可以添加照片，动画，高质量的声音，和完整的动态视频，所有的技术使得计算机更强大和更容易使用。

The operational amplifier is the most important basic block of all linear circuits. It has a wide range applications in such fields as analogue signal operations, amplification, filtering, waveforms producing, linear and non-linear signals handing, etc.

译：运算放大器是所有线性电路中最重要的基本器件。它的应 用十分广泛，包括模拟信号的运算，放大，滤波，波形发生 器，以及进行线性和非线性信号的处理等。

The term “operational amplifier” was originally applied to high gain amplifiers operating down to zero frequency which were used in analogue computers to perform certain mathematical operations. These high gain amplifier are now used for a wide variety of applications, but the name “operational amplifiers” or “op-amp” is normally use even though no mathematical operation are involved. The early operational amplifier employed discrete components, but it is now much more convenient to employ an integrated circuit. The circuit designers is not generally interested in the internal components of an integrated circuit, but only in the performance of the unit as a whole. Therefore, the symbol in Fig. 2 is used to denote the amplifier. It can be seen that there are two inputs, one output and connection the positive and negative supply lines.

译： 运算放大器这一术语最早适用于下限频率可低到零赫兹 的高增益放大器，它可用于模拟计算机中执行某些数学运算。 这种高增益的放大器现在已被广泛应用于各个方面，早已远 远超出数值运算的范围，但通常仍称之为运算放大器或OP- AMP。早期的运算放大器适用分立元件，但现在适用集成电 路就更为方便了。电路设计者通常对集成电路内波元件并不 感兴趣，只关心作为一个整体的单元性能。因此，图2所示 的符号用来表示运算放大器。由图可见，运放有两个输入端， 一个输出端以及正、负电源端子。

If the inverting input is made slightly more positive, the output will become more negative, this is why the name “inverting” is given to this input. if, the non-inverting input is made more positive, the output will also become more positive.

译：如果反向输入端正电压略微增加一点，那么输出负 电压变得更强，这就是为什么称这个输入端为“反向 输入端” 的原因。然而，如果同相收入电压正向增 大，输出端正电压也将变得更强。

Type 741 device is one of the best known general purpose operational amplifier and is also one of the cheapest of all linear integrated circuits. The device is actually available in a number of different packages. Readers will usually find the type of 741 shown in Fig. 3.This type of package is known as the 8 pin dual-in-line.

译：741型器件是众所周知的通用运算放大器之一，也 是所有的线性集成电路中最便宜的一种。这种器件实 际上具有不同的封装形式。读者通常会发现如图3所 示的741型器件最便于使用，这种封装形式为8管脚双 列直插式。

专业英语王立琦版课文翻译