OperationalAmplifiers毕业论文外文文献翻译及原文

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　　外 文 文 献 翻 译 文献、资料中文题目：运算放大器

　　文献、资料英文题目：Operational Amplifiers

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　　翻译日期： 2017.02.14

　　1

　　Operational Amplifiers

　　In 1943 Harry Black commuted from his home in New York City at Bell Labs in New Jersey by way of a ferry. The ferry ride relaxed Harry enabling him to do some conceptual thinking. Harry had a tough problem to solve; when phone lines were extended long distance, they needed amplifiers, and undependable amplifiers limited phone service. First, initial tolerances on the gain were poor, but that problem was quickly solved wuth an adjustment. Second, even when an amplifier was adjusted correctly at the factory, the gain drifted so much during field operation that the volume was too low or the incoming speech was distorted.

　　Many attempts had been made to make a stable amplifier, but temperature changes and power supply voltage extremes experienced on phone lines caused uncontrollable gain drift. Passive components had much better drift characteristics than active components had, thus if an amplifier?s gain could be made dependent on passive components, the problem would be solve. During one of his ferry trips, Harry?s fertile brain conceived a novel solution for the amplifier problem, and he documented the solution while riding on the ferry.

　　The solution was to first build an amplifier that had more gain than the application required. Then some of the amplifier output signal was fed back to the input in a manner that makes the circuit gain (circuit is the amplifier and feedback components) dependent on the feedback circuit rather than the amplifier gain. Now the circuit gain is dependent on the passive feedback components rather than the active amplifier. This is called negative feedback, and it is the underlying operating principle for all modern day opamps. Harry had documented the first intentional feedback circuit had been built prior to that time ,but the designers ignored the effect.

　　I can hear the squeals of anguish coming from the manager and amplifier designers. I imagine that they said something like this, “it is hard enough to achieve 30kHz gainbandwidth (GBW), and now this fool wants me to design an amplifier with 3MHz GBW. But ,he is still going to get a circuit gain GBW of 30kHz .” Well, time has proven Harry right ,but there is a minor problem. It seems that circuit designed with large pen loop gains sometimes oscillate when the loop is closed. A lot of people investigated the instability effect, and it was pretty well understood in the 1940s, but solving stability problems involved long, tedious, and

　　intricate calculations. Years passed without anybody making the problem solution simpler or more understandable.

　　In 1945 H. W. Bode presented a system for analyzing the stability of feedback system by using graphical methods. Until this time, feedback analysis was done by multiplication and division, so calculation of transfer functions was a time consuming and laborious task. Remember, engineers did not have calculators or computers until the ?70s, Bode presented a log technique that transformed the intensely mathematical process of calculating a feedback system?s stability into graphical analysis that was simple and perceptive. Feedback system design was still complicated, but it no longer was an art dominated by a few electrical engineers kept in a small dark room. Any electrical engineer could use Bode?s methods to find the stability of a feedback circuit, so the application of feedback to machines began to grow. There really wasn?t much call for electrical feedback design until computers and transducers become of age.

　　The first real-time computer was the analog computer! This computer used preprogrammed equations and input data to calculate control actions. The programming was hard wired with a series of circuit that performed math operations on the data, and the hard wiring limitation eventually caused the declining popularity of the analog computer. The heart of the analog computer was a device called an operational amplifier because it could be configured to perform many mathematical operations such as multiplication, addition, subtraction, division, integration, and differentiation on the input signals. The name was shortened to the familiar op amp, as we have come to know and love them. The op amp used an amplifier with a large open loop gain, and when the loop was closed, the amplifier performed the mathematical operations dictated by the external passive components. This amplifier was very large because it was built with vacuum tubes and it required a high-voltage power supply,but it was the heart of the analog computer, thus its large size and huge power requirements were accepted. Many early op amps were designed for analog computers, an it was soon found out the op amps had other uses and were handy to have around the physics lab .

　　At this time general-purpose analog computers were found in universities and large

　　company laboratories because they were critical to the research work done there. There was a parallel requirement for transducer signal conditioning in lab experiments, and op amps found their way into signal conditioning applications. As the signal conditioning applications expanded, the demand for op amps grew beyond the analog computer requirements , and even when the analog computers lost favor to digital computers, the op amps survived because of its importance in universal analog applications. Eventually digital computes replaced the analog computers, but the demand for op amps increased as measurement applications increased.

　　The first signal conditioning op amps were constructed with vacuum tubes prior to the introduction of transistors, so they were large and bulky. During the?50s, miniature vacuum tubes that worked from lower voltage power supplies enabled the manufacture of op amps that shrunk to the size lf a brick used in house construction, so the op amp modules were nick named bricks. Vacuum tube size and component size decreased until an op amp was shrunk to the size of a single octal vacuum tube. Transistors were commercially developed in the ?60s, and they further reduced op amp size to several cubic inches. Most of these early op amps were made for specific applications, so they were not necessarily general purpose. The early op amps served a specific purpose, but each manufacturer had different specifications and packages; hence, there was little second sourcing among the early op amps.

　　ICs were developed during the late 1950s and early 1960s, but it wasn?t till the middle 1960s that Fairchild released the μA709. This was the first commercially successful IC op am. TheμA709 had its share of problems, bur any competent analog engineer could use it, and it served in many different analog applications. The major drawback of theμA709 was stability; it required external compensation and a competent analog engineer to apply it. Also, theμA709 was quite sensitive because it had a habit of self-destruction under any adverse condition. TheμA741 followed theμA709, and it is an internally compensated op amp that does not require external compensation if operated under data sheet conditions. There has been a never-ending series of new op amps released each year since then, and their performance and reliability had improved to the point where present day op amps can be used for analog applications by anybody.

　　The op amp will continue to be a vital component of analog design because it is such a fundamental component. Each generation of electronic equipment integrates more functions on silicon and takes more of the analog circuit inside the IC. As digital applications increase, analog applications also increase because the predominant supply of data and interface applications are in the real world, and the real world is an analog world. Thus , each new generation of electronic equipment creates requirements for new analog circuit; hence, new generations of op amps are required to fulfill these requirements. Analog design, and op amp design, is a fundamental skill that will be required far into the future.

　　放 大 器

　　1943年，哈利布莱克乘火车或渡船从位于纽约市的家去新泽西州的贝尔实验室上班。在上班途中，哈利能够送下来，思考一些概念上的问题。哈利需要解决一个很棘手的问题：电话线在用于长途传输时就需要放大器，而性能不可靠的放大器限制了电话业务的扩展。首先，增益容差性能很差；但是，通过使用调节器，这个问题很快就解决了。第二，即使放大器在工厂里被调节正确，但在现场工作是增益还是漂移地很厉害，以至于音量太低或输入语音发生畸变。

　　为了制造出稳定的放大器，哈利已经进行了多次尝试；但是，温度变化和电话线上出现的供电电压极限使得增益漂移无法控制。无源器件比有源器件具有好得多漂移特性；假如能使放大器增益仅由无源器件决定的话，那么这个问题就会解决。在乘渡船上下班途中，哈利构想一个新颖的、解决放大器问题的办法，并在途中将它记录下来。

　　这个解决方案是这样的：首先设计一个增益比实际需求高的放大器，然后，将放大器输出信号的一部分反馈输入端，这使得电路增益（这里的电路由放大器和反馈器件组成）由反馈电路决定，而不是放大器增益决定，这样的话，电路增益就取决于无源反馈器件，而不是有源放大器。这个方案被称为“负反馈“，它是现代运算放大器的基本工作原理。哈利在乘坐渡船途中记录了第一个有意加入反馈的电路。此前，也一定有人无意中使用过反馈电路，但设计者忽视了这种作用！

　　管理者和放大器设计者可能会发生痛苦的抱怨。他们可能会说：“获得30kHz的增益带宽就够难了，现在这个傻瓜要我设计增益带宽为30MHz的放大器，而他还是想得到一个增益带宽为30kHz电路”。然而，时间已经证明哈利是正确，但有一个小问题哈利没有详细讨论——振荡问题。在环路闭合时候，开环增益设计得很大的电路有时会发生振荡。很多人都研究了这个不稳定现象，在20世纪40年代人们对它有了清晰的认识；不过，解决稳定问题需要长时间单调复杂的计算。许多年过去了，没有人能将解法简化或使之易于理解。

　　1945年，波特用图形化方法展示了一个用于分析反馈系统稳定性的系统。那时，反馈分析是用乘法和除法完成的。因此，计算传输函数是一件耗时费力的工作。需要知道的是：直到20世纪70年代，工程师才有了计算器和计算机。波特采用了一种对数方法——将分析反馈系统稳定的数学过程转换为容易的、好理解的图形化分析。虽然反馈系统的设计依然很复杂，但它再也不是一件只有少数电气工程师掌握的技术。任何电气工程师都可以使用波特的方法确定反馈电路的稳定性，并越来越多地将反馈应用到机器