《Analog-Amplifiers-模拟放大器-外文翻译.doc》由会员分享，可在线阅读，更多相关《Analog-Amplifiers-模拟放大器-外文翻译.doc（4页珍藏版）》请在taowenge.com淘文阁网|工程机械CAD图纸|机械工程制图|CAD装配图下载|SolidWorks_CaTia_CAD_UG_PROE_设计图分享下载上搜索。
1、Analog AmplifiersAt the most basic level, a signal amplifier does exactly what you expect it makes a signal bigger! However, the way in which it is done does vary with the design of the actual amplifier, the type of signal, and the reason why we want to enlarge the signal.We can illustrate this by c
2、onsidering the common example of a “Hi-Fi” audio system.In a typical modern Hi-Fi: system, the signals will come from a unit like a CD player, FM tuner, or a Tape/Minidisk unit. The signals they produce have typical levels of the order of 100 mV or so when the music is moderately loud. This is a rea
3、sonably large voltage, easy to detect with something like an oscilloscope or a voltmeter. However, the actual power levels of these signals are quite modest. Typically, these sources can only provide currents of a few milliamps, which by PVI means powers of just a few milliwatts. A typical loudspeak
4、er will require between a few Watts and perhaps over 100 Watts to produce loud sound. Hence we will require some form of Power Amplifier (PA) to “boost” the signal power level from the source and make it big enough to play the music.Fig. 1.1 shows four examples of simple analog amplifier stages usin
5、g various types of device. In each case the a.c. voltage gain will usually be approximated byprovided that the actual device has an inherent gain large enough to be controlled by the resistorvalues chosen.Note the negative sign in expression 1-1 which indicates that the examples allinvert the signal
6、 pattern when amplifying.In practice, gains of the order of up to hundred arepossible from simple circuits like this, although it is usually a good idea to keep the voltage gainbelow this. Note also that vacuum state devices tend to be called “valves” in the UK and “tubes”in the USA.Many practical a
7、mplifiers chain together a series of analog amplifier stages to obtain a high overall voltage gain. For example, a PA system might start with voltages of the order of 0.1 mV from microphones, and boost this to perhaps 10 to 100 V to drive loudspeakers. This requires an overall voltage gain of 109, s
8、o a number of voltage gain stages will be required.In many cases we wish to amplify the current signal level as well as the voltage. Theexample we can consider here is the signal required to drive the loudspeakers in a “Hi-Fi” system.These will tend to have a typical input impedance of the order of
9、8 Ohms. So to drive, say, 100Watts into such a loudspeaker load we have to simultaneously provide a voltage of 28 Vrms and3.5 Arms. Taking the example of a microphone as an initial source again a typical sourceimpedance will be around 100 Ohms. Hence the microphone will provide just 1 nA whenproduci
10、ng 0.1 mV. This means that to take this and drive 100 W into a loudspeaker the amplifiersystem must amplify the signal current by a factor of over 109 at the same time as boosting thevoltage by a similar amount. This means that the overall power gain required is 1018 i.e. 180dB!This high overall pow
11、er gain is one reason it is common to spread the amplifying function into separately boxed pre- and power-amplifiers. The signal levels inside power amplifiers are so much larger than these weak inputs that even the slightest leakage from the output back to the input may cause problems. By putting t
12、he high-power (high current) and low power sections in different boxes we can help protect the input signals from harm.In practice, many devices which require high currents and powers tend to work on the basis that it is the signal voltage which determines the level of response, and they then draw t
13、he current they need in order to work. For example, it is the convention with loudspeakers that thevolume of the sound should be set by the voltage applied to the speaker. Despite this, mostloudspeakers have an efficiency (the effectiveness with which electrical power is converted into acoustical po
14、wer) which is highly frequency dependent. To a large extent this arises as a natural consequence of the physical properties of loudspeakers. We wont worry about the details here,but as a result a loudspeakers input impedance usually varies in quite a complicated manner with the frequency. (Sometimes
15、 also with the input level.)Fig. 1.2 shows a typical example. In this case, the loudspeaker has an impedance of around 12 Ohms at 150 Hz and 5 Ohms at 1 kHz. So over twice the current will be required to play the same output level at 1 kHz than is required at 150 Hz. The power amplifier has no way t
16、o “know in advance” what kind of loudspeaker you will use, so simply adopts the convention of asserting a voltage level to indicate the required signal level at each frequency in the signal and supplying whatever current the loudspeaker then requires.This kind of behavior is quite common in electron
17、ic systems. It means that, in information terms, the signal pattern is determined by the way the voltage varies with time, and ideally the current required is then drawn. Although the above is based on a high-power example, a similar situation can arise when a sensor is able to generate a voltage in
18、 response to an input stimulus butcan only supply a very limited current. In these situations we require either a current amplifier or a buffer. These devices are quite similar, and in each case we are using some form of gain device and circuit to increase the signal current level. However, a curren
19、t amplifier always tries to multiply the current by a set amount. Hence it is similar in action to a voltage amplifier which always tries to multiply the signal current by a set amount. The buffer differs from the current amplifier as it sets out to provide whatever current level is demanded from it
20、 in order to maintain the signal voltage told to assert. Hence it will have a higher current gain when connected to a more demanding load.Analog circuits are circuits dealing with signals free to vary from zero to full power supply voltage. This stands in contrast to digital circuits, which almost e
21、xclusively employ “all or nothing” signals: voltages restricted to values of zero and full supply voltage, with no valid state in between those extreme limits. Analog circuits are often referred to as linear circuits to emphasize the valid continuity of signal range forbidden in digital circuits, bu
22、t this label is unfortunately misleading. Just because a voltage or current signal is allowed to vary smoothly between the extremes of zero and full power supply limits does not necessarily mean that all mathematical relationships between these signals are linear in the “straight-line” or “proportio
23、nal” sense of the word. Many so-called “linear” circuits are quite nonlinear in their behavior, either by necessity of physics or by design.The circuits make use of IC, or integrated circuit, components. Such components are actually networks of interconnected components manufactured on a single wafe
24、r of semiconducting material. Integrated circuits providing a multitude of pre-engineered functions are available at very low cost, benefiting students, hobbyists and professional circuit designers alike. Most integrated circuits provide the same functionality as “discrete” semiconductor circuits at
25、 higher levels of reliability and at a fraction of the cost. Usually, discrete-component circuit construction is favored only when power dissipation levels are too high for integrated circuits to handle. Perhaps the most versatile and important analog integrated circuit for the student to master is
26、the operational amplifier, or op-amp. Essentially nothing more than a differential amplifier with very high voltage gain, op-amps are the workhorse of the analog design world. By cleverly applying feedback from the output of an op-amp to one or more of its inputs, a wide variety of behaviors may be
27、obtained from this single device. Many different models of op-amp are available at low cost.A comparator circuit compares two voltage signals and determines which one is greater. The result of this comparison is indicated by the output voltage: if the op-amps output is saturated in the positive dire
28、ction, the noninverting input (+) is a greater, or more positive, voltage than the inverting input (-) , all voltages measured with respect to ground. If the op-amps voltage is near the negative supply voltage (in this case, 0 Volt, or ground potential) , it means the inverting input (-) , all volta
29、ges measured with respect to ground. If the op-amps voltage is near the negative supply voltage (in this case, 0 Volt, or ground potential) , it means the inverting input (-) has a greater voltage applied to it than the noninverting input (+) Y. This behavior is much easier understood by experimenti
30、ng with a comparator circuit than it is by reading someones verbal description of it. In this experiment, two potentiometers supply variable voltages to be compared by the op-amp. The output status of the op-amp is indicated visually by the LED. By adjusting the two potentiometers and observing the
31、LED, one can easily comprehend the function of a comparator circuit.翻译：模拟放大器在最基础的水平上,信号放大做到底你所期待的它是一种信号大!然而,以何种方式,它确实不同设计的实际放大器,这个类型的信号,为什么我们要放大信号。1的基础上,我们可以说明考虑到常见的例子是“高保真音响系统”。在一个典型的现代高保真:系统,信号会来自一个单位如CD播放器、调频调谐器,或磁带/ Minidisk单位。他们生产的信号有代表性的水平100毫伏或当音乐是适度的大声。这是一个相当大的电压,很容易检测和类似示波器或电压表。然而,实际的这些信号是很
32、谦虚。通常,这些资料仅能提供的电流milliamps,P = VI意味着异能,只有一些毫瓦的功率。一个典型的喇叭需要几瓦特,也许之间100瓦特产生巨大的声响。因此,我们会的需要某种形式的功放,“提高”的信号功率水平,从源头上并把它足够大,可以播放音乐。图1.1显示4简单模拟放大器阶段使用不同类型的装置。在每种情况下,交流电压增益通常将接近实际的设备byprovided内在获得足够大以控制电阻消极的标志值chosen.Note 1 - 1所表达的例子表明,所有翻转讯号模式时,所得的amplifying.In实践的订购100从简单的电路可能这样,虽然它通常是一个好主意保持电压增益下面这一点。另外,
33、真空装置往往被称为“阀”,在英国和“管在美国。许多实际放大器链在一起一系列模拟放大器的阶段,以获得一个高总电压增益。例如,一个PA系统可能开始与电压的次序0.1毫伏从麦克风,并提高到大约10至100 V驱动扬声器。这就要求总电压增益,所以很多的109电压增益阶段是必需的。在许多情况下我们想放大电流信号水平以及电压。这个我们可以考虑是这里的信号驱动扬声器需要在一个“高保真”系统。这些会有一个典型的输入阻抗的8欧姆。所以,说,100美国瓦茨成这样一个扩音器负荷,我们不得不同时提供一个电压的28 Vrms和3.5武器。以实例的麦克风作为初始又一个典型的源泉。源将有大约100欧姆阻抗。于是麦克风将提供
34、仅仅1钠时生产0.1毫伏。这意味着,借此和驱动扬声器进入100 W放大器放大系统的信号电流超过109的同时,增加了通过一个类似的金额。高压3这意味着整体功率增益-即要求。180dB型硅碳棒!这个高整体功率增益原因之一是它是普通的放大作用到单独装箱前和power-amplifiers。内部的信号功率放大器是如此水平要大得多,这些软弱一点点的输入与输出的泄漏回输入也会带来麻烦。由于把大功率(高电流)和低功率的部分我们可以帮助保护不同的输入信号,免受伤害。在实践中,很多设备需要高电流和权力往往工作的基础这是信号电压决定了反应的等级,他们得出了电流他们需要为了工作。4为例,它是用扩音器,本公约体积的声
35、音应由电压应用议长。尽管如此,大多数喇叭有效果,效率(转化为电能声功率)高度频率依赖性。这发生在很大程度上是很自然的结果的物理性质扬声器。我们不会担心的细节,但由于器的输入阻抗的变化相当复杂通常用这个频率。(有时还与输入电平。)图1.2展示一个典型的例子。在这种情况下,扬声器的阻抗周围有12欧姆欧姆,在150赫兹在1千赫兹。5所以在两次当前需要打在相同的产出水平比1赫兹在150赫兹。摘要功率放大器没有办法知道就好了。在推进“什么样的扬声器,你将使用,所以仅仅采用了公约的断言一个电压水平表明,所需要的信号频率的信号和供应不论目前喇叭然后要求。这种行为是相当普遍,在电子系统。这意味着,在信息术语,
36、信号的图案是由方式电压随时间的变化而变化,最好的目前需要的是那么的结论。尽管上述是基于一个大功率的例子,一个类似的情况可以出现在传感器能够产生电压响应输入刺激,但仅能提供一个很有限的电流。在这种情况下,我们需要一个电流放大或一个缓冲。这些设备都很相似,在每种情况下,我们都用某种形式的装置电路和增加信号电流的水平。然而,目前放大器总是试图通过一系列的电流。因此它是类似的行动的电压放大器总是试图乘信号电流通过一组数量。从目前的缓冲不同放大器的提供任何当前水平要求从它为了维护这个信号电压斩钉截铁地说。因此它会有更高的电流当连接到一个更严格的负荷。模拟电路电路处理信号的自由而从零到全部供电电压。这个站
37、与数字电路,它几乎完全使用“或”“信号电压限制:没有价值的零和电源电压,没有有效的状态在人之间的极限。模拟电路通常称为线性电路强调正确的信号范围内禁止连续数字电路,但这个标签不幸的是误导。仅仅因为一个电压或电流信号允许变化平稳两个极端之间零和电源限制并不意味着一切这些信号的数学关系的线性在“直线”或”“比例”的意思。许多所谓的“线性”电路是相当非线性在他们行为的必要性,通过物理或设计。这个电路利用集成电路元件。这样的部件互联网络的元件生产实际对单一晶圆的半导体材料。提供多种集成电路预制功能可在很低的成本、学生、爱好者和专业的电子线路设计吗一视同仁。大多数集成电路提供相同的功能,如“离散”半导体
38、电路较高的可靠性和成本的一小部分。通常,discrete-component电路建筑是只有当功耗青睐的水平很高的集成电路处理。也许最多才多艺的和重要的模拟集成电路为学生掌握是运算放大器、运算放大器。基本上没有什么比一个差放大具有非常高的电压增益,op-amps埋头苦干的人的模拟电路设计的世界。通过巧妙采用反馈放大器的输出,是一个或多个输入、各式各样的行为可以从这单一的设备。许多不同模型的运算放大器在低成本。一个比较电路比较两个电压信号和决定哪一个更大。这个结果表明,这种比较运算放大器的输出电压:如果不饱和聚酯树脂的产量积极的方向,反向输入(+)是一个更大的,或者更积极、电压超过了反向输入(-),所有的电压测量与地面。如果放大器的电压很近负电源电压(在这个例子中,0伏,或地电位),这意味着反向输入(-)有一个更大的电压比反向输入(+)。这种行为很容易地理解电路比对照药物是通过阅读别人的口头描述它。在这个实验中,两种电位计供应变量是比较电压放大器。输出现状的分析,指出放大器视觉上的领导。通过调整两个电位计和观察LED,就能很容易地理解的功能比较器电路。