专业英语演讲稿

INTRODUCTION

The operational [ˌɔp əˈrei ʃən əl] amplifier [ˈæmpləˌfa ɪə] is an extremely efficient and versatile [ˈvə:sətail ] 通用device. Its applications span the broad electronic industry filling requirements for signal conditioning, special transfer functions, analog [ˈænəˌl ɔ:g] 模拟instrumentation, analog computation, and special systems design. The analog assets [ˈæset ] of simplicity [simˈplisiti] and precision characterize circuits

[ˈsə:kit]utilizing [ˈju:tilaiz] operational amplifiers.

运算放大器是一个非常有效和通用设备。它的应用范围广泛的电子工业，信号调理，专项转移功能，模拟仪表，模拟计算，及特殊系统设计的灌装要求。简单性和精确度是使用运算放大器的模拟电路特点

The Feedback Technique

The precision and flexibility of the operational amplifier is a direct result of the use of negative feedback. Generally speaking, amplifiers employing feedback will have superior operating characteristics at a sacrifice [ˈsækrifais]of gain.

在运算放大器的精度和灵活性是利用负反馈的直接结果。一般来说，采用反馈的放大器有卓越的经营特点，在牺牲增益的代价下。

With enough feedback, the closed loop amplifier characteristics become a function of the feedback elements. In the typical feedback circuit, figure 1, the feedback elements are two resistors. The precision of the “closed loop” gain is set by the ratio [ˈrei ʃi əu] 比率of the two resistors and is practically independent of the “open loop” amplifier. Thus, amplification to almost any degree of precision can be achieved with ease.

有了足够的反馈，闭环放大器的特点成为一个功能的反馈元件。在典型的反馈电路中，图1中，反馈元件是两个电阻器。的精度的“闭环”的增益设置的两个电阻的比率实际上是独立的“开环”放大器。因此，放大到几乎任何的精确度，可以容易地实现。

Notation 符号

= Symbol (a) is a buffer [ˈb ʌf ə] 缓冲器 op 工作 amp 放大器

= Symbol (b) is a differential input, single ended output op amp. This symbol represents the most common types of op amps, including voltage feedback, and current feedback. It is often times pictured with the non-inverting input at the top and the inverting input at the bottom.

= Symbol (c) is a differential input, differential output op amp. The outputs can be thought of as “inverting” [inˈvə:t] 反转and “non-inverting”, and are shown across from

the opposite [ˈɔp əzit]相反 polarity [pəʊˈlærɪti] 极性 input for easy completion

[kəmˈpli:ʃən] 完成of feedback loops on schematics [ski:ˈmætɪk].

符号（a ）是一个缓冲器的运算放大器

•=符号（b ）是一个差分输入，单端输出的运算放大器。这个符号代表最常见的类型，包括电压反馈和电流反馈运算放大器。它通常是在顶部和在底部的倒相输入端与非反相输入描绘的时间。

•=符号（C ）是差分输入，差分输出运算放大器。输出可以被认为是“反转”和“非反相”，并示出从相反的极性的输入对面容易完成的反馈回路原理图

Power Connections电源连接

Power is supplied to each of these units at connections as shown in figure 4. Such a connection is implied in all operational amplifier circuits. The dual [ˈdju:əl]两部分

supply presents the same absolute value of voltage to ground from either side, while the center connection ultimately ['ʌltim ətli ]最宗defines the common line and ground potential. The exceptions to this are AC amplifier circuits that may use a single power supply. This is accomplished by creating a floating [ˈfləʊt ɪŋ] AC ground with DC blocking capacitors. In such circuits, a source of “half-supply” creates a “virtual ground” exactly half way between the positive supply and ground potentials.

电源供给到这些单元中的每一个，如在图4中所示的连接。这样的连接是隐含在所有的运算放大器电路。双电源呈现相同的绝对电压值从任一侧接地，而中心连接最终定义的公共线和接地电位。例外情况是可以使用单个电源的AC 放大器电路。这是通过创建一个浮动的AC 地面的隔直流电容器。在这种电路中，“半电源”的来源创建一个“虚拟地”正好有一半之间的正电源和接地电位的方法。

Electrical Circuit Models电气电路模型

The simplified models of the differential [ˌdɪf əˈren ʃəl] 差分input operational amplifiers are shown in figures 6 and 7.

在图6和图7中示出的差分输入运算放大器的简化模型。

As indicated in figure 6, the operational amplifier can be represented by an ideal voltage source whose value depends on the input voltage appearing across the inverting and non-inverting inputs plus the effects of finite [ˈfainait] 有限input and output impedances [imˈpi:dəns]阻抗. The value, A, is known as the open loop (without feedback) gain of the operational amplifier.

正如在图6中所示，运算放大器可以表示为一个理想电压源，其值取决于对输入电压的两端出现的反相和非反相输入端加上有限的输入和输出阻抗的影响。值，A ，是被称为在运算放大器的开环增益（没有反馈）。

The simplified model of the differential output operational amplifier (figure 7) is an accurate [ˈækjurit] approximation [əˌpr ɔks əˈme ɪʃən] 近似值only under special conditions of feedback (see “Balanced Amplifier” later in this handbook). Figure 6 represents the model of the differential output type when it is used as a single ended output device; the inverting output simply being ignored.

简化模型的差分输出运算放大器（图7）是一个准确近似，仅在特殊条件下的反馈（见“平衡放大器”，在本手册后面）。图6表示的差分输出的模型类型时，它被用作一个单端输出的移动设备简单地被忽略的反相输出。

The Ideal Operational Amplifier理想运算放大器

In order to introduce operational amplifier circuitry, we will use an ideal model of the operational amplifier to simplify the mathematics [ˌmæθiˈmætiks] involved in deriving gain expressions, etc., for the circuits presented. With this understanding as a basis, it will be convenient to describe the properties of the real devices themselves in later sections, and finally to investigate circuits utilizing practical operational amplifiers. 为了介绍运算放大器电路中，我们将使用一个理想的模型简化中获得的电路增益表达式等，所涉及的数学运算放大器的。有了这样的认识，以此为基础，可以方便的真实设备本身在后面的章节中描述的属性，最后调查利用实际的运算放大器电路。

To begin the presentation of operational amplifier circuitry [ˈsə:kitri], then, it is necessary first of all to define the properties of a mythical “perfect” operational amplifier. The model of an ideal operational amplifier is shown in figure 9.

首先介绍运算放大器电路，那么，它是必要的，首先要定义一个神话般的“完美”的运算放大器的性能。理想的运算放大器的模型是在图9中所示。

Defining the Ideal Operational Amplifier

= Gain: The primary function of an amplifier is to amplify, so the more gain the better. It can always be reduced with external circuitry, so we assume gain to be infinite

[ˈinfinit]无限.

增益：放大器的主要功能是放大的，所以更多的获得更好。它总是可以减少与外部电路，所以我们假设增益是无限

= Input Impedance: Input impedance is assumed to be infinite. This is so the driving source won’t be affected by power being drawn by the ideal operational amplifier. 输入阻抗：输入阻抗被认为是无限的。这是这样的驱动源将不会受到影响被绘制了理想的运算放大器的功率。

= Output Impedance: The output impedance of the ideal operational amplifier is assumed to be zero. It then can supply as much current as necessary to the load being driven.

输出阻抗：理想的运算放大器的输出阻抗被假定为零。然后，它可以提供尽可能多的电流所必需的被驱动的负载。

= Response Time: The output must occur at the same time as the inverting input so the response time is assumed to be zero. Phase shift will be 180︒. Frequency response will be flat and bandwidth infinite because AC will be simply a rapidly varying DC level to the ideal amplifier.

响应时间：输出必须在相同的时间发生的反相输入端，这样的响应时间被假定为零。相移为180 。频率响应是平的，无限的，因为交流会只是一个快速变化的DC 电平的理想放大器的带宽。

= Offset: The amplifier output will be zero when a zero signal appears between the inverting and non-inverting inputs.

偏移量：当一个零信号之间出现的反相和非反相输入端，放大器的输出将为零。

CIRCUITS AND ANALYSES USING THE IDEAL OPERATIONAL AMPLIFIER 用理想运算放大器的电路及分析

The Desirability of Feedback是可取的反馈

Consider the open loop amplifier used in the circuit of figure 10. Note that no current flows from the source into the inverting input - the summing point restraint derived in the previous section - hence, there is no voltage drop across RS and ES appears across the amplifier input. When ES is zero, the output is zero. If ES takes on any non-zero value, the output voltage increases to saturation [ˌsætʃəˈre ɪʃən] 饱和, and the amplifier acts as a switch.

考虑图10的电路中使用的开环放大器。请注意，从源代码编译成的反相输入端 - 来自上一节中的求和点约束 - 因此没有电流流过，有没有RS 两端的电压降和ES 出现整个放大器的输入。当ES 是零，其输出为零。如果ES 承担任何非零的值，输出电压增大到饱和，该放大器作为一个开关。

The open loop amplifier is not practical - once an op amp is pushed to saturation, its behavior is unpredictable. Recovery time from saturation is not specified for op amps (except voltage limiting types). It may not recover at all; the output may latch up. The output structure of some op amps, particularly rail-to-rail models, may draw a lot of current as the output stage attempts to drive to one or the other rail. For more details on op amps in open loop operation, consult reference 1.

开环放大器是不实际的 - 一旦一个运算放大器推到饱和，它的行为是不可预测的。未指定恢复时间从饱和运算放大器的（除了电压限制类型）。它可能无法收回; 输出锁存。作为输出级试图把车开到一个或其他铁路的一些运算放大器，尤其是轨到轨车型，可能会吸引大量的电流输出结构。对于运算放大器开环运行的详细信息，请参阅参考文献1。

Two Important Feedback Circuits

Figure 11 shows the connections and the gain equations for two basic feedback circuits. The application of negative feedback around the ideal operational amplifier results in another important summing point restraint: The voltage appearing between the inverting and non-inverting inputs approaches zero when the feedback loop is closed.

图11示出了两种基本的反馈电路的连接和信号的增益公式。周围的负反馈中的应用的理想的运算放大器的查询结果，在另一个重要的求和点克制：当反馈回路被关闭时的反相和非反相输入端之间出现的电压接近零。

Consider either of the two circuits shown in figure 11. If a small voltage, measured at the inverting input with respect to the non-inverting input, is assumed to exist, the amplifier output voltage will be of opposite polarity and can always increase in value (with infinite output available) until the voltage between the inputs becomes infinitesimally [ˌɪnf ɪn ɪˈtes ɪm əli] 无限small. When the amplifier output is fed back to the inverting input, the output voltage will always take on the value required to drive the signal between the inputs toward zero.

无论是在图11所示的两个电路考虑。如果一个小的电压，测量在相对于非反相输入端的反相输入端，被假定为存在，将放大器的输出电压的极性相反的，总是可以增加之间的电压值（可用具有无限大的输出），直到输入变得无穷小。当放大器的输出被反馈到反相输入端，其输出电压将总是采取所需的值来驱动的输入端之间的信号趋向于零。

Voltage Follower

The circuit in figure 12 demonstrates how the addition of a simple feedback loop to the open loop amplifier converts it from a device of no usefulness to one with many practical applications.

Analyzing this circuit, we see that the voltage at the non-inverting input is EI , the voltage at the inverting input approaches the voltage at the non-inverting input, and the output is at the same voltage as the inverting input. Hence, EO = EI , and our

analysis is complete. The simplicity of our analysis is evidence of the power and utility of the summing point restraints we derived and have at our disposal.

Our result also may be verified by mathematical analysis very simply. Since no

current flows at the non-inverting input, the input impedance of the voltage follower is infinite. The output impedance is just that of the ideal operational amplifier itself, i.e. zero. Note also that no current flows through the feedback loop, so any arbitrary (but finite) resistance may be placed in the feedback loop without changing the properties of the ideal circuit, shown in figure 13. No voltage would appear across the feedback

element and the same mathematical analysis would hold.

The feedback resistor is of particular importance if the op amp selected is a current-feedback type. The stability of current-feedback op amps is dependent

entirely on the value of feedback resistor selected, and the designer should use the value recommended on the data sheet for the device.

Unity gain circuits are used as electrical buffers to isolate circuits or devices from one another and prevent undesired interaction. As a voltage following power amplifier, this circuit will allow a source with low current capabilities to drive a heavy load.

The gain of the voltage follower with the feedback loop closed (closed loop gain) is unity. The gain of the ideal operational amplifier without a feedback loop (open loop gain) is infinity. Thus, we have traded gain for control by adding feedback. Such a severe sacrifice of gain – from infinity to unity - is not necessary in most circuits. The rest of the ideal circuits to be studied will give any (finite) closed loop gain desired while maintaining control through feedback.

Non-Inverting Amplifier

The circuit in figure 14 was chosen for analysis next because of its relation to the

voltage follower. It is re-drawn as in figure 15, which makes it evident that the voltage

follower is simply a special case of the non-inverting amplifier

Since no current flows into the inverting input, RO and RI form a simple voltage divider (figure16).

The same voltage must appear at the inverting and non-inverting inputs, so that:

From the voltage division formula

The input impedance of the non-inverting amplifier circuit is infinite since no current flows into the inverting input. Output impedance is zero since output voltage is ideally independent of output current. Closed loop gain is 1+R0/R1 hence can be any desired value above unity. Such circuits are widely used in control and instrumentation where non-inverting gain is required

INVERTING AMPLIFIER

The inverting amplifier appears in figure 17. This circuit and its many variations form the bulk of commonly used operational amplifier circuitry. Single ended input and output versions were first used, and they became the basis of analog computation. Today’s modern differential input amplifier is used as an inverting amplifier by

grounding the non-inverting input and applying the input signal to the inverting input terminal.

Since the amplifier draws no input current and the input voltage approaches zero

when the feedback loop is closed (the two summing point restraints), we may write:

Hence:

Input impedance to this circuit is not infinite as in the two previous circuits, the inverting input is at ground potential so the driving source effectively “sees” RI as the input impedance. Output impedance is zero as in the two previous circuits. Closed

loop gain of this circuit is

Integrator

If a capacitor is used as the feedback element in the inverting amplifier, shown in figure 21, the result is an integrator. An intuitive grasp of the integrator action may be obtained from the statement under the section, “Current Output,” that current through the feedback loop charges the capacitor and is stored there as a voltage from the output to ground. This is a voltage input current integrator.

Differentiator

Using a capacitor as the input element to the inverting amplifier, figure 22, yields a differentiator circuit. Consideration of the device in figure 23 will give a feeling for the

differentiator circuit.

Since the inverting input is at ground potential:

It should be mentioned that of all the circuits presented in this section, the

differentiator is the one that will operate least successfully with real components. The capacitive input makes it particularly susceptible to random noise and special techniques will be discussed later for remedying this effect.