1、Chapter 2 Electronics,Section 4 Operational Amplifiers,Text,New Words and Expressions,Exercises,End,Translation of Long Sentences,Section 4 Operational Amplifiers,Introduction Operational amplifiers are high-gain difference amplifiers, which were perfected during World War II. They became the founda

2、tion of analog computers, at one time analog computers were called differential analyzers because they are used to solve differential equations.,運算放大器是一種高增益的差分放大器, 它在第二次世界大戰(zhàn)期間得到完善,并成為 模擬計算機的基礎. 由于運算放大器被用來 解差分方程,因此一段時期內(nèi)模擬計算機被 稱為差分分析器.,運算放大器也是很多 重要儀器的主要組成部分.,Operational amplifiers are also the basis o

3、f many important instruments.,Section 4 Operational Amplifiers,The analog amplifier consists of a basic difference amplifier, implemented by feedback and other compensating amplifying circuits to give linear response, stability, freedom from drift, and other desirable properties.,Thus it is more dif

4、ficult to isolate the long-term changes that arise from variations in temperature and power-supply voltage and from other effects that cause the output voltage to drift.,模擬放大器由基本的差分放大器組成, 通過反饋以及其它補償放大電路實現(xiàn)線性反應 ,穩(wěn)定性,來自漂移的自由度以及其它 我們所期望的性能.,我們要求它具有復雜性, 因為運算放大器放大直流以及交流信號,在 放大階段不允許有容性耦合.,The complexity is

5、 required because operational amplifiers amplify dc as well as ac signals, capacitive coupling between amplifying stages is not permitted.,因此我們很難 隔離由溫度的變化和電源電壓以及其它引起 輸出電壓漂移的因素而產(chǎn)生的長效變化.,Section 4 Operational Amplifiers,After the invention of the transistor, solid-state operational amplifiers were int

6、roduced as integrated circuits.,Now operational amplifiers are used to make high-quality, low-power analog amplifier, and it is possible to avoid designing individual transistor amplifier stages for many application.,For most amplifying purposes and for many measuring and control applications, simpl

7、e arrangements of operational amplifiers with feedback circuits will meet the designers needs.,在發(fā)明了晶體管后,固態(tài)運算放大器被 引入成為集成電路.,現(xiàn)在運算放大器被用來 制造高品質(zhì),低功率的模擬放大器,因而我 們可以在很多應用場合免去了設計單個的晶 體管放大器的過程.,對于大多數(shù)要求放大和 很多測量和控制應用的場合,具有反饋電路 的簡單的運算放大器將滿足設計者的需要.,Section 4 Operational Amplifiers,packages (DIPs) or in other comp

8、act forms makes the solution of analog signal problems analogous in many respects to the solution of digital logic problems, that is, through the interconnection of integrated circuits.,The availability of operational amplifiers as integrated circuits in the form of dual in-line,Operational Amplifie

9、r Fig.2-5 shows the symbol for an operational amplifier. There are two inputs: the one marked with a plus sign is the noninverting input, and the one marked with a minus sign is the inverting input.,以雙列直插式封裝或以其它密封形式出現(xiàn)的 運算放大器做成的集成電路的可用性使模擬 信號問題在很多方面類似數(shù)字邏輯問題那樣 得到解決,也就是通過集成電路的相互連接 得到解決.,運算放大器,圖2-5顯示了運算

10、放大器的符號.它有 兩個輸入端:標有正號的為非倒向輸入端, 而標有負號的為倒向輸入端,由運算放大器 放大的電壓是兩個輸入端之間的電壓,The voltage amplified by the operational amplifier is the voltage difference between the two inputs.,Section 4 Operational Amplifiers,The open-circuit gain is so large, l05 to l06, that a voltage difference of only a few microvolts w

11、ill give an appreciable output. Because the operational amplifier is a difference amplifier, connections must always be made to both input terminals for proper operation.,Fig.2-5 A symbol for an operational amplifier,由于 開始增益是如此大,從l05到l06,所以僅僅 是幾微伏的電壓差將產(chǎn)生相當大的輸出電壓. 由于運算放大器是一種差分放大器,因此, 在兩個輸入端必須都連接電壓才能使

12、之正常 工作.,Section 4 Operational Amplifiers,If two different positive voltages are applied separately to the two inputs, the output of the operational amplifier will be at the maximum (saturated) value if the voltage at the noninverting input is larger than the voltage at the inverting input.,If the vo

13、ltages exchange their relative valuesthat is, if the inverting input exceeds the noninverting inputthe operational amplifier will switch to a minimum output, which is the saturated negative voltage.,如果兩個不同的正電壓分別被加在兩 個輸入端,而且非倒向輸入端的電壓大于倒 向輸入端的電壓,那么運算放大器的輸出端 電壓將處于最大值(飽和值),The switching occurs very quic

14、kly whenever the relative values of the voltages change.,如果電壓 進行相互交換其相對值也就是,如果倒 向輸入端的電壓大于非倒向輸入端的電壓 運算放大器將產(chǎn)生一個最小的輸出,即為 飽和負電壓.,每當相對電壓值改變時這種轉(zhuǎn) 換就會很快地發(fā)生.,Section 4 Operational Amplifiers,We will see that an operational amplifier is an excellent voltage comparator because it produces a large voltage swing

15、 at the instant of crossing, when an earlier relation in voltage magnitudes is reversed by only a few microvolts.,If the operational amplifier is to operate in its linear range, a very small voltage difference must exist between the inverting and the noninverting inputs.,我們將看到運算器是非 常好的電壓比較器,因為它在瞬間電壓

16、變換 時產(chǎn)生很大的電壓起伏.此時僅僅幾微伏的 電壓將使先前的電壓大小關系產(chǎn)生逆轉(zhuǎn).,如果運算放大器工作在其線性范圍內(nèi),在 其倒向輸入端和非倒向輸入端之間必須存在非 常小的電壓差.,In analyzing operational amplifying circuits, we assume, because of the large open-circuit gain, that the voltage difference across the inputs is negligible.,在分析運算放大電路時,我們 假設由于存在很大的開路電壓增益,所以輸入 端兩端的電壓差可以忽略不計.,Se

17、ction 4 Operational Amplifiers,In some cases we will set the voltage to zero. When a portion of the output signal is returned to the input as negative feedback, the voltage difference cannot grow large because the output changes to minimize the voltage difference between the inputs.,Two additional p

18、roperties are present in operational amplifiers. They are a very high input impedance, approximately l06, and a low output impedance, approximately l00.,在某些場合我 們將把電壓設為零.當輸出信號的一部分返回 輸入端作為負反饋,電壓差就無法增大因為輸 出改變使輸入端的電壓差減小.,另外兩個性質(zhì)也存在于運算放大器,它們 是非常高的輸入阻抗,大約l06,以及很小的 輸出阻抗,大約l00.,Section 4 Operational Amplifie

19、rs,These properties contribute to the usefulness of operational amplifiers by allowing signal sources with small current capabilities to drive operational amplifiers directly. In turn, operational amplifiers may drive devices that have severe signal requirements.,To summarize, a good operational amp

20、lifier is characterized by a very large open-circuit gain of a million or so, an extremely small difference voltage between the inverting and the noninverting input terminals, a very high input impedance, and a small output impedance. An ideal operational amplifier, however, would have an infinite g

21、ain,這些性質(zhì)使運算放大 器變得有用因為它可以允許信號源用非常小的 電流來驅(qū)動放大器,反過來,運算放大器可以 驅(qū)動具有很高信號要求的器件.,概括起來,一個好的運算放大器具有以下 特性: 非常大的大約一百萬的開路增益,倒向輸入 端和非倒向輸入端之間相當小的電壓差;很高 的輸入阻抗以及很小的輸出阻抗.而一個理想 的運算放大器將會有一個無窮大的增益.,Section 4 Operational Amplifiers,a zero difference voltage between inputs, an infinite input impedance, and a zero output imp

22、edance.,Many operational amplifiers require two equal but opposite supply voltages, one positive and one negative. Typical values are l2V or 15V.,輸入端之間的一個零電位差,一個無窮大的輸 入阻抗以及一個零輸出阻抗.,With a two-sided power supply of l5 V, the output signal is restricted to about l2V.,Other operational amplifiers may b

23、e operated with a single-ended power source, such as +15V. The useful range of the output voltage in an operational amplifier is approximately 80 percent of the supply voltages.,很多運算放大器要求兩個數(shù)值相等但符號相 反的供電電壓,一個為正而另一為負,典型的 值是12V或15V.,其它運算放大器可能工 作在單端輸入電源,比如說15V.運算放大 器的有用的輸出電壓范圍等于大約80%的供電 電壓,對于具有雙邊電源電壓15V

24、的運算放 大器,輸出信號被限制在大約12V.,Section 4 Operational Amplifiers,Many operational amplifiers have limitations, two of which need to be mentioned.,One is that the gain decreases rapidly as the frequency increases. At small frequenciesas low as l0 Hzthe voltage gain begins to drop. (Power begins to drop at -20

25、 dB per decade.),The gain-versus-frequency limitation is offset by the use of negative feedback to expand the frequency band. The other limitation is the rate at which most operational amplifiers can respond to a step change in the input signal. Compared to digital gates, operational amplifiers are

26、poor in this respect; common operational amplifiers change at a rate of approximately l V/s .,很多運算放大器都有其局限性,其中有 兩點需要在這里提到,一個局限性是隨著頻 率的增加其增益下降得很快.在低頻階段 如象10Hz那么低電路增益就開始下降 (功率在-20分貝處開始以每10分貝的速度 減小).,增益-相對-頻率的局限性通過負 反饋的補償作用而使頻帶得以增寬.另外一 個局限是大多數(shù)運算放大器對輸入信號的改 變所能起反應的速率.與邏輯門相比較,運 算放大器在這個方面的性能不算好,普通運 算放大器在大約1v/us的速率時可以改變狀 態(tài).,Section 4 Operational Amplifiers,A TTL digital gate changes from one state to the other nearly 500 times faster.,Return,The impor