函數(shù)信號(hào)發(fā)生器設(shè)計(jì)外文資料及翻譯

1、<p>　　函數(shù)信號(hào)發(fā)生器設(shè)計(jì)外文資料及翻譯</p><p><b>　　英文資料原文</b></p><p>　　WAVE-FORM GENERATORS</p><p>　　1.The Basic Priciple of Sinusoidal Oscillators</p><p>　　Many diffe

2、rent circuit configurations deliver an essentially sinusoidal output waveform even without input-signal excitation. The basic principles governing all these oscillators are investigated. In addition to determining the co

3、nditions required for oscillation to take place, the frequency and amplitude stability are also studied.</p><p>　　Fig.1-1 show an amplifier, a feedback network, and an input mixing circuit not yet connected

4、to form a closed loop. The amplifier provides an output signal as a consequence of the signal applied directly to the amplifier input terminal. The output of the feedback network is and the output lf the mixing circui

5、t (which is now simply an inverter) is </p><p>　　Form Fig.1-1 the loop gain is</p><p>　　Loop gain=</p><p>　　Fig.1-1 An amplifier with transfer gain A and feedback network F not ye

6、t connected to form a closed loop.</p><p>　　Suppose it should happen that matters are adjusted in such a way that the signalis identically equal to the externally applied input signal. Since the amplifier ha

7、s no means of distinguishing the source of the input signal applied to it, it would appear that, if the external source were removed and if terminal 2 were connected to terminal 1, the amplifier would continue to provide

8、 the same output signal as before. Note, of course, that the statement =means that the instantaneous values of andar</p><p>　　The Barkhausen Criterion We assume in this discussion of oscillators that the

9、 entire circuit operates linearly and that the amplifier or feedback network or both contain reactive elements. Under such circumstances, the only periodic waveform which will preserve, its form is the sinusoid. For a si

10、nusoidal waveform the conditionis equivalent to the condition that the amplitude, phase, and frequency ofandbe identical. Since the phase shift introduced in a signal in being transmitted through a re</p><p>

11、;　　The frequency at which a sinusoidal oscillator will operate is the frequency for which the total shift introduced, as a signal proceed from the input terminals, through the amplifier and feedback network, and back aga

12、in to the input, is precisely zero(or, of course, an integral multiple of 2). Stated more simply, the frequency of a sinusoidal oscillator is determined by the condition that the loop-gain phase shift is zero.</p>

13、<p>　　Although other principles may be formulated which may serve equally to determine the frequency, these other principles may always be shown to be identical with that stated above. It might be noted parenthetic

14、ally that it is not inconceivable that the above condition might be satisfied for more than a single frequency. In such a contingency there is the possibility of simultaneous oscillations at several frequencies or an osc

15、illation at a single one of the allowed frequencies.</p><p>　　The condition given above determines the frequency, provided that the circuit will oscillate ta all. Another condition which must clearly be met

16、is that the magnitude of and must be identical. This condition is then embodied in the follwing principle:</p><p>　　Oscillations will not be sustained if, at the oscillator frequency, the magnitude of the pr

17、oduct of the transfer gain of the amplifier and the magnitude of the feedback factor of the feedback network (the magnitude of the loop gain) are less than unity.</p><p>　　The condition of unity loop gainis

18、called the Barkhausen criterion. This condition implies, of course, both that and that the phase of –A F is zero. The above principles are consistent with the feedback formula . For if , then, which may be interpreted to

19、 mean that there exists an output voltage even in the absence of an externally applied signal voltage.</p><p>　　Practical Considerations </p><p>　　Referring to Fig.1-2, it appears that if at

20、 the oscillator frequency is precisely unity, then, with the feedback signal connected to the input terminals, the removal of the external generator will make no difference. If is less than unity, the removal of the ext

21、ernal generator will result in a cessation of oscillations. But now suppose that is greater than unity. Then, for example, a 1-V signal appearing initially at the input terminals will, after a trip around the loop and b

22、ack to the input</p><p>　　In every practical oscillator the loop gain is slightly larger than unity, and the amplitude of the oscillations is limited by the onset lf nonlinearity. </p><p>　　Fig.

23、1-2 Root locus of the three-pole transfer function in the s-plane. The poles without feedback () are ,,and,whereas the poles after feedback is added are ,,and .</p><p>　　2. Triangle/square generation</p&g

24、t;<p>　　Fig.2.1 shows a function generator that simultaneously produces a linear triangular wave and a square wave using two op-amps. Integratoris driven from the output ofwhere is wired as a voltage comparator th

25、at’s driven from the output of via voltage divider --. The square-wave output of switches alternately between positive and negative saturation levels.</p><p>　　Suppose, initially, that the output of is posit

26、ive, and that the output of has just switched to positive saturation. The inverting input of is at virtual ground, so a current equals. Becauseandare in series, and are equal. Yet, in order to maintain a constant curren

27、t through a capacitor, the voltage across that capacitor must change linearly at a constant rate. A linear voltage ramp therefore appears across,causing the output ofto start to swing down luinearly at a rate of 1/volts

28、per second. T</p><p>　　Fig.2.1 Basic function generator for both triangular, and square waves.</p><p>　　Consequently, the output ofswings linearly to a negative value until the--junction voltage

29、 falls to zero volts (ground), at which point enters a regenerative switching phase where its output abruptly goes to the negative saturation level. That reverses the inputs of and, sooutput starts to rise linearly until

30、 it reaches a positive value that causes the --junction voltage to reach the zero-volt reference value, which initiates another switching action.</p><p>　　The peak-to-peak amplitude of the linear triangular-

31、waveform is controlled by the --ratio. The frequency can be altered by changing either the ratios of --, the values of or, or by feeding from the output of through a voltage divider rather than directly from op-ampoutput

32、.</p><p><b>　　英文資料譯文</b></p><p><b>　　波形發(fā)生器</b></p><p><b>　　譯者：張緒景</b></p><p>　　1.正弦振蕩器基本原理</p><p>　　許多不同組態(tài)的電路，即使在沒有輸入信號(hào)

33、激勵(lì)的情況下，也能輸出一個(gè)基本上是正弦形的輸出波形。我們將在下文討論所有這些振蕩器的基本原理，除了確定產(chǎn)生振蕩所需的條件之外，還研究振蕩頻率和振幅的穩(wěn)定問題。</p><p>　　圖1.1表示了放大器、反饋網(wǎng)絡(luò)和輸入混合電路尚未連成閉環(huán)的情況。當(dāng)信號(hào)直接加到放大器的書入端時(shí)，放大器提供一個(gè)輸出信號(hào)。反饋網(wǎng)絡(luò)的輸出為，混合電路（現(xiàn)在就是一個(gè)反相器）的輸出為</p><p>　　由圖1-1，環(huán)

34、路增益為</p><p><b>　　環(huán)路增益=</b></p><p>　　圖1-1 尚未連成閉環(huán)的增益為A的放大器和反饋網(wǎng)絡(luò)F</p><p>　　假定恰好將信號(hào)調(diào)整到完全等于外加的輸入信號(hào)。由于放大器無法辨別加給它的輸入信號(hào)的來源，于是就會(huì)出現(xiàn)如下情況：如果除去外加信號(hào)源，而將2端同1端接在一起，則放大器將如以前一樣，繼續(xù)提供一個(gè)同樣的

35、輸出信號(hào)。當(dāng)然要注意，=這種說法意味著和的瞬時(shí)值在所有時(shí)刻都完全相等。條件=等價(jià)于，即環(huán)路增益必須等于1。</p><p>　　巴克豪森判據(jù) 在以下關(guān)于振蕩器的討論中我們假定，整個(gè)電路工作在線形狀態(tài)，并且放大器或反饋網(wǎng)絡(luò)或它們兩者是含有電抗元件的。在這些條件下，能保持波形形狀的唯一周期性波形是正弦波。對正弦波而言，條件=等同于和的幅度、相位和頻率都完全一樣的條件。因?yàn)樾盘?hào)在通過電抗網(wǎng)絡(luò)時(shí)引入的相移總是頻率的函數(shù)

36、，所以我們有如下重要原則：</p><p>　　正弦振蕩器的工作頻率是這樣一個(gè)頻率，在該頻率下，信號(hào)從輸入端開始，經(jīng)過放大器和反饋網(wǎng)絡(luò)后，又回到輸入端時(shí)，引入的總相移正好是零（當(dāng)然，或者是2的整數(shù)倍）。更簡單地說，正弦振蕩器的頻率取決于環(huán)路增益的相移為零這一條件。</p><p>　　雖然還可以總結(jié)出其他可用來確定頻率的原則，但可以證明，它們同上述原則是一致的。附帶說明一下，滿足上述條件的

37、頻率可能不止一個(gè)，這并不是不可理解的。在這種偶然情況下，有可能在幾個(gè)頻率處同時(shí)振蕩，或在所允許的幾個(gè)頻率中某一頻率處出現(xiàn)振蕩。</p><p>　　只要電路能振蕩，其頻率就由上述原則來確定。顯然還必須滿足另一個(gè)條件，即和的幅度必須相等。該條件概括為下述原則：</p><p>　　在振蕩頻率處，如果放大器的轉(zhuǎn)移增益和反饋網(wǎng)絡(luò)的反饋系數(shù)的乘積（環(huán)路增益的幅值）小于1，則振蕩不能維持下去。<

38、;/p><p>　　環(huán)路增益為1，即這個(gè)條件叫做巴克豪森判據(jù)。當(dāng)然，這個(gè)條件意味著不僅要求，而且要求—AF的相位為零。上述原則與反饋公式是一致的。因?yàn)槿绻?，則，這可以解釋為，即使沒有外加信號(hào)電壓，也仍然有輸出電壓。</p><p>　　若干實(shí)際的考慮 參考圖1-2可以看出，如果在振蕩頻率處正好為1，那么將反饋信號(hào)接到輸入端，再除去外部信號(hào)源將不會(huì)造成任何影響。</p><

39、p>　　圖1-2 三級(jí)點(diǎn)傳遞函數(shù)在S平面上的根軌跡。無反饋時(shí)（）的極點(diǎn)是,和。而加入反饋后的極點(diǎn)是,和</p><p>　　如果小于1，那么除去外部信號(hào)源將會(huì)導(dǎo)致停振?，F(xiàn)在假定大于1，那么，最初出現(xiàn)在輸入端的信號(hào)，例如是1v，再繞路一周又回到輸入端時(shí)，其幅值將大于1v。然后這個(gè)較大的電壓又會(huì)以更大的電壓再出現(xiàn)于輸入端，如此循環(huán)往復(fù)。于是，似乎在不受放大器中有源器件的非線性的限制時(shí)，振幅的增大才能繼續(xù)下去。隨

40、著振幅的增大，有源器件的非線性變得更加明顯。這種非線性的出現(xiàn)，就限制了震蕩的幅度，這是所有實(shí)際振蕩器工作的基本特征，正如以下討論所表明的那樣：條件并不是給出的可取值范圍，而是給出一個(gè)單一的精確值。限假設(shè)即使最初能滿足這個(gè)條件，由于電路元件特性，特別是晶體管特性受老化、溫度和電壓等影響發(fā)生變化（漂移），于是很顯然，如果整個(gè)振蕩器聽其自然，則在很短的時(shí)間內(nèi)，就會(huì)變得不是小于1，就是大于1。在前一種情況下，只是振蕩停止而已，而在后一種情況下，

41、我們就有需要用非線性來限制振幅。環(huán)路增益正好為1的振蕩器，實(shí)際上是一個(gè)根本不能實(shí)現(xiàn)的理想裝置。所以，在實(shí)際振蕩器的調(diào)試中，總是要調(diào)整多少比1大一些（比方說大50%），以保證在晶體管和電路參數(shù)發(fā)生偶然變化時(shí)，不致下降到1以下。上述兩條原則是在純理論基礎(chǔ)上必須要滿足的，同時(shí)，我</p><p>　　在每個(gè)實(shí)際的振蕩器中，環(huán)路增益都略大于1，并且振蕩幅度由非線性特性來限制。</p><p>　　

42、2. 三角波/方波發(fā)生器</p><p>　　圖2-1示出了一個(gè)用兩極運(yùn)放能同時(shí)產(chǎn)生線性三角波和方波的函數(shù)發(fā)生器。集成積分器由的輸出驅(qū)動(dòng)，作為電壓比較器，被的輸出，經(jīng)--分壓器分壓后所驅(qū)動(dòng)。的方波輸出于正負(fù)飽和電平間交替交換。</p><p>　　圖2-1 具有雙向三角波和方波輸出的基本函數(shù)發(fā)生器</p><p>　　假設(shè)，開始時(shí)，的輸出為正，的輸出恰好轉(zhuǎn)為正向飽和

43、。的反向輸入端虛假接地，則電流。因?yàn)楹褪谴?lián)的，所以=。然而為維持由恒定電流經(jīng)過，加在該電容上的電壓必須以恒定的速率線性變化。一個(gè)線性的斜坡電壓加至，使的輸出開始以的速率線性下降，這個(gè)輸出通過--分壓器送至的同相輸入端。</p><p>　　然后，的輸出朝負(fù)值線性變化，直至和連接點(diǎn)的電壓下降到0V。在該點(diǎn)翻轉(zhuǎn)動(dòng)作，使輸出突變到負(fù)飽和值。這樣就改變了和的輸入，使的輸出開始線性上升，直至升到某一正值為止，該值使--間