函数信号发生器设计外文资料及翻译

1、函数信号发生器设计外文资料及翻译 英文资料原文wave-form generators1.the basic priciple of sinusoidal oscillators many different circuit configurations deliver an essentially sinusoidal output waveform even without input-signal excitation. the basic principles governing all these oscillators are investigated. in addition t

2、o determining the conditions required for oscillation to take place, the frequency and amplitude stability are also studied. fig.1-1 show an amplifier, a feedback network, and an input mixing circuit not yet connected to form a closed loop. the amplifier provides an output signal as a consequence of

3、 the signal applied directly to the amplifier input terminal. the output of the feedback network is and the output lf the mixing circuit (which is now simply an inverter) is form fig.1-1 the loop gain is loop gain=fig.1-1 an amplifier with transfer gain a and feedback network f not yet connected to

4、form a closed loop.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 has no means of distinguishing the source of the input signal applied to it, it would appear that, if the external sourc

5、e were removed and if terminal 2 were connected to terminal 1, the amplifier would continue to provide the same output signal as before. note, of course, that the statement =means that the instantaneous values of andare exactly equal at all times. the condition=is equivalent to, or the loop gain mus

6、t equal unity. the barkhausen criterion we assume in this discussion of oscillators that the 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 sinuso

7、id. for a sinusoidal 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 reactive network is invariably a function of the frequency, we have the following importan

8、t principle: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 again to the input, is precisely zero(or, of course, an integral multiple

9、of 2). stated more simply, the frequency of a sinusoidal oscillator is determined by the condition that the loop-gain phase shift is zero.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 th

10、at stated above. it might be noted parenthetically 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 oscillation at a single one of the al

11、lowed frequencies.the condition given above determines the frequency, provided that the circuit will oscillate ta all. another condition which must clearly be met is that the magnitude of and must be identical. this condition is then embodied in the follwing principle:oscillations will not be sustai

12、ned if, at the oscillator frequency, the magnitude of the product 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.the condition of unity loop gainis called the barkhausen criterion. this condi

13、tion 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 mean that there exists an output voltage even in the absence of an externally applied signal voltage.practical consideratio

14、ns referring to fig.1-2, it appears that if at 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 external generator will result in a ce

15、ssation 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 back to the input terminals, appear there with an amplitude larger than 1v. this larger voltage will then reappear as

16、 a still larger voltage, and so on. it seems, then, that if is larger than unity, the amplitude of the oscillations will continue to increase without limit. but of course, such an increase in the amplitude can continue only as long as it is not limited by the onset of nonlinearity of operation in th

17、e active devices associated with the amplifier. such a nonlinearity becomes more marked as the amplitude of oscillation increases. this onset of nonlinearity to limit the amplitude of oscillation is an essential feature of the operation of all practical oscillators, as the following considerations w

18、ill show: the condition does not give a range of acceptable values of , but rather a single and precise value. now suppose that initially it were even possible to satisfy this condition. then, because circuit components and, more importantly, transistors change characteristics (drift) with ahe, temp

19、erature, voltage, etc., it is clear that if the entire oscillator is left to itself, in a very short time will become either less or larger than unity. in the former case the oscillation simply stops, and in the latter case we are back to the point of requiring nonlinearity to limit the amplitude. a

20、n oscillator in which the loop gain is exactly unity is an abstraction completely unrealizable in practice. it is accordingly necessary, in the adjustment of a practical oscillator, always to arrange to have somewhat larger (say 5 percent) than unity in order to ensure that, with incidental variatio

21、ns in transistor and circuit parameters, shall not fall below unity. while the first two principles stated above must be satisfied on purely theoretical grounds, we may add a third general principle dictated by practical considerations, i.e.:in every practical oscillator the loop gain is slightly la

22、rger than unity, and the amplitude of the oscillations is limited by the onset lf nonlinearity. fig.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 .2. triangle/square generationfig.2.1 shows

23、 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 thats driven from the output of via voltage divider -. the square-wave output of switches alternately between

24、positive and negative saturation levels.suppose, initially, that the output of is positive, 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

25、current 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 per second. that output is fed via the-divider to the non-in-verting input

26、 of.fig.2.1 basic function generator for both triangular, and square waves.consequently, the output ofswings linearly to a negative value until the-junction voltage falls to zero volts (ground), at which point enters a regenerative switching phase where its output abruptly goes to the negative satur

27、ation level. that reverses the inputs of and, sooutput starts to rise linearly until it reaches a positive value that causes the -junction voltage to reach the zero-volt reference value, which initiates another switching action.the peak-to-peak amplitude of the linear triangular-waveform is controll

28、ed 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.英文资料译文 波形发生器 译者：张绪景1.正弦振荡器基本原理许多不同组态的电路，即使在没有输入信号激励的情况下，也能输出一个基本上是正弦形的输出波形。我们将在下文讨论所有这些振荡器的基本原理，除了确定产

29、生振荡所需的条件之外，还研究振荡频率和振幅的稳定问题。图1.1表示了放大器、反馈网络和输入混合电路尚未连成闭环的情况。当信号直接加到放大器的书入端时，放大器提供一个输出信号。反馈网络的输出为，混合电路（现在就是一个反相器）的输出为由图1-1，环路增益为环路增益=图1-1 尚未连成闭环的增益为a的放大器和反馈网络f假定恰好将信号调整到完全等于外加的输入信号。由于放大器无法辨别加給它的输入信号的来源，于是就会出现如下情况：如果除去外加信号源，而将2端同1端接在一起，则放大器将如以前一样，继续提供一个同样的输出信号。当然要注意，=这种说法意味着和的瞬时值在所有时刻都完全相等。条件=等价于，即环路增益

30、必须等于1。巴克豪森判据 在以下关于振荡器的讨论中我们假定，整个电路工作在线形状态，并且放大器或反馈网络或它们两者是含有电抗元件的。在这些条件下，能保持波形形状的唯一周期性波形是正弦波。对正弦波而言，条件=等同于和的幅度、相位和频率都完全一样的条件。因为信号在通过电抗网络时引入的相移总是频率的函数，所以我们有如下重要原则：正弦振荡器的工作频率是这样一个频率，在该频率下，信号从输入端开始，经过放大器和反馈网络后，又回到输入端时，引入的总相移正好是零（当然，或者是2的整数倍）。更简单地说，正弦振荡器的频率取决于环路增益的相移为零这一条件。虽然还可以总结出其他可用来确定频率的原则，但可以证明，它们同

31、上述原则是一致的。附带说明一下，满足上述条件的频率可能不止一个，这并不是不可理解的。在这种偶然情况下，有可能在几个频率处同时振荡，或在所允许的几个频率中某一频率处出现振荡。只要电路能振荡，其频率就由上述原则来确定。显然还必须满足另一个条件，即和的幅度必须相等。该条件概括为下述原则：在振荡频率处，如果放大器的转移增益和反馈网络的反馈系数的乘积（环路增益的幅值）小于1，则振荡不能维持下去。环路增益为1，即这个条件叫做巴克豪森判据。当然，这个条件意味着不仅要求，而且要求af的相位为零。上述原则与反馈公式是一致的。因为如果，则，这可以解释为，即使没有外加信号电压，也仍然有输出电压。若干实际的考虑 参考图1-2可以看出，如果在振荡频率处正好为1，那么将反馈信号接到输入端，再除去外部信号源将不会造成任何影