函數(shù)信號(hào)發(fā)生器設(shè)計(jì)外文資料及翻譯-wenkub
2023-01-31 10:36:37 本頁(yè)面
【正文】 ed 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 the loop gain is Loop gain= An amplifier with transfer gain A and feedback network F not yet connected to 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 source 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 must 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 sinusoid. 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 important 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 of 2). Stated more simply, the frequency of a sinusoidal oscillator is determined by the condition that the loopgain 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 that
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