【文章內(nèi)容簡介】 utput required .These performance considerations, bined with economic factors, will dictate the form of oscillator to be used in a given application.振蕩器是通信系統(tǒng)中一種最基本的構(gòu)件。振蕩器是能把直流能量轉(zhuǎn)換成交流的一種電路。也就是說，振蕩器能產(chǎn)生波形。波形可以是任何形狀，但總有某一重復(fù)頻率。有各種不同的正弦波振蕩器用于各種電子電路。振蕩器類型的選擇基于如下的考慮：?所需的輸出頻率。?所需的頻率穩(wěn)定性?頻率是可變的嗎？如果是，其變化范圍是什么？ ④允許的波形失真。⑤所需的輸出功率。通過對這些性能的考慮，再加上經(jīng)濟方面的因素，就可確定在一給定應(yīng)用中所用的振蕩器類型。 The effect of charging the capacitor in Figure 44(a) to some voltage potential and then closing the switch results in the waveform shown in Figure 44(b) .The switch closure starts a current flow as the capacitor begins to discharge through the inductor. The inductor, which resists a charge in current flow, causes a gradual sinusoidal current buildup that reaches maximum when the capacitor is fully discharged. At this point the potential energy is zero, but since current flow is maximum, the magnetic field energy around the inductor is maximum. The magnetic field no longer maintained by capacitor voltage then starts collapse, and its counter EMF will keep current flowing in the same direction, thus charging the capacitor to opposite polarity of its original charge .This repetitive exchange of energy is known as the flywheel effect .圖44（a）中的電容器先充電到某個點位，然后閉合開關(guān)就會產(chǎn)生圖44（b）所示的波形。開關(guān)閉合所引起的電流，使電容器開始通過電感放電。電感會阻止電荷的流通，從而形成一個以正弦規(guī)律漸變的電流。當(dāng)電容器完全放電時，該電流達到最大值。此時，電位能量等于零。但因電流最大，故電感周圍的磁場能量達到最大。該磁場能量因失去電容器電壓的維持而開始減小，但其反電動勢將保持電流按相同的方向流動。因此電容器又開始充電，但極性與原來的充電相反。這種反復(fù)的能量交換就是所謂的飛輪效應(yīng)。 A typical waveform generator consists of four basic sections: