![]() Then it causes the output to get built up. If the open loop gain is less than one i.e., Aβ 1.Suppose, we provide only the output of the feedback circuit at the input of the amplifier and remove the originally applied input signal.Īfter the removal of V i, the loop gain of the oscillator is responsible for sustained oscillations. So, we can write, the closed loop gain of the oscillator with feedback, Then, the signal at the output of the amplifier will be given as, Now, when the output of the feedback circuit is provided to the amplifier along with the input. Then both feedback signal, as well as the input signal, will be in phase with each other. If the amplifier and feedback circuit introduces 0° phase shift. So, the signal achieved at the output of the feedback amplifier is given as, This voltage is then provided to the feedback network which is basically a resonant circuit in order to have the highest feedback at a frequency. So, at the output of the amplifier we get, Initially, V i is applied at the terminal of the amplifier with gain A. Here β basically defines the fraction of output which is provided as feedback to the input. The output of the amplifier is V o and that of the feedback network is V f. This feedback network has the feedback fraction β. Suppose, V i is the input applied at the terminal of the amplifier having gain A. The figure below represents the basic oscillator feedback circuit: So, in this section, we will get to know about the operation of the oscillator by circuit analysis. In the previous section, we got the idea about the basic working of an oscillator with the help of block diagram. Now, let’s move further in order to understand the detailed operation of an oscillator. The reason for this is that feedback provides a part of the output to the oscillatory circuit in the correct phase so as to have sustained oscillations. Thus, at the output of the amplifier, amplified oscillations are achieved because of the applied dc voltage.Īs we know that we have employed a positive feedback circuit over here. Since the amplifier amplifies the applied input at its terminal. Further, the oscillations of the tank circuit are fed to the amplifier. This ac signal is then given to the tank circuit through a feedback path. The amplifier basically changes the dc voltage provided by the supply into ac power. It is noteworthy here that the oscillatory circuit employed before the amplifier circuit in the above figure can be LC tank circuit, R-C network or quartz crystal. Here the feedback network is the frequency selective circuit. The figure below represents the block diagram of an oscillator: Thereby generating waveforms such as a square wave, sawtooth wave etc.Īs we have discussed earlier that an oscillator is nothing but a combination of amplifier along with a positive feedback circuit. Non-sinusoidal or Relaxation Oscillator: In this case, the achieved signal at the output of oscillator shows a quick rise and fall at different voltage levels.Sinusoidal or Harmonic Oscillator: Here the achieved signal at the output of oscillator shows continuous sinusoidal variation as a function of time.The oscillator is mainly classified on the basis of the signal generated at its output: However, oscillator simply requires dc voltage in order to produce ac signal of desired frequency. We are already aware of the fact that an amplifier needs ac input signal that is amplified and achieved at the output of the amplifier. The frequency ranges of the ac signal at the output of oscillator ranges from a few Hz to several GHz. But more specifically, oscillators are energy converter that transforms dc energy into equivalent ac energy. At the time of defining, we say oscillators are generators. ![]()
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