RC phase shift Oscillator is one of the major portions which an student of electronics should focus as many reputed companies ask numerous questions from it and so here we are providing you with some very important questions and answers on it. In this section we have provided important questions on RC phase shift oscillator with their explanations and most of the questions are frequently asked during the interviews.
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Frequently Asked RC Phase Shift Oscillator Questions with Answers
Q1. What is the frequency of RC phase shift oscillator?
Ans. To find resonant frequency of an RC phase shift oscillator, use the following formula
Q2. What is a phase shift oscillator?
Ans. “Phase shift oscillator” is the term given to a particular oscillator circuit topology that uses an RC network in the feedback loop of a tube, transistor, or opamp to generate the required phase shift at a particular frequency to sustain oscillations. They are moderately stable in frequency and amplitude, and very easy to design and construct.
Q3. Why RC oscillators cannot generate high frequency oscillations?
Ans. At high frequencies, resistors look like inductors or capacitors so the equations that govern
oscillation in RC oscillators no longer apply. In other words, because of those parasitic components, it gets more and more difficult to make a stable RC oscillator as frequencies go up. At some point it becomes easier and more stable to use other types of oscillators.
Q4. What are the applications of RC phase shift oscillators?
Ans. RC phase shift oscillators are mostly used at audio frequencies. Other than this, electronic organs makes use of this oscillator such as electronic musical instruments like pianos. Also used in equipment that emits beeps. Example, many GPS units beeps when they performs an action. Also used in voice synthesis.
Q5. What phase shift does RC phase shift oscillator produce?
Ans. RC phase shift oscillator produces a phase shift of 180 degrees between output and input signal. In the phase-shift oscillator, at least three RC sections are needed to give the required 180-degree phase shift for regenerative feedback. The values of resistance and capacitance are generally chosen so that each section provides about a 60-degree phase shift.
Q6. Why we need a phase shift between input and output signal?
Ans. To obtain the regenerative feedback in the phase-shift oscillator, we need a phase shift of 180 degrees between the output and the input signal. An RC network consists of three RC sections which provides the proper feedback and phase inversion to provide this regenerative feedback. Each section shifts the feedback signal 60 degrees in phase.
Q7. How is phase angle determined in RC phase shift oscillator?
Ans. Since the impedance of an RC network is capacitive, the current flowing through it leads the applied voltage by a specific phase angle. The phase angle is determined by the amount of resistance and capacitance of the RC section. If the capacitance is a fixed value, a change in the resistance value will change the phase angle. If the resistance could be changed to zero, we could get a maximum phase angle of 90 degrees. But since a voltage cannot be developed across zero resistance, a 90-degree phase shift is not possible.
Q8. How can we get a maximum phase angle of 90 degrees in RC phase shift oscillator?
Ans. By changing the resistance to zero, we can get a maximum phase angle of 90 degrees. But since we cannot develop voltage across zero resistance, so a 90 degree phase shift is not possible.
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