MODULE 3.
OSCILLATORS
1. What is an oscillator?
A. An oscillator is an electronic circuit that produces a continuous, oscillating signal, usually in the
form of a sine wave or square wave, without requiring an external input signal.
2.Describe the basic requirement for oscillation in an electronic circuit.
A.The basic requirements for oscillation are positive feedback and a total phase shift around the loop
of zero degrees or multiples of 360 degrees.
2. What is the role of the RC phase shift network in an RC phase shift oscillator?
A. The RC phase shift network provides the necessary phase shift that, when combined with the phase
shift of the amplifier, results in a total phase shift of 360 degrees around the loop for sustained
oscillations.
3 .How does a Colpitts oscillator work?
A. Colpitts oscillator uses a capacitor voltage divider as a feedback source. The capacitive divider sets
the frequency of oscillation, and the transistor or tube provides the necessary amplification.
3. Explain the principle of a Hartley oscillator.
A. A Hartley oscillator uses an LC circuit with two inductors and a capacitor. The frequency of
oscillation is determined by the inductors and the capacitor, and the inductor ratio can be varied to
change the frequency.
4. What distinguishes a crystal oscillator in terms of frequency stability?
A. A crystal oscillator uses a quartz crystal in its feedback path, which acts as a highly stable resonator
due to the piezoelectric properties of quartz, providing exceptional frequency stability.
5. Define frequency stability in oscillators.
A. Frequency stability refers to the ability of an oscillator to maintain a constant frequency over time
despite variations in temperature, voltage, or other environmental factors.
6. What is a BJT? How is it used in oscillators?
A. A Bipolar Junction Transistor (BJT) is a type of transistor that uses both electron and hole charge
carriers. In oscillators, it is often used as the active element providing the necessary amplification.
7. How does feedback influence an oscillator circuit?
A. Feedback refers to the process of routing a portion of the output signal back to the input. In
oscillators, positive feedback helps to sustain oscillations by continuously compensating for signal
losses in the circuit.
8. What is meant by the 'gain condition' for oscillations?
A. The gain condition for oscillations states that the loop gain must be equal to or greater than one to
initiate and sustain oscillations.
9. Explain the operation of an LC oscillator.
A. An LC oscillator uses an inductor (L) and a capacitor (C) to form a resonant circuit, which
determines the frequency of oscillation. The oscillator's amplifier compensates for energy lost in the
tank circuit, maintaining oscillation.
10. Describe the purpose of a feedback network in an oscillator.
A. The feedback network in an oscillator extracts a portion of the output signal and feeds it back into
the input. This network is crucial for determining the frequency and shape of the oscillation.
11. What is a generalized analysis of an oscillator?
A. A generalized analysis of an oscillator examines the conditions under which the circuit will oscillate,
the frequency of oscillation, and the stability of those oscillations under varying conditions.
12. How is the frequency of a RC phase shift oscillator determined?
A. The frequency of a RC phase shift oscillator is primarily determined by the values of the resistors
and capacitors in the phase shift network.
13. Why are FETs used in some oscillators?
A. Field-Effect Transistors (FETs) are used in oscillators for their high input impedance, which
minimizes loading on the oscillatory tank circuit, thereby stabilizing the frequency.
14. What factors affect the frequency stability of an oscillator?
A. Factors affecting frequency stability include temperature changes, power supply variations,
component aging, and mechanical stress.
