Oscillators Questions and Answers for Viva

Answer-1: Oscillators produce a waveform (mostly sine or square waves) of desired amplitude and frequency. They can take input from the output itself. For a complete oscillator circuit we require a feedback device, amplifier and feedback factor. Oscillators designed to produce a high-power AC output from a DC supply are usually called inverters.

Answer-2: An electronic oscillator is an electronic circuit that produces a repetitive electronic signal, often a sine wave or a square wave. They are widely used in innumerable electronic devices. Common examples of signals generated by oscillators include signals broadcast by radio and television transmitters, clock signals that regulate computers and quartz clocks, and the sounds produced by electronic beepers and video games.

Answer-3: There are two main types of electronic oscillator: the harmonic oscillator and the relaxation oscillator.

Answer-4: The harmonic, or linear, oscillator produces a sinusoidal output. The basic form of a harmonic oscillator is an electronic amplifier with the output attached to an electronic filter, and the output of the filter attached to the input of the amplifier, in a feedback loop. When the power supply to the amplifier is first switched on, the amplifier's output consists only of noise. The noise travels around the loop, being filtered and re-amplified until it increasingly resembles the desired signal.

Answer-5: There are many ways to implement harmonic oscillators, because there are different ways to amplify and filter. Some of the different circuits are:
Hartley oscillator
Colpitts oscillator
Cross-coupled LC oscillator
crystal oscillator
Phase-shift oscillator
RC oscillator (Wie.n Bridge and "Twin-T")

Answer-6: Inductve oscillators also known as LC oscillators are built of an tank circuit, which oscillates by charging and discharging a capacitor through an inductor. These oscillators are typically used when a tunable precision frequency source is necessary, such as with radio transmitters and receivers.

Answer-7: A phase-shift oscillator is a simple electronic oscillator. It contains an inverting amplifier, and a feedback filter which 'shifts' the phase of the amplifier output by 180 degrees at the oscillation frequency.The filter produces a phase shift that increases with frequency. It must have a maximum phase shift of considerably greater than 180? at high frequencies, so that the phase shift at the desired oscillation frequency is 180?.

Answer-8: The most common way of achieving this kind of filter is using three identical cascaded resistor-capacitor filters, which together produce a phase shift of zero at low frequencies, and 270 degrees at high frequencies. At the oscillation frequency each filter produces a phase shift of 60 degrees and the whole filter circuit produces a phase shift of 180 degrees.

Answer-9: The mathematics for calculating the oscillation frequency and oscillation criterion for this circuit is surprisingly complex, due to each R-C stage loading the previous ones. The calculations are greatly simplified by setting all the resistors (except the negative feedback resistor) and all the capacitors to the same values, if R1 = R2 = R3 = R, and C1 = C2 = C3 = C, then: f_oscillation = 1/2 pi R C sqrt(6).
And the oscillation criterion is: R_feedback= 29(R)

Answer-10: A version of this circuit can be made by putting an op-amp buffer between each R-C stage which simplifies the calculations. ?he voltage gain of the inverting channel is always unity.