Q.What is an oscillator?

An oscillator is an electronic circuit that converts steady DC energy from a supply into a continuous, repetitive AC output of a desired frequency, without any external AC input signal driving it. This is what separates it from an amplifier, which needs an input to produce an output. The frequencies an oscillator can generate range from a few hertz to several gigahertz, which is why oscillators sit at the core of radios, TV transmitters and receivers, radar sets, watches, clocks and computer clocks.

Oscillators are classified in two useful ways. By output waveform they are either sinusoidal (harmonic) oscillators, which produce a smooth sine wave of a single frequency, or non-sinusoidal (relaxation) oscillators, which produce square, rectangular, triangular or saw-tooth waves. By the feedback components that fix the frequency, sinusoidal oscillators are further divided into LC oscillators (Hartley, Colpitts), RC oscillators (phase-shift, Wien bridge) and crystal oscillators.

Each family has its niche. LC oscillators suit high (radio) frequencies; RC oscillators suit low (audio) frequencies because they need no bulky inductors and are compact and cheaper; crystal oscillators give the highest frequency stability. The limitation shared by LC and RC types is that resistor and inductor values drift with temperature, so their frequency is not perfectly constant, and LC circuits become bulky at low frequencies. Understanding these classes and their trade-offs is the foundation for the whole Karnataka 2nd PUC Electronics oscillator chapter and its question bank.