Q. Give the classification of Oscillators?
Depending on the type of the output waveform, oscillators are classified as sinusoidal (or harmonic) oscillators and relaxation oscillators. if the generated waveform is sinusoidal or nearly so with a definite frequency , the oscillator is said to be a sinusoidal oscillator. If the output waveform is non-sinusoidal (such as square or saw-tooth waveforms), the oscillator is termed a relaxation oscillator.
When the current-voltage characteristic of the active device in the oscillator has a negative slope over some portion of its operation, the oscillator is said to of negative resistance type. A tunnel diode oscillator is a negative resistance oscillator. If the oscillator contains a positive feedback amplifier with the loop gain adjusted for an infinite overall gain, the oscillator is called a feedback oscillator. Both negative resistance and feed back oscillators can be sinusoidal and relaxation types. Feedback-type sinusoidal oscillators can again be classified as LC(inductor-capacitor-) and RC (resistor-capacitor) oscillators.
Oscillators can also be grouped on the basis of the frequency of the generated signals. Thus oscillators producing signals in the audio frequency (AF) range, radio frequency (RF) range etc. are called audio frequency (AF) oscillators , radio frequency (RF) oscillators etc. The use of LC feedback oscillators is in generating RF signals. Eg. Tuned collector, Hartley, and Colpitt oscillators are oscillators of this class. The application of RC oscillators is mainly for the generation of AF waveforms. Phase-shift and Wien-bridge oscillators belong to this category. Sometimes, for a higher frequency stability, piezoelectric crystals are used in place of the LC circuit in a sinusoidal oscillator. Such oscillators are known as crystal oscillator.