Sinusoidal oscillators

An oscillator is the basic element of all ac signal sources and generates sinusoidal signals of known frequency and amplitude.It is one of the basic and useful instruments used in electrical and electronic measurements.For example,an oscillator finds wide application in electronic communication equipment.In AM (amplitude modulation)and FM (frequency modulation) superheterodyne receivers,"local" oscillators are used to assist in the reduction of the incoming radio frequency (RF) to a lower intermediate frequency (IF).Oscillator circuits are also employed in the "excite" section of a transmitter to generate the RF carrier.Other applications include their use as "clocks" in digital systems such as microcomputers,in the sweep circuits found in TV sets and oscilloscopes.

Since sinusoidal waveforms are encountered so frequently in electronic measurement work,the oscillator(sinewave generator)represents the largest single category of signal generators.This device covers the frequency range from a few Hz to many GHz

Although we speak of an oscillator as "generating" a sinusoidal signal,it is to be noted that it does not create energy,but merely acts as an energy converter.It simply converts unidirectional current drawn from a dc source of supply into alternating current of desired frequency.The function of an oscillator is reverse of that of a rectifier and,therefore,sometimes called inverter. However,we generally think of oscillators circuits as providing an ac voltage signal.

It is noteworthy here that although an alternator( ac generator) generates sinusoidal ac power of 50Hz,it cannot be called an oscillator.An alternator is a mechanical devices that has rotating parts,converts mechanical energy into ac energy but cannot produces ac energy of frequency converts dc energy into ac energy of frequency ranging from a few Hz to many GHz.

Though alternator generates large amount of ac power but for several application such as radio transmitters and receivers,radars etc.,an oscillator is preferred owing to its numerous advantages over alternators for such applications.

These advantage are:

(i)Portable and cheap in cost.

(ii)An oscillator is a non-rotating device.Consequently,there is no wear and tear and hence longer life.

(iii)Frequency of oscillation may be conveniently varied.

(iv)Voltage or current of any frequency (20 Hz to extremely high frequencies)adjustable over a wide range can be generated.

(v)Frequency once set remains constant for a considerable period time.

(vi)Voltage free from harmonic as well as rich with harmonics can be generated by sinusoidal oscillators and relaxation oscillators repectively.

(vii)High operation efficiency-due to absence of moving part,there is no wastage of energy owing to friction.