working principle of oscillator and types of oscillatory circuit

Function of oscillator,and types of oscillatory circuit for ganerating different types of oscillations

1. Oscillators Prepared by: Ms. A. K. Konkani

2. oscillators Many electronic devices require a source of energy at a specific frequency which may range from a few Hz to several MHz. This is achieved by an electronic device called an oscillator . Oscillators are extensively used in electronic equipment. For example, in radio and television receivers, oscillators are used to generate high frequency wave (called carrier wave ) in the tuning stages. Audio frequency and radio frequency signals are required for the repair of radio, television and other electronic equipment. Oscillators are also widely used in radar, electronic computers and other electronic devices. Oscillators can produce sinusoidal or non-sinusoidal ( e.g . square wave) waves.

3. Classification of Oscillators: Different types of oscillators are used for different applications. On the basis of frequency: Audio frequency oscillator.(up to 20 kHz) Radio frequency oscillator (up to 500 MHz) Microwave oscillator.(up to several GHz)

4. B) On the basis of active device used: Valve oscillator (triode or pentode) Transistor (BJT) oscillator Field effect transistor (FET) oscillator Uni junction transistor (UJT) oscillator Tunnel diode relaxation oscillator Integrated circuit oscillator

5. C) On the basis of wave shaped produced : Sine wave oscillator : It generates sinusoidal waves. Non sinusoidal oscillator : In this the wave shape produced is not sine wave but it may be square wave or triangular or saw tooth wave. D) On the basis of variability of frequency : Fixed frequency oscillator Variable frequency oscillator E) On the basis of method of generating oscillations : LC oscillator RC oscillator

6. Sinusoidal Oscillator An electronic device that generates sinusoidal oscillations of desired frequency is known as a * sinusoidal oscillator. Although we speak of an oscillator as “generating” a frequency, it should be noted that it does not create energy, but merely acts as an energy converter. It receives D.C energy and changes it into A.C energy of desired frequency.

7. Oscillatory Circuit A circuit which produces electrical oscillations of any desired frequency is known as an oscillatory circuit or tank circuit. A simple oscillatory circuit consists of a capacitor ( C ) and inductance coil ( L ) in parallel as shown in Fig.3.2 (a) and a switch is in position R . Now when the switch is brought to position P (fig. b) ,the capacitor C charges so positive charge is accumulated on the upper plate and negative charge is accumulated on the bottom plate.

8. Voltage across capacitor increases slowly and energy is stored in electric field. It is shown by oj in figure (f) . Now when the switch is brought to position Q from P (fig. c) capacitor gets connected across inductor L. Current through inductor rises slowly due to the voltage of the capacitor. Energy is stored in magnetic field and capacitor discharges and voltage of capacitor decreases ( jk in fig. f ) The current through inductor stops when the capacitor discharges completely so emf induced as shown in figure (d). So capacitor charges in the reverse direction (kl) and the energy is now stored in electric field.

9. Capacitor now discharges in reverse direction and due to electric current magnetic field now increases in reverse direction ( lm ). When capacitor discharges completely the magnetic field and current through the inductor maximum. Then the whole process is repeated and oscillations are produced. From the figure it is seen that the magnitude of voltage is decreasing and after some time it becomes zero and oscillations are stopped. This is called the damped oscillations . The oscillations damp out as there is loss of energy in inductor and capacitor. The voltage becomes zero when the energy is totally wasted.

10. Sustained or undamped oscillations We saw above that damped oscillations are produced in tuned circuit when the energy is given once. The oscillations produced are damped oscillations because at every oscillation there is waste of energy in capacitor and inductor. But if energy equal to the loss is supplied at every oscillation there is no decrease in voltage and sustained oscillations are produced.

11. Frequency of oscillations: The frequency of oscillations in the tank circuit is determined by the constants of the circuit viz L and C. The actual frequency of oscillations is the resonant frequency(or natural frequency) of the tank circuit given by: fr = 1/2π √ LC

12. Types of Sinusoidal Oscillations Sinusoidal electrical oscillations can be of two types viz damped oscillations and undamped oscillations . 1) Damped oscillations. The electrical oscillations whose amplitude goes on decreasing with time are called damped oscillations . Fig. Shows waveform of damped electrical oscillations.

13. Undamped oscillations . The electrical oscillations whose amplitude remains constant with time are called undamped oscillations . shows waveform of undamped electrical oscillations.

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