Colpitts oscilattor
OBJECTIVE: To study and calculate frequency of oscillations of Colpitt’s oscillator.
APPARATUS:
 Transistor BC 107 1 No.
 Capacitors 0.1µF  1 No, 0.01µF  2 Nos
 Inductor 5mH  1 No.
 Resistors 47KOhm, 1kO, 10kO, 1.5K 1 No.
 Decade inductance box
 CRO(Dual Channel ) (020 MHz)
 Function generator ( 1Hz to 1 MHz)
 Regulated power supply (030V)
 Connecting Wires
THEORY:
The tank circuit is made up of L_{1},C_{1} and C_{2} .The resistance R_{2} and R_{3} provides the necessary biasing. The capacitance C_{3} blocks the D.C component. The frequency of oscillations is determined by the values of L_{1},C_{4} and C_{5}, and is given by
f = 1 / (2(pi) (C_{T}L1)^{1/2}) Where C_{T} = C_{1}C_{2} / ( C_{1} + C_{2)}
The energy supplied to the tank circuit is of in phase. The tank circuit provides 180^{0 }out of phase. Also the transistor provides another 180^{0}. In this way, energy feedback to the tank circuit is in phase with the generated oscillations.
CIRCUIT DIAGRAM:
PROCEDURE:
Connections are to made as per circuit diagram.
Connect CRO output terminals and observe the waveform.
Calculate practically the frequency of oscillations by using the expression
f = 1 / T ( T= Time period of the waveform)
Repeat the above steps 2,3 for different values of L, and note down the practical values of oscillations of the Collpitt’s oscillator.
Compare the values of oscillations both theoretically and practically.
OBSERVATIONS:
Inductance ( mH )  Theoretical Frequency ( Hz )  Practical Frequency ( Hz ) 
MODELWAVEFORM:
PRECAUTIONS:
 The connections are to be connected properly.
 Transistor terminals should be identified properly.
 Readings should be taken without parallax error.
RESULT: Frequency of oscillations of Colpitt’s oscillator is measured practically and compared with theoretical values .
LEARNING OUTCOMES:
Students are able to Design and analyze Colpitts oscillator.
VIVA QUESTIONS:
 What are the applications of LC oscillator?
 What type of feedback is used in oscillators?
 What is the loop gain of an oscillator?
 What is the difference between amplifier and oscillator?
 What is the condition for oscillations?

UpdatedMar 05, 2020

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