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Colpitt’s Oscillators

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THEORY:

The tank circuit is made up of L1,C4 and C5 .The resistance R2 and R3 provides
the necessary biasing. The capacitance C2 blocks the D.C component. The frequency of
oscillations is determined by the values of L1,C4 and C5, and is given by
f = 1 / (2 (CTL1)1/2) Where CT = C1C2 / ( C1 + C2)
The energy supplied to the tank circuit is of correct phase. The tank circuit provides 1800 out
of phase. Also the transistor provides another 1800 . In this way, energy feedback to the tank
circuit is in phase with the generated oscillations.


PROCEDURE:

1. connections are made as per circuit diagram.
2. Connect CRO output terminals and observe the waveform.
3. Calculate practically the frequency of oscillations by using the expression
f = 1 / T ( T= Time period of the waveform)
4. Repeat the above steps 2,3 for different values of L, and note down the practically values of
oscillations of the collpitt’s oscillator.
5. Compare the values of oscillations both theoritically and practically.