In this note, Poly Notes Hub discuss about the Colpitts Oscillator. Also the Circuit Diagram of Colpitts Oscillator and Working of Colpitts Oscillator.
Author Name: Arun Paul.
Circuit Diagram of Colpitts Oscillator
Fig shows the circuit diagram of this Oscillator. It uses two capacitors and is placed across a common inductor L and the center of the two capacitors is tapped. The tank circuit is made up of C1, C2 and L. The frequency of Oscillations is determined by values of C1, C2, and L and is given by;
f = 1/(2π√LCτ)
where,
Cτ = C₁C₂/(C₁+C₂)
Note that C1-C2-L is also the feedback circuit that produces a phase shift of 180°.
Working of Colpitts Oscillator
When the circuit is turned on, the capacitors C1 and C2 are charged. The capacitors discharge through L, setting up oscillations of frequency determined by exp (1). The amplifier’s output voltage appears across C1 and feedback voltage is developed across C2. The voltage across it is 180° out of phase with the voltage developed across C1(Vout) as shown in Fig. It is easy to see that voltage feedback (voltage across C2) to the transistor provides positive feedback. The transistor produces a phase shift of 180° and a further phase shift of 180 is produced by C1- C2 voltage divider. In this way, feedback is properly phased to produce continuous undamped oscillation.
Feedback Fraction
The amount of feedback voltage in Colpitts Oscillator depends upon the feedback fraction mᵥ of the circuit. For this circuit,
The Feedback Fraction ( mᵥ ) = C₁⁄C₂
Applications of Colpitts Oscillator
- Used in Radio Receivers
- Used for Sin Wave Generation
- Used in Mobile Applications also.
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