Explain the operation of Colpiti's oscillator and state its applications

The resistors $R_1,R_2$ and $R_e$ will provide the biasing for transistors. $C_{c1}$ and $C_{c2}$ are coupling capacitors and $C_e$ is bypass capacitor.

The transistor is connected in the CE configuration, ∴ it introduces a phase shift of 180 degree between its i/p and o/p

The feedback network = 180-degree phase shift so as to make the total shift equal to 0. This will satisfy the condition for +ve feedback.

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Frequency. oscillations: $f = \frac{1}{2π \sqrt{L_1 C}} ,C=\frac{C_1 C_2}{C_1+C_2}$

In case of transistor phase shift oscillator, the transistor current gain is imp. The circuit analysis gives min value of $h_{fe}$ as, $C_1/C_2$.

The behavior of colpitt’s oscillator is very similar to that of Hartley oscillator for the simple reason that both of them use same basic LC oscillator except for phase shifting network.

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