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Question: short note on LC oscillator
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Subject: Electronic Devices and Circuits II

Topic: Oscillators

Difficulty: Medium

edc2(34) • 358 views
 modified 6 months ago  • written 8 months ago by
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• In LC oscillator the feedback network consists of inductor and capacitor .These LC component determines the frequency of oscillation.

• LC oscillators are also known as tuned oscillators. These oscillators can operate at high frequencies from 200 Khz to some Ghz.

• They are not suitable for low frequency operations because at low frequencies the value of inductor and capacitor is very large due to this the circuit becomes more bulky and expensive.

• Analysis of these type can revels that the following types of oscillators are obtained when the reactance elements are as designed.

Oscillator Type Reactance Element
Colpitts Oscillator C,C.L
Hartley Oscillator L,L,C
clapp Oscillator C,C,L and extra capacitor C
Tuned input and tuned output LC,LC

The basic LC oscillator tank circuit is as shown in the figure:

The frequency of oscillation of LC oscillator is given by F= 1/(2π√LC)

In case of colpitts oscillator C is the equivalent capacitor calculated by formula Ceq=(c1*c2)/((c1+c2))

In case of Hartley oscillator L is the equivalent inductance calculated BY formulaLeq =(L1+L2+2M).

M= mutual inductance between the two inductor.

It is easy to tune

Simple to construct and easy to operate at high frequency.

Poor frequency stability.

Applications

Used in local oscillator

RF source and high frequency function Generator.