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### ANALYSIS OF LC OSCILLATORS:

•     In the general form of a oscillator, any of the active devices such as Vacuum tube, transistor, FET, Operational amplifier may be used in the amplifier section.
•      Z1, and Z2 are reactive elements constituting the feedback tank circuit which determines the frequency of oscillations.

also provides temperature stabilization.

•     The radio frequency choke (R.F.C) offers  very high impedance to high frequency currents i.e., acts like a d.c short and open.
•     Thus it provide d.c load for collector and keeps a.c. currents out of d.c. s source.
•     The function of Cc and Cb to block d.c. and to provide an a.c. path.
•      Frequency determining network is a parallel resonant circuit consisting of inductors L1 and L2 and a variable capacitor C, the junction of L1 and L2  is earthed.

•     One side of L is connected to base via C and the other to emitter via C So, L the input circuit.
•     Similarly one end of L is connected to collector via C and other end id connected to emitter via Ce.
•     So, L is in the output circuit.
•     The two! are inductively coupled and form an auto ttansformer.

WORKING OF THE CIRCUIT:

•     When the collector supply voltage is switched on, a transient current  produced in the tank circuit.
•      The oscillatory current in the tank circuit produces voltage across L in this way a feedback between output and input circuit accomplished through auto transformer action.
•     So there is a phase reversal of 1800 between output and input.
•     The common-emitter amplifier also produces a further 180° phase shift between input and output voltages.
•     Thus total phase shift becomes 360°.
•     This makes the feedback positive which is the essential condition for oscillations.
•     When the loop gain | β | of the amplifier is greater than one, oscillations are sustained in the circuit.

FREQUENCY OF OSCILLATIONS:

The general equation for the oscillator is given by,