13-09-2013, 02:33 PM
RC PHASE SHIFT OSCILLATOR
Aim:
To design and construct a RC phase shift oscillator for the given frequency (f0).
Theory:
In the RC phase shift oscillator, the required phase shift of 180 ̊ in the feedback
loop from the output to input is obtained by using R and C components, instead of tank
circuit. Here a common emitter amplifier is used in forward path followed by three
sections of RC phase network in the reverse path with the output of the last section being
returned to the input of the amplifier. The phase shift Ф is given by each RC section
Ф=tanˉ1 (1/ωrc). In practice R-value is adjusted such that Ф becomes 60 ̊. If the value
of R and C are chosen such that the given frequency for the phase shift of each RC
section is 60 ̊. Therefore at a specific frequency the total phase shift from base to
transistor’s around circuit and back to base is exactly 360 ̊ or 0 ̊. Thus the Barkhausen
criterion for oscillation is satisfied
Procedure:
1. Connections are made as per the circuit diagram.
2. Switch on the power supply and observe the output on the CRO (sine wave).
3. Note down the practical frequency and compare with its theoretical frequency.
Result:
Thus RC phase shift oscillator is designed and constructed and the output sine
wave frequency is calculated as