RC phase shift oscillator

BJECTIVE:

To calculate the frequency of oscillations of RC phase shift oscillator and to compare theoretical and practical value.

APPARATUS:

TINA SOFTWARE

PC

CIRCUIT DIAGRAM:

THEORY:

RC-Phase shift Oscillator has a CE amplifier followed by three sections of RC phase shift feedback Networks. The output of the last stage is returned to the input of the amplifier. The values of R and C are chosen such that the phase shift of each RC section is 60º.Thus The RC ladder network produces a total phase shift of 180º between its input and output voltage for the given frequencies. Since CE Amplifier produces 180 º phase shift, the total phase shift from the base of the transistor around the circuit and back to the base will be exactly 360º or 0º. This satisfies the Barkhausen condition for sustaining oscillations.Total loop gain of this circuit is greater than or equal to 1, this condition used to generate the sinusoidal oscillations.

The frequency of oscillations of RC-Phase Shift Oscillator is,

PROCEDURE:

1. Start TINA. A blank circuit window will appear on the screen along with a component tool bar.
2. Using component tool bar place all the components on the circuit window and wire the circuit.
3. Observe the output signal and note down the output amplitude and time period (T_d).
4. Calculate the frequency of oscillations theoretically and verify it practically (f=1/T_d).
5. Repeat the above procedure for different values of R & C.

THEORITICAL CALCULATIONS:

R = 10Kohms, C = 0.001 µf

PRACTICAL CALCULATIONS:

T_d = time period of oscillations

f = 1/T_d

Tabular column:

MODEL WAVE FORMS:

RESULT: The frequency of oscillations of RC phase shift oscillator is calculated the theoretical and practical values are compared.

LEARNING OUTCOMES:

Students are able to design and analyze RC-phase shift oscillator.

VIVA QUESTIONS:

1. What are the conditions for generating oscillations?

Ans: To generate the oscillations the conditions are

1. Positive feedback used

 Oscillator circuit must satisfy  Barkhausen criteria which is 

2. The magnitude of the loop gain (Aß) must be unity. This means the product of gain of amplifier 'A' and the gain of feedback network 'ß' has to be unity.

3. The  phase shift around the loop must be 360° or 0°. This means, the phase shift through the amplifier and feedback network has to be 360° or 0°.

2.Give the formula for frequency of oscillations for RC phase shift oscillator?

Ans: 

3.What is the total phase shift produced by the RC ladder network?

Ans: 360⁰ is the total phase shift produced by the RC ladder network to satisfy the Barkhausen criteria.

4.Whether the RC phase shift oscillator is connected with positive feedback or negative feedback?

Ans: Positive feedback

5.What are the different types of oscillators?

Ans: 1. RC oscillators: RC phase shift oscillator,Wien bridge oscillator and Twin-T oscillator

2.LC oscillators: Hartley, Colpitts,Clapp and Armstrong oscillators.

3.Crystal oscillators

6. What is the gain of RC phase shift oscillator?

Ans: The gain of RC phase shift oscillator is unity.

7.What is the difference between damped oscillations and undamped oscillations?

Ans:

8.What are the applications of RC phase shift oscillators?

Ans:Used in signal generators, Musical instruments.

9.How many resistors and capacitors are used in RC phase shift network and why?

Ans: Three RC networks used, each network will provide 180⁰ phase shift and CE circuit will provide 180⁰ phase shift, finally at the end total phase shift is 360⁰ or 0⁰ to satisfy the barkhausen criteria.

10.How the Barkhausen criterion is satisfied in RC phase shift oscillator?

Ans:The ladder RC used to satisfy the Barkhausen criteria ,Three RC networks used, each network will provide 180⁰ phase shift and CE circuit will provide 180⁰ phase shift, finally at the end total phase shift is 360⁰ or 0⁰ to satisfy the barkhausen criteria.

11.What are the drawbacks of RC phase shift oscillator?

Ans:It will provide small signal level.