Op amp application as Oscillator

Operational amplifier

1. Op -Amp Application Sine Wave Oscillator Done by, Dr. D. Veera Vanitha , AP/ECE, School of Engineering, Avinashilingam Institute for Home Science and Higher Education for Women, Coimbatore.

2. Oscillator Oscillator is an electronic circuit that generates a periodic waveform on its output without an external signal source. It is used to convert dc to ac. They are used in Communications systems, digital systems (including computers) and test equipments. Applications Used as a local oscillator to transform the RF signals to IF signals in a receiver Used to generate RF carrier in a transmitter Used to generate clocks in digital systems Used as sweep circuits in TV sets and CRO

3. Introduction An oscillator is a circuit that produces a repetitive signal from a dc voltage. The feedback oscillator relies on a positive feedback of the output to maintain the oscillations. The effect of positive or regenerative feedback is to increase the systems gain, i.e , the overall gain with positive feedback applied will be greater than the gain without feedback The relaxation oscillator makes use of an RC timing circuit to generate a non sinusoidal signal such as square wave Sine wave Square wave Sawtooth wave

4. Types of oscillators Based on the feedback components used, the types of oscillators are: 1. RC oscillators Wien Bridge Phase-Shift Twin T Oscillator 2. LC oscillators Hartley Colpitts Clapp Crystal 3. Unijunction / relaxation oscillators

5. Basic Linear Oscillator and If V s = 0, the only way that V o can be nonzero is that loop gain A  =1 which implies that (Barkhausen Criterion) Noise signals and the transients associated with the circuit turning on provide the initial source signal that initiate the oscillation

6. Basic principles for oscillation

7. Wien-bridge Oscillator RC feedback oscillators are generally limited to frequencies of 1 MHz or less. The types of RC oscillators that we will discuss are the Wien-bridge and the phase-shift. It is a low frequency oscillator which ranges from a few kHz to 1 MHz.

8. Wien-bridge Oscillator The loop gain for the oscillator is; where, and

9. Wien-bridge Oscillator Hence Substituting for s For oscillation frequency f

10. Wien-bridge Oscillator Since at the frequency of oscillation, T ( j  ) must be real i.e., for zero phase condition, the imaginary component must be zero

11. Wien-Bridge oscillator output

12. RC Phase-Shift Oscillator The phase shift oscillator utilizes three RC circuits to provide 180º phase shift that when coupled with the 180º of the op-amp itself provides the necessary feedback to sustain oscillations. The gain must be at least 29 to maintain the oscillations. The frequency of resonance for the this type is similar to any RC circuit oscillator:

13. Phase-Shift Oscillator The gain must be at least 29 to maintain the oscillations