Phase shift oscillator circuit

Posted on Feb 7, 2014

The normal assumption is that the phase shift sections are independent of each other. Then using above Equation the loop phase shift is –1800, when the phase shift of each section is 600. This occurs when ω=2πf = 1.732/RC because the tangent of 600 = 1.732. The magnitude of β at this point is (1/2)3. So the gain, A, must be equal to 8 for the system gain to be equal to one.

Phase shift oscillator circuit
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Therefore theoretical gain of op-amp = 8 The practical gain to start an oscillation = 32.4 The practical gain to keep oscillation = 31.6 Theoretical frequency = 2.76 Khz Practical frequency = 3.78 Khz The main reason for this is RC sections are not buffered. That is they load each other. Also the tolerance of the values of components can vary the results. But still there is a remarkable reduction in distortion comparing to the wein bridge oscillator.

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