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The phase shift oscillator is a format that has a number of advantages over the Wien bridge oscillator. In particular the levels of distortion are normally lower and the frequency stability is also good, provided the components used are sufficiently stable themselves.
The oscillator is formed around the basic phase shift network which consists of three RC sections which provide a steep change in phase with frequency.
The simplest circuit consists of an operational amplifier, three capacitors and four resistors.
Calculating the frequency of oscillation from first principles is complex because each of the stages of the phase shift network loads is neighbour. However the calculations can be simplified to provide a couple of easy formulae to use.
The phase shift network resistors should all be set to the same value as should the capacitors, i.e. R1=R2=R3=R, and C1=C2=C3=C. In this case the values can be determined from the formulae given below.
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