Improved harmonic analysis of RC-active phase shift oscillators

This paper describes an improved method for calculating the harmonic distortion content of active-RC phase shift oscillators. The proposed method introduces the truncated harmonic transfer function (THTF) which is related to the two-sinusoidal-input describing function (TSIDF) of non-linear control theory. This allows accurate calculation of the distortion terms in oscillator systems containing higher signal levels and therefore higher levels of nonlinearity than is possible with conventional methods. Although the method is quite general in its application, in this paper it is demonstrated using examples employing the Wien RC-bandpass oscillator with a quadratic nonlinearity.