A simple multiphase sinusoidal oscillator using operational amplifiers is described. The system is made up of n cascaded first-order low-pass stages along with n unity gain inverters (n > 3). It produces 2n even phase signals that are equally spaced in phase and of equal amplitude, from low impedance sources. Two schemes are presented; one utilizing self-oscillation under the Barkhausen criterion and the other employing external signal injection through the phase-shifting network of the first. The negative feedback utilized in the operational amplifiers results in frequency and distortion performances that are superior to similar systems based on current conveyors.
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Stephan J. G. Gift (1997) studied this question.