must be a little bit larger so the oscillation will grow in amplitude rather than remain the same (small) amplitude. If the amplifier were ideal, then amplitude would increase without limit, but in practice amplifiers are nonlinear and their instantaneous gain varies. As the amplitude increases, amplifier saturation will decrease the amplifier's average gain. Consequently, the oscillation amplitude will keep increasing until the average loop gain of the circuit falls to unity; at that point, the amplitude will stabilize. When the oscillation frequency is high enough to be near the amplifier's cutoff frequency, the amplifier will contribute significant phase shift itself, which will add to the phase shift of the feedback network. Therefore, the circuit will oscillate at a frequency at which the phase shift of the feedback filter is less than 180 degrees. The single op-amp circuit needs a relatively high gain (about 30) to maintain the oscillation due to the RC sections loading each other. If each RC segment did not affect the others, a gain of about 8 to 10 would be sufficient for oscillation. An isolated version of the oscillator can be made by inserting an op-amp buffer between each RC stage (this also simplifies the modeling equations). References External links Electronic oscillators de:Phasenschieber#Phasenschiebergenerator