Editing RC oscillator (section)

===Quadrature oscillator===
The quadrature oscillator uses two cascaded [[op-amp]] integrators in a feedback loop, one with the signal applied to the inverting input or two integrators and an invertor.  The advantage of this circuit is that the sinusoidal outputs of the two op-amps are 90° [[out of phase]] (in quadrature).  This is useful in some communication circuits.

It is possible to stabilize a quadrature oscillator by squaring the sine and cosine outputs, adding them together, ([[Pythagorean trigonometric identity]]) subtracting a constant, and applying the difference to a multiplier that adjusts the loop gain around an inverter.  Such circuits have a near-instant amplitude response to the constant input and extremely low distortion.