Fast amplitude control in twin-T bridge RC oscillators

When a sinusoidal voltage is applied to the symmetrical twin-T bridge, the voltages at the inner nodes of the bridge have equal amplitudes and are shifted by 90°. If they are squared and summed, the resulting DC voltage can be used to control the gate of a field-effect transistor connected to the bridge. The oscillator with such a control system simultaneously has low distortion and fast amplitude transient response.