Unity-gain frequency-independent quadrature phase shifter
Ee Guan Tay, Vempati G. K. Murti · Electronics Letters · 1984
An active circuit which simultaneously provides unity gain and a Constant phase shift of 90° for sinusoidal inputs of varying frequency is described. It employs the voltage derived from a quadrature detector to modify the resistance of a voltage-controlled resistor incorporated in an active allpass phase shifter circuit.