RC active all-pass using Wien bridge and differential amplifier

This letter shows that the all-pass network function with arbitrary second-order complex poles and zeros can be realized by feedbacking the output of a Wien bridge circuit using a differential amplifier. The merit of this method is that the center frequency and amount of delay can be adjusted independently by changing two parameters. Recently various methods of realization of RC active all-pass networks have been suggested [1]-[4]. The advantages of the present method using a Wien bridge and a differential amplifier are 1) that the all-pass network function with arbitrary second-order complex poles and zeroes can be realized; and 2) that the delay characteristics can easily be adjusted in both frequency and delay axes.