Low-output-impedance First-order All-pass Filter Based on Single Active Element and Its Application in Multiphase Sinusoidal Oscillator

This article proposes a voltage-mode first-order all-pass filter and its application in a multiphase oscillator. The proposed circuit is designed with a single commercially available IC LT1228, single capacitor and single resistor. The proposed circuit performance can be operated at a wide frequency range and the phase response is shifted from 180 degrees to 0 degrees at a low-output-impedance port. Moreover, the amplitude of the signal can be directly controlled by adding external resistors without affecting the pole frequency and phase response. In addition, the proposed all-pass filters can be applied to the multiphase sinusoidal oscillator. The presented circuits were verified via a computer simulation and an experiment that confirmed the theoretical analysis.