Two New Active-RC Quadrature Sinusoidal Oscillators Using the Operational Amplifier

This paper presents two third-order active-RC quadrature sinusoidal oscillator configurations incorporating the operational amplifier (op-amp) with a minimal number of passive components. The proposed designs employ an inverting integrator followed by a two-stage RC phase-shift network, forming a feedback loop that satisfies the Barkhausen criterion for sustained oscillation. The circuits generate two sinusoidal outputs with a 90° phase difference. One of the designs incorporates just a single op-amp. Theoretical analyses are provided to derive the frequency and condition of oscillations. Experimental results confirm the validity of the designs and demonstrate good agreement with the analytical predictions. Because of their simplicity and low component count, the proposed oscillators are particularly suitable for integrated circuit implementation in communication and signal processing systems.