Active-only variable-gain low-pass filter for dual-mode multiphase sinusoidal oscillator application

Abstract

This research presents an active-only low-pass (LP) filter whose pole frequency and gain are independently tunable by means of bias current manipulation. The realization of the proposed LP filter required one operational amplifier, two operational transconductance amplifiers, and two MOS transistors. The multiphase sinusoidal oscillator (MSO) was subsequently realized by cascading n LP filters (n = 3) and loop-backing the output of the last LP filter to the input of the first LP filter. Simulations were carried out and the results revealed that the MSO could simultaneously achieve low impedance voltage and high impedance current outputs without the circuit topology alteration. The frequency of oscillation and the condition of oscillation could also be electronically tuned without disturbing each other. Furthermore, the sinusoidal signal of the MSO exhibited relatively low total harmonic distortion of about 0.8% at 2.75 MHz. To verify, a prototype of the active-only LP-based MSO (n = 3) was constructed and experiments were performed. The experimental findings were agreeable with the simulation results.