|Autors: Pandiev, I. M.|
Title: Analytical synthesis and implementation of low-frequency precision electronically controlled CFOA – based quadrature oscillator
Keywords: Analog circuits, all-pass filter, current-feedback operational amplifiers (CFOA), digital potentiometer, quadrature oscillator
Abstract: This paper describes the structure and operational principle of the proposed low-frequency digitally controlled quadrature oscillator, using monolithic CFOAs. The created oscillator is based on an all-pass filter that is synthesized by using a state variable approach and includes a cascade structure of two digitally controlled integrators and two adders. The oscillator employs linear digital control of the oscillation frequency within ±0.1% accuracy by controlling the time constants of the two integrators through two 1024 - position digital potentiometers. The efficiency of the circuit is demonstrated by comparing the simulation results for the electrical parameters with experimental results of sample circuits, working up to 130kHz with THD < 1%. The obtained results show good agreement with the theoretical hypotheses and analytical formulas.
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