Digitally Programmable All-Pass CFA Filter Based on Follow-the-Leader-Feedback Topology

This paper describes the structure and operational principle of a digitally programmable second-order all-pass filter using monolithic current-feedback amplifiers (CFAs). The proposed filter was synthesized by using general follow-the-leader-feedback (FLF) topology and includes cascade structure of two digitally controlled RC integrators and two summing amplifiers. The filter employs independent digital control of the pole frequency within 0.1 % resolution by controlling the time constants of the two integrators through two 1024 - position monolithic digital potentiometers, used as variable resistors. By connecting the output port to the input of the created filter, an electronic circuit of quadrature oscillator is obtained. The efficiency of the proposed oscillator is demonstrated by comparing the simulation results for the basic electrical parameters with experimental results of sample electronic circuits, working up to 130 kHz with total harmonic distortion (THD) below 1 %. The obtained results show good agreement with the theoretical assumptions.