High-Q low-cost RC active filters: The RIMF section

The real integrator multiple-feedback (RIMF) section is proposed in order to realize low-cost high- active second-order filters. It has been designed after taking into account the fact that a low-cost OA is in practice a real integrator, that is an ideal integrator with finite dc gain, input resistance, and output conductance; therefore the feedback network has been modified by adding a resistor. Hence, enhancement of the -factor, lower sensitivity of the resonant frequency with respect to the OA unity-gain bandwidth, and an easier tuning of the -factor are obtained in comparison with the classical multiple-feedback section. Furthermore, thermal drifts are minimized, by optimizing three free parameters. Results of exhaustive experiments confirm the theoretical developments.