Highly selective RC-active filters using mucroer polynomials

The complete design of a highly selective bandpass RC-active filter is presented, where special attention is payed to the choice of the approximating function. By using multiple critical route equiripple (mucroer) polynomials, a substantial reduction in maximum Q-factor and variance of the attenuation is obtained. This fact allows the use of biquadratic building blocks with only one operational amplifier (o.a.) in a cascade connection, without the need of multiple-loop feedback techniques. Furthermore, a much smoother group delay is achieved. The price payed for all these advantages is a slight increase in the number of 2ndorder sections to be cascaded. In the realisation, the real-integrator multiple-feedback (r.i.m.f.) section has been employed for its low-cost, easy-tuning, and high-Q capabilities. In the paper, the design and tuning procedure of this block are reported, together with the corresponding experimental results. Finally, a compensation technique of the Q-factor variability with the temperature is described and the experimental curves arc shown