Low-pass cascade filters with high attenuation rate in the stopband

In this paper, we present two biquadratic structures for cascade filter design, which are intended to provide high attenuation rate in the stopband area of frequency transfer characteristic. The filters optimized in this way can reach better electrical performances, such as higher maximal cut-off frequency or dynamic range, even with conventional (low power consumption) active devices. We present a modification of the well-known Sallen-Key filter and a biquadratic filter based on the second generation current conveyor CCII-. Presented approach relies on the elimination of parasitic transfer zeros in the real transfer function, which are caused by the non-ideal parameters of real active elements. Their impact is eliminated by unconventional definition of the filter output.