New Method for Flat IIR Filter Design with Improved Group Delay

This paper presents a new direct method for the design of IIR filters with flat magnitude response in both passband and stopband i.e Butterworth type filters. The proposed filters have an improved group delay compared with the traditional Butterworth filter. The designed filters are obtained using only a causal part of the designed IIR filter with exactly linear phase. The design parameters are the same as in traditional IIR filter design based on analog filters i.e. passband and stopband frequencies ωp and ωs, and passband droop and stopband attenuation Ap and As, respectively.