Subband filters using allpass structures

A novel design technique for multichannel power complementary filters using a minimum number of allpass sections is investigated and new results are reported in this context. In particular, specific power complementary design procedures are given for the three-band case using two allpass sections and for the four-band case using two as well as three allpass sections. In both cases a free variable allows the extra freedom to shape the filters to have the desired bandpass characteristics. This idea is illustrated in the three-band case by generating a lowpass, a bandpass, and a highpass power complementary filter combination using two allpass sections. These digital power complementary structures are attractive for VLSI design, since the actual number of filters to be implemented is smaller than that in a conventional design