Octagonal On-Chip Wideband Bandpass Filter With A Tunable Transmission Zero In 0.18-Mu M (Bi)-Cmos Technology

A novel on-chip wideband bandpass filter (denoted as BPF-A) and a BPF with a tunable transmission zero (denoted as BPF-B) are presented. The proposed BPFs, featuring two ring resonators, are routed in octagonal interwinding shape, and a wide bandwidth is realized by strong coupling between the two resonators in this special routing way. A transmission zero is generated by loading stubs at the input and output ports. To further improve the selectivity of the proposed BPF, a MOS-varactor is adopted at the end of the loaded stub to flexibly adjust the location of the transmission zero. Moreover, theoretical analyses of the BPFs are performed based on LC-equivalent circuit. The measured results show BPF-A has a center frequency of 31.9 GHz, a bandwidth of 51.5%, an insertion loss of 4.9 dB and a transmission zero at 70.7 GHz. The BPF-B shows flexible tunability of transmission zero.