Design of 60 GHz CMOS bandpass filters using complementary-conducting strip transmission lines

In this paper, the standard 0.18 μm CMOS technology is employed to design two compact 60 GHz bandpass filters using complementary-conducting strip transmission lines (CCS-TLs). The CCS-TL is a kind of synthetic quasi-TEM transmission line. For the integrated circuit process, this guided-wave structure not only automatically satisfies the requirement of the metal density design rules, but also provides the slow-wave effect to miniaturize circuit size. By applying CCS-TLs, two dual-mode ring filters, denoted as type-I and type-I filters, are developed with two-types of perturbation structures, namely step-impedance sections and shunt open stubs. The inserted perturbation structures are mainly utilized to produce a pair of transmission zeros for improving the passband selectivity. The core sizes of type-I and type-II filters are 360 μm × 210 μm and 330 μm × 240 μm, respectively. The type-I filter has a 3.86 dB insertion loss and a 36% 3-dB bandwidth at the center frequency 65.25 GHz, while the type-II filter has a 4.8 dB insertion loss and a 28.3% 3-dB bandwidth at the center frequency 63.5 GHz. The out-of-passband suppressions are all better than 20 dB.