A CMOS Miniaturized C-Band Active Bandpass Filter

This paper presents a novel topology of the CMOS active bandpass filter (BPF) at C-band. The parallel resonators in the BPF are realized by the monolithic synthetic quasi-TEM transmission line (TL), the so-called complementary conducting strip transmission line (CCS-TL). The characteristics of the CMOS monolithic CCS-TL are investigated by a series of experiments. The characteristics of the CCS-TL, including the characteristic impedance, phase constant, and attenuation constant, are extracted from the measured two-port scattering parameters for the filter design. The loss of the CCS-TL resonators is reduced by integrating an active network. A practical example of a second-order active BPF is designed and fabricated by using a typical 0.18mum CMOS 1P6M technology. The size of prototype is 1.23 mm by 0.88 mm. The measured results show the following characteristics. The center frequency of the proposed active BPF is 6.02 GHz. The bandwidth is 1.26 GHz, and the return-loss, which is measured based on 50Omega-system, is -7.5 dB. The insertion-loss of the BPF is 2.2dB when the BPF draws 3.0mA from a +1.8V power supply