A compact millimeter-wave CMOS bandpass filter using stepped-impedance cross resonator

This paper presents a compact millimeter-wave CMOS bandpass filter, which is composed of a stepped-impedance cross resonator with multi-figure edge-coupling to the input and output ports. The use of the stepped-impedance cross resonator gives advantageous transmission zeros in stopband, where their frequencies can be controlled by each stepped-impedance segment respectively. A demonstrated chip filter in 0.18 μm CMOS technology was implemented, which has a compact size of 0.48×0.92 mm². The measured insertion loss is 2.9 dB and the return loss is better than 20 dB in the passband range of 56.3 to 68.9 GHz. Two transmission zeros are located at 45.4 and 82.0 GHz, which result in a wide stopband suppression of 18 dB for f <; 48.3 GHz and f >; 77.8 GHz.