Low-loss and compact 2.4-GHz CMOS bandpass filter with finite transmission zeros

In this paper, a low-loss and high-selectivity compact CMOS bandpass filter at S band is presented. The filter based on lumped elements achieves low insertion loss and ultrawide bandwidth. Moreover, the resonators of the filter result in two finite transmission zeros. One transmission zero is in the lower stopband, and the other is in the upper stopband, thus improving the selectivity of the filter significantly. The filter is designed and fabricated in a standard 0.18-μm CMOS technology with a chip area of 745 mm × 790 mm including all testing pads. The filter achieves 2.7-dB insertion loss and 64% 3-dB bandwidth at 2.5 GHz. Measured results also show that the two transmission zeros are at 1.1 GHz and 4.8 GHz featuring 26.6-dB and 44.5-dB rejection, respectively.