High Quality Factor Extraction of Miniaturized Coupled Line Bandpass Filters Implemented Using RF Silicon Integrated Circuits

The methodology of quality factor extraction of distributed inductors from S-parameter measurements of miniaturized filters using diagonally-coupled lines is presented. It is found that the quality factor of the integrated filter implemented using standard CMOS technology can be increase by a multi-level coupled line, which is adopted to reduce the series resistance. The quality factors (Q) at 4.8 GHz with one and six layers are found to be 4.9 and 14.8, respectively, i.e. an improvement by a factor of 3 by increasing the layer numbers. The die area surrounded by the ground plane (for good shielding) was 0.7 x 0.4 mm(2) and was fabricated on 10 cm bulk silicon substrate with aluminum conductors. These quality factors are also compared with spiral inductors applied in conventional active filters. To the authors' knowledge, the quality factor of 14.8 presented in this study is the highest published value for bandpass filter inductors implemented using the standard CMOS process.