Modeling and implementation of on-chip millimeter-wave compact branch line couplers in a BiCMOS technology

In this paper, the modeling, design, and measurement of on-chip compact millimeter-wave branch line couplers are discussed. These couplers are realized with the Back End of Line (BEOL) wiring and enabled as a library device of a 0.13 micron SiGe BiCMOS process design kit. Like other library devices, this coupler device has a scalable layout pattern and a schematic symbol, which allows users to have couplers at different frequencies by inputting the dimensions. An accurate model for these branch line couplers is developed, which shows a good match with the measurements of the couplers designed for 60 GHz, 77 GHz and 94 GHz. Better than 19 dB return loss, better than 1.5 dB insertion loss and better than 21dB isolation have been observed. The side dimensions of these compact on-chip couplers are ranging from 440 microns to 530 microns.