Design of a Wideband D-Band Mixer Based on SiGe BiCMOS Technology

This paper presents the design and analysis of a wideband passive down-conversion mixer for D-band applications, implemented in a 90 nm SiGe BiCMOS process. The mixer employs a single-balanced, image-rejection topology. To achieve wide operational bandwidth, a compact hybrid coupler is designed using a quarter-wavelength coupled-line structure with a grounded termination, replacing the conventional three-quarter-wavelength transmission line. The mixing core utilizes heterojunction bipolar transistors (HBTs) with shorted base-collector terminals as diodes, optimized for minimal junction capacitance. A DC bias is introduced to lower the required local oscillator (LO) drive power, thereby reducing conversion loss. Full-wave electromagnetic simulations demonstrate that the mixer achieves a conversion loss of less than 15 dB across a 20 GHz bandwidth (114-134 GHz), with a minimum loss of 10.9 dB. The LO-to-RF isolation exceeds 24 dB over the entire band, and the input 1-dB compression point (IP1dB) is -0.78 dBm, indicating excellent linearity. The proposed mixer is well-suited for integration into D-band phased-array transceivers for communication and sensing systems.