A compact D‐band I/Q mixer with improved transformer balun

Abstract This article presents a D‐band down‐conversion I/Q mixer using 0.13‐µm SiGe BiCMOS technology. The mixer is implemented with 2 Gilbert cells. The Lange coupler is for quadrature LO input and the transformer balun is for the differential RF input. The balance performance of the transformer balun is improved by adding a parallel capacitor or short‐circuit ground in the center‐tap of the differential outputs. Owing to the improved transformer balun, the mixer achieves a measured conversion gain of 10 to 8.2 dB when the RF frequency varies from 120 to 140 GHz and the LO frequency is fixed at 130 GHz. In the corresponding frequency range, the measured amplitude and phase imbalance between I and Q channels are ±0.5 dB and ±8°, respectively. The RF‐to‐LO isolation is over 40 dB. The proposed mixer also exhibits a compact size with the core size of 0.6 × 0.24 mm 2 .