LO Leakage Suppression in Resistive Zero-IF IQ Mixers Beyond 100 GHz

In this article, the monolithic integration of an adaptive local oscillator (LO) leakage cancellation circuit together with an unbalanced resistive in-phase and quadrature (IQ) high-electron-mobility transistor (HEMT) mixer is presented. The proposed calibration algorithm for the cancellation signal is tolerant against any nonideal component responses. A typical LO-to-radio frequency (RF) isolation of 60 dB is achieved, which corresponds to a LO leakage of −55 dBm at saturated mixer operation. To the best of the authors’ knowledge, this is the highest reported performance of a monolithic approach beyond 100 GHz. As part of this work, the leakage cancellation’s sensitivity with regard to environmental changes is investigated. Furthermore, a semi-balanced IQ mixer is implemented in the same technology. An analytic equation for its LO suppression as a function of amplitude and phase imbalance is derived. Detailed comparisons of the output spectra of both mixers, their two-tone intermodulation distortion characteristics, and noise figures (NFs) complement this study.