On-chip post-production tuning of I/Q frequency converters using adjustable coupler terminations

This paper presents a broadband integrated double-balanced I/Q-upconverter at 73.5 GHz in a 50 nm InGaAs-based metamorphic high electron mobility transistor technology including Lange couplers with voltage-controlled variable termination resistance. The variable resistance is implemented by using resistive FETs. This MMIC is designed for broadband communication with controllable LO suppression at the output. Introducing Lange couplers with voltage-controlled termination resistance offers a post-production measure to optimize MMICs with respect to I/Q-imbalance and LO isolation. In comparison to conventional 50 Q termination resistances the LO isolation could be improved by up to 12 dB over a bandwidth of 20 GHz while maintaining near constant conversion gain.