A Compensation and Calibration Technique for Lumped Hybrid Couplers in Integrated Image-Reject Architectures

This paper presents a compensation and calibration technique for lumped-element Lange hybrid couplers. The target of the compensation is the reduction of the quadrature error introduced by lossy reactive components. An approximated, but reasonably accurate, analysis links the finite quality factor of the passive components to the quadrature error. A simple compensation technique, that corrects for the quadrature error, is proposed along with a calibration procedure. To verify the effectiveness of the proposed technique, a lumped-element Lange hybrid coupler working at an intermediate frequency of 3 GHz is embedded in a fully integrated image-reject up/down-converter implemented in a 28 nm bulk CMOS technology. Measurements show that the proposed technique yields an increase of the image rejection ratio from 24 dB to 45 dB for an up converted signal at 28 GHz.