A novel HU-shaped common-mode filter for GHz differential signals

A novel low-cost filter design for common-mode noise suppression in high-speed differential signals is proposed. It is realized by etching a HU-shaped defected-ground structure (DGS) to perturb the return current of the common-mode noise. A simple LC resonator model for the proposed structure is also developed with good agreement to the full-wave simulation and measurement result. It is found that over 15 dB of common-mode noise suppression can be achieved over a wide frequency ranges from 3.6 to 9.1 GHz, while the differential signals still keep good signal integrity in eye-pattern observation.