A GHz common-mode filter using negative permittivity metamaterial on low temperature co-fire ceramic (LTCC) substrate

A broadband common-mode noise suppression filter for GHz differential signals is proposed using effective negative permittivity transmission line metamaterial. The proposed structure possesses a complete ground plane for the use of the multilayer structure. The equivalent circuit models for odd mode and even mode are developed to derive the dispersion relation and understand the characteristic of common-mode suppression. A practical configuration with 4 cells is designed based on the Low-Temperature Co-Fire Ceramic (LTCC) fabrication technology. It is found the common mode noise can be reduced by the structure over 10 dB from 3.8 GHz to 7.1 GHz (FBW = 60 %) and over 50% of amplitude in time domain. The differential signal integrity in terms of insertion loss and transmission phase still shows a good quality in the proposed filter.