An ultra compact common-mode filter for RF Interference control in 3G wireless communication systems

A miniaturized common-mode suppression filter for GHz differential signals is realized using LTCC fabrication technology. The filter is realized in SMD-typed package with the physical size of 1.6 mm × 1.6 mm. Its equivalent circuit model is established to illustrate the properties of the common mode suppression and the differential mode propagation. It is found in measurement that the common-mode noise can be reduced over 10 dB from 1.8 GHz to 2.4 GHz in frequency domain, which covers the band of universal mobile telecommunication system (UMTS) in 3G wireless communication, and can be reduced about 30% in time domain under 1.4 Gbps PRBS. More importantly, the differential signal integrity, in terms of insertion loss and transmission phase in frequency domain and eye diagrams in time domain, is not degraded up to 5 GHz. To our best knowledge, it is the first SMD-type common-mode filter designed for gigahertz differential signals using LTCC technology.