A novel common mode choke and its application for 5 Gbps USB 3.0

A novel compact common mode choke is proposed and realized without using ferrite materials. It is fabricated on LTCC substrate and possesses a small size of 1.2 mm × 2.0 mm. It provides over 10 dB common mode suppression from 1.4 GHz to 3.7 GHz and still maintains the differential signal transmission up to 8 GHz. To validate the common mode choke on USB 3.0 cable, a series of experimental tests are executed, including eye diagram for differential signal, common mode noise suppression, and elimination of common mode current on cables. The eye diagram for the filter board keeps obvious eye width and eye height and almost the same result with that for the reference board. About 57 % common mode suppression is achieved after placing the common mode filter on the board with 8 mm skew line. Moreover, the common mode current on cables related to far field radiation is also measured by current probe and eliminated over 10 dB within designed stopband by using the common mode choke.