Optimal common-mode choke selection for the high definition video interface for the mobile application

Common-mode choke (CMC) is commonly used for filtering out common-mode noise. For differential interfaces, it is simple to select proper CMC by evaluating if CMC has high enough common-mode attenuation and low enough differential attenuation. However, it becomes more complicated if CMC is necessary for Mobile High-Definition Link (MHL). It is because MHL sends common-mode clock as well as differential data through a single pair of wires or interconnect media at the same time. Common-mode clock has to be carefully managed by transmitter circuit itself and CMC in order to minimize radiated emission while providing good quality clock signal enough to meet MHL specification. In this paper, optimal selection method of CMC for MHL application is proposed. As a result of the proposed method, base guideline of CMC for MHL application has been provided based on EMI, clock jitter, clock slew rate and data jitter measurements for various CMCs.