Optimal common-mode filter design for EMS improvement in TMDS structure including common-mode clock

Abstract

Transition Minimized Display Signal (TMDS) structure transmits differential data signal and the common mode clock signal through a single pair of differential signal transmission line. In mobile systems, RF transmitter (Tx) is a source of electromagnetic interference (EMI) that can degrade the electromagnetic susceptibility(EMS) of TMDS. In this paper, we adopt commercial common-mode filter (CMF) and perform an optimization study to ensure EMS performance of both the common mode clock and differential signal. Through electromagnetic and circuit simulation, it is shown that CMF of 50 ohm showed improved signal integrity of common-mode clock while removing RF Tx noise while securing eye opening specification of the differential-mode signal.