Ringing Noise Suppression for Differential Signaling in Unshielded Flexible Flat Cable

For the system requirement of higher density and increasing data rate, flexible flat cable (FFC) becomes a popular solution. When FFC is used for differential signaling, the voltage levels on ground lines differ from each other along the length of FFC. Moreover, the resonant effect caused from crosstalk noise reduces the signal quality. Modal analysis is applied in this paper for deriving two fundamental differential modes. Time delay differences for two modes are also calculated for various FFC structures. In order to suppress the resonant ringing noise, a novel approach to eliminate the time delay difference is proposed. A design chart is also proposed to give the best design region for FFC. The frequency and time domain simulation results validate the design chart. After minimizing the delay difference, the eye height improves 29%. The crosstalk effect is also considered to elaborate the improvement of resonance suppressing. At last, scattering parameters and differential impedance of FFC are also measured for verification.