Periodic Ground Structure for C-PHY Signaling in Mobile Applications

In this paper, we propose periodic slit ground structure (PSG) to improve the signal integrity of multilevel signals at high data rate such as MIPI C-PHY. Periodic slits are added in the upper and lower ground planes of the stripline structure, without adding additional layers or increasing area, to reduce crosstalk among neighboring lines. The proposed PSG structure can effectively improve the eye-diagram, especially eye height (EH) in multilevel signaling. The effectiveness of the proposed structure is validated through simulation and measurement of PCB-flexible printed circuit board (FPCB)-PCB structure that emulates the interconnected system of MIPI C-PHY signal transmission in a mobile system. The measurements from the test structures show that at a 2.5 Gsps data rate condition, the PSG structures show improvement in EH and eye width (EW) by 38.6% and 9.7%, respectively, compared to stripline structures. The proposed idea can be generally applied in PCB designs that will be used in high speed multilevel signal transmission to improve EH.