Crosstalk Suppression Technique for Multi-Wire High-Speed I/O Links

The use of differential signaling in modern high-speed serial data communication systems has enabled multiple Gb/s data rates. To sustain the growth of I/O bandwidth requirements, raising the signaling frequency of data links and the number of package I/O pins poses tremendous challenges because of the harsh signaling environment of FR4 printed circuit boards and the costs of die areas and IC packages. Simultaneous differential- and common-mode signaling can improve pin utilization and aggregate data bandwidth without increasing the signaling frequency of the high-speed transceivers. However, because inevitable transmission-line and circuit mismatches could cause signal crosstalk between the differential- and common-mode links, the achievable data bandwidth and power efficiency of this signaling approach are seriously limited.;A crosstalk cancellation technique based on the Code Division Multiple Access (CDMA) principles was proposed to suppress crosstalk in high-speed I/O systems. The technique effectively suppresses in-band crosstalk power by using a simple analog variant of CDMA. This concept has been verified by a CDMA-based four-wire signaling transceiver in a 90 nm standard CMOS technology. The transceiver achieved 16 Gb/s aggregate data rate (5.33 Gb/s/link) and 6 mW/Gb/s/wire power efficiency over four 6" FR4 PCB traces with BER < 10-12. Compared to conventional simultaneous differential- and common-mode signaling systems, the CDMA-based system provides 30x ∼ 100x improvement in BER.;This thesis is focusing on the theoretical analysis and transceiver implementation of the CDMA-based crosstalk cancellation technique. Furthermore, simplified mathematic expressions of crosstalk power are derived to reasonably estimate the residual crosstalk power in both conventional and CDMA-based systems. This crosstalk analysis approach can be applied to any NRZ high-speed serial link I/O system as long as the frequency domain responses of crosstalk conversion or coupling paths can be reasonably characterized. Finally, the application of the CDMA-based technique in on-chip digital communication systems for suppressing capacitive coupling between adjacent links is discussed.