Analysis and Design of an 8.5-Gb/s/Link Multi-Drop Bus Using Energy-Equipartitioned Transmission Line Couplers

An 8.5-Gb/s/link non-contact multi-drop bus is presented. The signal reflections that limit the data rates of conventional multi-drop bus interfaces are dramatically reduced by using transmission line couplers at each signal branching point. As an energy-equipartitioned technique provides the same signal level to every port, wider receiver margin is achieved. The data rate is improved by 1.8 times compared to the most advanced multi-drop bus interface. The theoretical analysis and design techniques of energy-equipartitioned transmission line couplers are discussed in this paper. The design methodologies were verified through simulations performed by using a full-3D EM-simulator and experiments with FR4 test boards. Due to the low-cut characteristics of the couplers, the low-frequency components are cut off so that differentiated pulses arrive at the receiver input point. A receiver detects and recovers the received pulses by integrating them using hysteresis characteristics. The design techniques of the transceiver for the transmission line couplers are also discussed in this paper. The proposed methods were verified by using a test chip fabricated with a 90-nm CMOS process. Experiments with a prototype of an eight-drop multi-drop bus system confirmed at a data rate of 8.5-Gb/s/link. The measured timing margin at the far-end module was 0.49-UI at a BER of 10^-12. The power consumption of the transceiver was 75.6-mW at a supply voltage of 1.2-V.