4 Gbps high-density AC coupled interconnection

AC coupled interconnects enable multi-gigabit-persecond communication data rates between integrated circuits with very high pin counts and low power consumption. AC coupling can be realized with either series capacitive or inductive coupling elements. Capacitive AC coupling offers better performance when low power I/O buffers are required and when there is sufficient area to dedicate to coupling capacitors in the top-level metal of each IC. At a slight expense of circuit complexity, inductive AC coupling can be used to bring I/O pad pitches down to 75 μm and maintain a controlled impedance connection. A novel physical structure, buried solder bumps, are used as a solution for providing DC power and ground connections across the same surface as the AC connections. When used in conjunction with NRZ-tolerant receivers, and current-mode signaling, highly effective interconnect structures can be built. As well as presenting both physical and circuit aspects of this work, experimental results are shown.