Energy Efficiency of Low Swing Signaling for Emerging Interposer Technologies

Interconnects often constitute the major bottleneck in the design process of low power integrated circuits (IC). Although 2.5-D integration technologies support physical proximity, the dissipated power in the communication links remains high. In this work, the additional power savings for interposer-based interconnects enabled by low swing signaling is investigated. The energy consumed by a low swing scheme is, therefore, compared with a full swing solution and the critical length of the interconnect, above which the low swing solution starts to pay off, is determined for diverse interposer technologies. The energy consumption is compared for three different substrate materials, silicon, glass, and organic. Results indicate that the higher the load capacitance of the communication medium is, the greater the energy savings of the low swing circuit are. Specifically, in cases that electrostatic discharge (ESD) protection is required, the low swing circuit is always superior in terms of energy consumption due to the high capacitive load of the ESD circuit, regardless the substrate material and the link length. Without ESD protection, the highest critical length is about 380 μm for glass and organic interposers. To further explore the limits of power reduction from low swing signaling for 2.5-D ICs, the effect of typical interconnect parameters such as width and space on the energy efficiency of low swing communication is evaluated.