Concurrent Multipoint-to-Multipoint Communication on Interposer Channels
Abstract: Chip-to-chip communication for next generation computing will require larger bandwidth density to support ever increasing data traffic between processors, memories and I/O. 3-D integration enables a large number of processor and memory chips to be densely packed on an interposer with fine-pitch interconnect lanes. Advanced signaling techniques such as pulse amplitude modulation (PAM) can be employed to improve bandwidth per lane. Most recent work on interposer-based chip-to-chip interconnects focus primarily on point-to-point serial links. Without adding costly routers, these designs will severely limit the overall system level concurrency. In this paper, we propose an ultrahigh-speed multipoint-to-multipoint link design for interposer channels, which supports PAM signaling. Each node on the link can send, receive, drop, or relay data at line rate without complex routing. This design enables splitting the physical link into segments, and allows multicast/broadcast. A proof-of-concept system prototype with up to 16 nodes integrated on a silicon interposer with up to 22-mm node spacing is designed and evaluated using circuit and system simulations. The PAM-4 transceiver and link interface circuits at each node are implemented using a standard 130-nm SiGe BiCMOS technology. The transceiver can achieve a data rate of 40-Gb/s/lane, with channel loss of -3.5 dB per segment at Nyquist frequency, and energy efficiency between 1.29-pJ/b between two neighboring nodes or 0.21-pJ/b more per additional nodes. Using a cycle-level system simulation, such a high-concurrency communication fabric can improve overall performance between 2% to 18% over baseline.
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