High-efficiency crossbar switches using capacitively coupled signaling

As process technologies have scaled, the increasing number of processor cores and memories on a single die has also driven the need for more complex on-chip interconnection networks. Crossbar switches are primary building blocks in such networks-on-chip, as they can be used as fast single-stage networks or as the core of the router switch in multi-stage networks. While crossbars offer non-blocking, single-hop, all-to-all communication, they tend to scale poorly with the number of nodes due to the latency and energy of the long wires and high-radix multiplexor structures needed. To combat these limitations, we propose a low-swing crossbar design that uses capacitively driven wires and capacitively coupled multiplexers. Capacitively driven wires offer low swing signaling, higher bandwidths, and low energy consumption, while capacitively coupled multiplexers offer reduced parasitic loading from the inactive inputs. We present a 16×16 64b low-swing crossbar switch designed in a TSMC 40nm CMOS bulk process. Post-layout simulation shows it operating at a maximum frequency of 2.2GHz, achieving a bandwidth of 2.56Tb/s at 0.9V (nominal Vdd) with an area of 0.94mm². Total energy consumption for full, half, and minimum bandwidths are 110pJ, 84pJ, and 64pJ respectively, thus offering an efficiency of 10.49 Tbps/W, a 3X improvement over previously published results.