Signaling over chip-scale global interconnect is consuming a larger fraction of total power in large processor chips, as processes continue to shrink. Solving this growing crisis requires simple, low-energy and area-efficient signaling for high-bandwidth data buses. This paper describes a balanced charge-recycling bus (BCRB) that achieves quadratic power savings, relative to signaling with full-swing CMOS repeaters. The scheme stacks two CMOS repeated wire links, one operating in the Vtop domain, between Vdd and Vmid=Vdd/2, the other, Vbot, between Vmid and GND. Unlike previous work, we require no voltage regulator to maintain the Vmid voltage at Vdd/2, to compensate for differences in data activity in Vtop and Vbot domains. The BCRB also uses simple single-ended signaling, to achieve higher bandwidth per unit bus width than differential buses and lower signaling energy than precharging schemes, since we take full advantage of low switching activity and bus-invert coding.
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