Charge-recovery computing on silicon

Three decades ago, theoretical physicists suggested that the controlled recovery of charges could result in electronic circuitry whose power dissipation approaches thermodynamic limits, growing at a significantly slower pace than the fCV² rate for CMOS switching power. Early engineering research in this field, which became generally known as adiabatic computing, focused on the asymptotic energetics of computation, exploring VLSI designs that use reversible logic and adiabatic switching to preserve information and achieve nearly zero power dissipation as operating frequencies approach zero. Recent advances in CMOS VLSI design have taken us to real working chips that rely on controlled charge recovery to operate at substantially lower power dissipation levels than their conventional counterparts. Although their origins can be traced back to the early adiabatic circuits, these charge-recovering systems approach energy recycling from a more practical angle, shedding reversibility to achieve operating frequencies in the hundreds of MHz with relatively low overhead. Among other charge-recovery designs, researchers have demonstrated microcontrollers, standard-cell ASICs, SRAMs, LCD panel drivers, I/O drivers, and multiGHz clock networks. In this paper, we present an overview of the field and focus on two chip designs that highlight some of the promising charge recovering techniques in practice.