This paper describes Boost Logic, a logic family which relies on voltage scaling, gate overdrive, and energy recovery, to achieve high energy efficiency at GHz frequencies. The key feature of our design is an energy recovering "boost" stage that provides a high gate overdrive to an aggressively voltage-scaled logic at near-threshold supply voltage. We have evaluated Boost Logic through post-layout simulation of an 8-bit carry-save multiplier in a 0.13μm CMOS process with Vth=340mV. At 1.6GHz and 1.3V supply voltage, the Boost multiplier dissipates 8.11pJ per computation, yielding 68% energy savings over its pipelined, voltage-scaled static CMOS counterpart. Using low Vth devices, the Boost Logic multiplier has been verified to operate at 2GHz with a 1.25V voltage supply and 8.50pJ energy dissipation per cycle

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 fCV/sup 2/ 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.

We have recently designed, fabricated, and successfully tested an experimental chip that validates a novel method for reducing clock dissipation through energy recovery. Our approach includes a single-phase sinusoidal clock signal, an L-C resonant sinusoidal clock generator, and an energy recovering flip-flop. Our chip comprises a dual-mode ASIC with two independent clock systems, one conventional and one energy recovering, and was fabricated in a micron bulk CMOS process. The ASIC computes a pipelined discrete wavelet transform with self-test and contains over 3500 gates. We have verified correct functionality and obtained power measurements in both modes of operation for frequencies up to 225MHz. In the energy recovering mode, our power measurements account for all of the dissipation factors, including the operation of the integrated resonant clock generator, and show a net energy savings over the conventional mode of operation. For example, at 115MHz, measured dissipation is between 60% and 75% of the conventional mode, depending on primary input activity. To our knowledge, this is the first ever published account of a direct experimentally-measured comparison between a complete energy recovering ASIC chip and its conventional implementation correctly operating in silicon at frequencies exceeding 100MHz.

With increasing clock frequencies and silicon integration, power aware computing has become a critical concern in the design of embedded processors and systems-on-chip. One of the more effective and widely used methods for power-aware computing is dynamic voltage scaling (DVS). In order to obtain the maximum power savings from DVS, it is essential to scale the supply voltage as low as possible while ensuring correct operation of the processor. The critical voltage is chosen such that under a worst-case scenario of process and environmental variations, the processor always operates correctly. However, this approach leads to a very conservative supply voltage since such a worst-case combination of different variabilities is very rare. In this paper, we propose a new approach to DVS, called Razor, based on dynamic detection and correction of circuit timing errors. The key idea of Razor is to tune the supply voltage by monitoring the error rate during circuit operation, thereby eliminating the need for voltage margins and exploiting the data dependence of circuit delay. A Razor flip-flop is introduced that double-samples pipeline stage values, once with a fast clock and again with a time-borrowing delayed clock. A metastability-tolerant comparator then validates latch values sampled with the fast clock. In the event of timing error, a modified pipeline mispeculation recovery mechanism restores correct program state. A prototype Razor pipeline was designed in a 0.18 /spl mu/m technology and was analyzed. Razor energy overhead during normal operation is limited to 3.1%. Analyses of a full-custom multiplier and a SPICE-level Kogge-Stone adder model reveal that substantial energy savings are possible for these devices (up to 64.2%) with little impact on performance due to error recovery (less than 3%).

In this paper, we present the design and experimental evaluation of an 8-bit energy-recovery multiplier with built-in self-test logic and an internal single-phase sinusoidal power-clock generator. Both the multiplier and the built-in self-test have been designed in SCAL-D, a true single-phase adiabatic logic family. Fabricated in a 0.5-/spl mu/m standard n-well CMOS process, the chip has an active area of 0.47 mm/sup 2/. Correct chip operation has been verified for clock rates up to 140 MHz. Moreover, chip dissipation measurements correlate well with HSPICE simulation results. For a selection of biasing conditions that yield correct operation at 140 MHz, total measured average dissipation for the multiplier and the power-clock generator is 250 pJ per operation.

This paper proposes an energy-recovering (a.k.a. adiabatic) static RAM with a novel driver that reduces power dissipation by efficiently recovering energy from the bit/word line capacitors. Powered by a single-phase sinusoidal power-clock, our SRAM delivers read and write operations with single-cycle latency. To that end, a precharge-low scheme is employed along with a modified sense amplifier design that achieves high efficiency at differential voltages near V/sub SS/. A simple control circuit is used to maintain driver operation in synchrony with the power-clock waveform. Feedback circuitry from the driver output to the control circuit ensures that out driver remains efficient, independent of the access pattern. Our energy recovering SRAM functions correctly while achieving substantial energy savings over a wide range of supply voltages and operating frequencies. Hspice simulations of a simple full-custom adiabatic 256/spl times/256 SRAM, that includes the energy recovering bit/word line drivers, the cell array, and the sense amplifiers, show over 2.6x energy savings at 3V, 300MHz in comparison with its conventional counterpart.

This paper presents the design and evaluation of an 8-bit adiabatic multiplier. Both the multiplier core and its built-in self-test logic have been designed using a true single-phase adiabatic logic family. Energy is supplied to the adiabatic circuitry via a sinusoidal power-clock waveform that is generated on-chip. In HSPICE simulations with post-layout extracted parasitics, our design functions correctly at clock frequencies exceeding 200 MHz. The total dissipation of the multiplier core and self-test circuitry approaches 130pJ per operation at 200MHz. Our 11,854-transistor chip has been fabricated in a 0.5&mgrm standard CMOS process with an active area of 0.470mm$^2$. Correct chip operation has been validated for operating frequencies up to 130MHz, the limit of our experimental setup. Measured dissipation correlates well with HSPICE simulations.

Recently discovered high-speed single-phase adiabatic logic families require efficient sinusoidal power-clock generators. In this paper we propose a low-power resonant clock-generator built around a zero-voltage switching push-pull power conversion topology. We describe a novel energy-efficient control circuit for this power converter, based on an asynchronous CMOS state machine. We also describe an integrated sub-micron CMOS implementation of our power converter and control circuits. Simulation results show efficiencies in excess of 90%, even under suboptimal tuning conditions, for frequencies over 200MHz. We have fabricated our clock generator in a 0.5�m standard CMOS process. Using an external surface-mount inductor as the resonant element, we have verified the correct operation of the clock generator when driving a singlephase adiabatic 8-bit multiplier.