Abstract-Subthreshold circuits have drawn a strong interest in recent ultralow power research. In this paper, we present a highly efficient subthreshold microprocessor targeting sensor application. It is optimized across different design stages including ISA definition, microarchitecture evaluation and circuit and implementation optimization. Our investigation concludes that microarchitectural decisions in the subthreshold regime differ significantly from that in conventional superthreshold mode. We propose a new general-purpose sensor processor architecture, which we call the Subliminal Processor. On the circuit side, subthreshold operation is known to exhibit an optimal energy point ( min ). However, propagation delay also becomes more sensitive to process variation and can reduce the energy scaling gain. We conduct thorough analysis on how supply voltage and operating frequency impact energy efficiency in a statistical context. With careful library cell selection and robust static RAM design, the Subliminal Processor operates correctly down to 200 mV in a 0.13-m technology, which is sufficiently low to operate at min . Silicon measurements of the Subliminal Processor show a maximum energy efficiency of 2.6 pJ/instruction at 360 mV supply voltage and 833 kHz operating frequency. Finally, we examine the variation in frequency and min across die to verify our analysis of adaptive tuning of the clock frequency and min for optimal energy efficiency. Index Terms-Sensor networks, subthreshold design, min , ultra low power design.
It is even possible to operate in the subthreshold regime and achieve excellent energy-efficiencies of 2.6 pJ/op at 320 mV and 833 kHz REF .
Energy-Efficient Subthreshold Processor Design
IEEE Transactions on Very Large Scale Integration (VLSI) Systems
IEEE Transactions on Very Large Scale Integration (VLSI) Systems
Computer Science