Approximation-Based System Implementation for Real-Time Minimum Energy Point Tracking over a Wide Operating Performance Region

摘要

This paper refers to the optimal voltage pair, which minimizesthe energy consumption of LSI circuits under a target delay constraint,as a Minimum Energy Point (MEP). This paper proposes an approximationbasedimplementation method for an MEP tracking system over a widevoltage region. This paper focuses on the MEP characteristics that the energyloss is sufficiently small even though the voltage point changes nearthe MEP. For example, the energy loss is less than 5% even though theestimated MEP differs by a few tens of millivolts in comparison with theactual MEP. Therefore, the complexity for determining the MEP is relaxedby approximating complex operations such as the logarithmic or the exponentialfunctions in the MEP tracking algorithm, which leads to hardware-/software-efficient implementation. When the MEP tracking algorithm isimplemented in software, the MEP estimation time is reduced from 1 msto 13 s by the proposed approximation. When implemented in hardware,the proposed method can reduce the area of an MEP estimation circuit to aquarter. Measurement results of a 32-bit RISC-V processor fabricated in a65-nm SOTB process technology show that the energy loss introduced bythe proposed approximation is less than 2% in comparison with the MEPoperation. Furthermore, we show that the MEP can be tracked within about45 microseconds by the proposed MEP tracking system.