Tracking energy efficiency of near-threshold design using process variation control techniques

Near-threshold operation offers energy efficiency at the expense of increased performance variability. Adaptive Voltage/Frequency Scaling (AVS/AFS) techniques can be used to mitigate performance variability, yet their impact on energy efficiency has not been characterized. This paper defines different system scenarios for near-threshold design and assesses the impact of AVS/AFS on energy efficiency for each case. It is found that AVS techniques are more effective for tracking energy efficiency in the case of low leakage systems, while AFS techniques provide better tracking in the high leakage case. Moreover, it is found that for near-threshold operating points chosen at relatively high supply voltages, both AVS and AFS show similar behavior regarding energy efficiency tracking. The analysis is validated using circuit level simulation of a logic data path on a 45 nm SOI process.