27.3 A 210mV 5MHz variation-resilient near-threshold JPEG encoder in 40nm CMOS

Operating circuits in the near-threshold region enables large energy savings. However, such circuits also pose many challenges, such as increased delay, unwanted leakage paths and high sensitivity to variations. Working in advanced nanometer CMOS technologies compromises the robustness of circuits even more due to the increased variability. Nonetheless, these technologies offer higher operating frequencies for ultra-low-voltage circuits. Transitioning to smaller technologies is attractive for digital near-threshold circuits, provided that the impact of the increased variability can be mitigated. Few prior works have considered the design of variation-resilient ultra-low-voltage circuits in CMOS technologies smaller than 65nm. The aim of this work is to design a large system that advances the state-of-the-art by not only reaching very low energy consumption, but also clock frequencies of tens of MHz, while providing high variation resilience. We present a full JPEG encoder fabricated in a 40nm CMOS technology, fully functional down to a supply voltage of 210mV. The JPEG encoder is able to operate at clock frequencies in a range from 5 to 275MHz for supplies from 210 to 550mV, and thus achieves very high ultra-low-voltage speed. At the minimum-energy point (MEP), the JPEG encoder consumes only 29.01pJ/pixel at an operating frequency of 41MHz (V_DD=330mV). The variation (σ/μ) of 26 dies at this point is only 9.4% for the frequency and 6.0% for the energy consumption.