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Sub-microWatt Scalable SoC

This work presents an ultra-low-power (ULP) internet-of-things (IoT) system-on-chip (SoC) using a triple-mode power management unit (PMU) to achieve self-adaptive power-performance scaling and energy-minimized operation. The proposed PMU comprises three modes: energy-aware mode, performance-aware mode, and minimum energy point (MEP) tracking mode. By controlling a microprocessor with the three modes, the SoC can adaptively scale its frequency and supply voltage based on either the input energy availability or the task priority. To achieve robust and rapid mode transitions, the SoC adopts fast dynamic voltage and frequency scaling (DVFS) and fast load transient response through asynchronous control. For energy-minimized operation, a sub-nW constant-energy-cycle algorithm keeps the microprocessor operating at the MEP with a 0.026 mm2 area overhead. In addition, the on-chip integration of a bias generator, clock, and power-on-reset block empowers the SoC to be a fully self-contained system. Fabricated in 65 nm CMOS, measurement results show that the SoC has a minimum power consumption of 194.3 nW at 180 Hz. The proposed PMU achieves 5.2 nW quiescent power and 92.6% peak efficiency meanwhile maintaining >80% efficiency from 190 nW to 3 mW. The MEPT circuits achieve <2.3% energy per cycle error and <18 mV voltage tracking error. The measured quiescent power of the MEPT circuits in the idle mode is 379 pW, which only accounts for 0.19% of the total system power. Measurements of the triple-mode transitions show that this SoC is well suited for resource-constrained IoT applications.

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