A Supply Voltage Control Method for Performance Guaranteed Ultra-Low-Power Microcontroller

This article presents the control circuit of a power converter that regulates the computing speed of a digital circuit. The proposed circuit implements a digital delay regulation of a digital delay line (DDL) matched with the ring oscillator (RO) that clocks the digital subsystem. The converter regulates the supply voltage of the digital subsystem so that the propagation delay through the DDL matches a time reference. Consequently, the frequency of the RO tracks the DDL delay and the frequency keeps a controlled value over process, voltage, and temperature (PVT). A 65-nm CMOS prototype validates the proposed method. The prototype includes an Arm Cortex-M33 CPU and memories optimized for sub-threshold operation. With the proposed method, the computing performance of the CPU is guaranteed for running real-time application while minimizing the supply voltage margins.

I. Introduction

Ultra-low-power microcontroller systems with a total operating power of a few require new power management techniques. First, most Internet of Things (IoT) circuits are designed to operate from power sources with variable voltage such as a discharging battery or energy harvester front ends. Second, maximizing the Energy per Cycle figure of the digital subsystem is essential to save power. Third, the power-dissipation of the control block of the power converter must dissipate significantly less power than the digital subsystem itself.