Abstract
With remarkable advances in IoT, big data, and AI, the fourth industrial revolution is upon us. Low power design methodologies and techniques have been greatly contributing to these advancements by addressing the critical issue of how to increase the device service life under a fixed and limited energy source. In particular, ultra-low power (ULP) technology, which exploits ultra-low voltage (ULV) operating circuit, has recently emerged as a cutting-edge technology for realizing ULP devices. Although a number of studies on ULV circuits have been made so far, and the results have been very successful, research on DC–DC converters optimized for the ULV operation must be carried out in order to use them ultimately in ULP devices. In this paper, a DC–DC converter with low power, small area, and high-resolution digital pulse width modulator (DPWM) for ultra-low voltage (ULV) operating IoT platforms is presented. The proposed DPWM design uses a much smaller number of D flip-flops than conventional ones, achieving significant power saving and area reduction while showing excellent resolution of power conversion. In addition, by utilizing the proposed DPWM, the DC–DC converters can take full advantage of the dynamic switch width modulation technology without overhead, greatly improving the power conversion efficiency under ultra light load conditions. A prototype DC–DC converter with the proposed DPWM is fabricated in Samsung 65nm technology, and the experimental work with this converter and a target ULV operating platform demonstrates that this converter is best suited for the target platform.
Highlights
Ultra-low power (ULP) IoT platforms are drawing attention from academia [1,2] and industry [3,4]by offering the most practical solution on how to extend the service life of IoT devices under limited small energy sources such as thin film batteries, photovoltaic cells, and thermoelectric generators.These ULP IoT platforms rely on ultra-low voltage (ULV) operation with near-/sub-threshold voltage operating circuits, in which power consumption can be up to several hundred times lower than the nominal voltage operating circuits
The proposed DC–DC converter design measures the load condition using a digital code originally designed for use in determining the duty cycle of the PWM signal in the proposed digital pulse width modulator (DPWM), which allows the selection of the appropriate switch among several switches
This line clearly shows that, when Pload ≤ 750 μW, the efficiency is much higher than the black line without additional circuitry, the DC–DC converter utilizes only digital code (e.g., 0110000[2] ) in the proposed DPWM to selectively combine orange and blue lines to maximize efficiency under all load conditions
Summary
Ultra-low power (ULP) IoT platforms are drawing attention from academia [1,2] and industry [3,4]. By offering the most practical solution on how to extend the service life of IoT devices under limited small energy sources such as thin film batteries, photovoltaic cells, and thermoelectric generators These ULP IoT platforms rely on ultra-low voltage (ULV) operation with near-/sub-threshold voltage operating circuits, in which power consumption can be up to several hundred times lower than the nominal voltage operating circuits. There have been several previous works that focus on the extremely low voltage operating circuits (e.g., less than 0.4 V) [12,13], whereby the DC–DC converters are designed to supply extremely low voltage, and their maximum efficiency occurs only at certain very low voltages and rapidly decreases at other output voltages These converters are not suitable for the IoT platforms that operate at least at tens of MHz frequency. The details of the proposed converter design are elucidated
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