Self-oscillating switched-capacitor DC-DC converter for energy harvesting
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Solution Overview
Problem
Efficient DC-DC up-conversion at low power levels, such as those encountered in mm-scale wireless systems and implantable devices, is challenging due to the size limitations of batteries and the inefficiencies of existing switched-capacitor (SC) converters, which are constrained by clock generation and level-conversion overheads.
Innovation Solution
A fully integrated self-oscillating switched-capacitor energy harvester is developed, featuring cascaded voltage doublers with internalized oscillators that reduce clocking power overhead, allowing operation with very weak power sources and enabling a wide load range by configuring the conversion ratio through modulating the low voltage applied to each doubler stage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If switched-capacitor DC-DC converters are used for energy harvesting at low power levels, then the system can be fully integrated on-chip with small form factor, but the conversion efficiency is constrained by clock generation and level-conversion overheads
Solution Approach 1:
The patent extracts and eliminates the separate clock generation circuitry from the switched-capacitor converter. The oscillator is fully integrated within the SC converter itself, removing the need for external clock sources and associated level-conversion overheads that were consuming significant power at low operating levels.
Solution Approach 2:
The patent creates a universal self-oscillating SC converter that can operate across an extremely wide load range (1000x) by completely integrating clock generation within the converter. This multi-functional design allows the same circuit to efficiently handle both clock generation and power conversion without requiring separate control circuits.
2Power
If conventional SC converters operate at very low power levels (tens of nW), then they can power mm-scale wireless systems, but the clock generation overhead becomes dominant and reduces efficiency
Solution Approach 1:
The patent implements self-service by making the SC converter self-oscillating. The converter generates its own clock signals internally through integrated oscillators, eliminating the need for external clock sources. This self-sustaining operation allows the device to function autonomously at ultra-low power levels without being burdened by external clocking overheads.
3Power
If the number of cascaded voltage doublers is increased to achieve higher conversion ratios, then the output voltage can be boosted, but the power overhead and complexity increase
Solution Approach 1:
The patent applies dynamics by making the converter reconfigurable. The number of active voltage doubler stages can be dynamically adjusted based on the desired output voltage and load conditions. This dynamic reconfiguration allows the system to optimize between conversion ratio and power overhead, activating only the necessary number of stages rather than always operating at maximum complexity.
Data Source
AI summary
A self-oscillating DC-DC converter structure is proposed in which an oscillator is completely internalized within the switched-capacitor network. This eliminates power overhead of clock generation and level shifting and enables higher efficiency at lower power levels. Voltage doublers are cascaded to form a complete energy harvester with a wide load range from 5 nW to 5 μW and self-starting operation down to 140 mV. Because each doubler is self-oscillating, the frequency of each stage can be independently modulated, thereby optimizing the overall conversion efficiency.