An Arithmetic VCR DC–DC Converter for Self-Powered Systems Using Decaying and Degrading Energy Sources

Energy sources such as biofuel cells, microbial fuel cells, zinc-air batteries, etc., exhibit gradual voltage degradation due to substrate depletion, electrolyte evaporation, and environmental factors, requiring efficient power regulation for continuous operation in energy-constrained IoT sensor nodes. A low-ripple multi-cell switched-capacitor DC-DC converter with arithmetic progression voltage conversion ratio (VCR) change is presented to address this challenge. The design eliminates bulky external load capacitors by implementing dual-stage complementary switching, thereby reducing output ripple while enabling compact integration suitable for miniaturized IoT sensor nodes. A floating N-well stacked MIM-on-MOS capacitor implementation minimizes bottom-plate parasitic losses, improving power conversion efficiency (PCE) across varying VCR modes. The arithmetic progression multi-cell (A-PMC) converter dynamically adjusts VCR transitions in 0.125× increments between 0.5× and 2.0× using a simple finite-state machine (FSM)-based control, enabling a gradual increase in VCR w.r.t input voltage decay without complex real-time feedback. Fabricated in a 65nm bulk CMOS process, the design occupies 1.28 mm², operates across a frequency range of 5 kHz to 250 kHz, and supports input voltages from 0.3 V to 1.8 V. The converter achieves a peak PCE of 88.81% at 2× VCR (93.76% at 1× VCR), with a power density of 0.1565 mW/mm². The converter’s performance is validated under multiple realistic input decay profiles relevant to IoT applications. The combination of fine-grained VCR control, ripple reduction, and optimized parasitic minimization enhances PCE and stability, making this converter well-suited for energy-harvesting and IoT-compatible applications.