Thermal Effects on Low-Power RF-to-dc Voltage Multiplier for Battery-Free Sensing and IoT

This work investigates and demonstrates the thermal effects on low-power RF-to-dc voltage multipliers based on Schottky diodes. Such a voltage multiplier is crucial to leverage dc output voltage rectified from low RF input power to meet the threshold voltage of battery-free sensors and Internet of Things devices. An analytical model is developed, considering thermal-sensitive diode SPICE parameters. The accuracy of this model has been verified based on a result comparison with commercial ADS Harmonic Balance simulator. The analytical model predicts the optimum operating temperature for enhanced RF-to-dc conversion efficiency. Further experimental results show that a 5stage voltage multiplier based on SMS7630 has an optimum temperature of $7.5^{\circ}\mathrm{C}$ at -25 dBm. This work can offer a reference or benchmark for optimizing RF-to-dc voltage multipliers at their operating temperatures and avoiding potential service interruptions due to temperature variations.