Optimum Temperatures for Enhanced Power Conversion Efficiency (PCE) of Zero-Bias Diode-Based Rectifiers

Ambient power rectifiers are pivotal for batteryless or self-powered internet of things architectures and self-sustained communication/sensor platforms. The core of rectifiers, a nonlinear device, has been subject to significant research and improvements recently, especially at a low-power level, where rectifying efficiency is so limited. Current responsivity (the key rectification parameter describing the nonlinearity) is known to be impacted by the operating temperature, as predicted by William Shockley's law. However, no work has been carried out to quantify the impact of temperature in the RF rectification process, nor to relate existing diodes with their optimum operating temperature range. To address those missing links, this article first develops an analytical method to predict power conversion efficiency (PCE) of rectifiers from approximate milli-watt down to nano-watt level. Next, it identifies the optimum operating temperature of rectifiers corresponding to peak PCE. It also reports that the previous PCE ceiling of 15% (at an input power level below -30 dBm) can be broken when rectifiers operate at their optimum temperatures. Enhanced PCE results are then validated experimentally on SMS7630 and HSMS-2850-based rectifiers when operating at their optimum temperatures. Noticeably, the SMS7630-based rectifier delivers efficiency of 17.5% at -30 dBm and 41.7% at -20 dBm, showing respectively comparable and better PCE than that of tunnel diode-based counterparts at similar power levels. This article also indicates that rectifier design should consider the operating temperature when selecting diodes to maximize rectifying potential.