A Hybrid Adaptive Digital Delay Compensated Active Rectifier With PWM-Based Technique and Resistor-Array Tuning for Wireless Power Transmission

This article presents a resistor-array-tuning-based hybrid adaptive digital delay compensated rectifier for wireless power transfer systems. A no-crossing problem and nonlinearity problem for conventional delay-compensations are analyzed. In order to enhance the robustness of digital control, the on-delay and off-delay are compensated with different compensation schemes. The on-delay is compensated with a comparator-offset-adjusted technique, while the off-delay is compensated with a pulsewidth modulation (PWM)-based technique to guarantee falling zero-voltage crossing and adjust off-delay time linearly. Compared with the previous works, the delay time is adjusted by tuning the voltage drop across resistor arrays instead of changing the injected offset current of push–pull comparator so as to improve the power conversion efficiency (PCE) and loop stability. Implemented in a 0.18-$\mu$m BCD process with a total area of 0.446 mm$^{2}$, the rectifier delivered a maximum output power of 54.5 mW. With a 13.56 MHz ac input voltage in the range of 2.5 and 3.3 V, the measurement results show the peak VCR of 96.1$\%$ and peak PCE of 93.1$\%$ for the load resistance of 2 k$\Omega$ and 500 $\Omega$, respectively.