A 6.78 MHz CMOS Active Rectifier With Hybrid Mode Delay Compensation for Wireless Power Transfer Systems

Abstract

This paper proposes a 6.78MHz CMOS active rectifier for wireless power transfer (WPT) systems with adaptive hybrid mode (HM) on/off-delay compensation. Both conventional current mode (CM) and voltage mode (VM) delay compensation schemes are discussed in this paper. CM compensation has strengths in compensation accuracy and range but shortcoming in power consumption. VM compensation has an advantage in power consumption but weaknesses in compensation range and accuracy. To find a balance between power loss and compensation range, the proposed active rectifier adopted CM for on-delay compensation and VM for off-delay compensation. Furthermore, by adding sample-based feedback loops to generate offset voltage for comparators adaptively, both on/off delays are well-compensated under different input power and loading conditions. This active rectifier was designed and simulated in SMIC $0.18~\mu \text{m}$ CMOS process with 3.3V devices. By using HM compensation, this active rectifier can improve at least 10% in power loss compared with conventional CM compensation. With output DC voltage ranging from 1.6V to 3V and loading resistor from $200\Omega $ to 1K $\Omega $ , the peak power conversion efficiency (PCE) is 95.4% with $200\Omega $ loading, peak voltage conversion ratio (VCR) is 97.5% with $500\Omega $ and maximum output power can reach 45 mW.

Keywords

• Active rectifier
• reverse current
• current mode compensation
• voltage mode compensation
• power conversion efficiency
• voltage conversion ratio