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A full-wave active rectifier switching at 13.56 MHz with compensated bias current for a wide input range for wirelessly powered high-current biomedical implants is presented. The four diodes of a conventional passive rectifier are replaced by two cross-coupled PMOS transistors and two comparator- controlled NMOS switches to eliminate diode voltage drops such that high voltage conversion ratio and power conversion efficiency could be achieved even at low AC input amplitude |VAC|. The comparators are implemented with switched-offset biasing to compensate for the delays of active diodes and to eliminate multiple pulsing and reverse current. The proposed rectifier uses a modified CMOS peaking current source with bias current that is quasi-inversely proportional to the supply voltage to better control the reverse current over a wide AC input range (1.5 to 4 V). The rectifier was fabricated in a standard 0.35 μm CMOS N-well process with active area of 0.0651 mm(2). For the proposed rectifier measured at |VAC| = 3.0 V, the voltage conversion ratios are 0.89 and 0.93 for RL=500 Ω and 5 kΩ, respectively, and the measured power conversion efficiencies are 82.2% to 90.1% with |VAC| ranges from 1.5 to 4 V for RL=500 Ω.

This paper examines the various design of a multiple-purpose portable functional electrical stimulator which is used in surface stimulation of paralyzed muscle of patients with stroke and results in limb activation. The functionality, circuit performance and reliability of the circuits will be examined. Analysis, design, and experimental results are presented.

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This paper discusses the near-field inductive coupling wireless power transfer (WPT) at the system level, with detailed analyses on each state-of-the-art WPT output voltage regulation topologies. For device miniaturization and power loss reduction, several novel architectures for efficient WPT were proposed in recent years to reduce the number of passive components as well as to improve the system efficiency or flexibility. These schemes are systematically studied and discussed in this paper. The main contribution of this paper is to provide design guidelines for WPT system design. In addition, possible combinations of the WPT building block configurations are summarized, compared, and investigated for potential new architectures.

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