A near-optimum 13.56 MHz active rectifier with circuit-delay real-time calibrations for high-current biomedical implants

This paper presents a 13.56MHz active rectifier with enhanced power conversion efficiency (PCE) and voltage conversion ratio (VCR) for high-current biomedical implants. Near-optimum operation with compensated circuit delays is achieved by the proposed real-time NMOS on/off calibrations, which minimize the reverse current and maximize the transistor conduction time under various process, voltage, temperature and loading conditions. Adaptive sizing (AS) is also introduced to optimize the PCE over a wide loading range. Measurements in TSMC 65nm show more than 36% and 17% improvement in PCE and VCR, respectively, by the proposed techniques. With 2.5V input amplitude, the rectifier achieves a peak PCE of 94.8% with an 80Ω loading, a peak VCR of 98.7% with a 1kΩ loading, and a maximum output power of 248.1mW.