A 40.68-MHz Active Rectifier With Cycle-Based On-/Off-Delay Compensation for High-Current Biomedical Implants

This article presents a 40.68-MHz active rectifier for high-current biomedical implants. Cycle-based timing control (CBTC) is proposed to significantly extend the duration for compensating both turn-on and turn-off delays of active diodes at 40.68 MHz, thereby improving both the power conversion efficiency (PCE) and the voltage conversion ratio (VCR) of the rectifier. The supply independent ramp, the delay-mimicking sample-and-hold (DMSH) circuit, and the low-voltage (LV)-stress startup scheme are also developed to maintain high PCE, and VCR, and ensure rectifier reliability over a wide input range. Implemented in standard 0.18-mu m CMOS, the proposed fully integrated rectifier delivers a maximum output power of 207 mW and operates at 40.68 MHz to enable the use of a small-diameter receiver coil of 4 mm. This rectifier is the first to achieve full turn-on and turn-off delay compensation at 40.68 MHz, so its maximum PCE and VCR obtain 86% and 96.3%, respectively. Compared with the prior art, this work not only provides more stable high PCE and VCR over a wider input range from 1.9 to 3.8 V at 40.68 MHz but also uses the smallest receiver coil for wireless power delivery.