A 434-MHz Bootstrap Rectifier With Dynamic ${V}_{\text{TH}}$ Compensation for Wireless Biomedical Implants

This letter presents a fully differential CMOS bootstrap rectifier with an effective dynamic threshold voltage (i.e., ${V}_{\text{TH}}$ ) compensation (DVC). The bootstrapping circuit for DVC, which consists of a dynamically biased transistor, a series resistor, and a parallel capacitor, dynamically generates a compensation voltage for the main rectifying pass transistors only when the ${V}_{\text{TH}}$ compensation is required. It significantly increases the proposed rectifier's power conversion efficiency (PCE) compared to other bootstrap rectifiers. The proposed rectifier operates at an industrial, scientific, and medical (ISM) band frequency of 434 MHz, and it is fabricated in a 0.18- $\mu$ m CMOS process together with two conventional bootstrap rectifiers for performance comparison. Measurement results validate that the proposed rectifier outperforms the conventional bootstrap rectifiers in terms of the output dc voltage level, voltage conversion ratio, and PCE. The proposed rectifier attains a peak PCE of 71 $\%$ at a load resistor of 3 k $\Omega$ and an operating frequency of 434 MHz.