A Differential Rectifier With VTH Compensation for High-Frequency RF Inputs.

A CMOS differential-drive bootstrap (BS) rectifier achieving an efficient dynamic threshold voltage ( VTH)-drop compensation at high-frequency RF inputs is proposed for small biomedical implants with wireless power transmission. A bootstrapping circuit with a dynamically controlled NMOS transistor and two capacitors is proposed to implement a dynamic VTH-drop compensation (DVC). The proposed bootstrapping circuit dynamically compensates the VTH drop of the main rectifying transistors by generating a compensation voltage only when the compensation is required, improving the power conversion efficiency (PCE) of the proposed BS rectifier. The proposed BS rectifier is designed for an ISM-band frequency of 433.92 MHz. A prototype of the proposed rectifier is co-fabricated in a 0.18- µm standard CMOS process with another configuration of the rectifier and two conventional BS rectifiers for fair performance comparison at various conditions. According to the measurement results, the proposed BS rectifier achieves better DC output voltage level, voltage conversion ratio, and PCE than the conventional BS rectifiers. With 0-dBm input power, 433.92-MHz frequency, and 3-k Ω load resistor, the proposed BS rectifier achieves a peak PCE of 68.5%.