A High Efficiency and High Power Density Active AC/DC Converter for Battery-Less US-Powered IMDs in a 28-nm CMOS Technology

In this paper, the design and experimental validation of an active rectifier for ultrasound-based implanted biomedical devices are presented. One of the main contributions is the adoption of an optimized design procedure based on the
$g_{m}/I_{D}$
of the transistors. Implemented in a 28-nm CMOS technology and powered by a 0.5-mm thickness and 1-mm2 surface area piezoelectric transducer, the rectifier delivers 1-mW of power to the output load. The adoption of a square wave to drive the transmitting power transducer is experimentally demonstrated to be more power effective. The rectifier exhibits a measured peak power conversion efficiency and a power density equal to 95% and 222mW/
$mm^{2}$
, respectively, revealing itself as the best trade-off between measured power conversion efficiency and power density within the literature of US-powered AC/DC converters.