A Full-Wave CMOS Rectifier with High-Speed Comparators for Implantable Medical Devices

In this paper, we present a CMOS full-wave rectifier with comparator-controlled switches for transmission of wireless power in implantable medical devices. It uses MOS transistors as low loss switches to provide high power conversion efficiency (PCE). The proposed fast comparator circuit, by controlling the switches in the rectifier, reduces the reverse leakage current in the negative cycle and increases the conduction time in the positive cycle so that more current flows into the output load and optimizes the rectifier power efficiency. The designed comparator does not require constant voltage source for its function and it is self-biased. The proposed rectifier is implemented using 0.18 mu m CMOS technology and provides 1.195V output DC voltage with a 190 Omega load resistance and AC input signal with the frequency of 13.56 MHz and peak-to-peak amplitude of 1.36 V. Under these conditions, PCE and voltage conversion efficiency (VCE) values are 85.5% and 88%, respectively. The peak PCE and VCE increase with a decrease in operation frequency and dimensions of transistors are optimized using multiple simulations for intended frequency.