A mm-sized implantable power receiver with adaptive matching

A wireless power transfer system for implanted medical devices which uses antenna area 100 times smaller than previous designs is presented. The optimum frequency for wireless power transmission through several cm of tissue to mm-sized antennae is demonstrated to be in the low GHz. Simultaneous conjugate matching is introduced which achieves 15dB higher link gain than resonant tuning for this link and adaptive matching circuits desensitize the link to placement in accuracy and tissue variation. For a 1mm placement inaccuracy the link gain with static matching would fall by 3.7dB but with adaptive matching the gain reduces by only 0.2dB. A high efficiency current-steering rectifier and regulator are developed which together with a 4mm² antenna deliver 140μW at 1.2V DC from a 4cm² transmit antenna and a 250mW, 915MHz source through 15mm of tissue. The rectifier efficiency is 65% for a 750m V amplitude received input. The power receiver IC incorporating the adaptive receive match, rectifier and regulator occupies 0.37mm² in 0.13μm CMOS.