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 c m of tissue to mm-sized antennae is demonstrated to be in the low G H z. 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 inaccuracy 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 4mm(2) antenna deliver 140 mu W at 1.2V DC from a 4cm(2) transmit antenna and a 250 mW, 915 M H z source through 15 mm of tissue. The rectifier efficiency is 65% for a 750mV amplitude received input. The power receiver IC incorporating the adaptive receive match, rectifier and regulator occupies 0.37mm(2) in 0.13 mu m CMOS.