A closed-loop power control function for bio-implantable devices

A wireless communication system with a closed-loop power control function for bio-implantable applications is described which keeps the power dissipation of implantable unit at the allowable level for human body. The function is controlled by monitoring an excessive current at the implantable unit and limiting the power transmission at the external interrogator unit. The implantable unit with the closed-loop power control function has been fabricated in a standard 0.18 mum CMOS technology, achieved less than 530 muW with a 1.8 V and the chip core size of 0.14 mm². The system uses inductive coupling at 13.56 MHz with internal and external coils. Experimental results confirm its stable power supply to the implantable unit over a coil distance of 0.5 to 10 mm.