A Wireless Power Interface for Rechargeable Battery Operated Neural Recording Implants

This paper describes an integrated analog front-end for wireless powering and recharging of miniature Li-ion batteries used in implantable neural recording microsystems. DC signal extraction from a wireless carrier is accomplished using Schottky barrier contact diodes with lower forward voltage drop for improved efficiency. The battery charger employs a new control loop that relaxes comparator resolution requirements, provides simultaneous operation of constant-current and constant-voltage loops, and eliminates the external current sense resistor from the charging path. The accuracy of the end-of-charge detection is primarily determined by the voltage drop across matched resistors and current-sources and the offset voltage of the sense comparator. Experimental results in 0.6 mum bulk CMOS technology indicate that plusmn1.3% (or plusmn20 muA) end-of-charge accuracy can be obtained under worst-case conditions for a comparator offset voltage of plusmn5 mV. The circuits occupy 1.735 mm² with a power dissipation of 8.4 mW when delivering a load current of 1.5 mA at 4.1 V (or 6.15 mW) for an efficiency of 73%