An ultra-low power RF interface for wireless-implantable microsystems

This paper presents an efficient radio frequency (RF) front-end for power and data telemetry in biomedical implantable devices. The fully integrated system includes amplitude shift keying (ASK) demodulator, low drop out (LDO) power regulator, full wave voltage rectifier and limiter circuit. The demodulator utilizes a new ultra low power envelope amplifier that removes the need for any voltage comparator or Schmitt trigger circuit. With a carrier frequency of 12 MHz and 1 Mbps data rate, the proposed ASK demodulator achieves a modulation index range from 5% up to 100% while consuming less than 35 μW from induced power. The regulator can provide a maximum stimulation current of 1.2 mA under a ripple suppressed 3.3 V supply. Designed in a 0.18 μm CMOS process, the system totally draws about 35 μA excluding the stimulation current.