Wireless Amperometric Neurochemical Monitoring Using an Integrated FSK Telemetry Circuit

A low-power integrated circuit for real-time wireless monitoring of neurochemical activity in the central nervous system is described. The chip is capable of conducting high-resolution amperometric measurements in four input-current settings. The chip architecture includes a current-based, first-order, sigma-delta analog-to-digital converter (LA ADC) and a frequency-shift-keyed (FSK) voltage-controlled oscillator (VCO) operating near 433MHz. It is fabricated using the AMI 0.5mum double-poly triple-metal n-well CMOS process, and requires only one off-chip component for operation. In a truly wireless fashion, measured dc current resolutions of 250fA, ~1.5pA, ~4.5pA and ~17pA were achieved for input currents in the range of plusmn5nA, plusmn 37nA, plusmn 150nA and plusmn 600nA, respectively, at a decimated sampling rate of 100Hz for all ranges. The ADC core and the VCO consume 21.7muA and 400muA from a 2.6-V power supply, respectively.