DESCRIPTION AND DEMONSTRATION OF A CMOS AMPLIFIER-BASED-SYSTEM WITH MEASUREMENT AND STIMULATION CAPABILITY FOR BIOELECTRICAL SIGNAL-TRANSDUCTION

An extracellular recording system incorporating an electrode array and an amplifier/stimulator CMOS chip is described and characterized. Imp ortant features of this custom VLSI chip include 16 instrumentation am plifiers with a gain of 50 and the incorporation of a cross-point arra y allowing designation of an extracellular microelectrode as either a stimulator or sensor. The planar array consisted of 32 microelectrodes , 14 mu m in diameter, and four larger reference electrodes. Microelec trodes, interconnecting traces, and bond pads were patterned with a 50 0-nm layer of gold. The interconnecting traces were passivated with a 1-mu m thick layer of silicon nitride to provide chemical and electric al insulation and microelectrode impedance was lowered utilizing elect rode position of platinum black. The amplifier exhibited a nearly flat frequency response with high pass and low pass corner frequencies of 0.7 Hz and 50 kHz, respectively. The input referred noise over the 50 kHz bandwidth was 12-16 mu V-RMS, well below the magnitude of previous ly reported extracellular potentials. Crosstalk between neighboring ch annels resulted in an output signal below the amplifier noise level, e ven for relatively large extracellular potentials. Using this system, extracellular recordings were demonstrated yielding typical peak-to-pe ak biopotentials of magnitude 0.9-2.1 mV and 100-400 mu V for chick ca rdiac myocytes and rat spinal cord neurons, respectively. The key comp onents of this extracellular recording system can be manufactured usin g industry standard thin him photolithographic techniques. (C) 1998 El sevier Science S.A. All rights reserved.