A multichannel CMOS analog front end IC for neural recordings

A multichannel integrated circuit for processing extracellular neural signals has been designed and manufactured. The analog CMOS IC consists of 17 parallel channels, each comprised of three cascaded stages: bandpass filter with gain, switched capacitor filters, and output buffer with selectable gain. The bandpass filter stage features an opamp with non-inverting resistor feedback and an off-chip capacitor in the feedback pathway to provide gain (43 dB) and one high pass filter pole (220 Hz). The low pass pole is set by the gain-bandwidth product of the opamp. In the switched capacitor filter stage, a one-pole high pass filter (500 Hz) cascades into a two-pole biquadratic low pass filter (5 kHz). The switched capacitor filters may be controlled by either an onboard tunable ring oscillator centered at 50 kHz or an off-chip clock. A four-phase clock splitter provides the necessary filter control-signals; a phase delay of 180° between the high and low pass clock lines maximizes settling time between the filters. The output buffer stage provides selectable gain at 20 dB or 32 dB. The IC was manufactured by AMI using a 0.5 μm triple metal double poly process, and measures 4.2 × 3.8 mm. The die is designed to be packaged in a flip-chip sub-assembly.