Artifact-Tolerant Opamp-Less Delta-Modulated Bidirectional Neuro-Interface

Abstract

We present a 16-channel bidirectional wireless neural interface with arbitrary-waveform neurostimulators triggered by remote closed-loop analysis of simultaneously recorded neural activity. The delta-modulated neural ADC uses no input capacitors and no statically-biased circuits such as opamps, saving both channel area (0.0054mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) and power (730nW). Delta modulation yields tolerance to input DC offsets of any value, up to the power rail voltage. The differential-difference comparator architecture offers super-GOhm input impedance ensuring that both of the differential inputs transfer functions are well matched, resulting in a superior 78dB rejection of common-mode (CM) signals and artifacts. The highly-oversampling nature of the ADC also renders it insensitive to stimulation artifacts with differential amplitudes of up to 10mV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> , maintaining an ENOB of 9.7 bits and 2.6μV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> integrated input-referred noise. Experimental results validate the key features of the design and include in-vivo recordings in behaving guinea pigs.