title: A Bidirectional Neural Interface IC With Chopper Stabilized BioADC Array and Charge Balanced Stimulator.
abstract: We present a bidirectional neural interface with a 4-channel biopotential analog-to-digital converter (bioADC) and a 4-channel current-mode stimulator in 180 nm CMOS. The bioADC directly transduces microvolt biopotentials into a digital representation without a voltage-amplification stage. Each bioADC channel comprises a continuous-time first-order ∆Σ modulator with a chopper-stabilized OTA input and current feedback, followed by a second-order comb-filter decimator with programmable oversampling ratio. Each stimulator channel contains two independent digital-to-analog converters for anodic and cathodic current generation. A shared calibration circuit matches the amplitude of the anodic and cathodic currents for charge balancing. Powered from a 1.5 V supply, the analog and digital circuits in each recording channel draw on average [Formula: see text] and [Formula: see text] of supply current, respectively. The bioADCs achieve an SNR of [Formula: see text] and a SFDR of [Formula: see text] , for better than 9-b ENOB. Intracranial EEG recordings from an anesthetized rat are shown and compared to simultaneous recordings from a commercial reference system to validate performance in-vivo . Additionally, we demonstrate bidirectional operation by recording cardiac modulation induced through vagus nerve stimulation, and closed-loop control of cardiac rhythm. The micropower operation, direct digital readout, and integration of electrical stimulation circuits make this interface ideally suited for closed-loop neuromodulation applications.
authors.forename: Elliot
authors.initials: E
authors.lastname: Greenwald
authors.forename: Ernest
authors.initials: E
authors.lastname: So
authors.forename: Qihong
authors.initials: Q
authors.lastname: Wang
authors.forename: Mohsen
authors.initials: M
authors.lastname: Mollazadeh
authors.forename: Christoph
authors.initials: C
authors.lastname: Maier
authors.forename: Ralph
authors.initials: R
authors.lastname: Etienne-Cummings
authors.forename: Gert
authors.initials: G
authors.lastname: Cauwenberghs
authors.forename: Nitish
authors.initials: N
authors.lastname: Thakor
mesh_terms: D000669:Amplifiers, Electronic; D000703:Analog-Digital Conversion; D004599:Electric Stimulation Therapy / Q000295:instrumentation*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D058542:Implantable Neurostimulators; D008904:Miniaturization; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*