A Bidirectional Neural Interface IC With Chopper Stabilized BioADC Array and Charge Balanced Stimulator

Elliot Greenwald, Ernest So, Qihong Wang, Mohsen Mollazadeh, Christoph Maier, Ralph Etienne-Cummings, Gert Cauwenberghs, Nitish Thakor

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


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 ΔΣ 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 1.54 μA and 2.13 μA of supply current, respectively. The bioADCs achieve an SNR of 58 and a SFDR of >70 dB, 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.

Original languageEnglish (US)
Article number7738450
Pages (from-to)990-1002
Number of pages13
JournalIEEE Transactions on Biomedical Circuits and Systems
Issue number5
StatePublished - Oct 2016


  • Chopper stabilization
  • Delta-Sigma
  • closed-loop neuromodulation
  • electrocorticography
  • electroencephalogram
  • neural recording
  • vagus nerve stimulation

ASJC Scopus subject areas

  • Biomedical Engineering
  • Electrical and Electronic Engineering


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