4.7 Article Proceedings Paper

A Trimodal Wireless Implantable Neural Interface System-on-Chip

Journal

IEEE TRANSACTIONS ON BIOMEDICAL CIRCUITS AND SYSTEMS
Volume 14, Issue 6, Pages 1207-1217

Publisher

IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/TBCAS.2020.3037452

Keywords

Stimulated emission; Capacitors; Biomedical optical imaging; Neuromodulation; Electrical stimulation; Wireless communication; Optical switches; Charge balancing; switched-capacitor based stimulation; trimodal neural interface; optogenetics; wireless power and data transmission

Funding

  1. NSF [ECCS-1407880, ECCS-1408318, ECCS-2024486]
  2. NSF ASSIST Center [EEC-1160483]
  3. NIH [1R21EB018561]
  4. NC State University

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A wireless and battery-less trimodal neural interface system-on-chip (SoC), capable of 16-ch neural recording, 8-ch electrical stimulation, and 16-ch optical stimulation, all integrated on a 5 x 3 mm(2) chip fabricated in 0.35-mu m standard CMOS process. The trimodal SoC is designed to be inductively powered and communicated. The downlink data telemetry utilizes on-off keying pulse-position modulation (OOK-PPM) of the power carrier to deliver configuration and control commands at 50 kbps. The analog front-end (AFE) provides adjustable mid-band gain of 55-70 dB, low/high cut-off frequencies of 1-100 Hz/10 kHz, and input-referred noise of 3.46 mu V-rms within 1 Hz-50 kHz band. AFE outputs of every two-channel are digitized by a 50 kS/s 10-bit SAR-ADC, and multiplexed together to form a 6.78 Mbps data stream to be sent out by OOK modulating a 434 MHz RF carrier through a power amplifier (PA) and 6 cm monopole antenna, which form the uplink data telemetry. Optical stimulation has a switched-capacitor based stimulation (SCS) architecture, which can sequentially charge four storage capacitor banks up to 4 V and discharge them in selected mu LEDs at instantaneous current levels of up to 24.8 mA on demand. Electrical stimulation is supported by four independently driven stimulating sites at 5-bit controllable current levels in +/-(25-775) mu A range, while active/passive charge balancing circuits ensure safety. In vivo testing was conducted on four anesthetized rats to verify the functionality of the trimodal SoC.

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