A Battery-Free Neural-Recording Chip Achieving 5.5 cm Fully-Implanted Depth by Galvanically-Switching Passive Body Channel Communication
Yili Shen, Changgui Yang, Yunshan Zhang, Weixiao Wang, Yuxuan Luo, Chaonan Yu, Kedi Xu, Gang Pan, Bo Zhao
Abstract
Wireless fully implanted devices are widely adopted for long-term neural-recording applications, where the cable-induced infection risk can be avoided. Battery-free communication based on wireless power transfer (WPT) can eliminate the battery to reduce the size of a wireless implant, realizing minimally invasive surgery. However, conventional battery-free implants suffer from a short communication range, such as inductive coupling, near-infrared (NIR) transmission, and active body-channel communication (BCC), which cannot apply to deep brain zones. Ultrasonic power transfer and communication benefit from a low channel loss, but the low carrier frequency leads to a low data rate, which is not able to transfer full-span neural signals such as spikes and multichannel signals. In this work, a galvanically-switching passive-BCC technique is proposed for neural implants, to extend the effective range of both power transfer and wireless communication. The brain tissue is utilized to form a galvanic loop for power delivery, while the neural-recording data switch the loop current to conduct passive BCC. The proposed technique is implemented in a neural recording chip fabricated in a 55-nm CMOS process. Through-tissue measurement shows that the chip realizes a battery-free communication range of 5.5 cm, with a bit-error rate (BER) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.4\ttimes10^{-6}$</tex-math> </inline-formula> . In the in-vivo demonstration, a 5.9-mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^3$</tex-math> </inline-formula> flexible prototype with the proposed chip inside is fully implanted into a Sprague–Dawley rat, where the neural signals are read battery-free through the passive-BCC technique.