A Battery-Free Neural Implant Achieving 6cm Reading Range and 36.2pJ/bit Efficiency by PWM Passive Body-Channel Communication

Minimally invasive wireless implants distributed in the nervous system can transfer various neural signals to an external device, offering an effective hardware tool for neuro-disorder monitoring. Battery-free wireless techniques based on wireless power transfer (WPT) have been adopted to minimize the neural implants, but the effective reading ranges of most conventional works are not long enough to access deep-tissue nerves. The existing ultrasonic coupling and binary-driven passive body-channel-communication (BCC) techniques extended the reading range but suffered from a low data rate and a high energy in wireless communication. In this work, we demonstrate a battery-free wireless neural implant based on the proposed pulse-width-modulation (PWM) passive-BCC technique, which improves the data rate and further reduces the energy per bit. The proposed technique is implemented in a neural-recording chip fabricated by a 65nm CMOS process. Measured results show that the proposed wireless neural implant achieves a battery-free reading range of 6cm, with an energy efficiency of 36.2pJ/bit. In-vivo experiment is performed in a Sprague-Dawley rat to record the neural signals wirelessly in a battery-free way.