High data-rate ultra low-power backscatter wireless communication systems for brain-computer interfaces

Abstract

Neural interfacing is a promising technology for effectively treating a multitude of challenging clinical conditions. Recent research has demonstrated that some tetraplegic patients can control robotic limbs using a brain-computer interface (BCI), signifying the beginning of an era wherein many forms of paralysis may be treatable with a neuro-prosthesis. However, the current state of the art is bulky, tethered, and impractical for applications outside a clinical lab setting. Moreover, current wireless communication approaches for brain computer interfaces~(BCI) do not meet the necessary specifications for power, size, and bandwidth. In contrast, we developed fully integrated BCIs equipped with high data-rate and low power miniaturized wireless backscatter communication systems to enable the development of autonomous brain-controlled prosthetics. First, we proposed a wireless $\mu$-Power, low-noise frequency mixing approach for extending the passband frequency response of existing neural interfaces. We demonstrated the translation of a pre-recorded mouse electrocorticogram from a frequency range of 0.5~Hz to 100~Hz up to an intermediate frequency (IF) of 407~Hz, thus enabling the use of an existing integrated circuit~(IC) for electrocorticography (ECoG), despite its low-frequency cutoff of 12~Hz. Subsequently, we presented a dual-band implantable BCI that integrates 47\%-efficient high frequency (HF) wireless power delivery into a 5~Mb/s ultra-high frequency (UHF) backscatter communication. The implant system supports ten neural channels sampled at 26.10~kHz and four electromyography (EMG) channels sampled at 1.628~kHz and can communicate with a custom software-defined-radio-based external system with a packet error ratio~(PER) that is better than 0.19~\%~at an implant depth of up to 3~cm. Finally, in order to enable neural plasticity experiments inside the home cages of freely behaving animals, we developed a 25~Mbps backscatter-based data uplink for Neurochip~3 using a differential quadrature phase shift keying (DQPSK) constellation. We statically collected $10^4$ packets from 126 locations, and the system exhibited effectively 0~\%~(PER) for all but two of the surveyed sites despite the reverberant cavity effects of the animal cage that critically impair the communication channel.