Dissertation talk: Ultra-Low Power Inductively-Coupled Wireless Transcranial Links
Presentation | December 4 | 4-5 p.m. | 531 Cory Hall
Wen Li, BWRC
Recent advancements in medical neural science and brain research have enabled demands for circuits and systems that interface with human/animal brain, which are called brain-machine interface (BMI). There are numerous applications for BMI: motor prosthetics, pre-surgical mapping, brain disease treatment and deep brain stimulation, just to name a few. In these applications, the large amount of data produced by neurons must be transmitted outside the skull to a powerful DSP to translate into action or to be analyzed. Wireless transfer of these data is the preferred option because of risk of infection caused by the wires going through the skull. A next generation 1024-channel implanted neural recorder that uses 20KS/s 8b ADC to capture action and field potential can generate up to 164Mb/s data, which imposes a stringent requirement on the throughput of the implanted wireless TX. In addition to throughput, TX power consumption must be kept as low as possible for longer battery life or safe wireless power transfer, while the power consumption of the RX chip outside the skull can be relaxed. Current state-of-the-art designs that use backscattering, ultra-wide-band (UWB) communication, or ultrasound suffer either from limited throughput or low TX energy efficiency. To overcome these challenges, we utilize inductive-coupling to achieve 200Mb/s data-rate and 1.5pJ/b TX energy efficiency.
In this talk, I will first briefly review the current state-of-art transcranial links. Then, I will present the 200Mb/s wireless transceiver design for neural implants built in 65nm CMOS using off-chip 10X10mm coupled inductors. In order to achieve such high data-rate, series de-Q resistors are employed to alleviate inter-symbol-interference (ISI) caused by the inductor self-resonance. The entire TX chip uses a single 0.5V supply to save power. To generate relatively clean 200MHz TX clock from 10MHz reference under 0.5V supply, an injection-locked PLL with fully-digital frequency tracking and spur suppression is adapted. The inductively-coupled transceiver achieves 5E-11 BER over 11mm-thick scalp and skull bone of an 8-week-old piglet and less than 1E-12 BER over 11mm air channel. Including PLL, the whole TX consumes only 300uW.