Implantable neural recording devices are being used by neuroscientists and neurosurgeons for monitoring the behaviour of particular parts of the brain. Traditionally, these implanted devices were wired and connected to the measurement and computation equipment to process the signals. Such a setup restricts the physical movement of the subject and limits the number and quality of the experiments or monitoring that can be performed. With the advancement of microelectronics manufacturing processes allowing lower power operation while simultaneously occupying a smaller area on chip, and circuit and system level architectural inventions, wireless multi-channel neural recording systems have become available during the last decade. However, the capabilities of neural recording implants are still limited by their power density in order not to harm the surrounding tissue by heat generation. If the operational capabilities of the neural recording implants are to be improved in terms of number of electrodes supported, number of simultaneous recording channels, on-chip signal processing, and operational longevity, new methods of power consumption reduction are required.
Such an ultra-low power neural recording device has multiple uses for both the scientists/researchers and the general public: i) it can be used for experiments that require continuous neural monitoring with minimal energy requirements and implant size, ii) it can be used as part of a point-of-care device for the patients, with the minimum amount of burden to the patient, such as the need to change batteries, weight due to batteries, etc., and iii) it can be used as part of a closed loop system of a bioelectronic system for alleviating certain pathological conditions, such as epilepsy, tinnitus, etc. Furthermore, if such a recording device can be supplemented with additional multi-modal measurement capabilities, it will be immensely useful for the researchers and medical personnel to better diagnose different pathologies.
During the course of this project, the main aim of the research was to find novel ways of power consumption reduction for such multi-modal and multi-purpose implantable bioelectronic devices. Based on our findings and using time-mode operation (a special mode of operation where the delay of a signal represents the information to be processed), a wireless neural recording chip was developed and implemented. The implemented microchip achieves three orders of magnitude lower energy dissipation when compared to the other implementations in the literature. Furthermore, the sensing and measurement capabilities of the proof of concept implementation were improved with the addition of imaging, temperature, and electroanalytical sensors.