Abstracts

Rationale: Deep brain stimulation and optical stimulation in optogenetics are two unique methods to control seizure activity. Currently, in the scientific community, devices to implement electrical or optical modulation are either tethered or wirelessly powered with a radiofrequency (RF) inductive link or battery. The tether is disadvantageous due to the restrictive environment, increased risk of infection from the percutaneous connector, and impractical implementation of large-group, longitudinal monitoring protocols. For inductive links, the internal coil (device antenna) prohibits full implantation, and the external coil limits freedom of movement. This technique is highly spatially dependent on an unpredictable alignment between the internal and external powering coils in a freely moving animal. Further, the range is limited to the reactive near-field. RF powering devices with the radiative far field, however, would allow more free ranging experiments with lower profile antennas. Custom circuitry with the far field powering would enable the epilepsy community to investigate untethered DBS and optical stimulation. Methods: Two custom application specific integrated circuits (ASICs) have been designed to be RF powered through electromagnetic radiation. The architecture contains a front-end fully differential neural amplifier, ADC, clock, and transmitter. A biphasic constant current stimulator or charge pump is also included for electrical and optical stimulation, respectively. The ASIC designs were sent to the X-FAB mixed-signal foundry to be fabricated under the 180 nm CMOS process. Results: From Cadence software simulations, the ASICs operate at 1.8V and on average, consume under 700 uW during non-stimulating conditions. The constant current stimulator drives ~170 uA across a 10 kOhm load, and the neural amplifier has 58 dB gain with approximately 1.5 kHz bandwidth. Empirical results from the ASICs are presented. Conclusions: Previously, our group has demonstrated LED based optical coupling, far field RF powering, and an ultralow power seizure detection ASIC. Integration of all these technologies into a singular device results in a first generation RF powered, closed-loop electrical or optical stimulator.