An Energy-Efficient Optically-Enhanced Highly-Linear Implantable Wirelessly-Powered Bidirectional Optogenetic Neuro-Stimulator

This paper presents an energy-efficient mm-scale self-contained bidirectional optogenetic neuro-stimulator, which employs a novel highly-linear mu LED driving circuit architecture as well as inkjet-printed custom-designed optical mu lenses for light directivity enhancement. The proposed current-mode mu LED driver performs linear control of optical stimulation for the entire target range (< 10 mA) while requiring the smallest reported headroom, yielding a significant boost in the energy conversion efficiency. A 30.46x improvement in the power delivery efficiency to the target tissue is achieved by employing a pair of printed optical mu lenses. The fabricated SoC also integrates two recording channels for LFP recording and digitization, as well as power management blocks. A micro-coil is also embedded on the chip to receive inductive power and our experimental results show a PTE of 2.24% for the wireless link. The self-contained system including the mu LEDs, mu lenses and the capacitors required by the power management blocks is sized 6 mm(3) and weighs 12.5 mg. Full experimental measurement results for electrical and optical circuitry as well as in vitro measurement results are reported.