A 216 nW/channel DSP engine for triggering theta phase-locked brain stimulation

We present an algorithm and, for the first time, a chip to predict the neural theta oscillation phase, for closed-loop phase-locked stimulation triggering. The performance, assessed on test data recorded from human hippocampus, achieves high precision and accuracy in targeting any theta phase with 25%, 50%, and 75% of the predictions falling within ±13, ±28, and ±53 degrees from the desired target phase, respectively. Design interleaving channel-depth optimization achieves 41% energy and 58% area savings compared to a single-channel design. The 32-channel chip consumes a 216 nW per channel and occupies a core area of 0.011 mm2 per channel in a 40nm low-power technology, making it suitable for implantable devices.