27.3 All-wireless 64-channel 0.013mm2/ch closed-loop neurostimulator with rail-to-rail DC offset removal

Accurate capture and efficient control of neurological disorders such as epileptic seizures that often originate in multiple regions of the brain, requires neural interface microsystems with an ever-increasing need for higher channel counts. Addressing this demand within the limited energy and area of brain-implantable medical devices necessitates a search for new circuit architectures. In the conventional designs [1-5], the channel area is dominated by the bulky coupling capacitors and/or capacitor banks of the in-channel ADC, both unavoidable due to the channel architecture, and unscalable with CMOS technology. Additionally, channel power consumption, typically dominated by the LNA, cannot be reduced lower than a certain limit without sacrificing gain and/or noise performance. In this paper, we present a 64-channel wireless closed-loop neurostimulator with a compact and energy-efficient channel architecture that performs both amplification and digitization in a single ΔΣ-based neural ADC, while removing rail-to-rail input DC offset using a digital feedback loop. The channel area and power consumption depend only on the active components and switching frequency, respectively, making the design both technology- and frequency-scalable.