Abstract

Responsive deep brain stimulation (DBS) requires recruiting deep brain structures without affecting the superficial neuronal population. Neurosurgeons widely use implanted electrodes, which are highly localized but invasive, to stimulate the deep brain. Temporally interfering stimulation (TIS) excites the deep brain non-invasively. This neuromodulation technique utilizes two high-frequency sinusoidal electric fields that do not recruit superficial neural structures but have a small frequency differential. The small differential causes a low-frequency interference envelope that stimulates deep regions and is steerable by changing the intensity of the electric fields without physically moving the electrodes. Using TIS as a non-invasive DBS method generates high-frequency stimulation artifacts at recording sites, which may saturate a conventional recording front-end. This paper presents a low-power bidirectional 64-channel CMOS neural-ADC that is immune to artifacts such as those in the TIS techniques or conventional biphasic stimulation. The presented DC-coupled chopped analog front-end leverages delta-spectrum shaping to remove electrode DC offset voltage and maintain the input impedance higher than 250 MΩ, which is sufficient for interfacing with non-invasive scalp electrodes. The AFE operates on the input signal difference to detect large and rapid stimulation artifacts. It incorporates both exponential tracking and boosted-rate sampling to recover within 100 μs. Upon recovery, the neural-ADC range and speed are reduced to achieve noise and power efficiency factors of 2.98 and 10.6, respectively. In vivo recordings from anesthetized mice demonstrate the unique capabilities of the presented architecture in resolving local field potentials from the surface and epidural electrodes.