SoC Dense DBS Lead Cortical Grid High-Density Multisite Sensing Stimulation/ Disease-Specific Biomarkers ML Classifier Prosthetic Control Versatile Closed-Loop Neural Interface (Binary/Multiclass) TDM FIR Test Blocks and Flip-Chip Pad Array 4 mm 2.9 mm TDM FEE 16-Ch. Stimulator (a) Energy-Aware Regularization Feature PowerFeature Distribution CH1 CH2 CH3 16 × 16 Switch Matrix CH254 CH255 CH256 Column Decoder Low 64-Ch TDM AFE 64-Ch TDM AFE 64-Ch TDM AFE 64-Ch TDM AFE Sigmoid p = σ(fTw - TH.) (b) CH1 CH2 CH3 16 × 16 Switch Matrix CH254 CH255 CH256 Column Decoder Channel Index Memory (2.93 kB) Feature Type Threshold Weight Feature Vector NeuralTree Hardware (≤ 64 MACs/window) f64 ... f3 w64 w3 f2 f1 Weight Vector ... w2 w1 × + Z-1 TH. (c) FIGURE 4: NeuralTree: An intelligent, ML-driven closed-loop neural interface [37], [38]. (a) Conceptual system-level diagram, highlighting high-channel-count cortical arrays and depth leads for high-density sensing and stimulation. (b) NeuralTree's training process involves 256-channel ECoG/LFP sensing, energy-aware regularization, and network pruning. (c) Dynamic inference using an on-chip, versatile, tree-structured neural network supporting neural signal classification for epilepsy, movement disorders, and BCI. AFE: analog front-end; FEE: feature extraction engine; HFO: high-frequency oscillation; LL: line length; LMP: local motor potential; LUT: lookup table; MUX: multiplexer; PAC: phase-amplitude coupling; PLV: phase-locking value; SE: spectral energy; TDM: time-division multiplexing. 46 FALL 2023 IEEE SOLID-STATE CIRCUITS MAGAZINE Decision LUT Dominant Class Node Addr 64-Ch TDM AFE SE HFOR PLV PAC MUX TDM FEE LL Hjorth LMP Single-Path Inference f1 fp w1 Network Pruning fp f2 w2 w64 fi fp f64 Energy-Aware Pruning Features Extracted Features Pruned High Temporal Spectral Phase 16.6% 81.8% 1.6% Motion Control Dual MUX-CHOP Dual MUX-CHOP Class 256-Ch. Class Labels CS-TDM AFE 256-Ch. TDM DSL NeuralTree 3.17 kB Memory 1.2 mm 2 mm N Y Y High-Density Neural Activity for NeuralTree Training