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HyDra: SOT-CAM Based Vector Symbolic Macro for Hyperdimensional Computing
DescriptionHyperdimensional computing (HDC) is a brain-inspired paradigm valued for its noise robustness, parallelism, energy efficiency, and low computational overhead. Hardware accelerators are being explored to further enhance its performance, but current solutions are often limited by application specificity and the latency of encoding and similarity search. This paper presents a generalized, reconfigurable on-chip training and inference architecture for HDC, utilizing spin-orbit-torque magnetic (SOT-MRAM) content-addressable memory (CAM). The proposed SOT-CAM array integrates storage and computation, enabling in-memory execution of key HDC operations: binding (bitwise multiplication), permutation (bit rotation), and efficient similarity search. To mitigate interconnect parasitic effect in similarity search, a four-stage voltage scaling scheme has been proposed to ensure accurate Hamming distance representation. Additionally, a novel bit drop method replaces bit rotation during read operations, and an HDC-specific adder reduces energy and area by 1.51× and 1.43×, respectively. Benchmarked at 7nm, the architecture achieves energy reductions of 21.5×, 552.74×, 1.45×, and 282.57× for addition, permutation, multiplication, and search operations, respectively, compared to CMOS-based HDC. Against state-of-the-art HD accelerators, it achieves a 2.27× lower energy consumption and outperforms CPU and eGPU implementations by 2702× and 23161×, respectively, with less than 3% drop in accuracy.