Multiplication plays a critical role in SRAM-based Computing-in-Memory (CIM) architectures. However, current SRAM-based CIMs face three major limitations. First, they do not fully exploit bit-level sparsity, resulting in unnecessary overhead in both latency and energy consumption. Second, the generation of numerous zero-dot products is superfluous. Third, the irregular organization of SRAM complicates the implementation. To address these issues, we propose Shift-CIM, a general-purpose approach that fully leverages bit-level sparsity within SRAM-based multiplications. Shift-CIM aligns the multipliers within the SRAM array, accumulating only the required dot products based on the non-zero bits of the multipliers. Shift-CIM achieves a regular SRAM organization by assembling two irregular SRAM arrays in a transposed manner. Our evaluations show that Shift-CIM is highly efficient, operating at a supply voltage of 0.9 V and a frequency of 833 MHz, while incurring only a 4.8% area overhead. Despite these modest requirements, Shift-CIM significantly accelerates multiplication operations, achieving up to 3.08× the performance improvement and a 60% reduction in energy consumption compared to state-of-the-art designs.

Digital SRAM-based CIM architectures must balance three critical factors: quantized neural network bitwidth, accuracy loss, and computational efficiency, each crucial to optimizing performance and efficiency. In Domain Specific Accelerators (DSAs), flexible and specific hardware design, when incorporated with tailored Power-of-2 (P-2) quantization schemes, addresses this issue. However, in CIMs, the absence of flexible and specific hardware to support dynamic switching between general and tailored quantization schemes hinders the adoption of efficient quantization methods. In this article, we propose the I n-situ S hift O peration based Acc elerator ( ISOAcc ) for efficient SRAM-based multiplication. The key idea is to introduce transmission gates near the SRAM array to enable the selection of bits from either the same or the neighbor line when data flows from one row to another. This functionally equals a shift operation. By configuring the transmission gates array in a cascade manner, ISOAcc can support 0 to 15-bit shift with a negligible overhead. The ISOAcc can directly leverage P-2 quantization schemes in hardware, thereby greatly reducing multiplication cycles. We have chosen five well-known neural networks to evaluate ISOAcc. The evaluations show that ISOAcc achieves an average performance improvement of 3.24× and an energy reduction of 75%, compared with the state-of-the-art (SOTA) SRAM-based CIM design, Bit-Parallel.