A/D Alleviator: Reducing Analog-to-Digital Conversions in Compute-In-Memory with Augmented Analog Accumulation

Compute-in-memory (CIM) has shown great promise in accelerating numerous deep-learning tasks. However, existing analog CIM (ACIM) accelerators often suffer from frequent and energy-intensive analog-to-digital (A/D) conversions, severely limiting their energy efficiency. This paper proposes A/D Alleviator, an energy-efficient augmented analog accumulation data flow to reduce A/D conversions in ACIM accelerators. To make it, switched-capacitor-based multiplication and accumulation circuits are used to connect the bitlines (BLs) of memory crossbar arrays and the final A/D conversion stage. In this way, analog partial sums can be accumulated both spatially across all adjacent BLs that store high-precision weights and temporarily across all input cycles before the final quantization, thereby minimizing the need for explicit A/D conversions. Evaluations demonstrate that A/D Alleviator can improve energy efficiency by 4.9× and 1.9× with a high signal-to-noise ratio, as compared to state-of-the-art ACIM accelerators.