CDACiM: A Charge-Domain Compute-in-Memory Macro for FP/INT MAC Operations with Reconfigurable Capacitor Digital-Analog-Converter

Advanced edge artificial intelligence (AI) chips need to balance flexible computation, high energy efficiency, and sufficient inference accuracy across diverse workloads. Many compute-in-memory (CiM) designs enable efficient neural network acceleration but focus solely on integer (INT) multiply-and-accumulate (MAC) operations, limiting precision. Some CiM macros add extra circuitry to support floating point (FP) MACs, but these dedicated exponent-handling blocks often waste area when running INT workloads. In this paper, we propose CDACiM, a charge-domain CiM macro that supports both FP and INT MAC operations with minimal overhead. CDACiM introduces a reconfigurable capacitor digital-to-analog converter (RCDAC) that performs both exponent summation and bitwise AND for mantissa multiplication. To calculate exponent offsets, we develop a shared single-slope ADC (SS-ADC) that finds the maximum exponent and computes differences in time domain simultaneously. Our design includes a sparsity-aware computation scheme with tunable thresholds that skips low-importance input-weight pairs, boosting energy efficiency through higher input sparsity. We also introduce a multi-bit input accumulation method that leverages ADC redundancy during quantization and normalization to improve performance. Implemented in a 40nm CMOS process, CDACiM demonstrates an excellent flexibility and trade-off between accuracy and resource usage. Notably, it is the first CiM design to reconfigure capacitor-based INT macro for parallel exponent computation. CDACiM achieves 16.2 TOPS/W for INT MACs and $\mathbf{1 5. 9}$ TFLOPS/W for FP MACs. It delivers a $\mathbf{1. 3 6 - 1. 4 8 \times}$ improvement in energy efficiency with minimal accuracy loss compared to recent FP CiM macros.