A Fully Differential 4-Bit Analog Compute-In-Memory Architecture for Inference Application

A robust, fully differential multiplication and accumulate (MAC) scheme for analog compute-in-memory (CIM) architecture is proposed in this article. The proposed method achieves a high signal margin for 4-bit CIM architecture due to fully differential voltage changes on read bit-lines (RBL/RBLBs). The signal margin achieved for 4-bit MAC operation is 32 mV, which is 1.14×, 5.82×, and 10.24× higher than the state-of-the-art. The proposed scheme is robust against the process, voltage, and temperature (PVT) variations and achieves a variability metric (σ/μ) of 3.64 %, which is 2.36× and 2.66× lower than the reported works. The architecture has achieved an energy-efficiency of 2.53 TOPS/W at 1 V supply voltage in 65 nm CMOS technology, that is 6.2× efficient than digital baseline HW [25]. Furthermore, the inference accuracy of the architecture is 97.6% on the MNIST data set with a LeNet-5 CNN model. The figure-of-merit (FoM) of the proposed design is 355, which is 3.28×, 3.58×, and 17.75× higher than state-of-the-art.