Recently, Adder Neural Networks (AdderNets) have gained widespread attention as an alternative to traditional Convolutional Neural Networks (CNNs) for deep learning tasks. AdderNets use lightweight addition operations to replace multiplication and accumulation (MAC) operations, but can keep almost the same accuracy compared to other CNNs. Nevertheless, challenges still exist with regards to hardware resources, power consumption, and communication bandwidth, primarily due to the ‘Von-Neumann bottlenecks’. However, computing-in-memory (CIM) architecture based on magnetic random-access memory (MRAM) has great potential for edge DNN implementation. In this paper, we propose a novel CIM paradigm using a novel Toggle-Spin-Torques (TST) driven MRAM for energy-efficient AdderNets (called CiTST_AdderNets). In CiTST_AdderNets, MRAM is driven by the interplay of the field-free spin orbit torque (SOT) effect and the spin transfer torque (STT) effect, which offers a fascinating prospect for energy efficiency and speed. Furthermore, a novel CIM paradigm is proposed to implement the dominating subtraction and sum operations in AdderNets, reducing data transfer and the related energy. Meanwhile, a highly parallel array structure integrating computation and storage is designed to support CiTST_AdderNets. In addition, a mapping strategy is proposed to efficiently map the convolution layer on the array. Fully connected layers can also be efficiently computed. The CiTST-AdderNets macro is designed by using a 65-nm CMOS process. Results show that our CiTST-AdderNets consumes about 1.65 mJ, 9.29 mJ, and 42.46 mJ for running VGG8, ResNet-50, and ResNet-18 respectively at 8-bit fixed-point precision. Compared to state-of-the-art platforms, our macro achieves an energy efficiency improvement of 1.45 x to 66.78 x.

SRAM based computing-in-memory (SRAM-CIM) techniques have been widely studied for neural networks (NNs) to solve the “Von Neumann bottleneck”. However, as the scale of the NN model increasingly expands, the weight cannot be fully stored on-chip owing to the big device size (limited capacity) of SRAM. In this case, the NN weight data have to be frequently loaded from external memories, such as DRAM and Flash memory, which results in high energy consumption and low efficiency. In this paper, we propose a hybrid-device computing-in-memory (HD-CIM) architecture based on SRAM and MRAM (magnetic random-access memory). In our HD-CIM, the NN weight data are stored in on-chip MRAM and are loaded into SRAM-CIM core, significantly reducing energy and latency. Besides, in order to improve the data transfer efficiency between MRAM and SRAM, a high-speed pipelined MRAM readout structure is proposed to reduce the BL charging time. Our results show that the NN weight data loading energy in our design is only 0.242 pJ/bit, which is 289$\times $less in comparison with that from off-chip DRAM. Moreover, the energy breakdown and efficiency are analyzed based on different NN models, such as VGG19, ResNet18 and MobileNetV1. Our design can improve$\mathbf {58\times \,\,to\,\,124\times }$energy efficiency.

Logic-in-memory architecture based on spintronic memories shows fascinating prospects in neural networks (NNs) for its high energy efficiency and good endurance. In this work, we leveraged two magnetic tunnel junctions (MTJs), which are driven by the interplay of field-free spin orbit torque (SOT) and spin transfer torque (STT) effects, to achieve a novel statefullogic-in-memory paradigm for ternary multiplication operations. Based on this paradigm, we further proposed a highly parallel array structure to serve for ternary neural networks (TNNs). Our results demonstrate the advantage of our design in power consumption compared with CPU, GPU and other state-of-the-art works.