Low-Power Binary Neuron Circuit with Adjustable Threshold for Binary Neural Networks Using NAND Flash Memory

Abstract

Recent studies have demonstrated that binary neural networks (BNN) could achieve a satisfying inference accuracy on representative image datasets. BNN conducts XNOR and bit-counting operations instead of high-precision vector-matrix multiplication (VMM), significantly reducing the memory storage. In this work, an analog bit-counting scheme is proposed to decrease the burden of neuron circuits with a synaptic architecture utilizing NAND flash memory. A novel binary neuron circuit with a double-gate positive feedback (PF) device is demonstrated to replace the sense amplifier, adder, and comparator, thereby reducing the burden of the complementary metal-oxide semiconductor (CMOS) circuits and power consumption. By using the double-gate PF device, the threshold voltage of the neuron circuits can be adaptively matched to the threshold value in the algorithms eliminating the accuracy degradation introduced by the process variation. Thanks to the super-steep SS characteristics of the PF device, the proposed neuron circuit with the PF device has an off-state current of 1 pA, representing 105 times improvement compared to the neuron circuit with a conventional metal-oxide-semiconductor field effect transistor (MOSFET) device. A system simulation of a hardware-based BNN shows that the low-variance conductance distribution (8.4 %) of the synaptic device and the adjustable threshold of the neuron circuit implement a highly efficient BNN with a high inference accuracy.