Effect of Device Variation on Mapping Binary Neural Network to Memristor Crossbar Array

Author(s):  
Wooseok Yi ◽  
Yulhwa Kim ◽  
Jae-Joon Kim
2021 ◽  
pp. 2103376 ◽  
Author(s):  
Sifan Li ◽  
Mei‐Er Pam ◽  
Yesheng Li ◽  
Li Chen ◽  
Yu‐Chieh Chien ◽  
...  

2021 ◽  
Vol 21 (3) ◽  
pp. 1833-1844
Author(s):  
Kyojin Kim ◽  
Kamran Eshraghian ◽  
Hyunsoo Kang ◽  
Kyoungrok Cho

Nano memristor crossbar arrays, which can represent analog signals with smaller silicon areas, are popularly used to describe the node weights of the neural networks. The crossbar arrays provide high computational efficiency, as they can perform additions and multiplications at the same time at a cross-point. In this study, we propose a new approach for the memristor crossbar array architecture consisting of multi-weight nano memristors on each cross-point. As the proposed architecture can represent multiple integer-valued weights, it can enhance the precision of the weight coefficients in comparison with the existing memristor-based neural networks. This study presents a Radix-11 nano memristor crossbar array with weighted memristors; it validates the operations of the circuits, which use the arrays through circuit-level simulation. With the proposed Radix-11 approach, it is possible to represent eleven integer-valued weights. In addition, this study presents a neural network designed using the proposed Radix-11 weights, as an example of high-performance AI applications. The neural network implements a speech-keyword detection algorithm, and it was designed on a TensorFlow platform. The implemented keyword detection algorithm can recognize 35 Korean words with an inferencing accuracy of 95.45%, reducing the inferencing accuracy only by 2% when compared to the 97.53% accuracy of the real-valued weight case.


2021 ◽  
Vol 21 (3) ◽  
pp. 1854-1861
Author(s):  
Jaeheum Lee ◽  
Jason K. Eshraghian ◽  
Sungjin Kim ◽  
Kamran Eshraghian ◽  
Kyoungrok Cho

There are many challenges in the hardware implementation of a neural network using nanoscale memristor crossbar arrays where the use of analog cells is concerned. Multi-state or analog cells introduce more stringent noise margins, which are difficult to adhere to in light of variability. We propose a potential solution using a 1-bit memristor that stores binary values “0” or “1” with their memristive states, denoted as a high-resistance state (HRS) and a low-resistance state (LRS). In addition, we propose a new architecture consisting of 4-parallel 1-bit memristors at each crosspoint on the array. The four 1-bit memristors connected in parallel represent 5 decimal values according to the number of activated memristors. This is then mapped to a synaptic weight, which corresponds to the state of an artificial neuron in a neural network. We implement a convolutional neural network (CNN) model on a framework (tensorflow) using an equivalent quantized weight mapping model that demonstrates learning results almost identical to a high-precision CNN model. This radix-5 CNN is mapped to hardware on the proposed parallel-connected memristor crossbar array. Also, we propose a method for negative weight representation on a memristor crossbar array. Then, we verify the CNN hardware on an edge-AI (e-AI) platform, developed on a field-programmable gate array (FPGA). In this e-AI platform, we represent five weights per crosspoint using CLB logics. We test the learning results of the CNN hardware using an e-AI platform with a dataset consisting of 4×4 images in three classes. We verify the functionality of our radix-5 CNN implementation showing comparable classification accuracy to high-precision use cases, with reduction of the area of the memristor crossbar array by half, all verified on a FPGA. Implementing the CNN model on the FPGA board can contribute to the practical use of edge-AI.


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