김율화 교수

We introduce a SRAM-based binary neural network (BNN) hardware which uses a single 6T SRAM cell for XNOR operation for the first time. The cell is 45% smaller than the previous 8T bitcell for XNOR operation. We also propose an in-memory calibration and batch normalization to achieve more reliable operation under the presence of process variation.

Resistive RAM (RRAM) has been presented as a promising memory technology toward deep neural network (DNN) hardware design, with nonvolatility, high density, high ON/OFF ratio, and compatibility with logic process. However, prior RRAM works for DNNs have shown limitations on parallelism for in-memory computing, array efficiency with large peripheral circuits, multilevel analog operation, and demonstration of monolithic integration. In this article, we propose circuit-/device-level optimizations t

In-memory computing (IMC) has emerged as a promising technique for enhancing energy efficiency of deep neural networks (DNNs). While embedded nonvolatile memory, such as resistive RAM (RRAM) is a good alternative to SRAM/DRAM for IMC owing to high density, low leakage, and nondestructive read, most prior works have not demonstrated using multilevel RRAM devices for array-level IMC operations. In this letter, we present an IMC prototype with 2-bit-per-cell RRAM devices for area-/energy-efficient

We introduce an area/energy-efficient precision-scalable neural network accelerator architecture. Previous precision-scalable hardware accelerators have limitations such as the under-utilization of multipliers for low bit-width operations and the large area overhead to support various bit precisions. To mitigate the problems, we first propose a bitwise summation, which reduces the area overhead for the bit-width scaling. In addition, we present a channel-wise aligning scheme (CAS) to efficiently

The weight-only quantization has emerged as a promising technique for alleviating the computational burden of large language models (LLMs) by employing low-precision integer (INT) weights, while retaining full-precision floating point (FP) activations to ensure inference quality. Despite the memory footprint reduction achieved through decreased bit-precision of weight parameters, the actual computing performance is often not improved significantly due to FP-INT multiply-accumulation (MAC) operat

Resistive Crossbar memory Arrays (RCA) have been gaining interest as a promising platform to implement Convolutional Neural Networks (CNN). One of the major challenges in RCA-based design is that the number of rows in an RCA is often smaller than the number of input neurons in a layer. Previous works used high-resolution Analog-to-Digital Converters (ADCs) to compute the partial weighted sum in each array and merged partial sums from multiple arrays outside the RCAs. However, such approach suffe

In Analog Computing-in-Memory (CIM) neural network accelerators, analog-to-digital converters (ADCs) are required to convert the analog partial sums generated from a CIM array to digital values. The overhead from ADCs substantially degrades the energy efficiency of CIM accelerators so that previous works attempted to lower the ADC resolution considering the distribution of the partial sums. Despite the efforts, the required ADC resolution still remains relatively high. In this article, we propos

Binary Neural Network (BNN) has a great potential to be implemented on Resistive memory Crossbar Array (RCA)-based hardware accelerators because it requires only 1-bit precision for weights and activations. While general structures to implement convolution or fully-connected layers in RCA-based BNN hardware were actively studied in previous works, Batch-Normalization (BN) layer, which is another key layer of BNN, has not been discussed in depth yet. In this work, we propose in-memory batch-norma

We present an in-memory binary neural network (BNN) accelerator based on 8-transistor and 2-capacitor (8T2C) SRAM cell. The proposed SRAM computing-in-memory (CIM) cells rely on DRAM-like charge sharing operations to avoid undesirable static currents and potential read-disturb problems in conventional resistive SRAM-CIM designs. In addition, unlike the previous capacitive SRAM-based CIM designs, the proposed SRAM CIM does not consume energy when the input value is 0, thereby achieving the higher

We propose an in-memory neural network accelerator architecture called MOSAIC which uses minimal form of peripheral circuits; 1-bit word line driver to replace DAC and 1-bit sense amplifier to replace ADC. To map multi-bit neural networks on MOSAIC architecture which has 1-bit precision peripheral circuits, we also propose a bit-splitting method to approximate the original network by separating each bit path of the multi-bit network so that each bit path can propagate independently throughout th

Recently, RRAM-based Binary Neural Network (BNN) hardware has been gaining interests as it requires 1-bit sense-amp only and eliminates the need for high-resolution ADC and DAC. However, RRAM-based BNN hardware still requires high-resolution ADC for partial sum calculation to implement large-scale neural network using multiple memory arrays. We propose a neural network-hardware co-design approach to split input to fit each split network on a RRAM array so that the reconstructed BNNs calculate 1-

In memristor crossbar array (MCA)-based neural network hardware, it is generally assumed that entire word-lines (WLs) are simultaneously enabled for parallel matrix-vector multiplication (MxV) operation. However, the error probability of MxV in a memristor crossbar array (MCA) increases as the resistance ratio (R-ratio) of a memristor decreases and the resistance variation and the number of simultaneously activated WLs increase. In this paper, we analyze the effect of R-ratio and variation of me

Implementing binary neural networks (BNNs) on computing-in-memory (CIM) hardware has several attractive features such as small memory requirement and minimal overhead in peripheral circuits such as analog-to-digital converters (ADCs). On the other hand, one of the downsides of using BNNs is that it degrades the classification accuracy. Recently, ResNet-style BNNs are gaining popularity with higher accuracy than conventional BNNs. The accuracy improvement comes from the high-resolution skip conne

Supporting variable precision for computing quantized neural network in a hardware accelerator is an efficient way to reduce overall computation time and energy. However, in the previous precision-scalable hardware, bit-reconfiguration logic increases the chip area significantly. In this paper, we demonstrate a compact precision-scalable accelerator chip using bitwise summation and channel-wise aligning schemes. The measurement results show that the peak performance per compute area is improved

In Long Short-Term Memory (LSTM) neural network models, a weight matrix tends to be repeatedly loaded from DRAM if the size of on-chip storage of the processor is not large enough to store the entire matrix. To alleviate heavy overhead of DRAM access for weight loading in LSTM computations, we propose a weight reuse scheme which utilizes the weight sharing characteristics in two adjacent time-step computations. Experimental results show that the proposed weight reuse scheme reduces the energy co