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455 results on '"Lee, Hyung-Min"'

12. Analog CMOS-based Resistive Processing Unit for Deep Neural Network Training

Author

Kim, Seyoung, Gokmen, Tayfun, Lee, Hyung-Min, and Haensch, Wilfried E.

Subjects
Computer Science - Emerging Technologies, Computer Science - Learning
Abstract

Recently we have shown that an architecture based on resistive processing unit (RPU) devices has potential to achieve significant acceleration in deep neural network (DNN) training compared to today's software-based DNN implementations running on CPU/GPU. However, currently available device candidates based on non-volatile memory technologies do not satisfy all the requirements to realize the RPU concept. Here, we propose an analog CMOS-based RPU design (CMOS RPU) which can store and process data locally and can be operated in a massively parallel manner. We analyze various properties of the CMOS RPU to evaluate the functionality and feasibility for acceleration of DNN training.

Published
2017
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13. High-Resolution Characterization of Aerosol Optical Depth and Its Correlation with Meteorological Factors in Afghanistan.

Author

Torabi, Sayed Esmatullah, Amin, Muhammad, Phairuang, Worradorn, Lee, Hyung-Min, Hata, Mitsuhiko, and Furuuchi, Masami

Subjects
MODIS (Spectroradiometer), ATMOSPHERIC aerosols, PEARSON correlation (Statistics), AIR quality, METEOROLOGICAL satellites
Abstract

Atmospheric aerosols pose a significant global problem, particularly in urban areas in developing countries where the rapid urbanization and industrial activities degrade air quality. This study examined the spatiotemporal variations and trends in aerosol optical depth (AOD) at a 550 nm wavelength, alongside key meteorological factors, in Kabul, Afghanistan, from 2000 to 2022. Using the Google Earth Engine geospatial analysis platform, daily AOD data were retrieved from the Moderate Resolution Imaging Spectroradiometer to assess monthly, seasonal, and annual spatiotemporal variations and long-term trends. Meteorological parameters such as temperature (T), relative humidity (RH), precipitation (PCP), wind speed (WS), wind direction, and solar radiation (SR) were obtained from the Modern Era Retrospective Analysis for Research and Applications. The Mann–Kendall test was employed to analyze the time-series trends, and a Pearson correlation matrix was calculated to assess the influence of the meteorological factors on AOD. Principal component analysis (PCA) was performed to understand the underlying structure. The results indicated high AOD levels in spring and summer, with a significant upward trend from 2000 to 2022. The findings revealed a positive correlation of AOD value with T, RH, WS, and PCP and a negative correlation with SR. The PCA results highlighted complex interactions among these factors and their impact on the AOD. These insights underscore the need for stringent air quality regulations and emission control measures in Kabul. [ABSTRACT FROM AUTHOR]

Published
2024
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33. Device‐Algorithm Co‐Optimization for an On‐Chip Trainable Capacitor‐Based Synaptic Device with IGZO TFT and Retention‐Centric Tiki‐Taka Algorithm

Author

Won, Jongun, primary, Kang, Jaehyeon, additional, Hong, Sangjun, additional, Han, Narae, additional, Kang, Minseung, additional, Park, Yeaji, additional, Roh, Youngchae, additional, Seo, Hyeong Jun, additional, Joe, Changhoon, additional, Cho, Ung, additional, Kang, Minil, additional, Um, Minseong, additional, Lee, Kwang‐Hee, additional, Yang, Jee‐Eun, additional, Jung, Moonil, additional, Lee, Hyung‐Min, additional, Oh, Saeroonter, additional, Kim, Sangwook, additional, and Kim, Sangbum, additional

Published
2023
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38. A 92%-Efficiency Inductor-Charging Switched-Capacitor Stimulation System With Level-Adaptive Duty Modulation and Offset Charge Balancing

Author

Eom, Kyeongho, Lee, Han-Sol, Park, Minju, Yang, Seung Min, Choe, Jong Chan, Hwang, Suk-Won, Suh, Young-Woo, and Lee, Hyung-Min

Abstract

This article proposes an inductor-charging switched-capacitor stimulation (iSCS) system capable of high-efficiency capacitor charging and high-efficacy decaying exponential stimulation. The iSCS system adopts a fast inductor-based charger with level-adaptive duty modulation and charging range detection that can efficiently charge capacitors from any residual voltage levels to the target voltages up to 3 V. The offset-control charge balancing (OC-CB) adaptively reduces the mismatch between cathodic and anodic charges. The iSCS prototype can charge 1- $\mu \text{F}$ capacitor from 0 V (1.5 V) to 3 V within 50 $\mu \text{s}$ (28 $\mu \text{s}$ ), achieving 90% (92.7%) capacitor charging efficiency. The iSCS system efficiency was measured up to 92%, which is >10% higher than state-of-the-art works. The iSCS also achieved higher stimulus efficacy thanks to its decaying exponential waveform. In vivo experiments for ocular muscle stimulation using the iSCS system resulted in a 20% increase in eye movement distance while consuming 13% less energy compared to the current-controlled stimulation system. This ensures higher system efficiency and enhanced stimulus efficacy.

Published
2024
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39. A 94.9% Efficiency Always-Power-Delivered SIDO Buck Converter With Continuous Current Balancing and Complementary Adaptive-Switching Regulation

Author

Jung, Woojoong, Park, Hyunjun, Kim, Minsu, and Lee, Hyung-Min

Abstract

This article proposes a single-inductor dual-output (SIDO) buck converter which always deliveries continuous power to outputs. The proposed converter has adopted complementary adaptive-switching regulation (CASR) with a continuous current balancing (CCB) mechanism and an auxiliary current path to passively bypass output switches in turn. The proposed converter and its control scheme can enhance output current continuities and power efficiencies while decreasing voltage ripples and fluctuations due to equivalent series resistance (ESR) and equivalent series inductance (ESL) at each output. The prototype converter was fabricated with the 180-nm CMOS process and comprises a 4.7- $\mu $ H inductor with 92- $\text{m}\Omega $ DCR, two 10- $\mu \text{F}$ output capacitors, and a 10- $\mu \text{F}$ capacitor for the auxiliary current path. The measured results verified that the always-power-delivered (APD) SIDO converter can generate 1.8 and 3.3 V from 5 V with a combined type-3 compensator (CT-3C), while providing continuous current to each output. The peak efficiency was 94.9% with the load conditions of 150 mA for 3.3 V and 75 mA for 1.8 V. In addition, the overall efficiencies were measured higher than 90% in all operation ranges.

Published
2024
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40. A 9-V-Tolerant Stacked-Switched-Capacitor Stimulation System With Level-Adaptive Switch Control and Rapid Stimulus-Synchronized Charge Balancing for Implantable Devices

Author

Park, Minju, Eom, Kyeongho, Lee, Han-Sol, Ku, Seung-Beom, and Lee, Hyung-Min

Abstract

This article proposes a stacked-switched-capacitor stimulation (SSCS) system that can provide up to 9-V stimulation without using an external high-voltage (HV) supply or HV conversion stages to supply the stimulator. With the level-adaptive switch control, SSCS can be HV tolerant using only low-voltage (LV) transistors. In addition, SSCS achieves high stimulation efficiency up to 71.4%, which includes charging and discharging efficiencies of 72.6% and 99.9%, respectively, to charge 1- $\mu \text{F}$ capacitor from 0 to 4 V by adopting the ac-to-capacitor charger and the stacked-capacitor stimulus discharger. Charge balancing (CB) can also be achieved in rapid time using the stimulus-synchronized CB (SS-CB) method which adaptively controls the pulsewidth of the recovery phase. The SSCS prototype verifies that the residual voltage up to 900 mV can be suppressed within four stimulation cycles and maintained within ±30 mV by utilizing SS-CB.

Published
2024
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48. Parameterization of polydisperse aerosol optical properties during hygroscopic growth

Author

Jung, Chang H., Han, Kyung Man, Yoon, Young Jun, Kim, Dongchul, Lee, Ji Yi, Lee, Hyung-Min, Um, J., Lee, S. S., and Kim, Yong Pyo

Subjects
Environmental Chemistry, General Materials Science, Pollution
Abstract

Aerosol water uptake and the related influence on its optical properties owing to the hygroscopic growth of polydisperse aerosols have a significant effect on air quality and climate. This study develops an analytical parameterization for a single hygroscopic optical parameter and the scattering enhancement factor for polydisperse aerosol sizes. Polydisperse lognormal size distributions for geometric mean diameters of 0.05–1 µm and geometric standard deviations of 1.3–2.5 are considered with real refractive indices between 1.35 and 1.6. The analytical expression obtained for the optical parameter is compared to Mie theory and reasonable agreements within the size range investigated in this study are observed. Further, our results show that the analytical expression could express polydispersed aerosol optical properties as a function of geometric mean diameter and geometric standard deviation of a lognormal distribution and the refractive index. The obtained analytical expression can be efficiently used for 3D models with a reduced computational burden. Copyright © 2023 American Association for Aerosol Research

Published
2023
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49. A Wide-Load-Range and High-Slew Capacitor-Less NMOS LDO With Adaptive-Gain Nested Miller Compensation and Pre-Emphasis Inverse Biasing

Author

Park, Hyunjun, Jung, Woojoong, Kim, Minsu, and Lee, Hyung-Min

Abstract

This article proposes an output capacitor-less NMOS low-dropout regulator (LDO) using wide-range adaptive-gain nested Miller compensation (WAG-NMC) and pre-emphasis inverse (PI) biasing. Due to WAG-NMC, the LDO can provide a wide range of load current ( $I_{\mathrm {LOAD}}$ ) from 0.1 to 300 mA while maintaining sufficiently high phase margin (PM) above 60° at all $I_{\mathrm {LOAD}}$ conditions. WAG-NMC also extends a loop bandwidth (BW) up to 17.5 MHz with using only small compensation capacitors ( $C_{\text {C}}$ ) of 6.3 pF in total. Moreover, PI biasing enhances a slew rate (SR) at the gate of the NMOS power transistor by injecting an adaptive PI current into a supersource follower (SSF), which further improves transient response. The proposed LDO fabricated in a 180-nm CMOS process was fully integrated with an on-chip load capacitor ( $C_{\text {L}}$ ) of 100 pF. The LDO ensures small undershoot and overshoot of 48 and 59 mV, respectively, against large $\Delta I_{\mathrm {LOAD}}$ of 299 mA due to wide-BW and high SR. The proposed LDO also achieves a best figure of merit (FoM) of 1.72 ps among the state of the arts.

Published
2023
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