• Journal of IKEEE
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• v.24 no.4
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• pp.1122-1128
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• 2020

Bandwidth Extension refers to restoring and expanding a narrow band signal(NB) that is damaged or damaged in the encoding and decoding process due to the lack of channel capacity or the characteristics of the codec installed in the mobile communication device. It means converting to a wideband signal(WB). Bandwidth extension research mainly focuses on voice signals and converts high bands into frequency domains, such as SBR (Spectral Band Replication) and IGF (Intelligent Gap Filling), and restores disappeared or damaged high bands based on complex feature extraction processes. In this paper, we propose a model that outputs an bandwidth extended signal based on an autoencoder among deep learning models, using the residual connection of one-dimensional convolutional neural networks (CNN), the bandwidth is extended by inputting a time domain signal of a certain length without complicated pre-processing. In addition, it was confirmed that the damaged high band can be restored even by training on a dataset containing various types of sound sources including music that is not limited to the speech.

• Journal of IKEEE
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• v.24 no.4
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• pp.1093-1097
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• 2020

This work describes the design and characterization of a Ku-band monolithic microwave integrated circuit (MMIC) power amplifier (PA) for satellite communication applications. The device technology used relies on 0.25 ㎛ gate length gallium arsenide (GaAs) pseudomorphic high electron mobility transistor (PHEMT) of wireless information networking (WIN) semiconductor foundry. The developed Ku-band PHEMT MMIC power amplifier has a small-signal gain of 22.2~23.1 dB and saturated output power of 34.8~35.4 dBm over the entire band of 13.75 to 14.5 GHz. Maximum saturated output power is a 35.4 dBm (3.47 W) at 13.75 GHz. Its power added efficiency (PAE) is 30.6~37.83% and the chip dimensions are 4.4 mm×1.9 mm. The developed 3 W PHEMT MMIC power amplifier is expected to be applied in a variety of Ku-band satellite communication applications.

• Journal of Ceramic Processing Research
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• v.19 no.5
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• pp.361-368
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• 2018

We investigated the interfacial properties of fluorocarbon self-assembled monolayers (FC-SAMs) with different alkyl chain lengths. It was found that the substrate characteristics were changed rapidly with the fabrication time and temperature of the SAM. FC-3SAM, which has the shortest alkyl chain in this study, showed a contact angle of $54.1^{\circ}$ when it was fabricated in an electric oven at $60^{\circ}C$ for the first minute. The FC-3SAM showed a contact angle of up to $76.9^{\circ}$ when it was fabricated in an electric oven at the same temperature condition for 180 minutes. FC-10SAM, which has the longest alkyl chain in this study, showed a contact angle of $64.7^{\circ}$ when it was fabricated at a temperature condition of $60^{\circ}C$ for 1 minute, and a contact angle of $98.7^{\circ}C$ at a temperature condition of $60^{\circ}C$ for 180 minutes. It was found that the FC-10SAM shows an increased contact angle and hydrophobic properties due to a well-aligned molecular structure resulting from a strong van der Waals force. In contrast, the FC-3SAM shows a small contact angle due to the intermolecular disorder resulting from a weak van der Waals force. The average roughness of FC-SAMs was investigated using AFM. The surface roughness of FC-SAMs, which verifies the results of contact angle, was confirmed. At a fabrication time of 120 minutes, the FC-10SAM showed an improvement in average roughness by 62% compared to that of FC-3SAM due to its good alignment.

• The Journal of the Convergence on Culture Technology
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• v.7 no.1
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• pp.564-569
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• 2021

In this paper, for the typical LED and the tilted LED, when there is no electrode, when 20% absorption (80% reflection) occurs at the electrode, and when 60% absorption (40% reflection) occurs at the electrode, the effect of the absorption at the electrode and the height of the active region on the photon extraction efficiency and the mean photon path length was investigated, and an appropriate height of the active region was proposed. In a typical LED, as the absorption of the electrode increases, the photon extraction efficiency decreases from 18% to 15% and 13%, and the photon extraction efficiency is highest when the height of the active area is located in the center between the two electrodes. In the tilted LED, as the absorption of the electrode increases, the photon extraction efficiency decreases from 38% to 33% and 25%, and the photon extraction efficiency is highest when the height of the active area is located in the center between the two electrodes. The tilted LED can increase the photon extraction efficiency more than twice than that of a typical LED, where photons are trapped inside the chip due to total reflection.

• Journal of IKEEE
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• v.25 no.4
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• pp.774-777
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• 2021

In this paper, we analyzed the gate controllability of 3D NAND Flash Memory with Charge Trap Flash using Ferroelectric (CTF-F) structure. HfO₂, a ferroelectric material, has a high-k characteristic besides polarization. Due to these characteristics, gate controllability is increased in CTF-F structure and on/off current characteristics are improved in Bit Line(BL). As a result of the simulation, in the CTF-F structure, the channel length of String Select Line(SSL) and Ground Select Line(GSL) was 100 nm, which was reduced by 33% compared to the conventional CTF structure, but almost the same off-current characteristics were confirmed. In addition, it was confirmed that the inversion layer was formed stronger in the channel during the program operation, and the current through the BL was increased by about 2 times.

• Journal of IKEEE
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• v.25 no.4
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• pp.591-597
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• 2021

This paper proposes an EMC-aware PCB design method to reduce electromagnetic emission, where trace length and teturn path of critical signal are shortened by changing chip location and trace layout on the PCB, while additional filters or decoupling capacitors are not required. In the proposed method, signal velocity is calculated for various signals on the PCB. Critical signal with the fastest signal velocity is determined and its return path is shortened as much as possible by placing chip location and trace routing first. Return path of critical signal should be carefully designed not to have discontinuity. Power plane and ground plane should be carefully designed not to be divided, since these planes are the reference of return path. The proposed method was applied to automotive directional Bluetooth speaker which failed to pass CISPR 32 and CISPR 25 EMC tests. Its PCB was redesigned based on the proposed method and it easily passed the EMC tests. The proposed method is useful to EMC-sensitive electronic equipments.

• Nuclear Engineering and Technology
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• v.54 no.10
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• pp.3614-3619
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• 2022

To operate the ion cyclotron resonance heating (ICRH) antennas in a better heating state and produce relatively low impurities, it is necessary to control the antenna spectrum by changing the antenna phasing. As the electrical length of the antenna feeding transmission lines is changing as a matter of the standing wave pattern at the ceramic supports, 90° elbows, T-connectors and antenna loops, we chose to measure the current at the grounding points of the antenna loops by antenna strap probe. The voltage drops along a small, several millimeter-long paths at the end of the antenna loops give a signal that is proportional to the current in the antenna loop. Through the simulation of the antenna strap probe and the actual measurement of the antenna phasing under vacuum conditions, the reliability of the antenna strap probe based diagnostic system have been successfully proved. Moreover, this system was successfully applied to the ICRH daily experiments in the spring of 2021. In the near future, the active real-time feedback control of the antenna phasing system will be developed based on this diagnostic system in the EAST tokamak.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.26 no.11
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• pp.1666-1671
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• 2022

The structure of a high-power gain-flattened long wavelength band (L-band) optical amplifier was optimized, which was implemented for 64-channel wavelength division multiplexed optical signals with a channel spacing of 50 GHz. The output characteristics of this L-band amplifier were measured and analyzed. The amplifier of the optimized two-stage amplification configuration had a flattened gain of 20 dB within 1 dB deviation between 1570 and 1600 nm for -2 dBm input power condition. The noise figure under this condition was minimized to within 6 dB in the amplification bandwidth. The gain flattening was realized by considering only the characteristics of gain medium in the amplifier without using additional optical or electrical devices. The proposed amplifier consisted of two stages of amplification stages, each of which was based on the erbium-doped fiber amplifier (EDFA) structure. The erbium-doped fiber length and pumping structures in each stage of the amplifier were optimized through experiments.

• Journal of IKEEE
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• v.26 no.4
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• pp.722-727
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• 2022

In this paper, we present the design and characterization of a power amplifier (PA) monolithic microwave integrated circuit (MMIC) in the X-band. The device is designed using a 0.25 ㎛ gate length AlGaN/GaN high electron mobility transistor (HEMT) on SiC process. The developed X-band AlGaN/GaN power amplifier MMIC achieves small signal gain of over 21.6 dB and output power more than 46.11 dBm (40.83 W) in the entire band of 9 GHz to 10 GHz. Its power added efficiency (PAE) is 43.09% ~ 44.47% and the chip dimensions are 3.6 mm × 4.3 mm. The generated output power density is 2.69 W/mm². It seems that the developed AlGaN/GaN power amplifier MMIC could be applicable to various X-band radar systems operating X-band.

• Journal of IKEEE
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• v.26 no.4
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• pp.568-576
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• 2022

Automatic modulation classification(AMC) is a core technique in Software Defined Radio(SDR) platform that enables smart and flexible spectrum sensing and access in a wide frequency band. In this study, we propose a simple yet accurate deep learning-based method that allows AMC for variable-size radio signals. To this end, we design a classification architecture consisting of two Convolutional Neural Network(CNN)-based models, namely main and small models, which were trained on radio signal datasets with two different signal sizes, respectively. Then, for a received signal input with an arbitrary length, modulation classification is performed by augmenting the input samples using a self-replicating padding technique to fit the input layer size of our model. Experiments using the RadioML 2018.01A dataset demonstrated that the proposed method provides higher accuracy than the existing methods in all signal-to-noise ratio(SNR) domains with less computation overhead.