• ETRI Journal
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• v.39 no.1
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• pp.62-68
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• 2017

In this paper, we present the design and characterization analysis of a cascode GaN field-effect transistor (FET) for switching power conversion systems. To enable normally-off operation, a cascode GaN FET employs a low breakdown voltage (BV) enhancement-mode Si metal-oxide-semiconductor FET and a high-BV depletion-mode (D-mode) GaN FET. This paper demonstrates a normally-on D-mode GaN FET with high power density and high switching frequency, and presents a theoretical analysis of a hybrid cascode GaN FET design. A TO-254 packaged FET provides a drain current of 6.04 A at a drain voltage of 2 V, a BV of 520 V at a drain leakage current of $250{\mu}A$, and an on-resistance of $331m{\Omega}$. Finally, a boost converter is used to evaluate the performance of the cascode GaN FET in power conversion applications.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.3
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• pp.199-207
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• 2021

This study aimed to improve the performance of the KTX (Korea Train Express) brake system. To develop a braking disc-hub for the high-speed rail, the model performance was analyzed by finite element analysis, and the analysis results were verified using the braking test results. In addition, heat transfer analysis, thermal stress analysis, natural frequency analysis, and static analysis were conducted to examine the mechanical performance of the braking system. By deriving the design factors and conducting parametric analyses according to the shape of the hub, this study derived the optimal specifications that could improve heat dissipation and reduce weight. The cooling efficiency and structural performance of the optimization model were improved during braking compared to the existing model. It is expected that the design verification will be carried out through analyses of the optimal specifications so that it can be used in the development of brakes in railway vehicles and motor vehicles.

• 한국연소학회:학술대회논문집
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• 2006.10a
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• pp.220-226
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• 2006

The effect of electric fields on the propagation speed of tribrachial flames has been investigated in a coflow jet by observing the transient flame propagation behavior after ignition. Without having electric fields, the propagation speed of tribrachial flame edges showed a typical behavior by having an inverse proportionality to the mixture fraction gradient at the flame edge. The behavior of flame propagation with the electric fields was investigated by applying high voltage to the central fuel nozzle and the enhancement of propagation speed has been observed by varying the applied voltage and frequency for AC electric fields. The propagation speed of tribrachial flame was also investigated by applying negative and positive DC voltages to the nozzle and similar improvements of the propagation speed were also observed. The propagation speeds of tribrachial flames in both the AC and DC electric fields were correlated well with the electric field intensity, defined by the electric voltage divided by the distance between the nozzle electrode and the edge of tribrachial flames.

• Journal of Electrical Engineering and Technology
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• v.12 no.4
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• pp.1627-1633
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• 2017

This paper proposes a voice enhancing ear-protection system which is based on feedback active noise control(FBANC). The proposed system selectively suppresses the background noise and preserves the talking voice by controlling the adaptive algorithm with the voice activity period detection module. The noise reduction performance of the proposed noise canceling algorithm is analytically derived for the two key performance affecting parameters, i.e., electro-acoustic coupling distance and noise bandwidth. The proposed system is also implemented with a floating-point DSP system and its performance is experimentally tested to compare with the analytically derived results. The achieved levels of noise reduction for the three different noise bandwidths cases, i.e., 10Hz, 50Hz, and 90Hz, are high to show 17.05dB, 10.54dB and 8.99dB, respectively. The feasibility of the proposed system is also shown by the peak noise reduction achieved more than 25dB while preserving the voice component in the frequency range between 200-800Hz.

• Proceedings of the IEEK Conference
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• 2008.06a
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• pp.247-248
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• 2008

A recent dynamic increase in demand for wireless multimedia services has greatly accelerated the research on dynamic channel adaptation of high quality video applications. In this paper, we explore a theoretical approach to cross-layer optimization between multimedia and wireless networks by means of a quality criterion termed "visual throughput" for downlink video transmission using a layered coding algorithm. We obtain the optimal loading ratio of orthogonal frequency division multiple access (OFDMA) subcarriers through an optimization problem balancing the trade-off relationship between inter-cell interference (ICI) and channel throughput. In the simulation, we show that the visual throughput gain at the cell boundary is increased by about 32%.

• Journal of the Korean Society for Precision Engineering
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• v.32 no.9
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• pp.799-805
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• 2015

The further development of information, communication and digital media technologies requires the use of advanced, miniaturized semiconductor chips that operate at a high frequency. Die bonding and wire bonding methods for semiconductor packaging have been replaced by direct attachment to the substrate after forming a bump on the chip. However, the height of the bump or ball is an important factor for defects during assembly. This paper proposes an algorithm to measure the height of the bumps or balls in semiconductor packaging with greater accuracy. The performance of the proposed algorithm is experimentally validated. Non-contact 3D measurements of a shiny round ball is quite difficult, and it is not easy to obtain accurate data. This paper thus proposes an optical method and technique to improve the measurement accuracy.

• Journal of the Institute of Electronics Engineers of Korea TE
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• v.37 no.2
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• pp.25-32
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• 2000

Digital watermarking has been recently proposed as the means of intellectual property right protection of multimedia data. We present a novel watermarking scheme to hide a copyright information in a digital image. The method Is based on the 2D DWT(Discrete Wavelet Transform) and image statistics. Gaussian and Laplacian noises as the watermarks are added to the large wavelet coefficients at the high and middle frequency bands in the wavelet domain. Experimental results show that the proposed Laplacian watermark is stronger to several common image distortions, such as noises, JPEG coding as different qualities, Gaussian blurring, and edge enhancement.

• Journal of electromagnetic engineering and science
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• v.6 no.3
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• pp.160-164
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• 2006

This paper describes a compact printed helical resonator and its application to a microwave oscillator circuit implemented in coplanar waveguide(CPW) technology. The high Q-factor and spurious-free characteristic of the resonator contribute to the phase noise reduction and the harmonic suppression of the resulting oscillator circuit, respectively. The designed resonator resonating at the frequency of 5.5 GHz showed a loaded Q of 180 in a chip area of only 40 % of the corresponding miniaturized hairpin resonator without any spurious resonances. The fully planar oscillator incorporated with this resonator showed additional phase noise reduction of 10.5 dB at 1 MHz offset and a second harmonic suppression enhancement of 6 dB when compared to those of a conventional CPW oscillator without the planar helical resonator(PHR) structure.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.4 no.2
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• pp.77-82
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• 2011

In this paper, we investigate source separation algorithms for stereo audio mixed using amplitude panning method. This source separation algorithms can be used in various applications such as up-mixing, speech enhancement, and high quality sound source separation. The methods in this paper estimate the panning angles of individual signals using the principal component analysis being applied in time-frequency tiles of the input signal and independently extract each signal through directional filtering. Performances of the methods were evaluated through computer simulations.

• Journal of information and communication convergence engineering
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• v.10 no.3
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• pp.225-230
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• 2012

The Korean nationwide differential global positioning system (NDGPS) reference station transmits a global positioning system (GPS) enhancement signal using minimum shift keying modulation with a 200 bps data rate. The ocean-based DGPS covers the service area of 100 NM with 300 W output power; on the other hand, the land-based DGPS transmits the output power of 500 W, which covers the service area of 100 km. The DGPS reference stations with high output power can radiate spurious signals, which may act as interference sources affecting the other DGPS reference stations or the wireless ground stations that utilize the medium frequency band. In this paper, the radiation spectrums of the DGPS reference stations are measured and analyzed in the spurious domain. The DGPS radiation spectrums are evaluated from the perspective of the interference effect.