• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2021.05a
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• pp.584-588
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• 2021

The impedance of the speaker is likely to be recognized as a fixed value. However, speaker impedance continues to vary with frequency variation, especially larger in resonant frequency region. The sound pressure level of loudspeakers is determined by the current flowing throughout the coil that consists loudspeakers. If loudspeakers are driven by voltage, sound pressure level of the loudspeaker is distorted by the variation of loudspeaker impedance. Current-drive of loudspeakers can solve this problem, but distortion of sound pressure level occurs in low frequencies due to resonance. The distortion can degrade the sound quality of the sound system. So to solve this problem, In this paper, we propose a resonance compensation circuit using DSP. we simulates audio systems using an equivalent model of loudspeakers to verify distortion of sound pressure level due to impedance variation and propose a circuit to compensate it. The proposed circuit is configured using a state variable filter and it can adjust the center frequency and output, so it will be used various sound systems.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.6
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• pp.1402-1409
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• 2007

In this paper, we propose various types of AGC algorithms for implementing the OFDM communication systems. For the high-speed packet transmission, in this paper, we assume the OFDM system with relatively long and repeated preambles. We propose the maximum sample value counter for counting the number of maximum sample. In the maximum sample value counter, we use the buffer for the digital signal buffering. Finally, the counting value of the maximum sample value counter controls the gain control signal generator by using gain control table automatically.

• Proceedings of the KIPE Conference
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• 2014.07a
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• pp.138-139
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• 2014

3레벨 NPC 인버터는 구조상 DC Link가 두 개의 커패시터로 직렬 구성되어 있어 두 커패시터 간의 전압 불균형의 문제가 발생한다. 중성점의 변동으로 인하여 스위치 소자의 소손과 제어기의 오작동 등 시스템의 안정도가 떨어지게 된다. 기존의 중성점 전압을 제어하는 오프셋 전압 인가 방식은 zero point 지점에서 불연속 스위칭 구간이 존재하기 때문에 중성점 제어가 불가능하다. 본 논문에서는 중성점 전압을 제어하기 위하여 DPWM 기법에서 중성점 전압을 제어하는 방식을 제안하였다. DC Link의 두 커패시터 전압 불균형이 발생하면 $60^{\circ}(+30^{\circ})$ DPWM 기법으로 Positive 벡터와 Negative 벡터의 스위칭 인가 시간을 조절하여 두 커패시터의 전압 균형을 이루게 한다. 시뮬레이션을 통하여 본 논문에서 제안한 방식에 대한 타당성을 검증하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.10
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• pp.928-936
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• 2013

3D crosstalk is one of the disturbing things to recognize 3D images. This is caused by the phenomenon that input image for left eye is transferred at the right eye and right eye is transferred at the left eye because of the imperfect isolation by the device characteristics. In this paper, we review the 3D PDP (Plasma Display Panel) operation using active shutter glasses and crosstalk measurement method and investigate the major cause of 3D crosstalk and extend conventional 3D crosstalk using full white and full black image input to Gray-to-Gray (GtoG) 3D crosstalk. We suggest a specific method to reduce Gray-to-Gray 3D crosstalk by using Look up Table (LUT) and sub-field mapping in PDP. And then, we verify the method by measuring GtoG 3D crosstalk rate through specific test images and numerical results.

• The KIPS Transactions:PartB
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• v.14B no.4
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• pp.263-272
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• 2007

This paper proposes a skeleton-based hierarchical shape description scheme, called a skeleton tree, for accurate shape-based image retrieval. A skeleton tree represents an object shape as a hierarchical tree where high-level nodes describe parts of coarse trunk regions and low-level nodes describe fine details of boundary regions. Each node refines the shape of its parent node. Most of the noise disturbances are limited to bottom level nodes and the boundary noise is reduced by decreasing weights on the bottom levels. The similarity of two skeleton trees is computed by considering the best match of a skeleton tree to a sub-tree of another skeleton tree. The proposed method uses a hybrid similarity measure by employing both Fourier descriptors and moment invariants in computing the similarity of two skeleton trees. Several experimental results are presented demonstrating the validity of the skeleton tree scheme for the shape description and indexing.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.6
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• pp.1443-1453
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• 1998

This paper presents the speech synthesis engine that converts the character strings kept in a computer memory into the synthesized speech sounds with enhancing the intelligibility and the naturalness by adapting the waveform processing method. The speech engine using demisyllable speech segments receives command streams for pitch modification, duration and energy control. The command based engine isolates the high level processing of text normalization, letter-to-sound and the lexical analysis and the low level processing of signal filtering and pitch processing. The TTS(Text-to-Speech) system implemented by using the speech synthesis engine has three independent object modules of the Text-Normalizer, the Commander and the said Speech Synthesis Engine those of which are easily replaced by other compatible modules. The architecture separating the high level and the low level processing has the advantage of the expandibility and the portability because of the mix-and-match nature.

• The Transactions of the Korean Institute of Power Electronics
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• v.15 no.6
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• pp.451-459
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• 2010

This paper describes the performance comparison results for a hybrid back-to-back converter, which is composed of a 3-level 24-pulse converter and a 3-level PWM converter, in order to interconnect a large scale wind farm with the power grid. Also it describes the performance comparison results when the 24-pulse converter operates in only firing-angle control, and both firing-angle and the zero-voltage control. For the purpose of systematic performance comparison, computer simulations with PSCAD/EMTDC software were carried out, and based on simulation results a scaled hardware model with 2 kVA rating was built and tested.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.76-76
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• 2013

Scanning Tunneling Microscopy는 개인용컴퓨터가 보급되고, 저잡음 아날로그 칩들을 구할 수 있으며, 압전세라믹 기술이 발달하기 시작한 1981년 스위스 IBM Zurich 연구소에서 H. Rohrer와 G. Binnig 박사에 의하여 발명되었다. 이 발명 7~8년 이전 미국 표준연구원의 R. Young 박사도 비슷한 시도를 하였지만, 이 때는 제어할 수 있는 컴퓨터가 없었고, 조절 회로의 잡음 레벨도 컸으며, 역학적 진동도 커서 목적을 달성할 수 없었다. STM의 발명 후 32년이 지난 지금, 조절용 컴퓨터의 발전은 물론, 조절용 역되먹임 회로 또한 digital signal processor나 FPGA를 사용하는 형태로 변화하여 전기적 잡음도 현저히 감소하였다 [1,2]. 동시에 측정 에너지 해상도를 개선하기 위하여 세계적으로 여러 그룹이 장치를 1 K 이하에서 작동할 수 있게 제작하였고, 0.3 K에서 작동하는 상업용 제품도 등장하였다. 이 결과 에너지 해상도는 30 meV 에서 2~3 ${\mu}eV$ 감소하였고, 온도변화에 따른 측정 위치의 변화도 피할 수 있게 되었다. 터널링 검침의 화학적 성분을 흡착과 같은 방법으로 조절하여, 공간 해상도는 물론 에너지 해상도도 더욱 줄일 수 있게 되었고, 스핀에 민감한 터널링 제어도 가능하게 되었다. 이제는 금속, 반도체, 초전도체는 물론 분자, 거대분자, 나노 크기의 양자점등도 측정이 가능하게 되었다. 분자진동 측정이 가능하며, 분자의 성분 분석이 가능하게 되었고, 스핀의 전도와 관련된 제반 문제들을 연구할 수 있게 되었다. 지금부터 10년 동안에는 포논의 측정과 전자와 포논 exciton 등이 관여된 다체계 현상, 이들의 동역학적 현상이 측정 가능하게 되었다. 핵자기 공명도 시도되고 있으며 화학적 구명 및 원자들 사이의 결합도 측정 가능하게 될 것이다. 이제 STM은 초고 진공에서 작동하는 Atomic Force Microscopy와 함께 지금까지 고체물리학 실험 장치가 만들어 내지 못하던 새로운 결과를 도출해 낼 것으로 기대한다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.9
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• pp.2280-2288
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• 2014

The conventional dimming control methods of LED (Light-emitting dioades) include Analog, PWM (Pulse Width Modulation), and FM (Frequency Modulation) Control. Analog dimming is controlled by adjusting forward current of Power LED. Although Analog dimming is possible to control linearly the brightness levels on a whole range (0%~100%), it comes into existence a variation of wavelength by changing the Power LED's forward current. PWM dimming has achieved by varying in duty of full current flowing to the Power LED. Generally, PWM dimming doesn't make variation of wavelength but have difficulty with adjusting the linear brightness level between 0% and 10%. FM dimming method is on the same wavelength as PWM dimming, however, it has problem of flickering at low level of dimming. This paper propose a efficient dimming control method of Power LED in order to overcome the disadvantages of the above mentioned methods. We apply to Analog method in low level of dimming control and use PWM method in dimming range from 10% to 100%. For the experiment, we design and implement a circuit and test the proposed method. Consequently, we can control the linear brightness of Power LED across the whole range and get the constant wave at different dimming level. The experimental results show the benefits of the proposed method.

• Proceedings of the Korean Information Science Society Conference
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• 2004.04a
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• pp.226-228
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• 2004

Twofish 알고리즘은 작은 부피의 로직, Triple-DES보다 강력한 암호화 레벨, 암호화 속도 등율 갖추어 모듈 설계 알고리즘으로 선정하였다. Twofish 알고리즘은 bitwired-XOR, Permutation, S-box, MDS, PHT를 걸치는 H함수를 각기 다른 키로 반복 라운드를 함으로써 대상 데이타를 암호화한다. 64~256bit의 키 크기와 라운딩 횟수를 조정하여 모듈의 부피나 처리속도를 유동성 있게 조절할 수 있는 장점이 있다. 하드웨어 기기와 응용에 사용하기 위하여 VHDL 모듈로 알고리즘을 설계하고 그 동작을 검증하였다. 구현된 회로는 기존의 방법에 비하여 파이프라인 단계를 적용함으로써 약 23%의 속도 향상을 얻을 수 있었다.