• Proceedings of the KIEE Conference
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• 2000.07d
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• pp.3088-3090
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• 2000

In this paper, we introduce a charge pump PLL architecture which employs precharge phase frequency detector(PFD) and sequential PFD to achieve high frequency operation and fast acquisition. Operation frequency is increased by using precharge PFD when the phase difference is within -${\pi}\;{\sim}\;{\pi}$ and acquisition time is shortened by using sequential PFD and increased charge pump current when the phase difference is larger than |${\pi}$|. SO error detection range of proposed PLL structure is not limited to -${\pi}\;{\sim}\;{\pi}$. By virtue of this multi-phase frequency detector structure, the maximum operating frequency of 423MHz at 2.5V and faster acquisition were achieved by simulation.

• Korean Journal of Optics and Photonics
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• v.16 no.4
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• pp.334-339
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• 2005

We studied the spatial filtering characteristics of a multi-phase hologram optical low-pass filter(HOLF). Using the Monte-Carlo based hologram generation program, we designed holograms whose diffraction patterns are circular shaped 21 beams and calculated the diffraction efficiencies and MTFs. 4-phase HOLF have the same diffraction efficiency as that of 2-phase HOLF. The MTF graphs of the two are also nearly alike. But 8-phase HOLF shows higher efficiency than those previously discussed and has larger MTF values in the low frequency region. 16-phase HOLF has just a little better characteristics than 8-phase. Considering the errors which can arise in the process of making holograms, 8-phase HOLF fits the goal of improving the resolution of spatial filter. We also fabricated 8-phase HOLF and .measured MTF The experimental results agree well with the theoretical expectations.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.4
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• pp.35-42
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• 2013

In this paper, the analog performance of FinFET structure was estimated by extracting the DC/AC characteristics of the 22 nm process FinFET structures with different layout considering spacer and SEG using 3D device simulator, Sentaurus. Based on the analysis results, layout methods to enhance the analog performance of multi-fin FinFET structures are proposed. By adding the spacer and SEG structures, the drive current of 1-fin FinFET increases. However, the unity gain frequency, $f_T$, reduces by 19.4 % due to the increase in the total capacitance caused by the added spacer. If the process element is not included in multi-fin FinFET, replacing 1-finger with 2-finger structure brings approximately 10 % of analog performance improvement. Considering the process factors, we propose methods to maximize the analog performance by optimizing the interconnect and gate structures.

• Journal of Ocean Engineering and Technology
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• v.29 no.2
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• pp.191-198
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• 2015

In this study, we proposed a new type of dual-buoy wave energy converter (WEC) exploiting multi-resonance and analyzed the experimental results from a model test in a 2-D wave flume. A dual-buoy WEC using multi-resonance has two advantages: high efficiency at the resonant frequencies and the potential to extend the frequency range available to extract wave power from the WEC. The suggested WEC was composed of an outer buoy and an inner buoy sliding vertically inside the outer buoy. As the power take-off device, a linear electric generator (LEG) consisting of permanent magnets and coils fixed at each buoy was adopted. Electricity was produced by the relative heave motion between the two buoys. To search for the optimal shape of a dual-buoy WEC, we conducted experiments on the heave motion of a two-body system in regular waves without an LEG installed. Model tests with six combinations of experimental models were conducted in order to find the motion characteristics of a dual-buoy WEC. It was found that model 2, which included a ring-shaped appendage to move the resonant frequency of the outer buoy toward a high value, showed a higher relative heave response amplitude operator (RAO) curve than model 1. In addition, the double-peak shape of the heave RAO curve shown for model 2 indicated the extension of the frequency range for extracting wave power in irregular waves.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.1
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• pp.231-238
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• 2017

Water supply safety index plays an important role on assessing the water supply capacity of hydrologic system. Due to the absence of consistent guidance, however, practical problems have been brought up on data period used for dam design and performance evaluation. Therefore, this study employed bivariate drought frequency analysis which is able to consider drought severity and duration simultaneously, in order to evaluate water supply capacity of multi-purpose dams. Drought characteristics were analyzed based on the probabilistic approach, and water supply capacity of five multi-purpose dams in Korea (Soyang River, Chungju, Andong, Daecheong, Seomjin River) were evaluated under the specific drought conditions. As a result, it would be possible to have stable water supply with their own inflow during summer and fall, whereas water shortage would occur even under the 1-year return period drought event during spring and winter due to low rainfall.

• Journal of Broadcast Engineering
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• v.4 no.1
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• pp.1-11
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• 1999

This paper introduces orthogonally multiplexed modulation and demodulation methods based on Wavelet Packet Bases and particularly describes Wavelet Packet Modulation (WPM) techniques that provide the designer of transmission signal set in time-frequency domain with tree structural information which can be adapted to given channel characterristics. Multi-dimensional signaling methods are also contrasted to common and different characteristics of conventional QAM. multi-tone modulation methods. The paper addresses the mothod how to find a best tree structure that has more adaptivity to impulse and narrowband tone pulse noises using a tunning algorithm which arbitrarily partitions the time-frequency space and makes a suitable orthogonal signaling waveforms. Simulation results exhibits a favorable performance over existing mod/demod methods specially for narrowband tone pulse and impulse interferences.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.1
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• pp.70-77
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• 1999

A miniaturized voltage controlled oscillator using multi-layer ceramic technology at PCS frequency band is designed and fabricated. To improve the phase noise characteristics and to reduce the size, the strip line which is embedded in a high performance multi-layer ceramic substrate is used as an inductor of VCO. And the fabricated VCO is very small size ($6mm\times6mm\times2mm$). At the bias condition of 3.3 V and 9mA, the output power and phase noise in the operating frequency range of 1,720~1,780 MHz are -3.7 dBm and -95 dBc/Hz at 10 KHz offset from the carrier, respectively. The phase noise and size are better than the conventional VCO using glass epoxy substrate.

• Journal of Advanced Navigation Technology
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• v.8 no.1
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• pp.73-80
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• 2004

In the case of Non-Line-of-Sight (NLOS), common telecommunication systems typically have Rayleigh distributed amplitude characteristics. However measurement result of Ultra Wideband (UWB) Multi-Band Orthogonal Frequency Division Multiplexing (MB-OFDM) system which is proposed as one of candidate standard in IEEE 802. 15. 3a for Wireless Personal Area Network (WPAN) shows that it has independent log normal fading in each cluster as well as in each ray within the cluster. Based on this clustering phenomenon observed, MB-OFDM channel model derived from Saleh-Valenzuela model with a couple of slight modifications. In this paper, channel remodeling for RF frequency hopping in MB-OFDM system is achieved, and performances of MB-OFDM system for each channel mode and data rate are verified using modified channel model.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.12B
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• pp.1637-1647
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• 2001

Multi-Code CDMA (MC-CDMA) can not only be integrated easily with a conventional system, but also achieve good spectral efficiency and high processing gain. However, it suffers from high value of peak-to-average power ratio (PAPR). In this paper, we propose the Multi-Phase CDMA (MP-CDMA) system that can provide variable rate service and is not susceptible to the non-linear characteristics of amplifier. The clipping is introduced between at the output of multi-code modulator and at the input of MPSK modulator in order to improve the performance of MPSK chip demodulator and reduce the system complexity, The system performances are compared for the different Number of codes and different clipping levels, respectively. The optimum clipping level is also evaluated for the different number of codes in both, AWGN and frequency flat fading channel.

• Proceedings of the IEEK Conference
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• 2002.07c
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• pp.1996-1999
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• 2002

Applying a higher frequency periodic control signal, a state of a chaotic pulse-train generator is quantized. The circuit has various co-existing super-stable periodic pulse-trains (ab. SSPTs) and generates one of them depending on the initial state. Also correlation characteristics of the SSPTs are analyzed precisely. We then consider application of the SSPTs to spread sequences of CDMA with pulse-train signals.