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Search Results: 1 - 10 of 7665 matches for " Changkun Park "
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A Brief Review: Stage-Convertible Power Amplifier Using Differential Line Inductor  [PDF]
Jonghoon Park, Changhyun Lee, Changkun Park
Wireless Engineering and Technology (WET) , 2012, DOI: 10.4236/wet.2012.34027
Abstract: In this review article, a stage-convertible RF power amplifier designed with a 0.18-μm RF CMOS process is described. A method to implement a low-power matching network is an essential technology for the stage-convertible power amplifier. Various low-power matching networks with distributed active transformers as an output power combiner are compared in terms of the amounts of undesired coupling, the chip size, and the amount of power loss. The feasibility of a differential line inductor for the stage-convertible power amplifier is assessed and explained. Finally, we show that the differential line inductor is a realistic means of reducing the overall chip size, enhancing the quality factor of the matching network, and minimizing the undesired coupling between the inter-stage matching network and any output matching network. Additionally, the operating mechanism of the stage-convertible power amplifier using the differential line inductor for a low-power matching network is described in detail.
Differential Transformer Using Bonder-Wires and Patterns on a Printed Circuit Board for RF Circuit Applications
Byungjoo Kang;Hoyong Hwang;Changkun Park
PIER , 2013, DOI: 10.2528/PIER12120402
Abstract: A transformer that uses bonder-wires and printed circuit board (PCB) patterns is proposed for RF circuit applications. The proposed transformer can be constructed without any additional processes. The PCB patterns are implemented using a typical FR4 substrate and gold bonder wires are used. The self-inductance of the transformer can be controlled according to the number of unit-transformers. Although the size of the transformer is larger than that of a fully-integrated transformer, the maximum available gain (MAG) is almost identical to that of other-types of transformers, which require additional cost or bulky size to obtain sufficient inductance. Additionally, we proposed a method to design the transformer with a symmetric structure for differential RF CMOS circuit applications. The transformer can applied to GHz-order RF CMOS circuits as an input and output matching component with low loss characteristics.
Study of the Inter-Stage Capacitor Effects of a RF Cmos Power Amplifier to Enhance its Efficiency
Hoyong Hwang;Donghwan Seo;Jonghoon Park;Changkun Park
PIER C , 2013, DOI: 10.2528/PIERC12122806
Abstract: In this work, we analyze the effects of an inter-stage capacitor located between the power stage input and the driver stage output on the overall efficiency of a RF CMOS power amplifier and on gate-drain reliability problems. To verify the analyzed effects, we designed a RF CMOS power amplifier with a center frequency of 1.85-GHz. Class-D amplifiers with a feedback resistor are used as driver stages, and a class-E amplifier is used as the power stage. A distributed active transformer is adapted for use in the output power combiner for high efficiency. The inter-stage capacitor between driver and the power stage is removed to enhance the switching operation of the power stage. By eliminating the inter-stage capacitor, the supply voltage of the driver stage can be decreased compared to that in a general amplifier. Accordingly, the power-added efficiency is improved and the gate-drain reliability problems are moderated compared to a general amplifier. The analyzed effect of the inter-stage capacitor is verified successfully using the measured results of the designed amplifiers.
Study of the Coil Structure for Wireless Chip-to-Chip Communication Applications
Changhyun Lee;Jonghoon Park;Jinho Yoo;Changkun Park
PIER Letters , 2013, DOI: 10.2528/PIERL13022002
Abstract: In this work, we propose a merged coil structure for wireless chip-to-chip communication technology. Using the proposed coil structure, the chip size can be reduced, and the transmitted power can be improved by approximately 5 dB compared to typical coil structure. To verify the feasibility of the coil, an electromagnetic simulation and a schematic simulation are performed. The coil was implemented using 50-nm digital CMOS technology. From the experimental results, the feasibility was proved.
Theoretical calculations on the atomic and electronic structure of β-SiC(110) surface

XIE Changkun,

科学通报(英文版) , 2002,
Abstract: We present a theoretical calculation of the atomic and electronic structure of β-SiC and its non-polar (110) surface using the full potential linear augmented plane wave (FPLAPW) approach. The calculated lattice constant and bulk modulus of β-SiC crystal are in excellent agreement with experimental data. The atomic and electronic structure of β-SiC(110) surface has been calculated by employing the slab and supercell model. It is found that the surface is characterized by a top-layer bond-length-contracting rotation relaxation in which the Si-surface atom moves closer towards the substrate while the C-surface atom moves outward. This relaxation is analogous to that of III-V semiconductor surface. The driving mechanism for this atomic rearrangement is that the Si atom tends to a planar sp2-like bonding situation with its three N neighbors and the N atom tends to a p3-like bonding with its three Si neighbors. Furthermore, surface relaxation induces the change from metallic to semiconducting characterization.
Simplified Model for Fire Resistance Analysis on Steel Staggered-truss System under Lateral Force
Changkun Chen,Dong Zhang,Guanglin Liu
International Journal of Image, Graphics and Signal Processing , 2010,
Abstract: In order to investigate the simplified method for the fire resistance analysis on the steel staggered-truss system (SSTS) under the lateral force, a three-dimensional (3-D) model, a plane cooperative (PC) model and a planar model are established by the finite element method respectively. The effect of slabs is considered in the models. The mechanical performances of SSTS at elevated temperature were analyzed and the interaction characteristics between the truss exposed to fire and its adjacent trusses are studied. The results obtained by the above different models were comparatively investigated to explore the applicability of different models for the analysis of SSTS under lateral force and high temperature. The results indicate that the adjacent trusses in SSTS under lateral force could keep good coordination at elevated temperature. When applied to the analysis for SSTS under lateral force at elevated temperature, the 3-D model is the best in accord with actual situation while it is complicated and the computation is time-consuming, and the planar model is simple and convenient while it may cause some considerable deviation, and the PC model could simulate the interactions between adjacent frame truss and the truss under fire effectively in the SSTS, whose result is in the propinquity of 3-D model and has an acceptable accuracy. The PC model without rigidly hinged bars (RHB) on the fire floor is recommended to analyze the fire response behaviors of staggered-steel truss system under lateral force.
Theoretical calculations on the atomic and electronic structure of β-SiC(110) surface
Changkun Xie,Pengshou Xu,Faqiang Xu,Haibin Pan
Chinese Science Bulletin , 2002, DOI: 10.1360/02tb9181
Abstract: We present a theoretical calculation of the atomic and electronic structure of β-SiC and its non-polar (110) surface using the full potential linear augmented plane wave (FPLAPW) approach. The calculated lattice constant and bulk modulus of β-SiC crystal are in excellent agreement with experimental data. The atomic and electronic structure of β-SiC(110) surface has been calculated by employing the slab and supercell model. It is found that the surface is characterized by a top-layer bond-length-contracting rotation relaxation in which the Si-surface atom moves closer towards the substrate while the C-surface atom moves outward. This relaxation is analogous to that of III-V semiconductor surface. The driving mechanism for this atomic rearrangement is that the Si atom tends to a planar sp2-like bonding situation with its three N neighbors and the N atom tends to a p3-like bonding with its three Si neighbors. Furthermore, surface relaxation induces the change from metallic to semiconducting characterization.
The Finite-Element Modeling of Dynamic Motions of a Constraint Wind Turbine and the System Diagnosis for the Safety Control  [PDF]
Raiwung Park
Engineering (ENG) , 2013, DOI: 10.4236/eng.2013.512123
Abstract:

The aim of this paper is to present a finite element modeling of the dynamic motion of a turbine rotor and its controller design with the mass unbalance under a crack on a rotating shaft. This process is an advanced method to the mathematical description of a system including an influence of a mass unbalance and a crack on the rotor shaft. As the first step, the shaft is physically modeled with a finite element method and the dynamic mathematical model is derived by using the Hamilton principle; thus, the system is represented by various subsystems. The equation of motion of a shaft with a mass unbalance and a crack is established by adapting the local mass unbalance and stiffness change through breathing and gaping from the existence of a crack. This is a reference system for the given system. Based on a fictitious model for transient behavior induced from vibration phenomena measured at the bearings, an elementary estimator is designed for the safety control and detection of a mass unbalance on the shaft. Using the state estimator, a bank of an estimator is established to get the diagnosis and the system data for a controller.

The effect of individualized music on agitation for home-dwelling persons with dementia  [PDF]
Heeok Park
Open Journal of Nursing (OJN) , 2013, DOI: 10.4236/ojn.2013.36061
Abstract:

Purpose: The purpose of this study was to test the effect of individualized music on agitation for homedwelling patients with dementia. Method: One group pre-post test was used for research design and a total of 26 subjects participated in this study. Individualized music intervention was subjects’ listening to their preferred music for 30 minutes prior to peak agitation time twice a week for a total of four sessions. The subject’s agitation levels were measured for three different points: thirty minutes prior to listening to music, 30 minutes while listening to the music, and after listening to the music throughout the 4 sessions. To measure the agitation level, the modified CohenMansfield Agitation Inventory was used. A Paired ttest was used for data analysis. Results: Most subjects were female (73.1%), Caucasian (92.4%), Protestant (50%), and independent activity (53.8%). The mean of the subjects’ MMSE scores was 8.08 (8.17). The most favorite music types included country/western music (31.0%), religious music (26.9%), and big band (26.9%). Agitation level decreased while listening to the music compared to the baseline (t = 3.70, p < .001). Conclusion: The findings of this study would provide meaningful data to develop an individualized music intervention protocol to control agitation for homedwelling patients with dementia.

 

Partially Funded Social Security and Inter-Generational Distribution  [PDF]
Hyeon Park
Theoretical Economics Letters (TEL) , 2014, DOI: 10.4236/tel.2014.49107
Abstract: This paper introduces a parametric model of partially funded social security system and analyzes inter-generational distribution of consumption and welfare in an OLG general equilibrium. This paper specifically aims to examine the effects of transition toward more funded system on saving and capital accumulation. It is shown that an increase in intensity of fundedness increases capital accumulation unless the income effect from interest rate change outweighs other effects and negatively affects the total saving severely. By deriving closed form solutions for the variables, this paper finds that an increase in the intensity of fundedness increases saving but decreases consumption, when population growth rate is greater than the net return to capital. This paper also finds that for a partially funded system, an increase in tax rate increases public saving but reduces private saving unambiguously, while the effects on consumption and capital accumulation are not conclusive.
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