• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.5
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• pp.949-954
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• 2007

In this work, temperature stable frequency-to-voltage converter is proposed. In FVC circuit input frequency is converted into output voltage signal. A FLL is similar to PLL in the way that it generates an output signal which tracks an input reference signal. A PLL is built on a phase detector, a charge pump, and a low pass filter. However, FLL does not require the use of the phase detector, the charge pump and low pass filter. The FVC is designed by using $0.25{\mu}m$ CMOS process technology. From simulation results, the variation of output voltage is less than ${\pm}2%$ in the temperature range $0^{\circ}C\;to\;75^{\circ}C$ when the input frequency is from 70MHz to 140MHz.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.9
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• pp.60-67
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• 2007

A signal conditioning circuit for capacitive displacement sensors was developed using a high frequency modulation/demodulation method, and its performance was evaluated. Since capacitive displacement sensors can achieve high resolution and linearity, they have been widely used as precision sensors within the range of several hundred micrometers. However, they inherently have a limitation in low frequency range and some nonlinearity characteristics and so a specially designed signal conditioning circuit is needed to handle these properties. The developed signal processing circuit consists of three parts: linearization, modulation/demodulation, and nonlinearity compensation. Each part was constructed discretely using several IC chips and passive elements. An evaluation system for precision displacement sensors was developed using a laser interferometer, a precision stage, and a PID position controller. The signal processing circuit was tested using the evaluation system in the respect of resolution, repeatability, linearity, and so on. From the experimental results, we know that a highly linear voltage output can be obtained successfully, which is proportional to displacement and the nonlinearity of output is less than 0.02% of full range. However, in the future, further investigation is required to reduce noise level and phase delay due to a low-pass filter. The evaluation system also can be applied effectively to calibration and evaluation of precision sensors and stages.

• The Journal of the Acoustical Society of Korea
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• v.32 no.5
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• pp.369-376
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• 2013

Using Lowson's acoustic analogy, low frequency noise of a wind turbine (WT) is predicted in time domain and the noise sources contributing to the low frequency noise is analyzed. To compute averaged pressure distribution on blades of the WT as noise source, XFOIL is utilized. The blade source domain is divided into several segments along the span direction to compute force exerted on air surrounding the blade segments, which is used as input for noise prediction. The noise sources are decomposed into three terms of force fluctuation, acceleration and velocity terms and are analyzed to investigate each spectral contribution. Finally, predicted spectra are compared with measured low frequency noise spectrum of a wind turbine in operation. It is found that the force fluctuation component contributes strongly in low frequency range with increasing wind speed.

• Journal of Korea Society of Industrial Information Systems
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• v.18 no.5
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• pp.9-14
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• 2013

This paper is designed frequency multiplier with low phase noise using DLL technique. The VCDL is designed using a differential structure to reduce common-mode noise. The proposed frequency multiplier is fabricated in a 65nm, 1.2V TSMC CMOS process, and the operating frequency range from 10MHz to 24MHz was measured. The SSB phase noise is measured to be -125dBc/Hz at 1MHz from 38.4MHz carrier. A total area of $0.032mm^2$were consumed in the chip, including the output buffer. Total current is 1.8mA at 1.2V supply voltage.

• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.4
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• pp.351-355
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• 2016

Welding machines are high-capacity systems used in a low-frequency range using IGBT. As their system is similar to a large transformer, most welding machines suffer a great loss because of hard switching and vast leakage inductance. A voltage-balancing circuit is designed to overcome these shortcomings. This circuit can reduce the transformer size by making it into a high frequency and reducing the input voltage by half and by adopting a serial structure that connects two full-bridges in a series to use a MOSFET with a good property at high frequency. In addition, a Schottky diode is used in the primary rectifier to overcome the low efficiency of most welding machines. To use the Schottky diode with a reliably relatively low withstanding voltage, an active snubber is adopted to effectively limit the ringing voltage of the diode cut-off voltage.

• Proceedings of the KIEE Conference
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• 1999.07f
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• pp.2653-2655
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• 1999

A technique to suppress the low frequency ripple voltage of the DC output voltage in three-phase buck diode rectifiers is presented. A pulse frequency modulation method is employed to regulate the output voltage of the rectifier and guarantee zero-current switching of the switch over the wide operating range. The pulse frequency control method used in this paper shows generally good performance such as low THD of the input line current and unity power factor. In addition, the pulse frequency method can be effectively used to suppress the low frequency voltage ripple appeared in the dc output voltage. The proposed technique illustrates its validity and effectiveness through the respective simulations and experiments.

• Journal of Electrical Engineering and Technology
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• v.11 no.3
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• pp.707-714
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• 2016

We present a piezoelectric energy harvester with stopper-engaged dynamic magnifier which is capable of significantly increasing the operating bandwidth and the energy (power) harvested from a broad range of low frequency vibrations (<30 Hz). It uses a mass-loaded polymer beam (primary spring-mass system) that works as a dynamic magnifier for another mass-loaded piezoelectric beam (secondary spring-mass system) clamped on primary mass, constituting a two-degree-of-freedom (2-DOF) system. Use of polymer (polycarbonate) as the primary beam allows the harvester not only to respond to low frequency vibrations but also generates high impulsive force while the primary mass engages the base stopper. Upon excitation, the dynamic magnifier causes mechanical impact on the base stopper and transfers a secondary shock (in the form of impulsive force) to the energy harvesting element resulting in an increased strain in it and triggers nonlinear frequency up-conversion mechanism. Therefore, it generates almost four times larger average power and exhibits over 250% wider half-power bandwidth than those of its conventional 2-DOF counterpart (without stopper). Experimental results indicate that the proposed device is highly applicable to vibration energy harvesting in automobiles.

• International Journal of Highway Engineering
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• v.19 no.5
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• pp.97-106
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• 2017

PURPOSES: This study aims to evaluate the effects of vehicle dynamic behaviors on ride quality. METHODS : Simulation and field test were conducted to analyze the behavior of a driving vehicle. The simulation program CarSIM was applied and an INS (Inertial Navigation System) was used for field experiments. A small simulator was developed to simulate vehicle behavior such as roll, pitch, and bounce. The panels evaluated the ride quality in five stages from "very satisfied"to "very dissatisfied."Experiments were conducted on a total of 144 cases of vehicle behavior combinations. RESULTS :In both simulation and field tests, pitch is the largest and yaw the smallest. Especially in the field test, the amount of yaw is very low, about 7% of pitch and 18% of roll. The sensitive and extensive analysis conducted related ride quality with changing the frequency and amplitude. It was found that the most sensitive frequency range is 8 Hz across all amplitudes. Moreover, the combination of the roll and bounce was most sensitive to the ride quality at the low-frequency range. CONCLUSIONS : This result show that the vertical vehicle behavior (bounce) as well as the rotational behavior (roll and pitch) are highly correlated with ride quality. Therefore, it is expected that a more reasonable roughness index can be developed through a combination of vertical and rotational vehicle behavior.

• The Journal of the Acoustical Society of Korea
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• v.19 no.1
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• pp.40-47
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• 2000

To obtain the acoustic properties of dispersive polyurethane with high attenuation, through transmission method was applied by ultrasonic. In through transmission method, the sound velocity and attenuation coefficient of specimen were obtained by using Sachse's method which can be applied to small size specimen. But there is a problem when the reference signal is selected, so the result is not precise. The more precise acoustic properties of polyurethane was obtained when two specimens with different thickness were used. To predict the acoustic properties of low frequency range, the acoustic properties extended to the low frequency range were calculated by Kramers - Kronig relation. As a result, we studied on the relation between the sound velocity and the attenuation coefficient with frequency.

• Journal of Power Electronics
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• v.11 no.3
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• pp.271-278
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• 2011

This paper presents a LLC resonant controller IC for secondary side control without external active devices to achieve low profile and low cost LED back light units. A gate driving transformer is adopted to isolate the primary side and the secondary side instead of an opto-coupler. A new integrated dimming circuitry is proposed to improve the dynamic current control characteristic and the current density of a LED for the brightness modulation of a large screen LCD. A dual-slope clock generator is proposed to overcome the frequency error due to the under shoot in conventional approaches. This chip is fabricated using 0.35 ${\mu}m$ BCD technology and the die size is $2{\times}2\;mm^2$. The frequency range of the clock generator is from 50 kHz to 500 kHz and the range of the dead time is from 50 ns to 2.2 ${\mu}s$. The efficiency of the LED driving circuit is 97 % and the current consumption is 40 mA for a 100 kHz operation frequency from a 15 V supply voltage.