• The Transactions of the Korean Institute of Electrical Engineers
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• v.45 no.2
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• pp.199-215
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• 1996

A new Class-D series-loaded resonant inverter topology which can minimize the influences of the stray inductances is presented. In the conventional Class-D inverters, the stray inductances not only result in the overvoltage which gives the switches voltage stresses, but also in the high frequency resonant currents during turn-off transients. The new Class-D inverter is superior to the conventional Class-D inverters with respect to minimization of the problems caused by the stray inductances and is more suitable for high power and high frequency inverter systems such as induction heating. The validity of the new Class-D inverter is verified by simulation and experimental results.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.12
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• pp.1060-1068
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• 2011

In this paper, Current-Mode Class-D(CMCD) RF Power Amplifier(PA) is designed and implemented at 900 MHz. Conventional CMCD PA has output parallel resonator to reconstruct a fundamental frequency component of the output signal. However the resonator can be removed by connecting inverse class-F PAs because even-harmonic components can be removed by CMCD PA's push-pull structure. Using load-pull, inverse class-F PA with GaN transistors is designed, and CMCD PA with the inverse class-F PA is implemented. The CMCD PA has 64.5 % drain efficiency, 34.2 dBm output power. Comparing with the drain efficiency of a CMCD PA with parallel resonator, the CMCD with the inverse class-F technology has 13.6 % improved drain efficiency.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.1
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• pp.110-114
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• 2008

In this paper, high efficient class F power amplifier with dual band has been realized. Dual band power amplifier have used modify stub matching for single FET, center frequency 2.14GHz and 5.2GHz respectively. Dual band amplifier is 32.65dBm output power, gain 11dB and PAE 36% at the 2.14GHz, 7dB gain at the 5.2GHz. Design of a dual band class F power amplifier using harmonic control circuit. The measured are 9.9dB gain, 30dBm output power and PAE 55% at the 2.14GHz, 11.7dB gain at the 5.2GHz. This paper is being used the load-pull method and it maximizes output power and it is using the only one transistor in the paper. As a result, this research will obtain a dual band high PAE power amplifier.

• Journal of Information Technology Services
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• v.6 no.1
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• pp.151-158
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• 2007

D-class computation requires multiplication of three Boolean matrices for each of all possible triples of $n{\times}n$ Boolean matrices and search for equivalent $n{\times}n$ Boolean matrices according to a specific equivalence relation. It is easy to see that even multiplying all $n{\times}n$ Boolean matrices with themselves shows exponential time complexity and D-Class computation was left an unsolved problem due to its computational complexity. The vector-based multiplication theory shows that the multiplication of three Boolean matrices for each of all possible triples of $n{\times}n$ Boolean matrices can be done much more efficiently. However, D-Class computation requires computation of equivalent classes in addition to the efficient multiplication. The paper discusses a theory and an algorithm for efficient D-class computation, and shows execution results of the algorithm.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.48 no.6
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• pp.56-61
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• 2011

A class-D audio amplifier is widely used in coil speaker. This paper presented the technique for applying a class-D audio amplifier to the ceramic flat speaker. This technique can be achieved by employing a matching transmitter in order to replace class-G amplifier that is drven by voltage level to class-D amplifier employing power driving method. Consequently, the presented technique can improve the efficiency by making the voltage driving level a litter larger. We evaluate the sound-level efficiency using the various mediums such as wood, plastic, and paper. From the simulation results, the proposed technique employing a class-D audio amplifier rather than a class-G one showed a 10% improvement. The proposed system can be applicable for the mobile appliances as an external slim speaker.

• Journal of Korea Multimedia Society
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• v.19 no.2
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• pp.460-468
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• 2016

The teaching method of colleges and universities is traditionally lectures then professors has described orally in class and students has listened to accompanying with papers, mid-terms, and final exams. Jon Bergmann and Aaron Sams have developed new way of teaching called flipped learning; Classwork at home and homework in class. By adapting the method, this paper researched how efficient it is and what factors tutors should consider for better results. Specifically this research examined the flipped learning applying to basic 3D graphics class of J University in Korea and students answered surveys and took a couple of tests. Since the most students of the class did not have any background of 3D graphics, it was the first time for them to work with 3 dimensional space coordinate system. As a result, the research showed positive side of flipped learning like increasing peers' interest to the class and positive attitude about video lectures watched before coming to class.

• Journal of the Korean Professional Engineers Association
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• v.10 no.2
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• pp.27-34
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• 1977

The principle, performance and applications of the unique Class-D power amplifier, having power conversion efficiency of 100% in ideal case, have been described.

• Journal of the Korean Society of Propulsion Engineers
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• v.3 no.4
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• pp.12-22
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• 1999

Operation of an electromagnetic shaker system using a Class-D amplifier may cause unacceptable electromagnetic interference to another electronic system, requiring the user to take whatever steps are necessary to correct the interference. A differential amplifier in a Class-D amplifier is used to decrease the effect of a common-mode noise voltage in a shaker system. To prevent a ground loop, a transformer is inserted in another shaker system. These methods show reduction of the unwanted vibration which has occurred before. A transformer in a charge amplifier was used to prevent a ground loop in a shaker system using a Class-AB amplifier a few years ago, but it was susceptible of noise in a shaker system using a Class-D amplifier. Hence we corrected a ground loop between a charge amplifier and a vibration control/analysis system without a transformer. The usefulness of this approach is illustrated by the results of experiments.

• ETRI Journal
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• v.35 no.5
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• pp.819-826
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• 2013

A class-D audio amplifier for a digital hearing aid is described. The class-D amplifier operates with a pulse-code modulated (PCM) digital input and consists of an interpolation filter, a digital sigma-delta modulator (SDM), and an analog SDM, along with an H-bridge power switch. The noise of the power switch is suppressed by feeding it back to the input of the analog SDM. The interpolation filter removes the unwanted image tones of the PCM input, improving the linearity and power efficiency. The class-D amplifier is implemented in a 0.13-${\mu}m$ CMOS process. The maximum output power delivered to the receiver (speaker) is 1.19 mW. The measured total harmonic distortion plus noise is 0.015%, and the dynamic range is 86.0 dB. The class-D amplifier consumes 304 ${\mu}W$ from a 1.2-V power supply.

• Nutritional Sciences
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• v.7 no.2
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• pp.107-112
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• 2004

This study investigated the interactions of bone health with several variables such as outdoor activity hours, nutritional status including habitual intake of calcium andvitamin D status in 72 high school girls aged 16-17 yearsattending day classes or night classes. The subjects consisted of 39 day-class students and 33 night-class students. Dietaty nutrient intakes were estimated using the 24-hour recall method. The daily activities of each subject were assessed using an activity questionnaire. Urinary calcium and creatinine excretion were assayed from subjects' 24-hoururine, while 25-OH-vitamin D[25-(OH)-D] and osteocalcin were measured from the subjects' fasting blood. Intake of energy, iron, vitamin A and vitamin C were worse in the night-class students. There was no significant difference in dietary calcium between the subjects in the different class types. Time spent on outdoor activities was significantly less in subjects attending night classes. Urinary calcium excretion of the night-class subjects was significantly higher than that of the day-class subjects (p<0.05). There was no significant difference in serum 25-(OH)-D level according to class type. Serum osteocalcin for night-class subjects was significantly higher than that for day-class subjects (p<0.01). It appeared that the night-class students had poorer dietary habits as well as fewer outdoor activities. Even though the estimated bone health of both groups of subjects appeared to be normal, the overall nutritional intake and duration of outdoor activities appeared to be important for maintaining bone health and lowering the future risk of osteoporosis.