Hong Jin Kim

Sungkyunkwan University, Sŏul, Seoul, South Korea

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Publications (7)13.49 Total impact

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    ABSTRACT: This paper presents a low power ring oscillator-based spread-spectrum clock generator with three-step frequency and voltage-controlled oscillator (VCO) gain calibration for S-ATA applications. To meet the low jitter requirements with a small VCO gain, a ring-type VCO with three step frequency calibration and gain calibration scheme is proposed. The proposed coarse tuning method selects the optimal tuning currents and capacitances of the ring VCO to optimize the phase noise. The gain of ring-type VCO can be reduced and kept constant with the proposed three-step frequency and VCO gain calibration. As a result, it can improve the phase noise characteristics of the ring-type VCO and make it more robust to the PVT variations. Also, charge pump up/down current mismatches are compensated with the current mismatch compensation block. This chip is fabricated with 65 nm CMOS technology, and the die area is 430 × 460 μm2. The power consumption is 12 mW at 1.2 V supply voltage. The measured RMS jitter and phase noise are 2.835 ps and −96.83 dBc/Hz at 1 MHz offset, respectively.
    Analog Integrated Circuits and Signal Processing 03/2014; 78(3). · 0.55 Impact Factor
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    ABSTRACT: In this paper, a Relaxation Oscillator with temperature compensation using BGR and ADC is presented. The current to determine the frequency of Relaxation Oscillator can be controlled. By adjusting the current according to the temperature using the code that is output from the ADC and BGR, was to compensate the output frequency of the temperature. It is fabricated in a 0.35 CMOS process with an active area of . Current consumption is 600 from a 5 V and the rate of change of the output frequency with temperature shows about .
    Journal of the Korea Industrial Information System Society. 01/2013; 18(5).
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    ABSTRACT: This paper presents a low-profile low-cost (LLC) resonant controller IC for LED backlight units fully operating at the secondary side. The integrated dimming circuitry is proposed to improve the dynamic current control characteristics and the LED current density for the brightness modulation of a large screen liquid crystal display. A dual-slope clock generator, including a soft start, is proposed in order to overcome the frequency error due to the undershoot found in conventional approaches. In addition, a new dead-time generator is proposed in order to implement an accurate dead time independent of the output frequency of the clock generator. Protection circuits, such as a under voltage lock out, thermal shut down, open LED detector, and shorted LED detector, have been implemented in order to improve the reliability of the controller IC. The chip is fabricated using 0.35 μm bipolar CMOS DMOS decimal technology; the die size is 2 mm × 2 mm. The frequency of the clock generator ranges from 50 to 500 kHz; the dead time ranges from 50 ns to 2.2 μs. The efficiency of the LED driving circuit is 91%. The current consumption of the LLC resonant controller IC is 40 mA for a 100 kHz operation frequency using a 15 V supply voltage.
    IEEE Transactions on Power Electronics 12/2011; · 4.08 Impact Factor
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    ABSTRACT: Two new biphenylquinolizidine alkaloids, 5-epi-dihydrolyfoline (1) and its stereoisomer, dihydrolyfoline (2), along with lagerine (3) were isolated from the aerial parts of Lagerstroemia indica. The structures of compounds 1-3 were elucidated by extensive spectroscopic techniques.
    Journal of Natural Products 04/2009; 72(4):749-52. · 3.29 Impact Factor
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    ABSTRACT: Chromatographic separation of the EtOAc fraction from the leaf and stem of Vitis amurensis led to the isolation of six oligostilbenoids (i.e., r-2-viniferin (1), trans-amurensin B (2), trans-epsilon-viniferin (3), gnetin H (4), amurensin G (5), (+)-ampelopsin A (8)) and four stilbenoids (i.e., trans-resveratrol (6), (+)-ampelopsin F (7), piceatannol (9), and trans-piceid (10)). The structures have been identified on the basis of spectroscopic evidence and physicochemical properties. The isolates were investigated for cytotoxic activity against three cancer cell lines in vitro using the MTT assay method. Amurensin G (5) and trans-resveratrol (6) showed significant cytotoxic activity against L1210, K562 and HTC116 cancer cell lines with IC(50) values ranging from 15.7 +/- 2.1 to 30.9 +/- 1.8 microM. (+)-Ampelopsin A (8) and trans-piceid (10) exhibited considerable cytotoxic activity against L1210 (IC(50) values of 30.6 +/- 4.1 and 28.7 +/- 2.81 microM, respectively) and K562 (IC(50) values of 38.6 +/- 0.82 and 24.6 +/- 0.76 microM, respectively). Gnetin H (4) showed only weak cytotoxic activity against L1210 with an IC(50) value of 40.1 +/- 4.23 microM. On the other hand, r-2-viniverin (1), trans-amurensin B (2), trans-epsilon-viniferin (3), (+)-ampelopsin F (7), and piceatannol (9) exhibited no activity on three cancer cell lines.
    Archives of Pharmacal Research 03/2009; 32(2):177-83. · 1.54 Impact Factor
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    ABSTRACT: In the course of screening plants used in Korean folk medicine as memory enhancers, a 70% ethanol extract of tuber from Corydalis turtschaninovii Besser (Papaveraceae) showed significant acetylcholinesterase (AChE) inhibitory activity. Repeated column chromatography led to the isolation of a new aporphine alkaloid, oxoglaucidaline (9), and a new protoberberine, pseudodehydrocorydaline (13) together with 14 known compounds (1-8, 10-12, and 14-16). The chemical structures of isolated compounds were elucidated base on extensive 1D and 2D NMR spectroscopic data. Compounds 1-16 were investigated in vitro for their anti-cholinesterase activity using the mice cortex AChE enzyme. In further study, the anti-amnesic activities of pseudoberberine (16) in mice on the learning and memory impairments induced by scopolamine (1.0 mg/kg, i.p.) were examined. This alkaloid (5.0 mg/kg, p.o.) administration significantly reversed cognitive impairments in mice by passive avoidance test (P<0.05). It also reduced escape latencies in training trials and prolonged swimming times in the target quadrant during the probe trial in the water maze task (P<0.05). These results indicated that Corydalis turtschaninovii due to its alkaloids have anti-cholinesterase activity and pseudoberberine and other alkaloids have anti-amnesic activities that may be useful for cognitive impairment treatment.
    Journal of Ethnopharmacology 06/2008; 119(1):74-80. · 2.76 Impact Factor
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    ABSTRACT: The stabilization of optimum pH for cells can cause a higher erythropoietin (EPO) production rate and a good growth rate with the prolonged culture span in recombinant Chinese hamster ovary (r-CHO) cells. Our strategy for stabilizing the optimum pH in this study is to reduce the lactate production by adding sodium lactate to a culture medium. When 40 mM sodium lactate was added, a specific growth rate was decreased by approximately 22% as compared with the control culture. However the culture longevity was extended to 187 h, and more than a 2.7-fold increase in a final accumulated EPO concentration was obtained at 40 mM of sodium lactate. On the condition that caused the high production of EPO, a specific glucose consumption rate and lactate production rate decreased by 23.3 and 52%, respectively. Activity of lactate dehydrogenase (LDH) in r-CHO cells increased and catalyzed the oxidation of lactate to pyruvate, together with the reverse reaction, at the addition of 40 mM sodium lactate. The addition of 40 mM sodium lactate caused the positive effects on a cell growth and an EPO production in the absence of carbon dioxide gas as well as in the presence of carbon dioxide gas by reducing the accumulation of lactate.
    Biotechnology and Bioprocess Engineering 12(1):60-72. · 1.28 Impact Factor