• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.1
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• pp.719-727
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• 2021

In the field of architecture, retractable devices capable of responding flexibly to the environment have been applied widely to large structures. Among these devices, the aesthetically pleasing retractable membrane is lightweight so that the membrane can be opened easily using only a traction device. On the other hand, because the towed membrane moves as it is connected to the main cable by a trolley, the number of trolleys needed increases in proportion to the roof's area. This study proposes an optimal model for an open-type trolley (OTT), which is used widely in these devices, using topology optimization. The analysis used the ANSYS program. A new model was proposed based on the results and reviewed through the feedback. Through this process, it was possible to develop a prototype with increased durability and reduced weight. For OTT, optimization was performed based on static analysis and the boundary conditions, so three prototypes were designed. A comparison of the proposed trolley with the conventional one under the same conditions revealed an up to 71.04% decrease in volume while the yield-strength reached 8.67 to 11.43%. In conclusion, the optimal trolley proposed was found to be reliable in terms of economy and stability.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.6 s.109
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• pp.597-604
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• 2006

An ultrawideband(UWB) $3.1{\sim}5.15$ GHz low-noise amplifier employing a novel input matching circuit and feedback topology are presented. The proposed UWB amplifier is Implemented in $0.18{\mu}m$ RF CMOS technology. Measurements show a NF of $3.4{\sim}3.9$ dB, a power gain of $12.8{\sim}14$ dB, better than -9.4 of input matching and, an input IP3 of -1 dBm, while comsuming only 14.5 mW of power.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.3
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• pp.283-291
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• 2015

In this paper, a negative impedance converter, the key element of non-Foster matching to enhance the bandwidth of matching high Q-factor passive element, is presented. Proposed negative impedance converter is implemented by the topology of Linvill's transistor negative impedance converter circuit. It is hard to forecast the operation of negative impedance circuit, because it is composed of gain element and positive feedback. Therefore the negative impedance circuit is implemented by hybrid type beforehand to check out the feasibility and it is designed by integrated circuit. The integrated circuit is fabricated by commercial $0.18{\mu}m$ SiGe BiCMOS process, and non-Foster matching is observed at 700~960 MHz band by cancelling the target reactance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.6
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• pp.427-434
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• 2013

In this paper, the design and layout of a 2.5 Gbps arrayed VCSEL driver for optical transceiver having arrayed multi-channel of integrating module is confirmed. In this paper, a 4 channel 2.5 Gbps VCSEL (vertical cavity surface emitting laser) driver array with automatic optical power control is implemented using $0.18{\mu}m$ CMOS process technology that drives a $1550{\mu}m$ high speed VCSEL used in optical transceiver. To enhance the bandwidth of the optical transmitter, active feedback amplifier with negative capacitance compensation is exploited. We report a distinct improvement in bandwidth, voltage gain and operation stability at 2.5Gbps data rate in comparison with existing topology. The 4-CH chip consumes only 140 mW of DC power at a single 1.8V supply under the maximum modulation and bias currents, and occupies the die area of $850{\mu}m{\times}1,690{\mu}m$ excluding bonding pads.

• Journal of Power Electronics
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• v.16 no.3
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• pp.1226-1235
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• 2016

For wearable health monitoring systems, a fundamental problem is the limited space for storing energy, which can be translated into a short operational life. In this paper, a highly efficient active voltage doubling rectifier with a wide input range for micro-piezoelectric energy harvesting systems is proposed. To obtain a higher output voltage, the Dickson charge pump topology is chosen in this design. By replacing the passive diodes with unbalanced-biased comparator-controlled active counterparts, the proposed rectifier minimizes the voltage losses along the conduction path and solves the reverse leakage problem caused by conventional comparator-controlled active diodes. To improve the rectifier input voltage sensitivity and decrease the minimum operational input voltage, two low power common-gate comparators are introduced in the proposed design. To keep the comparator from oscillating, a positive feedback loop formed by the capacitor C is added to it. Based on the SMIC 0.18-μm standard CMOS process, the proposed rectifier is simulated and implemented. The area of the whole chip is 0.91×0.97 mm², while the rectifier core occupies only 13% of this area. The measured results show that the proposed rectifier can operate properly with input amplitudes ranging from 0.2 to 1.0V and with frequencies ranging from 20 to 3000 Hz. The proposed rectifier can achieve a 92.5% power conversion efficiency (PCE) with input amplitudes equal to 0.6 V at 200 Hz. The voltage conversion efficiency (VCE) is around 93% for input amplitudes greater than 0.3 V and load resistances larger than 20kΩ.

• Journal of IKEEE
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• v.25 no.3
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• pp.517-527
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• 2021

This paper presents the phase-shift full-bridge DC-DC converter using the one-chip micom. The proposed converter primary is the full-bridge power topology that operates with the unipolar pulse-width modulation (PWM) by the phase-shift method, and the secondary is the full-bridge full-wave rectifier composed of four diodes. The control of proposed converter is performed by the one-chip micom and its MOSFET switches are driven by the bootstrap circuit. Thus the total system of proposed converter is simple. The proposed converter achieves high-efficiency using the resonant circuit and blocking capacitor. In this paper, first, the power-circuit operation of proposed converter is explained according to each operation mode. And the power-circuit design method of proposed converter is shown, and the software control algorithm on the micom and the feedback and switch drive circuits operating the proposed converter are described, briefly. Then, the operation characteristics of proposed converter are validated through the experimental results of a designed and implemented prototype converter by the shown design and implementation method in this paper. The highest efficiency in the results was about 92%.

• Journal of IKEEE
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• v.28 no.3
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• pp.445-450
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• 2024

This paper presents a varactor-less voltage-controlled oscillator (VCO) at W-band (75-110 GHz) with a compact size in a 0.15-㎛ GaAs pHEMT technology. For varactor-less frequency tuning, an inductive tuning circuit is employed. An active inductor is realized by the common-gate stage with gate termination and shows a wide tuning range with a high quality factor (Q-factor) compared with the conventional varactor diode. Colpitts topology with source feedback is employed for the oscillation core of the VCO. The varactor-less VCO exhibits a measured tuning range of 5.8 % and peak output power of 5.7 dBm at 88 GHz while the 146 mW of dc power is dissipated. Due to compact layout design, the chip size is only 0.48 mm².

• Journal of Korea Technology Innovation Society
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• v.11 no.2
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• pp.145-170
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• 2008

The existence of network is indeed the single most important factor that brings about new business phenomena in the new digital economy, especially in the IT industry. Network effect refers to a phenomenon that the increase in size of the network leads to increased network value and user utility. It determines the competitive structure of an industry and the performances of industry competitors (Shapiro and Varian, 1999). The phenomenon of increasing returns and winner-take-all enjoyed by the early winner in the competition can be attributed to the existence of positive feedback which increases the value of network and induces more users into join the network (Arthur, 1996; Shapiro and Varian, 1999; Song and Lee, 2003). This research attempts to shed light on the topic of innovation and competitive strategy of network-based industries. We analyze the case of the Korean mobile communications industry, in which a shift in technological paradigm from 2G to 3G brought new changes to the competitive structure of the industry. The Korean mobile communications industry makes an ideal case for analysis since it is an industry whose value is inherently dependent upon its user network. It is characterized by the typical increasing returns, in which a monopolizing player is enjoying firstmover's network effects. Because of the existence of network in the mobile communications industry, latecomers' disruptive innovations could not outcompete the incumbent's sustaining innovations. The contribution of this research lies in laying a groundwork for future studies by introducing a numerical simulation model to analyze the complexity theory and network effect.