• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.4
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• pp.415-424
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• 2004

Cooling the electronic equipment is one of the major focal points of the design process and the key to successful product launch. The two-phase loop thermosyphone which is a good candidate among many available options was investigated fur cooling of the high power amplifiers. The system is composed of evaporator which contains 6 parallel cold plates, fan cooled condenser, gas-liquid separator, and interconnecting tubes. Experiments were performed for several refrigerant charging values, hs and as a experiment result, the optimum charging value fur this system was proposed. In order to optimize the system design, the operating cycle pressure and inlet/outlet temperatures of evaporator and condenser are measured and analyzed. The effect of the three parameters such as flow rate and temperature of condenser cooling air, and thermal load on the evaporator are investigated. The lower the operating pressure and the cycle temperatures are also better to prevent the leakage of the system. The system invesigated in this paper can be directly used for cooling of a real unmanned wireless communication station.

• JSTS:Journal of Semiconductor Technology and Science
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• v.10 no.4
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• pp.309-315
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• 2010

A fully-differential low-voltage low-power electrocardiogram (ECG) amplifier by using the nonfeedback PMOS pseudo-resistors is proposed. It consists of two operational-transconductance amplifiers (OTA) in series (a preamplifier and a variable-gain amplifier). To make it insensitive to the gate leakage current of the OTA input transistor, the feedback pseudo-resistor of the conventional ECG amplifier is moved to input branch between the OP amp summing node and the DC reference voltage. Also, an OTA circuit with a Gm boosting block without reducing the output resistance (Ro) is proposed to maximize the OTA DC gain. The measurements shows the frequency bandwidth from 7 Hz to 480 Hz, the midband gain programmable from 48.7 dB to 59.5 dB, the total harmonic distortion (THD) less than 1.21% with a full voltage swing, and the power consumption of 233 nW in a 0.13 ${\mu}m$ CMOS process at the supply voltage of 0.7 V.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.6 s.183
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• pp.104-110
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• 2006

A design and control of electrostatic suspension system for flexible objects is presented. A number of electrode pairs of which the number depends on the object flexibility are positioned above the object and the voltages applied to each electrode pair are controlled, independently on the others, on the basis of the gap length. To implement the system with low cost and compactness, switched-voltage control scheme that is based on the relay feedback control is utilized. Relay feedback control method deploys only a single high-voltage power supply that can deliver a DC voltage of positive and/or negative polarity and thus high voltage amplifiers that are costly and bulky are not needed any more. It is shown that despite the inherent limit cycle property of the relay feedback based control, an excellent performance in vibration suppression is attained due to the presence of a relatively large squeeze film damping originating from the electrodes and levitated object. Employing fourteen electrode pairs, a thin aluminum plate with a thickness of 0.1 mm has been suspended at a gap length of 0.75mm.

• The Journal of the Korea institute of electronic communication sciences
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• v.3 no.2
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• pp.93-100
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• 2008

In this paper, Low Noise Block down converter(LNB) is designed for a Ka-band satellite television receiver only(TVRO) using commercially available MMIC. Designed Low Noise Block down-converter is composed of three stage amplifiers involving input noise matched at first amplification stage, image reject band pass filter, frequency mixer and intermediate frequency amplification. Through LNB Module power budget to obtain gain and attenuation, Optimum LNB devices satisfying Ka-band LNB technical specification are selected. Experimental results of designed Ka-band LNB yields conversion gain of over $58{\pm}1dB$, noise figure of less than 1.5dB and phase noise of -94.6dBc @10KHz.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.1
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• pp.17-22
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• 2009

A switch or circulator is used for distinguishing between the paths of transmitter and receiver in TDD systems. If the isolation between Tx and Rx paths is low in TDD systems, the output signal of the ransmitter acts as an interferer to the receiver even if the transceiver operates on the receiver mode. In this paper we propose a method to get high isolation characteristics between transmitting and receiving paths in TDD systems. We implement the module with a proposed improving method to verify the effect of the isolation improvement and the experimental results are presented. The isolation improvement of above 44.8 dB over the frequency bandwidth of 30 MHz is obtained from the implemented isolation improvement module.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.3 no.1
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• pp.63-69
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• 2010

In this paper, a new design method of asymmetrical configuration of main amplifier and peaking amplifier using changed bias point is proposed for excellent linearity, instead of the conventional Doherty structure. We have utilized the uneven wilkinson power divider for the unequal power drive at the input network of amplifiers. And we proposed a compensating method of the decreasing efficiency due to improving linearity using 3-stage Doherty structures. From the simulation results of asymmetrical Dohertry power amplifier and asymmetrical 3-stage Doherty power amplifier with uneven power drive are implemented. From the implementation and measurement results of the each amplifier, IMD characteristics have -55 dBc as the good efficiency of 13% compensates the decreased entire efficiency due to the improving linearity characteristics.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.8
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• pp.1215-1221
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• 2017

Parametric array transducers are used for highly directional speaker in an air environments. Piezoelectric micromachined ultrasonic transducers for parametric array transducers need DC-biased voltage driving signals in order to get high-directional quality-sound features. The existing power amplifier such as class A amplifiers has low efficiency and require large volume heatsinks. To overcome the above-mentioned disadvantages of the conventional amplifier, this paper proposes a new power amplifier system. The proposed power amplifier system ensures high linearity of output characteristic by utilizing the push-pull class B type amplifier. Furthermore, the proposed power amplifier system gets high efficiency because it contains the DC-DC converter-type power supply which can perform energy recovery and envelope tracking function. Also the paper suggests the detailed circuit topology. Its characteristics are verified by the detailed experimental results.

• Journal of Powder Materials
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• v.26 no.6
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• pp.463-470
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• 2019

Fe₃O₄/SiO₂/YVO₄:Eu³⁺ multifunctional nanoparticles are successfully synthesized by facile stepwise sol-gel processes. The multifunctional nanoparticles show a spherical shape with narrow size distribution (approximately 40 nm) and the phosphor shells are well crystallized. The Eu³⁺ shows strong photoluminescence (red emission at 619 nm, absorbance at 290 nm) due to an effective energy transfer from the vanadate group to Eu. Core-shell structured multifunctional nanoparticles have superparamagnetic properties at 300 K. Furthermore, the core-shell nanoparticles have a quick response time for the external magnetic field. These results suggest that the photoluminescence and magnetic properties could be easily tuned by either varying the number of coating processes or changing the phosphor elements. The nanoparticles may have potential applications for appropriate fields such as laser systems, optical amplifiers, security systems, and drug delivery materials.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.2
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• pp.295-300
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• 2005

In this paper we have designed a two-stage Class I power amplifier operated at 2.4CHz for Class-1 Bluetooth application. The power amplifier employs class-I topology to exploit its soft-switching property for high efficiency. The latch-structured pre-amplifier with amplifiers makes its output signal as sharp as possible for soft switching of the next power amplifier. It improves the overall efficiency of the proposed power amplifier. It shows 65.8$\%$ PAE, 20dB power gain and 20dBm output power.

• Korean Journal of Optics and Photonics
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• v.12 no.3
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• pp.205-211
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• 2001

We propose a constant inversion black box model of erbium-doped fiber amplifiers (EDFAs) for exact performance predictions for EDFAs operated in the gain-flattened condition. The validity of the newly proposed model was experimentally verified by predicting the performance of EDFAs for the L band, within 1.9% required pump power discrepancy. The role of ion pairing effects on the power conversion efficiency is also discussed. ussed.