• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.12
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• pp.6-13
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• 2009

For X-band phased array systems, a power amplifier, a 6-bit phase shifter, a 6-bit digital attenuator, and a SPDT transmit/receive (T/R) switch are fabricated and measured. All circuits are demonstrated by using CMOS 0.18 um technology. The power amplifier has 2-stage differential and cascade structures. It provides 1-dB gain-compressed output power ($P_{1dB}$) of 20 dBm and power-added-efficiency (PAE) of 19 % at 8-11 GHz frequencies. The 6-bit phase shifter utilizes embedded switched filter structure which consists of nMOS transistors as a switch and meandered microstrip lines for desired inductances. It has $360^{\circ}$ phase-control range and $5.6^{\circ}$ phase resolution. At 8-11 GHz frequencies, it has RMS phase and amplitude errors are below $5^{\circ}$ and 0.8 dB, and insertion loss of $-15.7\;{\pm}\;1,1\;dB$. The 6-bit digital attenuator is comprised of embedded switched Pi-and T-type attenuators resistive networks and nMOS switches and employes compensation circuits for low insertion phase variation. It has max. attenuation of 31.5 dB and 0.5 dB amplitude resolution. Its RMS amplitude and phase errors are below 0.4 dB and $2^{\circ}$ at 8-11 GHz frequencies, and insertion loss is $-10.5\;{\pm}\;0.8\;dB$. The SPDT T/R switch has series and shunt transistor pairs on transmit and receive path, and only one inductance to reduce chip area. It shows insertion loss of -1.5 dB, return loss below -15 dB, and isolation about -30 dB. The fabricated chip areas are $1.28\;mm^2$, $1.9mm^2$, $0.34\;mm^2$, $0.02mm^2$, respectively.

• Journal of the Korean earth science society
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• v.43 no.2
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• pp.239-252
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• 2022

Quality control methods for the first G-band vapor radiometer (GVR) mounted on a weather aircraft in Korea were developed using the GVR Precipitable Water Vapor (PWV). The aircraft attitude information (degree of pitch and roll) was applied to quality control to select the shortest vertical path of the GVR beam. In addition, quality control was applied to remove a GVR PWV ≥20 mm. It was found that the difference between the warm load average power and sky load average power converged to near 0 when the GVR PWV increased to 20 mm or higher. This could be due to the high brightness temperature of the substratus and mesoclouds, which was confirmed by the Communication, Ocean and Meteorological Satellite (COMS) data (cloud type, cloud top height, and cloud amount), cloud combination probe (CCP), and precipitation imaging probe (PIP). The GVR PWV before and after the application of quality control on a cloudy day was quantitatively compared with that of a local data assimilation and prediction system (LDAPS). The Root Mean Square Difference (RMSD) decreased from 2.9 to 1.8 mm and the RMSD with Korea Local Analysis and Precipitation System (KLAPS) decreased from 5.4 to 4.3 mm, showing improved accuracy. In addition, the quality control effectiveness of GVR PWV suggested in this study was verified through comparison with the COMS PWV by using the GVR PWV applied with quality control and the dropsonde PWV.

• Applied Chemistry for Engineering
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• v.25 no.5
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• pp.531-537
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• 2014

A catalytic plasma reactor was employed for the oxidation of isopropyl alcohol (IPA) classified as a volatile organic compound (VOC). Copper oxide (Cu : 0.5% (w/w)) supported on a multichannel porous ceramic consisting of ${\alpha}-Al_2O_3$ was used as a catalyst, which was directly exposed to the plasma created in it. The effects of discharge voltage and reaction temperature on the concentrations of IPA and its byproducts were examined to understand the behavior of the catalytic plasma reactor. Without thermal insulation, the reactor temperature increased up to $120^{\circ}C$ at an applied voltage of 17 kV (discharge power : 28 W), and the IPA at a flow rate of $1L\;min^{-1}$ ($O_2$ : 10% (v/v); IPA : 1000 ppm) was completely removed. At temperatures below $120^{\circ}C$, however, besides the desirable product $CO_2$, several unwanted byproducts such as acetone, formaldehyde and CO were also formed from IPA. On the other hand, when the reactor was thermally insulated, the plasma discharge increased the temperature up to $265^{\circ}C$ under the same condition and most of IPA was oxidized to $CO_2$. Without loading CuO on the ceramic support, the plasma discharge in the thermally insulated reactor produced nearly equal amounts of $CO_2$ and CO. On comparison, with the catalyst alone (temperature : $265^{\circ}C$), more than 70% of the removed IPA was simply converted into another type of VOC (acetone), indicating that the catalyst assisted by the plasma is more effective in the oxidation of IPA than that of the catalyst-alone process.

• Applied Chemistry for Engineering
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• v.17 no.2
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• pp.223-228
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• 2006

Pore-size controlled porous carbons for the catalyst supports of the direct methanol fuel cell were prepared from the mesophase pitch by using the silica spheres with different sizes. Pitch solution in THF and spheres were mixed, carbonized and etched by 5 M NaOH to make porous carbon. Specific surface area of the porous carbons was $14.7{\sim}87.7m^2/g$ and average pore diameter was 50~550 nm which were dependent on the size of silica spheres. Aqueous reduction method was used to load 60 wt% PtRu on the prepared porous carbon supports. The electro-oxidation activity of the supported 60 wt% Pt-Ru catalysts was measured by cyclic voltammetry and unit cell test. For the 60 wt% Pt-Ru/porous carbon synthesized by 50 nm silica, current density value in the cyclic voltammetry test was $123mA/cm^2$ at 0.4 V and peak power density in the unit cell test were 105 and $162mW/cm^2$ under oxygen at 60 and $80^{\circ}C$, respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.15 no.6
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• pp.252-259
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• 2005

Single crystal $CuGaSe_2$ layers were grown on thoroughly etched semi-insulating CaAs(100) substrate at $450^{\circ}C$ with hot wall epitaxy (HWE) system by evaporating $CuGaSe_2$ source at $610^{\circ}C$. The crystalline structure of the single crystal thin films was investigated by the photoluminescence (PL) and double crystal X-ray diffraction (DCXD). The carrier density and mobility of single crystal $CuGaSe_2$ thin films measured with Hall effect by Van der Pauw method are $4.87{\times}10^{17}cm^{-3}$ and $129cm^2/V{\cdot}s$ at 293 K, respectively. The temperature dependence of the energy band gap of the $CuGaSe_2$ obtained from the absorption spectra was well described by the Varshni's relation, $E_g(T)=1.7998eV-(8.7489{\times}10^{-4}eV/K)T^2/(T+335K)$. The voltage, current density of maxiumun power, fill factor, and conversion, efficiency of $n-CdS/p-CuGaSe_2$, heterojunction solar cells under $80mW/cm^2$ illumination were found to be 0.41 V, $21.8mA/cm^2$, 0.75 and 11.17%, respectively.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.7 no.6
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• pp.63-69
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• 2008

Reconfigurable RF one-chip solutions have been researched with the objective of designing for smaller-sized and more economical RF transceiver and it can be applied to a vehicular wireless terminal. The proposed voltage-controlled oscillator satisfies the targeted frequency range ($4.2{\sim}5.4\;GHz$) and the frequency planning which correspond to the standards such as CDMA(IS-95), PCS, GSM850, EGSM, WCDMA, WLAN, Bluetooth, WiBro, S-DMB, DSRC, GPS, and DVB-H/DMB-H/L(L Band). In order to improve phase noise performance, PMOS is adopted in the cross-coupled pair, the tail current source and MOS varactor in this VCO and differential-typed switching is proposed in capacitor array. Based on the measurement results, a total power dissipation is $5.3{\sim}6.0\;mW$ at 1.8 V power supply voltage. The oscillator is tuned from 4.05 to 5.62 GHz; The tuning range is 33%. The phase noise is -117.16 dBc/Hz at 1 MHz offset frequency and the FOM (Figure Of Merit) is $-180.84{\sim}-180.5$.

• Journal of the Korea Society of Computer and Information
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• v.17 no.8
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• pp.1-10
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• 2012

This paper proposes design space exploration methodology of many-core processors including multimedia specific instructions to support high-performance and low power ultrasound imaging for portable devices. To explore the impact of multimedia instructions, we compare programs using multimedia instructions and baseline programs with a same many-core processor in terms of execution time, energy efficiency, and area efficiency. Experimental results using a $256{\times}256$ ultrasound image indicate that programs using multimedia instructions achieve 3.16 times of execution time, 8.13 times of energy efficiency, and 3.16 times of area efficiency over the baseline programs, respectively. Likewise, programs using multimedia instructions outperform the baseline programs using a $240{\times}320$ image (2.16 times of execution time, 4.04 times of energy efficiency, 2.16 times of area efficiency) as well as using a $240{\times}400$ image (2.25 times of execution time, 4.34 times of energy efficiency, 2.25 times of area efficiency). In addition, we explore optimal PE architecture of many-core processors including multimedia instructions by varying the number of PEs and memory size.

• Journal of IKEEE
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• v.16 no.1
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• pp.28-33
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• 2012

Recently, with mobile devices increasing, as a variety of multimedia functions are needed, battery life is decreased. Accordingly the methods for extending the battery life has been proposed. In order to implement these methods, we have to know exactly the status of the battery, so we need a high resolution analog to digital converter(ADC). In case of the existing integrating sigma-delta ADC, it have not convert reset-time conversion cycle to function of resolution. Because of this reason, all digital values corresponding to the all number of bits will not be able to be expressed. To compensated this drawback, this paper propose that all digital values corresponding to the number of bits can be expressed without having to convert reset-time additional conversion cycle to function of resolution by using a up-down counter. The proposed circuit achieves improved SNDR compared to conventional converters simulation result. Also, this was designed for low power suitable for battery management systems and fabricated in 0.35um process.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.11
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• pp.1104-1112
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• 2013

This paper presents a wideband Colpitts voltage controlled oscillator(VCO) with nanosecond startup time and a center frequency of 8.35 GHz for a new bubble-type motion detector that has a bubble-layer detection zone at the specific distance from itself. The VCO circuit consists of two parts; one is a negative resistance part with a HEMT device and Colpitts feedback structure and the other is a resonator part with a varactor diode and shorted shunt microstrip line. The shorted shunt microstrip line and series capacitor are utilized to compensate for the input reactance of the packaged HEMT that changes from capacitive values to inductive values at 8.1 GHz due to parasitic package inductance. By tuning the feedback capacitors which determine negative resistance values, this paper also investigates startup time improvement with the negative resistance variation and tuning bandwidth improvement with the reactance slope variation of the negative resistance part. The VCO measurement shows the tuning bandwidth of 2.3 GHz(28 %), the output power of 4.1~7.5 dBm and the startup time of less than 2 nsec.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.1
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• pp.71-78
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• 2020

In the case of power generation using renewable energy, power production may not be smooth due to the influence of the weather. The energy storage system (ESS) is used to increase the efficiency of solar and wind power generation. ESS has been continuously fired due to a lack of battery protection systems, operation management, and control system, or careless installation, leading to very big casualties and economic losses. ESS stability and battery protection system operation management technology is indispensable. In this paper, we present a battery level calculation algorithm and a failure prediction algorithm for ESS optimization and stable operation. The proposed algorithm calculates the correct battery level by accumulating the current amount in real-time when the battery is charged and discharged, and calculates the battery failure by using the voltage imbalance between battery cells. The proposed algorithms can predict the exact battery level and failure required to operate the ESS optimally. Therefore, accurate status information on ESS battery can be measured and reliably monitored to prevent large accidents.