• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.7
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• pp.1044-1052
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• 1999

A 2-stage 1 watt MMIC(Monolithic Microwave Integrated Circuits) HPA(High Power Amplifiers) at 20 GHz band has been designed and fabricated. The $0.15\mu\textrm{m}$ with the width of $400\mu\textrm{m}$for single device pHEMT technology was used for the fabrication of this MMIC HPA. Due to the series feedback technique from source to ground, bias circuits and stabilization circuits on the main microstrip line, the stability factors(Ks) are more than one at full frequency. The independent operation for each stage and excellent S11, S22 less than -20 dB have been obtained by using lange couplers. For beginning the easy design, linear S-parameters have been extracted from the nonlinear equivalent circuit in foundry library, and equivalent circuits of devices at in/output ports were calculated from this S-parameters. The measured performances, which are in well agreement with the predicted ones, showed the MMIC HPA in this paper has the minimum 15 dB of linear gain, -20 dB of reflection coefficients and 31 dBm of output power over 17~25 GHz.

• JSTS:Journal of Semiconductor Technology and Science
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• v.10 no.4
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• pp.276-281
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• 2010

A 2.5 V feed-forward second-order deltasigma modulator for audio application is presented. A 9-level quantizer with a tree-structured dynamic element matching (DEM) was employed to improve the linearity by shaping the distortion resulted from the capacitor mismatch of the feedback digital-toanalog converter (DAC). A chopper stabilization technique (CHS) is used to reduce the flicker noise in the first integrator. The prototype delta-sigma analogto-digital converter (ADC) implemented in a 65 nm 1P8M CMOS process occupies 0.747 $mm^2$ and achieves 109.1 dB dynamic range (DR), 85.4 dB signal-to-noise ratio (SNR) in a 24 kHz audio signal bandwidth, while consuming 14.75 mW from a 2.5 V supply.

• BMB Reports
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• v.34 no.4
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• pp.299-304
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• 2001

The 3-Deoxy-D-arabinoheptulosonate 7-phosphate (DAHP) synthase is the first enzyme of aromatic amino acid-, folic acid-, and phenazine-1-carboxylic acid biosynthetic pathways. DAHP synthase of Bacillus sp. B-6 that produces phenazine-1-carboxylic acid was feedback inhibited by two intermediary metabolites of aromatic amino acid biosynthetic pathways, prephenate and chorismate, but not by other metabolites, such as anthranilic acid, shikimic acid, p-aminobenzoic acid, and 3-hydroxyanthranilic acid. DAHP synthase of Bacillus sp. B-6 was not inhibited by end products, such as aromatic amino acids, folic acid, and phenazine-1-carboxylic acid. The inhibition of DAHP synthase by prephenate and chorismate was non-competitive with respect to erythrose 4-phosphate and phosphoenolpyruvate. Prephenate and chorismate inhibited 50% of the DAHP synthase activity at concentrations of $2{\times}10^{-5}\;M$ and $1.2{\times}10^{-4}\;M$, respectively The synthesis of DAHP synthase of Bacillus sp. B-6 was not repressed by exogenous aromatic amino acids, folic acid, and phenazine 1-carboxylic acid, single or in combinations.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.9
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• pp.13-20
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• 1999

A 2-stage MMIC(monolithic Microwave Integrated Circuits) LNA(Low Noise Amplifiers) at 30GHz hand has been designed and fabricated for the Ka-band Satellite Communications. The $0.15 {\mu}m$ with the width of $80 {\mu}m$ pHEMT technology was used for the fabrication of this MMIC LNA. Using the series feedback technique, ultra low noise and excellent S11 could be obtained at the same time without the cost of gain at 30GHz-band. The stability factors(Ks) for each stage and overall stage are greater than 1 at full frequency bands by the bias circuits and stabilization circuit. The measured performances, which agree well with the predicted performances, show this 2-stage MMIC LNA has the gain of more than 15.7dB and noise figure of less than 2.09dB over 29GHz to 33GHz.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.1
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• pp.84-92
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• 2000

A GaAs MESFET MMIC transmitter for 2.4 GHz wireless local loop handset is designed and fabricated. The transmitter consists of a double balanced active mixer and a two stage driver amplifier with voltage negative feedback. In particular, a pair of CS-CG(common source-common gate) structure compensates the reduction in dynamic range caused by unbalanced complementary IF input signals. And to suppress the leakage local power at RF port, the mixer is designed by using phase characteristic between the ports of MESFET. At the bias condition of 2.7 V and 55.2 mA, the fabricated MMIC transmitter with chip dimensions of $0.75\times1.75 mm^2$ obtains a measured conversion gain of 38.6 dB, output $P_{idB}$ of 11.6 dBm, and IMD3 at -5 dBm RF output power of -31.3 dBc. This transmitter is well suited for WLL handset.

• The Journal of the Korea Contents Association
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• v.12 no.8
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• pp.264-273
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• 2012

The purpose of this study was to determine the test-retest reliability and the concurrent validity between tinetti mobility test (TMT), berg balance scale (BBS) and space balance 3D which is one of the computerized measurement and visual feedback balance assessment system in subacute stroke patients. Twenty three ambulatory acute stroke subjects were measured the TMT, BBS and space balance 3D. The test-retest reliability(intra-class correlation coefficient: ICC) indicated that the static and dynamic balance in space balance 3D considered moderate reliability and TMT, BBS were good reliability. In case of concurrent validity, there were moderate validity (p<.01) between static balance test with space balance 3D and each TMT, BBS. But there were only poor validity (p<.05) between center to forward-left, center to backward-left phase in dynamic balance test with space balance 3D and each TMT, BBS. These findings suggest that in subacute stroke patients the test-retest reliability and concurrent validity using the space balance 3D and TMT were valuable in balance test but there was limitation to evaluate dynamic balance test.

• Journal of computational fluids engineering
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• v.15 no.2
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• pp.7-13
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• 2010

Flight vehicles such as wheel wells and bomb bays have many cavities. The flow around a cavity is characterized as an unsteady flow because of the formation and dissipation of vortices brought by the interaction between the free stream shear layer and the internal flow of the cavity. The resonance phenomena can damage the structures around the cavity and negatively affect the aerodynamic performance and stability of the vehicle. In this study, a numerical analysis was performed for the cavity flows using the unsteady compressible three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equation with Wilcox's turbulence model. The Message Passing Interface (MPI) parallelized code was used for the calculations by PC-cluster. The cavity has aspect ratios (L/D) of 5.5 ~ 7.5 with width ratios (W/D) of 2 ~ 4. The Mach and Reynolds numbers are 0.4 ~ 0.6 and $1.6{\times}10^6$, respectively. The occurrence of oscillation is observed in the "shear layer and transient mode" with a feedback mechanism. Based on the Sound Pressure Level (SPL) analysis of the pressure variation at the cavity trailing edge, the dominant frequencies are analyzed and compared with the results of Rossiter's formula. The dominant frequencies are very similar to the result of Rossiter's formula and other experimental datum in the low aspect ratio cavity (L/D = ~4.5). In the high aspect ratio cavity, however, there are other low dominant frequencies of the leading edge shear layer with the dominant frequencies of the feedback mechanism.

• 한국전산유체공학회:학술대회논문집
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• 2009.11a
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• pp.13-18
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• 2009

Flight vehicles such as wheel wells and bomb bays have many cavities. The flow around a cavity is characterized as an unsteady flow because of the formation and dissipation of vortices brought about by the interaction between the free stream shear layer and the internal flow of the cavity. The resonance phenomena can damage the structures around the cavity and negatively affect the aerodynamic performance and stability of the vehicle. In this study, a numerical analysis was performed for the cavity flows using the unsteady compressible three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equation with Wilcox's turbulence model. The Message Passing Interface (MPI) parallelized code was used for the calculations by PC-cluster. The cavity has aspect ratios (L/D) of 2.5 ~ 7.5 with width ratios (W/D) of 2 ~ 4. The Mach and Reynolds numbers are 0.4 ~ 0.6 and $1.6{\times}106$, respectively. The occurrence of oscillation is observed in the "shear layer and transient mode" with a feedback mechanism. Based on the Sound Pressure Level (SPL) analysis of the pressure variation at the cavity trailing edge, the dominant frequencies are analyzed and compared with the results of Rossiter's formula. The dominant frequencies are very similar to the result of Rossiter's formula and other experimental data in the low aspect ratio cavity (L/D = ~ 4.5). In the large aspect ratio cavity, however, there are other low dominant frequencies due to the leading edge shear layer with the dominant frequencies of the feedback mechanism. The characteristics of the acoustic wave propagation are analyzed using the Correlation of Pressure Distribution (CPD).

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2003.11a
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• pp.322-325
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• 2003

A 7/21GHz frequency tripler, using a commercially available packaged pHEMT, was designed and fabricated on 15mil RO3003 substrate. Frequency conversion is realized using the third harmonic current of an class B amplifier with rejection feedback at fundamental with optimum load conductance at the third harmonic. The fabricated frequency tripler has achieved a conversion loss of 0.7dB for an input power of 0dBm at 21GHz. The experimental results show good agreement with the harmonic balance simulation.

• Proceedings of the IEEK Conference
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• 1998.06a
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• pp.469-472
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• 1998

InGaAsP/InP ridge waveguide(RWG) distributed feedback(DFB) lasers (LD) operating at 1.55.mu.m were fabricated by a two step MOCVD process. The CW laser threshold and the slope efficiency from these lasers are 22.5mA and 0.127mW/MA perfacet at room temperature. Single longitudinal mode operation with side mode suppression of more than 30dB is obtained at 5mW. The temperature sensitivity and characteristic temperature (T$_{0}$) from DFB lasers were obtained 1.0.angs./.deg. C and 50.3K between 20.deg. C and 70.deg. C, respectively.y.