• Proceedings of the Korean Magnestics Society Conference
• /
• 2000.09a
• /
• pp.522-529
• /
• 2000

We present a new procedure to evaluate the residual life of 1Cr-1Mo-0.25V steel by reversible magnetic permeability. The method is based on the existence of the first harmonics in the differential magnetization around the coercive force. The apparatus is based on the detection of the voltage induced in a coil using a lock-in amplifier tuned to a frequency of the exciting one. Results obtained for the first harmonics and Vickers hardness on the aged samples show that the peak interval of reversible permeability and Vickers hardness decrease as ageing time increases. The correlation between Vickers hardness and the peak interval of the reversible permeability could well be used to evaluate the residual life of 1Cr-1Mo-0.25V steel, nondestructively.

• Journal of the Korean Society for Precision Engineering
• /
• v.13 no.12
• /
• pp.30-37
• /
• 1996

On-line process control equipment for CO$_{2}$ laser cutting is not available for industrial applications. The major part of the industrial laser cutting machines are adjusted off-line by highly educated engineers. The quality inspection of the sample is visual and referred to different quality scales. Due to the lack of automation the potential laser users hesitate to implement the cutting method. The first step toward an automation of the process is the development of a process monitoring system and the research is cincentrated on the area of on-line quality monitoring during CO$_{2}$ laser cutting. The method is based on the detection of the emitted light from the cutting front by photo diode. The developed monitoring system consists of the OP Amplifier, A/D convertor, power supply and PC. The signal from the photo diode has been undertaken from Fourier analysis and statistical analysis with real time. The photograph of striation pattern was taken by metallurgical microscope. As a result, it is possible to predict the striation pattern according to the beam traveling speed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.20 no.8
• /
• pp.813-822
• /
• 2009

We have investigated operation of a 1:2:2 asymmetric 3-stage Doherty PA(Power Amplifier) and implemented using the Freescale's 4 W, 10 W PEP LDMOSFETS at 1 GHz. By employing the three peak efficiency characteristics, compared to the two peak N-way Doherty PA, the asymmetric 3-stage Doherty can overcome the serious efficiency degradation along the backed-off output power region and maximize the average efficiency for the modulation signal. To maximize the efficiency characteristic, the inverse class F PA has been designed as carrier and peaking amplifiers. Furthermore, to extract the proper load modulation operation, the adaptive gate bias control signal has been applied to the two peaking PAs based on the envelope tracking technique. For the 802.16e Mobile WiMAX(World Interoperability for Microwave Access) signal with 8.5 dB PAPR(Peak to Average Power Ratio), the proposed Doherty PA has shown 55.46 % of high efficiency at an average output power of 36.85 dBm while maintaining the -37.23 dB of excellent RCE(Relative Constellation Error) characteristic. This is the first time demonstration of applying the saturated PA and adaptive gate bias control technique to the asymmetric 3-stage Doherty PA for the highly efficient transmitter of the base-station application.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.17 no.7
• /
• pp.42-48
• /
• 2016

In this paper, a high-precision peak detector circuit that detects the output voltage information of a fly-back converter is proposed. The proposed design consists of basic analog elements with only one operational amplifier and three transistors. Because of its simple structure, the proposed circuit can minimize the delay time of the detection process, which has a strong impact on the precision of the regulation aspect of the fly-back converter. Furthermore, by using an amplifier and several transistors, the proposed detector can be fully integrated on-chip, instead of using discrete circuit elements, such as capacitors and diodes, as in conventional designs, which reduces the production cost of the fly-back converter module. In order to verify the performance of the proposed scheme, the peak detector was simulated and implemented by using a 0.35 m MagnaChip process. The gained results from the simulation with a sinusoidal stimulus signal show a very small detection error in the range of 0.3~3.1%, which is much lower than other reported detecting circuits. The measured results from the fabricated chip confirm the simulation results. As a result, the proposed peak detector is recommended for designs of high-performance fly-back converters in order to improve the poor regulation aspect seen in conventional designs.

• Journal of IKEEE
• /
• v.22 no.4
• /
• pp.1025-1030
• /
• 2018

The proposed modulator is designed by utilizing a conventional structure employing time division technique to realize the 4th order delta-sigma modulator using one op-amp. In order to reduce the influence of KT/C noise, the capacitance in the first and second integrators reused was chosen to be 20pF and capacitance of third and fourth integrators was designed to be 1pF. The stage variable technique in the low power reconfigurable op-amp was used to solve the stability issue due to different capacitance loads for the reduction of KT/C noise. This technique enabled the proposed modulator to reduce the power consumption of 15% with respect to the conventional one. The proposed modulator was fabricated with 0.18um CMOS N-well 1 poly 6 metal process and consumes 305uW at supply voltage of 1.8V. The measurement results demonstrated that SNDR, ENOB, DR, FoM(Walden), and FoM(Schreier) were 66.3 dB, 10.6 bits, 83 dB, 98 pJ/step, and 142.8 dB at the sampling frequency of 256kHz, oversampling ratio of 128, clock frequency of 1.024 MHz, and input frequency of 250 Hz, respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.30 no.6
• /
• pp.467-478
• /
• 2019

This paper describes the development and measurement results of a wide-band planar active phase array antenna system for an electronic warfare jamming transmitter. The system is designed as an $8{\times}8$ triangular lattice array using a $45^{\circ}$ slant wide-band antenna. The 64-element transmission channel is composed of a wide-band gallium nitride(GaN) solid state power amplifier and a gallium arsenide(GaAs) multi-function core chip(MFC). Each GaAs MFC includes a true-time delay circuit to avoid a wide-band beam squint, a digital attenuator, and a GaAs drive amplifier to electronically steer the transmitted beam over a ${\pm}45^{\circ}$ azimuth angle and ${\pm}25^{\circ}$ elevation angle scan. Measurement of the transmitted beam pattern is conducted using a near-field measurement facility. The EIRP of the designed system, which is 9.8 dB more than the target EIRP performance(P), and the ${\pm}45^{\circ}$ azimuth and ${\pm}25^{\circ}$ elevation beam steering fulfill the desired specifications.

• Journal of the Institute of Convergence Signal Processing
• /
• v.16 no.2
• /
• pp.56-62
• /
• 2015

In this study, we implemented an unconstraint ECG monitoring system on a chair. Nowadays, modern people spend most of their time sitting on the chair. Therefore, it is necessary to have an unconstraint ECG monitoring system that can be used for a long time. The implemented system can perform measurement even with clothes on and it has great advantage on motion artifacts. A pair of unconstraint electrodes are placed on the back of the chair. Amplifier and filters are designed to remove motion artifacts, The baseline noise and power line noise are filtered and very low level of bio-signal is amplified to give a final measurement. Control unit and wireless transmission unit are implemented. Analog signal is converted into digital signal and transmits biological signal to the PC and the smart phone. Therefore continuous ECG monitoring in daily life is made possible. A comparison experiment between Ag / AgCl electrode and unconstraint electrode is conducted to evaluate the performance of the implemented system. As a result, we confirm our unconstraint system can be used for daily life ECG monitoring.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.12 no.2
• /
• pp.167-174
• /
• 2012

The circuits including with Optical transceiver and clock data recovery, in this paper, SERDES (SERializer-DESerializer) are implemented to construct a GE-PON burst-mode transceiver supporting IEEE 802.3ah and a jig for measuring the burst-mode characteristics, that is to say, PON upstream optical transmission environment are manufactured to evaluate the performance of transceiver. we verified that the limiting amplifier compensated the gap of max. 26dB optical power by experiments. The startup acquisition lock time is 670ns in case of using VSC7123 and 2300ns in case of S2060 and the data acquisition lock time were measured to be 400ns and 600ns, respectively, in the upstream channel transmission in this work. While on the other, VSC7123 is satisfied with IEEE802.3ah recommendations.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.18 no.4 s.119
• /
• pp.379-388
• /
• 2007

This paper presents a real-time respiration and heartbeat detector comprised of a 1.6 GHz single-channel Doppler sensor and analog/digital signal processing block for remote vital sign detection. The RF front end of the Doppler sensor consists of an oscillator, mixer, low noise amplifier, branch-line hybrid and patch antenna. We apply artificial transmission lines(ATLs) to the branch-line hybrid, which leads to a size reduction of 40 % in the hybrid, while its performance is very comparable to that of a conventional hybrid. The analog signal conditioning block is implemented using second order Sallen-Key active filters and the digital signal processing block is realized with a LabVIEW program on a computer. The respiration and heartbeat detection is demonstrated at a distance of 50 cm using the developed system.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
• /
• 2008.04a
• /
• pp.199-205
• /
• 2008

In this study, a system to measure continuously the fuel concentration in a steady flow rig on the basis of Rayleigh scattering is presented. The system can be employed to measure both the temporal and the spatial distribution. Also, it is possible to calibrate the system for the measurement of accurate absolute concentration. Firstly, the system was tested at a calibration chamber for the determination of scattering cross section from propane, butane, acetylene, Freon-12 and Genetron 143a. After this, the system was adapted to a steady flow rig to measure the temporal and spatial fuel concentration. The rig is composed of cylinder head, intake manifold, injector, and transparent cylinder which can simulate internal combustion engine. To cope with the problem of Mie scattering interference, a software filter was developed, which is based on the rise time and the time constant of the photomultiplier-amplifier system. The results show that LRS can provide useful informations about concentration field and the software filter is very effective method to remove Mie interference.