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Minimization of Peak Current-Consumption in mobile-WiMAX and CDMA-cellular, Dual-mode Handsets
Youngcheol Park 대한전자공학회 2007 ITC-CSCC :International Technical Conference on Ci Vol.2007 No.7
Peak power consumption is estimated in dualmode dual-band handsets with mobile WiMAX (mWiMAX) and CDMA cellular functions. Due to the limited power-supplying capacity of batteries, dualoperatoin such as voice-call paging on a CDMA cellular network whilst a video conferencing through a mWiMAX network necessiates a precise power management for successful dual-mode handset-system design. Therefore, peak power consumptions for major blocks (mWiMAX, CDMA, Video processor block and etc) in DBDM handsets were estimated, and a peak-off capacitor is suggested to prevent from the potentially demaging peak values by reducing the peaking current during the transmit period in a TDD frame of the mWiMAX system.
Arbitrary Sampling Method for Nonlinearity Identification of Frequency Multipliers
Youngcheol Park,Hoijin Yoon 한국전자파학회JEES 2008 Journal of Electromagnetic Engineering and Science Vol.8 No.1
It is presented that sampling rates for behavioral modeling of quasi-memoryless nonlinear devices can be far less than the Nyquist rate of the input signal. Although it has been believed that the sampling rate of nonlinear device modeling should be at least the Nyquist rate of the output signal, this paper suggests that far less than the Nyquist rate of the input signal can be applied to the modeling of quasi-memoryless nonlinear devices, such as frequency multipliers. To verify, a QPSK signal at 820 ㎒ were applied to a frequency tripler, whereby the device can be utilized as an up-converting mixer into 2.46 ㎓ with the aid of digital predistortion. AM-AM, AM-PM and PM-PM can be successfully measured regardless of sampling rates.
Park Kwanho,Nam Sunghee,Choi Youngcheol,Kim Hyunae,Ma Yeongju,Kim Seonghyun,Kang Minuk,Nho Sikab 한국응용곤충학회 2013 한국응용곤충학회 학술대회논문집 Vol.2013 No.10
Larvae black soldier fly, Hermetia illucens, is beneficial because its larvae feed on organic materials derived from plants, animals and humans and promote the recycling of food waste and organic materials. Chymotrypsin serine protease is one of the main digestive proteases in the midgut of and is involved in various essential processes. In a previous study, a gene encoding a chymotrypsin-like protease, Hi-SP1, was cloned from the larvae of Hermetia illucens and characterized. The objective of this study was to compare the digestive enzyme activity with various enzymes such as papain, protease and α-chymotrypsin. And also, we investigated the antimicrobial activity of the Hi-SP1 against the spoilage relate bacteria. The growth of the bacteria was inhibited in nutrient broth containing the Hi-SP1.
Co-Simulation for Systematic and Statistical Correction of Multi-Digital-to-Analog-Convertor Systems
Youngcheol Park,Hoijin Yoon 한국전자파학회JEES 2017 Journal of Electromagnetic Engineering and Science Vol.17 No.1
In this paper, a systematic and statistical calibration technique was implemented to calibrate a high-speed signal converting system containing multiple digital-to-analog converters (DACs). The systematic error (especially the imbalance between DACs) in the current combining network of the multi-DAC system was modeled and corrected by calculating the path coefficients for individual DACs with wideband reference signals. Furthermore, by applying a Kalman filter to suppress noise from quantization and clock jitter, accurate coefficients with minimum noise were identified. For correcting an arbitrary waveform generator with two DACs, a co-simulation platform was implemented to estimate the system degradation and its corrected performance. Simulation results showed that after correction with 4.8 Gbps QAM signal, the signal-to-noise-ratio improved by approximately 4.5 dB and the error-vector-magnitude improved from 4.1% to 1.12% over 0.96 GHz bandwidth.
Park, Youngcheol,Yoon, Hoijin Elsevier 2017 MEASUREMENT -LONDON- Vol.105 No.-
<P>This paper presents a frequency interleaving method to correct non-ideal characteristics of wideband signal generators. By effectively segmenting a discrete Fourier transform dataset into frequency-interleaving blocks, the proposed method is computationally more efficient than the conventional method based on Fast Fourier Transform (FFT). In cases the quality of frequency analysis can be improved by zero padding such as characterizing impulse responses, this method is effective because it is possible to interleave two or more FFT results to achieve better frequency resolution. To verify the proposed method, an arbitrary signal generator was tested with a 64 quadrature-amplitude-modulation waveform. Compared with the original signal quality, the proposed method improves the in-band signal-to-noise ratio by 9 dB, and the error-vector magnitude decreases from 2.1%, to 0.78%(rms). In all cases, the computation speed was faster than that of conventional FFT. (C) 2017 Elsevier Ltd. All rights reserved.</P>
New cardiac MRI gating method using event-synchronous adaptive digital filter.
Park, Hodong,Park, Youngcheol,Cho, Sungpil,Jang, Bongryoel,Lee, Kyoungjoung Pergamon Press [etc.] 2009 Annals of biomedical engineering Vol.37 No.11
<P>When imaging the heart using MRI, an artefact-free electrocardiograph (ECG) signal is not only important for monitoring the patient's heart activity but also essential for cardiac gating to reduce noise in MR images induced by moving organs. The fundamental problem in conventional ECG is the distortion induced by electromagnetic interference. Here, we propose an adaptive algorithm for the suppression of MR gradient artefacts (MRGAs) in ECG leads of a cardiac MRI gating system. We have modeled MRGAs by assuming a source of strong pulses used for dephasing the MR signal. The modeled MRGAs are rectangular pulse-like signals. We used an event-synchronous adaptive digital filter whose reference signal is synchronous to the gradient peaks of MRI. The event detection processor for the event-synchronous adaptive digital filter was implemented using the phase space method-a sort of topology mapping method-and least-squares acceleration filter. For evaluating the efficiency of the proposed method, the filter was tested using simulation and actual data. The proposed method requires a simple experimental setup that does not require extra hardware connections to obtain the reference signals of adaptive digital filter. The proposed algorithm was more effective than the multichannel approach.</P>
다중 톤 신호의 통계적 특성 확보를 통한 광대역 신호 증폭기의 인접 채널 간섭 분석
박영철(Youngcheol Park) 한국전자파학회 2011 한국전자파학회논문지 Vol.22 No.12
본 논문에서는 광대역 무선 신호를 증폭하는 전력증폭기의 성능 테스트 시 인접 채널 간섭(ACLR) 특성을 측정하는 데 있어서, 효과적인 다중 톤 생성을 활용한 테스트 방안에 관하여 연구하였다. 그 동안 단일 주파수 정현파 신호를 테스트에 활용하는 경우 신호가 복잡해짐에 따라 오차가 증가하는 문제점이 있기에, 실제 변조 신호와의 측정 오차를 최소화하도록 다중 톤 신호를 설계하는 방식을 제안하였다. 제안된 다중 톤은 시간 축에서의 유사성을 확보하는 방식으로 설계되어 기존의 다중 톤 생성 방식 대비 더욱 적은 수의 톤으로 정확한 결과를 얻을 수 있다. 이의 검증을 위하여 802.11a 규격의 기저 대역 복소 신호를 다중 톤 신호로 대체하였으며, 이를 전력증폭기 성능 검증에 활용하였다. 그 결과, N=10 이상의 톤 수를 확보하는 경우 3차, 5차 비선형성에 의한 ACLR 특성이 실제 신호 활용한 경우와 1 ㏈ 이하의 오차를 나타내었다. In this paper, a design method of multi-tone signals for the measurement of adjacent-channel power-ratios on power amplifiers is suggested. Because most tests for power amplifiers in production are performed with single-tone signals, its testing accuracy is not guaranteed as the signal complexity increases. Therefore, the application of multi-tone signals to the testing is suggested by optimized complex coefficients of each tones for the best statistical similarity to the original modulated signal. From the verification, a 802.11a signal was replaced with a multi-tone signal of N=10, with the complex coefficients generated by the suggested method. The resulting measurements on the ACLR of 2.4 ㎓ power amplifier showed successful accuracy of less than 1 ㏈ discrepancy.
F급 전력증폭기의 출력 전력 불확도에 대한 DC 영향 분석 및 최적 바이어스 조건 도출에 관한 연구
박영철(Youngcheol Park),윤회진(Hoijin Yoon) 한국전자파학회 2014 한국전자파학회논문지 Vol.25 No.2
본 논문은 F급 무선 전력증폭기의 설계에 있어 바이어스 전압의 불확도가 출력 전력에 미치는 영향을 분석하고, 이를 최소화하는 바이어스 조건을 도출하였다. 이를 위하여 불확도 전파이론을 활용하여 전력증폭기의 출력 전력에 대한 드레인 및 게이트 바이어스 공급 전압의 불확도가 전파되는 영향에 대하여 이론적인 해석 및 측정 민감도에 대해 분석하였으며, 1.9 GHz에서 동작하는 F급 전력증폭기 회로에서의 전력 불확도에 대한 이론적, 실험적 분석 방법을 제시하였다. 더불어, 증폭기의 성능을 유지하면서 출력 불확도를 최소화하기 위한 최적의 바이어스 조건을 도출하였다. 그 결과, 1.17W 출력 전력에 대한 전원 공급 장치의 전압 불확도는 바이어스 조건에 따라 약 15~65 mW의 영향을 미치는 것으로 파악되었으며, 최적 바이어스 조건으로 측정할 경우 출력 전력은 0.37 dB 감소하는 반면에 출력 불확도는 15 mW 이하로 감소시킬 수 있음을 확인하였다. In this paper, the propagation effect of power supply uncertainty on the output of class-F power amplifier has been estimated. Also, a 1.9 GHz, 10 watt class-F power amplifier was measured to verify the estimation and to find the optimal biasing point. By approximating the propagation theory of uncertainties, the propagation effect of bias uncertainty was mathmatically calculated. As a result, the DC biases have propagated uncertainties of 15~70 mW. However, at the optimized bias point, the uncertainty in the output power could be dropped less than 15 mW while the output power has dropped by 0.37 dB.