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Ultrabroadband Linear Power Amplifier Using a Frequency-Selective Analog Predistorter
Mincheol Seo,Kyungwon Kim,Minsu Kim,Hyungchul Kim,Jeongbae Jeon,Myung-Kyu Park,Hyojoon Lim,Youngoo Yang IEEE 2011 IEEE Transactions on Circuits and Systems II: Expr Vol.58 No.5
<P>This brief presents an ultrabroadband (2- to 600-MHz band) linear power amplifier using a compact frequency-selective analog predistorter, which includes a capacitor having an optimized capacitance and a biased Schottky diode connected in series. It is shunted at the input of the main amplifier and has a frequency-selective third-order intermodulation generation capability using its optimized capacitance. A two-stage push-pull power amplifier, which has an ultrabroadband operation range from 2 to 600 MHz, was implemented and linearized using the proposed analog predistorter. It exhibited high 1-dB compression point (P1 dB) and power-added efficiency characteristics of over 43 dBm and 32% at each P1 dB for the entire operating band, respectively. At an average output power level of 36 dBm for the two-tone signal input, which has a tone spacing of 1 MHz, its third-order intermodulation distortion over the entire band is no higher than -39.1 dBc after linearization, as compared with -34.2 dBc before linearization.</P>
Mincheol Chang(장민철) 한국고분자학회 2021 한국고분자학회 학술대회 연구논문 초록집 Vol.46 No.2
Conjugated polymer (CP)-based organic field effect transistors (OFETs) have been considered as potential candidates for gas sensing applications because of their unique advantages, such as light weight, multiparameter accessibility, ease of large-scale fabrication, and superior sensing capability enabled by gate-tunable current modulation. Recent studies have demonstrated the successful application of CP-based OFETs in gas sensors and have highlighted the urgency for improving the charge mobility and morphological features of the CP films for enhancing the performance of these sensors toward their practical applicability. This talk will demonstrate novel processing strategies for tuning the morphologies and charge transport properties of CP thin films, resulting in significant improvement in gas sensing performance of the CP film-based OFET gas sensors.
Mincheol Seo,Hwiseob Lee,Jehyeon Gu,Hyungchul Kim,Ham, Junghyun,Wooyeol Choi,Yanghun Yun,Kenneth, K. O.,Youngoo Yang IEEE 2014 IEEE Transactions on Circuits and Systems II: Expr Vol. No.
<P>This brief presents an active second-harmonic injection technique to improve the efficiency and bandwidth for high-efficiency power amplifiers (PAs). An optimum third-harmonic termination condition was examined for higher efficiency after the second-harmonic injection using a multiharmonic load-pull simulation. It was determined that the optimum third-harmonic termination is the same as that of the inverse class-F PA. Based on this result, a high-efficiency PA with an optimized third-harmonic termination for the second-harmonic injection was designed for a center frequency of 1 GHz as a main amplifier. The overall system requires an auxiliary second-harmonic amplifier and a diplexer between the main and auxiliary PAs. The PA with an optimized third-harmonic termination for the second-harmonic injection was implemented using a 10-W GaN high-electron-mobility transistor for both the main and auxiliary power stages. Compared with the PA without second-harmonic injection, the bandwidth with a power-added efficiency of more than 80% is extended from 60 (960-1020 MHz) to 180 MHz (880-1060 MHz) after the second-harmonic injection.</P>
Option volume and stock returns: evidence from single stock options on the Korea Exchange
( Mincheol Woo ),( Meong Ae Kim ) 한국파생상품학회 2021 선물연구 Vol.29 No.4
Informed traders may prefer the options market to the stock market for reasons including the leverage effect, transaction costs, restrictions on short sale. Many studies try to predict future returns of stocks using informed traders’ behavior in the options market. In this study, we examine whether the trading volume ratios of single stock options have the predictive power for future returns of the underlying stock. By analyzing the stock price responses to the “preliminary announcement of performance” of 36 underlying stocks on the Korea Exchange from November 2014 to March 2021 and the trading volume of options written on those stocks, we investigate the relation between the option ratios, which are the call option volume to put option volume ratio (C/P ratio) and the option volume to stock volume ratio (O/S ratio), and the future returns of the underlying stock. We also examine which ratio is better in predicting the future returns. The authors found that both option ratios showed the statistically significant predictability about future returns of the underlying stock and that the return predictability of the O/S ratio is more robust than that of the C/P ratio. This study shows that indicators generated in the options market can be used to predict future underlying stock returns. Further, the findings of this study contributed to a dearth of literature pertaining to single stock options. The results suggest that the single stock options market is efficient and influences the price discovery in the stock market.
NEGF Approach to Three-Dimensional Carbon Nanotube Field Effect Transistor Simulations
Mincheol Shin 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.4
We have performed device simulations on three-dimensional carbon nanotube field effect transistors by solving the Poisson equation self-consistently with the quantum transport equations formulated in the the non-equilibrium Green's function approach. The single-band tight binding Hamiltonian is used for the charge transport on the carbon nanotube surface and detailed numerical aspects for self-consistent calculations, including our simple method to calculate the surface Green's function at the contacts, are presented. Simulation results from our in-house simulator for Schottky-barrier devices, as well as doped source/drain devices, are also demonstrated. We have performed device simulations on three-dimensional carbon nanotube field effect transistors by solving the Poisson equation self-consistently with the quantum transport equations formulated in the the non-equilibrium Green's function approach. The single-band tight binding Hamiltonian is used for the charge transport on the carbon nanotube surface and detailed numerical aspects for self-consistent calculations, including our simple method to calculate the surface Green's function at the contacts, are presented. Simulation results from our in-house simulator for Schottky-barrier devices, as well as doped source/drain devices, are also demonstrated.