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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>
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 Park,Seung Chan Hong,Yeoun-Woo Jang,Junseop Byeon,Jihun Jang,Minsung Han,Unsoo Kim,Kiwan Jeong,Mansoo Choi,Gunhee Lee 한국정밀공학회 2023 International Journal of Precision Engineering and Vol.10 No.5
Commercialization of flexible perovskite solar cells requires an effective scalable coating system that overcomes the inadequate wettability of conventional polymer-based flexible substrates. In this study, we have come up with a Film-Growth-Megasonic-Spray-Coating (FGMSC) method that continuously grows uniform perovskite film on large-area flexible substrates by using fine perovskite precursor droplets (< 10 μm). The film growth mechanisms of a perovskite layer (e.g. film coverage, roughness, and crystal grain size) according to the precursor droplet supply rate and the multiple spray was thoroughly investigated for manufacturing flexible perovskite solar mini-module. In complete automation that utilizes the two-dimensional transportation system, the FGMSC system has successfully fabricated a defect-free uniform perovskite layer on large-area flexible substrates with high reproducibility and flexibility by controlling perovskite film growth. The scalability of this system is proved through fabrication of a flexible perovskite solar mini-module with PCE of 16.10% from an active area of 35.1 cm2, which is the highest efficiency made by continuous spray coating systems. The encapsulated flexible mini-module retained 97% of its initial efficiency after 200 h under continuous 1-sun illumination. The results have suggested that f-PSCs can be effectively commercialized by using our FGMSC system.
Distinct gut microbiotas between southern elephant seals and Weddell seals of Antarctica
Mincheol Kim,Hyunjun Cho,Won Young Lee 한국미생물학회 2020 The journal of microbiology Vol.58 No.12
The gut microbiome provides ecological information about host animals, but we still have limited knowledge of the gut microbiome, particularly for animals inhabiting remote locations, such as Antarctica. Here, we compared fecal microbiota between southern elephant seals (Mirounga leonina) and Weddell seals (Leptonychotes weddelli), that are top predatory marine mammals in the Antarctic ecosystem, using 16S rRNA amplicon sequencing and assessed the relationships of the gut microbial communities to functional profiles using gut metabolite analysis. The bacterial community did not differ significantly by host species or sex at the phylum level, but the distinction at the family level was obvious. The family Ruminococcaceae (Firmicutes) was more abundant in southern elephant seals than in Weddell seals, and the families Acidaminococcaceae (Firmicutes) and Pasteurellaceae (Gammaproteobacteria) were uniquely present in Weddell seals. The fecal bacterial community structure was distinctively clustered by host species, with only 6.7% of amplicon sequence variants (ASVs) shared between host species. This result implies that host phylogeny rather than other factors, such as diet or age, could be the major driver of fecal microbiotic diversification. Interestingly, there was no apparent sex effect on bacterial community structure in Weddell seals, but the effect of sex was pronounced in adult southern elephant seals mainly due to the prevalence of Edwardsiella sp., suggesting that extreme sexual dimorphism may modulate the gut microbiota of southern elephant seals. Unlike the clear distinction in the taxonomic composition of fecal bacterial communities, there were no discernible differences in the profiles of potential microbial functions and gut metabolites between host species or sexes, indicating that functional redundancy dominates the gut microbiota of seals surveyed in this study.