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Prediction of the Arctic Oscillation in boreal winter by dynamical seasonal forecasting systems
Kang, Daehyun,Lee, Myong-In,Im, Jungho,Kim, Daehyun,Kim, Hye-Mi,Kang, Hyun-Suk,Schubert, Siegfried D.,Arribas, Alberto,MacLachlan, Craig American Geophysical Union 2014 Geophysical research letters Vol.41 No.10
This study assesses the skill of boreal winter Arctic Oscillation (AO) predictions with state-of-the-art dynamical ensemble prediction systems (EPSs): GloSea4, CFSv2, GEOS-5, CanCM3, CanCM4, and CM2.1. Long-term reforecasts with the EPSs are used to evaluate how well they represent the AO and to assess the skill of both deterministic and probabilistic forecasts of the AO. The reforecasts reproduce the observed changes in the large-scale patterns of the Northern Hemispheric surface temperature, upper level wind, and precipitation associated with the different phases of the AO. The results demonstrate that most EPSs improve upon persistence skill scores for lead times up to 2months in boreal winter, suggesting some potential for skillful prediction of the AO and its associated climate anomalies at seasonal time scales. It is also found that the skill of AO forecasts during the recent period (1997-2010) is higher than that of the earlier period (1983-1996).
A Multimode/Multiband Power Amplifier With a Boosted Supply Modulator
Daehyun Kang,Dongsu Kim,Jinsung Choi,Jooseung Kim,Yunsung Cho,Bumman Kim IEEE 2010 IEEE transactions on microwave theory and techniqu Vol.58 No.10
<P>A multimode/multiband power amplifier (PA) with a boosted supply modulator is developed for handset applications. A linear broadband class-F amplifier is designed to have a constant fundamental impedance across 1.7-2 GHz and its second and third harmonic impedances are located at the high-efficiency area. To reduce the circuit size for handset application, the harmonic control circuits are merged into the broadband output matching circuit for the fundamental frequency. An envelope-tracking operation delivers high efficiency for the overall power. The linearity is improved by envelope tracking (ET) through intermodulation-distortion sweet-spot tracking at the maximum output power level. The efficiency and bandwidth (BW) are enhanced by a boosted supply modulator. Multimode operation is achieved by an ET technique with a programmable hysteresis control and automatic switching current adaptation of the hybrid supply modulator. For demonstration purpose, the PA and supply modulator are implemented using an InGaP/GaAs heterojunction bipolar transistor and a 65-nm CMOS process. For a long-term evolution signal, the envelope-tracking (ET) PA delivers a power-added efficiency (PAE) and an error vector magnitude of 33.3%-39% and 2.5%-3.5%, respectively, at an average power of 27.8 dBm across 1.7-2 GHz. For a wideband code-division multiple-access signal across 1.7-2 GHz, the ET PA performs a PAE, an ACLR1, and an ACLR2 of 40%-46.3%, from -39 to -42.5 dBc, and -51 to -58 dBc, respectively, at an average output power of 30.1 dBm. The ET PA with an EDGE signal delivers a PAE, an ACPR1, and an ACPR2 of 37%-42%, from -56.5 to -59.3 dBc, and -63.5 to -69.5 dBc, respectively, at an average power of 28 dBm across the 300-MHz BW. These results show that the proposed design achieves highly efficient and linear power amplification for multimode/multiband wireless communication applications.</P>
Broadband HBT Doherty Power Amplifiers for Handset Applications
Daehyun Kang,Dongsu Kim,Junghwan Moon,Bumman Kim IEEE 2010 IEEE transactions on microwave theory and techniqu Vol.58 No.12
<P>A Doherty power amplifier for IEEE 802.16e mobile worldwide interoperability for microwave access (m-WiMAX) is fully integrated on a 1.2 × 1.2 × mm<SUP>2</SUP> die using a 2-μm InGaP/GaAs hetero-junction bipolar transistor (HBT) process. The direct input power dividing technique is employed on the chip. Broadband input and output matching techniques are used for broadband Doherty operation, and their effects are analyzed. A peaking amplifier 1.5 times larger than a carrier amplifier delivers high efficiency for m-WiMAX signal with a 9.6-dB crest factor and an 8.75-MHz bandwidth (BW). The PA with a supply voltage of 3.4 V has an EVM of 2.3% and a PAE of 31.5% at an output power of 24.75 dBm as well as an operating frequency of 2.6 GHz. A PAE over 30.3% and an output power of greater than 24.6 dBm with an EVM less than 3.15% and a gain variation of 0.2 dB are achieved across 2.5-2.7 GHz without any assisting linearization technique. After compensating AM-AM and AM-PM nonlinearity using a digital feedback predistortion algorithm, the PA exhibits a PAE of over 27% and an output power of over 23.6 dBm across 2.2-2.8 GHz while maintaining an EVM below 2.7%.</P>