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Secondary Electron Emission of ZnO Films
Choi, Jinsung,Lee, Sung Kwang,Choi, Joon Ho,Choi, Eun Ha,Jung, Ranju,Kim, Yunki The Korean Vacuum Society 2015 Applied Science and Convergence Technology Vol.24 No.6
We investigated secondary electron emission characteristics of ZnO thin films prepared by pulsed laser deposition method with respect to the ambient oxygen pressure and the substrate temperature during the deposition. X-ray diffraction, UV-Vis spectrometry, atomic force microscopy, and ${\gamma}$-FIB were used to examine the structural, optical transmission, surface morphology, and secondary electron emission properties of the films, respectively. The secondary electron emission coefficient of the ZnO films increases as the O/Zn ratio of the films increases which was thought to result from either the ambient oxygen pressure increase or the substrate temperature decrease and as the grain size of the films decreases. It was confirmed that ZnO has better secondary electron emission characteristics than those of MgO, which is currently widely used as a material for PDP protecting layers.
Jinsung Choi,Daehyun Kang,Dongsu Kim,Bumman Kim IEEE 2009 IEEE transactions on microwave theory and techniqu Vol.57 No.6
<P>This paper presents an optimized envelope tracking (ET) operation of a Doherty amplifier. Compared to the general ET/envelope elimination and restoration transmitter, it has an advantage of the extended dynamic range of 6 dB for the load modulation of a Doherty amplifier. Moreover, by modulating the supply voltage of the carrier amplifier, while that of the peaking amplifier is fixed, the supply modulator provides just half of the current for the same power amplifier output power. It results in a reduced chip size and the crest factor of the supply modulating signal is reduced by 6 dB, enhancing the efficiency of the supply modulator. The designed ET transmitter consisting of the Doherty amplifier and the supply modulator are fabricated in 2- mum HBT and 0.13-mum CMOS processes, respectively. It presents the efficiency improvement over the broad output power region. Especially at the 16-dB backed-off power level, more than 23% of power-added efficiency (PAE) is achieved. For WiBro application, it shows the PAE of 38.6% at an output power of 24.22 dBm with a gain of 24.62 dB. The error vector magnitude is 3.64%.</P>
A New Power Management IC Architecture for Envelope Tracking Power Amplifier
Jinsung Choi,Dongsu Kim,Daehyun Kang,Bumman Kim IEEE 2011 IEEE transactions on microwave theory and techniqu Vol.59 No.7
<P>A new supply modulator architecture for robust performance against the battery voltage variation is presented. The resulting modulator is an optimized power management integrated circuit (PMIC) for an envelope tracking (ET) power amplifier (PA). The basic topology of the PMIC is based on a hybrid switching amplifier combining a wideband class-AB buffered linear amplifier and a highly efficient switching-mode buck converter in a master-slave configuration. The additional boost converter regulates the supply voltage of the linear amplifier, while the supply of the buck converter is directly coupled to the battery. The proposed supply modulator achieves max/min efficiencies of 76.8/69.3% over the entire battery voltage range. The ET PA is operated at 4.5 V, providing higher output power, efficiency, and gain than at nominal 3.5-V design. The robust performance of the proposed PMIC is demonstrated.</P>
Jinsung Choi,Dongsu Kim,Daehyun Kang,Bumman Kim IEEE 2009 IEEE transactions on microwave theory and techniqu Vol.57 No.7
<P>This paper presents the realization of a linear polar transmitter supporting multistandard applications. The harmonic-tuned class-AB biased (class-AB/F) power amplifier (PA) with the novel envelope shaping method linearly amplifies the input signal with high efficiency. The hybrid switching supply modulator with programmable hysteretic comparator enables the multimode operation whatever the envelope signal characteristics such as the peak-to-average power ratio and the bandwidth are. The designed polar transmitter is fabricated with CMOS 0.13-mum technology and InGaP/GaAs 2-mum HBT process for the supply modulator and the PA, respectively. For the IEEE 802.16e m-WiMax signal, it shows a power-added efficiency (PAE), an average output power (Pout), and a gain of 34.3%, 23.9 dBm, and 27.9 dB, respectively. Without any predistortion techniques, it satisfies the overall spectrum emission mask specifications. The relative constellation error and the error vector magnitude for the m-WiMax signal are -30.5 dB and 2.98%, respectively. For a WCDMA signal, it presents a PAE, a Pout, and a gain of 46%, 29 dBm, and 27.8 dB, respectively. For the EDGE signal, it delivers a PAE of 45.3% at a Pout of 27.8 dBm with a gain of 29.4 dB. There is about a 7% improvement of the overall PAE for EDGE through the optimum multimode operation.</P>
A <tex> $\Delta\Sigma$</tex> -Digitized Polar RF Transmitter
Jinsung Choi,Jounghyun Yim,Jinho Yang,Jingook Kim,Jeonghyun Cha,Daehyun Kang,Dongsu Kim,Bumman Kim IEEE 2007 IEEE transactions on microwave theory and techniqu Vol.55 No.12
<P>This paper demonstrates a new polar transmitter architecture, which uses the digitized envelope signal to control the drain voltage of a switching mode power amplifier (PA). It is based on a novel polar modulation using the constant envelope modulated signal. Among the various constant envelope modulators, the DeltaSigma modulator is chosen for its noise-shaping characteristic. It enables the use of a highly efficient switching amplifier with high linearity. For demonstration, the overall transmitter is implemented and tested with a code-division multiple-access IS-95A signal. The class-D and class-F amplifiers are designed and compared for the optimum operation. The experimental results show that the amplifier with small device size is suitable for this application because of the fast switching requirement. For the class-F amplifier, the measured power-added efficiency is 51.7% at 22.1 dBm and the overall efficiency (considering the amplified quantization noise) is 31%. The adjacent channel power ratios at 885 kHz and 1.98 MHz are lower than -44.9 and -55.6 dBc at the output power range from 10.8 to 22.1 dBm without any pre-distortion techniques. The overall efficiency is improved to 48.6% with a three-level quantized DeltaSigma modulator. The results clearly show that the highly efficient switching mode PA can be controlled efficiently using a digital signal from the DeltaSigma envelope modulation technique.</P>
Power Amplifiers and Transmitters for Next Generation Mobile Handsets
Jinsung Choi,Daehyun Kang,Dongsu Kim,Jungmin Park,Boshi Jin,Bumman Kim 대한전자공학회 2009 Journal of semiconductor technology and science Vol.9 No.4
As a wireless handset deals with multiple application standards concurrently, RF transmitters and power amplifiers are required to be more power efficient and reconfigurable. In this paper, we review the recent advances in the design of the power amplifiers and transmitters. Then, the systematic design approaches to improve the performance with the digital baseband signal processing are introduced for the next generation mobile handset.
In-situ XPS Study of Core-levels of ZnO Thin Films at the Interface with Graphene/Cu
Jinsung Choi,Ranju Jung 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.73 No.10
We have investigated core-levels of ZnO thin films at the interface with the graphene on Cu foil using in-situ X-ray Photoelectron Spectroscopy (XPS). Spectral evolution of C 1s, Zn 2p, and O 1s are observed in real time during RF sputtering deposition. We found binding energy (BE) shifts of Zn 2p and `ZnO' state of O 1s depending on ZnO film thickness. Core-levels BE shifts of ZnO will be discussed on the basis of electron transfer at the interface and it may have an important role in the electronic transport property of the ZnO/graphene-based electronic device.