• ETRI Journal
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• 제36권6호
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• pp.924-930
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• 2014

This paper presents a $0.13{\mu}m$ CMOS 3-level envelope delta-sigma modulation (EDSM) RF signal generator, which synthesizes a 2.6 GHz-centered fully symmetrical 3-level EDSM signal for high-efficiency power amplifier architectures. It consists of an I-Q phase modulator, a Class B wideband buffer, an up-conversion mixer, a D2S, and a Class AB wideband drive amplifier. To preserve fast phase transition in the 3-state envelope level, the wideband buffer has an RLC load and the driver amplifier uses a second-order BPF as its load to provide enough bandwidth. To achieve an accurate 3-state envelope level in the up-mixer output, the LO bias level is optimized. The I-Q phase modulator adopts a modified quadrature passive mixer topology and mitigates the I-Q crosstalk problem using a 50% duty cycle in LO clocks. The fabricated chip provides an average output power of -1.5 dBm and an error vector magnitude (EVM) of 3.89% for 3GPP LTE 64 QAM input signals with a channel bandwidth of 10/20 MHz, as well as consuming 60 mW for both channels from a 1.2 V/2.5 V supply voltage.

• ETRI Journal
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• 제33권5호
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• pp.679-688
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• 2011

A new discrete-amplitude pulse width modulation (DAPWM) scheme for a high-efficiency linear power amplifier is proposed. A radio frequency (RF) input signal is divided into an envelope and a phase modulated carrier. The low-frequency envelope is modulated so that it can be represented by a pulse whose area is proportional to its amplitude. The modulated pulse has at least two different pulse amplitude levels in order that the duty ratios of the pulse are kept large for small input. Then, an RF pulse train is generated by mixing the modulated envelope with the phase modulated carrier. The RF pulse train is amplified by a switching-mode power amplifier, and the original RF input signal is restored by a band pass filter. Because duty ratios of the RF pulse train are kept large in spite of a small input envelope, the DAPWM technique can reduce loss from harmonic components. Furthermore, it reduces filtering efforts required to suppress harmonic components. Simulations show that the overall efficiency of the pulsed power amplifier with DAPWM is about 60.3% for a mobile WiMax signal. This is approximately a 73% increase compared to a pulsed power amplifier with PWM.

• 한국통신학회논문지
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• 제32권4C호
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• pp.379-388
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• 2007

In this paper, we propose an adaptive turbo decoding algorithm for high order modulation scheme combined with originally design for a standard rate-1/2 turbo decoder for B/QPSK modulation. A transformation applied to the incoming I-channel and Q-channel symbols allows the use of an off-the-shelf B/QPSK turbo decoder without any modifications. Adaptive turbo decoder process the received symbols recursively to improve the performance. As the number of iterations increase, the execution time and power consumption also increase as well. The source of the latency and power consumption reduction is from the combination of the radix-4, dual-path processing, parallel decoding, and early-stop algorithms. We implemented the proposed scheme on a field-programmable gate array (FPGA) and compared its decoding speed with that of a conventional decoder. From the result of implementation, we confirm that the decoding speed of proposed adaptive decoding is faster than conventional scheme by 6.4 times.

• Advances in nano research
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• 제3권1호
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• pp.49-54
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• 2015

The structure represents symmetrical metal electrode (gate 1) - front $SiO_2$ layer - n-Si nanowire FET - buried $SiO_2$ layer - metal electrode (gate 2). At the symmetrical gate voltages high conductive regions near the gate 1 - front $SiO_2$ and gate 2 - buried $SiO_2$ interfaces correspondingly, and low conductive region in the central region of the NW are formed. Possibilities of applications of nanosize FETs at the deep inversion and depletion as a distributed capacitance are demonstrated. Capacity density is an order to ${\sim}{\mu}F/cm^2$. The charge density, it distribution and capacity value in the nanowire can be controlled by a small changes in the gate voltages. at the non-symmetrical gate voltages high conductive regions will move to corresponding interfaces and low conductive region will modulate non-symmetrically. In this case source-drain current of the FET will redistributed and change current way. This gives opportunity to investigate surface and bulk transport processes in the nanosize inversion channel.

• Journal of Communications and Networks
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• 제12권6호
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• pp.544-557
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• 2010

This paper addresses the problem of controlling the envelope's power peak of single carrier modulated signals, band limited by root-raised cosine (RRC) pulse shaping filters, in order to reduce power amplifier back-off for very small aperture terminals ground stations. Magnitude modulation (MM) is presented as a very efficient solution to the peak-to-average power ratio problem. This paper gives a detailed description of the MM concept and its recent evolutions. It starts by extending the look-up-table (LUT) based approach of the MM concept to M-ary constellations with M ${\leq}$ 16. The constellation and RRC symmetries are explored, allowing considerable reduction on LUT computation complexity and storage requirements. An effective multistage polyphase (MPMM) approach for the MM concept is then proposed. As opposed to traditional LUT-MM solutions, MM coefficients are computed in real-time by a low complexity multirate filter system. The back-off from high-power amplifier saturation is almost eliminated (reduction is greater than 95%) with just a 2-stage MPMM system even for very demanding roll-off cases (e.g., ${\alpha}$ = 0,1). Also, the MPMM is independent of modulation in use, allowing its easy application to constellations with M > 16.

• 조명전기설비학회논문지
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• 제21권4호
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• pp.19-27
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• 2007

This paper presents a novel soft-switching PWM utility frequency AC to high frequency AC power conversion circuit incorporating boost H-bridge inverter topology, which is more suitable and acceptable for cost effective consumer induction heating applications. The operating principle and the operation modes are presented using the switch mode equivalent circuits and the operating voltage and current waveforms. The performances of this high-frequency inverter using the latest IGBTs are illustrated, which includes high frequency power regulation and actual efficiency characteristics based on zero voltage soft-switching(ZVS) operation ranges, and the power dissipation as compared with those of the conventional type high frequency inverter. In addition, a dual mode control scheme of this high frequency inverter based on asymmetrical pulse width modulation(PWM) and pulse density modulation(PDM) control scheme is discussed in this paper in order to extend the soft switching operation ranges and to improve the power conversion efficiency at the low power settings. The power converter practical effectiveness is substantially proved based on experimental results from practical design example.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제27권1호
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• pp.56-74
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• 2023

In order to obtain practical and high-quality satellite images containing high-frequency components, a large aperture optical system is required, which has a limitation in that it greatly increases the payload weight. As an attempt to overcome the problem, many multi-aperture optical systems have been proposed, but in many cases, these optical systems do not include high-frequency components in all directions, and making such an high-quality image is an ill-posed problem. In this paper, we use deep learning to overcome the limitation. A deep learning model receives low-quality images as input, estimates the Point Spread Function, PSF, and combines them to output a single high-quality image. We model images obtained from three rectangular apertures arranged in a regular polygon shape. We also propose the Modulation Transfer Function Loss, MTF Loss, which can capture the high-frequency components of the images. We present qualitative and quantitative results obtained through experiments.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 춘계학술대회 논문집
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• pp.283-288
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• 1995

Dynamic model of 3-way PWM high speed solenoid valve was derived considering reluctance and inductance of electromagnet through valve spool by Bondgraph modeling method. Computer simulations of hydraulic system with 3-wayhigh speed solenoid valve were performed and the results were compared to te experimental results in order to validate the PWM valve dynamic model obtained.

• 융합정보논문지
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• 제10권2호
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• pp.32-38
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• 2020

본 논문에서는 가시광 통신시스템에서 고속 전송을 위한 변조 기법에 대해서 분석하고, 최적의 비직교 다중 전송을 위한 Dimming level 및 송신 전력 비율에 대해서 연구하였다. 기존의 가시광 통신은 전송 속도를 높이기 위한 멀티전송이 어렵다는 단점이 있다. 송신단에서 고속 전송을 위해서는 반드시 다중 전송기법이 필요한데, 일반적인 가시광 통신은 다중 전송에 한계가 있기 때문에 고속 전송을 위한 다양한 연구가 진행되고 있다. 최근에는 이미지 센서인 Optical Camera Communication(OCC)을 가시광 통신에 적용한 VLC-OCC가 연구되어 기존 가시광 통신이 가지는 다중 전송의 한계를 극복하였다. 그러나 VLC-OCC 방식은 외부 조도의 영향을 더 많이 받고, 수신단에서 검출이 어렵다는 단점이 있다. 또한, 다중 전송을 위한 LED 매트릭스의 위치 인식과 딥러닝을 위한 데이터 셋 신호처리를 위한 Processing-time이 필요하기 때문에 시스템의 복잡도가 증가하게 된다. 이러한 문제를 해결하기 위해 본 논문에서는 비직교 다중 전송 방식을 적용한 고속 가시광 통신을 위한 다중 변조 방식과 그에 따른 향후 연구 방향을 제안하였다.

• 한국통신학회논문지
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• 제33권6A호
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• pp.599-606
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• 2008

본 논문에서는 GERAN 진화 시스템의 물리계층 표준을 바탕으로 고심볼률을 지원하는 경우 제안된 트레이닝 시퀀스(Training Sequence Codes, TSC)의 채널 추정 성능을 BER및 BLER을 통해 고찰하였다. 제안된 TSC를 시스템에 적용하여 도심 채널 환경에서 모의실험을 수행하고 그 결과를 타사에서 제안한 TSC와 비교하여 성능 차이가 거의 없음을 확인하였다. 또한 동일 채널 간섭이 발생하는 상황에서 연대최소자승기법 (Joint Least Square: JLS)을 적용한 채널 추정을 적용하였을 때도 비슷한 결과를 얻었다.