고양자효율 다양극 광전자증배관을 이용한 비정시간 측정 가능 PET

학위논문 (박사)-- 서울대학교 대학원 : 의과대학 의과학과, 2019. 2. 이재성.In vivo imaging of physiological activities in molecular level has proven to be useful for diagnosing diseases in early stage. Positron emission tomography (PET) is a widely used molecular imaging technique that provides three-dimensional images of functional changes with high sensitivity by estimating the distribution of injected radiotracers. The advent of time-of-flight (TOF) PET scanners has dramatically improved the quality of generated images, which led to enhanced diagnostic power and/or reduced scan time or patient radiation dose. Herein, a prototype TOF PET scanner based on advanced high-quantum-efficiency multianode photomultiplier tubes (PMTs) is presented. Superior time performance of the scanner was demonstrated and improvement of reconstructed images was confirmed from various phantom studies. Finally, our system was verified to be capable of serving as a demonstration system that provides experimental evidences of the benefits of excellent time performance and to be useful for validating the feasibility of new PET applications that have been traditionally challenging.생체 내의 생리적 현상을 분자 수준으로 촬영하는 것이 가능해짐에 따라 질병의 조기 진단이 가능해지고 있다. 양전자 방출 단층촬영기법(PET)은 이와 같은 분자 영상 기법 중 하나로, 체내에 주사한 방사성 의약품의 체내 분포를 추정함으로써 생리적 기능의 변화를 높은 민감도로 촬영하여 3차원 영상으로 제공한다. 비정 시간 측정 가능 PET 장치는 영상의 품질을 향상시킴으로써 질병을 진단할 확률을 높이거나 환자의 촬영 시간 또는 방사선 피폭 정도를 감소시키는 효과를 나타내는 것으로 알려져 있다. 이에 본 연구에서는 고양자효율 다양극 광전자증배관을 이용하여 고성능의 비정 시간 측정 PET 프로토타입을 개발하였다. 다양한 팬텀 촬영을 수행한 결과 이 프로토타입은 우수한 시간 성능과 향상된 영상을 제공함을 확인하였다. 본 시스템을 활용하여 우수한 시간 성능이 갖는 장점을 실험적으로 입증할 수 있음과 기술적인 한계로 적용이 불가능했던 새로운 PET 응용 분야의 실현 가능성 평가가 가능함을 확인하였다.Contents Abstract i Contents iii List of Figures v List of Tables vii General Introduction 1 Chapter 1. Development of TOF PET detectors 3 1.1. Background 3 1.2. Materials and Methods 4 1.2.1. Photomultiplier Tube 4 1.2.2. Detector Design 6 1.2.3. Front-end Electronics 7 1.2.4. Data Acquisition 9 1.2.5. Experimental Setup 10 1.2.6. Analysis 12 1.2.7. Timing Resolution Optimization 13 1.3. Results 14 1.3.1. Optimal Setup 14 1.3.2. Detector Performance 16 1.3.3. Verification of the Optimized Timing Resolution 19 1.4. Discussion 21 Chapter 2. Proof-of-concept prototype TOF PET system 23 2.1. Background 23 2.2. Materials and Methods 24 2.2.1. Prototype TOF PET Scanner 24 2.2.2. System Performance Measurement 26 2.2.3. Image Quality Measurement 27 2.2.4. Robustness to Errors in Data Correction 29 2.2.5. Partial Ring Geometry and Limited Angle Tomography 30 2.2.6. Joint Estimation of Activity and Attenuation 32 2.2.7. Comparison to Conventional 600-ps TOF PET 34 2.3. Results 35 2.3.1. System Performance Measurement 35 2.3.2. Image Quality Measurement 40 2.3.3. Robustness to Errors in Data Correction 44 2.3.4. Partial Ring Geometry and Limited Angle Tomography 47 2.3.5. Joint Estimation of Activity and Attenuation 49 2.4. Discussion 51 General Discussion 55 Reference 57 국문 초록 64Docto

A Study on Efficiency Enhancement of RF Power Amplifier for Mobile Communication

DoctorThe efficiency and linearity enhancement techniques of RF power amplifier (PA) for mobile communication have been studied. Those characteristics are very important design parameters for a base-station transmitter. However, it is difficult to simultaneously achieve these two characteristics because the PA should be operated in a large back-off region for the linearity, resulting in a low efficiency. In addition, recent modern mobile communication system requires broadband operation for multimode/multiband application. The digital pre-distortion (DPD), which is the most cost-effective solution for linearization, has been extensively studied. In this dissertation, the various techniques to improve efficiency, linearity, and bandwidth characteristics of the PA are presented. In detail, the broadband saturated PA with harmonic control circuits has been investigated. This saturated PA achieves the broadband operation characteristic as well as high efficiency. In addition, due to the modulated signal with a high peak-to-average ratio (PAPR), the PA should be highly efficiency in an average power region. For this purpose, this dissertation considers the Doherty PA and envelope tracking (ET) technique. The sequential DPD is explored to compensate the strong nonlinearity from the ET operation.Firstly, for the broadband transmitter with high efficiency, the broadband PA based on the saturated PA is proposed. The saturated PA has advantages for broadband operation with high efficiency due to large tolerance for the second harmonic tuning. However, it is difficult to achieve high efficiency across a wide bandwidth. To solve the problem, the harmonic control circuits are placed at the input and output of the device’s die. The saturated PA with the harmonic control circuit is designed using 120W GaN device, achieving a high efficiency and wide bandwidth characteristics simultaneously. This broadband saturated PA with the harmonic control circuits can be a promising candidate for PAs of the next generation multimode/multiband wireless communication systems.Secondly, in order to achieve the high efficiency in average output power region, Doherty PA, which is the most popular efficiency enhancement technique, is studied. In this dissertation, a new output combining circuit for asymmetric Doherty PA (ADPA) is proposed. The new combining circuit has an advantage for easy of implementation with a large matching tolerance, compared to the conventional output combining circuits.The ADPA has been implemented using the Cree Inc. CGH27060 and CGH40120 GaN HEMT devices and tested using WiMAX signal with 8.3 dB PAPR at 2.6GHz and achieves excellent performances.Thirdly, ET technique, the other promising candidate to enhance the efficiency at an average output power, is also investigated. We have proposed high frequency ET transmitter system using optimized supply modulator and the average PA in this dissertation. The average PA is optimized at the average power generation region for enhanced ET operation. The PA has been implemented using the Cree Inc. CGH35060 GaN HEMT device at 3.5 GHz. The improved supply modulator and proper ET shaping functions are applied. In the interlock experiment, the ET transmitter has delivered excellent performance. This proposed ET system provides a good linearity and high efficiency at the high frequency.Finally, we have proposed a two-stage ET PA operation and introduced a new sequential DPD architecture to linearize it. The ET technique is applied to both the drive and main power amplifiers to improve efficiency of the drive amplifier. In addition, to overcome a serious non-linearity due to the dual envelope tracking operation, a new sequential DPD architecture is also proposed. To validate the proposed two-stage ET PA and the sequential DPD operation, a drive PA using a Cree Inc. CGH40010 GaN HEMT and a main PA using a CGH27060 GaN HEMT are designed at 2.6-GHz. The two-stage ET PA is functions as expected and a very attractive architecture when the gain of the main stage is relatively low due to the ET operation

A Study on Design and Implementation of RF Power Amplifier for Improved Efficiency

Master본 논문은 기지국용 고효율 RF 전력증폭기 및 효율 향상 기술에 관한 것이다. 송신단 에서 전력증폭기는 DC 전력을 가장 많이 소모하는 부분으로 낮은 효율의 전력증폭기는 매우 큰 냉각 시스템을 필요로 하며 전체 시스템의 수명을 단축 시킨다. 이러한 문제를 해결하기 위해 고효율 특성을 가지며 쉽게 구현이 가능한 class P 전력증폭기에 대해 연구하였다. 최근 큰 Peak to Average Power Ratio (PAPR) 을 갖는 변조신호의 사용으로 최대출력 영역에서부터 많은 Backed-Off Power (BOP) 영역에서의 효율이 중요시 되고 있다. 이 논문에서는 큰 PAPR 신호에 대해서도 고효율 특징을 가질 수 있도록 도허티 전력증폭기 및 고효율 ET/HEER 전력 송신기를 위한 Bias Modulator (BM) 에 대해서도 연구 하였다.2장에서는 clsss P 전력증폭기에 대해 소개 하였고 이를 class F 및 class F-1 전력증폭기와 비교하였다. 제안된 Class P 전력증폭기는 복잡한 정합구조 없이도 설계 및 구현이 가능한 전력증폭기이다. ADS 시뮬레이터을 통해 고조파 성분들이 내부 캐패시터에 의해 조절되며 포화영역에서 비선형적으로 동작하는 캐패시터에 의해 고효율을 얻기 위해 필요한 전압성분을 만들어 낸다는 것을 알아냈다. 이를 검증하기 위해 Cree CGH40010 GaN HEMT 소자를 사용하여 class P 전력증폭기를 구현해 보았다. Class P 전력증폭기는 2.655GHz 의 Continuous Wave (CW) 신호에 대해 40.5dBm 에서 PAE 75% 의 고효율 성능을 보였다.3장에서는 평균출력 영역에서 고효율을 얻기 위한 방법으로 class P 도허티 전력증폭기에 대해서 연구하였다. Class P 도허티 전력증폭기는 2장에서 설명한 2개의 동일한 class P 전력증폭기로 구성된다. Class P 전력증폭기는 포화영역에서 고효율 특성을 가지기 때문에 load modulation 된 carrier 전력증폭기가 포화영역에서 동작하는 평균출력 영역과 carrier 및 peaking 전력증폭기가 동시에 포화영역에서 동작하는 최대출력 영역에서 최대 효율을 갖는다. 이러한 동작을 증명하기 위해 2개의 동일한 class P 전력증폭기를 사용하여 구현하였다. Class P 도허티 전력증폭기는 2.655GHz 의 사인파 신호에 대해 최대출력 영역과 6dB 낮은 평균출력 영역에서 모두에서 약 74% 의 효율을 가졌으며 802.16e 모바일 WiMAX PAPR 8dB 변조신호에 대해서도 36dBm 에서 약 60% 의 고효율 drain efficiency 를 보였다. 반면 포화동작 영역에서의 동작으로 발생하는 비선형성의 증가로 5.32 MHz offset 에서 adjacent channel leakage ratios (ACLRs) -15.4 dBc 의 비선형적인 특성을 보였다. 이를 보상하기 위해 Digital Feed-Back Pre-Distortion (DFBPD) 을 사용하여 선형화를 시켰으며 선형화 결과 23.6 dBc 증가 된 -39 dBc 의 비교적 만족스러운 성능을 얻을 수 있었다. 하지만 심각한 비선형성을 보상하기 위해 효율은 약 4% 감소 하였다.4장에서는 고효율 ET/HEER 전력 송신기를 위한 BM 에 대해서 연구하였다. BM 은 크게 고선형 특성을 갖는 linear stage 와 고효율 특성을 갖는 switch stage 로 구성 된다. 제안된 BM 을 분석하기 위해 ADS 시뮬레이터을 통해 동작을 살펴 보았으며 높은 효율을 갖는 switch stage 에서 대부분의 전류를 부하에 공급할 수 있도록 최적화 하였다. 시뮬레이션 결과 약 70% 효율을 가졌으며 실제로 구현한 BM 의 경우에도 WiMAX 10MHz 8.5dB PAPR 변조신호를 인가하였을 때 10Ω 고정된 부하에 대해서 시뮬레이션과 유사한 70.5% 의 고효율을 얻을 수 있었다.We have studied for efficiency enhancement techniques of high power amplifiers. The highly efficient PA design is very important because the most of DC power is consumed in PA. The PA with a low efficiency requires a very bulky cooling system and has a short life time. To improve the efficiency, a class P PA has been studied. The amplifier is driven into a saturated operation to self-generate harmonics, to enhance the efficiency. Due to self-generation, the amplifier dose not need any harmonic tuning circuit, resulting in a simple matching circuit structure. In addition, due to the modulated signal with a high peak to average ratio (PAPR), PA should be highly efficiency in an average power region as well as a peak power region. For this reason, we have studied the Doherty amplifier based on the class P PA and the bias modulator (BM) for Hybrid-Envelope Elimination and Restoration (EER) and Envelope-Tracking (ET) operations which can deliver the high efficiency for a high PAPR signal.Firstly, the class P PA is introduced and compared with class F and class F-1. The proposed class P PA is one of the possible easy design way to implement a highly efficient power amplifier without complicated harmonic matching circuit. Using the Advanced Design System (ADS) simulator, we have found that harmonic load impedances are determined by the internal nonlinear capacitor, which generates the required second harmonic voltage in saturated power level for making high efficiency. For a verification, the class P PA is implemented at 2.655GHz using Cree CGH40010 GaN HEMT device with the same matching topology analyzed in the simulation, and with a class AB bias. The implemented class-P PA delivered the expected performance with PAE of 75% at a saturated output power of 40.5 dBm for a 2.655GHz CW signal.Secondly, in order to achieve the high efficiency in average power level, class P Doherty power amplifier has been studied. Class P Doherty power amplifier is consisted of two symmetric class P PAs. Due to the characteristic of class P PA which maximizes the efficiency in saturated region, class P Doherty power amplifier could have high efficiencies at the average and peak power level where the load modulated carrier amplifier and peaking amplifier are in saturated regions, respectively. The proposed Doherty power amplifier is implemented using the two Cree CGH40010 GaN HEMT devices and consisted of the input power divider (hybrid coupler), carrier and peaking amplifiers, and output combining circuit (offset line and two quarter-wave transformers). For a 2.655 GHz continuous wave (CW) signal, the proposed Doherty power amplifier delivers the same efficiencies of approximately 74% at the 6dB backed-off output power and saturated power level. For 802.16e mobile WiMAX signal with 8.5dB PAPR to at the 0.01% level of the complementary cumulative distribution function (CCDF), the class P Doherty power amplifier delivers the adjacent channel leakage ratios (ACLRs) at an offset of 5.32 MHz and DE at 7-dB backed-off power level of 36 dBm -15.4 dBc and 60%, respectively. To compensate the nonlinear characteristics caused by the saturated operation, the proposed PA is linearized using the digital feed-back pre-distortion (DFBPD) linearization technique. The ACLRs at an offset of 5.32 MHz are improved to -39.0 dBc which is an improvement of 23.6 dB. However, the efficiencies are degraded by 4% because the peaking amplifiers are operated at with high PD signal in the middle power region to compensate the serious nonlinear AM-AM characteristic.Finally, we have proposed BM for Hybrid-EER and ET operations which can deliver a high efficiency for a high PAPR signal. The BM is composed of two parts: one is linear stage which plays an important role as an independent voltage source with good linearity and the other is switch stage which plays a vital role of a dependent current source with high efficiency. The proposed BM has a high efficiency and linearity because the most of current which is needed to load is supplied from the switch stage. The behavior of the BM is investigated through ADS simulator using the same model with implementation components. Based on the simulation results, the optimized BM is implemented on the constant 10Ω load for a average 10W output power. The implemented BM delivers about 70% efficiency for WiMAX 1FA 10MHz envelope signal with 8.5dB PAPR. In addition, the BM shows reasonably linear and efficient operation for the modulated signal. The proposed method is very useful to achieve improving PA, especially, at a high frequency. We believe that the proposed BM is well suited for improving efficiency of base station PA

광대역 동작을 위한 고효율 포화전력증폭기

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Chemical Interactions at phase interfaces in steel refining

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고효율 EER 전력 송신기

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A Highly Efficient Asymmetric Doherty Power Amplifier with a New Output Combining Circuit

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A highly Efficient Doherty Amplifier Considering Knee Voltage Effect

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Digitally Enhanced Linear Power Amplifier with High Performance

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Highly Efficient Envelope Tracking Transmitter for Base Station

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