正电子发射断层成像（PET）是核医学影像研究领域的核心之一。飞行时间（TOF）测量技术能够有效提高PET图像质量，是现代PET探测器的重要发展方向。基于连续晶体和硅光电倍增管（SiPM）阵列的闪烁探测器作为一种快速发展中的探测器结构，有可能对时间分辨能力有进一步优化提升，但需要进行能量分布和多时间戳测量来满足TOF-PET需要，对读出电路提出了多通道能量和时间信息独立获取能力的需求。本论文针对TOF-PET高时间测量应用背景，对SiPM多通道数字化信号读出电路进行了研究。本论文首先基于闪烁探测器的时间性能分析，对SiPM读出电路中广泛使用的共栅级前端电路时间性能进行了研究，并通过对二阶系统时间晃动特性进行系统性分析，提出了一种考虑了SiPM信号频率、输入电容和暗噪声和功耗等参数条件下的共栅级电路定时优化分析流程，用于指导高时间分辨前端电路的设计。使用片上数字化技术能够减少模拟信号因传输路径增加而造成的干扰，并利用串行化数据传输技术简化极大地系统互联的难度，但却存在功耗大、电路结构复杂、性能一致性需要标定等问题。本论文基于时间-幅度转换技术（TAC）配合片上ADC模块，实现了多通道时间-能量信息的独立采集和数字化输出，具有结构简单、功耗低、微分非线性好、温度稳定性好等优势；使用新的改进型采样逻辑电路，在优化TAC线性范围的同时矫正了由于计数器暂稳态现象引起的时间测量误差；利用SiPM的暗计数统计特性研究了多通道时间测量系统的自动标定方法，在不添加额外测试信号和电路模块的条件下实现通道间差异的在线标定，并简化了标定流程。基于以上研究，本文研制了一款应用于SiPM读出的64通道全数字化芯片DIET。在单通道功耗5.2mW的水平上，实现了多通道能量和时间信息的独立数字化，以及小于30ps时间测量精度（均方根）的高时间分辨能力。通过对芯片性能的详细测试，验证了所设计的采样电路抗暂稳态能力以及暗计数自动标定方法的可行性与有效性，并在多通道水平上实现了较好的线性和温度稳定性。原型芯片与国内外同类型的SiPM数字化读出芯片相比达到了较好的性能水平，并有效满足了连续晶体TOF-PET探测器对能量分布和多时间戳的测量需求。
Positron Emission Tomography (PET) is one of the most important research topic in the field of nuclear medical imaging systems. The Time-of-flight (TOF) technique can effectively improve the PET image quality and has been an important feature for morden PET systems. Detectors with monolithic scintillators and SiPM arrays have shwon a potential capability to improve timing resultion, but requiring the measurement of multiple time stamps as well as the energy distribution when used in TOF applications. Thus, the readout circuits should have the ability for individual acquisition of both energy and timing information, as well as achieving low power consumption and high density of input channels. This dissertation aim to study the multi-channel digitized readout circuits for SiPMs in the TOF-PET application.Based on the analysis of the timing reslotion in a scintillator detector system, the time jitter of the common-gate CMOS pre-amplifer, which is a widely used front-end structure for SiPM readouts, was thoroughly investigated. By invoking noise and waveform analysis in a second-order system, a method to optimize the timing resolution was proposed, considering the signal frequrency, dark counts and input capacitance of the SiPM detecotrs as well as the power consumption.On-chip digitization was selected for multi-channel readout since it provides short path and low distortion to the analog input signals and simplified the connections to the back-end systems by using serialization. However the complexity, high power consumption and the mismatch between channels are still challenging for the circuit design. A time-to-amplitude convertor (TAC) followed by a Wilkinson analog-to-digital convertor (ADC) was implemented for individual sampling and digitization of both time and energy information in multiple channels. By invoking this kind of circuit, a relatively low power, simple structure, good linearity and temperature stability were achieved. A new kind of capture logic was developed to eliminate the metastability affecting the measurement as well as optimize the linear range of the TAC integration. An automatic calibration method using the temporal distribution of SiPM dark counts was invoked to correct the non-uniformity of both the threshold of the discriminators and the gain of TACs in different channels. The method can provide simultaneous calibration process in multiple channels without the use of additional test modules and can simplified the whole calibration process.Based on the research mentioned above, a 64-channel, fully digitized prototype application specific integrated cituirt (ASIC) was designed and tested. Energy and time information were captured and digitized individually with a power consumption of 5.2 mW per channel and a timing resolution of 30 ps rms. Both the capability to eliminate the metastability and the automatic calibration method mentioned above were verified. Small differential non-linearity (DNL) and good temperature stability were achieved in multiple channels. The prototype ASIC has achieved a relatively good performance and is feasible for the measurement of both energy distribution and multi time stamps in the TOF-PET systems with monolithic scintillators.
