【作者】 张文普；

【导师】 袁祥辉；

【作者基本信息】 重庆大学 ， 仪器科学与技术， 2005， 博士

【摘要】 X 射线数字实时成像系统在医学、工业无损检测以及海关、机场、车站、码头的行包安全检查等领域得到广泛应用,X 射线图像传感器是其中的关键部件,现在用在X 射线实时检测领域的图像传感器大部分为电荷耦合器件CCD。由于CMOS 图像传感器比CCD 具有更强的抗辐射能力,还具有将图像传感器阵列、驱动和控制电路、信号处理电路、模数转换电路、全数字接口电路等实现单片集成以及量子效率高、光谱响应宽、响应均匀性好、工作电压低、对时钟脉冲要求低、体积小、重量轻、功耗低、高可靠、低成本等优点,因此在X 射线实时检测中更具有开发前景。而国内生产X 射线数字实时成像系统的厂商他们实行核心技术(如X射线图像传感器)从国外进口,以OEM 方式组装成整机。因此开展高性能X 射线CMOS 图像传感器的研究,在国内是一项具有开拓性和创新性的工作。本文的主要研究内容如下: 1.对采用电流镜积分读出电路的X 射线CMOS 图像传感器(简称为CMI-X-IS 图像传感器)的原理进行了研究,在此基础上,开展CMI-X-IS 图像传感器的设计工作,对CMI 单元、相关双采样CDS 和公共输出级电路进行分析。对根据CMI-X-IS 图像传感器的原理进行加工生产的芯片样品进行测试,测试的参数包括光电转换特性曲线、暗噪声和动态范围等,对这些参数进行分析,得出结论:采用电流镜积分读出电路可以构成一种CMOS 高灵敏度图像传感器。控制器件的设计参数,可以使光电流增益达到10 倍,从而使图像传感器灵敏度提高10倍;电流镜积分读出电路可以保证光电二极管的偏压接近于零(20mV 以内),因而可大大减小光电二极管的暗漏电流和噪声;该器件的光电流注入效率高,积分动态范围大,适合用于要求灵敏度高、动态范围大的应用。2.利用复杂可编程逻辑器件CPLD 设计满足CMI-X-IS 图像传感器时序要求的驱动信号源,并对实际应用出现的外部同步信号导致CMI-X-IS 图像传感器工作不正常的原因进行了分析,并采用“数字单稳态电路”使CMI-X-IS 图像传感器的F1、F2、ADST 为断续信号,从而使使CMI-X-IS 图像传感器工作正常。这种解决应用过程中出现问题的方法是独创性的,对类似的应用具有启示作用。设计CMI-X-IS 图像传感器的应用电路,并将此应用电路置于微焦点X 射线机的照射下,对不同密度、不同尺寸的材料进行了静态实验。实验表明,CMI-X-IS 图像传感器有较高的输出信号幅度(可以达到3 伏左右)、较好的均匀性、CMI-X-IS 可以清晰地反映出这几种材料的形状,能把不同密度的材料加以区分。因此这种传感器特别适合作为X 射线图像传感器来使用。3.分析与虚拟仪器采集数据有关的几个实际问题,利用NI 公司的数据采集卡和LabVIEW软件,设计CMI-X-IS 图像传感器的动态扫描成像系统和数据采集系统。实验表明,动态扫描更多还原

【Abstract】 X-ray real-time radioscopy imaging system can be used in many fields, such as medicine, industry non-destructive technology and baggage safety inspection in customs, airport, railway station,dock etc. X-ray image sensors are the key devices of the X-ray real-time radioscopy imaging system in which the CCD predominates at present. However, the CMOS image sensors can provide stronger anti-radiation capacity than CCD as well as Single Chip Integrating (SCI) with image sensors array, drive and control circuit, signal processing circuit, A/D conversion circuit and Completely Digital Interface Circuit (CDIC). The CMOS image sensors also possess high quantum efficiency, wide spectral response, good response uniformity, low supply voltage and low request of clock. At the same time, the small bulk, high reliability, low power consumption and low cost are the prominent advantages of the CMOS image sensors too, thus CMOS image sensor has more exploiture foreground in X-ray real-time radioscopy imaging system. The X-ray image sensors used in the X-ray real-time radioscopy imaging system produced by OEM in China are mainly imported. Therefore, it is an active and innovative work in our country to develop high performance X-ray CMOS image sensors. This dissertation accomplishes the research work as below: 1. The principles of X-ray Image Sensor using Current Mirroring Integration readout circuit (CMI-X-IS) were studied in detail and the unit CMI circuit, Correlative Double Sampling (CDS) circuit, and common output stage circuit were analyzed, then the design of the CMI-X-IS was achieved. The creative CMI-X-IS has been tested from photoelectric conversion properties, dark noise and dynamic range. Some conclusions are drawn out as following: the method of high sensitivity CMOS image sensor with CMI circuit is feasible; the photocurrent gain can reach 10 by controlling the design parameters of the device, consequently, the image sensor’s sensitivity can rise about decuple; the dark current and noise of the photodiodes can be reduced rapidly due to the CMI circuit can ensure the photodiodes’bias close to zero (less equal 20 mV); the device can be applied in the fields with request for high sensitivity and wide dynamic range because of its high photocurrent injection efficiency. 2.The drive signal source satisfied the timing relationship request by CMI-X-IS are generated by the Complex Programmable Logic Device(CPLD).The abnormal operation of CMI-X-IS, caused by external synchronization signal in realistic applications,is analyzed, and settled by “digital monostabillity circuit”,through which the F1,F2,and ADST becomes intermittence signals. This method for problems in practical applications is unique, and can be used in other similar occasions. The application circuit of CMI-X-IS is designed , and exposed in the micro-focus X-ray. Static experiments have been done for material of different densities and sizes. The experiment results indicate that CMI-X-IS has high output amplitude( about 3 voltages), good uniformity, and this sensor especially suits for X-ray imaging. The shapes made of different materials can be imaged clearly, and material of different densities can be distinguished. 3. Some practical problems related to virtual instrument data acquisition are analyzed. The dynamic scan imaging and data acquisition system are designed by data acquisition card of NI corperation and LabVIEW software. The experiment shows that white and black image of such objects as tooth can be clearly displayed by the dynamic scan imaging and data acquisition system. 4.This paper also analyzed CMI-X-IS’s dark current, nonuniformity of photic responsivity, and nonuniformity of scintillators responsivity, pulse noise’s influence in the X-ray.The image processing, for example: histogram equalization, contrast enhancement, linear filtering, mid-value filtering and self-adaptive filting, is implemented for tooth image obtained by CMI-X-IS.更多还原