Study On High Performance X-ray CMOS Image Sensor And Its Application

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.