Modeling and Analysis of Soft-Test/Repair for CCD-Based Digital X-Ray Systems

Modern X-ray imaging systems evolve toward digitization for reduced cost, faster time-to-diagnosis, and improved diagnostic confidence. For the digital X-ray systems, charge coupled device (CCD) technology is commonly used to detect and digitize optical X-ray image. This paper presents a novel soft-test/repair approach to overcome the defective pixel problem in CCD-based digital X-ray systems through theoretical modeling and analysis of the test/repair process. There are two possible solutions to cope with the defective pixel problem in CCDs: one is the hard-repair approach and another is the proposed soft-test/repair approach. Hard-repair approach employs a high-yield, expensive reparable CCD to minimize the impact of hard defects on the CCD, which occur in the form of noise propagated through A/D converter to the frame memory. Therefore, less work is needed to filter and correct the image at the end-user level while it maybe exceedingly expensive to practice. On the other hand, the proposed soft-test/repair approach is to detect and tolerate defective pixels at the digitized image level; thereby, it is inexpensive to practice and on-line repair can be done for noninterrupted service. It tests the images to detect the detective pixels and filter noise at the frame memory level and caches them in a flash memory in the controller for future repair. The controller cache keeps accumulating all the noise coordinates and preprocesses the incoming image data from the A/D converter by repairing them. The proposed soft-test/repair approach is particularly devised to facilitate hardware level implementation ultimately for real-time telediagnosis. Parametric simulation results demonstrate the speed and virtual yield enhancement by using the proposed approach; thereby highly reliable, yet inexpensive, soft-test/repair of CCD-based digital X-ray systems can be ultimately realized

BIST Design for CCD Based Digital Imaging System

This paper presents a BIST design for CCD-based digital imaging system. Pixels on a CCD are not free from defective or faulty pixels due to numerous causes such as imperfect fabrication, excessive exposure to light, radiation, sensing element aging, and excessive mechanical shock, to mention a few. Today\u27s high demand for high resolution CCDs is dictating defect/fault-tolerance in such devices. Especially, traditional on-device BIST cannot be readily employed on the imaging devices such as CCD due to the unique requirement that no pixel can be utilized to repair or bypass a defect on any other pixels. Therefore, the BIST technique designed and simulated in this paper is a technique to test and repair the defects on pixels off the device, referred to as off-device tolerance. The basic idea was proposed in our previous work in [2] where the off-device defect/fault tolerance was investigated and a soft-test/repair technique was theoretically proposed in order to demonstrate the efficiency and effectiveness in terms ofreliability, referred to as virtual yield. A Verilog-based design and simulation is provided to demonstrate the validity of the off-device soft-test/repair in terms of reliability (or virtual yield) enhancement and performance