Modeling and analysis of soft-test/repair for CCD-based digital X-ray systems

Abstract

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

“…Also, in order to validate the theoretical results on the impact of the distribution ofthe pixel defects on the yield, the random pixel defect distribution as was investigated in [2] will be simulated and tested by using the following distribution function as reported in [3 ] and the clustered pixel defect distribution as was investigated in [2].…”

“…It is assumed that the memory is defect/fault-free. In order to demonstrate the validity of the proposed theoretical soft-testing/repair [2] on the circuit design and simulation level, a testing circuitry is designed and presented as shown in Figure (1). The proposed BIST consists of the following primary modules.…”

“…A detailed principle has been presented in [2] and is based on the general observation in digital imaging systems that the pixels tend to exhibit similar values around the average. The constant C is the threshold for determining whether the pixel under test is defective or not.…”

“…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 defectlfault tolerance was investigated and a soft-testlrepair technique was theoretically proposed in order to demonstrate the efficiency and effectiveness in terms ofreliability, referred to as virtual yield. A Verilogbased design and simulation is provided to demonstrate the validity of the off-device soft-testlrepair in terms ofreliability (or virtual yield) enhancement andperformance.…”

On-line identification of faults in fault-tolerant imagers

“…Jin et al [6] compare the difference between a pixel and the average of the eight nearest neighbour pixels to a threshold level to determine which pixels are faulty. Tan and Acharya [7] use the difference between a pixel and the average of the four or eight nearest neighbour pixels combined with sequential probability ratio testing on multiple images to identify defects.…”