Off-device fault tolerance for digital imaging devices

Charged-coupled device (CCD) is one of the widely-used optical sensing device technologies for various digital imaging systems such as digital cameras, digital camcorders, and digital X-ray imaging systems. Pixels on a CCD may suffer from defective or faulty pixels due to numerous causes such as imperfect fabrication, excessive exposure to light radiation and sensing element aging to mention a few. As the use of high-resolution CCDs increase, defect and fault tolerance of such devices demands immediate attention. In this context, this paper proposes a testing and repair technique for defects/faults on such devices with inability of on-device fault tolerance, referred to as off-device fault tolerance. Digital image sensor devices such as CCD are by their nature, can not readily utilize traditional on-device fault tolerance techniques because each pixel on the device senses a unique image pixel coordinate. No faulty pixel can be replaced nor repaired by a sparse pixel as any displacement of an original pixel coordinate can not sense the original image pixel. Therefore, to effectively provide and enhance the reparability of such devices with inability of on-device fault tolerance, a novel testing and repair method for defects/faults on CCD is proposed based on the soft testing/repair method proposed in our previous work (Jin et al, 2003) under both single and clustered distribution of CCD pixel defects. Clustered fault model due to unwanted diffusion should be considered as practical model and for comparison purpose with single fault model. Also, a novel default/fault propagation model is proposed to effectively capture the on-device effects and faults off the device for an effectiveness and practicality of testing and repair process. The efficiency and effectiveness of the method is demonstrated with respect to the yield enhancement by the soft-testing/repair method under a clustered fault model as well as single fault model, as referred to as soft yield. Extensive numerical simulations are concluded.