CCD Image Sensors For High Speed Inspection Systems

Abstract

Automatic industrial visual inspection systems require high speed video output and the ability to discern fine detail under an extreme range of illumination conditions. In particular the field of robotic vision requires high speed readout rates in order to process very large volumes of data in real time. A new CCD image sensor technology (DYNASENSOR T"' CCD technology) has been developed which provides a very wide dynamic range and can discern fine spatial detail with light contrast ratios of greater than a million. This technology has been applied to the realization of linear and area high speed image sensor arrays. Further, these image sensors do not exhibit saturation effects and are free of blooming even at extremely high illumination levels. The basic high speed photoelement will be described and its theory of operation will be presented. For high speed this photoelement can operate in the conductive or integration mode. The transient analysis of the device will be described. This photoelement, which can be used to form linear arrays, will be compared to a conventional photodiode operating in the integration mode. Architectures of high speed linear image sensor arrays will be discussed. Fabricated silicon high speed low noise linear image sensors of various lengths (128x1 and 1024x1) which employ the DYNASENSOR CCD photoelement as well as random access array will be described. These arrays are low noise devices with noise equivalent electrons at room temperature of 50 to 150 electrons. Effective horizontal video data rates of 250 to 400 MI-Iz can be achieved if the detector is con-figured in a linear tapped architecture. The basic photoelement, which makes use of an optimized ion implanted doped profiled channel region can detect variations in light intensity on an object of over seven orders of magnitude. This is 103 to iO4 better than any reported CCD image sensor array. The typical noise equivalent power of these arrays is less than 10-10 w/c rn 2 at a wavelength of 0.632 μm which is ideally suited for industrial applications.