Universal pixel-synchronous data acquisition system for high-resolution CCD image sensors

Abstract

The use of CCD sensors in optical metrology requires synchronous sampling of the image with a good signalnoise performance. . A system has been developed to digitize optimally the signals from high-resolution CCD sensors. The data acquisition system is split into two parts -the first is a storage unit for the IBM PC/AT family of computers with a fast, digital, input-output interface, with 8-bit transmission speed DC-4OMHz and 16 bit operation DC-2OMHs. The digitization of the analogue signal is performed on separate units, up to 2m from the computer. Separating the analogue processing from the computer and using a separate power supply not only reduces the electrical noise from the digital electronics to a minimum but also allows greater flexibility in designing custom 'front ends' for a wide range of sensors. The storage card has two 1M byte banks of memory. These are normally used to provide double buffering of 1M pixel images, but can also be used to store 2M byte images without double buffering. Practical experience, using 8 and 10 bit video front ends, indicates that the geometrical resolution possible with modern CCD sensors is approaching 1/100 of the pixel period. The digital signal processing required for this performance does not depend on the CCD camera's PSF and it is insensitive to variations offocus and orientation.