High-speed-camera based on a CMOS active pixel sensor

Standard CMOS technologies offer great flexibility in the design of image sensors, which is a big advantage especially for high framerate systems. For this application we have integrated an active pixel sensor with 256 x 256 pixel using a standard 0.5μm CMOS technologie. With 16 analog outputs and a clockrate of 25-30 MHz per output, a continuous framerate of more than 5000 Hz is achieved. A global synchronous shutter is provided, but it required a more complex pixel circuit of five transistors and a special pixellayout to get a good optical fill factor. The active area of the photodiode is 9 x 9 μm. These square diodes are arranged in a chess pattern, while the remaining space is used for the electronic circuit. Fill factor is nearly 50%. The sensor is embedded in a high-speed camera system with 16 ADCs, 256Mbyte dynamic RAM, FPGAs for high-speed real time image processing, and a PC for user interface, data archive and network operation. Fixed pattern noise, which is always a problem of CMOS sensors, and the mismatching of the 16 analog channels is removed by a pixelwise gain-offset correction. After this, the chess pattern requires a reconstruction of all the missing pixels, which can be done by a special edge sensitive algorithmn. So a high quality 512 x 256 image with low remaining noise can be displayed. Sensor, architecture and processing are also suitable for color imaging.