Optical system design for characterization of photo-response non-uniformity (PRNU) of CMOS image sensors

We present an optical system and method to measure the photo-response non-uniformity (PRNU) of CMOS image sensors at different illumination conditions. By using a tunable monochromatic light source with the collimated beam output, the wavelength and incident angle of the light input can be arbitrarily selected. We demonstrate that such a spectrally and angularly resolved measurement provides valuable information on the correlation between the image noise, the crosstalk, and the layer structure. We discuss the measurement results of the PRNU for a CMOS RGB image sensor at wavelengths of 550 nm and 650 nm at incidence angles of 0 and 30 degrees. The PRNU of each color channel shows a different dependence on the incidence angle, which can be explained based on the layer structure and the crosstalk behavior. We conclude that the investigation on the correlation between the PRNU and the crosstalk can be very useful to evaluate and improve the design and construction of the image sensors for better image quality.