Wide dynamic range CMOS pixels with reduced dark current

Abstract

The sensitivity of logarithmic pixels at low light levels is limited by the dark current that flows through the load transistor in the pixel in addition to the photocurrent. This dark current also degrades the performance of cameras containing these pixels by increasing the residual fixed pattern noise following fixed pattern noise correction. The performance of logarithmic pixels will therefore be improved if the dark current can be reduced. A review of the sources of dark current has led to the design of a new layout for a logarithmic pixel. Results are reported that show that this layout significantly reduces the dark current in the pixel. In addition, a simple change to the bias voltages applied to the proposed pixel means that the new layout can simultaneously exhibit a linear response at low light levels and a logarithmic response at higher light levels. Experimental results from both modes of operations are presented.