Partial reset HDR image sensor with improved fixed pattern noise performance

Abstract

An efficient method is presented to achieve 4T pixel dynamic range extension whilst keeping the fixed pattern noise (FPN) low. The method utilizes the floating diffusion node as a secondary photocharge integration node with a partial reset applied to the floating diffusion node. The output image signal is a recombination of the linear signal integrated in the photodiode node, and a compressed signal integrated in the floating diffusion node. The recombination algorithm suppresses the FPN stemming from the variable transfer gate potential barrier height. An image sensor array of 1344x1008 pixels was built in 0.11um technology. We demonstrate the preservation of low light sensitivity of 4T pixels, a dark noise of 3.5e-, and a dynamic range for the current sensor of 115 dB, with potential to greatly exceed 120-dB. Further, the FPN stemming from the transfer gate potential barrier height variation does not degrade the image; the pixel compressive response can be controlled on a per frame basis depending on the scene, and the HDR scene is captured during one frame. The sensor combines the properties that are crucial for automotive and other machine vision applications.