Makers of complementary metal oxide semiconductor (CMOS) image sensors for the automotive market face growing challenges with respect to achieving high-dynamic-range (HDR) imaging that delivers improved flicker mitigation and enhanced performance in low-light conditions. Implementing lateral overflow integration capacitor (LOFIC) technology in single-exposure LED flicker mitigation (LFM) sensors can help optimize dynamic range and reduce image flicker.

CMOS image sensors convert photons to electrons to create digital images in still and video cameras. As light enters the camera and is focused onto the image sensor, each pixel accumulates an electrical charge that’s proportional to the local incident light. The image sensor’s analog-to-digital converters processes the electrical signals to yield a digital image. This established approach has continued to evolve with emerging technology requirements—mostly notably, the need for HDR capabilities that enable the sensor to achieve crisp image capture, even in areas of the scene that are extremely bright or dark.

Existing HDR imaging techniques often struggle to provide consistent performance in terms of dynamic range, flicker mitigation and low-light performance. Pulse-width modulation (PWM) in LED light sources can cause image detection problems when short exposure times are used. If the exposure window falls in between the LED pulses, the sensor misses detecting the LED light source. Video stream flicker is created by frames missing the “on” pulse when the sensor tries to capture bright LED light with a short exposure time; however, increasing exposure time to capture the LED pulse can cause pixel saturation.

In the automotive market, flicker from LED traffic lights or signs pose a serious challenge for HDR solutions, preventing driver-assistance and autonomous driving systems from being able to correctly detect lighted traffic signs. Mitigating this challenge requires an approach that can be easily integrated into a CMOS image sensor. Some solutions that have achieved good LFM capabilities have resulted in reduced image quality, especially for low-light, high temperature operation and other conditions.