June 15, 2017: Narayan Purohit, the Product Line Manager of Automotive Image Sensors, ON Semiconductor said that LED lighting has brought a number of improvements to road signage and cars and furthermore, Advanced Driver Assistance Systems (ADAS) such as autonomous braking, new parking sensors and so on assist the drivers towards road safety. However, when ADAS and LED lighting are merged together, LED lights pose challenges to car safety sensors, he added.
Importance of car LED lighting
LED car lighting has successfully inspired new designs and styles in cars. Also, LEDs are being increasingly used in road signage these days right from motorway notifications to traffic lights at intersections, emergency signals and road-side signs.
Importance of ADAS
On the other hand, ADAS has also become extensively popular among car manufacturers and consumers. It offers an important tool that assists drivers to respond to road signs in a correct manner so as to aid them to handle traffic situations, thus improving their overall safety.
A wide array of systems fall under the category of ADAS such as autonomous emergency braking, blind-spot detection, traffic-sign recognition, rearward parking assistance and virtual mirrors.
However, the increasing use of LEDs in road signs and car lighting poses an altogether different type of challenge to the vision-sensing systems of vehicles, remarked Purohit.
LED lighting like signage can glimmer several hundred times a second that may cause traditional electronic shutter modes to create image artefacts. The effects tend to worsen while capturing bright view thus causing the shutter to place the integration time much shorter than the frame length. This often leads to failure to detect an illuminated LED. Also, this may prevent systems like traffic-signal recognition, brake-light detection and night-vision support from functioning in a correct manner.
In order to resist the effects of LED flicker, ON Semiconductor has put into practice superior LED Flicker Mitigation (LFM) in the AR0231 sensor. LFM includes transfer gate operations and vibrant shutter gate that facilitate the integration period to be extensive over the frame window.
The sensor supports multi-camera organization to inside eight pixel clocks without decreasing the highest frame rate. This helps in enhancing the performance of ADAS systems that depend upon images from multiple cameras like virtual mirror replacement.