Despite the continuous advancement of automotive technology, including collision structures, airbags, brakes, and tires, which has helped improve vehicle safety, we still face various road risks. Moreover, these risks are constantly changing. Driving conditions such as low light intensity significantly increase road hazards, which not only pose challenges to drivers but also challenge the sensors in advanced driving assistance systems (ADAS) of vehicles. In harsh nighttime and low light environments, high-performance automotive sensors are needed to ensure driving safety.
It is obvious that there is a greater risk on the road under low light conditions. One of the main reasons why low light environments increase driving danger is the limitation of human vision. In dark conditions, drivers often fail to detect risks in a timely manner or are completely unaware of them. Moreover, facing lights can make the driver dazzle and make the problem even more serious. In addition, factors such as driver drowsiness or drunk driving can further increase the risk. Faced with these factors and environmental conditions, ADAS functionality can help reduce accidents, making the performance of underlying sensors crucial for ensuring safety.
Low light performance
Onsemi is well aware of the complexity of automotive applications and has therefore developed the AR0220AT. This 1.7 megapixel (MP) sensor is designed specifically for ADAS functionality. The power of this sensor comes from its advanced dual conversion gain (DCG) and larger 4.2 µ m pixel design. Many sensor manufacturers adopt pixel sized designs, using a combination of small and large photo diodes, but this can easily lead to saturation issues and unnecessary artifacts under low light conditions.
Through DCG technology, we can use larger pixel sizes, and sensors can dynamically adjust the conversion gain of pixels, thereby adjusting the response according to the dynamic range of the scene. This technology can achieve precise imaging of high dynamic range (HDR) environments and reduce flickering effects from pulsed light sources such as car headlights and brake lights.
In nighttime scenes, image noise and artifacts may mask the danger on the road or be mistaken for danger. Under dark conditions, the high sensitivity and low noise images of AR0220AT can accurately display the road conditions ahead (Figure 1).
Figure 1: Comparison between competitor's sensor (left side) and Onsemi ART0220AT (right side).
Please note the decrease in low light performance and the appearance of artifacts in the left image
In typical challenging scenarios, such as sunrise or sunset, the ambient light is weak while the sunlight is strong.
Figure 2: Comparison of signal-to-noise ratio performance between competing products (left) and Ansemy (right)
Other design considerations
There are other important considerations for the safety provided by sensors and for car manufacturers who wish to effectively implement this technology. This sensor uses embedded hardware mechanisms to monitor all images in real-time, marking each frame as "good" or "potential problem". In this way, the ADAS controller can fully ensure the accuracy of each frame of the image, prevent erroneous images from triggering unnecessary vehicle intervention, and enable the system to perform correct operations.
For Onsemi, integrated ball grid array (iBGA) packaging is a reasonable choice. Because compared to chip level packaging (CSP) used in many competitive solutions, iBGA has a compact design and higher thermal stability. Unlike CSP design, iBGA is less prone to deformation in many automotive applications under harsh high temperature conditions. The AR0220AT has also been optimized and its operating power consumption has been reduced to 269mW, which not only reduces the operating temperature but also further reduces sensor noise and improves low light performance.
Figure 3: Competitive products (left) and Ansemy products (right)
Comparison of color loss caused by angle performance
Summary
The reliability and image quality of automotive image sensors are crucial, requiring high performance under various conditions to ensure safety in any road conditions. When designing a camera system that meets such needs, many characteristics need to be considered, but perhaps the most important ones are the dynamic range and low light performance of the sensor. Manufacturers can rely on the high performance and ease of integration of AR0220AT to provide higher levels of security and autonomy for ADAS systems.
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