How ON Semiconductor's Advanced Image Sensors Improve Road Safety

While advances in automotive technology, including crash structures, airbags, brakes and tires, have helped improve vehicle safety, we still face a variety of road risks. And, these risks are constantly changing. Driving conditions such as low-light levels significantly increase road hazards, and such driving conditions not only challenge drivers, but also put the sensors in a vehicle's advanced driver assistance system (ADAS) to the test. High-performance automotive sensors are needed to ensure safety in harsh nighttime and low-light environments.

Obviously, in low-light conditions, the road is at greater risk. The Insurance Institute for Highway Safety (IIHS) found that in 2021. 54 percent of roadway fatalities in the U.S. will occur in low-light conditions between 18:00 p.m. and 6:00 a.m., despite the fact that there will be fewer vehicles on the road during that time. Similarly, the National Highway Traffic Safety Administration (NHTSA) states that more than 70% of pedestrian fatalities occur at night.

One of the main reasons that low-light conditions increase driving hazards is the limitations of human vision. In dark conditions, drivers are often unable to recognize risks in time or notice them at all. Moreover, opposing headlights can dazzle drivers, making the problem even worse. In addition, factors such as drowsy drivers or drunk drivers can further increase the risk. In the face of these factors and environmental conditions, ADAS functionality can help to minimize accidents, and thus the performance of the underlying sensors is critical to ensuring safety.

Low-light performance

Recognizing the complexity of automotive applications, ONSEMI developed the AR0220AT. This 1.7 megapixel (MP) sensor is designed for ADAS functionality. The sensor's strong performance comes from advanced double conversion gain (DCG) and a larger 4.2 μm pixel design. Many sensor manufacturers have adopted large and small pixel designs using a combination of small and large photodiodes, but this is prone to saturation issues and unwanted artifacts in low-light conditions.

With DCG technology, we can use larger pixel sizes, and the sensor can dynamically adjust the conversion gain of the pixel to adjust the response to the dynamic range of the scene. This technology enables accurate imaging of high dynamic range (HDR) environments and reduces the flickering effect from pulsating light sources such as car headlights and brake lights.

In nighttime scenes, image noise and artifacts can mask hazards on the road or be mistaken for them. In dark conditions, the AR0220AT's high sensitivity and low-noise images accurately show the road ahead.

In typical challenging scenarios, such as sunrise or sunset, the ambient light is low and the sun's rays are strong.

Other Design Considerations

There are other important considerations for the safety provided by the sensor and for automakers looking to effectively implement the technology. The sensor uses an embedded hardware mechanism to monitor all images in real time, labeling each frame as either “good” or “potential problem”. In this way, the ADAS controller can fully ensure the accuracy of each frame, preventing false images from triggering unwanted vehicle interventions and enabling the system to perform the correct operation.

The integrated ball grid array (iBGA) package was a logical choice for ON Semiconductor. This is because the iBGA design is compact and more thermally stable than the chip-scale packages (CSPs) used in many competing solutions. Unlike CSP designs, iBGAs are less susceptible to deformation at the harsh high temperatures faced by many automotive applications. The AR0220AT is also optimized to operate at 269 mW, which not only reduces operating temperatures, but also further reduces sensor noise and improves low-light performance.

Summary

The reliability and image quality of automotive image sensors are critical and need to maintain high performance under a wide range of conditions to ensure safety under any road conditions. There are many features to consider when designing a camera system to meet such needs, but perhaps the most important are the sensor's dynamic range and low-light performance. Manufacturers can rely on the high performance and ease of integration of the AR0220AT to provide a higher level of safety and autonomy for ADAS systems.