Overview
Although vehicle technologies such as crash structures, airbags, brakes, and tires have steadily improved safety, road risks remain and continue to evolve. Driving conditions with low illumination significantly increase hazard levels and pose challenges not only to human drivers but also to sensors used by advanced driver assistance systems (ADAS). High-performance automotive image sensors are required to maintain safety in demanding night and low-light environments.
Low-light performance
Low-light conditions increase driving risk largely due to the limits of human vision. In darkness, drivers often cannot perceive hazards in time or may not notice them at all. Oncoming headlights can cause glare, worsening the situation. Factors such as drowsiness or impaired driving further increase risk. ADAS functions can help reduce accidents, so underlying sensor performance is critical to ensuring system effectiveness.
onsemi developed the AR0220AT, a 1.7 megapixel sensor designed for ADAS functions. Its performance is driven by an advanced dual conversion gain (DCG) architecture and a larger 4.2 μm pixel design. Some vendors use dual-pixel-size approaches that combine small and large photodiodes, but that can introduce saturation issues and unwanted artifacts in low-light conditions.
With DCG, larger pixel sizes can be used while the sensor dynamically adjusts pixel conversion gain to match the scene dynamic range. This enables accurate imaging in high dynamic range (HDR) scenes and reduces flicker from pulsed light sources such as headlights and brake lights.
In nighttime scenes, image noise and artifacts can obscure or be mistaken for hazards. Under dark conditions, the AR0220AT’s high sensitivity and low-noise imaging can more accurately show the roadway ahead (Figure 1).
Figure 1: Comparison of a competitor sensor (left) and onsemi AR0220AT (right).
Note the reduced low-light performance and artifacts in the left image.
In challenging scenes such as sunrise or sunset, ambient light is low while direct sunlight can be strong, which stresses sensor dynamic range and artifact control.
Other design considerations
Beyond core imaging performance, there are additional factors important to vehicle manufacturers when deploying sensors for safety-critical applications. The AR0220AT uses embedded hardware mechanisms to monitor every image in real time, flagging each frame as "good" or "potential issue." This enables the ADAS controller to verify frame integrity, avoid false triggers from bad frames, and ensure correct system actions.
For packaging, an integrated ball grid array (iBGA) is a practical choice. Compared with chip-scale packaging (CSP) used in many competing solutions, iBGA is compact and offers improved thermal stability. Unlike CSP, iBGA is less prone to deformation under the high-temperature conditions encountered in many automotive environments. The AR0220AT is also optimized for low operating power, down to 269 mW, which lowers operating temperature, reduces sensor noise, and further improves low-light performance.
Conclusion
Reliability and image quality of automotive image sensors are essential for maintaining performance across varied conditions. When designing camera systems for safety-critical ADAS functions, dynamic range and low-light performance are among the most important sensor characteristics. The AR0220AT combines high sensitivity, low noise, and integration features to support ADAS imaging requirements.
