Applications of Automotive Image Sensors

In recent years, driven by the government's implementation of automobile safety laws, consumer driving experience and the trend of autonomous driving, the field of automotive image sensors has experienced explosive growth. Automotive image sensors have a wide range of applications. Image sensors with excellent performance and advanced image processing capabilities not only improve driving safety but also enhance user driving experience, becoming a hot technology in the automotive field in recent years. Forecasts show that the compound annual growth rate (CAGR) of automotive CMOS sensor market revenue will reach 28% between 2014 and 2018. Let's learn about the relevant content with the automotive electronics editor below.

Main application areas of automotive image sensors

Automotive image sensors are widely used, including vision applications such as reversing images, front view, rear view, top view, panoramic parking images, mirror replacement, in-cabin applications such as passenger monitoring, fatigue driving monitoring, dashboard control, driving recorder (DVR), airbags, and advanced driver assistance systems (ADAS) such as forward collision warning, lane departure warning, automatic high beam control, traffic sign recognition, pedestrian detection, adaptive cruise control, blind spot detection, night vision, etc.

Key performance factors affecting imaging quality

Low-light performance, dynamic range and image information processing capabilities are key factors affecting imaging quality.

1. Low-light performance is table stakes

Low-light performance is very important for automotive imaging systems. Excellent low-light performance can improve driving safety in low-light conditions such as at night. Image sensor manufacturers all aim to "see in the dark."

2. High Dynamic Range (HDR)

HDR is another important feature for automotive imaging system applications, ensuring that the camera can clearly present scene details in a wide range of light, dark and high light contrast conditions, improving the accuracy of image information and thus enhancing safety.

3. Wide-angle fisheye distortion correction (DEWARP)

Wide-angle fisheye lenses have the advantage of a wide field of view when used for vehicle-mounted imaging, but the collected image information will produce a certain degree of distortion. The DEWARP technology can be used to perform real-time correction on the video image distortion produced by the wide-angle fisheye lens and restore and flatten the image.

4. Image Overlay

Image overlay refers to the combination of image sensor and image processing auxiliary chip to achieve image extension, zoom, right view, two-board left/right view, triple screen and reversing dynamic auxiliary line. Image overlay function can better assist the driver to see the surrounding environment and reduce the accident rate.

ON Semiconductor's automotive image sensor solutions

Since launching the world's first automotive CMOS image sensor in 2004, ON Semiconductor has provided dedicated imaging solutions for the automotive industry for more than 10 years. It has become the world's leader in automotive image sensors, accounting for 46% of the entire automotive sensor market and 70% of the image sensors used for ADAS. It ranks first in the rear-view imaging field and ADAS field. In terms of quality and performance, ON Semiconductor's automotive image sensors are fully compliant with AEC-Q100, and provide excellent low-light performance, high dynamic range (HDR, >120dB) with multiple exposures on a single chip, and automotive-grade application optimizations such as fisheye distortion correction and image overlay. In 2015, it launched the world's first image sensor that supports ASIL (Automotive Safety Integrity Level). For some applications, ON Semiconductor also provides global shutter image sensors with excellent performance, such as near-infrared (NIR) solutions for cabin fatigue detection applications. In order to keep up with the market's move towards high-definition, ON Semiconductor has launched a large number of 1-megapixel solutions and will develop more 1080p sensors in the future.

Figure 1: Automotive image sensor applications and ON Semiconductor market position

ASX344/340/350AT is a system-on-chip (SoC) for reversing images. It integrates an image signal processor on a single chip. The enhanced pixel performance provides higher visibility in low-light conditions, supports up to 4 layers of image overlay to provide more reversing information to the display system, supports digital zoom and pan, and has an additional optical center point correction function, which can provide customers with lens center point correction function after camera assembly and production, thereby saving costs. All three image sensors are fully AEC-Q100 certified and have a wide operating temperature range of -40°C to 105°C. The differences between them are: ASX344AT also integrates fisheye distortion correction function and provides UART control interface, positioning as a "high-performance" solution; ASX350AT has an optical format of 1/5 inch, which is different from ASX344/340AT's 1/4 inch, positioning as a "cost-effective" solution; and ASX340AT is positioned as a "mainstream" solution. Designers can choose targeted solutions based on the specific needs of target customers.

Table 1: ASX344/340/350AT specifications

Table 2: ASX344/340/350AT configuration options

The fisheye distortion correction function of ASX344AT provides 180° wider scene coverage, and the sensor dynamic range reflects the good DR-Pix pixel technology, which is safer than the lens without fisheye correction both during the day and at night. As shown in Figure 1, the lens without fisheye correction does not capture the image information of the Minions, but after fisheye correction, the driver can see the two Minions behind the car from the display, thus avoiding safety hazards when reversing.

Figure 2: ASX344AT fisheye distortion correction example (left: daytime; right: nighttime)

The ASX34xAT series provides better color saturation and contrast than similar competing devices both during the day (typically 100-200 lux bright light) and at night (typically about 10 lux at night when a car reversing camera uses brake lights and reversing lights). As shown in the red circle in Figure 2, under daytime lighting conditions of 180 lux, the image captured by the competing device is over-sharpened and has gray spots on the color boundaries; under nighttime lighting conditions of 9.5 lux, the image captured by the competing device is over-sharpened and has more noise.

Figure 3: Imaging comparison of ASX34x and competing devices

When existing ADAS and vision applications merge, ASIL will be the reference point for compliance and applicability of new systems, and ASILB compliance is the goal of current ADAS designers. ON Semiconductor has launched the world's first 2.3 million pixel CMOS image sensor AR0231AT that supports ASILB. The device uses breakthrough technology to reduce LED flicker (LFM), establishing a new benchmark for ADAS applications. LFM technology eliminates high-frequency LED flicker from traffic lights and automotive LED lighting, allowing traffic signal reading algorithms to work under all lighting conditions. AR0231AT has a 1/2.7-inch (6.82mm) optical format and a 1928 (horizontal) x1208 (vertical) active pixel array. It uses the latest 3.0-micron back-illuminated (BSI) pixels (back-illuminated sensors generally provide higher sensitivity than front-illuminated sensors) and ON Semiconductor's DR-Pix? technology, providing dual conversion gain to improve performance under all lighting conditions. It captures images in linear, HDR or LFM mode and provides frame-to-frame context switching between modes. The AR0231AT provides up to 4-exposure HDR, captures more than 120dB of dynamic range with excellent noise performance, can synchronously support multiple cameras to easily implement multiple sensor nodes in automotive applications, and achieves user programmability through a simple two-wire serial interface. It also has multiple data interfaces, including MIPI (Mobile Industry Processor Interface), parallel and HiSPi (High Speed ​​Serial Pixel Interface). Other key features include optional automatic or user-controlled black level control, support for spread spectrum clock input and multi-color filter array selection.

For challenging applications such as driver monitoring, ON Semiconductor has introduced the industry’s first global shutter sensor, the AR0135AT, which offers 10 times lower dark current and 4 times higher shutter efficiency than previous generation products.

此外，安森美半导体还提供先进的图像协处理器用于总系统方案，如AP0200AT图像协处理器经优化用于后视摄像机并提供以太网输出，集成支持镜头畸变校正和鱼眼矫正的空间转换引擎(STE)，和精密的叠加图形引擎;AP0201AT图像协处理器也提供以太网输出，针对基于以太网的全景倒车摄像;AP0202AT图像协处理器针对数字全景倒車摄像，采用24位并行输出;AP0102AT图像协处理器针对100万像素720p后视摄像，含STE和叠加图形引擎。这些协处理器都提供符合汽车安全完整性等级(ASIL)A级和B级的功能安全特性。AP020x系列可与现有的图像传感器如100万像素AR0140AT、AR0132AT和AR0136AT及新的200万像素1080p传感器AR0230AT结合协调使用。

Conclusion

Installing cameras in cars can eliminate the blind spots of traditional mirrors, reduce traffic accident rates, and is also the basis for the rapidly developing Internet of Vehicles. It will gradually be promoted and applied in practice, and even become a standard feature of cars. Image sensors are the heroes behind it. ON Semiconductor is the global leader in automotive image sensors. Its product and solution lineup covers all segments, including vision and ADAS applications, providing high dynamic range, excellent low-light sensitivity, and excellent performance over a wide temperature range. At the same time, it provides global shutter solutions with excellent performance for emerging fields such as in-cabin detection. It is fully compliant with AEC-Q100, and in line with market trends and customer needs, it continues to promote new product development, moving towards higher resolution, adding more interfaces, and complying with ASIL.

The above is an introduction to the application of automotive image sensors in automotive electronics. If you want to know more related information, please pay more attention to eeworld. eeworld Electronic Engineering will provide you with more complete, detailed and updated information.