Image sensor targets driverless cars

October 22, 2014 // By Christoph Hammerschmidt
Melexis has developed a CMOS image sensor that offers ASIL-ready support functions. The device is designed for use in camera-based Advanced Driver Assistance Systems and driverless cars. Excellent low-light capabilities enable downstream electronics to detect pedestrians even in the night.

The MLX75421 Blackbird is an automotive grade, high dynamic range (HDR) image sensor with an extensive set of on-chip functional safety (ASIL) support functions. It has been architected for automotive safety applications where driving decisions are taken automatically, based on the images of one or multiple cameras. Examples are automatic emergency braking (AEB), electronic mirrors/camera monitor systems (CMS) and autonomous evasive steering. The device is also optimized for next generation viewing applications like surround/rear view systems with object detection functions.

The MLX75421 Blackbird's set of ASIL support functions are explicitly aimed at a cost-effective implementation of ASIL systems. These functions take care of the digital aspects but moreover also cover the sensor’s analog functions and the sensor interface. As a result, the sensor generates an embedded 'frame valid’ flag for every frame based on intensive run-time self-testing.

With a resolution of 1344x1008 pixels, the MLX75421 Blackbird has a 1/3” optical format. It features a 4 stabilized kneepoint HDR response curve which provides up to 125dB of HDR inside every frame. The HDR full frame rate is 45fps, while 60fps can be achieved when capturing image data from 800 rows. This makes the image sensor also compatible with 720p applications. The device runs fully automatically in HDR mode without the need for a companion chip.

Designed for low noise operation, the MLX75421 Blackbird has a dark leakage of less than 5 electrons/s at 25°C and dark temporal noise of less than 4.4 electrons for a 1/30s exposure time. This results in an SNR1 illuminance value of 0.005 lux for light with a wavelength of 535nm over a 1/30s exposure time. This translates into excellent low-light performance and meets upcoming NCAP 5-star rating requirements which anticipate that the vehicle "sees" good enough in the night to detect pedestrians and bicycles even at night.

The device has a wide operating temperature range of -40°C to +115°C, which benefits its temperature robustness. The MLX75421