Automotive Image Sensor Eliminates Flicker from LED Traffic Lights
Omnivision's new CMOS image sensor offers high low-light performance while mitigating image flicker from LED traffic lights and signals in automotive exterior cameras.
Omnivision is expanding its automotive image sensor portfolio with the OX05D10 5-megapixel (MP) CMOS image sensor. The new CMOS image sensor follows the release of the OX08D10 8 MP sensor announced last September at AutoSens Brussels.
Omnivision’s OX08D10 8-MP a-CSP CMOS image sensor. Image used courtesy of Omnivision
The OXO5D10 serves automotive cameras in advanced driver assistance systems (ADAS) and autonomous driving (AD) applications. Built with Omnivisions’s 2.1 µm single-pixel TheiaCel technology, the new image sensor delivers high-performance traffic signal LED flicker mitigation (LFM) without compromising dynamic range, low-light performance, or image resolution.
More Key Specifications
The OXO5D10 features a 2880 x 1920 array of 2.1 µm x 2.1 µm pixels, with a total image area of 6064.8 µm x 4048.8 µm in chip-scale packaging (CSP).
The 5 MP sensor offers 140 dB of image dynamic range, with over 110 dB of dynamic range when LED flicker mitigation is required. Digital images can be captured at up to 60 frames per second (fps). Power to the chip is via 3.3 V analog and 1.1 V digital supplies with standard 1.8 V/ 3.3 V I/O rails. The sensor is qualified for the extended automotive operating temperature range up to 125 °C.
LED Flicker in Traffic Lighting
The CMOS image sensors used in exterior automotive camera applications employ photodetector arrays to convert light photons to electrons, generating still or video digital images. As with most cameras, individual image frames are created during a fixed exposure time, where the sensors collect light to produce a digital representation of the surrounding environment.
Modern traffic lights and signals often use pulse-width modulated (PWM) LED light sources. For PWM operation, the LEDs are turned on and off at very high frequencies that are not detectable by the human eye to conserve power and mitigate thermal issues.
Exterior camera image distortion from LED flicker. Image used courtesy of Omnivision
However, PWM operation of lighting can be a challenge for automotive CMOS image sensors where short exposure times can lead to “missed” LED pulses that distort the digital representation of the traffic signal. This phenomenon is referred to as LED flicker and can impact ADAS operations and even introduce safety hazards.
What Is LED Flicker Mitigation (LFM)?
LED flicker mitigation (LFM) extends the exposure time for the CMOS image sensor so that the high-frequency PWM flicker is filtered out. Increasing exposure times can negatively impact the sensors' dynamic range by saturating detection channels with additional light and hurting low-light performance.
LOFIC technology in a CMOS image sensor. Image used courtesy of Image Sensors World
Omnivision’s TheiaCel LFM sensor technology overcomes this issue by using lateral overflow integration capacitors (LOFIC). LOIFC technology allows the sensor to collect more signal electrons in each pixel via a large storage capacitor without saturating the channel. In this manner, LFM can be implemented more aggressively without compromising low-light signal-to-noise ratios (SNR) or dynamic range.
