Automotive 3.0 µm Pixel High Dynamic Range Sensor with LED Flicker Mitigation

Abstract

We present and discuss parameters of a high dynamic range (HDR) image sensor with LED flicker mitigation (LFM) operating in automotive temperature range. The total SNR (SNR including dark fixed pattern noise), of the sensor is degraded by floating diffusion (FD) dark current (DC) and dark signal non-uniformity (DSNU). We present results of FD DC and DSNU reduction, to provide required SNR versus signal level at temperatures up to 120 °C. Additionally we discuss temperature dependencies of quantum efficiency (QE), sensitivity, color effects, and other pixel parameters for backside illuminated image sensors. Comparing +120 °C junction vs. room temperature, in visual range we measured a few relative percent increase, while in 940 nm band range we measured 1.46x increase in sensitivity. Measured change of sensitivity for visual bands—such as blue, green, and red colors—reflected some impact to captured image color accuracy that created slight image color tint at high temperature. The tint is, however, hard to detect visually and may be removed by auto white balancing and temperature adjusted color correction matrixes.

HDR CMOS Image Sensors for Automotive Applications

“…The equation suggests that a shortened exposure time decreases the probability to detect the LED pulse; thus, the LED flicker arises more significantly. Simulation of the light detectability was reported in the literature [47], [90].…”

“…6. In order to reduce integration time ratio between the longest exposure and shortest exposure and to mitigate LED flicker, the fusion of MEHDR and single-exposure HDR (SEHDR) approach is currently popular, such that combination with multiple pixel gain [52], [53], dual photodiode [54], [55], lateral overflow integration capacitor (LOFIC) [56], and pulsed integration [46], [47], [56]. By these methods, over 120-dB DR can be achieved.…”

Highly Efficient Lossless Coding for High Dynamic Range Red, Clear, Clear, Clear Image Sensors

“…Some manufacturers (e.g., STMicroelectronics, On Semiconductor) offer special HDR image sensors They are also known as wide dynamic range (WDR) sensors since they produce images with the dynamic range up to 132 dB or 22 bits [ 22 , 23 ]. Such ultra-high values are reached using different techniques including multiple exposures or split pixel technology supported by tone mapping and automatic HDR image processing even inside the imaging chip [ 2 , 22 , 23 , 24 ]. Using the multiple exposure technique the HDR image data is constructed by combination of three exposures (integration time) for each pixel.…”

Automotive 2.1 μm Full-Depth Deep Trench Isolation CMOS Image Sensor with a 120 dB Single-Exposure Dynamic Range

“…Thus, a single exposure with a longer integration time is necessary along with HDR. To satisfy these, the lateral overflow integration capacitor (LOFIC) technology has been introduced, which can store excess electrons generated during the long exposure time using a large in-pixel capacitor [3][4][5][6]. The high-capacity MOS and metal-insulator-metal capacitors can be used as in-pixel capacitors, of which the unit capacitance of the in-pixel capacitors is known to be around few 10 fF/µm 2 , corresponding to about 60 ke-/µm 2 [1].…”