The presence of dark current, signal charge which is not due to photons, has been a performance limiter for image sensors. There has been a 5000x decrease over 40 years and there is the assumption that this trend will continue. However, the decrease has been accompanied by a change of the nature of the generation mechanism as is seen in characterization data related to voltages and temperature. The present limiting root cause of dark current needs to be determined to guide further improvement. It is also interesting to speculate on the ultimate limitation of dark current in defect-free silicon.
Most of the snapshot HDR (High Dynamic Range) image sensors have a non-linear, programmable, response curve that requires multiple register settings. The complexity of the settings is such that most algorithms reduce the number of parameters to only two or three and calculate a smooth response curve that approaches a log response. The information available in the final image depends on the compression rate of the response curve and the quantization step of the device. In this early stage proposal, we make use of scene information and discrete information transfer to calculate the response curve shape that maximizes the information in the final image. The image may look different to a human but contains more useful information for machine vision processing. One important field of use of such sensors with programmable dynamic range is automotive on-board machine vision and more specifically autonomous vehicles.
In this paper, a 128x128, 34μm pixel-pitch, room temperature infrared image sensor and processor is presented. With a measured power consumption of 8.9mW (540μW / pixel) in full operating mode (image acquisition and data processing), the sensor exhibit a Noise Equivalent Temperature Difference (NETD) of 190mK at room temperature and doesn't require a Thermo-Electric Cooler (TEC). The circuit also features a novel ∑Δ Analogue to Digital Conversion architecture, 12 frames of Built-in SRAM and 128 column-wise full-custom processors that target a broad range of applications such as 2-points corrected IR camera or feature extraction for privacy-compliant presence detection, localization and counting. Built-in analogue and digital pixel-level offset pre-correction improves operability and manufacturing yields thus pushing bolometers IR technology one step forward towards high-end applications for consumer market.