A 2.97μm-Pitch Event-Based Vision Sensor with Shared Pixel Front-End Circuitry and Low-Noise Intensity Readout Mode

Abstract

Event-based vision sensors (EVS) detect temporal contrast changes with high dynamic range using pixel-parallel comparison with a relative threshold. To achieve this detection feature, an EVS pixel comprises a logarithmic amplifier, a sampling circuit of the initial voltage, at least one comparator, and in-pixel logic circuitry [1]. The complexity of pixel circuitry constrains the pixel size. A back-illuminated (BI) stacked EVS reduces the pixel size to around <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$5\mu \mathsf{m}[2,3]$</tex> , but many applications looking to take advantage of EVS require smaller pixel sizes and higher resolutions. To meet speed requirements in terms of event detection, an asynchronous frame-free readout based on an arbiter circuit is often applied to EVS. Though asynchronous readout achieves response times of several <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$10\mu \mathbf{s}$</tex> in low-activity scenes, the unpredictable arbitration time degrades time accuracy and affects system-level features such as recognition accuracy in high-activity scenes. There have been several efforts to increase event throughput with innovative circuit techniques [4], [5], but the additional processing increases the post-processing cost to reconstruct a frame from asynchronous event data. A frame format synchronized with a stable time accuracy is suitable for recent post-processing approaches performed using a convolutional neural network. Moreover, conventional image acquisition with very low noise is still helpful for the complex tasks combined with event-based vision sensing. Recent proposals combining event detection and intensity acquisition have serious limitations due to random noise or propagation delays from arbitration [6], [7].