A QVGA 143 dB Dynamic Range Frame-Free PWM Image Sensor With Lossless Pixel-Level Video Compression and Time-Domain CDS

TLDR

The sensor is a QVGA CMOS array of autonomous pixels with event‑based change detection and PWM imaging circuitry. Each pixel autonomously initiates exposure upon detecting brightness change, asynchronously requests output via an arbitrated channel, encodes grayscale values in inter‑event intervals, and employs a time‑domain correlated double sampling technique to reduce fixed‑pattern noise. The autonomous operation yields lossless video compression with factors up to ~1000 for static scenes, achieves an intra‑scene dynamic range of 143 dB (125 dB at 30 fps), and delivers an SNR > 56 dB (9.3 bit) under >10 Lx illumination.

Abstract

The biomimetic CMOS dynamic vision and image sensor described in this paper is based on a QVGA (304×240) array of fully autonomous pixels containing event-based change detection and pulse-width-modulation (PWM) imaging circuitry. Exposure measurements are initiated and carried out locally by the individual pixel that has detected a change of brightness in its field-of-view. Pixels do not rely on external timing signals and independently and asynchronously request access to an (asynchronous arbitrated) output channel when they have new grayscale values to communicate. Pixels that are not stimulated visually do not produce output. The visual information acquired from the scene, temporal contrast and grayscale data, are communicated in the form of asynchronous address-events (AER), with the grayscale values being encoded in inter-event intervals. The pixel-autonomous and massively parallel operation ideally results in lossless video compression through complete temporal redundancy suppression at the pixel level. Compression factors depend on scene activity and peak at ~1000 for static scenes. Due to the time-based encoding of the illumination information, very high dynamic range - intra-scene DR of 143 dB static and 125 dB at 30 fps equivalent temporal resolution - is achieved. A novel time-domain correlated double sampling (TCDS) method yields array FPN of <;0.25% rms. SNR is >56 dB (9.3 bit) for >10 Lx illuminance.