Global shutter CMOS vision sensors and event cameras for on-chip dynamic information

The on-chip extraction of dynamic information from a scene can be addressed with either frame-based CMOS vision, also called smart image sensors, or dynamic vision sensors, also known as event cameras. When implemented with a pinned photodiode (PPD) as a 4-transistor active pixel sensor (4T-APS), the former brings about the benefits of low temporal noise and dark current but without high dynamic range (HDR). The latter comes with the benefits of HDR and a fast event detection rate with low power consumption. The drawback is the background activity noise, which leads to additional hardware or algorithms to keep it low. This paper analyzes the mismatch and noise of a global shutter 4T-APS implementation with local HDR through an overflow capacitor and correlated double sampling (CDS) to provide low noise events through frame differencing. The aim is to narrow the gap with dynamic vision sensors in terms of event rate and dynamic range. We show that our solution would be competitive with event cameras in scenarios with slow moving objects and a relatively wide dynamic range (85 dB).

keywords: CMOS vision sensors, dynamic vision sensors, event cameras, frame difference, high dynamic range, smart image sensors