Integrated vision sensor for detecting boundary crossings

In this paper, we detail a simple solution for counting objects that cross a field of view. We reduce the problem to detecting localized illumination changes on two spatially separated borders. Each circular border is formed from pixels that measure the magnitude of local changes in illumination relative to the global average. These local change signals are summed over each border and then amplified. Off-chip processing determines the movement direction by cross-correlating these signals with appropriate delays. We have implemented the crossing-detection functionality with low complexity and power consumption using a 5.3 mm² area on a standard 5 V 0.8 μm double-poly double-metal CMOS process. Crossing objects that cover 1/8 of the border, with contrasts down to a few percent, can be detected.