Compact Analog Temporal Edge Detector Circuit With Programmable Adaptive Threshold for Neuromorphic Vision Sensors

This paper presents a low-power compact analog circuit for processing time varying signals. The proposed circuit implements temporal differentiation, amplification and rectification, i.e., separation of outputs into on and off pathways. It is based on a hysteretic differentiator circuit, commonly used in neuromorphic vision sensors to implement temporal edge detection. This paper presents a thorough analysis of the original circuit and identifies the source of the problems and limitations it has for processing real-world sensory signals. The steps required to solve this problem are presented as well as an extended circuit with tunable gain and adaptable threshold that allows thresholding of small temporal changes (noise) and high-pass filtering of large temporal changes. The new circuit proposed is particularly suited for focal plane implementation of both gradient based and token based motion algorithms that require robust detection of temporal discontinuities. The circuit has been designed and successfully integrated into a 64 × 1 test prototype motion chip, fabricated in standard 350 nm CMOS technology. The paper provides extensive experimental characterization results.