An ON-OFF temporal filter circuit for computing motion energy

Motion energy units are important components of biologically inspired algorithms for image motion analysis. We describe an analog VLSI temporal filter circuit that can be cascaded with a spatial filter to implement the spatio-temporal filters required to compute motion energy. This circuit adopts an ON-OFF differential representation used by a previously developed chip for spatial filtering. It has two main advantages over previous continuous-time temporal filtering circuits used to compute motion energy. First, its outputs are in exact quadrature phase, rather than an approximation. Second, it halves the total temporal filter order required to compute motion energy. We describe the filter architecture, analyze its dynamics theoretically, and provide measurement results from a prototype fabricated in a 1.5-[micro]m CMOS n-well process. Index Terms--Analog VLSI, image processing, neural chips, neuromorphic engineering.