2D Focal Plane Steerable and Scalable Cortical Filters

We describe a 25x25 pixel image sensor which spatially filters a set of input currents supplied by an array of phototransistors by two orientation selective image filters. The filters are similar to even and odd Gabor filters, which have been used to model the receptive fields of neurons in the visual cortex. The circuit architecture implementing the image filter consists of two resistive networks which are coupled by transconductance amplifiers. The tuned orientation can be steered and the filter response scaled by adjusting the conductances of the resistors and gains of the transconductance amplifiers. The architecture implemented here is a 2D extension of a previous 1D architecture with some modifications which enable one chip to implement filters of arbitrary orientation.