Focal plane implementation of 2D steerable and scalable Gabor-type filters

We describe the analog CMOS VLSI implementation of a cellular neural network (CNN) architecture which spatially filters a 2D image by two orientation selective image filters. The image is represented by a set of input currents supplied by an on-chip array of photosensors. The filters are similar to even and odd Gabor filters. The CNN architecture is implemented using two resistive networks 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 through externally supplied bias voltages. The circuit operation is explained via a variational principle, which defines the filter output as the minimum of a cost function. We report test results from both 25 x 25 and 45 x 45 pixel arrays.