Analog VLSI circuits as physical structures for perception
in early visual tasks.

Luigi Raffo
DIEE - University of Cagliari, Piazza d'Armi, 09123 Cagliari, ITALY
Silvio P. Sabatini, Gian Marco Bo, and Giacomo M. Bisio
DIBE - University of Genoa, Via Opera Pia 11a, 16145 Genova, ITALY

A variety of computational tasks in early vision can be formulated through
lattice networks. The cooperative action of these networks depends on the
topology of interconnections, both feedforward and recurrent ones.
This paper shows that it is possible to consider a distinct general architectural
solution for all recurrent computations of any given order.
The Gabor-like impulse response of a 2nd-order network is analyzed in detail,
pointing out how a near-optimal filtering behavior in space and frequency domains
can be achieved through excitatory/inhibitory interactions without impairing the
stability of the system. These architectures can be mapped, very efficiently
at transistor level, on VLSI structures operating as analog perceptual engines.
The problem of hardware implementation of early vision tasks can, indeed,
be tackled by combining these perceptual agents through suitable weighted sums.
A 17-node analog current-mode VLSI circuit has been implemented on a
CMOS 2 , NWELL, single-poly, and double-metal technology, to demonstrate
the feasibility of the approach. Applications of the perceptual engine to various
machine vision algorithms are  proposed.