Analog Electronic Neural Networks

The interest in analog circuit techniques for implementing neural nets is undiminished, as is indicated by a large number of recent designs, coming from universities as well as from industry. One group of circuits are networks containing the "multiply-accumulate" neurons with a large interconnectivity. The main motivation for using analog circuit techniques is the fact that the multiply-accumulate operation can be implemented compactly, if only a moderate precision of the computation is required. Other types of networks are more algorithm-specific, hard-wired for one function, for example Kohonen networks, or neuromorphic designs implementing functions found in the visual or the auditory system. Most neural nets are built with standard CMOS technology, except for a few designs in CCD technology. A few analog neural net chips are now commercially available, and more and more reports of applications are appearing. This is a significant step in the development of analog neural nets, as now their usefulness is being put to the test in "real-world" applications.