New Transistor replicates neurons
03/01/1998
New transistor replicates neurons
Frogs are stupid. They can`t calculate digits of p, they can`t transmit data over long distances, they have no grasp of most problems that an average desktop computer considers routine. Yet, as a fly buzzes past, the frog can identify it as food, compute its trajectory, and flick its tongue out to make the catch, all in a fraction of a second. Even the most advanced supercomputers are stumped by such real-time processing problems.
Tadashi Shibata, of the University of Tokyo, and Tadahiro Ohmi, of Tohoku University, suggest that organic brains can offer valuable models for silicon-based designs. Speaking at the 1997 IEDM meeting, Shibata proposed the neuMOS (nMOS) transistor, a simple analog to organic neurons.
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An organic brain consists of "grey matter," a thin layer of neurons with many convoluted folds covering the surface, and "white matter," a three-dimensional interconnect making up the majority of brain mass. Some monkeys have larger brains relative to body weight than humans, but human brains have the largest fraction of white matter. While replicating such high-density interconnections is likely to be impossible, Shibata suggested that the superior speed of electronic circuitry can help overcome this limitation.
An organic neuron receives inputs from multiple sources, weighting the relative importance of each. When the inputs sum to a threshold value, the neuron fires. It thus achieves an on/off signal by way of analog processing. The nMOS (see figure) replicates this multi-input structure. Multiple electrodes contact a single floating gate. When the sum of the voltages, weighted by resistors, exceeds the threshold voltage, the transistor turns on. According to Shibata, a 3-input exclusive NOR gate requires only four nMOS transistors, far fewer than conventional MOSFET implementations.
The authors used nMOS transistors to construct a proof-of-concept associator for hardware recognition. Conventional software compression of a VGA (640 ? 480 pixels) image takes about 20 sec with typical CISC processors, but, Shibata claimed, required only 30 msec using the nMOS associator. The nMOS transistor, he said, should provide a very cost-effective way to achieve ultra-high density integration of functions on a chip. - K.D.