To recapitulate from the cited prior articles: EHW is characterized as evolutionary in a quasi-genetic sense. The essence of EHW is to construct and test a sequence of populations of circuits that function as incrementally better solutions of a given design problem through the selective, repetitive connection and/or disconnection of capacitors, transistors, amplifiers, inverters, and/or other circuit building blocks. The connection and disconnection can be effected by use of field programmable transistor arrays (FPTAs). The evolution is guided by a search and optimization algorithm (in particular, a genetic algorithm) that operates in the space of possible circuits to find a circuit that exhibits an acceptably close approximation of the desired functionality. The evolved circuits can be tested by mathematical modeling (that is, computational simulation) only, tested in real hardware, or tested in combinations of computational simulation and real hardware.
In principle, the application of the EHW concept to temperature compensation could be straightforward: If, for example, a change in temperature were to change the functionality of an EHW circuit such as to cause a measure of the error in the functionality to exceed a specified threshold, then the process of evolutionary automated synthesis could be resumed, possibly taking account of previous circuit configurations in the population. The evolutionary process would be stopped once an evolved circuit performed with an error below the threshold.
The application of the EHW concept to temperature compensation has been demonstrated in computational simulations and in experiments on real FPTAs at controlled temperatures. In one set of computational simulations, an AND gate was evolved to function at a temperature of 27ºC. As shown in the upper part of the figure, its response deteriorated as the temperature was increased to 180ºC. The evolutionary process was then begun toward a new version of the circuit in the hope of restoring the desired AND-gate function at 180ºC. As shown in the lower part of the figure, the evolution yielded a close approximation of the desired result.
This work was done by Adrian Stoica of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Electronics/Computers category. NPO-21146