Rationale

Evolutionary algorithms can design electronic circuits that conventional electronics design methods cannot. Take a basic notion of an evolutionary process as the repeated action of selection upon individuals replicating with heritable variations [6]. Then an evolutionary algorithm can proceed by making undirected stochastic variations; a selection mechanism makes those variations that give rise to better observed behaviour more likely to persist, to be further embellished by subsequent rounds of variation and selection.

In contrast, every step in the derivation of a circuit design using conventional methods is taken with respect to some model of how it will affect final circuit behaviour. Even in a stage of iterative modification and testing, the alterations are chosen with reference to some model of their expected effect.

A circuit's behaviour may be termed emergent [3,1,2] if it cannot feasibly be predicted in detail given only a knowledge of the individual components and how they are interconnected. An evolutionary algorithm, needing no model to predict the effects of the component-level variations applied, can craft an emergent circuit behaviour, whereas conventional methods can not. The latter must constrain the components' interactions, designing within the subset of possible circuit structures and dynamics for which the necessary models are tractable.

Previous experiments have confirmed that an evolutionary algorithm can derive a circuit beyond the scope of conventional methods in this way [9,13], but raised the issue of robustness. Here, robustness is the ability of a circuit to operate adequately over a specified range of variations in temperature, fabrication, power-supply voltage, and so on. Notice that these perturbations are often at the level of physical components. The constraints of conventional design, in allowing models of how the components affect the overall behaviour, also simplify the achievement of robustness. How much robustness is required is part of the specification of an application, but some is nearly always necessary.

The main benefit of allowing evolution to explore designs without constraint is that the circuits produced can be different to those otherwise obtainable, e.g. [5]. This novelty means that the circuits might be better in some circumstances, for example being smaller, more power efficient, or displaying graceful degradation. This paper reports an experiment showing that evolutionary design can be induced to produce a robust circuit, without having to impose the customary constraints on what designs can be explored. The paper finishes with a discussion of the wider implications of the result.