Evolutionary experiments with a fine-grained reconfigurable architecture for analog and digital CMOS circuits

The paper describes the architectural details of a fine-grained programmable transistor array (PTA) architecture and illustrates its use in evolutionary experiments on the synthesis of both analog and digital circuits. A PTA chip was built in CMOS to allow circuits obtained through evolutionary design using a simulated PTA to be immediately deployed and validated in hardware and, moreover, enables a benchmarking and comparison of evolutions carried out via simulations only (extrinsic evolution) with the chip-in-the-loop (intrinsic) evolutions. The evolution of an analog computational circuit and a logical inverter are presented. Synthesis by software evolution found several potential solutions satisfying the a priori constraints, however, only a fraction of these proved valid when ported to the hardware. The circuits evolved directly in hardware proved stable when ported to different chips. In either case, both software and hardware experiments indicate that evolution can be accelerated when gray-scale (as opposed to binary switches) were used to define circuit connectivity. Overall, only evolution directly in hardware appears to guarantee a valid solution.