Autonomous mobile systems: Fuzzy controller design with VLSI approach

The design approach for fuzzy controller for autonomous mobile systems is discussed here. Silicon area & operational speed are the major constraints for fuzzy controllers. The digital approach has greater flexibility, easier design automation, and good compatibility with other digital systems but they are more complex. The designs have been carried out in the digital domain with VHDL. The proposed work focuses on control of speed & distance as two parameters with rectangular, triangular & trapezoidal membership functions. It also describes the implementation of a membership function circuit using MOSFETs. It implements the simplified inference mechanism wherein MOS analog circuits are used to represent signals as currents. However, the whole system is externally communicated through voltages, thus enabling simple interface with conventional control circuitry. The design requires only one differential pair for each membership function & the output currents are automatically normalized. The normalization circuit is integrated within the fuzzifier. By choosing different reference voltages and different W/L ratios, various types of membership functions can be accomplished.