On Designing Mixed-Signal Fuzzy Logic Controllers as Embedded Subsystems in Standard CMOS Technologies

Abstract: A digitally-programmable analogue Fuzzy Logic Controller (FLC) is presented. Input and output signals are processed in the analog domain whereas the parameters of the controller are stored in a built-in digital memory. Some new functional blocks have been designed whereas others were improved towards the optimisation of the power consumption, the speed and the modularity while keeping a reasonable accuracy, as it is needed in several analogue signal processing applications. A nine-rules, two-inputs and one-output prototype was fabricated and successfully tested using a standard CMOS 2.4µ technology, showing good agreement with the expected performances, namely: from 2.22 to 5.26 Mflips (Mega fuzzy logic inferences per second) at the pin terminals (@CL=13pF), 933 µW power consumption per rule (@Vdd=5V) and 5 bits of resolution. Since the circuit is intended for a subsystem embedded in an application chip (@CL \leq 5pF)up to 8 Mflips may be expected.