A Novel Reconfigurable Membership Function Circuit for Analog Fuzzy Logic Controller

A novel reconfigurable membership function circuit (RMFC) for analog fuzzy logic controller (FLC) is presented. The reconfigurable characteristic makes it more suitable in industrial control applications when compared with the MFC proposed in [1]. By proper signal arrangement, the RMFC can re-sample the same input current in different configuration, which reduces the number of MFC in analog FLC. Thus, the power consumption and circuitry are smaller than the MFC proposed in [2]. The full current mode circuitry ensures a low power supply voltage and high speed. The analog input signal is processed directly without any need of an A/D or D/A interface. SPECTRE simulation results validate the feasibility of the proposed RMFC that is implemented in 0.35m CMOS with a battery of 1.5-V supply. Key Words--Fuzzy logic controller (FLC), Membership function circuit (MFC), low voltage, current mode. Fuzzy logic is designed to mimic the human thinking process by incorporating the uncertainty inherent to all physical systems [3]. Relying on the human nature of the fuzzy logic, an increasing number of successful applications have been developed, such as automatic process control, pattern-recognition systems, fuzzy neurons, chaos, etc. Rapid developments in semiconductor, computing, and communication technologies turned portable devices such as personal digital assistants and laptops with wireless connectivity in powerful and ubiquitous equipments. Moreover, a new generation of sensors called “smart” sensors consists of three basic elements; a physical transducer, a controller/ memory core and a network interface [4]. The physical transducer senses the physical quantity and converts it to an electrical signal. The signal is fed to an A/D converter to produce a digital value for use by the controller. On the other hand, the analog to digital (A/D) converter circuit or the (D/A) occupies a considerable amount of resources in a portable device. Smart sensors or portable devices equipped with analog FLC have a bright future because their compatibility with the analog fuzzy world is higher. Moreover, analog FLC usually presents better performance than digital implementations in real-time control systems when speed is a concern. Also, current mode circuits exhibit a good potential since using current as a signal carrier implies no restrictions from the supply voltage. Moreover, simple current basic building blocks easily fulfil a small circuitry requirement, as well as high speed. This paper presents a novel reconfigurable membership function circuit for switched-current mode analog FLC. Its reconfigurable characteristics and low supply voltage are attractive for portable devices and smart sensors. A FLC consists of four fundamental units: fuzzification unit, inference unit, defuzzification unit and rule base unit as shown in figure 1. CSCAS 2007 2007 163 A Novel Reconfigurable Membership Function Circuit for Analog Fuzzy Logic Controller Ngai Kong, Seng-Pan U 1 and R.P. Martins 2 Analog and Mixed-Signal VLSI Laboratory, FST, University of Macau, Macao, China (E-mail: [email protected]) 1 – Also with Chipidea Microelectronics (Macao) Ltd., 2 – On leave from Instituto Superior Técnico/UTL, Lisbon, Portugal Abstract—A novel reconfigurable membership function circuit (RMFC) for analog fuzzy logic controller (FLC) is presented. The reconfigurable characteristic makes it more suitable in industrial control applications when compared with the MFC proposed in [1]. By proper signal arrangement, the RMFC can re-sample the same input current in different configuration, which reduces the number of MFC in analog FLC. Thus, the power consumption and circuitry are smaller than the MFC proposed in [2]. The full current mode circuitry ensures a low power supply voltage and high speed. The analog input signal is processed directly without any need of an A/D or D/A interface. SPECTRE simulation results validate the feasibility of the proposed RMFC that is implemented in 0.35m CMOS with a battery of 1.5-V supply.A novel reconfigurable membership function circuit (RMFC) for analog fuzzy logic controller (FLC) is presented. The reconfigurable characteristic makes it more suitable in industrial control applications when compared with the MFC proposed in [1]. By proper signal arrangement, the RMFC can re-sample the same input current in different configuration, which reduces the number of MFC in analog FLC. Thus, the power consumption and circuitry are smaller than the MFC proposed in [2]. The full current mode circuitry ensures a low power supply voltage and high speed. The analog input signal is processed directly without any need of an A/D or D/A interface. SPECTRE simulation results validate the feasibility of the proposed RMFC that is implemented in 0.35m CMOS with a battery of 1.5-V supply. Key Words--Fuzzy logic controller (FLC), Membership function circuit (MFC), low voltage, current mode. Fuzzy logic is designed to mimic the human thinking process by incorporating the uncertainty inherent to all physical systems [3]. Relying on the human nature of the fuzzy logic, an increasing number of successful applications have been developed, such as automatic process control, pattern-recognition systems, fuzzy neurons, chaos, etc. Rapid developments in semiconductor, computing, and communication technologies turned portable devices such as personal digital assistants and laptops with wireless connectivity in powerful and ubiquitous equipments. Moreover, a new generation of sensors called “smart” sensors consists of three basic elements; a physical transducer, a controller/ memory core and a network interface [4]. The physical transducer senses the physical quantity and converts it to an electrical signal. The signal is fed to an A/D converter to produce a digital value for use by the controller. On the other hand, the analog to digital (A/D) converter circuit or the (D/A) occupies a considerable amount of resources in a portable device. Smart sensors or portable devices equipped with analog FLC have a bright future because their compatibility with the analog fuzzy world is higher. Moreover, analog FLC usually presents better performance than digital implementations in real-time control systems when speed is a concern. Also, current mode circuits exhibit a good potential since using current as a signal carrier implies no restrictions from the supply voltage. Moreover, simple current basic building blocks easily fulfil a small circuitry requirement, as well as high speed. This paper presents a novel reconfigurable membership function circuit for switched-current mode analog FLC. Its reconfigurable characteristics and low supply voltage are attractive for portable devices and smart sensors. A FLC consists of four fundamental units: fuzzification unit, inference unit, defuzzification unit and rule base unit as shown in figure 1.