Analog signal-selector circuit for quick gas detection from gas-sensor arrays

A Sixteen Input Maximum/Minimum Analog signal-selector Circuit (SIMMAC) is designed, simulated, and implemented using 2 μm p-well (Orbit) CMOS technology. The circuit is useful in recognition of gas types from measurements of thin-film gas-sensor arrays. The output signal of each thin-film gas detector is typically a function of bias voltages, temperature and pressure, film type, frequency, and gas type. Gas sensor arrays provide profiles of resistivity vs. temperature, for a particular PPM, and/or profiles of resistivity vs. pressure at a particular temperature. Since different chemical gas types have peak resistivity values at a certain temperature and a certain pressure, a selector circuit is needed to identify chemical gas components. The SIMMAC design is based on a multiple-input current comparator median circuit. Simulation results gave an accuracy of better than 94% with analog input signal values from 1.6 to 3.6 V. The SIMMAC is suitable for gas detection from a sensor-array of up to 16-elements with known models and negligible signal distortion. Further, it may be used as a post processor to select the winning synapse in an unsupervised neural network for pattern recognition with distorted and unidentified models of gas mixtures