| An integrated circuit was designed to access and read a prototype chemical sensor array. The addressing was accomplished using row and column decoders with master- slave D flip flops. The analog output circuit, containing logarithmic trans-impedance amplifiers, source follower circuits and transistor switches, converted the logarithmic sub-threshold sensor current to a voltage signal, and read out the voltage from the sensor. To demonstrate the feasibility of this approach, the circuits were integrated and fabricated with a 2x2 "pseudo-sensor" array on a chip using CMOS technology. Functional testing of the fabricated design verified that the integrated circuit accessed and read each sensor successfully. The experimental Vout-Isensor curves from a single sensor confirmed the expected logarithmic relationship between current and output voltage from the sensor. A cross talk experiment demonstrated that the row and column decoders in the digital circuit efficiently routed digital signals to their respective rows and columns. Given the feasibility of the design has been verified, this type of circuit could be used to realize a truer "electronic nose" where a much large float-gate, FET sensor array could be used. |
