Interface circuitry and its integration

There are two possible ways of interfacing gas sensors with their associated interface circuitry the hybrid approach and the monolithic approach. 

As chemo-resistive sensors are based on a change in conductivity at high operating temperatures, so main circuit blocks required for interfacing these sensors are driving circuits for micro-heaters, temperature control units and sensing material interface circuits. 

7 Diagram of a temperature control circuit, in which the same heater is used for measuring the temperature (adapted from Bota eta ., 2004). (VDD, supply voltage. V,g reference voltage.) 

A relatively simple scheme has been reported by Barrettino et al. (2002). A large dynamic range of sensing material was compressed by using two 

8 Resistance controlled oscillator circuit for gas sensing material interface (adapted from Grassi et a ., 2007). Q and Q are two complementary signals at the output of the flip flop. 

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