A CCII-Based Low-Voltage Low-Power Read-Out Circuit for DC-Excited Resistive Gas Sensors

In this paper, we propose a low-voltage (LV) low-power (LP) oscillating circuit suitable for the read-out of DC-excited resistive gas sensors, based on Second Generation Current Conveyors (CCIIs). This low-cost fully integrable front-end is able to evaluate the resistive behavior of gas sensors, without any preliminary calibration, operating a Resistance to Time (R-T) conversion and exciting the sensor with a DC voltage. Through the use of CCIIs, all the Current-Mode (CM) benefits in LV LP integrated architecture design are achieved. The developed interface, designed at transistor level, is able to operate with a low supply voltage (+/- 0.75 V), showing a low power consumption of about 700 mu W, and, hence, it is suitable for portable applications. Both CADENCE simulations on the designed integrated solution and experimental results, achieved using a PCB prototype, have shown a linear characteristic and a good agreement with theoretical expectations, for more than four decades of resistive variation. Experimental measurements, conducted employing low cost commercial components (AD844 as CCII and Figaro TGS 2600 device as resistive gas sensor), have confirmed the good performances of the developed read-out circuit as resistive gas sensor interface.