Gas concentration measuring device with high resolution

There is provided a usable in conjunction with a control of the air / fuel ratio in internal combustion engines of motor vehicles, gas concentration measuring apparatus which includes a built in form of a layer laminated assembly sensor element and a sensor circuit. The sensor circuit comprises a current measuring resistor, at least one amplifier and analog / digital converter. The current sense resistor is used to measure a current flowing through the sensor element current signal is generated at the sensor element upon application of a voltage. The amplifier serves to amplify the current signal for supplying it to one of the analog / digital converter for determining the concentration of the air / fuel ratio within a measuring range of a plurality of measurement ranges, which are determined over a wide gas concentration measurement range. The gain of the current signal leads to an increase of the level of the input signal for the analog / digital converter, whereby the resolving power is enhanced in determining the air / fuel ratio.