Planar air-to fuel ratio sensor and driving circuit therefor

Abstract

A planar air-to-fuel (A/F) ratio sensor and a driving circuit therefor are provided. A circuit for driving a planar A/F ratio sensor having a structure wherein an exhaust gas side electrode is shared by a pumping cell and a sensing sell, or a structure wherein an air side electrode is shared by the pumping cell and the sensing cell, is comprised of a comparator for comparing a voltage measured in the sensing cell with a predetermined reference voltage corresponding to the voltage the sensing cell when the pumping cell is within a limit current range to output a voltage which is proportional to the difference between two compared voltages, an integrator for integrating the output of the voltage comparator to output a voltage, an adder for adding a voltage for compensating an electromotive force of the pumping cell to the output voltage of the integrator and an A/F ratio detector for sensing the current flowing through the pumping cell from a voltage output from the adder and applied to the pumping cell to detect an A/F ratio. Therefore, damage to the electrode can be prevented, and the response characteristic between the sensing cell and pumping cell and the accuracy in measuring the A/F ratio can be improved. Also, shift of the current limit region into a region where a voltage V.sub.p is greater than 0 can be compensated by an internal electromotive force of the pumping cell.