| 摘要 |
PURPOSE:To reduce an error of an air to fuel ratio output caused by the error of an input offset voltage of a differential amplifier and to improve the accuracy by constituting the title device so that a detection resistance having an optimum resistance value in the measuring range of a control current can be use for a current detecting circuit. CONSTITUTION:A feedback resistance 35 attached to an operational amplifier 34 operates so as to allow a current IP1 to flow through the feedback resistance Rf35 so that a voltage applied to an inversion input of the operational amplifier 34 becomes equal to a voltage applied to a non-inversion input. In this case, the relation of IP1 and IP satisfies IP1=Rt2XIP/(Rt1+Rt2+Rs). The current detection resistance of IP1 is the feedback resistance Rf35, and the potential difference of the non-inversion input of the operational amplifier 34 and its output is shown as V=IP1XRf. That is, by amplifying this potential difference by a differential amplifier 32, at the time of a prescribed air to fuel ratio, a prescribed air to fuel ratio output Vout is obtained. |
