| 摘要 |
A limiting current A/F sensor 30 generates a current signal corresponding to an air-fuel ratio in response to a voltage applied by a bias control circuit 10. After a sensor current Ip is received as a voltage signal via a voltage follower 17, it is outputted to an A/D converter 41 having a predetermined input voltage range 0 to 5V. A sensor current detection circuit 15 has a plurality of current detection resistors 15a, 15b. In order to variably set the resistance value in the sensor current detection circuit 15, so that the voltage applied to the A/D converter remains within the usable range, and the sensitivity of the system is adequately high, a switch circuit 18 is switched depending on whether the A/F value being detected is in the zone near the stoichiometric ratio or in other air-fuel ratio zones. During manufacture, resistors 12, 13 may be trimmed while the output voltage is being measured, to set a precise reference voltage V a . |
