Controller of air-fuel ratio sensor

A controller of an air-fuel ratio sensor for controlling and outputting a first application voltage to a first terminal of the air-fuel ratio sensor and a second application voltage to a second terminal of the air-fuel ratio sensor, the controller comprising:

• a first voltage application circuit having
• a first Digital-to-Analog (D/A) converter that converts a first input digital value and outputs an analog voltage, and
• a first operational (OP) amplifier configured to receive the analog output voltage from the first D/A converter at a non-inverted input terminal, and to output a voltage from an output terminal, wherein the voltage output from the first OP amplifier is directly input into an inverted input terminal of the first OP amplifier and input to the first terminal of the air-fuel ratio sensor;
• a second voltage application circuit having
• a second D/A converter that converts a second input digital value and outputs an analog voltage, and
• a second operational (OP) amplifier configured to receive the analog output voltage from the second D/A converter at a non-inverted input terminal, and to output a voltage from an output terminal, wherein the voltage output from the second OP amplifier is directly input into an inverted input terminal of the second OP amplifier and input to the second terminal of the air-fuel ratio sensor;
• a current sensing resistor having a resistance value and disposed at a position between the output terminal of the first OP amplifier and the output terminal of the second OP amplifier, the current sensing resistor for sensing a sensor current (Is) that flows in the air-fuel ratio sensor;
• an Analog-to-Digital (A/D) converter configured to receive a voltage across the current sensing resistor as an input, to convert the voltage across the current sensing resistor by an A/D conversion, and to output a digital value;
• and
• a digital processor configured to receive the digital value output from the A/D converter and to output the first input digital value to the first D/A converter and the second input digital value to the second D/A converter based on the digital value from the A/D converter,
• wherein the digital processor includes:
• an adjuster configured to adjust the second input digital value to adjust the voltage output from the second OP amplifier to a preset voltage;
• a calculator configured to calculate a digital value of the sensor current flowing in the current sensing resistor based on a ratio of the digital value output by the A/D converter to the resistance value of the current sensing resistor;
• and
• a control unit configured to control the first input digital value based on a calculation result of the calculator for controlling the output voltage of the first OP amplifier as a voltage Vu based on an equation Vu=Vout±(Vtar+Is×Rs),
• wherein Vtar is a target voltage applied to the air-fuel ratio sensor, Is is the sensor current, Rs is the resistance value of the current sensing resistor, (Vtar+Is×Rs) is an adjusting factor, and Vout is the preset voltage;
• wherein the adjusting factor is added to the preset voltage when the voltage output from the first OP amplifier is applied to the first terminal of the air-fuel ratio sensor and the voltage output from the second OP amplifier is applied to the second terminal of the air-fuel ratio sensor;
• and
• wherein the adjusting factor is subtracted from the preset voltage when the voltage output from the first OP amplifier is applied to the second terminal of the air-fuel ratio sensor and the voltage output from the second OP amplifier is applied to the first terminal of the air-fuel ratio sensor.