Correcting circuit, correcting method, and sensor apparatus
A correcting circuit includes a correction current synthesizer synthesizing a correction current based on an output signal of a sensor, a current adjuster adjusting a determining current which corresponds to a correction amount based on the correction current, and a correction voltage generator generating a correction voltage for correcting a voltage signal based on the determining current, so as to correct an output characteristic of a voltage signal output in correspondence to the output signal of the sensor.
1. A correcting circuit comprising:
a correction current synthesizer synthesizing a correction current based on an output signal of a sensor;
a current adjuster adjusting a determining current which corresponds to a correction amount based on the correction current; and
a correction voltage generator generating a correction voltage for correcting a voltage signal based on the determining current, so as to correct an output characteristic of a voltage signal output in correspondence to the output signal of the sensor.
2. The correcting circuit according to claim 1 , further comprising:
a voltage-current converter including a differential pair receiving an input of a differential input voltage between a voltage obtained by voltage conversion of the output signal of the sensor and a reference voltage, and outputting a differential output current of a first current and a second current to the correction current synthesizer,
wherein the correction current synthesizer comprises:
a first resistor and a second resistor coupled in series with each other between differential output lines of the differential pair;
a first transistor comprising a gate coupled to a point between the first resistor and the second resistor and a drain coupled to the differential output line which carries the first current;
a second transistor comprising a gate coupled to a point between the first resistor and the second resistor and a drain coupled to the differential output line which carries the second current;
a third transistor comprising a gate coupled to the drain of the first transistor and carrying a third current described by a quadratic function of the differential input voltage;
a fourth transistor comprising a gate coupled to the drain of the second transistor and carrying a fourth current described by a quadratic function of the differential input voltage;
a fifth transistor comprising a gate commonly coupled to the first and second transistors and a source commonly coupled to the first and second transistors and carrying a fifth current; and
a current synthesizer synthesizing the correction current from the third, fourth and fifth currents.
3. The correcting circuit according to claim 2 ,
wherein the current synthesizing circuit comprises a current mirror circuit comprising an input coupled to the fifth transistor, and outputs coupled to the third and the fourth transistors via switches, respectively,
wherein a characteristic of the correcting current varies based on a combination of the switches and the current mirror circuit.
4. The correcting circuit according to claim 2 ,
wherein the voltage-current converter is adjusted by a dummy circuit corresponding to the correction current synthesizer, the dummy circuit comprising a third resistor corresponding to the first and second resistors, a sixth transistor corresponding to the third and fourth transistors, and a fourth resistor carrying a sixth current corresponding to the correction current.
5. The correcting circuit according to claim 1 ,
wherein the current adjuster comprises a weighted current mirror D/A converter.
6. The correcting circuit according to claim 1 ,
wherein the correction voltage generator comprises:
a current reversing circuit, which includes a current mirror circuit comprising an input coupled to an output of the current adjuster and switches switching a direction of the determining current; and
a current-voltage converter converting the determining current to the correction voltage.
7. The correcting circuit according to claim 2 ,
wherein the differential pair includes a pair of transistors to which the differential input voltage is input,
wherein each source of the pair of transistors is coupled in series with a transistor group made up of a plurality of transistors; and
wherein each back gate of the pair of transistors and the transistors in the transistor group is coupled to the source of the pair of transistors.
8. A correcting method comprising:
adjusting an offset so that a voltage signal output in correspondence with an output signal from a sensor is corrected when a physical quantity that is to be a reference is applied to the sensor;
adjusting a gain so that a voltage signal output in correspondence with the output signal of the sensor is a voltage corresponding to the physical quantity when the physical quantity is applied to the sensor;
selecting a correction voltage characteristic so that an output characteristic of the voltage signal approaches linear; and
adjusting a correction amount.
9. The correcting method according to claim 8 ,
wherein when the characteristic of the correction voltage is selected, the output characteristic of the voltage signal, prior to correction, is approximated by a quadratic function in order to select the correction voltage.
10. A sensor apparatus comprising:
a sensor signal-voltage converter for voltage converting an output signal of a sensor;
a voltage amplifier amplifying the voltage obtained by the sensor signal-voltage converter;
a voltage-current converter converting the output voltage of the voltage amplifier to a current;
a correction current synthesizer synthesizing a correction current based on the output current of the voltage-current converter;
a current adjuster adjusting a determining current which corresponds to a correction amount based on the correction current;
a correction voltage generator generating a correction voltage based on the determining current obtained by the current adjuster, wherein the correction voltage correcting the output voltage of the voltage amplifier so that an output characteristic of a voltage signal approaches linear; and
an output buffer amplifier outputting, as the voltage signal, a voltage resulting from the correction of the output voltage of the voltage amplifier using the correction voltage.
11. The sensor apparatus according to claim 10 further comprising:
a memory adapted to correction information,
wherein the output characteristic of the voltage signal is corrected by supplying bit information as the correction information.