SENSOR OUTPUT COMPENSATION CIRCUIT

A sensor output compensation circuit includes a differential amplifier circuit to amplify, as a sensor output, a differential voltage between detection voltages measured in two detection signal output terminals of a sensor including a sensor element that has a resistance value that changes depending on a detected physical quantity and that is connected by bridge connection, a temperature sensor circuit to detect an ambient temperature, and a temperature coefficient sensitivity compensation circuit to apply, to two power terminals of the sensor, a bias voltage to cancel a variation in sensitivity of the sensor output as the ambient temperature changes, based on the ambient temperature that is detected by the temperature sensor circuit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sensor output compensation circuit to adjust the sensitivity of the output of a sensor that includes a sensor element connected by bridge connection.

2. Description of the Related Art

An existing sensor output compensation circuit of this kind relates to, for example, a magnetoresistive element amplifier circuit disclosed in Japanese Unexamined Patent Application Publication No. 11-194160.

The magnetoresistive element amplifier circuit includes a magnetoresistive element in which four strong magnetoresistive element patterns are connected by bridge connection and performs differential amplification of the output voltage of the magnetoresistive element by connecting a differential amplifier circuit to two output terminals of the magnetoresistive element. The differential amplifier circuit includes an offset adjustment circuit that makes the midpoint potential of the amplified output voltage variable and that sets the midpoint potential to a predetermined potential by using a variable resistor. At a subsequent position, a temperature compensation circuit that adjusts a variation in the amplitude of the output voltage due to a change in temperature is provided as a sensor output compensation circuit.

However, the existing temperature compensation circuit disclosed in Japanese Unexamined Patent Application Publication No. 11-194160 uses a thermistor element for a temperature compensation resistor and can accordingly provide only temperature compensation depending on thermistor characteristics. For this reason, a temperature range in which the temperature compensation can be provided is limited, sensitivity compensation with respect to a wider range of a temperature variation cannot be provided, and accordingly, the sensitivity temperature compensation of the sensor output is limited. Since the characteristics of the thermistor element vary, temperature compensation characteristics accordingly vary due to the variation, and this poses a problem for increasing the precision of the temperature compensation. The use of the thermistor element for the temperature compensation circuit makes it difficult to provide the temperature compensation circuit as an IC (high integration) and makes the temperature compensation circuit difficult to reduce the size and cost.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide sensor output compensation circuits that are each able to uniformly provide sensitivity temperature compensation of a sensor output with precision in all temperature regions and reduce the size and cost of the circuit.

A sensor output compensation circuit according to a preferred embodiment of the present invention includes a differential amplifier circuit to amplify, as a sensor output, a differential voltage between detection voltages measured in two detection signal output terminals of a sensor including a sensor element that has a resistance value that changes depending on a detected physical quantity and that is connected by a bridge connection, a temperature sensor circuit to detect ambient temperature, and a temperature coefficient sensitivity compensation circuit to apply, to two power terminals of the sensor, a bias voltage to cancel a variation in sensitivity of the sensor output as the ambient temperature changes, based on the ambient temperature that is detected by the temperature sensor circuit.

With this structure, the variation in the sensitivity of the sensor output as the ambient temperature changes is canceled and adjusted in a manner in which the temperature coefficient sensitivity compensation circuit applies the bias voltage to cancel the variation to the two power terminals of the sensor. Accordingly, unlike the existing temperature compensation circuit that is disclosed in Japanese Unexamined Patent Application Publication No. 11-194160 and that provides only the temperature compensation depending on the thermistor characteristics, a temperature range in which the temperature compensation can be provided is not limited. In addition, temperature compensation characteristics do not vary due to a thermistor element unlike existing cases. For this reason, sensitivity temperature compensation can be uniformly provided with precision in all temperature regions. The sensor output compensation circuit can be provided without using a thermistor element for a temperature compensation circuit. Accordingly, the sensor output compensation circuit can be provided as an IC, and the size and cost of the sensor output compensation circuit can be reduced.

For this reason, preferred embodiments of the present invention provide sensor output compensation circuits that are each able to uniformly provide the sensitivity temperature compensation of a sensor output with precision in all temperature regions and that reduce the size and cost of the circuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Sensor output compensation circuits according to preferred embodiments of the present invention will now be described with reference to the drawings.

FIG.1is a circuit diagram illustrating a schematic configuration of the whole of a sensor output compensation circuit according to a preferred embodiment of the present invention.

The sensor output compensation circuit receives the output of a TMR (Tunneling Magneto-Resistive) sensor2, compensates a sensor output in various ways, and is provided as an IC corresponding to a sensor output compensation IC1. As for the TMR sensor2, a TMR element the resistance value of which changes depending on a magnetic field that is a physical quantity to be detected is connected by bridge connection, a predetermined voltage is applied to two power terminals2aand2bfor operation. The magnetic field that is detected by the TMR sensor2is measured as a voltage difference between two detection signal output terminals2cand2d, which is applied as the sensor output to signal input terminals1aand1bof the sensor output compensation IC1. The TMR sensor2is used, for example, to monitor an electric current that is supplied to a motor of a hybrid vehicle.

Various kinds of compensation provided by the sensor output compensation IC1include linearity compensation for the sensor output, sensitivity compensation, temperature coefficient sensitivity (TCS) compensation, offset compensation, and temperature-characteristic-of-offset (TCO) compensation. Compensation concerning variations in these kinds of compensation due to the TMR sensor2is also included.

The linearity compensation is compensation to remove a nonlinearity component from the sensor output and guaranteeing the linearity of the sensor output. The offset compensation is compensation to cancel out the offset voltage that is measured in the two detection signal output terminals2cand2dwhen the TMR sensor2detects no magnetic field. The temperature-characteristic-of-offset compensation is compensation to cancel out a temperature variation in the offset voltage. The sensitivity compensation is compensation to cancel out a variation in the sensitivity of the TMR sensor2due to the TMR sensor2. The sensitivity of the TMR sensor2is obtained by dividing, by a rated magnetic field, an output span voltage that is obtained by subtracting the offset voltage from the rated output voltage of the sensor output compensation IC1and means a change in output voltage per unit magnetic field. The temperature coefficient sensitivity compensation is compensation to cancel out a temperature variation in temperature coefficient sensitivity that represents what degree the output span voltage changes at maximum at compensation temperature.

The sensor output compensation IC1includes a differential amplifier circuit3that includes an instrumentation amplifier and a compensation amplifier circuit4that adjusts the output of the differential amplifier circuit3. The differential amplifier circuit3includes operational amplifiers31and32that amplify detection voltages that are measured in two detection signal output terminals2cand2dof the TMR sensor2and an operational amplifier33that performs the differential amplification of the amplified detection voltages. A differential voltage between the detection voltages that are measured in the two detection signal output terminals2cand2dis dealt with as a substantial sensor output. The differential amplifier circuit3outputs an output A that is obtained by amplifying the sensor output with an amplification factor α expressed as the following expression (1):

α=(R3/R2)×{1+(2×R1)/R0},  (1)where R1=R1′, R2=R2′, and R3=R3′ are satisfied, R0is a variable resistor, and R0, R1, R2, R3, R1′, R2′, and R3′ are resistance values and resistors that are connected to the operational amplifiers31to33as illustrated.

The sensitivity of the sensor output is adjusted in a manner in which the variable resistor R0is made variable, and a variation therein due to the TMR sensor2is compensated for. A variable voltage source VREF1is connected to a non-inverting input terminal of the operational amplifier33with the resistor R3′ interposed therebetween. The offset voltage of the sensor output is adjusted in a manner in which the output voltage of the variable voltage source VREF1is made variable and is adjusted such that an output voltage VOUT that is measured in an output terminal OUT of the sensor output compensation IC1is zero or approximately zero when the TMR sensor2detects no magnetic field.

The compensation amplifier circuit4includes an operational amplifier41to which a variable resistor R4and a variable resistor R5are connected and outputs, as the output voltage VOUT, an output B that is obtained by the inverting amplification of the output A of the differential amplifier circuit3to the output terminal OUT of the sensor output compensation IC1. As a result, the sensor output is amplified with an amplification factor3expressed as the following expression (2):

An amplification factor (R5/R4) of the compensation amplifier circuit4changes when the resistance value of the variable resistor R4or R5to be connected is changed. According to the present preferred embodiment, the resistance values of the variable resistors R4and R5are made variable in a manner in which connections between multiple resistors, not illustrated, are switched by multiple switches, not illustrated, and the combined resistance value of the multiple resistors is changed.

The sensor output compensation IC1according to the present preferred embodiment includes a linearity compensation circuit5that adjusts the linearity of the sensor output, a temperature coefficient sensitivity compensation circuit that adjusts the temperature coefficient sensitivity of the sensor output, and a temperature-characteristic-of-offset compensation circuit7that adjusts the temperature characteristics of the offset voltage of the sensor output. According to the present preferred embodiment, the temperature coefficient sensitivity compensation circuit includes a temperature coefficient sensitivity rough-adjustment compensation circuit6aand a temperature coefficient sensitivity fine-adjustment compensation circuit6b. The differential amplifier circuit3, the compensation amplifier circuit4, the linearity compensation circuit5, the temperature coefficient sensitivity rough-adjustment compensation circuit6a, the temperature coefficient sensitivity fine-adjustment compensation circuit6b, and the temperature-characteristic-of-offset compensation circuit7are included in a compensation block8of the sensor output compensation IC1.

The sensor output compensation IC1also includes a regulator circuit (VREG)9, a reference voltage circuit (VREF)10, and a temperature sensor circuit11. The regulator circuit9generates a standard voltage from a voltage that is applied to a power terminal VDD. The reference voltage circuit10generates reference voltages that are used in, for example, the temperature coefficient sensitivity rough-adjustment compensation circuit6a, the temperature coefficient sensitivity fine-adjustment compensation circuit6b, and the temperature-characteristic-of-offset compensation circuit7from the standard voltage that is generated by the regulator circuit9. The temperature sensor circuit11detects ambient temperature as a voltage by using a diode and outputs detected voltage conversion temperature to the temperature coefficient sensitivity rough-adjustment compensation circuit6aand the temperature-characteristic-of-offset compensation circuit7. The TMR sensor2and the sensor output compensation IC1are adjacent to each other, and accordingly, the ambient temperature that is detected by the temperature sensor circuit11is detected as the ambient temperature of the TMR sensor2.

The sensor output compensation IC1also includes an EEPROM12that enables a user to rewrite a stored content. Setting data is written on the EEPROM12from a data terminal DATA by the user. Depending on the setting data, the settings of compensation operations by using the various compensation circuits in the compensation block8are adjusted, and settings of temperature detection by using the temperature sensor circuit11are adjusted.

According to the present preferred embodiment, the linearity adjustment is provided by the linearity compensation circuit5in a manner in which the amplification factor (R5/R4) of the compensation amplifier circuit4is made variable as described later. The amplification factor (R5/R4) is made variable in a manner in which connection states between the multiple resistors that are included in the variable resistor R4are switched by the multiple switches depending on the setting data that is written on the EEPROM12. The temperature coefficient sensitivity compensation is provided by the temperature coefficient sensitivity rough-adjustment compensation circuit6aand the temperature coefficient sensitivity fine-adjustment compensation circuit6bin a manner in which the resistance values of variable resistors R11to R14described later and reference voltages VREF3and VREF4(seeFIG.5) are switched depending on the setting data that is written on the EEPROM12. The temperature-characteristic-of-offset compensation is provided by the temperature-characteristic-of-offset compensation circuit7in a manner in which connection states between switches75and76(seeFIG.8) described later are switched depending on the setting data that is written on the EEPROM12. The temperature sensor circuit11is adjusted depending on the setting data that is written on the EEPROM12such that a voltage of 1 [V] is outputted as the voltage conversion temperature when the ambient temperature is about 25° C., for example.

FIG.2is a circuit diagram for describing the function of the linearity compensation circuit5in the sensor output compensation IC1illustrated inFIG.1. InFIG.2, the same or corresponding components to those inFIG.1are designated by the same reference signs, and the description thereof is omitted.

The linearity compensation circuit5includes multiple comparators51,52,53, . . . , and5n. The output voltage of the differential amplifier circuit3is applied to first input terminals of the comparators51,52,53, . . . , and5n, and predetermined reference voltages VREF_L1, VREF_L2, VREF_L3, . . . and VREF_Ln that are outputted from the reference voltage circuit10are applied to second input terminals. The reference voltages VREF_L1, VREF_L2, VREF_L3, . . . , and VREF_Ln correspond to sensor outputs depending on the magnetic field that causes predetermined distortion that is created in the sensor output and that has nonlinearity and are set in advance by using the setting data that is written on the EEPROM12.

The linearity compensation circuit5makes the amplification factor (R5/R4) of the compensation amplifier circuit4variable into an amplification factor to cancel the distortion in a manner in which the multiple switches that are included in the variable resistor R4are switched, and the resistance value of the variable resistor R4is made variable, depending on the result of comparison between the multiple reference voltages and the output voltage of the differential amplifier circuit3.

In the description herein, the amplification factor (R5/R4) of the compensation amplifier circuit4is made variable in a manner in which the multiple switches that are included in the variable resistor R4are switched, and the resistance value of the variable resistor R4is made variable. However, the amplification factor (R5/R4) of the compensation amplifier circuit4may be made variable in a manner in which the multiple switches that are included in the variable resistor R5are switched, and the resistance value of the variable resistor R5is made variable.

FIG.3Ais a graph illustrating an example of a relationship between the magnetic field that is applied to the TMR sensor2and the sensor output that is measured as the differential voltage between the detection signal output terminals2cand2dwhen the magnetic field is applied to the TMR sensor2. The horizontal axis of the graph represents the magnetic field [mT] that is applied to the TMR sensor2, and the vertical axis represents the sensor output [mV]. A characteristic line y represents a change in the sensor output with respect to the magnetic field when the ambient temperature of the sensor output compensation IC1is about 25° C., for example, and represents the linearity characteristics of the sensor output. The characteristic line y is expressed as the following polynomial expression (3):

y=−6.469e−0.7x3−1.512e−0.6x2+2.175e−0.2x+4.306e−0.3,   (3)where a magnetic field x is a variable.

In the graph, the characteristic line y appears to be linear but includes nonlinear components expressed by a first term and a second term in a right-hand side of the expression (3). A graph illustrated inFIG.3Brepresents a relationship between the magnetic field and the sensor output except for a linear component in a third term in the right-hand side. The horizontal axis of the graph represents the magnetic field [mT] that is applied to the TMR sensor2, and the vertical axis represents the sensor output [mV] except for the linear component. A characteristic line y′ represents the distortion of the sensor output that has nonlinearity. The distortion affects the precision of detection of the magnetic field by using the TMR sensor2, and accordingly, the linearity compensation circuit5adjusts the distortion.

In the graph, the distortion is seen in a magnetic field region of about +8 [mT] or more and a magnetic field region of about −8 [mT] or less. Accordingly, when the sensor output is obtained with respect to a predetermined magnetic field in each magnetic field region, the linearity compensation circuit5cancels the distortion by making the amplification factor of the compensation amplifier circuit4variable.

FIG.4Ais a graph illustrating an example of a control signal v that is outputted from the linearity compensation circuit5to the switches of the variable resistor R4. The horizontal axis of the graph represents the magnetic field [mT] that is applied to the TMR sensor2, and the vertical axis represents the voltage [V] of the control signal v. A characteristic line a represents a change in input voltages that are applied to the input terminals1aand1bof the sensor output compensation IC1due to the magnetic field. A characteristic line b represents a change in the output voltage VOUT that is outputted to the output terminal out of the sensor output compensation IC1due to the magnetic field. Characteristic lines c, d, e, and f represent control signals v1, v2, v3, and v4to correct the distortion of a sensor output of about +8 [mT] or more in a positive magnetic field illustrated inFIG.3B. Characteristic lines g, h, i, and j represent control signals v5, v6, v7, and v8to correct the distortion of a sensor output of about −8 [mT] or less in a negative magnetic field. The control signals v1to v8change between a high level of about +5 [V] and a low level of about 0 [V]. For example, a change into the low level results in close control of switches sw1to sw8.

In the graph, as for the distortion of the sensor output in a magnetic field region of about +8 [mT] or more, when the magnetic field is about +7 [mT], the level of the control signal v1that is represented by the characteristic line c is reduced, and the close control of the switch sw1is consequently provided. Consequently, the resistance value of the variable resistor R4is made variable, and the amplification factor of the compensation amplifier circuit4is changed into an amplification factor to cancel the distortion in the magnetic field. When the magnetic field is about +10 [mT], the level of the control signal v2that is represented by the characteristic line d is reduced, and the close control of the switch sw2is consequently provided, or when the magnetic field is about +13 [mT], the level of the control signal v3that is represented by the characteristic line e is reduced, and the close control of the switch sw3is consequently provided, or when the magnetic field is about +15 [mT], the level of the control signal v4that is represented by the characteristic line f is reduced, and the close control of the switch sw4is consequently provided. Consequently, the resistance value of the variable resistor R4is made variable, and the amplification factor of the compensation amplifier circuit4is changed into the amplification factor to cancel the distortion in the magnetic field.

Similarly, as for the distortion of the sensor output in a magnetic field region of about −8 [mT] or less, the close control of the switches sw5to sw8is provided by using the control signals v5to v8that are represented by the characteristic lines g to j, and consequently, the resistance value of the variable resistor R4is made variable, and the amplification factor of the compensation amplifier circuit4is changed into the amplification factor to cancel the distortion in the magnetic field.

FIG.4Bis a graph illustrating the distortion of the sensor output after the nonlinearity of the sensor output is compensated for by controlling the resistance value of the variable resistor R4by using the linearity compensation circuit5. The horizontal axis of the graph represents the magnetic field [mT] that is applied to the TMR sensor2, and the vertical axis represents the percentage [%] of a distortion component that is included in the output voltage VOUT that is outputted to the output terminal out of the sensor output compensation IC1. A characteristic line k represents variation characteristics of the distortion component that is included in the output voltage VOUT with respect to a change in the magnetic field.

The distortion of the sensor output in a magnetic field region of about +8 [mT] or more decreases in the right-hand direction as the magnetic field increases as illustrated inFIG.3B. However, it is understood from the characteristic line k that when the levels of the control signals v1, v2, v3, and v4are sequentially reduced when the magnetic field is about +7 [mT], about +10 [mT], about +13 [mT], or about +15 [mT], the amplification factor of the compensation amplifier circuit4is increased, the percentage of the distortion component consequently increases in the right-hand direction, and a decrease in the distortion illustrated inFIG.3Bis canceled.

The distortion of the sensor output in a magnetic field region of about −8 [mT] or less increases in the left-hand direction as the magnetic field decreases as illustrated inFIG.3B. However, it is similarly understood from the characteristic line k that when the levels of the control signals v5to v8are sequentially reduced as the magnetic field decreases, the amplification factor of the compensation amplifier circuit4is decreased, the percentage of the distortion component consequently decreases in the left-hand direction, and an increase in the distortion illustrated inFIG.3Bis canceled.

The percentage of the distortion component increases in the right-hand direction in a positive magnetic field region and temporarily decreases in the right-hand direction due to a decrease in the original distortion illustrated inFIG.3B, and decreases in the left-hand direction in a negative magnetic field region and temporarily increases in the left-hand direction due to an increase in the original distortion illustrated inFIG.3B. Accordingly, as illustrated inFIG.4B, the characteristic line k varies upward and downward into a zigzag manner, but the range of the variation in the distortion component is reduced to about ±0.1 [%] or less, and the linearity of the sensor output is guaranteed.

As for the sensor output compensation IC1according to the present preferred embodiment as described above, the amplification factor of the compensation amplifier circuit4is made variable in a manner in which connections between the multiple resistors that are connected to the compensation amplifier circuit4as the variable resistor R4are switched under control of the multiple switches of the linearity compensation circuit5, and the combined resistance value of the multiple resistors is changed. The switching operation of the switches is performed when the output voltage of the differential amplifier circuit3is compared with the predetermined multiple reference voltages VREF_L1, VREF_L2, VREF_L3, . . . , and VREF_Ln and becomes a voltage corresponding to the sensor output depending on the magnetic field that causes the predetermined distortion. The switching operation of the switches adjusts the amplification factor of the compensation amplifier circuit4to the amplification factor to cancel the predetermined distortion in the output of the differential amplifier circuit3depending on the output voltage of the differential amplifier circuit3, and the linearity of the sensor output is guaranteed.

That is, as for the sensor output compensation IC1according to the present preferred embodiment, the distortion that has nonlinearity in the sensor output as the magnetic field changes is compensated for in a manner in which the amplification factor of the compensation amplifier circuit4that adjusts the output of the differential amplifier circuit3is made variable into the amplification factor to cancel the distortion by using the linearity compensation circuit5. Accordingly, a circuit reaction speed increases, and the nonlinearity compensation of the sensor output is provided at a high speed unlike an existing nonlinearity compensation circuit (see Japanese Unexamined Patent Application Publication No. 2003-248017) that feeds back the sensor output and provides linearity compensation. The sensor output compensation circuit needs no adder circuits unlike existing cases, and accordingly, the circuit scale of the sensor output compensation IC1can be reduced.

FIG.5is a circuit diagram for describing the functions of the temperature coefficient sensitivity rough-adjustment compensation circuit6aand the temperature coefficient sensitivity fine-adjustment compensation circuit6bin the sensor output compensation IC1illustrated inFIG.1. InFIG.5, the same or corresponding components as those inFIG.1are designated by the same reference signs, and the description thereof is omitted. The temperature coefficient sensitivity rough-adjustment compensation circuit6aand the temperature coefficient sensitivity fine-adjustment compensation circuit6bare included in the temperature coefficient sensitivity compensation circuit that applies a bias voltage to cancel a variation in the sensitivity of the sensor output as the ambient temperature changes to the two power terminals2aand2bof the TMR sensor2, based on the ambient temperature that is detected by the temperature sensor circuit11. The TMR sensor2can make sensor sensitivity variable by adjusting the bias voltage and can accordingly adjust the temperature characteristics of the sensitivity by making the bias voltage variable with respect to the ambient temperature.

The temperature coefficient sensitivity rough-adjustment compensation circuit6aincludes an inverting amplifier circuit that includes an operational amplifier61, a rough-adjustment variable resistor R11, and a rough-adjustment variable resistor R12. The reference voltage VREF3that is generated by the reference voltage circuit10is applied to a non-inverting input terminal of the operational amplifier61. The temperature coefficient sensitivity rough-adjustment compensation circuit6areceives the voltage conversion temperature that is outputted depending on the ambient temperature from the temperature sensor circuit11. The inverting amplification of the voltage conversion temperature is performed with an amplification factor (R12/R11) that corresponds to a change ratio of the sensitivity of the sensor output to the ambient temperature, a bias voltage Va is generated and is applied to the power terminal2aof the two power terminals2aand2b.

FIG.6Ais a graph illustrating an example of the temperature characteristics concerning the sensitivity of the sensor output. The horizontal axis of the graph represents the ambient temperature [° C.] of the TMR sensor2, and the vertical axis represents the volatility [%] of the sensitivity at the ambient temperature when a magnetic field of about 20 [mT] is applied to the TMR sensor2. A characteristic line m represents characteristics of the volatility of the sensitivity as the ambient temperature changes and is expressed as the following expression (4):

m=−0.0952x+2.4[%],  (4)where the ambient temperature is a variable x.

As illustrated by the characteristic line m in the graph, the volatility of the sensitivity has temperature characteristics that have a linear slope (−0.0952x) and that linearly decrease as the temperature increases. Accordingly, according to the present preferred embodiment, the bias voltage Va that has the linear slope (+0.0952x) opposite that of the characteristic line m is applied as a temperature compensation voltage to the two power terminals2aand2bof the TMR sensor2, and the sensitivity is adjusted such that the characteristic line m is characterized so as to be flat with respect to the change in the ambient temperature, in order to prevent the sensitivity from being affected by the influence of a change in the ambient temperature.

For this purpose, according to the present preferred embodiment, the voltage conversion temperature that is outputted from the temperature sensor circuit11and that has a slope the polarity of which is the same or substantially the same as that of the characteristic line m is inputted into the temperature coefficient sensitivity rough-adjustment compensation circuit6a, and the inverting amplifier circuit of the temperature coefficient sensitivity rough-adjustment compensation circuit6ainverts the polarity of the slope of the voltage conversion temperature. The voltage conversion temperature is amplified with the amplification factor (R12/R11) of the inverting amplifier circuit such that the magnitude of the slope of the voltage conversion temperature is equal or substantially equal to the magnitude of the slope of the characteristic line m, that is, the amplification factor that corresponds to the change ratio of the sensitivity of the sensor output to the ambient temperature, and the temperature compensation voltage that corresponds to the bias voltage Va is generated.

FIG.7is a graph illustrating a change in the voltage conversion temperature that is outputted from the temperature sensor circuit11with respect to the ambient temperature. The horizontal axis of the graph represents the ambient temperature [° C.] of the sensor output compensation IC1, and the vertical axis represents the output voltage [V] of the temperature sensor circuit11at the ambient temperature. A characteristic line o represents the temperature characteristics of the voltage conversion temperature that is the output voltage of the temperature sensor circuit11. As illustrated in the graph, the characteristic line o of the voltage conversion temperature and the characteristic line m of the volatility of the sensitivity have a slope that linearly decreases as the temperature increases and that has a negative polarity.

The inverting amplifier circuit of the temperature coefficient sensitivity rough-adjustment compensation circuit6achanges the amplification factor (R12/R11) when the resistance value of the rough-adjustment variable resistor R11or the rough-adjustment variable resistor R12to be connected is changed. The resistance values of the rough-adjustment variable resistor R11and the rough-adjustment variable resistor R12are made variable in a manner in which connections between multiple rough-adjustment resistors are switched by multiple switches, and the combined resistance value of the multiple rough-adjustment resistors is changed. The switching operation of the switches adjusts the amplification factor (R12/R11) of the inverting amplifier circuit to the amplification factor to cancel the variation in the sensitivity that is caused by the ambient temperature, and the magnitude of the slope of the characteristic line o of the voltage conversion temperature is adjusted to the magnitude of the slope of the characteristic line m of the volatility of the sensitivity. The inverting amplifier circuit performs the inverting amplification of the voltage conversion temperature, and consequently, the polarity of the slope of the characteristic line o of the voltage conversion temperature is opposite the polarity of the slope of the characteristic line m of the volatility of the sensitivity.

Accordingly, the bias voltage Va that is obtained by the inverting amplification of the voltage conversion temperature that is outputted from the temperature sensor circuit11with the amplification factor (R12/R11) that corresponds to the change ratio of the sensitivity to the ambient temperature is applied as a sensitivity temperature compensation voltage to the power terminal2aof the two power terminals2aand2bof the TMR sensor2. Accordingly, variation components of the sensitivity that is included in the sensor output that are measured in the two detection signal output terminals2cand2dof the TMR sensor2are canceled in a manner in which the bias voltage Va that changes with the opposite polarity and the same or substantially the same change ratio as the change ratio of the sensitivity to the ambient temperature is applied to the power terminal2aof the sensor. In addition, a dedicated circuit to compensate for the temperature coefficient sensitivity is not provided, and the variation components of the sensitivity are canceled by using the temperature sensor circuit11.

FIG.6Bis a graph illustrating the ambient temperature characteristics of the volatility of the sensitivity after the temperature compensation in the above manner. The horizontal axis of the graph illustrated inFIG.6Brepresents the ambient temperature [° C.], and the vertical axis represents the volatility [%] of the sensitivity at the ambient temperature when a magnetic field of about 20 [mT] is applied to the TMR sensor2as in the graph inFIG.6A. A characteristic line n represents the volatility of the sensitivity with respect to the ambient temperature. As illustrated in the graph, the volatility of the sensitivity of the sensor output compensation IC1after compensation is within a small range of about ±0.03 [%] or less.

According to the present preferred embodiment, however, the temperature compensation of the sensitivity is provided with higher precision, and accordingly, the temperature coefficient sensitivity fine-adjustment compensation circuit6bthat is included in the temperature coefficient sensitivity compensation circuit generates a minute-compensation bias voltage to further cancel a minor variation in the sensitivity of the sensor output that remains as illustrated inFIG.6Bafter canceling due to the action of the temperature coefficient sensitivity rough-adjustment compensation circuit6a. The generated minute-compensation bias voltage is applied as a bias voltage Vb to the power terminal2bof the two power terminals2a,2b.

The temperature coefficient sensitivity fine-adjustment compensation circuit6bincludes an inverting amplifier circuit that includes an operational amplifier62, a fine-adjustment variable resistor R13, and a fine-adjustment variable resistor R14, and a sensitivity compensation voltage circuit63. A reference voltage VREF4that is generated by the reference voltage circuit10is applied to a non-inverting input terminal of the operational amplifier62. The sensitivity compensation voltage circuit63generates a sensitivity compensation voltage on which the minute-compensation bias voltage to cancel the minor variation in the sensitivity of the sensor output that remains is based. The inverting amplifier circuit that includes the operational amplifier62performs the inverting amplification of the sensitivity compensation voltage that is generated by the sensitivity compensation voltage circuit63with an amplification factor (R14/R13), generates the minute-compensation bias voltage, and outputs the minute-compensation bias voltage to the power terminal2b.

The amplification factor (R14/R13) changes when the resistance value of the fine-adjustment variable resistor R13or the fine-adjustment variable resistor R14that is connected to the operational amplifier62is changed. The resistance values of the fine-adjustment variable resistor R13and the fine-adjustment variable resistor R14are made variable in a manner in which connections between multiple fine-adjustment resistors are switched by multiple switches, and the combined resistance value of the multiple fine-adjustment resistors is changed. The switching operation of the switches adjusts the magnitude of the minute-compensation bias voltage that is generated by the temperature coefficient sensitivity fine-adjustment compensation circuit6b, and the minor variation in the sensitivity of the sensor output that remains after canceling due to the action of the temperature coefficient sensitivity rough-adjustment compensation circuit6ais appropriately canceled.

As for the sensor output compensation IC1according to the present preferred embodiment as described above, the variation in the sensitivity of the sensor output as the ambient temperature changes is canceled and adjusted in a manner in which the bias voltage Va to cancel the variation is applied to the two power terminals2aand2bof the sensor by using the temperature coefficient sensitivity compensation circuit as described above. Accordingly, unlike the existing temperature compensation circuit that is disclosed in Japanese Unexamined Patent Application Publication No. 11-194160 and that provides only temperature compensation depending on thermistor characteristics, a temperature range in which the temperature compensation can be provided is not limited. In addition, the temperature compensation characteristics do not vary due to a thermistor element unlike existing cases. For this reason, the sensitivity temperature compensation can be uniformly provided with precision in all temperature regions. The sensor output compensation circuit can be provided without using a thermistor element for a temperature compensation circuit. Accordingly, the sensor output compensation circuit can be provided as an IC, and the size and cost of the sensor output compensation circuit can be reduced.

As for the sensor output compensation IC1according to the present preferred embodiment, the minor variation in the sensitivity of the sensor output that remains after canceling due to the action of the temperature coefficient sensitivity rough-adjustment compensation circuit6ais canceled in a manner in which the bias voltage Vb to further cancel the minor variation is generated as the minute-compensation bias voltage by using the temperature coefficient sensitivity fine-adjustment compensation circuit6band is applied to the power terminal2bof the two power terminals2aand2b. For this reason, the sensitivity temperature compensation can be uniformly provided with higher precision in all temperature regions.

The bias voltage of the TMR sensor2is adjusted at two positions of the power terminals2aand2b, and consequently, the temperature coefficient sensitivity compensation circuit can have a rough-adjustment function and a fine-adjustment function. This enables the temperature coefficient sensitivity rough-adjustment compensation circuit6aand the temperature coefficient sensitivity fine-adjustment compensation circuit6bto be optimally designed. For this reason, the circuit constants of elements that are included in the circuits can be optimized, the adjustment resolution of the circuits can be improved, and the areas of the circuits can be reduced or prevented from increasing. The sensor output compensation IC1according to the present preferred embodiment directly controls the bias voltage of the TMR sensor2and can adjust the sensor sensitivity, and detection precision is ensured.

FIG.8is a circuit diagram for describing the function of the temperature-characteristic-of-offset compensation circuit7in the sensor output compensation IC1illustrated inFIG.1. InFIG.8, the same or corresponding components as those inFIG.1are designated by the same reference signs, and the description thereof is omitted.

The temperature-characteristic-of-offset compensation circuit7refers the ambient temperature that is detected by the temperature sensor circuit11and applies a reference voltage VREF2to cancel the variation in the offset voltage of the sensor output as the ambient temperature changes to a reference voltage terminal of the compensation amplifier circuit4.

The temperature variation in the offset voltage of the sensor output is illustrated in a graph illustrated inFIG.9A. The horizontal axis of the graph represents the ambient temperature [° C.] of the sensor output compensation IC1, and the vertical axis represents the volatility [%] of the offset voltage at the ambient temperature, based on the offset voltage when the ambient temperature is about 25° C., for example. Characteristic lines represent the temperature characteristics of offset voltages concerning multiple TMR sensors2. As illustrated in the graph, the temperature characteristics of the offset voltages linearly vary with linear slopes. The temperature-characteristic-of-offset compensation circuit7applies the reference voltage VREF2to cancel the variation to the reference voltage terminal that is a non-inverting input terminal of the operational amplifier41in the compensation amplifier circuit4.

According to the present preferred embodiment, the temperature-characteristic-of-offset compensation circuit7includes a first inverting amplifier circuit72that includes an operational amplifier71, a second inverting amplifier circuit74that includes an operational amplifier73, the first switch75, and the second switch76.

As for the first inverting amplifier circuit72, a resistor R7and a variable resistor R8are connected to the operational amplifier71, and a reference voltage VREF21is applied to a non-inverting input terminal of the operational amplifier71. The first inverting amplifier circuit72performs the inverting amplification of the ambient temperature that is detected by the temperature sensor circuit11as a voltage with an amplification factor (R8/R7) that corresponds to the volatility of the offset voltage. The volatility of the offset voltage corresponds to the slope of each characteristic line in the graph illustrated inFIG.9A. The resistance value of the variable resistor R8is adjusted, and consequently, the amplification factor (R8/R7) is matched with the volatility of the offset voltage.

As for the second inverting amplifier circuit74, a resistor R9and a variable resistor R10are connected to the operational amplifier73, and a reference voltage VREF22is applied to a non-inverting input terminal of the operational amplifier73. The second inverting amplifier circuit74performs the inverting amplification of the output of the first inverting amplifier circuit72with an amplification factor (R10/R9) and inverts the polarity thereof. The resistance value of the variable resistor R10is adjusted, and consequently, the amplification factor (R10/R9) is basically set to 1. When the variation in the offset voltage with respect to the ambient temperature increases as the ambient temperature increases, the close control of the second switch76is provided, and the output of the second inverting amplifier circuit74is inputted as the reference voltage VREF2into the reference voltage terminal of the operational amplifier41.

Accordingly, for example, in a case where the temperature characteristics of the offset voltage of the sensor output compensation IC1are represented by using a characteristic line p that linearly increases in the right-hand direction such that the variation with respect to the ambient temperature increases as the ambient temperature increases in the graph illustrated inFIG.9A, a voltage that is outputted from the temperature sensor circuit11such that the voltage decreases as the ambient temperature increases and that is represented by a characteristic line that linearly decreases in the right-hand direction is first converted into a voltage that has a slope the magnitude of which is equal or substantially equal to the magnitude of the volatility of the offset voltage of the characteristic line p and that has characteristics increasing in the right-hand direction such that the polarity of the slope is inverted by using the first inverting amplifier circuit72in the temperature-characteristic-of-offset compensation circuit7. The close operation of the second switch76is provided, and accordingly, the voltage is converted into the reference voltage VREF2that has characteristics decreasing in the right-hand direction such that the polarity of the slope is inverted by using the second inverting amplifier circuit74. For this reason, the compensation amplifier circuit4amplifies the output voltage including the offset voltage that is outputted from the differential amplifier circuit3and that is represented by using the characteristic line p that linearly rises in the right-hand direction, based on the reference voltage VREF2, and consequently, the variation in the offset voltage due to the temperature characteristics is canceled.

FIG.9Bis a graph illustrating the temperature characteristics of offset voltages that are adjusted by the temperature-characteristic-of-offset compensation circuit7concerning four TMR sensors2. The horizontal axis and the vertical axis of the graph are the same as those inFIG.9A. In the graph illustrated inFIG.9B, the characteristic line p before adjustment is illustrated. As illustrated by using an arrow that is represented by using a dashed line, the slope is tilted downward by the offset compensation described above, and the temperature characteristics of the offset voltage concerning the TMR sensor2that has the characteristic line p are adjusted into temperature characteristics that have a flat or substantially flat slope.

The close control of the first switch75is provided in the case where the variation in the offset voltage with respect to the ambient temperature decreases as the ambient temperature increases, and the output of the first inverting amplifier circuit72is inputted as the reference voltage VREF2into the reference voltage terminal of the operational amplifier41. Accordingly, for example, in the case where the temperature characteristics of the offset voltage of the TMR sensor2are represented by using a characteristic line q that linearly decreases in the right-hand direction such that the variation with respect to the ambient temperature decreases as the ambient temperature increases in the graph illustrated inFIG.9A, a voltage that is outputted from the temperature sensor circuit11such that the voltage decreases as the ambient temperature increases and that is represented by a characteristic line that linearly falls in the right-hand direction is converted into the reference voltage VREF2that has a slope the magnitude of which is equal or substantially equal to the magnitude of the volatility of the offset voltage of the characteristic line q and that has characteristics increasing in the right-hand direction such that the polarity of the slope is inverted by using the first inverting amplifier circuit72in the temperature-characteristic-of-offset compensation circuit7because the close control of the first switch75is provided. For this reason, the compensation amplifier circuit4amplifies the output voltage including the offset voltage that is outputted from the differential amplifier circuit3and that is represented by using the characteristic line q that linearly decreases in the right-hand direction, based on the reference voltage VREF2, and consequently, the variation in the offset voltage due to the temperature characteristics is canceled as in the graph illustratedFIG.9B.

As for the sensor output compensation IC1according to the present preferred embodiment as described above, in the case where the variation in the offset voltage with respect to the ambient temperature increases as the ambient temperature increases, the output of the second inverting amplifier circuit74is inputted into the reference voltage terminal of the compensation amplifier circuit4by using the second switch76. Accordingly, the first inverting amplifier circuit72performs the inverting amplification of the ambient temperature that is detected by the temperature sensor circuit11as a voltage with the amplification factor (R8/R7) that corresponds to the volatility of the offset voltage, the second inverting amplifier circuit74inverts the polarity, an ambient temperature inverting signal that decreases with the volatility of the offset voltage as the ambient temperature increases is inputted as the reference voltage VREF2into the reference voltage terminal of the operational amplifier41from the second inverting amplifier circuit74. For this reason, the compensation amplifier circuit4amplifies the output of the differential amplifier circuit3, based on the ambient temperature inverting signal, and consequently, the sensor output in which the temperature variation in the offset voltage is canceled is obtained from the compensation amplifier circuit4.

In the case where the variation in the offset voltage with respect to the ambient temperature decreases as the ambient temperature increases, the output of the first inverting amplifier circuit72is inputted into the reference voltage terminal of the operational amplifier41by using the first switch75. Accordingly, the ambient temperature inverting signal that increases with the volatility of the offset voltage as the ambient temperature increases, which is obtained by inverting amplification performed by the first inverting amplifier circuit72with the amplification factor (R8/R7) that corresponds to the volatility of the offset voltage, is inputted as the reference voltage VREF2into the reference voltage terminal of the operational amplifier41from the first inverting amplifier circuit72. For this reason, the compensation amplifier circuit4amplifies the output of the differential amplifier circuit3, based on the ambient temperature inverting signal, and consequently, the sensor output in which the variation in the offset voltage as the ambient temperature changes is canceled is obtained from the compensation amplifier circuit4.

That is, as for the sensor output compensation IC1according to the present preferred embodiment, the variation in the offset voltage of the sensor output as the ambient temperature changes is canceled in a manner in which the compensation amplifier circuit4that compensates the output of the differential amplifier circuit3amplifies the output of the differential amplifier circuit3, based on the reference voltage VREF2that is applied to the reference voltage terminal of the operational amplifier41from the temperature-characteristic-of-offset compensation circuit7. Accordingly, a single compensation operation enables the offset voltage to be easily adjusted with precision. For this reason, the temperature compensation of the offset voltage of the sensor output can be easily and accurately provided, unlike the existing offset adjustment circuit that is disclosed in Japanese Unexamined Patent Application Publication No. 11-194160 and that adjusts the offset of the sensor output merely by adjusting the midpoint potential of the output of the differential amplifier circuit by using the variable resistor.

As for the sensor output compensation IC1according to the present preferred embodiment, the circuits that are included in the sensor output compensation circuit are mounted in the same IC. Accordingly, variations caused by differences in mounting components that are included in the circuits and wiring lines between the circuits that are included in the sensor output compensation circuit are reduced. For this reason, the sensor output compensation IC1provides the compensation of the sensor output with precision. In addition, the IC can provide all of the compensation functions. The compensation can be provided with precision for every TMR sensor2with a relatively simple circuit structure in a manner in which the sensor output of the TMR sensor2that is adjusted is monitored. As for the adjustment of the compensation of the compensation circuits, the selection of setting data to be written on the EEPROM12enables a compensation value to be easily selected.

The temperature sensor circuit11is mounted in the same IC as the other circuits that are included in the sensor output compensation circuit, and consequently, the relative position of the temperature sensor circuit11with respect to the other circuits is always constant. For this reason, differences between the ambient temperature that is detected by the temperature sensor circuit11and the ambient temperatures of the other circuits are small. In the case where the temperature sensor circuit11is provided in another IC that differs from an IC in which the other circuits are provided, a parasitic resistance component of a wiring joint that connects the temperature sensor circuit11and the IC by using wire bonding, for example, eliminates a difference between the ambient temperature that is detected by the temperature sensor circuit11and an ambient temperature that is used for the IC. As a result, the sensor output compensation IC1according to the present preferred embodiment can provide the temperature compensation of the sensor sensitivity and the offset voltage with precision.