Sensor output compensation circuit

Abstract

Provided is a sensor output compensation circuit that enables accurate detection of a physical quantity by removing, from a sensor output, influence of a residual magnetic field remaining in a sensor. A differential amplification circuit 3 amplifies a sensor output extracted as a differential voltage between an output of a first composite calculation circuit 13 and an output of a second composite calculation circuit 14, on the basis of predetermined detection voltages appearing at detection signal output terminals 2c and 2d in each of TMR sensors 2 which form a pair. The TMR sensors 2 are used in a pair and disposed side by side at relative positions where influences of residual magnetic fields remaining in the respective TMR sensors 2 cancel each other out, and voltages are applied, to the TMR sensors 2, in directions opposite to each other. The first composite calculation circuit 13 adds a detection voltage appearing in one phase at the detection signal output terminal 2c that is one of said terminals in each of the TMR sensors 2 forming a pair. In addition, the second composite calculation circuit 14 adds a detection voltage appearing in the other phase at the detection signal output terminal 2d that is the other of said terminals in each of the TMR sensors 2 forming a pair.

Description

[Technical field]

[0001] The present invention relates to a sensor output compensation circuit for compensating the output of a sensor in which sensor elements are bridge-connected. [Background technology]

[0002] Conventionally, an example of this type of sensor output compensation circuit is an amplifier circuit for a magnetoresistive element disclosed in Patent Document 1.

[0003] This amplifier circuit for a magnetoresistance element comprises a magnetoresistance element in which four ferromagnetic magnetoresistance element patterns are bridge-connected as a sensor, and a differential amplifier circuit is connected to a pair of output terminals of the magnetoresistance element to differentially amplify the output voltage of the magnetoresistance element. The differential amplifier circuit is provided with an offset adjustment circuit that uses a variable resistor to vary the midpoint potential of the amplified output voltage to a predetermined potential, and a temperature compensation circuit is provided downstream of the offset adjustment circuit to compensate for fluctuations in the amplitude of the output voltage due to temperature changes. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-194160 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the conventional sensor output compensation circuit disclosed in Patent Document 1 can only compensate for the offset of the sensor and the fluctuation in the amplitude of the output voltage. In some sensors that detect physical quantities, a residual magnetic field may accumulate in the sensor due to the influence of the applied magnetic field. For such sensors, the conventional sensor output compensation circuit cannot remove the influence of the residual magnetic field remaining in the sensor from the sensor output, and cannot accurately detect the physical quantity. [Means for solving the problem]

[0006] The present invention has been made to solve such problems, A pair of sensors, each of which is composed of a bridge-connected sensor element whose resistance value changes according to the physical quantity being detected, are arranged in relative positions that mutually cancel the effects of residual magnetic fields. and, A pair of sensors a differential amplifier circuit for amplifying a sensor output corresponding to a physical quantity detected by the sensor, the sensor output being extracted based on a predetermined detection voltage appearing at each detection signal output terminal; a bias circuit that applies a voltage to a pair of power supply terminals of one of the pair of sensors in a direction opposite to that of a voltage to be applied to a pair of power supply terminals of the other of the pair of sensors; 、 a first synthesis calculation circuit that adds or averages each detection voltage appearing at each detection signal output terminal of the same one of the pair of sensors; a second synthesis arithmetic circuit that adds or averages the detection voltages appearing at the detection signal output terminals of the other of the pair of sensors; A differential amplifier circuit amplifies a difference voltage between the output of the first synthesis arithmetic circuit and the output of the second synthesis arithmetic circuit as a sensor output. A sensor output compensation circuit was constructed.

[0007] According to this configuration, the influence of the residual magnetic field remaining in the sensor is cancelled without improving the sensor itself by arranging a pair of sensors in relative positions that mutually cancel out the influence of the residual magnetic field, and applying voltages in opposite directions to a pair of power supply terminals of each sensor by a bias circuit. The sensor output corresponding to the physical quantity detected by the sensor is extracted based on a predetermined detection voltage appearing at each detection signal output terminal of the pair of sensors, and is amplified by a differential amplifier circuit. Therefore, the influence of the residual magnetic field remaining in the sensor can be removed from the sensor output, and the physical quantity can be accurately detected by the sensor output compensation circuit. Effect of the Invention

[0008] Therefore, according to the present invention, it is possible to provide a sensor output compensation circuit that can remove the influence of the residual magnetic field remaining in the sensor from the sensor output and accurately detect a physical quantity. [Brief description of the drawings]

[0009] [Figure 1] 1 is a circuit diagram showing a schematic overall configuration of a sensor output compensation circuit according to a first embodiment of the present invention. [Diagram 2] 2 is a circuit diagram for explaining a function of a linearity compensation circuit in the sensor output compensation circuit shown in FIG. 1. [Diagram 3] Graph (a) shows the change in sensor output relative to the magnetic field, and graph (b) shows the distortion of the sensor output that appears due to nonlinearity. [Figure 4] 13A is a graph showing a control signal output from the linearity compensation circuit to change the resistance value of variable resistor R4, and FIG. 13B is a graph showing the distortion of the sensor output after compensation by the linearity compensation circuit. [Diagram 5] 2 is a circuit diagram for explaining a function of a sensitivity temperature characteristic compensation circuit in the sensor output compensation circuit shown in FIG. 1. [Figure 6] 1A is a graph showing the results of measuring the temperature characteristics of the sensitivity of the sensor output, and FIG. 1B is a graph showing the change in the regulation of the output voltage output from the sensor output compensation circuit with respect to the ambient temperature. [Figure 7] 1A is a graph showing the temperature characteristics of the sensitivity of the sensor output after compensation by the sensitivity temperature characteristic compensation circuit, and FIG. 1B is a graph showing the voltage characteristics of the ambient temperature used for the sensitivity temperature characteristic compensation. [Figure 8] 2 is a circuit diagram for explaining a function of an offset temperature characteristic compensation circuit in the sensor output compensation circuit shown in FIG. 1. [Figure 9] 4A is a graph showing the temperature characteristics of the rate of change of an offset voltage, and FIG. 4B is a graph showing the temperature characteristics of the rate of change of an offset voltage after being compensated for by an offset temperature characteristic compensation circuit. [Figure 10] 2 is a diagram illustrating the layout of a pair of TMR sensors in the sensor output compensation circuit shown in FIG. 1. [Figure 11] FIG. 5 is a circuit diagram showing a schematic overall configuration of a sensor output compensation circuit according to a second embodiment of the present invention. [Figure 12] FIG. 11 is a circuit diagram showing a schematic overall configuration of a sensor output compensation circuit according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Next, an embodiment of the sensor output compensation circuit of the present invention will be described.

[0011] FIG. 1 is a circuit diagram showing a schematic overall configuration of a sensor output compensation circuit according to a first embodiment of the present invention.

[0012] The sensor output compensation circuit is a circuit that inputs the output of a pair of TMR (Tunneling Magneto-Resistive) sensors 2 and performs various compensations for the sensor output, and is made into an IC to be the sensor output compensation IC1. Each TMR sensor 2 is configured by bridge-connecting TMR elements whose resistance value changes according to the magnetic field, which is a physical quantity to be detected, and operates when a predetermined voltage is applied to a pair of power supply terminals 2a and 2b. The magnetic field detected by each TMR sensor 2 appears as a voltage difference between the pair of detection signal output terminals 2c and 2d. The voltage difference appearing in one TMR sensor 2 is applied to the signal input terminals 1a and 1b of the sensor output compensation IC1, and the voltage difference appearing in the other TMR sensor 2 is applied to the signal input terminals 1c and 1d of the sensor output compensation IC1. Such a TMR sensor 2 is used, for example, to monitor the current supplied to the motor of a hybrid vehicle.

[0013] When the applied magnetic field becomes stronger, the residual magnetic field accumulates inside the TMR sensor 2, and hysteresis appears in the magnetic field detected by the residual magnetic field. For this reason, in this embodiment, a pair of TMR sensors 2 are used, and as shown in FIG. 10, the TMR sensors 2 are arranged side by side in relative positions where the effects of the residual magnetic fields remaining in each TMR sensor 2 are mutually offset. That is, a bias voltage Vbias is applied to one power terminal 2a of one TMR sensor 2 by a reference voltage circuit 10 (described later) constituting a bias circuit, and the other power terminal 2b is grounded to GND. Then, the direction of the current flowing in the bridge-connected magnetoresistance element patterns r1, r2, r3, and r4 according to the detected magnetic field is set to a direction H1 from top to bottom in the figure. One power terminal 2a of the other TMR sensor 2 is grounded to GND, and a bias voltage Vbias is applied to the other power terminal 2b by the reference voltage circuit 10. The direction of the current flowing through the bridge-connected magnetoresistance element patterns r1, r2, r3, and r4 in response to the detected magnetic field is set to direction H2, which is 180° opposite to direction H1, from bottom to top in the figure. By reversing the direction of the current flowing through each TMR sensor 2 in this way, it becomes possible to cancel out the hysteresis characteristics of each TMR sensor 2.

[0014] The differential amplifier circuit 3 amplifies a sensor output corresponding to the magnetic field detected by the TMR sensor 2, which is extracted based on a predetermined detection voltage appearing at each of the detection signal output terminals 2c, 2d of the pair of TMR sensors 2. In this embodiment, the differential amplifier circuit 3 amplifies the difference voltage between the output of the first synthesis arithmetic circuit 13 and the output of the second synthesis arithmetic circuit 14 as the sensor output.

[0015] The first synthesis operation circuit 13 is composed of an adder circuit in which resistors R11, R12, and R13 are connected to an operational amplifier 34, and a reference voltage VREF3 is applied to the inverting input terminal of the operational amplifier 34 from the regulator circuit 10. This first synthesis operation circuit 13 adds each detection voltage appearing in one phase to each detection signal output terminal 2c of one of the pair of TMR sensors 2. In addition, the second synthesis operation circuit 14 is composed of an adder circuit in which resistors R14, R15, and R16 are connected to an operational amplifier 35, and a reference voltage VREF4 is applied to the inverting input terminal of the operational amplifier 35 from the regulator circuit 10. This second synthesis operation circuit 14 adds each detection voltage appearing in the other phase to each detection signal output terminal 2d of the other of the pair of TMR sensors 2.

[0016] In this embodiment, the first synthesis arithmetic circuit 13 and the second synthesis arithmetic circuit 14 are each configured with an adder circuit, but they may be configured with an averaging circuit that averages each detection voltage appearing in one phase at each detection signal output terminal 2c and each detection voltage appearing in the other phase at each detection signal output terminal 2d. Also, the gain Av of each operational amplifier 34, 35 in the first synthesis arithmetic circuit 13 and the second synthesis arithmetic circuit 14 is preferably set to 1 or less (Av≦1) so as not to unnecessarily amplify the offset voltage of each TMR sensor 2, because the downstream differential amplifier circuit 3 is configured with an instrumentation amplifier and has a good CMRR (common-mode rejection ratio) and the like.

[0017] The various compensations performed by the sensor output compensator IC1 include linearity compensation for the sensor output, sensitivity compensation, temperature coefficient sensitivity compensation (TCS: Temperature Coefficient Sensitivity), offset compensation, and temperature characteristic of offset compensation (TCO: Temperature Characteristic of Offset). In addition, compensation for variations in each of these compensations due to individual TMR sensors 2 is also included.

[0018] Linearity compensation is compensation that removes nonlinear components from the sensor output to ensure the linearity of the sensor output. Offset compensation is compensation that cancels out the offset voltage that appears at the pair of detection signal output terminals 2c, 2d when no magnetic field is detected by each TMR sensor 2. Offset temperature characteristic compensation is compensation that cancels out the temperature fluctuation of the offset voltage. Sensitivity compensation is compensation that cancels out the variation in the sensitivity of each individual TMR sensor 2 for the pair of TMR sensors 2. The sensitivity of the pair of TMR sensors 2 is the value obtained by dividing the output span voltage, which is the rated output voltage of the sensor output compensation IC1 minus the offset voltage, by the rated magnetic field, and means the change in output voltage per unit magnetic field. Sensitivity temperature characteristic compensation is compensation that cancels out the temperature fluctuation of the sensitivity temperature characteristic, which indicates the maximum degree to which the output span voltage changes at the compensation temperature.

[0019] The sensor output compensation IC1 includes a differential amplifier circuit 3 configured by an instrumentation amplifier, and a compensation amplifier circuit 4 that compensates for the output of the differential amplifier circuit 3. The differential amplifier circuit 3 includes operational amplifiers 31 and 32 that respectively amplify the output of the first synthesis arithmetic circuit 13 and the output of the second synthesis arithmetic circuit 14, and an operational amplifier 33 that differentially amplifies each of the amplified outputs. The difference voltage between the output of the first synthesis arithmetic circuit 13 and the output of the second synthesis arithmetic circuit 14 is treated as a substantial sensor output. If the resistors connected to the operational amplifiers 31 to 33 and their resistance values ​​are R0, R1, R2, R3, R1', R2', and R3' as shown in the figure, the differential amplifier circuit 3 outputs an output A obtained by amplifying the sensor output with an amplification factor α expressed by the following equation (1). α=(R3 / R2)×{1+(2×R1) / R0} …(1) Here, R1=R1', R2=R2', R3=R3', and R0 is a variable resistor.

[0020] The sensitivity of the sensor output is adjusted by varying the variable resistor R0 to compensate for individual variations in each TMR sensor 2. In addition, a variable voltage source VREF1 is connected via a resistor R3' to the non-inverting input terminal of the operational amplifier 33. The offset voltage of the sensor output is adjusted by varying the output voltage of this variable voltage source VREF1, so that the output voltage VOUT that appears at the output terminal OUT of the sensor output compensation IC1 becomes zero when no magnetic field is detected by each TMR sensor 2.

[0021] The compensation amplifier circuit 4 is composed of an operational amplifier 41 connected to variable resistors R4 and R5, and outputs an output B obtained by inverting and amplifying the output A of the differential amplifier circuit 3, to the output terminal OUT of the sensor output compensation IC 1 as an output voltage VOUT. As a result, the sensor output is amplified by an amplification factor β shown in the following equation (2). β = α × (R5 / R4) =(R3 / R2)×{1+(2×R1) / R0}×(R5 / R4) …(2)

[0022] The amplification factor (R5 / R4) of the compensation amplifier circuit 4 is changed by changing the resistance value of the connected variable resistor R4 or R5. In this embodiment, the resistance values ​​of the variable resistors R4 and R5 are changed by switching the connections between a plurality of resistors (not shown) with a plurality of switches (not shown) to change the combined resistance value of the plurality of resistors.

[0023] The sensor output compensation IC1 of this embodiment includes a linearity compensation circuit 5 that compensates for the linearity of the sensor output, a sensitivity temperature characteristic compensation circuit 6 that compensates for the sensitivity temperature characteristic of the sensor output, and an offset temperature characteristic compensation circuit 7 that compensates for the temperature characteristic of the offset voltage of the sensor output. The differential amplifier circuit 3, compensation amplifier circuit 4, linearity compensation circuit 5, sensitivity temperature characteristic compensation circuit 6, offset temperature characteristic compensation circuit 7, first synthesis arithmetic circuit 13, and second synthesis arithmetic circuit 14 constitute a compensation block 8 of the sensor output compensation IC1.

[0024] The sensor output compensation IC1 also includes a regulator circuit (VREG) 9, a reference voltage circuit (VREF) 10, and a temperature sensor circuit 11. The regulator circuit 9 generates a reference voltage from the voltage input to the power supply terminal VDD. The reference voltage circuit 10 generates, from the reference voltage generated by the regulator circuit 9, reference voltages for each value used in the sensitivity temperature characteristic compensation circuit 6 and offset temperature characteristic compensation circuit 7, and a bias voltage Vbias to be applied to each TMR sensor 2 as a bias circuit. The temperature sensor circuit 11 detects the ambient temperature using a diode, and outputs the detected ambient temperature as a voltage to the sensitivity temperature characteristic compensation circuit 6 and offset temperature characteristic compensation circuit 7. Since each TMR sensor 2 and the sensor output compensation IC1 are disposed in close proximity to each other, the ambient temperature detected by the temperature sensor circuit 11 is detected as the ambient temperature of each TMR sensor 2.

[0025] The sensor output compensation IC1 also includes an EEPROM 12 whose contents can be rewritten by the user. Setting data is written to this EEPROM 12 by the user through the data terminal DATA. Depending on this setting data, the compensation operation settings of the various compensation circuits in the compensation block 8 are adjusted, and the temperature detection settings in the temperature sensor circuit 11 are also adjusted.

[0026] In this embodiment, the compensations performed by the linearity compensation circuit 5 and the sensitivity temperature characteristic compensation circuit 6 are performed by varying the amplification factor (R5 / R4) of the compensation amplifier circuit 4 as described later, and the amplification factor (R5 / R4) is varied by switching the connection state between the multiple resistors constituting each of the variable resistors R4, R5 by multiple switches according to the setting data written in the EEPROM 12. The compensation performed by the offset temperature characteristic compensation circuit 7 is also performed by switching the connection state of each of the switches 75, 76 (see FIG. 8) described later according to the setting data written in the EEPROM 12. In addition, the temperature sensor circuit 11 is adjusted so as to output a voltage of 1 [V] when the ambient temperature is 25° C. according to the setting data written in the EEPROM 12.

[0027] Figure 2 is a circuit diagram for explaining the function of the linearity compensation circuit 5 in the sensor output compensation IC 1 shown in Figure 1. In this figure, parts that are the same as or correspond to those in Figure 1 are given the same reference numerals and their explanation will be omitted.

[0028] The linearity compensation circuit 5 is composed of a plurality of comparators 51, 52, 53, ..., 5n. The output voltage of the differential amplifier circuit 3 is commonly input to one input terminal of each of the comparators 51, 52, 53, ..., 5n, and predetermined reference voltages VREF_L1, VREF_L2, VREF_L3, ..., VREF_Ln output from the reference voltage circuit 10 are input to the other input terminal. Each of these reference voltages VREF_L1, VREF_L2, VREF_L3, ..., VREF_Ln corresponds to each sensor output according to a magnetic field that causes each predetermined distortion that appears with nonlinearity in the sensor output, and is preset by setting data written in the EEPROM 12.

[0029] The linearity compensation circuit 5 changes the amplification factor (R5 / R4) of the compensation amplifier circuit 4 to an amplification factor that cancels out distortion by changing the resistance value of the variable resistor R4 by switching multiple switches that constitute the variable resistor R4 depending on the comparison result between the multiple reference voltages and the output voltage of the differential amplifier circuit 3.

[0030] Note that, although the case has been described where the amplification factor (R5 / R4) of the compensation amplifier circuit 4 is varied by varying the resistance value of the variable resistor R4 through switching of multiple switches constituting the variable resistor R4, the amplification factor (R5 / R4) of the compensation amplifier circuit 4 may also be varied by varying the resistance value of the variable resistor R5 through switching of multiple switches constituting the variable resistor R5.

[0031] 3(a) is a graph showing an example of the relationship between the magnetic field applied to the pair of TMR sensors 2 and the sensor output that appears as a differential voltage between the output of the first synthesis calculation circuit 13 and the output of the second synthesis calculation circuit 14 when each magnetic field is applied to the pair of TMR sensors 2. The horizontal axis of the graph is the magnetic field [mT] applied to the pair of TMR sensors 2, and the vertical axis is the sensor output [mV]. The characteristic line y represents the change in the sensor output with respect to each magnetic field when the ambient temperature of the sensor output compensation IC1 is 25°C, and indicates the linearity characteristic of the sensor output. This characteristic line y is expressed by the following polynomial (3) with the magnetic field x as a variable. y=-6.469e -0.7 x 3 -1.512e -0.6 x 2 +2.175e -0.2 x+4.306e -0.3 …(3)

[0032] In the graph, the characteristic line y appears to be linear at first glance, but it contains nonlinear components shown in the first and second terms on the right side of equation (3). If the linear component of the third term on the right side is removed to show the relationship between the magnetic field and the sensor output, the graph shown in Figure 3(b) is obtained. The horizontal axis of the graph represents the magnetic field [mT] applied to the pair of TMR sensors 2, while the vertical axis represents the sensor output [mV] excluding the linear component. The characteristic line y' represents the distortion of the sensor output that appears due to nonlinearity. This distortion affects the magnetic field detection accuracy of the TMR sensor 2, so the distortion is compensated for by the linearity compensation circuit 5.

[0033] As can be seen from the graph, the distortion exists in magnetic field regions of approximately +8 mT or more and approximately -8 mT or less. Therefore, when a sensor output for a predetermined magnetic field is obtained in these magnetic field regions, the distortion is cancelled out by varying the amplification factor of the compensation amplifier circuit 4 using the linearity compensation circuit 5.

[0034] FIG. 4(a) is a graph showing an example of a control signal v given to each switch of the variable resistor R4 from the linearity compensation circuit 5. The horizontal axis of the graph represents the magnetic field [mT] given to the pair of TMR sensors 2, and the vertical axis represents the voltage [V] of the control signal v. Characteristic lines c, d, e, and f represent control signals v1, v2, v3, and v4 that correct the distortion of the sensor output of about +8 [mT] or more in the positive magnetic field shown in FIG. 3(b), and characteristic lines g, h, i, and j represent control signals v5, v6, v7, and v8 that correct the distortion of the sensor output of about -8 [mT] or less in the negative magnetic field. Each of the control signals v1 to v8 changes between a high level of +5 [V] and a low level of 0 [V], and when it changes to a low level, for example, each of the switches sw1 to sw8 is controlled to close.

[0035] In the graph, the distortion of the sensor output in the magnetic field region of about +8 [mT] or more is changed to an amplification factor of the compensation amplifier circuit 4 by closing the switch sw1 by changing the control signal v1 shown by characteristic line c to a low level when the magnetic field is about +7 [mT], changing the resistance value of the variable resistor R4, and changing the amplification factor of the compensation amplifier circuit 4 to an amplification factor that cancels out the distortion in the magnetic field at that time. Also, when the magnetic field is about +10 [mT], the switch sw2 is closed by changing the control signal v2 shown by characteristic line d to a low level when the magnetic field is about +13 [mT], changing the switch sw3 by changing the control signal v3 shown by characteristic line e to a low level when the magnetic field is about +13 [mT], and changing the switch sw4 by changing the control signal v4 shown by characteristic line f to a low level when the magnetic field is about +15 [mT], changing the resistance value of the variable resistor R4, and changing the amplification factor of the compensation amplifier circuit 4 to an amplification factor that cancels out the distortion in each magnetic field.

[0036] Similarly, for distortion of the sensor output in the magnetic field region of approximately -8 mT or less, the switches sw5 to sw8 are closed and controlled by the control signals v5 to v8 represented by characteristic lines g to j, thereby varying the resistance value of the variable resistor R4 and changing the amplification factor of the compensation amplifier circuit 4 to an amplification factor that cancels out the distortion in each magnetic field.

[0037] 4(b) is a graph showing the distortion of the sensor output after the nonlinearity of the sensor output has been compensated for by such resistance value control of the variable resistor R4 by the linearity compensation circuit 5. The horizontal axis of the graph represents the magnetic field [mT] applied to the TMR sensor 2, and the vertical axis represents the proportion [%] of the distortion component contained in the output voltage VOUT outputted to the output terminal out of the sensor output compensation IC1. Furthermore, characteristic line k represents the fluctuation characteristic of the distortion component contained in the output voltage VOUT in response to a change in the magnetic field.

[0038] The distortion of the sensor output in the magnetic field region of approximately +8 mT or more decreases in a downward sloping manner as the magnetic field increases, as shown in Figure 3(b). However, from characteristic line k, it can be seen that at each of the timings when the control signals v1, v2, v3, and v4 successively go low in the magnetic fields of approximately +7 mT, approximately +10 mT, approximately +13 mT, and approximately +15 mT, the amplification factor of the compensation amplifier circuit 4 is increased, causing the proportion of distortion components to increase in a upward sloping manner, thereby counteracting the reduction in distortion shown in Figure 3(b).

[0039] The distortion of the sensor output in the magnetic field region below approximately -8 mT increases to the left as the magnetic field decreases, as shown in Figure 3(b). However, from characteristic line k, it can be seen that at each timing when the control signals v5 to v8 successively go low in response to the decrease in the magnetic field, the amplification factor of the compensation amplifier circuit 4 is reduced, causing the proportion of the distortion component to decrease to the left, thereby counteracting the increase in distortion shown in Figure 3(b).

[0040] In addition, the proportion of the distortion component increases upward and to the right in the positive magnetic field region, and then temporarily decreases downward and to the right due to the decrease in the original distortion shown in Figure 3(b). Also, in the negative magnetic field region, it decreases downward and to the left, and then temporarily increases upward and to the left due to the increase in the original distortion shown in Figure 3(b). Therefore, although the characteristic line k fluctuates up and down in a zigzag pattern as shown in Figure 4(b), the fluctuation range of the distortion component is kept to ±0.1% or less, and the linearity of the sensor output is guaranteed.

[0041] Thus, according to the sensor output compensation IC1 of this embodiment, the amplification factor of the compensation amplifier circuit 4 is varied by switching the connections between the multiple resistors connected to the compensation amplifier circuit 4 as the variable resistor R4 by controlling the multiple switches of the linearity compensation circuit 5, thereby changing the combined resistance value of the multiple resistors. The switching of the switch is performed when the output voltage of the differential amplifier circuit 3 is compared with multiple preset reference voltages VREF_L1, VREF_L2, VREF_L3, ..., VREF_Ln and becomes a voltage corresponding to each sensor output according to the magnetic field causing each predetermined distortion. By switching the switch, the amplification factor of the compensation amplifier circuit 4 becomes an amplification factor that cancels each predetermined distortion from the output of the differential amplifier circuit 3 according to the output voltage of the differential amplifier circuit 3, thereby ensuring the linearity of the sensor output.

[0042] That is, according to the sensor output compensation IC1 of this embodiment, the distortion that appears in the sensor output with nonlinearity in response to the change in the magnetic field is compensated for by changing the amplification factor of the compensation amplifier circuit 4, which compensates for the output of the differential amplifier circuit 3, to an amplification factor that cancels the distortion, by the linearity compensation circuit 5. Therefore, unlike the conventional nonlinearity compensation circuit (see JP 2003-248017 A), the distortion of the sensor output can be compensated for without feeding back the sensor output. This increases the response speed of the circuit, and the nonlinearity of the sensor output is compensated for at high speed. In addition, since the sensor output compensation circuit does not require an adder circuit as in the conventional sensor output compensation circuit, the circuit size of the sensor output compensation IC1 can be reduced.

[0043] Fig. 5 is a circuit diagram for explaining the function of the sensitivity temperature characteristic compensation circuit 6 in the sensor output compensation IC1 shown in Fig. 1. In this figure, the same or corresponding parts as in Fig. 1 are given the same reference numerals and their explanation will be omitted.

[0044] The sensitivity temperature characteristic compensation circuit 6 is composed of a plurality of comparators 61, 62, 63, ..., 6n. The ambient temperature detected as a voltage by the temperature sensor circuit 11 is commonly input to one input terminal of each of the comparators 61, 62, 63, ..., 6n, and predetermined reference voltages VREF_T1, VREF_T2, VREF_T3, ..., VREF_Tn output from the reference voltage circuit 10 are input to the other input terminal. Each of these reference voltages VREF_T1, VREF_T2, VREF_T3, ..., VREF_Tn corresponds to a voltage corresponding to the ambient temperature that causes a predetermined variation in the sensitivity of the sensor output, and is preset by setting data written in the EEPROM 12.

[0045] The sensitivity temperature characteristic compensation circuit 6 changes the amplification factor (R5 / R4) of the compensation amplifier circuit 4 to an amplification factor that cancels out fluctuations that appear in the sensitivity of the sensor output in response to changes in ambient temperature by changing the resistance value of variable resistor R5 by switching multiple switches that make up variable resistor R5 depending on the comparison result between these multiple reference voltages and the ambient temperature detected as a voltage by the temperature sensor circuit 11.

[0046] Note that, although the case has been described where the amplification factor (R5 / R4) of the compensation amplifier circuit 4 is varied by changing the resistance value of the variable resistor R5 through switching of multiple switches constituting the variable resistor R5, the amplification factor (R5 / R4) of the compensation amplifier circuit 4 may also be varied by changing the resistance value of the variable resistor R4 through switching of multiple switches constituting the variable resistor R4.

[0047] 6(a) is a graph showing the results of measuring the temperature characteristics of the sensor output sensitivity for multiple pairs of TMR sensors 2. The horizontal axis of the graph represents the ambient temperature [°C] of the TMR sensor 2, and the vertical axis represents the rate of variation [%] of sensitivity at each ambient temperature, with the sensor output sensitivity at an ambient temperature of 25°C as the reference. Each characteristic line shows the sensitivity-temperature characteristics for each of the multiple pairs of TMR sensors 2.

[0048] As shown in the graph, in the temperature range where the ambient temperature is lower than 25°C, the rate of change of the sensitivity increases linearly to the positive side as the temperature decreases. On the other hand, in the temperature range where the ambient temperature is higher than 25°C, the rate of change of the sensitivity increases non-linearly to the negative side as the temperature increases.

[0049] Fig. 6(b) is a graph showing how much the output voltage VOUT of the sensor output compensation IC1 fluctuates when the amplification factor of the compensation amplifier circuit 4 is changed according to each ambient temperature that causes a given fluctuation in sensitivity, based on the temperature characteristic of the sensitivity shown in Fig. 6(a). The horizontal axis of the graph shows the ambient temperature [°C], and the vertical axis shows the fluctuation rate [%] of the output voltage VOUT. The characteristic line m shows the change in the fluctuation rate of the output voltage VOUT with respect to the ambient temperature.

[0050] From characteristic line m, in a temperature region where the ambient temperature is lower than 25°C, the regulation rate of the output voltage VOUT decreases linearly to the negative side and downward to the left as the ambient temperature decreases, acting to cancel out the regulation rate of the sensitivity shown in Figure 6(a) which increases linearly to the left and upwards. Also, in a temperature region where the ambient temperature is higher than 25°C, the regulation rate of the output voltage VOUT increases non-linearly to the positive side and upwards to the right as the ambient temperature increases, acting to cancel out the regulation rate of the sensitivity shown in Figure 6(a) which decreases non-linearly to the right and downwards.

[0051] FIG. 7(a) is a graph showing the temperature characteristic of the sensitivity of the sensor output after compensation by the above-mentioned sensitivity temperature characteristic compensation. The horizontal axis of the graph shows the ambient temperature [°C] of the TMR sensor 2, and the vertical axis shows the fluctuation rate [%] of the sensitivity at each ambient temperature, with the sensor output sensitivity at an ambient temperature of 25°C as the reference. Characteristic line n shows the sensitivity temperature characteristic of the sensor output compensated by the fluctuation rate of the output voltage VOUT shown in FIG. 6(b). As shown in the graph, the fluctuation rate of the sensor output sensitivity after compensation falls within a small fluctuation range of +0.04[%] to -0.02[%].

[0052] 7(b) is a graph showing the voltage characteristics of the ambient temperature used in the above-mentioned sensitivity temperature characteristic compensation. The horizontal axis of the graph shows the ambient temperature [°C] of the sensor output compensation IC1, and the vertical axis shows the output voltage [V] of the temperature sensor circuit 11 at each ambient temperature. The characteristic line o shows the temperature characteristic of the output voltage of the temperature sensor circuit 11.

[0053] Thus, according to the sensor output compensation IC1 of this embodiment, the amplification factor of the compensation amplifier circuit 4 is varied by switching the connections between the multiple resistors connected to the compensation amplifier circuit 4 as the variable resistor R5 by controlling the multiple switches of the sensitivity temperature characteristic compensation circuit 6, thereby changing the combined resistance value of the multiple resistors. The switching of the switch is performed when the ambient temperature detected as a voltage by the temperature sensor circuit 11 is compared with multiple preset reference voltages VREF_T1, VREF_T2, VREF_T3, ..., VREF_Tn and becomes a voltage corresponding to the ambient temperature causing each predetermined fluctuation. By switching the switch, the amplification factor of the compensation amplifier circuit 4 becomes an amplification factor that cancels each predetermined fluctuation in sensitivity caused by the ambient temperature from the output of the differential amplifier circuit 3, and the sensitivity temperature characteristic of the sensor output is compensated.

[0054] That is, according to the sensor output compensation IC1 of this embodiment, the variation appearing in the sensitivity of the sensor output due to the change in the ambient temperature is compensated for by changing the amplification factor of the compensation amplifier circuit 4, which compensates for the output of the differential amplifier circuit 3, to an amplification factor that cancels the variation, by the sensitivity temperature characteristic compensation circuit 6. Therefore, unlike the conventional temperature compensation circuit disclosed in Patent Document 1, which can only perform temperature compensation depending on the thermistor characteristics, the temperature range in which temperature compensation can be performed is not limited, and the sensitivity temperature compensation of the sensor output sensitivity can be performed for a wider range of ambient temperature fluctuations. In addition, the variation of the thermistor element does not appear in the temperature compensation characteristics as in the conventional case, and it is possible to achieve high accuracy of the sensitivity temperature compensation. In addition, since the sensor output compensation circuit can be configured without using a thermistor element in the temperature compensation circuit, it is possible to make the sensor output compensation circuit an IC, and the sensor output compensation circuit can be made smaller and less expensive.

[0055] Fig. 8 is a circuit diagram for explaining the function of the offset temperature characteristic compensation circuit 7 in the sensor output compensation IC1 shown in Fig. 1. In this figure, the same or corresponding parts as in Fig. 1 are given the same reference numerals and their explanation will be omitted.

[0056] The offset temperature compensation circuit 7 refers to the ambient temperature detected by the temperature sensor circuit 11, and inputs a reference voltage VREF2 to the reference voltage terminal of the compensation amplifier circuit 4, which cancels fluctuations in the offset voltage of the sensor output that appear in response to changes in ambient temperature.

[0057] The temperature fluctuation of the offset voltage of the sensor output is shown in the graph shown in FIG. 9(a). The horizontal axis of the graph represents the ambient temperature [°C] of the sensor output compensation IC1, and the vertical axis represents the fluctuation rate [%] of the offset voltage at each ambient temperature, with the offset voltage at an ambient temperature of 25°C as the reference. Each characteristic line represents the temperature characteristic of each offset voltage for multiple pairs of TMR sensors 2. As shown in the graph, the temperature characteristic of each offset voltage varies linearly with a linear gradient. The offset temperature characteristic compensation circuit 7 inputs a reference voltage VREF2 that cancels out this fluctuation to the reference voltage terminal, which is the non-inverting input terminal of the operational amplifier 41 in the compensation amplifier circuit 4.

[0058] In this embodiment, the offset temperature characteristic compensation circuit 7 includes a first inverting amplifier circuit 72 configured with an operational amplifier 71, a second inverting amplifier circuit 74 configured with an operational amplifier 73, a first switch 75, and a second switch .

[0059] The first inverting amplifier circuit 72 is configured by connecting a resistor R7 and a variable resistor R8 to an operational amplifier 71, and a reference voltage VREF21 is applied to the non-inverting input terminal of the operational amplifier 71. This first inverting amplifier circuit 72 inverts and amplifies the ambient temperature detected as a voltage by the temperature sensor circuit 11 with an amplification factor (R8 / R7) corresponding to the fluctuation rate of the offset voltage. The fluctuation rate of the offset voltage corresponds to the slope of each characteristic line in the graph shown in Figure 9(a), and the amplification factor (R8 / R7) is adjusted to the fluctuation rate of the offset voltage by adjusting the resistance value of the variable resistor R8.

[0060] The second inverting amplifier circuit 74 is configured by connecting a resistor R9 and a variable resistor R10 to the operational amplifier 73, and a reference voltage VREF22 is applied to the non-inverting input terminal of the operational amplifier 73. The second inverting amplifier circuit 74 inverts and amplifies the output of the first inverting amplifier circuit 72 with an amplification factor (R10 / R9) and inverts the polarity. The amplification factor (R10 / R9) is basically set to 1 by adjusting the resistance value of the variable resistor R10. The second switch 76 is controlled to be closed when the fluctuation of the offset voltage with respect to the ambient temperature increases with an increase in the ambient temperature, and the output of the second inverting amplifier circuit 74 is input to the reference voltage terminal of the operational amplifier 41 as the reference voltage VREF2.

[0061] Therefore, for example, in the graph shown in FIG. 9(a), when the temperature characteristic of the offset voltage is represented by a straight characteristic line p with an upward slope, in which the fluctuation with respect to the ambient temperature increases with an increase in the ambient temperature, the voltage represented by the downward slope, which is output from the temperature sensor circuit 11 and decreases with an increase in the ambient temperature, is first converted by the first inverting amplifier circuit 72 in the offset temperature characteristic compensation circuit 7 into a voltage with an upward slope characteristic with the same magnitude of the fluctuation rate of the offset voltage of the characteristic line p and an inverted polarity of the slope. Then, the second switch 76 is controlled to be closed, so that this voltage is converted by the second inverting amplifier circuit 74 into a reference voltage VREF2 with a downward slope characteristic with an inverted polarity of the slope. Therefore, the compensation amplifier circuit 4 amplifies the output voltage including the offset voltage represented by the upward slope, which is output from the differential amplifier circuit 3, based on this reference voltage VREF2, thereby canceling the fluctuation due to the temperature characteristic of the offset voltage.

[0062] 9(b) is a graph showing the temperature characteristics of the offset voltages of the four pairs of TMR sensors 2 after compensation by the offset temperature characteristic compensation circuit 7. The horizontal and vertical axes of the graph are the same as those in FIG. 9(a). The graph shown in FIG. 9(b) shows a characteristic line p before compensation, and the temperature characteristics of the offset voltages of the pair of TMR sensors 2 that had this characteristic line p are compensated to have a temperature characteristic with a nearly flat slope, as shown by the dotted arrow, by the offset compensation described above.

[0063] Moreover, the first switch 75 is controlled to close when the fluctuation of the offset voltage with respect to the ambient temperature decreases with an increase in the ambient temperature, and the output of the first inverting amplifier circuit 72 is input as a reference voltage VREF2 to the reference voltage terminal of the operational amplifier 41. Therefore, when the temperature characteristic of the offset voltage of the pair of TMR sensors 2 is represented by a characteristic line q that slopes downward to the right and decreases with an increase in the ambient temperature in the graph shown in FIG. 9(a), the voltage represented by the characteristic line that slopes downward to the right and is output from the temperature sensor circuit 11 and decreases with an increase in the ambient temperature is converted by the first inverting amplifier circuit 72 in the offset temperature characteristic compensation circuit 7 into a reference voltage VREF2 whose slope is the same as the magnitude of the fluctuation rate of the offset voltage of the characteristic line q and whose slope is reversed. Therefore, the compensation amplifier circuit 4 amplifies the output voltage including the offset voltage represented by the straight downward sloping characteristic line q output from the differential amplifier circuit 3 using this reference voltage VREF2 as a standard, and thus the fluctuation in the offset voltage due to the temperature characteristics is cancelled out, as shown in the graph in Figure 9(b).

[0064] Thus, according to the sensor output compensation IC1 of this embodiment, when the variation of the offset voltage with respect to the ambient temperature increases with an increase in the ambient temperature, the output of the second inverting amplifier circuit 74 is input to the reference voltage terminal of the compensation amplifier circuit 4 by the second switch 76. Therefore, the ambient temperature detected as a voltage by the temperature sensor circuit 11 is inverted and amplified by the first inverting amplifier circuit 72 with an amplification factor (R8 / R7) corresponding to the variation rate of the offset voltage, and the polarity is inverted by the second inverting amplifier circuit 74, and an ambient temperature inverted signal that decreases with the variation rate of the offset voltage with an increase in the ambient temperature is input from the second inverting amplifier circuit 74 as the reference voltage VREF2. Therefore, the compensation amplifier circuit 4 amplifies the output of the differential amplifier circuit 3 based on the ambient temperature inverted signal, so that the compensation amplifier circuit 4 can obtain a sensor output in which the temperature variation of the offset voltage is cancelled.

[0065] Furthermore, when the variation of the offset voltage with respect to the ambient temperature decreases with an increase in the ambient temperature, the first switch 75 inputs the output of the first inverting amplifier circuit 72 to the reference voltage terminal of the operational amplifier 41. Therefore, the first inverting amplifier circuit 72 inverts and amplifies the ambient temperature inverted signal with an amplification factor (R8 / R7) corresponding to the variation rate of the offset voltage, and the ambient temperature inverted signal increases with an increase in the ambient temperature at the variation rate of the offset voltage, and the ambient temperature inverted signal is input from the first inverting amplifier circuit 72 as the reference voltage VREF2 to the reference voltage terminal of the operational amplifier 41. Therefore, the compensation amplifier circuit 4 amplifies the output of the differential amplifier circuit 3 based on the ambient temperature inverted signal, so that a sensor output in which the variation of the offset voltage that appears with respect to changes in the ambient temperature is cancelled out can be obtained from the compensation amplifier circuit 4.

[0066] That is, according to the sensor output compensating IC1 of this embodiment, the fluctuation of the offset voltage of the sensor output appearing in response to the change in the ambient temperature is cancelled out by the compensating amplifier circuit 4, which compensates for the output of the differential amplifier circuit 3, amplifying the output of the differential amplifier circuit 3 based on the reference voltage VREF2 input from the offset temperature characteristic compensation circuit 7 to the reference voltage terminal of the operational amplifier 41. Therefore, the offset voltage is compensated for easily and precisely with a single compensation operation. Therefore, unlike the conventional offset adjustment circuit disclosed in Patent Document 1, which adjusts the offset of the sensor output simply by adjusting the midpoint potential of the differential amplifier circuit output with a variable resistor, the temperature compensation of the offset voltage of the sensor output can be easily and accurately performed.

[0067] In addition, in the sensor output compensation IC1 according to this embodiment, each circuit constituting the sensor output compensation circuit is mounted on the same IC. Therefore, the variation caused by the wiring between the circuits constituting the sensor output compensation circuit and the difference in the mounting of the components constituting each circuit is reduced. Therefore, each compensation of the sensor output by the sensor output compensation IC1 is performed with high accuracy. In addition, it becomes possible to mount all compensation functions on the IC. In addition, by monitoring the sensor output of a pair of TMR sensors 2 to be compensated, each pair of TMR sensors 2 can be compensated with high accuracy with a relatively simple circuit configuration. In addition, the compensation adjustment of each compensation circuit can be easily and selectively selected by selecting the setting data to be written to the EEPROM 12.

[0068] In addition, by mounting the temperature sensor circuit 11 on the same IC as the other circuits constituting the sensor output compensation circuit, the relative position of the temperature sensor circuit 11 with respect to the other circuits is always constant. Therefore, the ambient temperature detected by the temperature sensor circuit 11 has less error with the ambient temperature of the other circuits. In addition, when the temperature sensor circuit 11 is provided separately from the ICs of the other circuits, there is no error between the ambient temperature detected by the temperature sensor circuit 11 and the ambient temperature used in the IC due to parasitic resistance components of the wiring connection parts connecting the temperature sensor circuit 11 and the IC by wire bonding. As a result, the sensor output compensation IC1 according to this embodiment makes it possible to perform temperature compensation of the sensor sensitivity and offset voltage with high accuracy.

[0069] According to the sensor output compensation IC1 of this embodiment, the influence of the residual magnetic field remaining in the TMR sensor 2 is cancelled without improving the sensor itself by arranging the pair of TMR sensors 2 in relative positions that mutually cancel out the influence of the residual magnetic field, as shown in Fig. 10, and applying bias voltages Vbias in opposite directions to the pair of power supply terminals 2a, 2b of each TMR sensor 2 by the reference voltage circuit 10. Then, the sensor output corresponding to the magnetic field detected by the pair of TMR sensors 2 is extracted based on the predetermined detection voltages appearing at the respective detection signal output terminals 2c, 2d of the pair of TMR sensors 2, that is, the respective detection voltages appearing at one detection signal output terminal 2c of each TMR sensor 2 and the respective detection voltages appearing at the other detection signal output terminal 2d of each TMR sensor 2, and is amplified by the differential amplifier circuit 3. Therefore, it is possible to remove the influence of the residual magnetic field remaining in each TMR sensor 2 from the sensor output, suppress hysteresis, and the magnetic field can be accurately detected by the sensor output compensation IC1.

[0070] Furthermore, according to the sensor output compensation IC1 of this embodiment, the sensor output is taken as a difference voltage between a voltage output from a first synthesis calculation circuit 13 obtained by adding or averaging each detection voltage appearing in one phase at each detection signal output terminal 2c of one of the pair of TMR sensors 2, and a voltage output from a second synthesis calculation circuit 14 obtained by adding or averaging each detection voltage appearing in the other phase at each detection signal output terminal 2d of the other of the pair of TMR sensors 2, and is amplified by the differential amplifier circuit 3. Therefore, since the sensor output is taken from the difference voltage between the outputs of the pair of TMR sensors 2, it is possible to obtain a sensor output in which the variations in each TMR sensor 2 are averaged, and a circuit configuration that can handle the variations in each TMR sensor 2 is obtained, making it possible to detect the magnetic field more accurately.

[0071] As a secondary effect, by using multiple TMR sensors 2, it becomes easier to determine if a TMR sensor 2 has failed. If a TMR sensor 2 fails, it will no longer operate in proportion to the external magnetic field, and a pair of TMR sensors 2 will always output a sensor output with a constant voltage value in response to changes in the external magnetic field. By detecting this state, it becomes possible to determine whether a TMR sensor 2 has failed.

[0072] 11 is a circuit diagram showing the overall schematic configuration of a sensor output compensation IC1A constituting a sensor output compensation circuit according to a second embodiment of the present invention, in which the same reference numerals are used to designate the same or corresponding parts as those in FIG. 1, and their explanation will be omitted.

[0073] The sensor output compensation IC1A according to the second embodiment differs from the sensor output compensation IC1 according to the first embodiment in that it uses only the detection voltages appearing at the detection signal output terminals 2c, 2d of one of the pair of TMR sensors 2, and in that it does not include the first synthesis arithmetic circuit 13 and the second synthesis arithmetic circuit 14.

[0074] That is, in the sensor output compensation IC1A according to the second embodiment, the differential amplifier circuit 3 directly inputs and amplifies each detection voltage appearing at the pair of detection signal output terminals 2c, 2d of one TMR sensor 2 to the inverting input terminals of the operational amplifiers 31, 32 via the input terminals 1a, 1b, and differentially amplifies each amplified detection voltage by the operational amplifier 33. That is, the differential amplifier circuit 3 amplifies the difference voltage between the detection voltages appearing at the detection signal output terminals 2c, 2d of one TMR sensor 2 of the pair of TMR sensors 2 as the sensor output.

[0075] A load (not shown) having a level equivalent to the input impedance appearing between the input terminals 1a and 1b is connected between the unused detection signal output terminals 2c and 2d of the other TMR sensor 2, thereby balancing the load with the one TMR sensor 2 being used. In addition, the TMR sensor 2 to be used may be any one of the pair.

[0076] In the sensor output compensation IC1A according to the second embodiment, the influence of the residual magnetic field remaining in the TMR sensor 2 is also cancelled without improving the sensor itself by arranging the pair of TMR sensors 2 in relative positions that mutually cancel out the influence of the residual magnetic field, as shown in Fig. 10, and applying bias voltages Vbias in opposite directions to the pair of power supply terminals 2a, 2b of each TMR sensor 2 by the reference voltage circuit 10. Then, the sensor output corresponding to the magnetic field detected by the pair of TMR sensors 2 is extracted based on the predetermined detection voltages appearing at the respective detection signal output terminals 2c, 2d of the pair of TMR sensors 2, that is, the respective detection voltages appearing at the respective detection signal output terminals 2c, 2d of one of the TMR sensors 2, and is amplified by the differential amplifier circuit 3. Therefore, according to the sensor output compensation IC1A according to the second embodiment, the configuration of the sensor output compensation IC1A can be simplified, the circuit area can be reduced, and the cost can be reduced, while the influence of the residual magnetic field remaining in the pair of TMR sensors 2 can be removed from the sensor output, and the magnetic field can be accurately detected.

[0077] 12 is a circuit diagram showing the overall schematic configuration of a sensor output compensation IC1B constituting a sensor output compensation circuit according to a third embodiment of the present invention, in which the same reference numerals are used to designate the same or corresponding parts as those in FIG. 1, and their explanation will be omitted.

[0078] The sensor output compensation IC1B according to the third embodiment differs from the sensor output compensation IC1 according to the first embodiment in that it uses only the detection voltage appearing at the detection signal output terminal 2c of one TMR sensor 2 of the pair of TMR sensors 2 and the detection voltage appearing at the detection signal output terminal 2d of the other TMR sensor 2 of the pair of TMR sensors 2, and in that it does not include the first synthesis arithmetic circuit 13 and the second synthesis arithmetic circuit 14.

[0079] That is, in the sensor output compensation IC 1B according to the third embodiment, the differential amplifier circuit 3 directly inputs the detection voltage appearing at one detection signal output terminal 2c of one TMR sensor 2 to the inverting input terminal of the operational amplifier 31 via the input terminal 1a and amplifies it. Also, the detection voltage appearing at the other detection signal output terminal 2d of the other TMR sensor 2 is directly input to the inverting input terminal of the operational amplifier 32 via the input terminal 1d and amplifies it. Then, the amplified detection voltages are differentially amplified by the operational amplifier 33. That is, the differential amplifier circuit 3 amplifies the difference voltage between the detection voltage appearing at one detection signal output terminal 2c of one TMR sensor 2 in one phase and the detection voltage appearing at the other detection signal output terminal 2d of the other TMR sensor 2 in the other phase as the sensor output.

[0080] A load (not shown) is connected to each of the unused detection signal output terminals 2 d and 2 c of each TMR sensor 2 so that the loads between the TMR sensors 2 are balanced.

[0081] 10, the influence of the residual magnetic field remaining in the TMR sensor 2 is cancelled without improving the sensor itself by arranging a pair of TMR sensors 2 in relative positions that mutually cancel out the influence of the residual magnetic fields, and applying a bias voltage Vbias in mutually opposite directions to a pair of power supply terminals 2a, 2b of each TMR sensor 2 by a reference voltage circuit 10. The sensor output is then extracted as a difference voltage between a detection voltage appearing in one phase at one detection signal output terminal 2c of one TMR sensor 2 and a detection voltage appearing in the other phase at the other detection signal output terminal 2d of the other TMR sensor 2, and is amplified by a differential amplifier circuit 3.

[0082] Therefore, like the sensor output compensation IC1A according to the second embodiment, the sensor output compensation IC1B according to the third embodiment can simplify the configuration of the sensor output compensation IC1B, reduce the circuit area and reduce costs, and remove the influence of the residual magnetic field remaining in the TMR sensor 2 from the sensor output, thereby enabling accurate detection of the magnetic field. Also, like the sensor output compensation IC1 according to the first embodiment, the sensor output compensation IC1B according to the third embodiment obtains the sensor output from the differential voltage between the outputs of a pair of TMR sensors 2, making it possible to obtain a sensor output that averages the variations in each TMR sensor 2, thereby obtaining a circuit configuration that can accommodate the variations in each TMR sensor 2, and enabling more accurate detection of the magnetic field. [Explanation of symbols]

[0083] 1,1A,1B…Sensor output compensation IC 2. TMR sensor 2a, 2b...A pair of power supply terminals of the TMR sensor 2 2c, 2d: A pair of detection signal output terminals of the TMR sensor 2 3. Differential amplifier circuit 4...Compensation amplifier circuit 5...Linearity compensation circuit 51, 52, 53, …, 5n … Comparators 6…Sensitivity temperature compensation circuit 61, 62, 63, …, 6n … Comparators 7…Offset temperature compensation circuit 72…First inverting amplifier circuit 74…Second inverting amplifier circuit 75…First switch 76…Second switch 13...First composite calculation circuit 14…Second composite calculation circuit

Claims

1. A pair of sensors, each of which is configured by connecting sensor elements whose resistance value changes in response to a detected physical quantity in a bridge connection, and which are arranged in relative positions such that the effects of residual magnetic fields are mutually offset; a differential amplifier circuit that amplifies a sensor output corresponding to a physical quantity detected by the sensor, the sensor output being taken based on a predetermined detection voltage appearing at each detection signal output terminal of the pair of sensors; a bias circuit that applies a voltage to a pair of power supply terminals of one of the pair of sensors in a direction opposite to a voltage to be applied to a pair of power supply terminals of the other of the pair of sensors; a first synthesis calculation circuit that adds or averages each detection voltage appearing at each detection signal output terminal of the same one of the pair of sensors; a second synthesis arithmetic circuit that adds or averages the detection voltages appearing at the detection signal output terminals of the other of the pair of sensors; The differential amplifier circuit amplifies a difference voltage between the output of the first synthesis arithmetic circuit and the output of the second synthesis arithmetic circuit as the sensor output. Sensor output compensation circuit.

2. 2. The sensor output compensation circuit according to claim 1, wherein the sensor element is a TMR element.

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