Sensor amplifying circuit

Abstract

A sensor amplifier circuit (100) is provided with: a differential amplifier circuit (110) that amplifies a differential voltage between a pair of output signals from a sensor circuit (50); and a compensation circuit (150) that, on the basis of the output voltage of the differential amplifier circuit (110), generates a compensation signal for compensating for non-linear distortion of the output voltage. The differential amplifier circuit (110) is configured from a current feedback-type instrumentation amplifier circuit (CFIA). The compensation circuit (150) includes at least one current amplification circuit (OTA) (160) configured so as to output a current corresponding to the output voltage, and outputs the sum of the output currents from the at least one current amplification circuit (160) as a compensation signal. A compensation signal from a compensation circuit (150) is input to a current feedback loop in a current feedback-type instrumentation amplifier circuit.

Description

Technical Field

[0001] The present disclosure relates to a sensor amplification circuit, and more particularly, to a technique for compensating a sensor output using a bridge circuit. Background Art

[0002] Japanese Patent Publication No. 2003-248017 (Patent Document 1) discloses a sensor circuit that improves the detection accuracy by compensating the sensor output to improve the S / N ratio. The sensor circuit of Japanese Patent Publication No. 2003-248017 (Patent Document 1) includes: a detection unit (preamplifier unit) having a sensor element, a power supply unit (sensor application circuit) that serves as a power supply provided to the detection unit, and an amplifier unit (main amplifier unit) that amplifies the signal from the detection unit. The sensor application circuit includes a constant voltage circuit, a sensitivity temperature compensation circuit, and a nonlinear compensation circuit, and the nonlinear compensation circuit is configured in a feedback loop of the sensor circuit output. In the sensor circuit of Japanese Patent Publication No. 2003-248017 (Patent Document 1), the nonlinear compensation circuit is used to move the potential applied from the constant voltage circuit to the preamplifier unit, thereby improving the linearity of the sensor circuit.

[0003] Prior Art Literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2003-248017 Summary of the invention

[0006] Problem that the invention aims to solve

[0007] As a sensor circuit using a sensor element formed in a bridge circuit, for example, there is a magnetic sensor using a tunneling magnetoresistive (TMR) element. Such a magnetic sensor is sometimes used as a current sensor in electric vehicles such as electric vehicles (EV) or hybrid vehicles (HV). In such applications, in addition to high-precision sensor output, high-speed responsiveness is also required from the perspective of vehicle operability and safety.

[0008] In the sensor circuit disclosed in Japanese Patent Publication No. 2003-248017 (Patent Document 1), the accuracy can be improved by using a sensitivity temperature compensation circuit and a nonlinear compensation circuit. However, the nonlinear compensation circuit is formed in the voltage feedback loop of the sensor circuit output, and the sensor circuit output is fed back to the input side of the preamplifier unit. Therefore, the responsiveness of the circuit is inevitably delayed, and there is a possibility that the required responsiveness cannot be ensured.

[0009] The present disclosure has been made to solve such a problem, and an object of the present disclosure is to improve linearity while ensuring high responsiveness in an amplifier circuit of a sensor using a bridge circuit.

[0010] Technical solutions to solve problems

[0011] The sensor amplifier circuit involved in the present disclosure is a circuit for amplifying the output of a sensor circuit in which four sensor elements are bridge-connected. The sensor amplifier circuit comprises: a differential amplifier circuit for amplifying the differential voltage of a pair of output signals from the sensor circuit; and a compensation circuit for generating a compensation signal for compensating for the nonlinear distortion of the output voltage based on the output voltage of the differential amplifier circuit. The differential amplifier circuit is composed of a current feedback instrumentation amplifier circuit (Current Feedback Instrumentation Amplifier: CFIA). The compensation circuit includes at least one current amplifier circuit (Operational Transconductance Amplifier: OTA, operational transconductance amplifier) ​​configured to output a current corresponding to the output voltage, and outputs the sum of the output currents from the at least one current amplifier circuit as a compensation signal. The compensation signal from the compensation circuit is input into the current feedback loop in the current feedback instrumentation amplifier circuit.

[0012] Effects of the Invention

[0013] In the sensor amplifier circuit disclosed in the present invention, a current feedback instrument amplifier circuit (CFIA) is used to form a differential amplifier circuit, and a compensation signal for nonlinear distortion generated by a compensation circuit including a current amplifier circuit (OTA) is fed back to the current feedback loop of the CFIA circuit. In this way, by feeding back the intermediate signal (current signal) in the differential amplifier circuit, an amplifier (operational amplifier) ​​is formed without passing through an input stage, so that the responsiveness can be improved compared to a voltage feedback compensation circuit such as Patent Document 1. Therefore, it is possible to improve linearity while ensuring high responsiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1FIG. 1 is a schematic diagram showing the configuration of a sensor system using the sensor amplifier circuit according to the first embodiment.

[0015] Figure 2 FIG. 1 is a first diagram for explaining an outline of linear compensation in a sensor amplifier circuit.

[0016] Figure 3 FIG. 2 is a second diagram for explaining an outline of linear compensation in a sensor amplifier circuit.

[0017] Figure 4 It is an equivalent model for calculating the transfer function of the sensor amplifier circuit.

[0018] Figure 5 It is shown in Figure 4 FIG. 1 is a diagram showing the output of the sensor amplifier circuit when the reference voltage of the linear compensation circuit is changed in the equivalent model.

[0019] Figure 6 This is a schematic configuration diagram of a sensor system using the sensor amplifier circuit according to the second embodiment.

[0020] Figure 7 This is a diagram for explaining an overview of temporal changes in a compensation signal caused by a filter circuit.

[0021] Figure 8 FIG. 1 is a schematic diagram showing the configuration of a sensor system using the sensor amplifier circuit according to the third embodiment. DETAILED DESCRIPTION

[0022] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In addition, the same reference numerals are given to the same or corresponding parts in the drawings, and their description will not be repeated.

[0023] [Implementation Method 1]

[0024] (Overview of sensor system)

[0025] Figure 1 FIG. 1 is a schematic diagram of a sensor system 10 using the sensor amplifier circuit 100 according to the first embodiment. Figure 1 The sensor system 10 includes a sensor circuit 50 and a sensor amplifier circuit 100 .

[0026] The sensor circuit 50 has a structure in which four sensor elements 51 to 54 are bridge-connected. Figure 1 In the example, sensor elements 51 to 54 are each a tunneling magnetoresistive (TMR) element, which is a magnetic sensor whose resistance value changes according to the detected magnetic field. In addition, sensor elements 51 to 54 can be any element whose resistance value changes according to the detected physical quantity, and other resistance elements can also be used.

[0027] Sensor elements 51 and 52 are connected in series between a pair of power supply terminals 5a and 5b. In addition, sensor elements 53 and 54 are also connected in series between a pair of power supply terminals 5a and 5b. The sensor circuit 50 operates by applying a given voltage to the power supply terminals 5a and 5b, and generates a voltage difference between a pair of signal output terminals 5c and 5d according to the detected magnetic field. The signal output terminal 5c is a connection node between the sensor element 51 and the sensor element 52, and the signal output terminal 5d is a connection node between the sensor element 53 and the sensor element 54.

[0028] The signal output terminals 5 c and 5 d are respectively connected to the input terminals T1 and T2 of the sensor amplifier circuit 100 . That is, the difference voltage between a pair of output signals of the sensor circuit 50 is provided as an input to the sensor amplifier circuit 100 .

[0029] The sensor amplifier circuit 100 includes an output terminal T3, a differential amplifier circuit 110, a linear compensation circuit 150, and an output amplifier 190 in addition to input terminals T1 and T2. The sensor amplifier circuit 100 amplifies the output signal from the sensor circuit 50 received at the input terminals T1 and T2 using the differential amplifier circuit 110 and the output amplifier 190, and outputs the amplified signal from the output terminal T3. In addition, when amplification is performed in the differential amplifier circuit 110, the sensor amplifier circuit 100 compensates for nonlinear distortion in the sensor circuit 50 using the linear compensation circuit 150.

[0030] The differential amplifier circuit 110 is formed of a so-called current feedback instrumentation amplifier (CFIA), and includes amplifiers 111 to 113 , reference voltages V1 and V2 , a subtractor 115 , and resistors R1 and R2 .

[0031] Each of the amplifiers 111 to 113 is a transconductance type operational amplifier that outputs a current corresponding to the potential difference input to the inverting input terminal and the non-inverting input terminal from the output terminal. The inverting input terminal and the non-inverting input terminal of the input stage amplifier 111 are connected to the input terminals T1 and T2, respectively, and the output signal from the sensor circuit 50 is input. The output terminal of the amplifier 111 is connected to the inverting input terminal of the output stage amplifier 112 via the subtractor 115.

[0032] The reference voltage V1 is connected to the non-inverting input terminal of the amplifier 112. The amplifier 112 outputs a current corresponding to the differential voltage between the output signal from the amplifier 111 and the reference voltage V1 from the output terminal. In addition, there is a given impedance at the input terminal of the amplifier 112, so the current signal output from the amplifier 111 is converted into a voltage signal by the impedance and input to the amplifier 112. Resistors R1 and R2 connected in series are connected between the output terminal of the amplifier 112 and the ground potential. The current signal output from the amplifier 112 is converted into a voltage signal by the resistors R1 and R2 and provided to the output amplifier 190. The output amplifier 190 is an arbitrary amplifier circuit that amplifies the output signal from the differential amplifier circuit 110 and outputs it to an external device via the output terminal T3.

[0033] The connection node between the resistor R1 and the resistor R2 is connected to the inverting input terminal of the amplifier 113. The resistors R1 and R2 also function as voltage-dividing resistors, and the signal obtained by dividing the output signal from the amplifier 112 is input to the inverting input terminal of the amplifier 113. The reference voltage V2 is connected to the non-inverting input terminal of the amplifier 113. The amplifier 113 outputs a current corresponding to the difference voltage between the output signal of the amplifier 112 after the voltage division and the reference voltage V2 from the output terminal. The output terminal of the amplifier 113 is connected to the subtractor 115. The current feedback loop of the CFIA is formed by the amplifier 113.

[0034] The linear compensation circuit 150 includes a buffer 151, a plurality of current amplifier circuits (OTA) 161 to 16n, and comparison circuits 181 to 18n. In the following description, the current amplifier circuits 161 to 16n are collectively referred to as "current amplifier circuit 160", and the comparison circuits 181 to 18n are collectively referred to as "comparison circuit 180". In addition, the current amplifier circuits do not necessarily need to be multiple, and the current amplifier circuit may also be one.

[0035] The current amplifier circuits 161 to 16n are connected in parallel between the input terminal and the output terminal of the linear compensation circuit 150. The output signal from the differential amplifier circuit 110 is supplied to the inverting input terminals of the current amplifier circuits 161 to 16n via the buffer 151 and the corresponding comparison circuits 181 to 18n. In addition, the reference voltages VL1 to VLn are connected to the non-inverting input terminals of the current amplifier circuits 161 to 16n, respectively. The output terminals of the current amplifier circuits 161 to 16n are connected to the subtractor 115 as a current feedback loop in the differential amplifier circuit 110.

[0036] The output signal of each inverting terminal of the comparison circuits 181 to 18n is connected to the signal from the buffer 151. The reference voltages VC1 to VCn are connected to the non-inverting terminals of the comparison circuits 181 to 18n, respectively. If the output voltage of the differential amplifier circuit 110 exceeds the corresponding reference voltage, the comparison circuits 181 to 18n each output a given voltage. By setting the reference voltages VC1 to VC to different values, the compensation point in the linear compensation circuit 150 can be set as the output voltage of the differential amplifier circuit 110 increases.

[0037] If the output voltage of the corresponding comparison circuit exceeds the independently set reference voltage VL1-VLn, the current amplifier circuits 161-16n each output a given current. Through the combination of the comparison circuits 181-18n and the current amplifier circuits 161-16n, as the output voltage of the differential amplifier circuit 110 increases, as the output voltage of the linear compensation circuit 150 increases, the output current from the linear compensation circuit 150 increases in stages.

[0038] In addition, the reference voltages VL1 to VLn of the current amplifier circuits 161 to 16n are used to adjust the output timing of the output current at the compensation point determined by the comparison circuits 181 to 18n, but this is not necessary, and the reference voltages VL1 to VLn may also be set to zero.

[0039] In the differential amplifier circuit 110, if the output current from the linear compensation circuit 150 increases, the input current of the amplifier 112 decreases, and the output voltage also decreases accordingly. In the sensor amplifier circuit 100 of the first embodiment, the feedback signal of the linear compensation circuit 150 is not input to the input side of the amplifier 111 of the input stage, but is input to the current loop on the output side of the amplifier 111. That is, the compensation performed by the linear compensation circuit 150 is not compensation for switching the gain (i.e., the slope of the output signal) of the differential amplifier circuit 110, but compensation for providing an offset to the output signal. Therefore, it is possible to suppress a sharp change in the output signal at the compensation timing as in the case of switching the gain, so that the change in the output signal caused by the compensation can be made gentle, and the discontinuity of the output waveform can be reduced.

[0040] Since feedback control is used in compensation, even in a case where, for example, the sensor signal continuously increases and decreases at the compensation point, that is, Figure 1 Even when a signal such as a signal crossing the reference voltage VL1 is continuously input to the current amplifier circuit 161, the compensation operation can be continued without oscillation. Furthermore, since feedback is performed in the current feedback loop as the midpoint of the differential amplifier circuit, the influence on the response time can be reduced compared to the case of feedback to the input stage of the circuit.

[0041] (Description of linear compensation)

[0042] Next, use Figure 2 as well as Figure 3 The linear compensation in the sensor amplifier circuit 100 will be described. Figure 2 : is a diagram showing the simulation results of the error distortion of the sensor output signal with respect to the magnetic field with respect to the ideal straight line in the sensor circuit 50. Figure 3 FIG. 1 is a diagram showing the output voltage of the sensor amplifier circuit 100 with respect to the magnetic field when linear compensation is adopted.

[0043] Reference Figure 2 In addition to the proportional linear component, the output signal from the sensor circuit 50 may also contain a cubic function error distortion component as shown by the dotted line LN11 in relation to the change in the magnetic field. Therefore, when the output signal from the sensor circuit 50 is used directly without applying linear compensation, the error gradually increases as the magnitude (absolute value) of the magnetic field increases.

[0044] In the linear compensation circuit 150 in the first embodiment, as described above, whenever the output voltage of the differential amplifier circuit 110 reaches a given reference voltage set for each current amplifier circuit 160, a given compensation current is output from the corresponding current amplifier circuit, thereby applying an offset in the direction of decreasing the output voltage.

[0045] exist Figure 2 In the example, every time the magnetic field reaches m1, m2, and m3, an offset is applied in the direction where the error becomes smaller. By performing linear compensation, the linear error is approximately within ±0.02% over the entire detection range.

[0046] At this time, the ratio of the change in the interval from m1 to m2 (i.e., the slope) is the same as the slope of the dotted line LN11 in the same interval. Similarly, the slope in the interval from m2 to m3 is the same as the slope of the dotted line LN11 in the same interval. In other words, in the compensation performed by the linear compensation circuit 150, the gain does not change regardless of whether the compensation is performed or not. Therefore, compared with the compensation based on gain switching, it can be set to a smooth change.

[0047] picture Figure 3 In this way, the output voltage from the sensor amplifier circuit 100 behaves like the solid line LN20 relative to the ideal linear output (dashed line LN21). That is, if the magnetic field reaches m1, m2, and m3, that is, if the error between the output voltage (solid line LN20) and the linear output (dashed line LN21) becomes greater than a given error, the output voltage can be reduced by linear compensation. Figure 3In this way, the output voltage (solid line LN20) changes to track the ideal linear output (dashed line LN21).

[0048] In addition, in order to improve the detection accuracy of the sensor using linear compensation, it is necessary to set multiple compensation points to perform more precise compensation. However, in this case, it is necessary to increase the number of current amplifier circuits 160 in the linear compensation circuit 150, so the size of the circuit will increase, which may become a major factor hindering the miniaturization of the entire device. Therefore, the number of current amplifier circuits 160 can be appropriately selected in consideration of the required detection accuracy of the sensor and the allowable size of the sensor amplifier circuit 100.

[0049] Figure 4 is an equivalent model for calculating the transfer function of the sensor amplifier circuit 100. Figure 4 In the model, for ease of explanation, a current amplifier circuit 160 is provided in the linear compensation circuit 150. Figure 4 In the differential amplifier circuit 110, the transconductance of the amplifiers 111 to 113 is set to g. m , the transconductance of the current amplifier circuit 160 of the linear compensation circuit 150 is set to g mr In addition, the gain of the comparison circuit 180 of the linear compensation circuit 150 is set to Ac. Figure 4 In the model, the reference voltage of the current amplifier circuit 160 of the linear compensation circuit 150 and the reference voltages V1 and V2 of the amplifiers 112 and 113 of the differential amplifier circuit 110 are set to zero.

[0050] Figure 4 The transfer function in the model becomes as follows (1).

[0051] [Mathematical formula 1]

[0052]

[0053] In formula (1), (V in ·g m ) is the input voltage term from the sensor circuit 50, (V CO ·A C ·g mr ) becomes the compensation voltage term based on the linear compensation circuit 150. As shown in equation (1), the transconductance g of the current amplifier circuit 160 in the linear compensation circuit 150 is mr is included in the common term, so the actual transconductance g mr The influence of will also affect the input voltage term (ie, the gain G of the differential amplifier circuit 110) shown in equation (2) in .

[0054] [Mathematical formula 2]

[0055]

[0056] According to the above formula (2), in order to reduce the linear compensation circuit 150 to gain G in The influence of the differential amplifier circuit 110 is preferably m The transconductance g of the linear compensation circuit 150 is mr Set as small as possible (g mr < <g m ).

[0057] Figure 5 It shows that when using Figure 4 In the case of the model shown in FIG. 1 , when the compensation current output from the current amplifier circuit 160 is changed, the output voltage V out Relative to the input voltage V in The simulation results of the changes in Figure 5 In the case of line LN31, the compensation current output from the current amplifier circuit 160 is the smallest, and the compensation current output from the current amplifier circuit 160 increases toward line LN36.

[0058] like Figure 5 As shown, even if the compensation current output from the current amplifier circuit 160 changes, the output voltage V out Relative to the input voltage V in In other words, if the compensation current output from the current amplifier circuit 160 is increased, the output voltage V out Deviate in the downward direction.

[0059] In the first embodiment, whenever the magnitude of the detected magnetic field increases and reaches m1, m2, or m3, the compensation current output from the current amplifier circuit 160 increases, so conceptually the output voltage V out Become like Figure 5 However, as in Figure 2 As explained in the in It shows nonlinear behavior like a cubic function, so through feedback such as Figure 5 As shown, the output voltage V out The compensation current is decreased in stages, thereby improving linearity.

[0060] As described above, by adopting a structure in which the differential amplifier circuit 110 is formed of a current feedback instrument amplifier circuit (CFIA), and a linear compensation circuit 150 formed of a current amplifier circuit (OTA) is used to feed back a compensation current corresponding to the output voltage to a current feedback loop of the differential amplifier circuit 110, it is possible to improve the linearity of the output signal while ensuring high responsiveness compared to a voltage feedback compensation circuit.

[0061] In addition, the “amplifiers 111 , 112 , 113 ” in the first embodiment correspond to the “first amplifier”, “second amplifier”, and “third amplifier” in the present disclosure, respectively. The “resistors R1 , R2 ” in the first embodiment correspond to the “voltage-dividing resistor” in the present disclosure.

[0062] [Implementation Method 2]

[0063] In the second embodiment, a configuration in which a filter circuit is provided in the linear compensation circuit is described.

[0064] Figure 6 1 is a schematic diagram of a sensor system 10A using a sensor amplifier circuit 100A according to Embodiment 2. In the sensor amplifier circuit 100A, the linear compensation circuit 150 in Embodiment 1 is replaced with a linear compensation circuit 150A. The other structures in the sensor amplifier circuit 100A are the same as those of the sensor amplifier circuit 100, and the repeated description of the repeated elements will not be repeated.

[0065] Reference Figure 6 In the linear compensation circuit 150A, the non-inverting input terminals of the current amplifier circuits 161 to 16n are connected to low-pass filters (LPF) 171 to 17n, respectively. That is, the output voltage of each comparison circuit 181 to 18n is supplied to each current amplifier circuit 161 to 16n via the corresponding low-pass filter 171 to 17n. By configuring the low-pass filter, the change of the signal input to each current amplifier circuit 161 to 16n becomes gentle, so as Figure 7 As shown, the compensation current IL output from the current amplifier circuit 160 also changes more gently (solid line LN40 ) than when there is no low-pass filter (dashed line LN41 ).

[0066] With such a configuration, although the responsiveness of the feedback loop is slightly reduced, a sudden change in the compensation current can be suppressed, so that a change in the output voltage when the compensation current is added to each compensation point can be suppressed, and the linearity can be further improved.

[0067] In addition, Figure 6In the embodiment, a low-pass filter is connected to the inverting input terminal side of each current amplifier circuit 161 to 16n, but a low-pass filter may be provided at the output terminal side of each current amplifier circuit 161 to 16n instead. Alternatively, a common low-pass filter may be provided at the output terminal side of the current amplifier circuits 161 to 16n.

[0068] [Implementation method 3]

[0069] In the third embodiment, a configuration in which the reference voltage in each current amplifier circuit is deleted and a voltage dividing circuit is provided instead in the linear compensation circuit is described.

[0070] Figure 6 1 is a schematic diagram of a sensor system 10B using a sensor amplifier circuit 100B according to Embodiment 3. In the sensor amplifier circuit 100B, the linear compensation circuit 150 in Embodiment 1 is replaced with a linear compensation circuit 150B. The other structures of the sensor amplifier circuit 100B are the same as those of the sensor amplifier circuit 100, and the repeated description of the repeated elements will not be repeated.

[0071] Reference Figure 8 In the linear compensation circuit 150B, a voltage divider circuit is connected between the non-inverting input terminal of the current amplifier circuit 161-16n and the comparison circuit 181-18n. Each voltage divider circuit is composed of two resistors (resistors R11-R1n and resistors R21-R2n) connected in series. One end of each resistor R21-R2n is connected to the output terminal of the corresponding comparison circuit 181-18n, and the other end is connected to the ground potential via the corresponding resistor R11-R1n. The connection node between the resistor R21-R2n and the resistor R11-R1n is connected to the non-inverting input terminal of the corresponding current amplifier circuit 161-16n.

[0072] In the linear compensation circuit 150 of the first embodiment, independent reference voltages VL1 to VLn are provided for each current amplifier circuit 161 to 16n. However, if the number of current amplifier circuits increases, the number of reference voltages also increases, and thus the number of circuits for outputting reference voltages also increases. As a result, the area of ​​the IC substrate for forming the sensor amplifier circuit increases, and the overall device including the sensor amplifier circuit may also increase in size. On the other hand, when the reference voltage is reduced and fixed to 0V, the flexibility of the output current selection decreases, and the linearity of the output voltage may not be sufficiently improved.

[0073] In the linear compensation circuit 150B of the third embodiment, a voltage divider circuit composed of resistors is formed at the inverting input terminal of each current amplifier circuit 161 to 16n, so that the input voltage to each current amplifier circuit 161 to 16n can be independently adjusted with a small substrate area. As a result, the linearity of the output voltage can be improved while suppressing the enlargement of the sensor amplifier circuit.

[0074] In addition, the low-pass filter described in Embodiment 2 may be further arranged at the subsequent stage of the voltage dividing circuit.

[0075] [Way]

[0076] (Item 1) A sensor amplifier circuit according to one embodiment amplifies the output of a sensor circuit in which four sensor elements are bridge-connected. The sensor amplifier circuit comprises: a differential amplifier circuit that amplifies the differential voltage of a pair of output signals from the sensor circuit; and a compensation circuit that generates a compensation signal for compensating for the nonlinear distortion of the output voltage based on the output voltage of the differential amplifier circuit. The differential amplifier circuit is composed of a current feedback instrument amplifier circuit (CFIA). The compensation circuit includes at least one current amplifier circuit (OTA) configured to output a current corresponding to the output voltage, and outputs the sum of the output currents from the at least one current amplifier circuit as a compensation signal. The compensation signal from the compensation circuit is input to a current feedback loop in the current feedback instrument amplifier circuit.

[0077] (Item 2) In the sensor amplifier circuit described in Item 1, the compensation circuit further includes: a comparison circuit for setting a compensation point based on at least one current amplifier circuit according to the output voltage.

[0078] (Item 3) In the sensor amplifier circuit described in Item 2, the compensation circuit further includes: a filter circuit that filters the output of the comparison circuit and supplies the filter to the at least one current amplifier circuit.

[0079] (Item 4) In the sensor amplifier circuit described in Item 3, the filter circuit is a low-pass filter.

[0080] (Item 5) In the sensor amplifier circuit described in Item 4, the current compensation circuit includes a plurality of current amplifier circuits, and a filter circuit is provided for each of the plurality of current amplifier circuits.

[0081] (Item 6) In the sensor amplifier circuit described in any one of Items 2 to 4, the compensation circuit further includes: a voltage divider circuit that divides the output of the comparison circuit and supplies the voltage to the at least one current amplifier circuit.

[0082] (Item 7) In the sensor amplifier circuit described in Item 6, the compensation circuit includes a plurality of current amplifier circuits, and a comparison circuit is provided for each of the plurality of current amplifier circuits.

[0083] (Item 8) In the sensor amplifier circuit described in Items 1 to 7, the compensation circuit includes a first current amplifier circuit and a second current amplifier circuit. When the output voltage reaches a first threshold value, the first current amplifier circuit outputs a first compensation current. When the output voltage reaches a second threshold value greater than the first threshold value, the second current amplifier circuit outputs a second compensation current.

[0084] (Item 9) In the sensor amplifier circuit described in any one of Items 1 to 7, the current feedback instrument amplifier circuit includes a first amplifier, a second amplifier, and a third amplifier, each of which is constituted by a current amplifier circuit (OTA), a subtractor, and a voltage divider resistor. The first amplifier, the second amplifier, and the third amplifier each include an inverting input terminal, a non-inverting input terminal, and an output terminal. A pair of output signals from the sensor circuit includes a first signal and a second signal. The first signal is input to the inverting input terminal of the first amplifier. The second signal is input to the non-inverting input terminal of the first amplifier. The output terminal of the first amplifier is connected to the inverting input terminal of the second amplifier via the subtractor. The non-inverting input terminal of the second amplifier is connected to a first reference voltage. The output terminal of the second amplifier is connected to the inverting input terminal of the third amplifier via a voltage divider resistor. The non-inverting input terminal of the third amplifier is connected to a second reference voltage. The output terminal of the third amplifier is connected to the subtractor. The output of the compensation circuit is connected to the subtractor.

[0085] The embodiments disclosed this time should be considered as illustrative in all aspects and not restrictive. The scope of the present invention is indicated by the claims rather than the description of the embodiments described above, and is intended to include all changes within the meaning and scope equivalent to the claims.

[0086] Description of Reference Numerals

[0087] 5a, 5b: power terminals;

[0088] 5c, 5d: signal output terminals;

[0089] 10, 10A, 10B: sensor system;

[0090] 50: sensor circuit;

[0091] 51, 52, 53, 54: sensor elements;

[0092] 100, 100A, 100B: sensor amplification circuit;

[0093] 110: differential amplifier circuit;

[0094] 111, 112, 113: amplifier;

[0095] 115: Subtractor;

[0096] 150, 150A, 150B: linear compensation circuit;

[0097] 151: Buffer;

[0098] 160~161n: current amplifier circuit;

[0099] 171~17n: filter circuit;

[0100] 181~18n: comparison circuit;

[0101] 190: output amplifier;

[0102] R1, R2, R11~R1n, R21~R2n: resistance;

[0103] T1, T2: input terminals;

[0104] T3: output terminal;

[0105] V1, V2, VC0~VCn, VL0~VLn: reference voltage.

Claims

1. A sensor amplifier circuit for amplifying the output of a sensor circuit in which four sensor elements are bridge-connected, wherein: The sensor amplification circuit has: a differential amplifier circuit for amplifying a differential voltage of a pair of output signals from the sensor circuit; as well as a compensation circuit that generates a compensation signal for compensating for nonlinear distortion of the output voltage based on the output voltage of the differential amplifier circuit, The differential amplifier circuit is composed of a current feedback instrument amplifier circuit (Current Feedback Instrumentation Amplifier: CFIA). The compensation circuit includes at least one current amplifier circuit (Operational Transconductance Amplifier: OTA) configured to output a current corresponding to the output voltage, and outputs a sum of output currents from the at least one current amplifier circuit as the compensation signal. The compensation signal from the compensation circuit is input to a current feedback loop in the current feedback instrumentation amplifier circuit.

2. The sensor amplifier circuit according to claim 1, wherein: The compensation circuit further includes: a comparison circuit, which is used to set a compensation point based on the at least one current amplification circuit according to the output voltage.

3. The sensor amplifier circuit according to claim 2, wherein: The compensation circuit further includes: a filter circuit that filters the output of the comparison circuit and supplies the filtered output to the at least one current amplification circuit.

4. The sensor amplification circuit according to claim 3, wherein: The filter circuit is a low pass filter.

5. The sensor amplification circuit according to claim 4, wherein: The compensation circuit includes a plurality of current amplifying circuits. The filter circuit is provided for each of the plurality of current amplifier circuits.

6. The sensor amplifier circuit according to any one of claims 2 to 4, wherein: The compensation circuit further includes: a voltage divider circuit that divides the output of the comparison circuit and supplies the voltage to the at least one current amplification circuit.

7. The sensor amplification circuit according to claim 6, wherein: The compensation circuit includes a plurality of current amplifying circuits. The voltage dividing circuit is provided for each of the plurality of current amplifying circuits.

8. The sensor amplifier circuit according to any one of claims 1 to 7, wherein: The compensation circuit includes a first current amplifier circuit and a second current amplifier circuit. If the output voltage reaches the first threshold, the first current amplifier circuit outputs a first compensation current. When the output voltage reaches a second threshold value greater than the first threshold value, the second current amplifier circuit outputs a second compensation current.

9. The sensor amplifier circuit according to any one of claims 1 to 7, wherein: The current feedback instrument amplifier circuit comprises: The first amplifier, the second amplifier and the third amplifier are respectively constituted by a current amplifier circuit (OTA); a subtractor; and Voltage divider resistor, The first amplifier, the second amplifier, and the third amplifier each include an inverting input terminal, a non-inverting input terminal, and an output terminal. A pair of output signals from the sensor circuit includes a first signal and a second signal, The first signal is input to the inverting input terminal of the first amplifier. The second signal is input to the non-inverting input terminal of the first amplifier. The output terminal of the first amplifier is connected to the inverting input terminal of the second amplifier via the subtractor. A first reference voltage is connected to the non-inverting input terminal of the second amplifier. The output terminal of the second amplifier is connected to the inverting input terminal of the third amplifier via the voltage dividing resistor. A second reference voltage is connected to the non-inverting input terminal of the third amplifier. The output terminal of the third amplifier is connected to the subtractor. The output of the compensation circuit is connected to the subtractor.

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