Detection circuit

Abstract

To provide a detection circuit of a sensor capable of automatically correcting the offset or gain of an output signal.SOLUTION: A detection circuit 100 of a torque sensor according to the present invention includes: a pickup coil 110 that, when a signal of frequency F1 is applied, outputs a pair of analog detection signals V1, V2 differing in amplitude depending on the torque of the object being measured; and a torque detection unit 160 that receives the pair of analog signals V1, V2. The torque detection unit 160 includes an A / D converter 162 that converts the analog detection signal V1 of the pair to a digital detection signal, a signal processing unit 164 that generates an output signal Vout representing the torque of the object being measured, on the basis of the converted digital detection signal, and a memory 166 that stores correction data. The signal processing unit 164 corrects the offset and gain of the output signal Vout by using the correction data.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a detection circuit of a sensor, and particularly to a detection circuit of a torque sensor and temperature compensation of the detection circuit.

Background Art

[0002] Torque is the magnitude of the force acting when an object rotates with respect to a fixed axis of rotation, and is a torsional moment (turning force, twisting force). Torque sensors for detecting such torque include magnetostrictive, strain gauge, piezoelectric, optical, spring, and capacitance types. For example, a magnetostrictive torque sensor uses a magnetostrictive material to detect torque. Measurement of rotational torque is performed non-contact by exciting the magnetostrictive material of the shaft from a coil on the fixed side and measuring the change in permeability.

[0003] For example, FIG. 1 shows a detection circuit of a magnetostrictive torque sensor disclosed in Patent Document 1. As shown in the figure, on the outer periphery of a torque transmission shaft 1 made of a magnetostrictive material, a pair of magnetic anisotropic portions 2, 2 that are inclined in opposite directions at an angle of about ±45 degrees with respect to the axial direction of the transmission shaft 1 are formed. Around the magnetic anisotropic portions 2, 2, a pair of detection coils 3, 3 and a single excitation coil 4 for exciting the detection coils 3, 3 are provided, and the excitation coil 4 is connected to an AC power source 5. Detection signals V1, V2 with different amplitudes corresponding to the change in permeability of the magnetic anisotropic portions 2, 2 based on the application of torque to the shaft 1 are generated in the detection coils 3, 3.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] FIG. 2 shows a conventional example of a detection circuit for a magnetostrictive torque sensor mounted on an electric assist bicycle. As shown in the figure, the detection circuit 10 includes a pickup coil (torque sensor element) 20 for picking up torque such as an electric shaft, an external variable oscillator 30 connected to the pickup coil 20, rectifier circuits 40-1 and 40-2 connected to nodes N1 and N2 of the pickup coil 20, low-pass filters (LPFs) 50-1 and 50-2 connected to the rectifier circuits 40-1 and 40-2, a differential amplifier 60 connected to the filters 50-1 and 50-2, a 2.5V reference voltage generator 70, and a 5V power supply 80. These elements are mounted on a circuit board.

[0006] In response to the application of a constant frequency F1 to the pickup coil 20 by the external variable oscillator 30, detection signals V1 and V2 having amplitude voltages proportional to the torque are generated at nodes N1 and N2 of the pickup coil 20, respectively. The detection signals V1 and V2 are input to the differential input terminals of the differential amplifier circuit 60 through the rectifier circuits 40-1 and 40-2 and the LPFs 50-1 and 50-2, and the differential amplifier circuit 60 outputs an analog output signal Vout obtained by amplifying the difference between the detection signals V1 and V2. The 2.5V reference voltage generator 70 converts the voltage supplied from the 5V power supply 80 to 2.5V and supplies this as an offset voltage to the differential amplifier circuit 60, and the differential amplifier circuit 60 generates an analog output signal Vout representing torque centered around the offset voltage of 2.5V.

[0007] In such a detection circuit 10, calibration of the output signal Vout, that is, adjustment of the offset and gain (sensitivity) of the output signal Vout requires manual adjustment of the trim resistors on the circuit board one by one, and the work is complicated and time-consuming.

[0008] An object of the present invention is to solve such a conventional problem and provide a detection circuit for a sensor capable of automatically correcting the offset and gain of an output signal. A further object of the present invention is to provide a detection circuit for a sensor having a temperature compensation function.

Means for Solving the Problem

[0009] The detection circuit of the sensor according to the present invention includes a sensing means that outputs a pair of analog detection signals with different amplitudes according to the state of the object to be measured when a signal of a certain frequency is applied, and a detection means connected to the sensing means. The detection means includes an A / D converter that converts the pair of analog detection signals into digital detection signals, a signal processing unit that generates an output signal representing the state of the object to be measured based on the converted digital detection signals, and a memory that stores correction data. The signal processing unit corrects the offset and gain of the output signal using the correction data read from the memory.

[0010] In one aspect, the signal processing unit further performs temperature compensation of the output signal based on the detection result of the temperature sensor. In one aspect, the signal processing unit performs the following process. Vout = A·(1 + ΔT·T cg )·(V1 - V2)+(V offset + ΔT·T co ) Vout: Output signal, A: Gain, V offset : Offset voltage, T cg : Temperature coefficient for gain, T co : Temperature coefficient for offset, ΔT: Temperature detected by the temperature sensor In one aspect, the detection means further includes a D / A converter that converts the output signal into a digital signal. In one aspect, the detection means further includes an output switching unit for outputting the output signal as an analog output or a digital output. In one aspect, the sensing means further includes a rectifying circuit and an LPF, and the pair of analog detection signals are converted into a DC voltage via the rectifying circuit and the LPF. In one aspect, the sensing means further includes a level conversion circuit that converts the DC voltage to a level that can be input to the detection means. In one aspect, the sensing means includes a pickup coil, and the pickup coil includes a series connection of a coil and a resistor and includes a series-parallel circuit. A constant frequency signal is applied to the series-parallel circuit, and an analog detection signal corresponding to torque is output from the connection node of one coil and resistor and the connection node of the other coil and resistor. Further, in one aspect, the detection circuit includes an oscillation circuit that generates a constant frequency signal, and the oscillation circuit includes an amplitude control circuit that controls the amplitude of the oscillation signal according to a temperature change. In one aspect, the amplitude control circuit changes the amplitude so as to cancel the temperature characteristics of the sensing means. In one aspect, the oscillation circuit includes a Wien bridge oscillation circuit, and the Wien bridge oscillation circuit includes a temperature-sensitive element such as a thermistor for temperature compensation in the negative feedback of the operational amplifier.

Advantages of the Invention

[0011] According to the present invention, it is possible to automatically correct or adjust the offset and gain (sensitivity) of the output signal. Further, temperature adjustment and non-linearity correction can be performed, and the accuracy as a sensor can be improved. Further, unlike the prior art, there is no need to manually adjust the trim resistor on the circuit board, that is, the offset and gain of the output signal can be automatically corrected in a product in which a circuit board including a sensor element is mounted. Further, by controlling the amplitude of the oscillation signal according to a temperature change, temperature compensation of the detection circuit can be performed.

Brief Description of the Drawings

[0012]

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[0013] The detection circuit of the sensor according to the present invention is not particularly limited, but is applied to, for example, a detection circuit of a torque sensor, and the detection circuit of the torque sensor is mounted on, for example, an electric assist bicycle or the like. EXAMPLES

[0014] Next, embodiments of the present invention will be described in detail. FIG. 3 is a diagram showing the configuration of a detection circuit of a torque sensor according to a first embodiment of the present invention. The detection circuit 100 of the torque sensor in this embodiment includes a pickup coil 110 arranged to be close to or coupled to a measurement object to which torque is applied, such as a shaft or a transmission shaft, an oscillation circuit 120 that applies a signal of a constant frequency F1 to the pickup coil 110, a pair of rectifier circuits 130-1 and 130-2 connected to the pickup coil 110, a pair of low-pass filters (LPFs) 140-1 and 140-2 respectively connected to the rectifier circuits 130-1 and 130-2, a pair of level conversion circuits 150-1 and 150-2 respectively connected to the LPFs 140-1 and 140-2, and a torque detection unit 160 connected to the level conversion circuits 150-1 and 150-2.

[0015] The pickup coil 110 is a torque sensing element for sensing the torque of the measurement object. In this example, it includes resistors R1, R2, R3, R4 and coils L1, L2. The serially connected coils L1, resistor R1, R2 and the serially connected coils L2, resistor R3, R4 are connected in parallel. Resistors R1 and R3 are internal resistances, and resistors R2 and R4 are resistors for detecting the voltage difference of the coils caused by the expansion and contraction of the torque. A signal of a constant frequency F1 is applied from the oscillation circuit 120 to the connection part Na of the coils L1 and L2 and the connection part Nb of the resistors R2 and R4. In response to the excitation of the signal of the frequency F1, detection signals V1 and V2 having amplitude voltages proportional to the torque are generated at the connection node N1 of the resistors R3 and R4 and the connection node N2 of the resistors R1 and R2, respectively. The detection signals V1 and V2 are in the same phase but are signals with the same frequency and different amplitudes according to the torque. For example, when the torque applied to the measurement object is relatively large, the amplitude difference between the detection signals V1 and V2 increases proportionally, and when the torque is small, the amplitude difference between the detection signals V1 and V2 decreases proportionally. Alternatively, the relationship between the torque and the amplitude difference may be opposite.

[0016] The rectifier circuits 130-1 and 130-2 receive the detection signals V1 and V2 respectively and rectify the detection signals V1 and V2. The rectifier circuits 130-1 and 130-2 include, for example, a diode bridge circuit and a capacitor, full-wave rectify the input detection signals V1 and V2, and then smooth the full-wave rectified signals.

[0017] The LPFs 140-1 and 140-2 remove high-frequency noises such as ripple included in the detection signals V1 and V2 output from the rectifier circuits 130-1 and 130-2, and output the detection signals V1 and V2 with the noises removed to the level conversion circuits 150-1 and 150-2.

[0018] The level conversion circuits 150-1 and 150-2 adjust the voltage levels of the detection signals V1 and V2 received from the LPFs 140-1 and 140-2. Specifically, the DC components of the detection signals V1 and V2 are increased or decreased to a level that can be input to the torque detection unit 160 that executes digital arithmetic processing.

[0019] The torque detection unit 160 receives the analog detection signals V1 and V2 from the level conversion circuits 150-1 and 150-2, executes digital arithmetic processing internally, and outputs an analog output signal Vout with the offset and gain automatically corrected. Also, when the detection circuit 100 includes a temperature sensor, an analog output signal Vout compensated for temperature based on the detection result of the temperature sensor is output.

[0020] The torque detection unit 160 includes an A / D converter 162 that converts the analog detection signals V1 and V2 received from the level conversion circuits 150-1 and 150-2 into digital detection signals V1 and V2, a signal processing unit 164 that performs arithmetic processing on the digital detection signals V1 and V2 output from the A / D converter 162 to calculate torque and correct offsets and gains, a memory 166 that stores correction data for correcting offsets and gains, and a D / A converter 168 that converts the digital output signal Vout output from the signal processing unit 164 into an analog signal. The digital output signal Vout is a signal representing torque with offsets and gains corrected, and the D / A converter 168 outputs an analog output signal Vout corresponding to the digital output signal Vout to the outside from the output terminal.

[0021] The A / D converter 162 digitally converts the analog detection signals V1 and V2 respectively, and provides the converted digital detection signals V1 and V2 to the signal processing unit 164. The signal processing unit 164 calculates, by digital arithmetic, the torque of the object to be measured sensed by the pickup coil 110 based on the digital detection signals V1 and V2. As described above, the amplitude difference between the detection signals V1 and V2 is proportional to the torque applied to the object to be measured, and the signal processing unit 164 calculates the torque based on the amplitude difference.

[0022] Furthermore, the signal processing unit 164 automatically corrects or adjusts the offset and gain of the output signal Vout. There are variations among individual devices of the torque sensor and its detection circuit, and due to these variations, the zero point and gain of the output signal Vout vary from device to device. In order to correct such variations, it is necessary to appropriately correct the output signal Vout. The memory 166 stores correction data for correcting offsets and gains, and the signal processing unit 164 corrects the offset and gain of the output signal Vout based on the correction data read from the memory 166. When the detection circuit 100 includes a temperature sensor, the signal processing unit 164 performs temperature compensation of the output signal Vout based on the temperature detected by the temperature sensor.

[0023] In one aspect, the torque detection unit 160 includes a DSP (Digital Signal Processor) as an IC for digital processing. The DSP includes an A / D converter 162, a signal processing unit 164, a memory 166 (such as an EEPROM or a flash memory, etc.), a D / A converter 168, a controller, and the like. This controller controls arithmetic processing for calculating torque and correcting offsets and gains. For example, when calculating torque from detection signals V1 and V2, it reads correction data for offsets and gains from the memory 166 and corrects the offsets and gains of the output signal Vout using the read correction data. The correction data is generated, for example, using calibration data prepared in advance during calibration performed at the time of product shipment, and the generated correction data is stored in the memory 166.

[0024] The signal processing unit 164 calculates a digital output signal Vout with corrected offsets and gains and temperature compensation, for example, according to the following arithmetic expression. Vout = A·(1 + ΔT·T cg )·(V1 - V2)+(V offset + ΔT·T co ) A: Gain V offset : Offset voltage T cg : Temperature coefficient for gain T co : Temperature coefficient for offset ΔT: Temperature detected by the temperature sensor

[0025] A (Gain), V offset (Offset voltage), T cg (Temperature coefficient for gain), T co(Temperature coefficient for offset) is stored in the memory 166 as correction data generated during calibration. When calculating the output signal Vout from the detection signals V1 and V2 received from the pickup coil 110 during torque measurement, the signal processing unit 164 automatically corrects the output signal Vout using the correction data read from the memory 166.

[0026] The D / A converter 168 converts the digital output signal Vout into an analog output signal Vout. The analog output signal Vout converted by the D / A converter 168 is output to the outside through the output terminal.

[0027] Next, the operation of the detection circuit 100 of the torque sensor according to this embodiment will be described. An AC signal with a constant frequency F1 is applied to the pickup coil (torque sensing element) 110. The amplitude of this AC signal is proportional to the power supply voltage level. The pickup coil 110 is excited by the AC signal, and detection signals V1 and V2 having amplitudes proportional to the torque applied to the object to be measured are generated at nodes N1 and N2. The detection signals V1 and V2 are converted into DC voltages proportional to the amplitude through the rectifier circuits 130-1, 130-2, LPFs 140-1, 140-2, and then converted into DC voltage levels that can be input to the general-purpose IC of the torque detection unit 16 through the level conversion circuits 150-1, 150-2, and input to the torque detection unit 160.

[0028] In the torque detection unit 160, the analog detection signals V1 and V2 are converted into digital detection signals V1 and V2 via the A / D converter 162, and a digital output signal Vout is generated based on the digital detection signals V1 and V2. The digital output signal Vout is corrected for offset and gain (sensitivity) including temperature compensation, and further the non-linearity is adjusted. The digital output signal Vout is converted into an analog output signal Vout by the D / A converter 168 and output to the outside from the output terminal.

[0029] According to this embodiment, when calculating the digital output signal Vout from the analog detection signals V1 and V2 received from the pickup coil (coil sensing element) 110, the offset and gain of the output signal Vout are automatically corrected based on the correction data stored in the memory 166. Therefore, there is no need to manually adjust the trimming resistors as in the prior art, and the work efficiency can be improved.

[0030] Next, a second embodiment of the present invention will be described. FIG. 4 shows the configuration of the detection circuit 100A of the torque sensor according to the second embodiment, and the same components as those in FIG. 3 are denoted by the same reference numerals. In this embodiment, the torque detection unit 160A includes an output unit 170 for outputting the digital output signal Vout in digital form instead of the D / A converter 168 of the first embodiment.

[0031] The output unit 170 can correspond to a synchronous serial communication interface that communicates data in synchronization with a clock of an arbitrary communication standard, for example, I 2 C (Inter-Integrated Circuit) or SPI (Serial Peripheral Interface). The output unit 170 includes a buffer for temporarily storing the digital output signal Vout generated by the signal processing unit 164, a register for parallel / serial conversion, etc. For example, the output signal Vout may be output in synchronization with a serial clock signal supplied from the outside.

[0032] According to this embodiment, a digital output signal Vout with corrected offset and gain can be provided.

[0033] Next, a third embodiment of the present invention will be described. FIG. 5 shows the configuration of the detection circuit 100B of the torque sensor according to the third embodiment, and the same components as those in FIGS. 3 and 4 are denoted by the same reference numerals. In this embodiment, the torque detection unit 160B includes the D / A converter 168 shown in the first embodiment, the output unit 170 shown in the second embodiment, and an output switching unit 172 for switching between the analog output signal Vout and the digital output signal Vout.

[0034] The output switching unit 172 selects the analog output signal Vout from the D / A converter 168 or the digital output signal Vout from the output unit 170 in response to a manual operation such as a dip switch or in response to a switching control signal from a controller (not shown), and outputs the selected output signal Vout from an external terminal. The external terminals include, for example, a GND terminal, a Vcc terminal, an analog output terminal, and a digital output terminal.

[0035] According to this embodiment, the analog output signal Vout or the digital output signal Vout can be selectively output according to the application.

[0036] Next, a configuration example in which the detection circuit of the torque sensor of this embodiment is applied to an electric assist bicycle is shown in FIG. 6. The electric assist bicycle 200 includes a shaft 210 that receives power by stepping on a pedal, a detection circuit 100 / 100A / 100B of a torque sensor that detects the torque of the shaft, a controller 220, a drive circuit 230, a battery 240, a motor 250, and a wheel 260.

[0037] The shaft 210 transmits the power stepped on by the passenger to the wheels 260, and the motor 250 uses the electric power from the battery 240 to rotate the wheels 260 so as to assist the power. The detection circuits 100 / 100A / 100B detect the torque applied to the shaft 210, and an output signal Vout representing the detected torque is provided to the controller 220. The controller 220 controls the drive circuit 230 to rotate the wheels 260 with power corresponding to the torque applied to the shaft 210 based on the output signal Vout.

[0038] Next, a fourth embodiment of the present invention will be described. The fourth embodiment relates to a temperature correction method for a detection circuit of a sensor, and enables appropriate correction of the temperature characteristics of sensitivity (gain) without incurring a large cost for temperature correction during mass production.

[0039] The temperature compensation of the detection circuit of the sensor is performed, for example, by actually applying a load (torque) in a stable constant temperature bath. Since there are variations in the pickup coils (coil sensing elements), they are exposed to a specified temperature in the constant temperature bath, and when the overall temperature is stable, a load (torque) of a certain level or more is applied, and correction data for offset and sensitivity (gain) is written to the memory 166 so as to obtain an ideal output.

[0040] However, applying torque in a constant temperature bath has problems such as the jig for implementing it becoming large, and further cost due to the complexity of the system for performing more at once, resulting in poor cost effectiveness.

[0041] In the fourth embodiment, the amplitude of the AC signal (sine wave) of the oscillation circuit is made variable by the resistance change of a temperature-sensitive element such as a thermistor, thereby performing correction of sensitivity (gain), suppressing errors, and avoiding the need to apply a load (torque) in a constant temperature bath.

[0042] FIG. 7 is a diagram showing an example of a Wien bridge oscillator circuit according to a fourth embodiment of the present invention, and this Wien bridge oscillator circuit is replaced with the oscillator circuits 120 of the detection circuits 100, 100A, and 100B in FIGS. 3 to 5. The Wien bridge oscillator circuit 300 is configured using an amplifier such as an operational amplifier and a bridge circuit formed by an RC series circuit and an RC parallel circuit. The RC circuit provides a phase difference of 0 degrees and a gain of 1 at a specific frequency, and under this condition, oscillation is maintained and a stable AC signal (sine wave) is generated.

[0043] As shown in FIG. 7, the Wien bridge oscillator circuit 300 includes an operational amplifier 310, resistors R1, R2, R3, R4, R5, capacitors C1, C2, and diodes D1, D2. Resistors R1 and capacitor C1 are connected in series in the feedback path between the non-inverting input terminal (+) and the output terminal OUT of the operational amplifier 310, and resistors R2 and capacitor C2 are connected in parallel between the non-inverting input terminal (+) and GND. Also, a resistor R4 and an amplitude limiting circuit 320 are connected in parallel with the resistor R4 in the feedback path between the inverting input terminal (-) and the output terminal OUT of the operational amplifier 310, and a resistor R3 is connected between the inverting input terminal (-) and GND. The amplitude limiting circuit 320 includes a resistor R5 and diodes D1, D2 connected in series with the resistor R5, and the diodes D1, D2 are connected in parallel with each other such that their polarities are reversed. Diode D1 allows current to flow from the output terminal OUT to GND, and diode D2 allows current to flow from GND to the output terminal OUT, and a sine wave oscillation signal is generated at the output terminal OUT.

[0044] In the Wien bridge oscillator circuit 300 according to this embodiment, the amplitude limiting circuit 320 is a circuit element added to vary the amplitude of the generated sine wave. Since the amplitude limiting circuit 320 has a resistor R5 connected in parallel with the resistor R4, the combined resistance of the feedback path between the inverting input terminal (-) and the output terminal OUT becomes smaller than when only the resistor R4 is present, reducing the voltage drop in the feedback path. Thereby, the amplitude limiting circuit 320 can change the amplitude of the sine wave according to the difference in the value of the resistor R5.

[0045] FIG. 8 is a graph illustrating the relationship between the value of resistor R5 and the amplitude (peak voltage Vpp) of the sine wave. In this illustration, as the value of resistor R5 increases, the amplitude Vpp of the sine wave increases, and the relationship between resistor R5 and amplitude Vpp is generally linear. By using a temperature-sensitive element such as a PTC thermistor (a thermistor with positive temperature characteristics) or an NTC thermistor (a thermistor with negative temperature characteristics) for resistor R5, the slope of amplitude Vpp can be changed. An NTC thermistor is, for example, an oxide semiconductor ceramic containing components such as manganese, nickel, cobalt, etc., and a PTC thermistor is, for example, a semiconductor ceramic such as barium titanate (BaTiO 3 ) etc.

[0046] FIG. 9 is a graph illustrating the change in the amplitude of the oscillation signal (sine wave) with respect to temperature. The solid line shows the temperature characteristics when using a general resistor, the dotted line shows the temperature characteristics when using NTC thermistor A, and the dashed line shows the temperature characteristics when using NTC thermistor B. When using a general resistor, the amplitude Vpp of the oscillation signal generally decreases linearly as the temperature increases. On the other hand, when using NTC thermistors A and B, depending on the characteristics of the thermistors, the amplitude Vpp of the oscillation signal changes from decreasing to increasing at an inflection point around 25 degrees. Also, in the case of NTC thermistor A, the degree of increase in amplitude Vpp is larger than that of NTC thermistor B. The rate of change of amplitude Vpp with respect to temperature can be adjusted by resistor R5, and the amplitude Vpp of the oscillation signal can be changed so as to cancel out the temperature characteristics of the torque sensing element itself.

[0047] In this way, by controlling the amplitude of the AC signal of the Wien bridge oscillator circuit, an AC signal with a temperature characteristic opposite to that of the torque sensing element's temperature sensitivity (gain) is generated so as to cancel it out, thereby enabling temperature compensation of the torque sensor element.

[0048] Note that the configuration of the amplitude limiting circuit 320 shown in FIG. 7 is an example, and the present invention is not limited thereto. The configuration of the temperature-sensitive element formed between the output terminal OUT and the inverting input terminal (-) is arbitrary. In short, any configuration that can control the resistance of the feedback path in accordance with temperature changes is acceptable.

[0049] In the above description, the detection circuit of the torque sensor has been exemplified. However, the present invention is not limited thereto. In addition to the torque sensor, the detection circuit can also be applied to sensors that use the change in the amplitude of a frequency signal as a detection means, such as sensors that detect vibration or ultrasonic waves. Further, it can also be applied to an oscillation circuit (such as a twin-T oscillation circuit).

[0050] As described above, the preferred embodiments of the present invention have been described in detail. However, the present invention is not limited to specific embodiments, and various modifications and changes are possible within the scope of the gist of the invention described in the claims.

Explanation of Reference Numerals

[0051] 100, 100A, 100B: Detection circuit of torque sensor 110: Pickup coil 120: Oscillation circuit 130-1, 130-2: Rectifier circuit 140-1, 140-2: LPF 150-1, 150-2: Level conversion circuit 160: Torque detection unit 162: A / D converter 164: Signal processing unit 166: Memory 168: D / A converter 170: Output unit 172: Output switching unit 300: Wien bridge oscillation circuit 310: Operational amplifier 320: Amplitude limiting circuit

Claims

1. A detection circuit for a sensor, comprising: a sensing means for outputting a pair of analog detection signals having different amplitudes according to the state of the object to be measured when a signal of a constant frequency is applied; detecting means connected to said sensing means; the detection means includes an A / D converter that converts the pair of analog detection signals into digital detection signals, a signal processing unit that generates an output signal representing a state of the object to be measured based on the converted digital detection signals, and a memory that stores correction data; The signal processing unit corrects the offset and gain of the output signal using the correction data read from the memory.

2. The detection circuit according to claim 1 , wherein the signal processing unit further performs temperature compensation of the output signal based on a detection result of a temperature sensor.

3. The detection circuit according to claim 2 , wherein the signal processing unit performs the following processes. Vout=A・(1+ΔT・T ｃｇ )・(V1-V2)+(V ｏｆｆｓｅｔ +ΔT・T ｃｏ ) Vout: Output signal A: Gain V ｏｆｆｓｅｔ : offset voltage T ｃｇ : Temperature coefficient for gain T ｃｏ : Temperature coefficient for offset ΔT: Temperature detected by the temperature sensor

4. 2. The detection circuit of claim 1, wherein said detection means further comprises a D / A converter for converting said output signal into a digital signal.

5. 2. The detection circuit according to claim 1, wherein said detection means further comprises an output switching section for outputting said output signal as an analog signal or a digital signal.

6. 2. The detection circuit according to claim 1, wherein the sensing means further includes a rectifier circuit and a LPF, and the pair of analog detection signals are converted into a DC voltage through the rectifier circuit and the LPF.

7. 6. The detection circuit of claim 5, wherein said sensing means further includes a level conversion circuit for converting said DC voltage to a level that can be input to said detection means.

8. 4. The detection circuit according to claim 1 or 3, wherein the sensing means includes a pickup coil, the pickup coil including a series-parallel circuit in which a coil and a resistor are connected in series, a constant frequency signal is applied to the series-parallel circuit, and an analog detection signal corresponding to the torque is output from a connection node between one coil and the resistor and a connection node between the other coil and the resistor.

9. 2. The detection circuit according to claim 1, further comprising an oscillation circuit for generating an oscillation signal, the oscillation circuit including an amplitude limiting circuit for varying the amplitude of the oscillation signal in response to a temperature change.

10. 10. The detection circuit of claim 9, wherein the amplitude limiting circuit varies the amplitude to counteract a temperature characteristic of the sensing means.

11. The detection circuit according to claim 10 , wherein the oscillator circuit includes a Wien bridge oscillator circuit, the Wien bridge oscillator circuit including the amplitude limiting circuit in a negative feedback of an operational amplifier.

12. 12. The detection circuit of claim 11, wherein the amplitude limiting circuit includes a thermistor connected in parallel with a resistor connected between the inverting input terminal and the output terminal of an operational amplifier.

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