Physical quantity measuring device

Abstract

The present invention provides a physical quantity measuring device comprising: an element having a bridge resistor that outputs an analog signal indicating a physical quantity to be measured in response to the flow of a drive current; an AD converter that converts the analog signal output from the element into a digital signal; a current mirror circuit that duplicates the drive current flowing through the element as a duplicate current; and a generation circuit that generates a reference voltage for output to the AD converter by converting the duplicate current into a current-voltage.

Description

Technical Field

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[0001] The present invention relates to a physical quantity measuring device, a reference voltage generating device, and a sensor.

Background Art

[0002] Patent Document 1 describes "a magnetic sensor that AD-converts a Hall electromotive force signal detected by a Hall element driven at a constant voltage using a reference voltage ADVR generated by a replica Hall element." Patent Document 2 describes "a magnetic detection device that removes the offset voltage of a Hall element and the offset voltage of an amplifier that amplifies the output of the Hall element." [Prior Art Documents] [Patent Documents] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-99089 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-283503

Summary of the Invention

Problems to be Solved by the Invention

[0003] In a sensor element using a bridge circuit, it is desired to reduce the chip size while suppressing the influence of the temperature characteristics of the resistors constituting the bridge circuit and the influence of the offset due to variations in the performance between the resistors.

Means for Solving the Problems

[0004] In a first aspect of the present invention, there is provided a physical quantity measuring device including an element having bridge resistors and outputting an analog signal indicating a physical quantity to be measured in response to the flow of a drive current, an AD converter that converts the analog signal output from the element into a digital signal, a current mirror circuit that replicates the drive current flowing through the element as a replicated current, and a generation circuit that generates a reference voltage for output to the AD converter by converting the replicated current into a current-voltage conversion.

[0005] In the physical quantity measuring device, the element is a Hall element that is driven by the drive current and outputs an electromotive force generated in response to the surrounding magnetic field as the analog signal.

[0006] In any of the physical quantity measuring devices, the Hall element may have a first terminal pair to which the drive current is input or the analog signal is output, and a second terminal pair to which the analog signal is output when the drive current is input to the first terminal pair, and to which the drive current is input when the analog signal is output from the first terminal pair. Any of the physical quantity measuring devices may further include a switch circuit that switches between the terminal pair through which the drive current flows and the terminal pair that outputs the analog signal between the first terminal pair and the second terminal pair.

[0007] Any of the physical quantity measuring devices may further include a power supply unit that controls the drive current supplied to the element so that the drive voltage applied to the element remains constant.

[0008] In a second embodiment of the present invention, a reference voltage generation device is provided, comprising: an AD converter that converts an analog signal output from an element having a bridge resistor that outputs an analog signal indicating a physical quantity to be measured in response to the flow of a drive current into a digital signal; and a generation circuit that generates a reference voltage to be output to the AD converter by converting the replicated current output from a current mirror circuit that replicates the drive current flowing through the element as a replicated current into a current-voltage.

[0009] In a third aspect of the present invention, a sensor is provided comprising: an element having a bridge resistor and outputting an analog signal indicating a physical quantity to be measured in response to the flow of a drive current; a current mirror circuit that replicates the drive current flowing through the element as a replicated current; and an output unit that outputs the replicated current to a generation circuit that generates a reference voltage for output to an AD converter by converting the replicated current into a current-voltage.

[0010] In the sensor, the element may be a Hall element that is driven by the drive current and outputs an electromotive force generated in response to the surrounding magnetic field as the analog signal.

[0011] It should be noted that the above summary of the invention does not enumerate all of its features. Furthermore, subcombinations of these features may also constitute an invention. [Brief explanation of the drawing]

[0012] [Figure 1] This figure shows an example of the circuit and configuration included in the physical quantity measuring device 100 of this embodiment. [Figure 2A] This figure shows an example of the connection relationship of the Hall element 40. [Figure 2B] This figure shows an example of a different connection relationship for the Hall element 40 than that shown in Figure 2A. [Figure 3] This figure shows another example of the circuit and configuration included in the physical quantity measuring device 100 of this embodiment. [Figure 4] This is a circuit diagram showing an example of the configuration of the IV conversion circuit 85a. [Figure 5] This is a circuit diagram showing an example of the configuration of the IV conversion circuit 85b. [Figure 6] This figure shows a further alternative example of the circuit and configuration included in the physical quantity measuring device 100 of this embodiment. [Modes for carrying out the invention]

[0013] The present invention will be described below through embodiments of the invention, but these embodiments are not intended to limit the invention as defined in the claims. Furthermore, not all combinations of features described in the embodiments are necessarily essential to the solution of the invention.

[0014] Figure 1 shows an example of the circuit and configuration included in the physical quantity measuring device 100 of this embodiment. The physical quantity measuring device 100 comprises an amplifier 10, a current mirror circuit 20, a switch circuit 30, a Hall element 40, a timing control circuit 50, an anti-aliasing filter 70, a generation circuit 80a, and an AD (Analog to Digital) converter 90.

[0015] The physical quantity measuring device 100 measures physical quantities such as magnetic field, velocity, and / or acceleration as analog values ​​using elements including a bridge circuit such as a Hall element 40, and outputs the measured physical quantities as digital values ​​obtained by digital conversion. In this case, a reference voltage is input to the AD converter 90 of the physical quantity measuring device 100 to reduce the influence of the temperature characteristics of the elements. The physical quantity measuring device 100 of this embodiment can provide a reference voltage with a simple configuration and cancel out the influence of the offset voltage of the elements.

[0016] The amplifier 10 receives an input voltage Vin and forms a voltage follower based on the input voltage. By controlling the gate voltage of the MOS transistor in the current mirror circuit 20, the MOS transistor in the current mirror circuit 20 is controlled as a current source. The input voltage Vin supplied to the amplifier 10 may be supplied as a constant voltage. Thus, the physical quantity measuring device 100 of this embodiment functions as a physical quantity measuring device that drives the Hall element 40 with a constant voltage. In other words, the amplifier 10 is an example of a "power supply unit" that controls and supplies a drive current Id to the Hall element 40 so that the drive voltage applied to the element is constant. In this embodiment, a constant voltage driven circuit that drives the Hall element 40 with a constant voltage is shown, but the power supply that drives the Hall element 40 is not limited to a constant voltage power supply, and for example, a power supply that supplies a constant current may be used.

[0017] The current mirror circuit 20 supplies a drive current Id for driving the Hall element 40 based on the power supply voltage Vdd and the input voltage Vin, and mirrors the drive current Id and provides it to the generation circuit 80a. The current mirror circuit 20 includes a MOS transistor 22 and a MOS transistor 24.

[0018] The MOS transistor 22 and the MOS transistor 24 are P-type MOS transistors, and the source electrodes of the MOS transistor 22 and the MOS transistor 24 are connected to a power supply line to which the voltage Vdd is applied. On the other hand, the gate electrodes of the MOS transistor 22 and the MOS transistor 24 are connected in parallel to the amplifier 10.

[0019] In the present embodiment, the sizes of the MOS transistor 22 and the MOS transistor 24 are set to be equal. Also, the gate voltages applied to the MOS transistor 22 and the MOS transistor 24 are equal, and the same voltage Vdd is applied to the source electrodes of the MOS transistor 22 and the MOS transistor 24. Therefore, the source-drain current of the MOS transistor 22 and the source-drain current of the MOS transistor 24 become equal, and a replicated current obtained by replicating a current having the same magnitude as the drive current Id is supplied from the drain electrode of the MOS transistor 22 and the drain electrode of the MOS transistor 24. Thereby, the current mirror circuit 20 is configured. The drain electrode of the MOS transistor 22 is connected to the Hall element 40 and supplies the drive current Id of the Hall element 40 to the Hall element 40.

[0020] Note that the sizes of MOS transistor 22 and MOS transistor 24 do not necessarily have to be set equal. The change in the current flowing through MOS transistor 24 only needs to follow the change in the current flowing through MOS transistor 22. For example, the size of MOS transistor 24 may be reduced compared to MOS transistor 22, and the current flowing through MOS transistor 24 may be made smaller than the current flowing through MOS transistor 22. Thus, the current flowing through MOS transistor 24 only needs to increase or decrease in proportion to the current flowing through a sensor element such as hall element 40, and the absolute value of the current flowing through MOS transistor 24 may be arbitrarily designed according to the desired power consumption, etc.

[0021] When hall element 40 detects a magnetic field and supplies a hall voltage, or when hall element 40 undergoes temperature fluctuations, the resistance constituting hall element 40 fluctuates due to temperature characteristics. Although hall element 40 of the present embodiment is driven at a constant voltage, when the resistance value of hall element 40 fluctuates, the drive current of hall element 40, that is, the source-drain current of MOS transistor 22 fluctuates. The gate voltage of MOS transistor 22 is set equal to the gate voltage of MOS transistor 24, and when the source-drain current of MOS transistor 22 fluctuates, the source-drain current of MOS transistor 24 fluctuates so as to replicate the source-drain current of MOS transistor 22.

[0022] Switch circuit 30 switches the connection relationship of the bridge circuit within hall element 40 by swapping the terminal pair in the input direction to hall element 40 and the terminal pair in the output direction. Thereby, the influence of the offset in the output voltage due to manufacturing tolerances of the resistance within hall element 40 can be reduced.

[0023] The switch circuit 30 switches the connection relationship of the four terminals of the Hall element 40, thereby switching the roles of the four terminals of the Hall element 40. As a result, the configuration of the switch circuit 30, the Hall element 40, and the timing control circuit 50 implements the so-called spinning current method of the Hall element 40, and reduces the effect of resistance offset in the bridge circuit which is the equivalent circuit of the Hall element 40. Specifically, the four terminals of the Hall element 40 are the terminal to which the input voltage Vin is applied and to which the drive current Id is supplied, the terminal connected to the internal ground (internal ground voltage Vss), the terminal set to the positive Hall voltage, and the terminal set to the negative Hall voltage. Therefore, one end of the switch circuit 30 is connected to the drain terminal of the MOS transistor 22, the internal ground, and the non-inverting input terminal of the amplifier 52 and the inverting output terminal of the amplifier 54, to which the differential voltage that becomes the output from the Hall element 40 is supplied. On the other hand, the other end of the switch circuit 30 is connected to the four terminals of the Hall element 40.

[0024] The switching of connections performed by the switch circuit 30 may be controlled by the timing control circuit 50. For example, the switching of connections of the switch circuit 30 may be performed by supplying different voltages from the timing control circuit 50, but the control method of the switching is not limited.

[0025] The Hall element 40 is an element that outputs an electromotive force generated in response to the surrounding magnetic field as an analog signal. The Hall element 40 can be represented as a resistive bridge circuit, with one of the two diagonally opposite terminals of this resistive bridge circuit connected to the input voltage Vin and the other to the internal ground (Vss). This terminal pair is an example of a "first terminal pair" that outputs an analog signal indicating the Hall electromotive force when a drive current Id is input or when the connection relationship of the terminal pair is switched by the spinning current method. As a result, an applied voltage (Vin-Vss) is applied to these two diagonally opposite terminals of the Hall element 40, and the drive current Id of the Hall element flows through the MOS transistor 22. In this embodiment, the physical quantity measuring device 100 uses the Hall element 40 as an element for measuring physical quantities, but an analog element with a bridge resistor that indicates the physical quantity to be measured in response to the flow of drive current may be used, and the Hall element is merely one example. The element used to measure physical quantities may be one that measures physical quantities such as magnetic fields, velocity, and / or acceleration as analog values. When the surrounding magnetic field fluctuates while this current is flowing, a Hall electromotive force (VHP-VHN) corresponding to the fluctuation in the magnetic field is generated between two other diagonal terminals (VHP, VHN). This makes it possible to detect fluctuations in the magnetic field. These two terminals are an example of a "second terminal pair" to which an analog signal indicating the Hall electromotive force is output when a drive current is input to the first terminal pair, and to which a drive current is input when an analog signal indicating the Hall electromotive force is output from the first terminal pair. Therefore, the switch circuit 30 corresponds to a circuit that switches between the terminal pair that carries the drive current and the terminal pair that outputs the analog signal between the first and second terminal pairs.

[0026] The timing control circuit 50 switches the timing at which the switch circuit 30 switches the connection relationship of the Hall element 40. In the Hall element 40, voltages (input voltage Vin and) are applied diagonally to the four terminals arranged on the quadrilateral of the bridge circuit, and the Hall voltages from the other two diagonal terminals are read.

[0027] Therefore, the timing control circuit 50 switching the connection relationship of these terminals is equivalent to switching the voltage every 90 degrees. Since the sum of the interior angles of a quadrilateral is 360 degrees, the timing control circuit 50 will relatively switch the connection angle between 0 degrees (setting it to 360 × n degrees (where n is an integer) will result in the same value), 90 degrees, 180 degrees, and 270 degrees. As an example, the timing control circuit 50 may perform switching by repeating multiple cycles, with each of these four connection angle values ​​being taken once as one cycle. The interval between switching timings controlled by the timing control circuit 50 may be at a speed sufficiently faster than the temperature rise of the Hall element 40. In particular, the interval between switching timings controlled by the timing control circuit 50 may be short enough within one cycle that the effect of the change in resistance due to the temperature characteristics of the Hall element 40 can be ignored.

[0028] Amplifier 52 constitutes a non-inverting amplifier circuit. One of the Hall voltages of the Hall element 40 (for example, VHP) is applied to the non-inverting input terminal of amplifier 52.

[0029] On the other hand, amplifier 54 constitutes an inverting amplifier circuit. The other of the Hall voltages of the Hall element 40 (for example, VHN) is applied to the inverting input terminal of amplifier 54.

[0030] Resistors 55, 57, and 59 are resistors that allow amplifiers 52 and 54 to function as amplification circuits, and resistors that adjust the differential output voltage. Resistors 62 and 64 are resistors that adjust the differential output voltage and also function as resistors that perform low-pass filtering on each of the differential voltages in the anti-aliasing filter 70.

[0031] The anti-aliasing filter 70 is a low-pass filter that operates to prevent aliasing errors from appearing in the converted signal when the AD converter 90 performs AD conversion. In this embodiment, the anti-aliasing filter 70 performs low-pass filtering on each of the differential voltages. The anti-aliasing filter 70 in this embodiment is composed of an amplifier 71, a capacitor 73, a resistor 75, a capacitor 77, and a resistor 79.

[0032] Resistor 62, amplifier 71, capacitor 73, and resistor 75, which are resistors that adjust the differential voltage input to the anti-aliasing filter 70, constitute a low-pass filter. On the other hand, resistor 64, amplifier 71, resistor 75, and capacitor 77 also constitute a low-pass filter. As a result, low-pass filtering is performed on both differential voltages output by amplifiers 52 and 54. The anti-aliasing filter 70 applies the output differential voltages to terminals O1 and O2, respectively.

[0033] The generation circuit 80a generates a reference voltage ADVREF for the AD converter 90 when performing AD conversion, according to the duplicated current which is a duplicate of the drive current Id of the Hall element 40 supplied from the current mirror circuit 20. The generation circuit 80a applies the reference voltage ADVREF to terminal REF. The generation circuit 80a includes a resistor 82 and an amplifier 84.

[0034] In the figure, the generation circuit 80a is shown as a circuit that constitutes an integrated circuit on the same chip as the physical quantity measuring device 100. However, the generation circuit 80a and the AD converter 90 may be provided on a separate chip from the Hall element 40 that constitutes the sensor element, thereby forming a "reference voltage generation device". In this case, a current mirror circuit 20 may be provided on the sensor side, and a duplicated current may be output toward the generation circuit 80a. Thus, the terminal to which the duplicated current is supplied from the current mirror circuit 20 may constitute an "output unit" that outputs the duplicated current.

[0035] Resistor 82 converts the current Id into a reference voltage ADVREF. That is, the generation circuit 80a may generate a reference voltage by converting the current Id into a voltage using resistor 82. Note that resistor 82 also has temperature characteristics. The influence of these temperature characteristics of resistor 82 may be suppressed by selecting the material and composition of the resistor element 82. Alternatively, the influence of the temperature characteristics of resistor 82 may be corrected by acquiring the temperature of the measurement environment, etc., and other means. The Hall element 40 is an element in which the Hall electromotive force is generated by the movement of carriers such as holes or free electrons. In Figure 2A or Figure 2B described later, the Hall element 40 is represented as a bridge circuit as an equivalent circuit, but the temperature change of carrier mobility has a large influence on the Hall electromotive force from the Hall element 40. By having resistor 82 output a reference voltage ADVREF based on the current Id, it is possible to remove the influence that appears on the Hall electromotive force due to the temperature characteristics of the Hall element 40 from the output voltage of the AD converter 90.

[0036] In some cases, instead of using resistor 82 and without using the current mirror circuit 20, a replica Hall element is used to generate the reference voltage ADVREF for the AD converter 90. In this case, the Hall voltage output from the replica Hall element is generated as the reference voltage ADVREF. The temperature characteristics of the replica Hall element can be set to be close to those of the Hall element 40. This configuration also compensates for the temperature characteristics of the Hall element 40. However, the replica Hall element ends up being about the same size as the Hall element 40, and when using a replica Hall element, the footprint cannot be reduced as sufficiently as when not using a replica Hall element.

[0037] In this embodiment, the generation circuit 80a is used to generate a reference voltage ADVREF based on the replicated current of the drive current Id supplied from the current mirror circuit 20. As a result, even if the Hall element 40's temperature rises and it exhibits different resistance values ​​due to its temperature characteristics, a reference voltage ADVREF based on the mirrored current value of the fluctuating drive current Id is output. The AD converter 90 outputs a digital output value of the Hall electromotive force based on the ratio of the reference voltage ADVREF to the Hall electromotive force of the Hall element 40. Since both the reference voltage ADVREF and the Hall electromotive force fluctuate in accordance with the change in the drive current Id, the influence of fluctuations in the Hall electromotive force due to the temperature characteristics of the Hall element 40 can be eliminated from the digital output value of the AD converter 90.

[0038] Amplifier 84 is a voltage follower. A voltage generated across resistor 82 based on the drive current Id is applied to the non-inverting input terminal of amplifier 84. This terminal is short-circuited to the output terminal of amplifier 84. The output voltage from amplifier 84 is applied to terminal REF as a reference voltage ADVREF.

[0039] The AD converter 90 converts the analog signal output from the Hall element 40 into a digital signal. In other words, the AD converter 90 functions as an AD converter that converts the analog signal output from an element having a bridge resistor that outputs an analog signal indicating the physical quantity to be measured in response to the flow of drive current into a digital signal.

[0040] In this example, the AD converter 90 describes an example in which a signal based on the voltage values ​​applied to terminals O1 and O2 and a reference voltage ADVREF are integrated at the same timing. However, a double integration type in which the input signal VIN and the reference voltage ADVREF are integrated at different timings is also possible. Furthermore, the AD converter 90 can be any AD converter that outputs a digital signal according to the ratio of a signal based on the voltage values ​​applied to terminals O1 and O2 and the reference voltage ADVREF. A ΔΣ type AD converter may be used, or an integrating type AD converter may be used. In the figure, the AD converter 90 is shown as an external configuration of the chip of the physical quantity measuring device 100. However, the entire generation circuit 80 and AD converter 90 may be configured as circuit elements within the integrated circuit constituting the physical quantity measuring device 100, with the entire integrated circuit provided on a single chip. The AD converter 90 of this embodiment includes an integrator 92, a comparator 94, a flip-flop 96, and a counter 98. The integrator 92 and comparator 94 function as the analog output signal section of the AD converter 90, while the flip-flop 96 and counter 98 function as the digital signal output section of the AD converter 90.

[0041] The integrator 92 functions as an input adder that adds the signal while integrating, switching the polarity of the reference voltage ADVREF by rotating it forward or inverting it. However, a single-ended differential signal converter or the like may be provided between the integrator 92 and terminals O1 and O2, and a device that converts the signal from the Hall element into a single-ended signal may be provided. In this case, the value of the single-ended signal relative to the reference voltage ADVREF is added while integrating.

[0042] The comparator 94 amplifies the summing input signal output from the integrator 92, which is an input adder, to generate an analog output signal having a predetermined amplitude, and functions as an analog output signal determination unit that determines the magnitude of the amplitude of this analog output signal by comparing it with a predetermined voltage.

[0043] The flip-flop 96 and counter 98 function as a digital signal output unit. The digital signal output unit calculates a count value based on a signal indicating the magnitude of the analog output signal output from the comparator 94, and outputs this count value as a digital signal. The output of the flip-flop 96 is also input to the integrator 92 to switch the reference voltage ADVREF and add it. The counter 98 counts the converted value and outputs a digital signal of the level counted as a digital value. The reference voltage ADVREF in the AD converter 90 may be adjusted so that the temperature characteristics of the resistor 82 do not affect the digital signal of the Hall voltage detection result.

[0044] Figure 2A shows an example of the connection relationship of the Hall element 40. The Hall element 40 is composed of resistors 42, 44, 46, and 48.

[0045] Thus, the Hall element 40 is described as a bridge circuit including four resistors 42, 44, 46, and 48 as its equivalent circuit. These four resistors 42, 44, 46, and 48 may have offsets due to manufacturing tolerances or other reasons. The Hall element 40 in this embodiment is driven by a constant voltage, and as in Figure 1, the drive voltage is represented as Vin. Furthermore, in the following, the internal ground voltage Vss is calculated as Vss=0.

[0046] The resistance value of resistor 42 is assumed to be R. In this case, if the other three resistors have an offset relative to resistor R, the resistance value of resistor 44 is R + ΔR1, the resistance value of resistor 46 is R + ΔR2, and the resistance value of resistor 48 is R + ΔR3. Thus, when there is an offset in the four resistors 42, 44, 46, and 48, the offset resistance value can be determined based on the resistance value of any one of the four resistors.

[0047] In the following section, we will calculate the influence of the offset resistance values ​​in the four resistors 42, 44, 46, and 48 on the voltage output from the bridge circuit. In this embodiment, the reference voltages ADVREF1 and ADVREF2 of the AD converter 90 are generated from the mirrored current values ​​of the Hall element drive currents Id1 and Id2. As a result, the influence of the offset resistance values ​​in the four resistors 42, 44, 46, and 48 is canceled out in the output value of the AD converter 90 based on the voltage output from the bridge circuit.

[0048] In the formula for calculating the output voltage of the Hall element 40 below, if the bridge circuit is a sensor element such as the Hall element 40, the detected voltage will be superimposed on the output voltage value. For simplicity, in the following calculation, the detected output voltage value is set to 0 to check how the effect of the offset resistor is canceled out.

[0049] In this case, the equivalent resistance of this bridge circuit is given by equation (1).

number

number

number

[0050] The differential voltage SensO1 of the Hall element is expressed by the following equation (4).

number

number

[0051] Figure 2B shows an example of a different connection relationship for the Hall element 40 compared to Figure 2A. The switch circuit 30 rotates the connection relationship of the Hall element 40 by 90 degrees compared to Figure 2A.

[0052] In this case, since the connection relationship changes, the formula for the equivalent resistance will be expressed by the following formula (6).

number

number

number

[0053] The differential voltage SensO2 of the Hall element is given by equation (9) below.

number

number

number

[0054] Therefore, by using the spinning current method, the effect of the offset resistance value is eliminated at the output of the AD converter 90. In the configuration of the physical quantity measuring device 100 of this embodiment, a replica Hall element is not used, and the value obtained by multiplying the replica current of the drive current Id by the resistance R' of the resistor 82 in equations (3) and (4) is derived as the reference voltage ADVREF of the AD converter 90. When generating the reference voltage ADVREF using a replica Hall element, even if the replica Hall element can reproduce the temperature characteristics of the Hall element 40, the offset between the resistance constituting the replica Hall element and the resistance constituting the Hall element 40 may differ. Details are omitted, but in this case, when ADOUT1 + ADOUT2 is calculated, the relationship does not cancel each other out as shown in equation (11). Therefore, when a replica Hall element is used, the offset resistance of the Hall element 40 and the replica Hall element may have an effect. While a circuit that uses a replica Hall element to generate the reference voltage of the AD converter 90 may be effective in compensating for the temperature characteristics of the Hall element, a configuration that references the drive current Id of the Hall element 40 when generating the reference voltage ADVREF, as in this embodiment, may be more effective in compensating for the resistance offset. Therefore, the configuration of the physical quantity measuring device 100 in this embodiment is effective not only in reducing the footprint by not using a replica Hall element, but also in compensating for the resistance offset.

[0055] Figure 3 shows another example of the circuit and configuration included in the physical quantity measuring device 100 of this embodiment. In the following, the physical quantity measuring device 100 shown in Figure 3 will be described, mainly focusing on the differences from the embodiment in Figure 1. The physical quantity measuring device 100 of this embodiment includes a generation circuit 80b instead of a generation circuit 80a.

[0056] The generation circuit 80b is a circuit that generates a reference voltage as a differential voltage. The generation circuit 80b includes an IV conversion circuit 85, an amplifier 87, and an amplifier 89. The specific configuration of the IV conversion circuit 85 will be described in detail with reference to Figures 4 and 5.

[0057] The output from the IV conversion circuit 85 is input to the non-inverting input terminal of amplifier 87, and amplifier 87 outputs the positive reference voltage of the differential voltage reference voltage. On the other hand, the output from the IV conversion circuit 85 is input to the inverting input terminal of amplifier 89, and amplifier 87 outputs the negative reference voltage of the differential voltage reference voltage. Amplifiers 87 and 89 function as voltage followers, applying their respective output voltages to terminals REF1 and REF2. As a result, a reference voltage as a differential voltage is output, and the AD converter 90 of this embodiment operates using the differential voltage reference voltage.

[0058] Figure 4 is a circuit diagram showing an example of the configuration of the IV conversion circuit 85a. The IV conversion circuit 85 in Figure 3 may be the IV conversion circuit 85a of this embodiment. The IV conversion circuit 85a includes MOS transistors 102, 104 and 106, resistor 108, amplifier 110, and resistor 112.

[0059] MOS transistor 102 functions as a current source, supplying a current that references the source-drain current flowing through MOS transistor 24. MOS transistor 102 is a PMOS transistor.

[0060] MOS transistors 104 and 106 are NMOS transistors. MOS transistor 104 is a reference transistor for MOS transistor 106.

[0061] The magnitude of the drain-source current flowing through MOS transistor 106 is proportional to the magnitude of the drain-source current flowing through MOS transistor 104. The gate terminal of MOS transistor 104 is connected to the gate terminal of MOS transistor 106. Furthermore, the drain terminal of MOS transistor 104 is short-circuited to the gate terminals of both MOS transistor 104 and MOS transistor 106. The source terminals of both MOS transistor 104 and MOS transistor 106 are connected to the internal ground (internal ground potential Vss). In this connection relationship, the drain-source current flowing through MOS transistor 106 is proportional to the drain-source current flowing through MOS transistor 104, in proportion to the size ratio of MOS transistor 104 and MOS transistor 106. In particular, when MOS transistor 104 and MOS transistor 106 are of equal size, they form a current mirror circuit.

[0062] Resistor 108 performs IV conversion based on the drive current Id mirrored by MOS transistor 102. This generates a reference voltage Vr1 between the drain terminal of MOS transistor 102 and resistor 108, and this reference voltage is applied to terminal REF2 via amplifier 87, which is a voltage follower.

[0063] A current flows through resistor 112 that references the reference current flowing into MOS transistor 106. A voltage is supplied to the connection point of resistors 108 and 112 using amplifier 110. This generates a reference voltage Vr2, which is then applied to terminal REF1 via amplifier 89, which is a voltage follower.

[0064] Figure 5 is a circuit diagram showing an example of the configuration of the IV conversion circuit 85b. The IV conversion circuit 85 in Figure 3 may be the IV conversion circuit 85b of this embodiment. The explanation will mainly focus on the differences from the IV conversion circuit 85a.

[0065] The IV conversion circuit 85b includes variable resistors 122 and 124 in place of the fixed resistors 108 and 112 of the IV conversion circuit 85a. The resistance values ​​of variable resistors 122 and 124 are controlled by the resistance control circuit 120. The resistance control circuit 120 may control the resistance values ​​of variable resistors 122 and 124 based on values ​​stored in a memory device (not shown). By using the IV conversion circuit 85b of Figure 5, a reference voltage with a desired differential voltage can be output based on the drive current of the Hall element 40.

[0066] With this configuration, the reference voltage of the AD converter 90 can be supplied as a differential voltage using the generation circuit 80b. Thus, even in the embodiments shown in Figures 3 to 5, which use a differential voltage as the reference voltage, the temperature characteristics of the Hall element 40 can be compensated with a simple configuration that reduces the footprint without using a replica Hall element, and the effect of the offset of the resistors constituting the Hall element 40 can also be reduced.

[0067] Figure 6 shows a further alternative example of the circuit and configuration included in the physical quantity measuring device 100 of this embodiment. Below, the physical quantity measuring device 100 of this embodiment will be described, focusing on the differences from the physical quantity measuring device 100 described in Figure 1. The physical quantity measuring device 100 of this embodiment includes a constant current source 15 and an amplifier 86 instead of the amplifier 10, current mirror circuit 20, and generation circuit 80. The physical quantity measuring device 100 of this embodiment is common with the physical quantity measuring device 100 of Figure 1 in other configurations.

[0068] The constant current source 15 is a current source that supplies a constant current to the Hall element 40. The constant current source 15 is connected to a power line that supplies an internal voltage Vdd. In the embodiment shown in Figure 1, the physical quantity measuring device 100 drives the Hall element 40 with a constant voltage supplied from the amplifier 10, but the constant current source 15 in this embodiment drives the Hall element 40 with a constant current.

[0069] Since the resistance of the Hall element 40 fluctuates according to the temperature characteristics of the Hall element 40, the voltage supplied to the Hall element 40 from the constant current source 15 via the switch circuit 30 fluctuates. The non-inverting input terminal of the amplifier 86 is supplied with a voltage equal to the voltage supplied to the Hall element 40.

[0070] Amplifier 86 has its inverting input terminal and output terminal short-circuited and outputs a reference voltage ADVREF as a voltage follower. The reference voltage ADVREF is a voltage corresponding to the voltage supplied to the Hall element 40, and therefore fluctuates according to the temperature characteristics of the Hall element 40. The output terminal of amplifier 86 is connected to terminal REF, and in this embodiment as well, the reference voltage ADVREF, which fluctuates according to the temperature characteristics of the Hall element 40, is applied to terminal REF.

[0071] In this embodiment, the fluctuation in the resistance value of the sensor element, such as the Hall element 40, directly corresponds to the dynamic range of the reference voltage ADVREF. When the temperature characteristics of the sensor element are small, the circuit of this embodiment can be used instead of the circuit that drives the Hall element 40 with a constant voltage as shown in Figure 1. In such cases, the physical quantity measuring device 100 of this embodiment can also compensate for the temperature characteristics of the Hall element 40 with a simple configuration that reduces the footprint, without using a replica Hall element, and the effect of the offset of the resistors constituting the Hall element 40 can also be reduced.

[0072] Although the present invention has been described above using embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various modifications or improvements can be made to the above embodiments. It will be clear from the claims that such modified or improved forms may also be included in the technical scope of the present invention.

[0073] It should be noted that the execution order of operations, procedures, steps, and stages in the apparatus, systems, programs, and methods shown in the claims, specifications, and drawings is not explicitly stated as "before," "prior to," etc., and that these can be implemented in any order unless the output of a previous process is used in a later process. Even if the operation flow in the claims, specifications, and drawings is described using phrases such as "first," "next," etc. for convenience, it does not mean that it is essential to perform the operations in that order. [Explanation of Symbols]

[0074] 10 Amplifiers 15 Constant current source 20 Current Mirror Circuit 22,24 MOS transistors 30 Switch Circuits 40 Hall elements 42, 44, 46, 48 resistors 50 Timing control circuit 52,54 Amplifier 55, 57, 59, 62, 64 resistors 70 Anti-aliasing filters 71 Amplifier 73, 77 Capacitors 75, 79 resistors 80 Generation circuit 82 resistors 85 IV conversion circuit 86, 87, 89 Amplifier 90 AD Converters 92 Integrator 94 Comparator 96 Flip-flops 98 counter 102, 104, 106 MOS transistors 108,112 resistors 110 Amplifier 120 Resistor Control Circuit 122,124 Variable resistor

Claims

1. A device having a bridge resistor that outputs an analog signal indicating the physical quantity to be measured in response to the flow of drive current, An AD converter that converts the analog signal output from the element into a digital signal, A current mirror circuit that replicates the drive current flowing through the element as a replicated current, A generation circuit generates a reference voltage to be output to the AD converter by converting the replicated current into a current-voltage converter. A physical quantity measuring device equipped with the following features.

2. The physical quantity measuring device according to claim 1, wherein the element is a Hall element that is driven by the drive current and outputs an electromotive force generated in response to the surrounding magnetic field as the analog signal.

3. The Hall element has a first terminal pair to which the drive current is input or the analog signal is output, and a second terminal pair to which the analog signal is output when the drive current is input to the first terminal pair, and to which the drive current is input when the analog signal is output from the first terminal pair. The aforementioned physical quantity measuring device is The physical quantity measuring device according to claim 2, further comprising a switch circuit that switches between a terminal pair for supplying drive current and a terminal pair for outputting the analog signal between the first terminal pair and the second terminal pair.

4. A physical quantity measuring device according to any one of claims 1 to 3, further comprising a power supply unit that controls and supplies the drive current to the element so that the drive voltage applied to the element remains constant.

5. An AD converter that converts the analog signal output from an element having a bridge resistor that outputs an analog signal indicating the physical quantity of the object to be measured in response to the flow of drive current into a digital signal, A generation circuit generates a reference voltage to be output to the AD converter by converting the replicated current output from a current mirror circuit, which replicates the drive current flowing through the element as a replicated current, into a current-voltage converter. A reference voltage generating device equipped with the following features.

6. A device having a bridge resistor that outputs an analog signal indicating the physical quantity to be measured in response to the flow of drive current, A current mirror circuit that replicates the drive current flowing through the element as a replicated current, The output section outputs the replicated current to a generation circuit that generates a reference voltage for output to an AD converter by converting the replicated current into a current-voltage, and A sensor equipped with the following features.

7. The sensor according to claim 6, wherein the element is a Hall element that is driven by the drive current and outputs an electromotive force generated in response to the surrounding magnetic field as the analog signal.

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