JP2021103112A - Sensor device - Google Patents

Abstract

To provide a sensor device that can reduce noise as suppressing a variation in an offset adjustment range of a bridge circuit.SOLUTION: In a channel between a fifth node N5 to which a first reference voltage Vra is applied and a first node N1, third resistance R3 and first resistance R1 are series-connected via a third node N3, and in a channel between a sixth node N6 to which a second reference voltage Vrb is applied and a second node N2, fourth resistance R4 and second resistance R2 are series-connected via a fourth node N4. A resistance value of a variable resistance element M1 parallel connected to a voltage-dividing circuit 21 is controlled in accordance with a control signal Vg obtained by amplifying a voltage difference between the third node N3 and fifth node N5 with an error amplifier circuit U1. Since a resistance ratio R1/R3 and resistance ratio R2/R4 are equal, a voltage difference Vn between the first node N1 and second node N2 is almost proportional to a difference (Vrb-Vra) between the reference voltages.SELECTED DRAWING: Figure 1

Description

The present invention relates to a sensor device that detects a physical quantity by a bridge circuit, and more particularly to a sensor device capable of adjusting the offset of the output of the bridge circuit.

A bridge circuit is generally used to obtain a detection value of a sensor element (pressure sensor, magnetic sensor, etc.) whose resistance value changes according to a physical quantity. At the output of the bridge circuit, an offset voltage is generated due to variations in the resistance values of the sensor elements and the like. As a method of adjusting this offset voltage, a method of inserting a resistor in parallel or in series with the sensor element, a method of adding a voltage to the output of a bridge circuit, and the like are known (see Patent Document 1 below).

However, when a resistor for adjusting the offset voltage is formed inside the IC, the resistance value varies from manufacturing lot to several tens of percent, so that the offset voltage adjustment range varies from manufacturing lot to manufacturing lot. There is a profit. In addition, there is a disadvantage that the output sensitivity of the bridge circuit varies due to the variation in the resistance for adjustment. Further, since the temperature characteristics of the adjusting resistor and the sensor element are different, even if the offset voltage is adjusted at a certain temperature, there is a disadvantage that the offset voltage fluctuates (drifts) according to the temperature change. .. It is difficult to completely match the temperature characteristics of the sensor element and the resistor, and as a result, the temperature characteristics of the offset voltage deteriorate.

Therefore, the inventor of the present application has developed a sensor device that keeps the voltage difference between the nodes at both ends of the voltage dividing circuit for adjusting the offset voltage provided in the bridge circuit constant by the constant voltage circuit (see Patent Document 2 below). In this sensor device, the voltage difference between the nodes at both ends of the voltage divider circuit is kept constant, so even if there are manufacturing variations in the impedance of the sensor elements that make up the bridge circuit, the voltage divider ratio of the voltage divider circuit can be adjusted. The change range of the offset voltage becomes almost constant, and the variation in the offset adjustment range for each production lot can be significantly suppressed. In addition, since the voltage difference between the nodes at both ends of the voltage divider circuit is kept constant, the output sensitivity of the bridge circuit varies due to the variation in the resistance value of the voltage divider circuit, and the temperature characteristics of the voltage divider circuit and the sensor element differ. Fluctuations in the offset voltage due to the above can also be effectively suppressed.

Japanese Unexamined Patent Publication No. 1-311284 JP-A-2017-166890

In the sensor device of Patent Document 2 described above, a differential amplifier circuit and an error amplifier circuit are used in a constant voltage circuit that keeps the voltage difference between both ends of the voltage dividing circuit constant. The differential amplifier circuit usually includes about 1 to 3 operational amplifiers, and when combined with the operational amplifiers of the error amplifier circuit, the constant voltage circuit includes about 2 to 4 operational amplifiers in total. In general, operational amplifiers generate relatively large noise such as flicker noise. When a large amount of noise is generated in the circuit of the first stage of the sensor device that handles a minute signal, it becomes a major cause of deterioration of measurement accuracy. In order to reduce the noise generated by the operational amplifier, it is possible to increase the size of the elements (transistors, etc.) that make up the operational amplifier, but doing so increases the area of the circuit and causes an increase in cost.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a sensor device capable of reducing noise while suppressing variations in the offset adjustment range of a bridge circuit.

The sensor device according to the present invention includes a bridge circuit having a plurality of impedance elements having at least a part of impedance corresponding to a physical quantity to be detected, and an offset adjusting circuit for adjusting the offset of the output voltage of the bridge circuit. To be equipped. The bridge circuit includes two series circuits each including two or more of the impedance elements connected in series between two power supply nodes to which power is supplied. The offset adjustment circuit is inserted into the intermediate path of at least one of the series circuits of the two series circuits, and divides the voltage difference generated between the first node and the second node at both ends in the inserted intermediate path. It has a voltage dividing circuit that outputs the divided voltage from the output node, and a constant voltage circuit that keeps the voltage difference between the first node and the second node in the voltage dividing circuit constant. The voltage dividing circuit can adjust the voltage dividing ratio. When adjusting the offset, the voltage difference between the output node of the voltage divider circuit in one of the series circuits and the intermediate node of the other series circuit, or the output node of the voltage divider circuit in one of the series circuits. The voltage dividing ratio is adjusted so that the voltage difference between the one and the output node of the voltage dividing circuit in the other series circuit approaches a predetermined value. The constant voltage circuit is connected in parallel with the voltage dividing circuit, and is provided in a path between a variable resistance element whose resistance value changes according to a control signal and a first node and a third node. A resistor, a second resistor provided in the path between the second node and the fourth node, and a path between the fifth node and the third node to which the first reference voltage is applied are provided. Amplifies the voltage difference between the third resistor, the fourth resistor provided in the path between the sixth node to which the second reference voltage is applied and the fourth node, and the third node and the fourth node. However, it includes an error amplification circuit that outputs the control signal according to the result of the amplification. The resistance ratio of the first resistance to the third resistance is equal to the resistance ratio of the second resistance to the fourth resistance.

According to this configuration, the voltage difference between the first node and the second node in the voltage dividing circuit is kept constant. Therefore, even if there are manufacturing variations in the impedances of the plurality of impedance elements, the range of change in the voltage of the output node due to the adjustment of the voltage division ratio is substantially constant. As a result, the voltage difference between the output node of the voltage divider circuit in one of the series circuits and the intermediate node of the series circuit of the other, and the output node of the voltage divider circuit in one of the series circuits and the series circuit of the other With respect to the voltage difference of the voltage dividing circuit from the output node in the above, the range of change due to the adjustment of the voltage dividing ratio is substantially constant. Therefore, even if there is a manufacturing variation in the impedance of the plurality of impedance elements, the offset adjustment range is substantially constant and the variation is suppressed.

Further, according to this configuration, in the path between the fifth node and the first node to which the first reference voltage is applied, the third resistor and the first resistor pass through the third node. In the path between the sixth node and the second node to which the second reference voltage is applied while being connected in series, the fourth resistor and the second resistor pass through the fourth node. Are connected in series. The resistance value of the variable resistance element connected in parallel with the voltage dividing circuit is a signal obtained by amplifying the voltage difference between the third node and the fourth node by the error amplifier circuit. It is controlled according to. When the resistance value of the variable resistance element is controlled so that the voltage difference between the third node and the fourth node becomes sufficiently small, the resistance ratio of the first resistance to the third resistance and the fourth resistance Since the resistance ratio of the second resistor is equal to that of the second resistor, the voltage difference between the first node and the second node is a voltage difference substantially proportional to the difference between the first reference voltage and the second reference voltage. Be kept. Compared with the case where the differential amplifier circuit is provided in front of the error amplifier circuit, the number of operational amplifiers used is small, so that the amount of noise generated is reduced.

Preferably, the resistance value of the first resistor and the resistance value of the second resistor are equal to each other.
According to this configuration, the variation in the offset voltage of the error amplifier circuit due to the input current of the error amplifier circuit or the like is reduced.

Preferably, the intermediate potential between the two potentials of the fifth node and the sixth node is equal to the intermediate potential between the two potentials of the two power supply nodes.
According to this configuration, when the potentials of the first node and the second node at both ends in the voltage dividing circuit and the intermediate potential between the two potentials of the two power supply nodes are close to each other, the current flows through the first resistor. The current and the current flowing through the second resistor can be easily approximated.

Preferably, the sensor device has three or more fifth resistors connected in series between the two power nodes and two intermediates in a plurality of intermediate nodes to which the three or more fifth resistors are connected. The nodes are the fifth node and the sixth node.
According to this configuration, the first reference voltage and the second reference voltage are generated at the two intermediate nodes in the three or more fifth resistors connected in series between the two power supply nodes.

Preferably, the two power supply nodes are the fifth node and the sixth node.
According to this configuration, the voltage of one node in the two power supply nodes is used as the first reference voltage, and the voltage of the other node in the two power supply nodes is used as the second reference voltage.

Preferably, the voltage divider circuit has a constant resistance value between the first node and the second node, a resistance value between the first node and the output node, and the second node. The resistance value between and the output node is adjustable.

According to this configuration, the voltage division ratio is adjusted by adjusting the resistance value between the first node and the output node and the resistance value between the second node and the output node. Is possible. Further, since the resistance value between the first node and the second node is constant, the voltage applied to the impedance element hardly changes by adjusting the voltage division ratio. As a result, the sensitivity of converting the change in physical quantity into the change in impedance in the impedance element is less affected by the adjustment of the voltage division ratio.

Preferably, a constant voltage is supplied to the two power supply nodes, and the plurality of impedance elements have the same temperature coefficient of impedance.

According to this configuration, since the temperature coefficients of the impedances of the plurality of impedance elements are the same, the ratio of the impedances of the plurality of impedance elements is unlikely to change depending on the temperature. Further, since a constant voltage is supplied to the two power supply nodes and the voltage difference between the nodes at both ends in the voltage dividing circuit is kept constant, the impedance ratio of the plurality of impedance elements depends on the temperature. If it is hard to change, the voltage applied to the plurality of impedance elements is also hard to change depending on the temperature. Therefore, the offset of the output voltage of the bridge circuit is unlikely to change with temperature.

According to the present invention, noise can be reduced while suppressing variations in the offset adjustment range of the bridge circuit.

FIG. 1 is a diagram showing an example of the configuration of the sensor device according to the present embodiment. FIG. 2 is a diagram showing an example of the configuration of the sensor device according to the present embodiment, and shows an example in which the power supply voltage is divided by a resistor to generate a reference voltage. FIG. 3 is a diagram showing an example of the configuration of the sensor device according to the present embodiment, and shows an example in which the power supply voltage is used as the reference voltage. FIG. 4 is a diagram showing a bridge circuit of the first comparative example. 5A and 5B are diagrams showing the results of a simulation of the output voltage performed on the bridge circuit of the first comparative example shown in FIG. FIG. 5A shows an upper limit value in the adjustment range, and FIG. 5B shows a lower limit value in the adjustment range. 6A and 6B are diagrams showing the results of a simulation of the output voltage performed on the sensor device shown in FIG. FIG. 6A shows an upper limit value in the adjustment range, and FIG. 6B shows a lower limit value in the adjustment range. FIG. 7 is a diagram showing a sensor device of the second comparative example. FIG. 8 is a diagram showing the results of noise simulation performed on the sensor devices shown in FIGS. 2 and 7, and shows the relationship between the offset adjustment voltage and noise.

FIG. 1 is a diagram showing an example of the configuration of the sensor device 1 according to the embodiment of the present invention. The sensor device 1 shown in FIG. 1 includes a bridge circuit 10 having four impedance elements Z1 to Z4, and an offset adjusting circuit 20 for adjusting the offset of the output voltage Vo of the bridge circuit 10.

Impedance elements Z1 to Z4 (hereinafter, may be referred to as "impedance element Z" without distinction) are elements (sensor elements) having impedance corresponding to physical quantities of detection targets such as magnetic field, temperature, and pressure. is there. In an example of this embodiment, the four impedance elements Z1 to Z4 have the same temperature coefficient.

The bridge circuit 10 has two series circuits 11A and 11B. The series circuits 11A and 11B include two impedance elements Z connected in series between the two power supply nodes Np1 and Np2, respectively. The series circuit 11A includes impedance elements Z1 and Z2, and the series circuit 11B includes impedance elements Z3 and Z4. The power node Np1 is connected to the power line, and the power node Np2 is connected to the ground GND. A constant power supply voltage VDD is supplied to the two power supply nodes Np1 and Np2.

One terminal of the impedance element Z1 is connected to the power supply node Np1, and the other terminal is connected to one terminal of the impedance element Z2 via a voltage dividing circuit 21 described later. The other terminal of the impedance element Z2 is connected to the power supply node Np2 (ground GND). One terminal of the impedance element Z3 is connected to the power supply node Np1, and the other terminal is connected to one terminal of the impedance element Z4. The other terminal of the impedance element Z4 is connected to the power supply node Np2 (ground GND).

The offset adjusting circuit 20 has a voltage dividing circuit 21 and a constant voltage circuit 22 in the example of FIG.

The voltage dividing circuit 21 is inserted in the intermediate path of the series circuit 11A (the path connecting the two impedance elements Z1 and Z2), and the nodes at both ends (first node N1 and second node) in the inserted intermediate path. The voltage difference Vn generated in N2) is divided, and the divided voltage is output from the output node Non. In the voltage divider circuit 21, the resistance value between the first node N1 and the second node N2 at both ends is constant, the resistance value between the first node N1 and the output node Non, and the second node N2 and the output. The resistance value to and from the node Non is adjustable.

The voltage dividing circuit 21 is configured by using, for example, a variable resistor (potentiometer). Specifically, the voltage dividing circuit 21 selects a plurality of resistors connected in series between the first node N1 and the second node N2, and one of the intermediate nodes of these resistors connected in series. It is configured to include a multiplexer that connects to the output node Non. The voltage divider ratio of the voltage divider circuit 21 is adjusted by switching the selection of the intermediate node by the multiplexer.

The constant voltage circuit 22 keeps the voltage difference Vn between the first node N1 and the second node N2 at both ends of the voltage dividing circuit 21 constant. The constant voltage circuit 22 shown in FIG. 1 includes a variable resistance element M1, an error amplifier circuit U1, a first resistance R1, a second resistance R2, a third resistance R3, and a fourth resistance R4.

The variable resistance element M1 is connected in parallel with the voltage dividing circuit 21, and the resistance value changes according to the control signal Vg output from the error amplifier circuit U1. In the example of FIG. 1, the variable resistance element M1 is an n-type MOS transistor, the drain is connected to the first node N1, the source is connected to the second node N2, and the control signal Vg is input to the gate. The variable resistance element M1 is not limited to the MOS transistor, and may be another type of transistor (bipolar transistor or the like).

The first resistor R1 is provided in the path between the first node N1 and the third node N3. The second resistor R2 is provided in the path between the second node N2 and the fourth node N4. The third resistor R3 is provided in the path between the fifth node N5 and the third node N3 to which the first reference voltage Vra is applied. The fourth resistor R4 is provided in the path between the sixth node N6 and the fourth node N4 to which the second reference voltage Vrb is applied.

Assuming that the first resistor R1, the second resistor R2, the third resistor R3, and the fourth resistor R4 have resistance values "R1", "R2", "R3", and "R4", respectively, the following relationship is established. ..

K = R1 / R3 = R2 / R4 ... (1)

In formula (1), "K" represents the resistivity. As shown in the formula (1), the resistivity ratio (R1 / R3) of the first resistor R1 to the third resistor R3 and the resistivity ratio (R2 / R4) of the second resistor R2 to the fourth resistor R4 have the same value. Has "K".

The error amplifier circuit U1 amplifies the difference between the voltage of the third node N3 and the voltage of the fourth node N4, and outputs a control signal Vg according to the result of the amplification. Since the gain of the error amplifier circuit U1 is sufficiently large, the feedback control works so that the voltage of the third node N3 and the voltage of the fourth node N4 are substantially equal to each other. By this feedback control, the voltage difference Vn between the voltage Va of the first node N1 and the voltage Vb of the second node N2 is approximately expressed by the following equation.

Vn = K · (Vrb-Vba)… (2)

As can be seen from the equation (2), the voltage difference Vn between the first node N1 and the second node N2 is a constant value that is not affected by the manufacturing variation of the impedance of the impedance element Z.

However, the relationship of the equation (2) is that the current Ia flowing through the first resistor R1 and the current Ib flowing through the second resistor R2 are sufficiently smaller than the current flowing through the series circuit 11A (current flowing through the impedance elements Z1 and Z2). It holds in. Therefore, the series resistance value (R1 + R3) of the first resistor R1 and the third resistor R3 and the series resistance value (R2 + R4) of the second resistor R2 and the fourth resistor R4 are sufficiently higher than the resistance values of the impedance elements Z1 and Z2. Larger is desirable.

Further, in the sensor device 1 according to the present embodiment, in one example, the resistance value of the first resistor R1 and the resistance value of the second resistor R2 are equal. Thereby, the variation of the offset voltage of the error amplifier circuit U1 due to the input current of the error amplifier circuit U1 and the like can be reduced.

Further, in the sensor device 1 according to the present embodiment, in one example, the intermediate potential ((Vra + Vrb) / 2) between the potentials of the fifth node N5 and the sixth node N6 is both the two power supply nodes Np1 and Np2. It is equal to the intermediate potential (VDD / 2) between the potentials. As a result, when the voltage Va of the first node N1 and the voltage Vb of the second node N2 are in the vicinity of "VDD / 2", the current Ia flowing through the first resistor R1 and the current Ib flowing through the second resistor R2 are approximated. It becomes easier to do. When the current Ia and the current Ib are close to each other and the difference between the currents (Ia-Ib) becomes small, a voltage drop corresponding to the current difference (Ia-Ib) is generated in the impedance elements Z1 and Z2. The voltage Vo error is easily suppressed.

Here, an example of a circuit for applying a reference voltage (Vra, Vrb) used in the sensor device 1 will be described with reference to FIGS. 2 and 3.

FIG. 2 is a diagram showing an example of a sensor device 1 provided with a circuit that generates a first reference voltage Vra and a second reference voltage Vrb, and fifth resistors R51 to R53 are added to the sensor device 1 shown in FIG. It is a thing. In the sensor device 1 shown in FIG. 2, three fifth resistors R51, R52, and R53 are connected in series between the power supply nodes Np1 and Np2, and the two intermediate nodes in the series connection circuit are the fifth node N5 and the fifth. It has 6 nodes N6.

One terminal of the fifth resistor R51 is connected to the power supply node Np1, the other terminal of the fifth resistor R51 and one terminal of the fifth resistor R52 are connected via the sixth node N6, and the fifth resistor R52 The other terminal and one terminal of the fifth resistor R53 are connected via the fifth node N5, and the other terminal of the fifth resistor R53 is connected to the power supply node Np2.

In the sensor device 1 shown in FIG. 2, the resistance values (particularly R51 and R53) of the fifth resistors R51 to R53 are set so that the reference voltage (Vra, Vrb) does not easily change according to the currents Ia and Ib. , It is desirable that it is sufficiently smaller than the series resistance value (R1 + R3) of the first resistor R1 and the third resistor R3 and the series resistance value (R2 + R4) of the second resistor R2 and the fourth resistor R4.

Further, in the sensor device 1 shown in FIG. 2, in one example, the resistance value of the fifth resistor R51 and the resistance value of the fifth resistor R53 are substantially equal. As a result, the intermediate potential ((Vra + Vrb) / 2) between the potentials of the 5th node N5 and the 6th node N6 becomes the intermediate potential (VDD / 2) between the two potentials of the two power supply nodes Np1 and Np2. Approximately equal

FIG. 3 is a diagram showing an example of a sensor device 1 using a power supply voltage as a reference voltage (Vra, Vrb). In the sensor device 1 shown in FIG. 1, the fifth node N5 is connected to the power supply node Np2, and a ground level voltage is applied. Further, the sixth node N6 is connected to the power supply node Np1, and the power supply voltage VDD is applied. When the power supply voltage VDD is 5 [V], in order to set the offset voltage adjustment range (voltage difference Vn) to 50 [mV], the resistance ratio K should be set to about 0.01 by the equation (2). Good.

As shown in FIG. 3, by using the voltages of the power supply nodes Np1 and Np2 as they are as the reference voltage (Vra, Vrb), the circuit for generating the reference voltage (Vra, Vrb) becomes unnecessary. It can be simplified. Further, since there is no power consumption by the circuit for generating the reference voltage (Vra, Vrb), the power consumption can be reduced.

Next, the operation of the sensor device 1 having the above-described configuration will be described.
As an example, it is assumed that the direction of change in impedance with respect to the physical quantity to be detected is opposite between the pair of impedance elements Z1 and Z4 and the pair of impedance elements Z2 and Z3. Specifically, for example, when the physical quantity (magnetic field or the like) to be detected increases, the impedance increases in the pair of impedance elements Z1 and Z4, and the impedance decreases in the pair of impedance elements Z2 and Z3. On the contrary, when the physical quantity (magnetic field or the like) to be detected becomes small, the impedance decreases in the pair of impedance elements Z1 and Z4, and the impedance increases in the pair of impedance elements Z2 and Z3.

When the physical quantity to be detected increases, the impedance of the impedance element Z3 decreases and the impedance of the impedance element Z4 increases. Therefore, the voltage Vop of the intermediate node Nop (the node connecting the impedance elements Z3 and Z4) of the series circuit 11B increases. To rise. Further, since the impedance of the impedance element Z1 increases and the impedance of the impedance element Z2 decreases, the voltage Va of the first node N1 and the voltage Vb of the second node N2 decrease, respectively. Here, assuming that the voltage difference Vn between the first node N1 and the second node N2 is kept constant by the constant voltage circuit 22 and the voltage dividing ratio of the voltage dividing circuit 21 does not change, the output with respect to the second node N2. The voltage of the node Non is kept constant. Therefore, when the voltage Vb of the second node N2 decreases, the voltage Von of the output node Non also decreases. As a result, the voltage Vop increases and the voltage Von decreases, so that the output voltage Vo (= Vop-Von) of the bridge circuit 10 changes in the positive direction.

When the physical quantity to be detected becomes small, the voltage Vop decreases and the voltage Von increases due to the reverse operation of the above operation, so that the output voltage Vo of the bridge circuit 10 changes in the negative direction. In this way, the output voltage Vo of the bridge circuit 10 changes according to the physical quantity to be detected.

The output voltage Vo of the bridge circuit 10 (voltage difference between the intermediate node Nop of the series circuit 11B and the output node Non of the voltage dividing circuit 21) becomes a predetermined value (for example, zero) when the physical quantity to be detected is a reference value. Is required. In the sensor device 1 according to the present embodiment, the voltage dividing ratio of the voltage dividing circuit 21 is adjusted so that the deviation (offset) of the output voltage Vo with respect to the predetermined value becomes small. When the voltage dividing ratio of the voltage dividing circuit 21 is adjusted, the voltage Von of the output node Non changes within the range from the voltage Vb of the second node N2 to the voltage Va of the first node N1. However, since the voltage difference Vn of the first node N1 and the second node N2 is constantly controlled by the constant voltage circuit 22, the range of change of the voltage Von, that is, the adjustment range of the offset of the output voltage Vo is always constant. ..

Next, the results of simulating the temperature characteristics of the output voltage in the bridge circuit will be described with reference to FIGS. 4 to 6.

FIG. 4 is a diagram showing a bridge circuit 100 of the first comparative example, and shows a general bridge circuit having a variable resistor (potentiometer) 105 for offset adjustment.
In the bridge circuit 100 of the first comparative example shown in FIG. 4, a series circuit of the resistor 101 and the resistor 102 and a series circuit of the resistor 103 and the resistor 104 are connected between the power supply voltage VDD and the ground GND, respectively. The variable resistor 105 is inserted into an intermediate path connecting the resistor 101 and the resistor 102. The resistor 106 is a resistor for temperature compensation and is connected in parallel with the variable resistor 105. The difference between the voltage Vop of the intermediate node to which the resistors 103 and 104 are connected and the voltage Von of the intermediate terminal of the variable resistor 105 is the output voltage of the bridge circuit 100.

5A and 5B are diagrams showing the simulation results of the voltage von performed on the bridge circuit 100 of the first comparative example shown in FIG. 4, and the variation and the temperature change of the voltage von on one side provided with the variable resistor 105. Is shown. FIG. 5A shows an upper limit value in the adjustment range, and FIG. 5B shows a lower limit value in the adjustment range. In each figure, "TYPE" indicates a representative value, "MAX" indicates the maximum value of variation, and "MIN" indicates the minimum value of variation. In this simulation, the resistance values of the four resistors 101, 102, 103, 104 constituting the bridge circuit 100 of the first comparative example are 2000 [Ω], and the temperature coefficient is 1860 [ppm / ° C.]. The variable resistor 105 is configured by connecting 32 resistors in series, and the resistance value of each resistor is 2.36 [Ω] and the temperature coefficient is 2900 [ppm / ° C]. The resistance value of the temperature compensating resistor 106 is 126.6 [Ω], and the temperature coefficient is 1300 [ppm / ° C.].

In the simulations of FIGS. 5A and 5B, the power supply voltage VDD is 4 [V], and the design voltage Von adjustment range is 2 ± 0.025 [V]. However, due to manufacturing variations in resistance values, the adjustment range varies widely from ± 0.018 [V] to ± 0.035 [V]. Further, despite the provision of the resistor 106 for temperature compensation, a large change in the voltage Von due to the temperature occurs.

On the other hand, FIGS. 6A and 6B are diagrams showing the simulation results of the voltage von performed on the sensor device 1 shown in FIG. 2, and show the variation and the temperature change of the voltage von of the output node Non. FIG. 6A shows an upper limit value in the adjustment range, and FIG. 6B shows a lower limit value in the adjustment range. In the simulations of FIGS. 6A and 6B, the same resistance value conditions as those of the resistors 101, 102, 103, and 104 in the simulations of FIGS. 5A and 5B are applied to the impedance elements Z1, Z2, Z3, and Z4 of the bridge circuit 10, respectively. The same resistance value condition as that of the variable resistor 105 is applied to the voltage dividing circuit 21. The power supply voltage VDD is 4 [V], which is the same as the simulation of FIGS. 5A and 5B. The voltage difference Vn between the first node N1 and the second node N2 of the voltage dividing circuit 21 is controlled to be 0.05 [V] by the constant voltage circuit 22.

According to the simulation results of FIGS. 6A and 6B, the graphs of "TYPE", "MAX", and "MIN" showing the influence of the variation in the resistance value of the impedance element Z are almost the same. Therefore, it can be seen that the adjustment range of the voltage Von hardly changes even if the resistance value of the impedance element Z varies in manufacturing. Further, even if the resistance values of the impedance elements Z1 and Z2 change according to the temperature, the voltage Von of the output node Non is almost constant, and the fluctuation of the offset voltage due to the temperature characteristics of the resistance is suppressed. I understand.

Next, the result of simulating the noise of the sensor device will be described with reference to FIGS. 7 and 8.

FIG. 7 is a diagram showing the sensor device 200 of the second comparative example, which is the same as the sensor device described in FIG. 1 of Patent Document 2 described above. That is, the sensor device 200 of the second comparative example shown in FIG. 7 replaces the constant voltage circuit 22 of the sensor device 1 in the present embodiment with the constant voltage circuit 220. The constant voltage circuit 220 is connected in parallel with the voltage dividing circuit 21, and the voltage difference Vn between the variable resistance element 221 whose resistance value changes according to the control signal Vg and the nodes (N1, N2) at both ends of the voltage dividing circuit 21. Includes a differential amplifier circuit 222 that amplifies the voltage, and an error amplifier circuit 223 that amplifies the difference between the output voltage Vamp and the reference voltage Vref of the differential amplifier circuit 222 and outputs a control signal Vg according to the result of the amplification. ..

FIG. 8 is a diagram showing the results of noise simulation for the sensor device 1 shown in FIG. 2 and the sensor device 200 of the second comparative example shown in FIG. 7, respectively, and shows the relationship between the offset adjustment voltage and the noise. In this simulation, the voltage difference Vn between the voltage Va and the voltage Vb is set to 50 [mV]. The offset adjustment voltage on the horizontal axis represents the voltage Von when the voltage between the voltage Va and the voltage Vb is set to zero. -25 [mV] on the horizontal axis corresponds to the voltage Vb, and 25 [mV] corresponds to the voltage Va.

In FIG. 8, the thick dotted line represents the noise of the sensor device 200 of the second comparative example, and the thick solid line represents the noise of the sensor device 1 shown in FIG. As can be seen from the graph of FIG. 8, the noise of the sensor devices 1,200 increases as the offset adjustment voltage shifts in the positive or negative direction with respect to zero. Comparing with the offset adjustment voltage in the vicinity of 25 [mV], the noise of the sensor device 1 shown in FIG. 2 is about 1/3 of the noise of the sensor device 200 of the second comparative example.

As described above, according to the sensor device 1 according to the present embodiment, the voltage difference Vn between the first node N1 and the second node N2 at both ends of the voltage dividing circuit 21 is kept constant. Therefore, even if there are manufacturing variations in the impedances of the four impedance elements Z, the range of change in the voltage Von of the output node Non due to the adjustment of the voltage dividing ratio of the voltage dividing circuit 21 is substantially constant. As a result, the range of change of the output voltage Vo (voltage difference between the intermediate node Nop and the output node Non) of the bridge circuit 10 due to the adjustment of the voltage division ratio becomes substantially constant. Therefore, it is possible to keep the adjustment range of the offset of the output voltage Vo constant without being affected by the manufacturing variation of the impedance of the impedance element Z.

Further, according to the sensor device 1 according to the present embodiment, the third resistor R3 and the first resistor R1 are formed in the path between the fifth node N5 and the first node N1 to which the first reference voltage Vra is applied. The fourth resistor R4 and the second resistor R2 are connected in series via the third node N3 and in the path between the sixth node N6 and the second node N2 to which the second reference voltage Vrb is applied. It is connected in series via the fourth node N4. The resistance value of the variable resistance element M1 connected in parallel with the voltage dividing circuit 21 is a control signal Vg which is a signal obtained by amplifying the voltage difference between the third node N3 and the fourth node N4 by the error amplifier circuit U1. It is controlled according to. When the resistance value of the variable resistance element M1 is controlled so that the voltage difference between the third node N3 and the fourth node N4 becomes sufficiently small, the resistance ratio of the first resistance R1 to the third resistance R3 (R1 / R3). Since the resistance ratio (R2 / R4) of the second resistor R2 to the fourth resistor R4 is equal, the voltage difference Vn between the first node N1 and the second node N2 is the first reference voltage Vra and the second reference voltage. The voltage difference is maintained to be roughly proportional to the difference from Vrb (Vrb-Vra). As a result, since the front stage of the error amplifier circuit U1 is composed of resistors (R1 to R4), it is possible to reduce the number of operational amplifiers used as compared with the case where the differential amplifier circuit is provided in the front stage of the error amplifier circuit U1. The amount of noise generated can be effectively reduced.

According to the sensor device 1 according to the present embodiment, by making the resistance value of the first resistor R1 equal to the resistance value of the second resistor R2, the error amplifier circuit U1 caused by the input current of the error amplifier circuit U1 or the like The variation of the offset voltage can be reduced.

According to the sensor device 1 according to the present embodiment, there is an intermediate potential ((Vra + Vrb) / 2) between the potentials of the 5th node N5 and the 6th node N6, and between the potentials of the two power supply nodes Np1 and Np2. By making the intermediate potential (VDD / 2) equal, the current Ia flowing through the first resistor R1 when the voltage Va of the first node N1 and the voltage Vb of the second node N2 are in the vicinity of "VDD / 2". The difference (Ia-Ib) between the current and the current Ib flowing through the second resistor R2 becomes smaller. Therefore, the error of the output voltage Vo due to this difference in current (Ia-Ib) is likely to be suppressed.

According to the sensor device 1 according to the present embodiment, since the temperature coefficients of the impedances of the four impedance elements Z constituting the bridge circuit 10 are the same, the impedance ratios of the four impedance elements Z are unlikely to change depending on the temperature. .. Further, since a constant power supply voltage VDD is supplied to the two power supply nodes Np1 and Np2, and the voltage difference Vn between the first node N1 and the second node N2 of the voltage dividing circuit 21 is kept constant, 4 If the ratio of impedances in one impedance element Z is unlikely to change with temperature, the voltage applied to the four impedance elements Z is also unlikely to change with temperature. Therefore, the offset of the output voltage Vo of the bridge circuit 10 is less likely to change with temperature, as shown in the simulation results of FIGS. 6A and 6B. That is, even if the temperature of the environment changes, the offset adjustment is less likely to deviate, so that it is possible to detect a physical quantity with high accuracy in a wide temperature range.

According to the sensor device 1 according to the present embodiment, the resistance value between the first node N1 and the second node N2 in the voltage dividing circuit 21 is constant, and the voltage difference between the first node N1 and the second node N2. Since Vn is kept constant by the constant voltage circuit 22, the voltage applied to the impedance elements Z1 and Z2 does not change by adjusting the voltage dividing ratio and becomes substantially constant. As a result, the sensitivity of the impedance elements Z1 and Z2 for converting the change in the physical quantity into the change in the impedance is less affected by the adjustment of the voltage division ratio. That is, the adjustment of the offset of the output voltage Vo is less likely to affect the detection sensitivity of the physical quantity, and good detection accuracy can be obtained.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and includes various variations.

In the above-described embodiment, the offset adjustment circuit 20 is provided only in one of the two series circuits 11A and 11B in the bridge circuit 10 in the series circuit 11A, but the present invention is not limited thereto. In another embodiment of the present invention, a similar offset adjusting circuit 20 is provided in both of the two series circuits 11A and 11B, and the output voltage is adjusted by adjusting the voltage dividing ratio of the voltage dividing circuit 21 in each offset adjusting circuit 20. The offset of Vo may be adjusted. As a result, the voltages applied to the four impedance elements Z1 to Z4 become substantially equal, and it becomes easy to align the detection sensitivities of the physical quantities in each impedance element Z, so that better detection accuracy can be obtained.

In the embodiment shown in FIG. 2 described above, the reference voltage (Vra, Vrb) is generated by dividing the power supply voltage by the resistors (R51 to R53), but the method of generating the reference voltage (Vra, Vrb) is Not limited to this example. For example, a reference voltage (Vra, Vrb) may be generated using a bandgap reference circuit or the like.

In the above-described embodiment, each of the four impedance elements Z in the bridge circuit 10 is a sensor element and has an impedance corresponding to a physical quantity to be detected, but the present invention is not limited thereto. In another embodiment of the present invention, some of the plurality of impedance elements constituting the bridge circuit may have a fixed impedance.

In the above-described embodiment, a constant power supply voltage VDD is supplied to the power supply nodes Np1 and Np2, but in another embodiment of the present invention, a constant current is supplied to the power supply nodes Np1 and Np2 from a constant current source. May be good.

1 ... Sensor device, 10 ... Bridge circuit, 11A, 11B ... Series circuit, Z, Z1 to Z4 ... Impedance element, 20 ... Offset adjustment circuit, 21 ... Voltage divider circuit, 22 ... Constant voltage circuit, M1 ... Variable resistance element, U1 ... Error amplifier circuit, R1 ... 1st resistance, R2 ... 2nd resistance, R3 ... 3rd resistance, R4 ... 4th resistance, R51-R53 ... 5th resistance, N1 ... 1st node, N2 ... 2nd node, N3 ... 3rd node, N4 ... 4th node, N5 ... 5th node, N6 ... 6th node, Np1, Np2 ... Power supply node, Nop ... Intermediate node, Non ... Output node, Vra ... 1st reference voltage, Vrb ... 2nd reference voltage, Vg ... Control signal

Claims (5)

A bridge circuit having a plurality of impedance elements having at least a part impedance corresponding to the physical quantity to be detected, and
It is provided with an offset adjustment circuit for adjusting the offset of the output voltage of the bridge circuit.
The bridge circuit has two series circuits each including two or more of the impedance elements connected in series between two power supply nodes to which power is supplied.
The offset adjustment circuit
It is inserted into the intermediate path of at least one of the series circuits of the two series circuits, and the voltage difference generated between the first node and the second node at both ends in the inserted intermediate path is divided and the divided voltage is divided. With a voltage divider circuit that outputs from the output node,
It has a constant voltage circuit that keeps the voltage difference between the first node and the second node in the voltage dividing circuit constant.
The voltage dividing circuit can adjust the voltage dividing ratio, and the voltage dividing circuit can be adjusted.
When adjusting the offset, the voltage difference between the output node of the voltage divider circuit in one of the series circuits and the intermediate node of the other series circuit, or the output node of the voltage divider circuit in one of the series circuits. The voltage dividing ratio is adjusted so that the voltage difference between the one and the output node of the voltage dividing circuit in the other series circuit approaches a predetermined value.
The constant voltage circuit
A variable resistance element that is connected in parallel with the voltage divider circuit and whose resistance value changes according to the control signal.
A first resistor provided in the path between the first node and the third node,
A second resistor provided in the path between the second node and the fourth node,
A third resistor provided in the path between the fifth node to which the first reference voltage is applied and the third node, and
A fourth resistor provided in the path between the sixth node to which the second reference voltage is applied and the fourth node, and
It includes an error amplification circuit that amplifies the voltage difference between the third node and the fourth node and outputs the control signal according to the result of the amplification.
The resistivity ratio of the first resistor to the third resistor is equal to the resistivity ratio of the second resistor to the fourth resistor.
Sensor device. The resistance value of the first resistor is equal to the resistance value of the second resistor.
The sensor device according to claim 1. The intermediate potential between the two potentials of the fifth node and the sixth node is equal to the intermediate potential between the two potentials of the two power supply nodes.
The sensor device according to claim 2. It has three or more fifth resistors connected in series between the two power nodes.
The two intermediate nodes in the plurality of intermediate nodes to which the three or more fifth resistors are connected are the fifth node and the sixth node.
The sensor device according to any one of claims 1 to 3. The two power supply nodes are the fifth node and the sixth node.
The sensor device according to any one of claims 1 to 3.

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