JP2001183165A - Sensor abnormality detecting circuit and physical quantity detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized abnormality detecting circuit capable of accurately detecting abnormalities without delay in a sensor 10 in which the output voltages V1 and BV2 of a pair of output terminals J1 and J2 each change from a predetermined equilibrium-point voltage according to the physical quantity of an object to be detected by the same amount in the positive direction and negative direction. SOLUTION: The abnormality detecting circuit is provided with reference-voltage generating circuits 21-24 to generate the same voltage VE as the equilibrium-point voltage of the sensor 10, an operational amplifier 12 in which the voltage VE is inputted to its non-inverse input terminal and a resistance 15 is connected between is output terminal and inverse input terminal, a resistance 13 in which one output voltage V1 of the sensor 10 is impressed on its one end and its other end is connected to the inverse input terminal of the operational amplifier 12, a resistance 14 in which the other output voltage V2 of the sensor 10 is impressed in its one end, its other end is connected to the inverse input terminal of the operational amplifier 12, and its resistance value is set at the same value as that of the resistance 13, and a determining circuit 16 to output a signal indicating an anomaly in the case that the output voltage of the operational amplifier 12 lies outside a predetermined voltage range (VE±α).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for controlling an output voltage generated at a pair of output terminals by the same voltage in a positive direction and a negative direction based on a predetermined equilibrium point voltage in accordance with a physical quantity to be detected. The present invention relates to an abnormality detection circuit for detecting an abnormality of a changing sensor.

[0002]

2. Description of the Related Art Conventionally, as a sensor of this type, for example, as shown in FIGS. 6 (a) to 6 (c), four sensors whose respective resistance values change due to strain and which are connected in a loop are formed. Gauge resistance (generally consisting of diffusion resistance,
There is a pressure sensor 100 having 1, 2, 3, 4 (also called strain gauges).

In such a pressure sensor 100, the above 4
Gauge resistors 1 to 4 are formed on a Si (silicon) substrate 101, and the Si substrate 101 has, for example, a cylindrical metal diaphragm 10 to which a pressure P such as a hydraulic pressure is applied.
2 is joined to the end face by a joining member 103.

[0006] Among the connection points A to D of the gauge resistors 1 to 4, a specific connection point A (in the example of FIG. 6, a connection point between the gauge resistors 1 and 4) and the connection point A Counting 2
The drive voltage VD is applied between the second connection point C (the connection point between the gauge resistors 2 and 3 in the example of FIG. 6), and the other two connection points B and D (in the example of FIG. 6, A connection point B between the gauge resistors 1 and 2 and a connection point D) between the gauge resistors 3 and 4 form a pair of output terminals J1 and J2.

Further, each of the gauge resistors 1, 2, 3, 4
Let R1, R2, R3, and R4 be the respective resistance values of the gauge resistors 1, 2, 3, and 4. The resistance values and the arrangement on the Si substrate 101 are designed so as to satisfy the following equation 1. Has been determined above. In Equation 1, R0 is a resistance value of each of the gauge resistors 1, 2, 3, and 4 when the pressure P = 0. ΔR represents an increase or decrease in the resistance value when the pressure P is applied. When the pressure P = 0, ΔR = 0
It is.

[0006]

R1 = R3 = R0−ΔR, R2 = R4 = R0 + ΔR Equation 1 Therefore, when the pressure P = 0, a connection point B between the gauge resistors 1 and 2 (hereinafter, this connection point B is referred to as First output terminal J
1) and a second output voltage generated at a connection point D between the gauge resistors 3 and 4 (hereinafter, this connection point D is referred to as a second output terminal J2). V2 are both equal to the equilibrium point voltage V0 (= VD / 2), which is half the drive voltage VD.

When a pressure P is applied to the metal diaphragm 102 (pressure P = N ≠ 0), the Si substrate 101
When distortion occurs in each of the above gauge resistors 1 to 4, FIG.
As shown in (1), the first output voltage V1 becomes higher than the equilibrium point voltage V0 by ΔV1, and the second output voltage V2 becomes lower than the equilibrium point voltage V0 by ΔV2. And Δ
Both V1 and ΔV2 have the same value (ΔV1 = ΔV2) from the symmetry of the Wheatstone bridge (Equation 1 above). That is, the first output terminal J1 and the second output terminal J2
Output voltages V1 and V2 generated in each of the above-mentioned conditions change by the same voltage in the positive direction and in the negative direction based on the equilibrium point voltage V0 according to the pressure P as the physical quantity to be detected. V1−V0 | = | V2−V0 |

Accordingly, the signal processing circuit for inputting the output voltages V1 and V2 of the pressure sensor 100 detects the pressure P based on the potential difference (V1-V2) between the two output voltages V1 and V2. Then, based on the above principle, the pressure P can be detected with higher accuracy.

The above is the normal operation. For example, FIG.
As shown in (c), the Si substrate 101 and the bonding member 103
If the resistance value of any of the four gauge resistors 1 to 4 is not a normal value due to the occurrence of a crack K in the sensor, the equilibrium point voltage V0 and the sensitivity of the sensor change, and the detection accuracy of the pressure P deteriorates. Resulting in. In the case of such a failure, FIG.
, The absolute value of the difference between the first output voltage V1 and the original equilibrium point voltage V0 (| V1−V0 | = ΔV1)
And the absolute value of the difference between the second output voltage V2 and the original equilibrium point voltage V0 (| V2−V0 | = ΔV2) occurs.

Here, such an abnormality of the sensor cannot be detected even if the potential difference (V1-V2) between the two output voltages V1 and V2 is monitored. This is because the sensor equilibrium point voltage V0 is a virtual potential that does not exist on the circuit. Therefore, as a technique for detecting such a sensor abnormality, Japanese Patent Application Laid-Open No.
It is described that a circuit configuration as shown in FIG. 7 is employed.

That is, as shown in FIG. 7, in the abnormality detecting device described in the above publication, two resistors 106 and 10 for dividing the driving voltage VD applied to the pressure sensor 100 into ２.
7, two switches SW1 and SW2 having three contact positions a, b and c, and an information processing device 108 including an A / D converter, a D / A converter, and an MPU (microprocessor unit). ing.

In this abnormality detecting device, the information processing device 108 controls the switches SW1 and SW2, and sets the contact positions of the switches SW1 and SW2 to the position a, so that both output voltages of the pressure sensor 100 are changed. V1, V2
(V1-V2), and both switches SW
By setting the contact position of SW1 and SW2 to the position b, one output voltage V1 of the pressure sensor 100 and the resistances 106, 1
07 (ie, VD / 2, which is the same voltage as the original equilibrium point voltage V0 of the pressure sensor 100) V3, and further, both switches SW
By setting the contact position of SW1 and SW2 to the position of c, the other output voltage V2 of the pressure sensor 100 and the resistances 106, 1
07 (V2−V3) from the divided voltage V3.

Further, the information processing device 108 captures the contact positions of the switches SW1 and SW2 at the positions b and c, respectively, at "V1-V3" and "V2-V3".
V3 ”to calculate a voltage“ V1 + V2-2 · V3 ”, and calculate the calculated voltage (V1 + V2-2 · V
If 3) exceeds a predetermined threshold, the sensor 10
0 is determined to be abnormal.

That is, in the abnormality detection device described in the above publication, conceptually, a value (V1-V0) obtained by subtracting the equilibrium point voltage V0 (= V3) from one output voltage V1 of the sensor 100.
A value (V1 + V2-2 · V3) obtained by adding a value (V2−V0) obtained by subtracting the equilibrium point voltage V0 (= V3) from the other output voltage V2 of the sensor 100 becomes 0 in a normal state. Paying attention to the added value (V1 + V2-2 · V
Abnormality of the sensor 100 is detected based on 3).

According to this abnormality detecting device, FIG.
By detecting the imbalance between the two output voltages V1 and V2 as illustrated in (e), it is possible to detect that the sensor 100 is abnormal.

[0016]

However, the above-mentioned conventional abnormality detecting device has the following problems. : First, since the above-mentioned added value (V1 + V2-2 · V3) is obtained by sequentially switching the contact positions of the two switches SW1 and SW2, accurate abnormality detection is performed based on the output voltages V1 and V2 at the same time. Can not. That is, after setting the contact positions of the switches SW1 and SW2 to the position b, c
If the pressure P applied to the pressure sensor 100 changes and the output voltages V1 and V2 change normally before reaching the position, there is a possibility that it is erroneously determined to be abnormal.

And two more switches SW1,
The contact position of SW2 is sequentially switched, and the added value (V1 +
Since V2-2 · V3) is obtained, a delay occurs after an abnormality occurs in the sensor 100 until the abnormality can be detected. : In the above-described conventional abnormality detection device, the switch SW
1, an information processing device 108 having an MPU for controlling the SW2 and performing an arithmetic operation for abnormality detection is required. When a sensor unit having such an abnormality detection function is configured, the sensor unit becomes large. It will be large and expensive.

The present invention has been made in view of such a problem, and each output voltage generated at a pair of output terminals is adjusted in a positive direction and a negative direction based on a predetermined equilibrium point voltage according to a physical quantity to be detected. It is an object of the present invention to provide a small-scale abnormality detection circuit that can accurately and accurately detect an abnormality of a sensor that changes by the same voltage each time, and a physical quantity detection device using the abnormality detection circuit. .

[0019]

In order to achieve the above object, the abnormality detecting circuit according to the first aspect of the present invention generates a signal at a first output terminal J1 as shown in FIG. The first output voltage V1 and the second output voltage V2 generated at the second output terminal J2 are set in a positive direction and a negative direction based on a predetermined equilibrium point voltage V0 according to a physical quantity to be detected. A reference voltage generating circuit 11 for generating a reference voltage VE substantially equal to the equilibrium point voltage V0, and a reference voltage generating circuit 11 for detecting an abnormality of the sensor 10 formed so as to change by the same voltage. An operational amplifier (op-amp) 12 having a reference voltage VE generated by a generation circuit 11 input to one input terminal, and one end of the sensor 10
, A first resistor 13 having the other end connected to the other input terminal of the operational amplifier 12, and a second output voltage V2 of the sensor 10 at one end.
Is applied, the other end is connected to the other input terminal of the operational amplifier 12, and the resistance value is set to the first resistance 1
3, a third resistor 15 connected between the output terminal of the operational amplifier 12 and the other input terminal, and an output voltage VOU of the operational amplifier 12.
A determination circuit 16 for outputting a signal indicating that the sensor 10 is abnormal when T is outside a voltage range set for quality determination;

In FIG. 1, one input terminal of the operational amplifier 12 is a non-inverting input terminal (+), and the other input terminal of the operational amplifier 12 is an inverting input terminal (-). FIG. 1 illustrates a case where the sensor 10 to be subjected to abnormality detection is the same sensor as the pressure sensor 100 described with reference to FIG. 6, but the abnormality detection circuit of the present invention also applies to other sensors. Can be applied.

In such an abnormality detection circuit, the resistance values of the first resistor 13 and the second resistor 14 are R,
Let X · R be the resistance value of the resistor 15 of the operational amplifier 12.
Is the output voltage VOUT of the following equation (2).

[0022]

VOUT = −X ｛(V1−VE) + (V2−VE) Ｖ + VE (2) That is, from the operational amplifier 12, the reference voltage VE is used as a reference, and one output voltage V1 of the sensor 10 is used as a reference. Voltage V
A voltage VOUT proportional to a value obtained by adding a value obtained by subtracting E and a value obtained by subtracting the reference voltage VE from the other output voltage V2 of the sensor 10 is output.

The output voltages V1 and V2 of the sensor 10 are
Of the above, if the first output voltage V1 changes in the positive direction according to the increase in the physical quantity to be detected, and the second output voltage V2 changes in the negative direction according to the increase in the physical quantity to be detected, , The absolute value (| V1−VE |) of the difference between the first output voltage V1 and the reference voltage VE is set to ΔV1 ′, and the second output voltage V
Assuming that the absolute value (| V2−VE |) of the difference between the reference voltage VE and the reference voltage VE is ΔV2 ′, the equation 2 becomes the following equation 3, and the operational amplifier 12 outputs ΔV
A voltage VOUT proportional to the difference between 1 'and .DELTA.V2' is output.

[0024]

VOUT = −X (ΔV1′−ΔV2 ′) + VE (3) The output voltage VOUT of the operational amplifier 12 is obtained by changing the reference voltage VE generated by the reference voltage generation circuit 11 to the equilibrium point voltage V0 of the sensor 10. Is approximately equal to
If 0 is normal, it becomes almost VE as can be seen from the above equations (2) and (3).

On the other hand, if an abnormality occurs in the sensor 10,
When the balance between the two output voltages V1 and V2 is lost, that is, as illustrated in FIG.
When the phenomenon that the absolute value ΔV1 of the difference between the second output voltage V2 and the equilibrium point voltage V0 does not become equal to the absolute value ΔV1 of the difference between the output voltage VOUT of the operational amplifier 12 and It will be shifted in the positive or negative direction from the reference voltage VE.

Therefore, in this abnormality detection circuit, the judgment circuit 16 judges whether the output voltage VOUT of the operational amplifier 12 is out of the voltage range for judging pass / fail. 10 outputs a signal indicating that it is abnormal.

According to the abnormality detection circuit of the first aspect, the abnormality of the sensor 10 can be accurately detected based on the output voltages V1 and V2 at the same time.
Moreover, there is almost no delay from the occurrence of an abnormality in the sensor 10 to the detection of the abnormality. Further, the abnormality of the sensor 10 can be detected with a very small circuit configuration without providing a high-performance information processing device such as an MPU.

As can be seen from the above detection principle, it is desirable that the reference voltage VE generated by the reference voltage generation circuit 11 be the same as the equilibrium point voltage V0 of the sensor 10. However, even if the reference voltage VE does not completely match the equilibrium point voltage V0 of the sensor 10, the error can be absorbed in the pass / fail judgment voltage range in the judgment circuit 16, so that in this sense, In the present invention, the reference voltage VE is set to the sensor 1
0 is almost the same as the equilibrium point voltage V0.

By the way, in the abnormality detecting circuit of the present invention, one end of the first resistor 13 is directly connected to the first output terminal J1 of the sensor 10, and one end of the second resistor 14 is connected to the second output terminal J2 of the sensor 10. May be directly connected to the output terminal J2, but depending on the structure of the sensor 10, from the output terminals J1 and J2 to the circuit portion including the operational amplifier 12 and the first to third resistors 13, 14, and 15. When a current flows, the output voltages V1 and V2 may be shifted.

Therefore, in the abnormality detection circuit according to the second aspect, as shown in FIG. 1, the first output voltage V1 of the sensor 10 is input and the first output voltage V1 is changed to the first output voltage V1. A first buffer 17 applied to one end of a resistor 13 and a second output voltage V2 of the sensor 10 are input, and a second output voltage V2 is applied to one end of a second resistor 14. A buffer 18 is provided. That is, the first buffer 17 is provided between the first output terminal J1 of the sensor 10 and the first resistor 13, and the second buffer 14 is provided between the second output terminal J2 of the sensor 10 and the second resistor 14. , A second buffer 18 is provided.

According to the abnormality detecting circuit of the second aspect, the current is supplied from the output terminals J1 and J2 of the sensor 10 to the circuit portion including the operational amplifier 12 and the first to third resistors 13, 14, and 15. Is prevented from flowing, and the sensor 1
The abnormality of 0 can be more accurately detected.

Further, in addition to the first buffer and the second buffer, a reference voltage VE generated by a reference voltage generating circuit is inputted to calculate the reference voltage VE. A third buffer for inputting to the one input terminal of the amplifier may be provided.

On the other hand, each of the first buffer, the second buffer, and the third buffer does not output the same voltage as the input voltage. A level shift circuit that outputs a voltage shifted by a specific voltage Vsf as an output voltage can also be used. Note that the value of the voltage Vsf for the shift is:
It may be either positive or negative. Further, each buffer may be a level shift circuit having the same configuration.

That is, when such a level shift circuit is used as the first to third buffers, a voltage (Vsf) obtained by shifting the first output voltage V1 of the sensor by Vsf is applied to one end of the first resistor. = V1 + Vsf), and one end of the second resistor is connected to the second output voltage V2 of the sensor by Vsf.
Is applied (= V2 + Vsf),
A voltage (= VE + Vsf) obtained by shifting the reference voltage VE by Vsf is input to the one input terminal of the operational amplifier, and all three input voltages are equal to the same voltage Vs.
The shift is performed by f. So even in this case,
From the operational amplifier, a value obtained by subtracting the reference voltage VE from one output voltage V1 of the sensor and the other output voltage V2 of the sensor are obtained.
Is subtracted from the reference voltage VE, and a voltage VOUT proportional to a value obtained by adding the values is output (see Equation 2), and the same effect as that of the above-described abnormality detection circuit according to claims 1 to 3 can be obtained. it can.

In general, the level shift circuit has a simpler configuration than a buffer configured to output the same voltage as the input voltage.
There is an advantage that the circuit scale can be reduced.
Next, in the abnormality detection circuit according to the fifth aspect, the first output voltage V1 generated at the first output terminal and the second output voltage V2 generated at the second output terminal are detected. This is for detecting an abnormality of a sensor formed so as to change by the same voltage in the positive direction and the same voltage in the negative direction based on the predetermined equilibrium point voltage V0 according to the physical quantity.

An abnormality detection circuit according to a fifth aspect of the present invention includes a reference voltage generation circuit for generating a reference voltage VE substantially equal to the equilibrium point voltage V0, and one of the reference voltage VE generated by the reference voltage generation circuit. An operational amplifier input to an input terminal, a first differential amplifier having a first output voltage V1 of the sensor as a non-inverting input, and a reference voltage VE generated by the reference voltage generating circuit as an inverting input, A second differential amplifier having a second output voltage V2 of the sensor as a non-inverting input and a reference voltage VE generated by the reference voltage generating circuit as an inverting input; A first resistor having an output voltage V1S applied thereto and the other end connected to the other input terminal of the operational amplifier;
The output voltage V2S of the second differential amplifier is applied to one end, the other end is connected to the other input terminal of the operational amplifier, and the resistance value is set to be the same as the first resistance. 2, the third resistor connected between the output terminal of the operational amplifier and the other input terminal, and the output voltage VOUT of the operational amplifier are out of the voltage range set for quality judgment. A determination circuit for outputting a signal indicating that the sensor is abnormal.

That is, in the abnormality detection circuit according to the fifth aspect, the first and second buffers are provided in place of the first and second buffers in the abnormality detection circuit according to the second aspect. . In the abnormality detection circuit according to the fifth aspect, assuming that the amplification factors (amplification degrees) of the first differential amplifier and the second differential amplifier are Y, the output voltage V1S of the first differential amplifier.
Is given by Expression 4, and the output voltage V of the second differential amplifier is
2S is expressed by Expression 5.

[0038]

V1S = Y (V1-VE) + VE Expression 4

[0039]

V2S = Y (V2−VE) + VE Equation 5 The output voltage VOUT of the operational amplifier is obtained by replacing V1 and V2 in Equation 2 with V1S and V2S, respectively, as shown in Equation 6 below. Become like

[0040]

V OUT = −X · Y {(V1−VE) + (V2−VE)} + VE (6) As can be seen from Equation 6, according to the abnormality detection circuit of the fifth aspect, the output voltage of the sensor When the balance between V1 and V2 is lost, the output voltage VOUT of the operational amplifier becomes the reference voltage VOUT.
It will deviate greatly from E in the positive or negative direction.

For this reason, it is possible to more reliably detect an abnormality in the sensor. In general, an operational amplifier has an offset voltage, but the operational amplifier can be operated in a region where the influence of the offset voltage is sufficiently small, and the abnormality detection accuracy can be further improved.

Further, the first and second differential amplifiers fulfill the same role as the first and second buffers according to the second aspect. That is, it is also possible to prevent excess current from flowing from the output terminal of the sensor to the circuit portion including the operational amplifier and the first to third resistors.

In the abnormality detection circuit according to any one of the first to fifth aspects, the determination circuit may be configured such that the output voltage VOUT of the operational amplifier is higher than a reference voltage VE generated by a reference voltage generation circuit. Is higher than a first determination voltage (VE + α) that is higher by a predetermined voltage α, and the second determination is that the output voltage VOUT of the operational amplifier is lower by a predetermined voltage β than a reference voltage VE generated by a reference voltage generating circuit. When the voltage is lower than the voltage (VE-β), a signal indicating that the sensor is abnormal may be output.

As a specific configuration example, a first determination voltage higher than the reference voltage VE by a predetermined voltage α and a reference voltage V
A determination voltage generation circuit for generating a second determination voltage lower than E by a predetermined voltage β is provided, and the first determination voltage and the second determination voltage generated by the determination voltage generation circuit are supplied to the determination circuit To be done. Then, the determination circuit determines that the output voltage VOUT of the operational amplifier is higher than the higher one of the two supplied voltages (that is, the first determination voltage), and that the output voltage VOUT of the operational amplifier is The lower of the two supplied voltages (ie, the second determination voltage)
If it is lower than this, it may be configured to output a signal indicating that the sensor is abnormal. Note that the predetermined voltages α, β
Are desirably set to the same value, but can be intentionally set to different values.

However, in the abnormality detecting circuit according to the fourth aspect of the present invention, which includes the first to third buffers each including a level shift circuit, the term "+ VE" in the above-mentioned equations (2) and (3) is "+ (VE +
Vsf) ", and the output voltage VOUT of the operational amplifier becomes" Vsf).
Since the voltage is based on “E + Vsf”, it is particularly effective to configure the circuit as described in claim 7.

That is, in the abnormality detection circuit according to claim 7, in the abnormality detection circuit according to claim 4, in addition to the determination voltage generation circuit for generating the first determination voltage and the second determination voltage, The first determination voltage generated by the determination voltage generation circuit is set to the same specific voltage V as that of the first to third buffers.
a fourth buffer that shifts by sf and supplies the same to the determination circuit; and a fifth buffer that shifts the second determination voltage generated by the determination voltage generation circuit by the specific voltage Vsf and supplies the second determination voltage to the determination circuit. And Then, the determination circuit determines that the output voltage VOUT of the operational amplifier is a voltage supplied from the fourth buffer (that is, the first determination voltage + Vs
f) and the output voltage VOUT of the operational amplifier
Is lower than the voltage supplied from the fifth buffer (that is, the second determination voltage + Vsf), and outputs a signal indicating that the sensor is abnormal.

According to the abnormality detection circuit of the seventh aspect, not only the output voltage VOUT of the operational amplifier but also the voltage range for the pass / fail judgment in the judgment circuit is shifted as a whole by the specific voltage Vsf. Therefore, accurate abnormality determination can be performed without resetting the first determination voltage and the second determination voltage by adjusting the determination voltage generation circuit or the like.

On the other hand, in the abnormality detecting circuits according to the first to seventh aspects, as a sensor to be subjected to the abnormality detection, as described in the eighth aspect, the respective resistance values change due to the distortion and are connected to each other in a loop. Have four gauge resistances,
Of the connection points between the gauge resistors, a drive voltage is applied between a specific connection point and a second connection point counted from the specific connection point, and the other two connection points are connected to the second connection point. The pressure sensor may be the first and second output terminals.

With this configuration, it is possible to accurately detect the abnormality of the pressure sensor having the four gauge resistors without delay even with a small circuit configuration. In particular, in this type of pressure sensor, the difference between each of the output voltages V1 and V2 and the equilibrium point voltage V0 is usually small, so the configuration of claim 5 is effective.

Here, when the sensor for abnormality detection is a pressure sensor, the reference voltage generation circuit divides the drive voltage VD applied to the pressure sensor to generate the reference voltage VE. At least two resistances. For example, as shown in FIG. 1, the reference voltage generation circuit 11 can be configured by two resistors 11a and 11b that divide the drive voltage VD. In this case, the resistance values of the two resistors 11a and 11b may be set so that the reference voltage VE is generated at a connection point between the two resistors.

The number of resistors for dividing drive voltage VD is three.
There may be more than one. That is, the resistance value of each resistor may be set so that the divided voltage generated at the connection point between any of the resistors becomes the target reference voltage VE. According to the abnormality detection circuit of the ninth aspect, even if the drive voltage VD to the pressure sensor fluctuates and the actual equilibrium point voltage V0 of the pressure sensor changes, the equilibrium point voltage V0
, The reference voltage VE changes. Therefore, even if the drive voltage VD fluctuates, the abnormality of the pressure sensor can be accurately detected.

Next, the physical quantity detecting device according to the tenth aspect includes a first output voltage generated at the first output terminal and a second output voltage.
And a second output voltage generated at an output terminal of the sensor is formed so as to change by the same voltage in the positive direction and the same voltage in the negative direction based on a predetermined equilibrium point voltage in accordance with the physical quantity to be detected. A detection signal indicating a physical quantity to be detected is output from an output terminal based on the first output voltage and the second output voltage of the sensor.

In particular, the physical quantity detecting device according to claim 10 is for detecting abnormality of the sensor.
When a signal indicating that the sensor is abnormal is output from the determination circuit of the abnormality detection circuit, the abnormality detection circuit is output from the output terminal instead of the detection signal. Outputs a specific signal indicating occurrence.

According to such a physical quantity detection device, when the sensor is normal, a detection signal indicating the physical quantity to be detected is output from the output terminal, but when an abnormality occurs in the sensor, the output signal is output. A specific signal indicating the occurrence of an abnormality is output from the terminal. Therefore, other devices such as an electronic control device that inputs and processes the detection signal from the physical quantity detection device only detect that the input detection signal has changed to the above-described specific signal, and the sensor does not operate. It can be determined whether or not the signal is normal, and there is no need to separately provide a signal line.

[0055]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a sensor abnormality detecting circuit according to an embodiment of the present invention will be described with reference to the drawings. First, FIG. 2 is a circuit diagram illustrating a configuration of the abnormality detection circuit according to the first embodiment.

The abnormality detecting circuit of the first embodiment is for detecting an abnormality of the pressure sensor 10 having the same configuration as the pressure sensor 100 described with reference to FIG. This is a more specific detection circuit. In FIG. 2, the same components as those shown in FIGS. 1 and 6 are denoted by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIG. 2, the abnormality detection circuit of the first embodiment has the following (1-1) to
(1-3) is different. (1-1): Each gauge resistor 1 constituting the pressure sensor 10
From the connection points A to D, between the connection point A between the gauge resistors 1 and 4 and the connection point C between the gauge resistors 2 and 3, from the connection point A side to the connection point C side, Four resistors 21,
22, 23 and 24 are sequentially connected in series.

Therefore, the drive voltage VD applied to the pressure sensor 10, that is, the drive voltage VD applied between the connection point A and the connection point C is equal to the four resistances 21 to 24.
In the first embodiment, the resistance values of the four resistors 21 to 24 are divided by the respective resistors 21 to 24.
The following voltages (1) to (3) are set to be generated at the connection points between ２４ to ２４24.

(1): At the connection point between the resistor 22 and the resistor 23, a voltage which is a half of the driving voltage VD and which is the same as the equilibrium point voltage V0 of the two output voltages V1 and V2 of the pressure sensor 10 is applied. , The reference voltage VE. The connection point between the resistors 22 and 23 is connected to the non-inverting input terminal of the operational amplifier 12.

(2): The connection point between the resistor 21 and the resistor 22 has a predetermined voltage α higher than the reference voltage VE (= VD / 2).
A first determination voltage VH (= VE + α) that is only higher is generated. (3): A second determination voltage VL (= VE-α) lower than the reference voltage VE (= VD / 2) by the predetermined voltage α is generated at a connection point between the resistors 23 and 24. I do.

In the first embodiment, the four resistors 21 to 24 correspond to the reference voltage generation circuit 11. As the resistors 21 to 24, thin-film resistors having almost no temperature dependency are used, and the resistance value may be adjusted by laser trimming, or no trimming may be used if the ratio of the resistors can be made with high accuracy.

(1-2): As the first buffer 17,
Operational amplifier 25 with inverted input terminal and output terminal connected
Is used. The non-inverting input terminal of the operational amplifier 25 is connected as an input terminal of the first buffer 17 to a first output terminal J1 of the pressure sensor 10 (connection point B between the gauge resistors 1 and 2). An output terminal of the operational amplifier 25 is connected to one end of the first resistor 13 as an output terminal of the first buffer 17.

Similarly, an operational amplifier 26 having an inverting input terminal and an output terminal connected to each other is used as the second buffer 18. The non-inverting input terminal of the operational amplifier 26 is connected as an input terminal of the second buffer 18 to a second output terminal J2 of the pressure sensor 10 (a connection point D between the gauge resistors 3 and 4). An output terminal of the operational amplifier 26 is connected to one end of the second resistor 14 as an output terminal of the second buffer 18.

(1-3): A window comparator 27 is provided as the judgment circuit 16. The window comparator 27 determines that the first output voltage VOUT of the operational amplifier 12 is generated at the connection point between the resistor 21 and the resistor 22.
And a first comparator (comparator) 28 that outputs a low-level signal when the voltage is higher than the determination voltage VH, and a high-level signal otherwise.
A second comparator 2 that outputs a high-level signal when OUT is lower than a second determination voltage VL generated at a connection point between the resistors 23 and 24, and outputs a low-level signal otherwise.
9, a first AND gate 30 that outputs a high-level signal when the outputs of both comparators 28 and 29 are both at a high level, and outputs a low-level signal otherwise.
A second AND gate 31 that outputs a high-level signal when both outputs of the comparators 28 and 29 are at a low level, and outputs a low-level signal otherwise, and outputs of the two AND gates 30 and 31 And an OR gate 32 that outputs a logical sum signal of

Therefore, from the OR gate 32 of the window comparator 27, the output voltage VOUT of the operational amplifier 12 is changed from the second determination voltage VL (= VE-α) to the first voltage.
Is within the voltage range (corresponding to the voltage range set for quality determination) up to the determination voltage VH (= VE + α), a low-level signal is output.

On the other hand, when the output voltage VOUT of the operational amplifier 12 is out of the above voltage range (VE ± α), that is, whether the output voltage VOUT of the operational amplifier 12 becomes higher than the first determination voltage VH. Alternatively, when the voltage becomes lower than the second determination voltage VL, a high-level signal indicating that the pressure sensor 10 is abnormal is output from the OR gate 32 of the window comparator 27.

In the abnormality detection circuit of the first embodiment as described above, the operational amplifier 25 as the first buffer 17
From the voltage V1 which is the same as the first output voltage V1 of the pressure sensor 10 (the output voltage V1 generated at the first output terminal J1).
Similarly, the operational amplifier 26 serving as the second buffer 18 outputs the second output voltage V
2 (the output voltage V2 generated at the second output terminal J2).

In the abnormality detection circuit of the first embodiment, the resistance of the third resistor 15 is X times the resistance of the first and second resistors 13 and 14 (where X is larger than 1). Value). Therefore, the output voltage VOUT of the operational amplifier 12 is given by the above-described equations (2) and (3). If the pressure sensor 10 is normal (that is, the output voltage V1, V2 of the pressure sensor 10 is deviated from the reference voltage VE). Is the same), the output voltage VOUT of the operational amplifier 12 becomes equal to the reference voltage VE.

On the other hand, if an abnormality occurs in the pressure sensor 10 and the balance between the two output voltages V1 and V2 is lost,
The output voltage VOUT of the operational amplifier 12 shifts in the positive or negative direction from the reference voltage VE. When the output voltage VOUT of the operational amplifier 12 deviates from the voltage range (VE ± α) for quality determination, the window comparator 27 (more specifically, the OR gate 32) indicates that the pressure sensor 10 is abnormal. A high-level signal is output.

According to the abnormality detection circuit of the first embodiment, the abnormality of the pressure sensor 10 can always be accurately detected based on the output voltages V1 and V2 at the same time. There is almost no delay from the occurrence of an abnormality in 10 until the abnormality can be detected. And furthermore
Without providing a high-performance information processing device such as an MPU,
An abnormality of the pressure sensor 10 can be detected with a very small circuit configuration.

Further, since the driving voltage VD applied to the pressure sensor 10 is divided by the resistors 21 to 24 to generate the reference voltage VE, the driving voltage VD fluctuates and the actual Even if the equilibrium point voltage V0 changes,
The reference voltage VE can always be set to the same value as the equilibrium point voltage V0. Therefore, the driving voltage V applied to the pressure sensor 10
Even if D fluctuates, the abnormality of the pressure sensor 10 can be accurately detected.

Further, a first buffer 17 comprising an operational amplifier 25 is provided between the first output terminal J 1 of the pressure sensor 10 and the first resistor 13.
Since the second buffer 18 composed of the operational amplifier 26 is provided between the second output terminal J2 and the second resistor 14, the output terminals J1 and J2 of the pressure sensor 10 are provided.
From the operational amplifier 12 and the first to third resistors 13, 14,
15 flows into the circuit portion consisting of
2 can be prevented from being displaced, and the abnormality of the pressure sensor 10 can be detected more accurately.

FIG. 3 is a circuit diagram showing the configuration of the abnormality detection circuit according to the second embodiment. The abnormality detection circuit according to the second embodiment also has the same configuration as the abnormality detection circuit according to the first embodiment.
This is for detecting an abnormality of the pressure sensor 10 having the same configuration as the pressure sensor 100 described with reference to FIG. In FIG. 3, the same components as those shown in FIG. 2 are denoted by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIG. 3, the abnormality detection circuit of the second embodiment has the following (2-1) and (2-2) when compared with the abnormality detection circuit of the first embodiment (FIG. 2). Is different. (2-1): First buffer 1 composed of operational amplifier 25
7, a first differential amplifier 35 having a first output voltage V1 of the pressure sensor 10 as a non-inverting input and a reference voltage VE generated at a connection point between the resistors 22 and 23 as an inverting input.
It has.

Similarly, instead of the second buffer 18 comprising the operational amplifier 26, the second differential voltage having the non-inverting input of the second output voltage V2 of the pressure sensor 10 and the inverting input of the reference voltage VE is used. An amplifier 36 is provided. More specifically, the first differential amplifier 35 includes an operational amplifier 41 having a non-inverting input terminal connected to the first output terminal J1 of the pressure sensor 10, an operational amplifier 41 connected to the resistor 22 and the resistor 23, and A resistor 42 connected between the inverting input terminal of the amplifier 41 and
It comprises a resistor 43 connected between the output terminal of the operational amplifier 41 and the inverting input terminal, and the output terminal of the operational amplifier 41 serves as the output terminal of the first differential amplifier 35.
It is connected to one end of the first resistor 13. In this case, the non-inverting input terminal of the operational amplifier 41 becomes the non-inverting input terminal of the first differential amplifier 35, and the end of the resistor 42 opposite to the operational amplifier 41 side is connected to the first inverting terminal. It is an inverting input terminal of the differential amplifier 35.

Similarly, the second differential amplifier 36 includes an operational amplifier 44 having a non-inverting input terminal connected to the second output terminal J2 of the pressure sensor 10, and an operational amplifier 44 having a connection point between the resistors 22 and 23. A resistor 45 is connected between the inverting input terminal of the amplifier 44 and a resistor 46 is connected between the output terminal and the inverting input terminal of the operational amplifier 44. The output terminal of the operational amplifier 44 is The output terminal of the second differential amplifier 36 is connected to one end of the second resistor 14.
In this case, the non-inverting input terminal of the operational amplifier 44 becomes the non-inverting input terminal of the second differential amplifier 36, and the end of the resistor 45 on the side opposite to the operational amplifier 44 side is
This is an inverting input terminal of the second differential amplifier 36.

Further, the resistors 42, 43, 45,
The resistance values of the resistors 46 are set such that the ratio of the resistance values of the resistors 43 and 42 and the ratio of the resistance values of the resistors 46 and 45 are the same. Therefore, the value obtained by dividing the resistance value of the resistor 43 by the resistance value of the resistor 42 and the value obtained by dividing the resistance value of the resistor 46 by the resistance value of the resistor 45 are represented by “Rb / R
a ", the amplification factor Y of the first differential amplifier 35 and the second differential amplifier 36 becomes" 1 + Rb / Ra ", and the output of the first differential amplifier 35 is obtained from Expressions 4 and 5 described above. Voltage (that is, voltage applied to one end of the first resistor 13) V1
S and the output voltage of the second differential amplifier 36 (that is, the voltage applied to one end of the second resistor 14) V2S are respectively
Equations 7 and 8 below are obtained.

[0078]

V1S = (1 + Rb / Ra) × (V1−VE) + VE Equation 7

[0079]

V2S = (1 + Rb / Ra) × (V2−VE) + VE (Equation 8) The output voltage VOUT of the operational amplifier 12 is obtained by converting V1 and V2 in Equation 2 into V1S in Equations 7 and 8, respectively. And V
By replacing with 2S, the following equation 9 is obtained.

[0080]

VOUT = −X (1 + Rb / Ra) × {(V1−VE) + (V2−VE)} + VE (Equation 9) As can be seen from Equation 9, the abnormality detection of the second embodiment is performed. In the circuit, both output voltages V1,
If the balance of V2 is lost, the output voltage VOUT of the operational amplifier 12 will deviate more from the reference voltage VE in the positive or negative direction.

(2-2): For this reason, in the abnormality detection circuit of the second embodiment, the first judgment voltage VH generated at the connection point between the resistors 21 and 22 is higher than that in the first embodiment. The resistance values of the four resistors 21 to 24 are set such that the second determination voltage VL generated at the connection point between the resistors 23 and 24 is slightly lower than that in the first embodiment. ing. In other words, the voltage range for determining pass / fail (VE ±
α) is slightly extended around the reference voltage VE.

According to the abnormality detection circuit of the second embodiment as described above, when the output voltages V1 and V2 of the pressure sensor 10 are out of balance, the output voltage VOUT of the operational amplifier 12 deviates more greatly from the reference voltage VE. Therefore, it is possible to more accurately determine whether or not the pressure sensor 10 is abnormal, and to perform more accurate abnormality detection.

Further, the influence of the offset voltage of the operational amplifier 12 can be reduced. Further, the operational amplifiers 41 and 44 constituting the first and second differential amplifiers 35 and 36 are similar to the first and second buffers 17 and 18 (the operational amplifiers 25 and 26) in the first embodiment. Also plays a role. That is, the output terminals J1,
From J2, the operational amplifier 12 and the first to third resistors 13, 1
An extra current is prevented from flowing through the circuit portion composed of the circuits 4 and 15.

Next, FIG. 4 is a circuit diagram showing the configuration of the abnormality detection circuit according to the third embodiment. Note that the abnormality detection circuit of the third embodiment also has the same configuration as the abnormality detection circuit of the first embodiment.
This is for detecting an abnormality of the pressure sensor 10 having the same configuration as the pressure sensor 100 described with reference to FIG. In FIG. 4, the same components as those shown in FIG. 2 are denoted by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIG. 4, the abnormality detection circuit of the third embodiment has the following (3-1) and (3-2) when compared with the abnormality detection circuit of the first embodiment (FIG. 2). Is different. (3-1): A buffer 51 having a configuration described later is provided instead of the buffer 17 of the voltage follower circuit using the operational amplifier 25. Similarly, a buffer 52 having a configuration described later is provided in place of the buffer 18 of the voltage follower circuit using the operational amplifier 26.

(3-2): The reference voltage VE generated at the connection point between the resistor 22 and the resistor 23 is input between the connection point between the resistor 22 and the resistor 23 and the non-inverting input terminal of the operational amplifier 12. A buffer 53 is added. Further, the resistor 21
Connection point between the resistor and the resistor 22 and the window comparator 27
Is not directly connected to the non-inverting input terminal of the first comparator 28, but the resistor 21 and the resistor 2
A buffer 54 having a first determination voltage VH generated at a connection point with the second input as an input is added. And similarly, resistor 2
3 and the resistor 24 and the window comparator 2
7 and the non-inverting input terminal of the second comparator 29
Instead of being directly connected, a buffer 55 having a second determination voltage VL generated at a connection point between the resistor 23 and the resistor 24 as an input is added therebetween.

Here, the five buffers 51 to 55
Is a level shift circuit that outputs a voltage (= Vi + Vsf) obtained by shifting the input voltage Vi by a specific voltage Vsf as an output voltage Vo. For example, the level shift circuit has a configuration as shown in FIG. As shown in FIG. 5A, each of the buffers 51 to 55 includes an NPN transistor 60 having a collector connected to a drive voltage VD (specifically, a high potential side of the drive voltage VD) applied to the pressure sensor 10. That N
A resistor R is connected between the emitter of the PN transistor 60 and the ground potential (ie, the low potential side of the drive voltage VD). The base of the NPN transistor 60 is an input terminal of the buffer, and the emitter of the NPN transistor 60 is an output terminal of the buffer.

Therefore, a voltage (= Vi) obtained by shifting the input voltage Vi from the buffers 51 to 55 to the lower potential side by the base-emitter voltage Vbe of the NPN transistor 60.
−Vbe) is output as the output voltage Vo. That is, the voltage Vsf for shifting the input voltage Vi, which is the specific voltage Vsf, is “−Vbe”.

In the abnormality detection circuit according to the third embodiment including the buffers 51 to 55, the voltage Vo1 output from the buffer 51 to one end of the first resistor 13 is equal to the first output voltage of the pressure sensor 10. The voltage V1 is shifted to the lower potential side by the above Vbe (= V1−Vbe). Similarly, the voltage Vo2 output from the buffer 52 to one end of the second resistor 14 is equal to the second output of the pressure sensor 10. Voltage V
2 is shifted to the lower potential side by the above Vbe (= V2
−Vbe). Further, the voltage VoE output from the buffer 53 to the non-inverting input terminal of the operational amplifier 12
Is a voltage (= VE−Vbe) obtained by shifting the reference voltage VE to the lower potential side by the above Vbe. That is, the first to third
Input voltages Vo1, Vo2, V to a signal processing circuit portion comprising resistors 13, 14, 15 and operational amplifier 12 of FIG.
oE are all shifted to the lower potential side by the same voltage Vbe.

Therefore, as can be seen from the above equation (2), also in the abnormality detection circuit of the third embodiment, the output voltage VOUT of the operational amplifier 12 changes from the first output voltage V1 of the pressure sensor 10 to the reference voltage VE. Is subtracted from a value obtained by subtracting the reference voltage VE from the second output voltage V2 of the pressure sensor 10, and is a voltage proportional to a value obtained by adding the values.

Further, in this configuration, the output voltage VOUT of the operational amplifier 12 changes with reference to "VE-Vbe". That is, the voltage range for pass / fail determination) is also shifted to the lower potential side by the above-described voltage Vbe, and becomes "VH-Vbe" to "VL-Vbe". This is because the voltage supplied from the buffer 54 to the non-inverting input terminal of the first comparator 28 is equal to the first determination voltage VH
Is shifted to the lower potential side by the above Vbe (= VH−
Vbe), and the voltage supplied from the buffer 55 to the non-inverting input terminal of the second comparator 29 is a voltage obtained by shifting the second determination voltage VL to the lower potential side by the above Vbe (= VL−Vbe). ).

Therefore, the same operation and effect as the abnormality detection circuit of the first embodiment can be obtained by the abnormality detection circuit of the third embodiment. In addition, accurate abnormality determination can be performed without adjusting the resistance values of the resistors 21 to 24 and resetting the first and second determination voltages VH and VL.

In particular, since the level shift circuit has a simpler configuration than the voltage follower circuit using the operational amplifier, the advantage of the abnormality detection circuit of the third embodiment is that the circuit scale can be reduced. is there.
In the third embodiment, the buffer 51 corresponds to a first buffer, the buffer 52 corresponds to a second buffer,
The buffer 53 corresponds to a third buffer. The buffer 54 corresponds to a fourth buffer, and the buffer 55 corresponds to a fifth buffer. The resistance 21
24 are not only used as the reference voltage generation circuit 11,
It also functions as the determination voltage generation circuit according to claim 7.

The buffers 51 to 55 are as shown in FIG.
In addition to the level shift circuit shown in FIG.
The level shift circuit shown in each of (B), (C), and (D) can be used. First, in the level shift circuit shown in FIG. 5B, the NPN transistor 60 in the level shift circuit of FIG.
This is replaced with two NPN transistors 61 and 62. The base of the first-stage NPN transistor 61 becomes the input terminal of the buffer, and the second-stage NPN transistor
The emitter of the transistor 62 is the output terminal of the buffer.

In the level shift circuit of FIG. 5B, the base-emitter voltage of the first-stage NPN transistor 61 is set to “Vbe1”, and the base-emitter voltage of the second-stage NPN transistor 62 is set to “Vbe1”. "Vbe2"
Then, a voltage (= Vi− (Vbe1 + V) obtained by shifting the input voltage Vi to the lower potential side by “Vbe1 + Vbe2”
be2) is output as the output voltage Vo. That is, the voltage component Vsf for shifting the input voltage Vi.
Becomes “− (Vbe1 + Vbe2)”.

Next, the level shift circuit shown in FIG. 5C includes a PNP transistor 70 having a collector connected to the ground potential, an emitter of the PNP transistor 70 and a drive voltage VD (specifically, a high drive voltage VD). (Potential side). And PNP
The base of the transistor 70 is an input terminal of the buffer, and the emitter of the PNP transistor 70 is an output terminal of the buffer. That is, this level shift circuit is the same as the level shift circuit shown in FIG.
In this configuration, the PN transistor 60 is replaced with a PNP transistor 70.

In the level shift circuit of FIG. 5C, a voltage (= Vi + Vbe) obtained by shifting the input voltage Vi to the higher potential side by the base-emitter voltage Vbe of the PNP transistor 70 is used as the output voltage Vo. Will be output. That is, the voltage component Vsf for shifting the input voltage Vi is “Vbe”.

In the level shift circuit shown in FIG. 5D, the PNP transistor 70 in the level shift circuit shown in FIG. 5C is connected to two Darlington-connected PNP transistors.
It is replaced with transistors 71 and 72. The base of the first-stage PNP transistor 71 is an input terminal of the buffer, and the emitter of the second-stage PNP transistor 72 is an output terminal of the buffer.

In the level shift circuit of FIG. 5D, the base-emitter voltage of the first-stage PNP transistor 71 is set to “Vbe1”, and the base-emitter voltage of the second-stage PNP transistor 72 is set to “Vbe1”. "Vbe2"
Then, the voltage (= Vi + (Vbe1 + Vbe) obtained by shifting the input voltage Vi to the higher potential side by “Vbe1 + Vbe2”
be2) is output as the output voltage Vo. That is, the voltage component Vsf for shifting the input voltage Vi.
Becomes “Vbe1 + Vbe2”.

Next, as a fourth embodiment, the first embodiment
To a pressure detection device 80 as a physical quantity detection device including any of the abnormality detection circuits of the third embodiment,
This will be described with reference to FIG. As shown in FIG. 8, the pressure detection device 80 of the present embodiment includes the pressure sensor 10 described above, a first output voltage V1 and a second output voltage V1 of the pressure sensor 10.
2 and amplifies the potential difference between the two output voltages V1 and V2, an analog voltage signal corresponding to the pressure P detected by the pressure sensor 10 (corresponding to a detection signal indicating a physical quantity to be detected, In the present embodiment, 0.5V-4.
An amplifier 82 for outputting a 5V voltage signal) and an amplifier 82
Output terminal 84 for outputting the output of the circuit to the outside, and an output circuit 8 provided between the output terminal 84 and the amplifier 82.
6 and an abnormality detection circuit 88.

Incidentally, the abnormality detecting circuit 88 is provided with the first to the above-mentioned.
It is one of the abnormality detection circuits of the third embodiment (FIGS. 2 to 4), and is provided for detecting an abnormality of the pressure sensor 10. The amplifier 82 has a temperature compensation function. Here, the output circuit 86 is connected to the abnormality detection circuit 8.
When the low level signal is output from the window comparator 27 (specifically, the OR gate 32), the output of the amplifier 82 is supplied as it is to the output terminal 84 and output to the outside.

On the other hand, the window comparator 2
7 when a high-level signal is output from the output terminal 7, the voltage of the output terminal 84 is set to a voltage that is not within the predetermined voltage range of 0.5 V to 4.5 V (specifically, regardless of the output of the amplifier 82). , 0.3V or less or 4.7V or more)
To

That is, in the pressure detecting device 80, when a signal indicating that the pressure sensor 10 is abnormal is output from the window comparator 27, the output terminal 84
As a specific signal indicating the occurrence of an abnormality, a voltage different from that in a normal state is output.

The pressure detecting device 80 of this embodiment as described above
According to the above, another device such as an electronic control device that receives an analog voltage signal from the device 80 and detects pressure receives a voltage outside the predetermined voltage range (0.3 V or less). Or 4.7 V or more), it is possible to determine whether the pressure sensor 10 is normal or not, and it is not necessary to separately provide a signal line.

As described above, one embodiment of the present invention has been described, but it goes without saying that the present invention can take various forms. For example, in the abnormality detection circuit of FIG.
A buffer (corresponding to a third buffer) similar to the buffers 17 and 18 in FIG. 2 is provided between the connection point between the resistor 2 and the resistor 23 and the non-inverting input terminal of the operational amplifier 12. The reference voltage VE may be input to the twelve non-inverting input terminals. That is, each of the buffers 51 to 55 in the abnormality detection circuit of FIG. 4 can be replaced with a buffer of a voltage follower circuit using an operational amplifier.

In the abnormality detection circuit shown in FIG. 3, a buffer using a voltage follower circuit is provided between the connection point between the resistors 22 and 23 and the connection point between the resistors 42 and 45. The reference voltage V is applied to the connection point between the resistor 42 and the resistor 45 and the non-inverting input terminal of the operational amplifier 12.
If E is applied, the reference voltage VE does not deviate at all, and abnormality detection with higher accuracy becomes possible. Note that the resistance values of the resistors 21 to 24 are
If the resistance value is sufficiently small with respect to the resistance value of No. 6, the reference voltage VE does not greatly shift, and such a buffer may be provided as needed.

Further, in the abnormality detection circuit of FIG.
Between the first output terminal J1 of the pressure sensor 10 and the first differential amplifier 35, and the second output terminal J of the pressure sensor 10
A buffer may be provided between the second differential amplifier 36 and the second differential amplifier 36, respectively. On the other hand, the abnormality detection circuit of each of the above embodiments detects an abnormality of the pressure sensor 10 having the same configuration as the pressure sensor 100 described with reference to FIG. 6, but the present invention is not limited to such a pressure sensor. , FIG.
The same applies to an acceleration sensor having the same circuit configuration as in (a) and other sensors.

When the equilibrium point voltage V0 of the sensor whose abnormality is to be detected is not likely to change during normal operation (for example, when the drive voltage VD of the pressure sensor 10 in the above embodiment does not change), the reference voltage VE And the first and second
The determination voltages VH and VL may be generated by a constant voltage circuit.

Incidentally, the operational amplifier and the comparator have an offset voltage as an error.
These are described as sufficiently small and negligible. Further, in each of the abnormality detection circuits of FIGS. 2 and 3 and its modified example, the buffer may be constituted by a circuit other than a voltage follower circuit using an operational amplifier.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating an abnormality detection circuit according to the first and second embodiments of the present invention;

FIG. 2 is a circuit diagram illustrating an abnormality detection circuit according to the first embodiment.

FIG. 3 is a circuit diagram illustrating an abnormality detection circuit according to a second embodiment.

FIG. 4 is a circuit diagram illustrating an abnormality detection circuit according to a third embodiment.

FIG. 5 is a circuit diagram illustrating a level shift circuit as a buffer.

FIG. 6 is an explanatory diagram illustrating a pressure sensor.

FIG. 7 is an explanatory diagram illustrating a conventional technique.

FIG. 8 is a block diagram illustrating a configuration of a pressure detection device according to the embodiment.

[Explanation of symbols]

1-4: Gauge resistance 10, 100: Pressure sensor 11
... Reference voltage generating circuits 11a, 11b, 21 to 24, 42, 43, 45, 46
... resistor 12 ... operational amplifier 13 ... first resistor 14 ... second resistor 15 ... third resistor 16 ... judgment circuit 17,51 ... first buffer 18,
52 second buffer 27 window comparator 28 first comparator
29 second comparator 30 first AND gate 31 second AND gate 32 OR gate 35 first differential amplifier 36 second differential amplifier 5
3 Third buffer 54 Fourth buffer 55 Fifth buffer 80
Pressure detecting device 82: Amplifier 84: Output terminal 86: Output circuit 88
... Abnormality detection circuit

Claims (10)

[Claims] 1. A first output voltage generated at a first output terminal and a second output voltage generated at a second output terminal are:
An abnormality detection circuit for detecting an abnormality of a sensor formed so as to change by the same voltage in each of the positive direction and the negative direction with reference to a predetermined equilibrium point voltage according to the physical quantity of the detection target, A reference voltage generating circuit for generating a reference voltage substantially equal to the equilibrium point voltage; an operational amplifier having a reference voltage generated by the reference voltage generating circuit input to one input terminal; An output voltage is applied, the other end is connected to a first resistor connected to the other input terminal of the operational amplifier, and one end is applied with a second output voltage of the sensor, and the other end is connected to the operational amplifier. A second resistor connected to the other input terminal of the amplifier and further having a resistance value set to be the same as the first resistor; and a second resistor connected between the output terminal of the operational amplifier and the other input terminal. 3 resistance and the performance A determination circuit that outputs a signal indicating that the sensor is abnormal when the output voltage of the amplifier is out of a voltage range set for quality determination; and circuit. 2. The sensor abnormality detection circuit according to claim 1, wherein a first output voltage of the sensor is input, and the first output voltage is applied to one end of the first resistor. And a second buffer that receives a second output voltage of the sensor and applies the second output voltage to one end of the second resistor. Abnormality detection circuit. 3. The abnormality detection circuit for a sensor according to claim 2, wherein a reference voltage generated by the reference voltage generation circuit is input, and the reference voltage is input to the one input terminal of the operational amplifier. An abnormality detection circuit for a sensor, comprising: a third buffer. 4. The sensor abnormality detection circuit according to claim 3, wherein the first buffer, the second buffer, and the third buffer are configured to shift an input voltage by a specific voltage. And a level shift circuit that outputs the output as an output voltage. 5. A first output voltage generated at a first output terminal and a second output voltage generated at a second output terminal are:
An abnormality detection circuit for detecting an abnormality of a sensor formed so as to change by the same voltage in each of the positive direction and the negative direction with reference to a predetermined equilibrium point voltage according to the physical quantity of the detection target, A reference voltage generating circuit for generating a reference voltage substantially equal to the equilibrium point voltage; an operational amplifier having a reference voltage generated by the reference voltage generating circuit input to one input terminal; a first output voltage of the sensor A non-inverting input, a first differential amplifier having a reference voltage generated by the reference voltage generating circuit as an inverting input, and a second output voltage of the sensor as a non-inverting input, the reference voltage generating circuit A second differential amplifier having the generated reference voltage as an inverting input, an output voltage of the first differential amplifier applied to one end, and the other end connected to the other input terminal of the operational amplifier; The output voltage of the second differential amplifier is applied to one end of the first resistor, and the other end is connected to the other input terminal of the operational amplifier. And a third resistor connected between the output terminal of the operational amplifier and the other input terminal, and an output voltage of the operational amplifier set for pass / fail determination. A determination circuit that outputs a signal indicating that the sensor is abnormal when the voltage is out of the specified voltage range. 6. The abnormality detection circuit for a sensor according to claim 1, wherein the determination circuit is configured such that an output voltage of the operational amplifier is higher than a reference voltage generated by the reference voltage generation circuit. Is also higher by a predetermined voltage.
And outputting the signal when the output voltage of the operational amplifier is lower than a second determination voltage lower by a predetermined voltage than the reference voltage generated by the reference voltage generation circuit. An abnormality detection circuit for a sensor, comprising: 7. The abnormality detection circuit for a sensor according to claim 4, wherein the first determination voltage is higher than the reference voltage by a predetermined voltage and is higher than the reference voltage. A fourth determination voltage generating circuit for generating a low second determination voltage, and a fourth voltage to be supplied to the determination circuit after shifting the first determination voltage generated by the determination voltage generation circuit by the specific voltage. A buffer, and a fifth buffer that shifts the second determination voltage generated by the determination voltage generation circuit by the specific voltage and supplies the second determination voltage to the determination circuit, wherein the determination circuit includes the operational amplifier Output voltage of the fourth
And when the output voltage of the operational amplifier is lower than the voltage supplied from the fifth buffer, the signal is output. Characteristic sensor abnormality detection circuit. 8. The sensor abnormality detection circuit according to claim 1, wherein each of the sensors has four gauges each of which has a resistance value that changes due to strain and is connected to each other in a loop. A driving voltage is applied between a specific connection point and a second connection point counted from the specific connection point among connection points between the gauge resistors, and the other two A connection point being a pressure sensor having the first and second output terminals. 9. The sensor abnormality detection circuit according to claim 8, wherein the reference voltage generation circuit includes at least two resistors that divide the drive voltage to generate the reference voltage. Sensor abnormality detection circuit. 10. A first output voltage generated at a first output terminal and a second output voltage generated at a second output terminal determine a predetermined equilibrium point voltage according to a physical quantity to be detected. A sensor formed so as to change by the same voltage in each of the positive direction and the negative direction as a reference, and based on the first output voltage and the second output voltage of the sensor, the physical quantity of the detection target A physical quantity detection device which outputs a detection signal indicating the following from an output terminal, comprising: the abnormality detection circuit according to any one of claims 1 to 9 for detecting abnormality of the sensor, and the abnormality detection circuit. When a signal indicating that the sensor is abnormal is output from the determination circuit, a specific signal indicating occurrence of abnormality is output from the output terminal instead of the detection signal. Characterized by Physical quantity detection device.