JPH11148878A - Drift reduction circuit of pressure sensor and reset system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a reduction circuit in which the drift of a pressure sensor is corrected at low costs. SOLUTION: An electric charge is generated across a crystal 2 according to a strain clue to an applied voltage. An integrating circuit 3 converts the electric charge generated across the crystal 2 into a voltage. When a reset signal RE is input, a reset circuit 4 resets the integrating circuit 3 so as to cancel a cumulative error. A main cause for a drift is the existence of the leakage current Ia of an FET 23 flowing out from a capacitor 22 and the existence of the leakage current Ib of the capacitor 22 itself. When a diode 5 is added to the input line of a sensor in a reverse bias state, a correction current Ic whose magnitude is identical to that of the leakage current of the sensor and whose flow direction is opposite is supplied from the diode 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure sensor used in an ABS hydraulic control system and the like, and more particularly, to a drift reduction circuit and a reset method of a pressure sensor.

[0002]

2. Description of the Related Art Conventionally, there has been known a piezoelectric pressure sensor of a type that converts charges generated by distortion caused by pressure applied to a piezoelectric element into a voltage. In particular, a piezoelectric pressure sensor using crystal as a piezoelectric element has excellent characteristics in that temperature characteristics and stability are high due to characteristics of the crystal itself, and a special drive circuit is not required. FIG. 9 is a circuit diagram of a conventional piezoelectric pressure sensor unit. Piezoelectric pressure sensor unit 1f
Comprises a crystal 2 serving as a piezoelectric element, an integration circuit 3 for converting charges generated at both ends of the crystal 2 into a voltage, and a reset circuit 4 for resetting the integration circuit 3. Since the output of the piezoelectric pressure sensor unit 1f is a relative output, various errors are accumulated. The reset circuit 4 turns on the field effect transistor (FET) 23 immediately before the pressure measurement, resets the integrating circuit 3, and cancels the accumulated error in order to minimize the accumulated error. The addition of the reset circuit 4 enables measurement with a relatively long measurement time and pseudo absolute value measurement.

However, since the charge generated in the crystal 2 is as small as several p-coulombs per atmosphere, there is a leakage current of the FET 23 flowing out of the capacitor 22 of the integration circuit 3 and a leakage current of the capacitor 22 itself. A drift occurs in the pressure sensor unit 1f of No. 9. Therefore, in order to finish the sensor with high accuracy by reducing the drift, it is necessary to reduce the leakage current by several tens to several hundreds n depending on the characteristics of each element itself.
It must be kept below the A order level. Therefore, there is a problem that the sensor becomes very expensive.

On the other hand, in the case of measurement in which the measurement time is short, the measurement interval is long as the capacitor 22 discharges spontaneously, or the detection level is high enough to absorb a drift error, the accuracy of parts is simplified. By omitting the reset circuit, the configuration of the sensor can be simplified. However, in such a configuration, since errors such as drift are accumulated immediately after the power is turned on, it is impossible to perform measurement with a long measurement time, short measurement interval, or absolute value measurement. On the other hand, when the piezoelectric pressure sensor unit 1f of FIG. 9 is incorporated in, for example, an ABS (Antilock Braking System) oil pressure detection system for an automobile, as shown in FIG. 10, the sensor output signal SEN-OUT from the sensor unit 1f is output. The MPU 14a in the control unit 13a has received the signal, and the MPU 14a has output the reset signal RE for operating the reset circuit 4.

[0005]

As described above, the conventional pressure sensor has a problem that if the accuracy of measurement is to be increased, the sensor becomes very expensive. Further, if a simple configuration without the reset circuit is used, there is a problem that measurement with a long measurement time, measurement with a short measurement interval, or absolute value measurement becomes impossible. Also, in a system incorporating a pressure sensor, there is a problem that the pressure sensor unit and the control unit must be connected by two signal lines, a signal line for transferring a sensor output signal and a signal line for transferring a reset signal. Was. SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has a drift reduction circuit capable of inexpensively correcting drift of a pressure sensor, and a reset method capable of reducing the number of signal lines between a pressure sensor unit and a control unit. The purpose is to provide.

[0006]

According to a first aspect of the present invention, there is provided a drift reducing circuit for a pressure sensor, comprising: a piezoelectric element which generates an electric charge in response to a strain caused by an applied pressure; And a reset circuit for resetting the integration circuit, and a diode in a reverse bias state added to a connection point between the piezoelectric element and the input terminal of the integration circuit. in this way,
By providing a reverse-biased diode at the connection point between the piezoelectric element and the input terminal of the integrating circuit, a correction current having the same magnitude as the leakage current of the sensor causing drift and flowing in the opposite direction is supplied from the diode. Therefore, the leakage current of the sensor can be canceled by the correction current, and the apparent drift can be canceled. According to another aspect of the present invention, the semiconductor device includes an off-bias adjustment circuit for adjusting an off-bias of a transistor in the reset circuit, and a reverse-bias adjustment circuit for adjusting a reverse bias of the diode. is there. Thus, by providing the off-bias adjustment circuit and the reverse bias adjustment circuit, the off-bias value of the transistor is changed,
The reverse bias value of the diode, or both, can be changed to match the characteristics of the sensor leakage current that causes drift. According to a third aspect of the present invention, there is provided a temperature detection circuit for detecting an ambient temperature, a storage device for storing an off-bias value of the transistor and a reverse bias value of a diode at each temperature, and the temperature detection circuit. A control circuit that reads an off-bias value and a reverse bias value corresponding to the detected current ambient temperature from a storage device and controls the off-bias adjustment circuit and the reverse bias adjustment circuit. . As described above, the control circuit controls the off-bias adjustment circuit and the reverse bias adjustment circuit based on the off-bias value and the reverse bias value read from the storage device, so that the drift can be canceled even when the ambient temperature changes. it can.

According to a fourth aspect of the present invention, there is provided a piezoelectric element which generates an electric charge in response to a strain caused by an applied pressure, an integrating circuit for converting electric charges generated at both ends of the piezoelectric element into a voltage, and resetting the integrating circuit. In a system including a sensor unit including a reset circuit and a control unit that receives a sensor output signal from the sensor unit and outputs a reset command signal to the sensor unit, the control unit includes a sensor output signal from the sensor unit. The signal line receiving the signal and the signal line outputting the reset command signal are shared, and the signal line is used to connect to the sensor unit. The sensor unit includes a resistor inserted in series with the signal line, Determines whether to activate the reset circuit by detecting the voltage across the resistor That is one having a reset detection circuit. In this way, the number of signal lines between the sensor unit and the control unit can be reduced by sharing the signal line for passing the sensor output signal and the signal line for transmitting the reset command signal and providing the resistor and the reset detection circuit in the sensor unit. Can be reduced. According to a fifth aspect of the present invention, when resetting the sensor unit, the control unit outputs a reset command signal including a pair of an H level signal and an L level signal,
The reset detection circuit in the sensor unit includes a gate circuit. When the voltage of the resistor on the sensor unit side is the H level detection voltage of the gate circuit and the voltage on the control unit side is L level, or the voltage on the sensor unit side Is the L level detection voltage of the gate circuit, and when the voltage on the control unit side is H level, the reset circuit is operated.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a circuit diagram of a piezoelectric pressure sensor unit according to a first embodiment of the present invention. Piezoelectric pressure sensor unit 1
Is a crystal 2 having one end connected to a first input terminal of an integration circuit described later and the other end grounded, and an integration circuit 3 having a first input terminal connected to one end of the crystal 2 and a second input terminal grounded. , A reset circuit 4 for resetting the integrating circuit 3, and a drift reducing diode 5 whose anode is connected to the first input terminal of the integrating circuit 3 and whose cathode is connected to the power supply.

The integrating circuit 3 has an operational amplifier 21 having a first input terminal connected to one end of the crystal 2 and a second input terminal grounded, and is provided between a first input terminal and an output terminal of the operational amplifier 21. And a condenser 22. The reset circuit 4 includes a field effect transistor (hereinafter, referred to as FET) 23 having one of a drain and a source connected to the first input terminal of the operational amplifier 21 and the other of a drain and a source connected to the output terminal of the operational amplifier 21. ,
A PNP transistor 24 having an emitter connected to the power supply and a collector connected to the gate of the FET 23, a resistor 25 having one end connected to the base of the transistor 24, and a resistor having one end connected to the power supply and the other end connected to the base of the transistor 24. 26, a resistor 27 having one end connected to the collector of the transistor 24 and the other end connected to a power supply (negative).

In such a piezoelectric pressure sensor unit 1, electric charges are generated at both ends of the quartz crystal 2 in accordance with the distortion caused by the applied pressure. The integrating circuit 3 converts the charges generated at both ends of the crystal 2 into a voltage and outputs the voltage as a sensor output signal SEN-OUT. Also, the “L” level reset signal RE is
, The transistor 24 is turned on, and a voltage higher than the threshold value is applied to the gate of the FET 23 via the emitter-collector of the transistor 24. As a result, the FET 23 is turned on, and the capacitor 22 of the integration circuit 3 is forcibly discharged. Thus, the integration circuit 3 is reset, and the accumulated error is cancelled.

The main causes of the drift in the piezoelectric pressure sensor described above are the leakage current Ia of the FET 23 flowing out of the integrating capacitor 22 and the leakage current Ib of the capacitor 22 itself.

Therefore, in the present embodiment, a diode 5 having a leakage current characteristic similar to the characteristic of the total leakage current (sum of leakage currents of Ia, Ib, etc.) of the sensor causing drift is selected. 5 is added to the input line of the sensor in a reverse bias state as shown in FIG. Thereby, the correction current Ic having the same magnitude as the leakage current of the sensor and flowing in the opposite direction is supplied from the diode 5. In this way, by canceling the sensor leakage current with the correction current Ic, apparent drift can be canceled, and the drift can be easily reduced.

Embodiment 2 FIG. 2 is a circuit diagram of a piezoelectric pressure sensor unit showing another embodiment of the present invention, and the same components as those in FIG. 1 are denoted by the same reference numerals. When the correction current cannot be corrected due to the shortage of the correction current in the circuit of one embodiment using one correction diode, the correction diodes 5-1 to 5-1 to 5-5 are used as in the piezoelectric pressure sensor unit 1a shown in FIG. Use multiple -n. Diodes 5-1 to 5-1
By the sum of the characteristics of 5-n, it is possible to match the characteristic of the total leakage current of the sensor which causes the drift, so that the drift can be apparently canceled.

Embodiment 3 FIG. 3 is a circuit diagram of a piezoelectric pressure sensor unit showing another embodiment of the present invention, and the same components as those in FIG. 1 are denoted by the same reference numerals. If the correction cannot be completed even by using a plurality of correction diodes, the off-bias adjustment circuit 6 for adjusting the off-bias of the FET 23 in the reset circuit 4 and the diode 5 as in the piezoelectric pressure sensor unit 1b shown in FIG. A reverse bias adjustment circuit 7 for adjusting the reverse bias is added.

The off-bias adjustment circuit 6 connected to the other end of the resistor 27 can change the off-bias value (gate voltage at the time of off) of the FET 23 by adjusting the output voltage. Can be changed. The reverse bias adjustment circuit 7 connected to the cathode of the diode 5 can change the reverse bias value of the diode 5 by adjusting the output voltage, thereby changing the leakage current of the diode 5.

In this manner, by changing the off-bias value of the FET 23, changing the reverse bias value of the correcting diode 5, or changing both of them, the characteristics of the total leakage current of the sensor causing drift may be reduced. They can be matched and apparently cancel the drift.

Embodiment 4 FIG. 4 is a circuit diagram of a piezoelectric pressure sensor unit showing another embodiment of the present invention, and the same components as those in FIG. 1 are denoted by the same reference numerals. In the above embodiment, since the correction current curve basically depends on the leakage current characteristic of the correction diode, the curve of the correction current is accurately adjusted to the curve of the total leakage current characteristic of the sensor, or the temperature characteristic is improved. Highly accurate drift correction is difficult.

In the present embodiment, a temperature detecting circuit 8, a control circuit 9, and a storage device 10 such as an EPROM are added to the circuit of the third embodiment as in the piezoelectric pressure sensor unit 1c shown in FIG. I have. In the storage device 10, the off-bias value of the FET 23 and the reverse bias value of the diode 5 at each temperature are stored in advance.

The control circuit 9 reads from the storage device 10 the off-bias value of the FET 23 and the reverse bias value of the diode 5 corresponding to the current ambient temperature detected by the temperature detection circuit 8. Then, the control circuit 9 supplies the read off-bias value to the off-bias adjustment circuit 6a, and outputs the reverse bias value to the reverse bias adjustment circuit 7a.
Give to.

The off-bias adjusting circuit 6a controls the off-bias value of the FET 23 by adjusting the output voltage.
Change to the value entered from. Reverse bias adjustment circuit 7a
Changes the reverse bias value of the diode 5 to the value input from the control circuit 9 by adjusting the output voltage. With the above configuration, drift can be canceled even if the ambient temperature changes, so that more accurate drift correction can be performed.

Embodiment 5 FIG. 5 is a circuit diagram of a piezoelectric pressure sensor unit showing another embodiment of the present invention, and the same components as those in FIGS. 1 and 4 are denoted by the same reference numerals. In the present embodiment, an OTP (one time programmable read only memory) is used instead of the storage device 10 of FIG.
y) or a storage device 10a which is a writable nonvolatile memory such as an EEPROM. This makes it possible to automatically set the correction value to be stored in the storage device 10a, and to perform more accurate drift correction.

First, the setting of the correction value in the storage device 10a is performed according to the following procedure. (1) The ambient temperature of the piezoelectric pressure sensor unit 1d is set by temperature setting means (not shown). (2) The surrounding pressure of the pressure sensor unit 1d is set by pressure setting means (not shown). (3) After a predetermined time has passed so that the temperature of the pressure sensor unit 1d becomes equal to the set ambient temperature, a trigger signal is given to the control circuit 9a.

(4) Control circuit 9a receiving trigger signal
When the sensor output signal SEN-OUT is larger than the reference output value at the set ambient temperature and the set ambient pressure stored in the storage device 10a in advance, the off-bias adjustment circuit 6a and the reverse bias adjustment circuit 6a reduce the signal SEN-OUT. The adjustment circuit 7a is operated. (5) When the sensor output signal SEN-OUT is smaller than the reference output value, the control circuit 9a outputs the signal SEN-OUT.
The off-bias adjustment circuit 6a and the reverse bias adjustment circuit 7a are operated so that OUT increases. (6) When the reference output value and the sensor output signal SEN-OUT match, the control circuit 9a writes the off-bias value and the reverse bias value at this time together with the temperature detected by the temperature detection circuit 8 to the storage device 10a. .

(7) The above operations (2) to (5) are repeated for several points while changing the ambient pressure within the working pressure range. (8) The above operations (1) to (7) are repeated for several points while changing the ambient temperature within the operating temperature range. After setting the correction values as described above, the control circuit 9 a
Based on the correction values (off-bias value and reverse bias value) and the detected temperature stored in a, interpolation calculation of the correction value is performed, and the corrected correction value and temperature after the interpolation calculation are written in the storage device 10a.

In the actual drift correction, the control circuit 9a stores the off-bias value of the FET 23 and the reverse bias value of the diode 5 corresponding to the current ambient temperature detected by the temperature detecting circuit 8 in accordance with the current ambient temperature. Apparatus 1
0a, the read off-bias value is applied to the off-bias adjustment circuit 6a, and the reverse bias value is applied to the reverse bias adjustment circuit 7a.

The off-bias adjusting circuit 6a controls the off-bias value of the FET 23 by adjusting the output voltage.
Change to the value entered from a. Reverse bias adjustment circuit 7
“a” changes the reverse bias value of the diode 5 to the value input from the control circuit 9a by adjusting the output voltage.

As described above, in this embodiment, the setting of the correction value in the storage device 10a can be automatically performed.
Normally, the ambient temperature set for the sensor unit 1d,
Ambient pressure is predetermined. Therefore, if these values, the setting order, and the reference output value (true value of the sensor output signal SEN-OUT) at the set ambient temperature and the set ambient pressure are preset in the storage device 10a, the ambient temperature and the When the setting of the ambient pressure is completed, the correction value can be automatically set only by repeatedly giving the trigger signal to the sensor unit 1d.

Therefore, the correction value can be set for a plurality of pressure sensor units at the same time, and no matter how many pressure sensor units are set,
It is only necessary to provide one common trigger signal to each pressure sensor unit. If a large number of pressure sensor units are set at the same time, the correction value setting time per unit can be reduced. This is because the correction value is stored in the storage device 10 as compared with the time required to change the ambient pressure and the ambient temperature.
Since the time set for a is negligibly short, even if the correction value setting for 10 units is repeated 10 times and the correction value setting for 100 units is performed, the correction value setting for 1000 units is repeated 10 times. This is because even if the correction values are set for 10,000 units, the required time is almost the same.

6. Embodiment 6 FIG. 6 shows an ABS using a piezoelectric pressure sensor unit according to another embodiment of the present invention.
It is a block diagram of a hydraulic pressure detection system. The control unit 13 detects the pressure applied to the sensor unit 1e (crystal 2) based on the sensor output signal SEN-OUT output from the piezoelectric pressure sensor unit 1e, and determines each control value based on the detected pressure. .

A signal line connected to the input terminal IN of the MPU 14 for receiving the sensor output signal SEN-OUT;
Output terminal OU of MPU 14 that outputs a reset command signal
The signal line connected to T is unified and provided for connection with the pressure sensor unit 1e. In the pressure sensor unit 1e, a reset detection resistor 11 is inserted in series with the signal line connected to the control unit 13. The reset detection circuit 12 detects the voltage across the resistor 11 and determines whether or not the reset circuit 4 should be operated.

The control unit 13 normally has a sensor output signal SEN-OU from the pressure sensor unit 1e.
Since the impedance becomes high in the state receiving T, almost no current flows through the resistor 11 and no potential difference occurs between both ends of the resistor 11. Further, since the output of the pressure sensor unit 1e is provided with a buffer (the operational amplifier 21), the level of the sensor output signal SEN-OUT almost changes with respect to the impedance change of the signal line due to the reset command signal output of the control unit 13. Not affected.

Therefore, the control unit 13 is not affected by the addition of the reset detection resistor 11,
The sensor output signal SEN-OUT can be received. Then, the reset detection circuit 12 can individually detect the voltage (sensor output signal SEN-OUT) on the sensor unit 1e side and the voltage MPU-OUT on the control unit 13 side among the voltages at both ends of the resistor 11, and output the sensor output. The signal SEN-OUT and the reset command signal output by the MPU 14 can be individually detected.

Here, the possible values of the voltage SEN-OUT of the resistor 11 on the sensor unit 1e side are classified into the following six. (A) SEN-OUT <(1/5) VDD (b) (1/5) VDD ≦ SEN-OUT ≦ VIL (c) VIL <SEN-OUT <VIH However, each gate detects “L” level. (D) VIL <SEN-OUT <VIH However, when each gate detects "H" level. (E) VIH≤SEN-OUT≤ (4/5) VDD (f) SEN-OUT> (4/5) VDD

Here, VDD is a power supply voltage. Also,
VIL is the maximum value that each gate recognizes as an "L" level input. Therefore, if a voltage lower than this is applied, it is guaranteed that the input voltage is at the “L” level. Similarly, VIH
Is the minimum value that each gate recognizes as an "H" level input. Therefore, if a voltage higher than this is applied, it is guaranteed that the input voltage is at the “H” level. VILH is about 0.
At a voltage near 3 VDD, VIH is a voltage near 0.7 VDD.

The control unit 1 of the resistor 11
The value that the voltage MPU-OUT on the third side can take is MPU14
Irrespective of the presence or absence of the output of the reset command signal from the CPU, it is classified into the following three. (G) MPU-OUT <(1/5) VDD (h) (1/5) VDD ≦ MPU-OUT ≦ (4/5)
VDD (i) MPU-OUT> (4/5) VDD

Therefore, the sensor unit 1 of the resistor 11
e-side voltage SEN-OUT and control unit 13
The combination of the side voltage MPU-OUT is 6 × 3 = 18
As described above, the reset detection circuit 12 determines that the input is the reset input and outputs the “L” level reset signal RE when the following condition is satisfied.

(A) When the voltage SEN-OUT of the reset detection resistor 11 on the sensor unit 1e side is equal to or higher than the "H" level detection voltage of the gate IC, the control unit 1
The voltage MPU-OUT on the third side is equal to or less than (1/5) VDD. (B) The voltage SEN-OUT on the sensor unit 1e side of the reset detection resistor 11 is equal to or less than the "L" level detection voltage of the gate IC, and the control unit 13 side Voltage MPU
-OUT is more than (4/5) VDD

That is, out of the 18 combinations, the reset detection circuit 12 determines that the input is a reset input,
The output of the reset signal RE of the level is based on the condition (a).
When the voltage SEN-OUT is the condition (d) and the voltage MPU-OUT is the condition (g),
If the voltage SEN-OUT is the condition (e) and the voltage MPU-OU
When T is the condition (g), the voltage SEN-OUT may be the condition (f) and the voltage MPU-OUT may be the condition (g).

As a combination that satisfies the condition (b), the voltage SEN-OUT is the condition (a) and the voltage MPU
When −OUT is the condition (i), the voltage SEN-OUT is the condition (b), and when the voltage MPU-OUT is the condition (i),
When the voltage SEN-OUT is the condition (c), the voltage MPU-OU
T may be (i). All the remaining twelve combinations are not detected as reset.

FIG. 7 is a circuit diagram of the reset detection circuit 12 for realizing the above operation. Reset detection circuit 12
Is the control unit 1 with the resistor 11 connected to the inverting input terminal.
Comparator 3 to which voltage MPU-OUT on the 3 side is input
1, a comparator 32 in which the voltage MPU-OUT is input to the non-inverting input terminal, an inverter gate 33 for inverting the logic of the voltage SEN-OUT on the sensor unit 1e side of the resistor 11, a negative logic of the output of the comparator 31 and the voltage SEN-OUT NAND gate 34 for taking product, comparator 3
2 and the output of the inverter gate 33, a NAND gate 35, the AND gate 36 of the output of the NAND gate 34 and the output of the NAND gate 35, and one end connected to the power supply and the other end connected to the comparator 32 The resistor 37 is connected to the inverting input terminal of the comparator 32, one end is connected to the inverting input terminal of the comparator 32, and the other end is connected to the comparator 3.
1 is connected to the non-inverting input terminal, one end is connected to the non-inverting input terminal of the comparator 31, and the other end is grounded. The other end is connected to the power supply, and the other end is connected to the output of the comparator 32. A resistor 40 having one end connected to the power supply and the other end connected to the output of the comparator 31.
1 is comprised.

The voltage V31 at the non-inverting input terminal of the comparator 31 is set to (1/5) VDD, and the voltage V32 at the inverting input terminal of the comparator 32 is set to (4/5) V
DD is set.

Next, the operation of the reset detection circuit 12 will be described. When the condition (A) is satisfied, the voltage MPU-OUT of the resistor 11 on the control unit 13 side becomes (１ ／)
Since it is equal to or lower than VDD, the output of the comparator 31 becomes “H” level and the output of the comparator 32 becomes “L” level.
Therefore, the input to the first input terminal of the NAND gate 34 becomes “H” level, and the input to the first input terminal of the NAND gate 35 becomes “L” level.

When the condition (a) is satisfied, the resistance 1
Since the voltage SEN-OUT on the sensor unit 1e side is equal to or higher than the “H” level detection voltage of the gate IC, the input to the second input terminal of the NAND gate 34 is “H” level, N
The input to the second input terminal of the AND gate 35 is “L” by being logically inverted by the inverter gate 33.
Level. Therefore, the output of NAND gate 34 is at "L" level and the output of NAND gate 35 is at "H" level, and AND gate 36 outputs "L" level reset signal RE. Thus, the reset circuit 4
Operates, and the integration circuit 3 is reset.

When the condition (b) is satisfied, the voltage MPU-OUT on the control unit 13 side of the resistor 11 becomes (4)
/ 5) Since it is equal to or higher than VDD, the output of the comparator 31 becomes “L” level and the output of the comparator 32 becomes “H” level. Therefore, the input to the first input terminal of the NAND gate 34 is at “L” level, and the input to the first input terminal of the NAND gate 35 is at “H” level.

When the condition (b) is satisfied, the resistance 1
Since the voltage SEN-OUT of the first sensor unit 1e is equal to or lower than the “L” level detection voltage of the gate IC, the input to the second input terminal of the NAND gate 34 is “L” level, N
The input to the second input terminal of the AND gate 35 is “H” by being logically inverted by the inverter gate 33.
Level. Therefore, the output of NAND gate 34 is at "H" level and the output of NAND gate 35 is at "L" level, and AND gate 36 outputs "L" level reset signal RE. Thus, the reset circuit 4
Operates, and the integration circuit 3 is reset.

Under the conditions other than the above, the output of the AND gate 36 becomes "H" level and the sensor unit 1e
Is not reset. Also, the sensor output signal SEN-O
When the UT level is near the threshold of the gate IC, NAN
Although the value of the second input terminal of the D gate 34 and the value of the input terminal of the inverter gate 33 become uncertain, the outputs of the comparators 31 and 32 at this time both become "L" level.
First input terminal of AND gate 34 and NAND gate 3
5, the value of the first input terminal is at the “L” level. Therefore,
Regardless of the value of the second input terminal of the NAND gate 34 and the value of the input terminal of the inverter gate 33, the output of the AND gate 36 becomes "H" and the sensor unit 1e is not reset.

FIG. 8 shows the voltage MPU- on the control unit 13 side among the voltages across the reset detection resistor 11.
It is a figure showing a waveform of OUT. Control unit 1
The voltage MPU-OUT on the third side becomes the level of the sensor output signal SEN-OUT when the MPU 14 does not output the reset command signal (the sensor input period in FIG. 8),
When the MPU 14 is outputting a reset command signal from the output terminal OUT, the level becomes the level of the reset command signal.

Here, the MPU 14 includes the sensor unit 1
When resetting e, as shown in FIG. 8, a reset is performed in which a signal of an "H" level ((4/5) VDD or more) and a signal of an "L" level ((1/5) VDD or less) are paired. Outputs command signal. Such a reset command signal is M
When output from the PU 14, either of the above conditions (a) or (b) is satisfied, whereby the sensor unit 1e is reset.

As described above, the control unit 13
The reset command signal output from the controller is a signal that is a set of an "H" level signal and an "L" level signal, and the reset detection circuit 12 is configured by a gate circuit to use the threshold value of the gate circuit. Thereby, without complicating the configuration of the control unit 13 and the reset detection circuit 12, the sensor unit 1e and the control unit 1
The number of signal lines between the three can be reduced.

Reset detection circuit 1 according to this embodiment
To reduce the number of signal lines between the sensor unit 1e and the control unit 13 without using the
Using techniques such as AM modulation, FM modulation, and pulse modulation,
It is necessary to multiplex two signals on one signal line.
However, in such a technique, the configurations of the reset detection circuit 12 and the control unit 13 are complicated.

In this embodiment, the sensor unit according to the first embodiment is used as an example of the sensor unit combined with the control unit 13.
It goes without saying that other sensor units may be used. Needless to say, the system incorporating the pressure sensor unit is not limited to the ABS oil pressure detection system.

[0052]

According to the present invention, by providing a diode in a reverse bias state at the connection point between the piezoelectric element and the input terminal of the integration circuit as described in claim 1, the sensor which causes drift may be provided. Since a correction current having the same magnitude as the leakage current and flowing in the opposite direction is supplied from the diode, the leakage current of the sensor can be canceled by the correction current, and apparent drift can be canceled. As a result, drift correction of the pressure sensor can be realized at low cost.

Further, by providing an off-bias adjustment circuit and a reverse bias adjustment circuit, the off-bias value of the transistor in the reset circuit or the reverse bias value of the diode is changed. Or
Alternatively, both of them can be changed to match the characteristics of the leakage current of the sensor that causes the drift, and more accurate drift correction can be realized. In addition, since the individual variations of the pressure sensor itself can be corrected, the accuracy of the components and the accuracy of the fabrication can be simplified, and the cost can be realized at a lower cost than when the drift is reduced by the component characteristics of the pressure sensor.

Further, by providing the temperature detection circuit, the storage device, and the control circuit as described in claim 3, the drift of the pressure sensor can be canceled even if the ambient temperature changes. Drift correction can be realized at low cost. In addition, since the individual variations of the pressure sensor itself can be corrected, the accuracy of the components and the accuracy of the fabrication can be simplified, and the cost can be realized at a lower cost than when the drift is reduced by the component characteristics of the pressure sensor. Further, if a type that can be written to the storage device is used, the correction value (off-bias value and reverse bias value) setting for the storage device can be automated, and the correction value setting is performed simultaneously for a plurality of pressure sensors. You can also.

According to a fourth aspect of the present invention, a signal line for transferring a sensor output signal and a signal line for transferring a reset command signal are shared, and a resistor and a reset detecting circuit are provided in the sensor unit. The number of signal lines between the control unit and the control unit can be reduced. As a result, the number of signal lines and the number of connector poles is reduced, so that the case can be reduced in size and mounting inside the actuator becomes easy.

According to a fifth aspect of the present invention, the reset command signal is a signal in which the H-level signal and the L-level signal are paired, and the reset detection circuit is constituted by a gate circuit. The number of signal lines between the sensor unit and the control unit can be reduced without complicating the configurations of the control unit that outputs the signal and the reset detection circuit. Further, by providing different criteria for the sensor output signal, the reset command signal can be detected for any sensor output signal level.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a piezoelectric pressure sensor unit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a piezoelectric pressure sensor unit showing another embodiment of the present invention.

FIG. 3 is a circuit diagram of a piezoelectric pressure sensor unit showing another embodiment of the present invention.

FIG. 4 is a circuit diagram of a piezoelectric pressure sensor unit showing another embodiment of the present invention.

FIG. 5 is a circuit diagram of a piezoelectric pressure sensor unit showing another embodiment of the present invention.

FIG. 6 is a block diagram of an ABS oil pressure detection system using a piezoelectric pressure sensor unit according to another embodiment of the present invention.

FIG. 7 is a circuit diagram of a reset detection circuit.

FIG. 8 is a diagram showing a voltage waveform on a control unit side among voltages at both ends of a reset detection resistor.

FIG. 9 is a circuit diagram of a conventional piezoelectric pressure sensor unit.

10 is a block diagram of a conventional ABS oil pressure detection system using the piezoelectric pressure sensor unit of FIG.

[Explanation of symbols]

1, 1a, 1b, 1c, 1d, 1e: Piezoelectric pressure sensor unit, 2: Crystal, 3: Integration circuit, 4, Reset circuit, 5, 5-1, 5-2: Diode, 6, 6a: Off bias Adjustment circuit, 7, 7a ... reverse bias adjustment circuit, 8
... Temperature detection circuit, 9, 9a ... Control circuit, 10, 10a ...
Storage device, 11: resistor, 12: reset detection circuit, 13
... Control unit, 14 ... MPU.

Claims (5)

[Claims] A piezoelectric element that generates an electric charge in response to a strain caused by an applied pressure; an integration circuit that converts an electric charge generated at both ends of the piezoelectric element into a voltage; a reset circuit that resets the integration circuit; A diode in a reverse bias state added to a connection point between the input terminal of the integration circuit and the input terminal of the integration circuit. 2. The drift reduction circuit for a pressure sensor according to claim 1, wherein an off-bias adjustment circuit for adjusting an off-bias of a transistor in the reset circuit, and a reverse bias for adjusting a reverse bias of the diode. A drift reduction circuit for a pressure sensor, comprising: an adjustment circuit. 3. The drift reduction circuit for a pressure sensor according to claim 2, wherein a temperature detection circuit for detecting an ambient temperature, and a storage device for storing an off-bias value of the transistor and a reverse bias value of the diode at each temperature. Reading the off-bias value and the reverse bias value corresponding to the current ambient temperature from the storage device in accordance with the current ambient temperature detected by the temperature detection circuit, and controlling the off-bias adjustment circuit and the reverse bias adjustment circuit And a circuit for reducing the drift of the pressure sensor. 4. A sensor unit comprising: a piezoelectric element that generates an electric charge in response to a strain caused by an applied pressure; an integrating circuit that converts electric charges generated at both ends of the piezoelectric element into a voltage; a reset circuit that resets the integrating circuit; A control unit that receives a sensor output signal from the unit and outputs a reset command signal to the sensor unit, wherein the control unit includes a signal line that receives the sensor output signal from the sensor unit and a reset command signal. The output signal line is shared, and the signal line is used to connect to the sensor unit. The sensor unit detects a resistor inserted in series with the signal line, and detects a voltage across the resistor. And a reset detection circuit for determining whether to activate the reset circuit. Reset method of the pressure sensor, characterized in that. 5. The pressure sensor reset method according to claim 4, wherein the control unit outputs a reset command signal having a pair of an H level signal and an L level signal when resetting the sensor unit. The reset detection circuit in the sensor unit includes a gate circuit, and when the voltage of the resistor on the sensor unit side is the H level detection voltage of the gate circuit and the voltage on the control unit side is the L level, A reset circuit for activating the reset circuit when the voltage on the side is an L level detection voltage of a gate circuit and the voltage on the control unit is at an H level.