Patent Grant
11506555
The present invention relates to a piezoelectric sensor that measures a physical amount by a piezoelectric element, integrates a current signal of the measurement result, and amplifies and outputs thereof.
A piezoelectric sensor using a piezoelectric element that generates charges in response to a physical deformation amount is excellent in sensitivity and has accuracy that is not deteriorated even in high-temperature environment; therefore, the piezoelectric sensor is often used as a sensor for measuring combustion pressure of an engine.
The piezoelectric element 301 includes a pair of electrodes on a surface thereof, to output a charge signal from the electrodes in response to a stress applied to the piezoelectric element 301. In the piezoelectric element 301, since a configuration routing a wire from the electrodes and inputting thereof to a circuit block becomes highly complicated, as shown in
In the integrating operation amplifier 305, between the negative-side input terminal and the output terminal, the charging capacity 304 and the discharging resistor 303 are connected in parallel, and the reference voltage source 306 is connected to a positive-side input terminal; accordingly, an integrating circuit is constituted by the integrating operation amplifier 305, the charging capacity 304 and the discharging resistor 303.
An AC charge signal outputted from the piezoelectric element 301 is accumulated, via the DC breaking capacity 302 for cutting the DC component, in the charging capacity 304 provided between the input and output of the integrating operation amplifier 305, to be converted into an integrated voltage signal Vo1. Here, as the integrating operation amplifier 305, the one with high inputting impedance is used, and thereby it becomes possible to correctly detect even minute charge signal of the piezoelectric element 301. The discharging resistor 303 is provided to prevent the charging capacity 304 from being saturated when positive-negative balance in the AC charge signal is uneven, and it is necessary that a charge-discharge time constant determined by the charging capacity 304 and the discharging resistor 303 is sufficiently longer than a period of the detection signal.
The reference voltage source 306 is to apply a predetermined bias voltage to the integrating circuit and the amplifier circuit, and a voltage regulator circuit or the like utilizing a band-gap voltage of a transistor is generally used.
At a later stage of the integrating operation amplifier 305, there is provided the amplifier circuit that amplifies the output signal Vo1 of the integrating operation amplifier 305 to output an output signal Vout of the piezoelectric sensor. The amplifier circuit is constituted by the amplifying operation amplifier 309, the amplification resistor a 307 and the amplification resistor b 308, and has a configuration in which the amplification resistor b 308 is connected between the negative-side input terminal and the output terminal of the amplifying operation amplifier 309 and the reference voltage source 306 is connected to the positive-side input terminal via the amplification resistor a 307.
The circuit block can be configured with discrete components; however, in terms of space and costs, it is advantageous to form the circuit block into a single integrated circuit. In the conventional example shown in
It is necessary to suppress variations in measurement sensitivity of the output signal Vout of the piezoelectric sensor in each product as small as possible. However, regarding the magnitude of charge signals generated from the piezoelectric element, a relatively large difference occurs in the generated charges due to a slight difference in a production process of piezoelectric element crystals or processing accuracy thereof, and accordingly, it is difficult to satisfy an accuracy required for the output signal Vout of the piezoelectric sensor.
Therefore, it is performed in general that the accuracy in the output signal Vout is secured by providing an adjustment mechanism for the amplification factor to the amplifier circuit to adjust the amplification factor in a sensor assembly process.
Moreover, there is also a method that uses a commercially available laser trimmable resistor to the amplification resistor a, the amplification resistor b, or both, to thereby adjust the resistance value by the laser.
However, these adjustment methods have a problem that the amplification factor cannot be adjusted in the state in which the sensor is completed.
When the adjustment of the amplification factor is performed by cutting of the board wiring or the laser trimmable resistor as described above, the circuit board 606 is required to be exposed to the outside; the adjustment of the amplification factor is performed in a semi-finished state in which the rear housing 609 is not attached, and thereafter, attachment and welding of the rear housing 609 is carried out.
The production procedures described above include complicated processes and result in increase of the production costs. Moreover, since the amplification factor adjustment is carried out in a different state from that of the finished product, the amplification factor in the state of the finished product sometimes differs from the amplification factor when being adjusted, and therefore, the problem that the amplification factor is not set correctly as desired also occurs.
Moreover, in general, the adjustment of the amplification factor is performed while actually applying pressure or the like to the sensor and monitoring the output; however, in the case of the above-described methods, the cut patterns or the written trimmable resistor is irreversible; accordingly, there is also a problem that the high-accuracy adjustment is difficult.
The present invention has been made to solve the above-described problem, and has an object to provide a piezoelectric sensor capable of adjusting an amplification factor or the like with high accuracy in a short time in a state of a finished product.
To solve the above-described problem, there is provided a piezoelectric sensor according to the present invention including: a piezoelectric element for detecting a pressure; an integrating circuit that integrates a current signal outputted from the piezoelectric element to convert the current signal into a voltage signal; an amplifier circuit that amplifies an output from the integrating circuit to output thereof to outside; a reference voltage source that prescribes an offset voltage of an output signal outputted from the amplifier circuit; a writable memory that stores information for setting an amplification factor of the amplifier circuit; and a writing terminal for writing the information to the memory, wherein the integrating circuit, the amplifier circuit, the reference voltage source and the memory are contained in a single integrated circuit.
In the piezoelectric sensor, the writing terminal is provided to an external-connection connector that connects the single integrated circuit and the outside.
Moreover, a piezoelectric sensor according to the present invention includes: a piezoelectric element for detecting a pressure; an integrating circuit that integrates a current signal outputted from the piezoelectric element to convert the current signal into a voltage signal; an amplifier circuit that amplifies an output from the integrating circuit to output thereof to outside; a reference voltage source that prescribes an offset voltage of an output signal outputted from the amplifier circuit; a writable memory that stores information for setting the offset voltage of the reference voltage source; and a writing terminal for writing the information to the memory, wherein the integrating circuit, the amplifier circuit, the reference voltage source and the memory are contained in a single integrated circuit.
In the piezoelectric sensor, the writing terminal is provided to an external-connection connector that connects the single integrated circuit and the outside.
Moreover, a piezoelectric sensor according to the present invention includes: a piezoelectric element for detecting a pressure; an integrating circuit that integrates a current signal outputted from the piezoelectric element to convert the current signal into a voltage signal; an amplifier circuit that amplifies an output from the integrating circuit to output thereof to outside; a reference voltage source that prescribes an offset voltage of an output signal outputted from the amplifier circuit; a clip circuit for limiting an output from the amplifier circuit within a prescribed range; a writable memory that stores information for setting a clip voltage of the clip circuit; and a writing terminal for writing the information to the memory, wherein the integrating circuit, the amplifier circuit, the reference voltage source, the clip circuit and the memory are contained in a single integrated circuit.
In the piezoelectric sensor, the writing terminal is provided to an external-connection connector that connects the single integrated circuit and the outside.
According to the present invention, it is possible to provide a piezoelectric sensor capable of adjusting an amplification factor with high accuracy in a short time in a state of a finished product.
An exemplary embodiment of a piezoelectric sensor according to the present invention will be described based on drawings.
The piezoelectric element 101 includes a pair of electrodes on a surface thereof, to output a charge signal from the electrodes in response to a stress applied to the piezoelectric element 101. In the piezoelectric element 101, one of the electrodes is grounded and the other electrode is connected to a negative-side input terminal of the integrating operation amplifier 105 via the DC breaking capacity 102.
In the integrating operation amplifier 105, between a negative-side input terminal and an output terminal, the charging capacity 104 and the discharging resistor 103 are connected in parallel, and the reference voltage source 106 is connected to a positive-side input terminal; accordingly, an integrating circuit is constituted by the integrating operation amplifier 105, the charging capacity 104 and the discharging resistor 103.
An AC charge signal outputted from the piezoelectric element 101 is accumulated, via the DC breaking capacity 102 for cutting the DC component, in the charging capacity 104 provided between the input and output of the integrating operation amplifier 105, to be converted into an integrated voltage signal Vo1.
The reference voltage source 106 is to apply a predetermined bias voltage to the integrating circuit and the amplifier circuit.
At a later stage of the integrating operation amplifier 105, there is provided the amplifier circuit that amplifies the output signal Vo1 of the integrating operation amplifier 105 to output an output signal Vout of the piezoelectric sensor. The amplifier circuit is constituted by the amplifying operation amplifier 109, the amplification resistor a 107 and the amplification resistor b 108, and has a configuration in which the amplification resistor b 108 is connected between the negative-side input terminal and the output terminal of the amplifying operation amplifier 109 and the reference voltage source 106 is connected to the positive-side input terminal via the amplification resistor a 107.
In the example, the integrating operation amplifier 105, the amplifying operation amplifier 109, the reference voltage source 106, the amplification resistor a 107 and the amplification resistor b 108 are formed into an integrated circuit to be configured as the integrated circuit 110. Moreover, the integrated circuit 110 is provided with the non-volatile memory 111 that stores information for setting an amplification factor of the amplifier circuit. At connection points between the integrated circuit 110 and the outside thereof, input-output terminals are provided; at the connection point between the integrating operation amplifier 105 and the piezoelectric element 101, there is provided the signal input terminal 115, at the connection point between the output of the integrating operation amplifier 105 and the discharging resistor 103, the charging capacity 104, there is provided the feedback terminal 112, and, at the connection point between the output of the amplifying operation amplifier 109 and the outside, there are provided the signal output terminal 113 and further, a writing terminal 114 for writing information to the non-volatile memory 111 from the outside.
The example is characterized by including the non-volatile memory 111 that stores information for setting the amplification factor of the amplifier circuit inside the integrated circuit 110, inputting information to the non-volatile memory 111 by the writing terminal 114, and controlling a value of the amplification resistor a 107 by the information to make the amplification factor of a detection signal variable. The amplification resistor a 107 is configured with a ladder resistor to make a value thereof variable. By incorporating the non-volatile memory 111 into the integrated circuit 110, it is possible to keep a mount area of the circuit block compact.
In the example, the resistor whose value is controlled by the non-volatile memory 111 is the amplification resistor a 107; however, the configuration may be such that the value of the amplification resistor b 108 is controlled or both the amplification resistor a 107 and the amplification resistor b 108 are controlled.
The information to be stored in the non-volatile memory 111 is written by inputting serial data from the writing terminal 114 connected to the non-volatile memory 111. There are many kinds of write formats of serial data that have already been widely distributed, and therefore, the format may be appropriately selected therefrom to be adopted. The number of writing terminals 114 changes in response to the kinds of the formats; however, in general, the more the number of terminals of the write format become, the higher the writing can be done.
A configuration example that changes a resistance value by the non-volatile memory 111 is shown in
Examples of the non-volatile memory 111 include a rewritable memory, such as an EEPROM or a flash ROM, and a recordable memory, such as an OTPROM or a fuse ROM, and both types can be used in the present invention.
When the recordable memory is used, by adopting a configuration combining rewritable volatile memory and non-volatile memory, it becomes possible to correctly adjust the amplification factor. In other words, in the amplification factor adjustment process, the method is to monitor the output voltage and perform adjustment while writing the information to the volatile memory, and, at the time when the appropriate amplification factor is determined, to write a value thereof to the non-volatile memory.
Since the data writing speed of the volatile memory is much higher than that of the non-volatile memory, the above-described configuration combining the volatile memory and the non-volatile memory is useful when a rewritable non-volatile memory is used.
In other words, in the amplification factor adjustment process at the time of producing, a female-side connector, which have conduction with all of the user terminals 703 and writing terminal 114, is coupled to the external-connection connector 702, and, while monitoring the output signal when the pressure is applied to the sensor by the user terminals 703, the data is written to the writing terminal 114 to adjust the amplification factor.
The writing terminal 114 is used only in the amplification factor adjustment process in producing; however, in the case of the connector in
The configuration of the connector shown in
Note that, in the above, description was given of the case in which the sensor side included a male connector; however, a case in which the sensor side includes the female connector can be applied exactly in the same way. Moreover, in
As another method to solve the problem of the number of terminals, there is provided a configuration in which the user terminal also serves as the writing terminal to eliminate the need for a dedicated writing terminal. A configuration example of an integrated circuit corresponding to the method is shown in
By setting the above-described prescribed voltage higher than the power-supply voltage range to be used by the user (for example, when the user power-supply voltage is 4.5V to 5.5V, the prescribed voltage is set at 6.0V), the user can always use the dual-purpose terminal 813 as the output terminal. Then, in the amplification factor adjustment process in producing, the amplification factor can be adjusted by procedures in which, first, the power-supply voltage Vdd is raised to not less than the prescribed value to write the information to the non-volatile memory 111, and next, the power-supply voltage is lowered to the user power-supply voltage, which is less than the prescribed value, to monitor the value of the output signal Vout.
Note that, in the above, description was given of a case of the single writing terminal; however, by causing the power-supply terminal to serve as the dual-purpose terminal, the case of two writing terminals is applicable.
Next, another example of the piezoelectric sensor according to the present invention will be described.
In this example, inside the integrated circuit 110, there is provided a non-volatile memory 911 that is connected to the amplification resistor a 107 and a reference voltage source 906 and stores information for determining the amplification factor of the amplifier circuit and information for determining an offset voltage of the reference voltage source 906; therefore, by the information written to the non-volatile memory 911, at least one of the value of the amplification resistor a 107 and the offset voltage of the reference voltage source 906 is controlled, to thereby make the amplification factor of the detection signal variable.
The reference voltage VR outputted from the reference voltage source 906 prescribes the DC offset voltage of the output signal Vout. Normally, the reference voltage VR is constant; however, as shown in
One of the objects to make the reference voltage VR variable is a case in which the required DC offset voltage differs depending on the user or the model. When the offset voltage is known in advance, it is possible to prepare the integrated circuit in conformity to the value, or to adjust the reference voltage value by a variable resistor; however, if the offset voltage value can be incorporated by the non-volatile memory 911 built in the integrated circuit 110, it becomes possible to use the same integrated circuit for different models, and moreover, to save effort in adjusting variable resistor by hand work.
Another object to make the reference voltage VR variable is to perform fine adjustment of the reference voltage. In general, the reference voltage source is often configured with a band-gap regulator that is less affected by production variations in semiconductors; however, in a lot or between lots of the integrated circuit, voltage variations from several millivolts to tens of millivolts occur.
If such variations in the offset voltage are not allowed on the user side, it is necessary to suppress the variations by performing fine adjustment of the reference voltage. When a pressure signal is not inputted, the DC offset voltage is outputted for the output signal Vout, and therefore, by writing data to the non-volatile memory 911 while monitoring the output signal Vout, it is possible to perform fine adjustment of the reference voltage.
A circuit configuration example that makes the reference voltage variable is shown in
The voltage VB outputted from the band-gap regulator 1001 is converted into the reference voltage VR by the operation amplifier 1002 and the two variable resistors 1003 and 1004. It becomes possible to adjust the value of the reference voltage VR by controlling the resistance values of the variable resistors 1003 and 1004 based on the signal from the non-volatile memory 911.
Between the above-described two objects to change the DC offset voltage, namely, the change for each model and the fine adjustment, accuracy and width of the adjustment significantly differ. Therefore, to make it possible to perform adjustment for both, two pairs of variable resistors may be prepared to allow coarse adjustment and fine adjustment to be separately controlled.
In some cases, an engine combustion pressure sensor for a vehicle, as the piezoelectric sensor, is required to have an output voltage clip function. This is a function of performing voltage clip control to the voltage exceeding an upper limit voltage and a lower limit voltage that have been predetermined and causing the sensor to output a voltage within a range from the lower limit to the upper limit of the voltage, the function being used for fault diagnosis of the sensor. When a voltage out of the clip voltage range is monitored by an engine-side ECU that receives the sensor output, occurrence of abnormal situations, such as a fault in sensor or cable disconnection, is assumed.
In the upper limit clip circuit, a gate of an npn transistor is connected to a connection point of resistors 1105 and 1106 that are connected in series between the power-supply voltage Vdd (not shown) and the GND, a collector of the npn transistor is connected to the power-supply voltage Vdd, and an emitter thereof is connected to the GND via a resistor. The emitter of the npn transistor is connected to a base of a pnp transistor. Then, a collector of the pnp transistor is connected to the GND and an emitter thereof is connected to the amplifier circuit output line. The configuration draws the base-emitter voltage of the npn transistor into the divided voltage of the resistors 1105 and 1106 and adds the base-emitter voltage of the pnp transistor to set the maximum prescribed voltage.
Moreover, in the lower-side clip circuit, a gate of the pnp transistor is connected to a connection point of resistors 1107 and 1108 that are connected in series between the power-supply voltage Vdd (not shown) and the GND, the collector of the pnp transistor is connected to the GND, and the emitter thereof is connected to the power-supply voltage Vdd via a resistor. The emitter of the pnp transistor is connected to a base of the npn transistor. Then, the collector of the npn transistor is connected to the power-supply voltage Vdd and the emitter thereof is connected to the amplifier circuit output line. In the configuration, the divided voltage of the resistors 1107 and 1108 is substantially the same as the minimum prescribed voltage.
Normally, the clip voltage is constant; however, similar to the offset voltage described in Example 2, by making the value of the clip voltage variable depending on the contents of the non-volatile memory, it is possible to provide a combustion pressure sensor with a higher additional value. A configuration example is shown in
The objects of making the clip voltage variable are, similar to the offset voltage described in Example 2, to cover differences in setting due to the models and to respond to fine adjustment. In the case of the clip circuit shown in
So far, the present invention has been described based on three examples; however, the piezoelectric sensor according to the present invention is not limited to the examples and also includes various modifications added to the above-described examples within the scope not departing from the gist of the present invention.
| Number | Date | Country | Kind |
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| PCT/JP2017/011258 | 3/21/2017 | WO |
| Publishing Document | Publishing Date | Country | Kind |
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| WO2017/164183 | 9/28/2017 | WO | A |
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