JP2008185398A - Pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pressure sensor which is highly precise, good in performance yield, and easy to manufacture. <P>SOLUTION: In the low pressure side of severe allowable error, the output of a first amplifier circuit 21 is adopted as the sensor output, and in the high pressure side of not so severe allowable error, the output of a second amplifier circuit 22 is adopted as the sensor output. Thereby, for only the low pressure side of severe allowable error, adjustment for satisfying the condition is necessary and for the high pressure side, difficult adjustment can be eliminated. Thereby, the pressure sensor which is highly precise, moreover good in performance yield, and easy to manufacture can be provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a pressure sensor that amplifies a detection signal corresponding to pressure and outputs the amplified signal as a sensor output.

In recent years, high accuracy of pressure sensors has been demanded from the system side. In the current pressure sensor, the signal from the sensor chip is amplified by one amplifier circuit (see, for example, Patent Document 1). In such a pressure sensor, the characteristics are adjusted so as to fall within the allowable error range of the product so that the sensor output corresponds to the pressure range to be detected. The correction value in the amplifier circuit is set so that the characteristics are within the allowable error range of the product for the entire pressure range to be detected, that is, the entire range from low pressure to high pressure.
JP-A-6-258117

  However, although the characteristics are adjusted, the sensor characteristics change due to the effects of variations in the adjustment and the temperature characteristics of the sensor. Therefore, a high-accuracy area such as a tolerance of 0.4% FS has a characteristic yield. It is bad and difficult to manufacture. Note that 0.4% FS means that the error of the sensor output (V) with respect to the pressure to be detected with respect to the full scale is 0.4% or less. For example, when the sensor output changes from 0.5 to 4.5 V with respect to 0 to 17 MPa which is the pressure to be detected, an error with respect to 4.0 (= 4.5−0.5) which is full scale. Is 0.016V.

  In view of the above points, an object of the present invention is to provide a pressure sensor that is highly accurate, has a good characteristic yield, and is easy to manufacture.

  In order to achieve the above object, in the present invention, a sensing unit (11) that generates an output corresponding to a change in pressure to be measured, and a first amplifier circuit that amplifies and outputs the output of the sensing unit (11) ( 21), the second amplifier circuit (22) for amplifying and outputting the output of the sensing unit (11), and the output of the first amplifier circuit (21) and the output of the second amplifier circuit (22) as sensor outputs. And a data storage unit (31) for storing sensitivity, offset, and offset temperature characteristic correction data in the first amplifier circuit (21) and the second amplifier circuit (22). The output based on the correction data based on the correction data of the first amplifier circuit (21) is narrower than the output based on the correction data based on the correction data of the second amplifier circuit (22). Have It is characterized in that.

  According to such a pressure sensor, the output of the first amplifier circuit (21) is adopted as the sensor output in a pressure range where the tolerance is severe, and the second amplifier circuit is used in a pressure range where the tolerance is relatively severe. The output of (22) can be adopted as the sensor output. Therefore, it is only necessary to make an adjustment that satisfies the condition only in the pressure range where the allowable error is severe, and it is possible to eliminate difficult adjustment in the pressure range where the allowable error is not so severe. As a result, it is possible to provide a pressure sensor that is highly accurate, has a good characteristic yield, and is easy to manufacture.

  For example, the switching circuit (23) is based on the output of either the first amplifier circuit (21) or the second amplifier circuit (22) until the pressure to be measured reaches a threshold value. The output of (21) can be used as the sensor output, and when the pressure to be measured reaches the threshold value, the output of the second amplifier circuit (22) can be used as the sensor output. This makes it possible to provide a highly accurate pressure sensor when the low pressure side is in a pressure range where the tolerance is severe and the high pressure side is in a pressure range where the tolerance is not so severe.

  Similarly, the switching circuit (23) is based on the output of either the first amplifier circuit (21) or the second amplifier circuit (22) until the pressure to be measured reaches the threshold value. The output of the circuit (22) can be used as a sensor output, and when the pressure to be measured reaches a threshold value, the output of the first amplifier circuit (21) can be used as a sensor output. This makes it possible to provide a highly accurate pressure sensor when the high pressure side is in a pressure range where the tolerance is severe and the low pressure side is in a pressure range where the tolerance is not so severe.

  In addition, the switching circuit (23) may switch the output to be employed so that the output of only one of the first amplification circuit (21) and the second amplification circuit (22) is used as the sensor output in advance. it can. In this way, it is possible to cope with the case where it is desired to use only one of them as a sensor output according to product standards.

  In addition, such a pressure sensor is a signal provided with a sensor chip (10) including a sensing unit (11), a first amplifier circuit (21), a second amplifier circuit (22), and a switching circuit (23). The processing chip (20) and the data storage chip (30) provided with the data storage unit (31) can be used as three chips. The sensor chip (10) including the sensing unit (11), the first amplifier circuit (21), the second amplifier circuit (22), and the switching circuit (23) are provided, and the data storage unit (31). ) May be two chips. Furthermore, the sensing unit (11), the first amplifier circuit (21), the second amplifier circuit (22), the switching circuit (23), and the data storage unit (31) may be configured as one chip.

  Moreover, you may make it provide the offset correction part (40) for performing offset correction of a 1st amplifier circuit (21).

  As described above, by providing the offset correction unit (40) in the first amplifier circuit (21) corresponding to the pressure range regarded as a strict allowable error, it is possible to achieve higher accuracy.

  Further, if a temperature sensor (50) that transmits temperature-related data to the offset correction unit (40) is provided, higher accuracy can be achieved.

  The case where the number of amplifier circuits of the present invention is two has been described above, but the number is not limited to two, and two or more amplifier circuits may be used. In this case, the switching circuit (23) switches which output of the plurality of amplification circuits (21, 22) is the sensor output, and the data storage unit (31) selects the plurality of amplification circuits. The correction data of sensitivity, offset, and offset temperature characteristic in (21, 22) is stored, and the outputs of the plurality of amplifier circuits (21) corrected based on the correction data have different allowable errors. It only has to correspond to the width.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals in the drawings.

(First embodiment)
A first embodiment of the present invention will be described. FIG. 1 is a circuit block diagram of a pressure sensor according to the present embodiment. Hereinafter, the pressure sensor of this embodiment will be described with reference to this drawing.

  As shown in FIG. 1, the pressure sensor includes a sensor chip 10, a signal processing chip 20, and a data storage chip 30.

  The sensor chip 10 is formed with a sensing unit 11 that performs pressure detection. The sensing unit 11 includes a Wheatstone bridge circuit including four diffusion resistors (strain gauges) 11a to 11d, and performs pressure detection based on a constant current I supplied from the signal processing chip 20. That is, when a pressure is applied to the sensing unit 11, the intermediate potentials at two points of the Wheatstone bridge circuit (potentials at points A and B in the figure) change according to the magnitude of the applied pressure. The potential difference between the intermediate potentials is output as a detection signal corresponding to the pressure. This detection signal is input to the signal processing chip 20 and finally output as a sensor output.

  The signal processing chip 20 includes a first amplifier circuit 21, a second amplifier circuit 22, and a high voltage / low voltage switching circuit 23.

  In the case of this embodiment, the first amplifier circuit 21 functions as a low-voltage amplifier circuit, and is used as an amplifier circuit on the low-pressure side of the pressure range to be detected. The first amplifier circuit 21 includes three amplifiers 21a to 21c, resistors 21d to 21i, and a voltage source 21j that forms a reference voltage Vref. The two amplifiers 21a and 21b respectively input the potentials at points A and B of the Wheatstone bridge circuit in the sensor chip 10, and the outputs of the amplifiers 21a and 21b change based on the input potentials. The potential fluctuation is amplified by an inverting amplifier circuit including an amplifier 21c and resistors 21h and 21i, and is output as a sensor output.

  In the case of this embodiment, the second amplifier circuit 22 functions as a high voltage amplifier circuit, and is used as an amplifier circuit on the high voltage side of the pressure range to be detected. Similarly to the first amplifier circuit 21, the second amplifier circuit 22 includes three amplifiers 22a to 22c, resistors 22d to 22i, and a voltage source 22j that forms a reference voltage Vref. Each of the two amplifiers 22a and 22b inputs the potentials at points A and B of the Wheatstone bridge circuit in the sensor chip 10, and the outputs of the amplifiers 22a and 22b change based on the input potentials. The fluctuation in potential is amplified by an inverting amplifier circuit including an amplifier 22c and resistors 22h and 22i, and is output as a sensor output.

  The high voltage / low voltage switching circuit 23 switches whether the sensor output of the first amplifier circuit 21 or the second amplifier circuit 22 is used. This switching is performed using either the output of the first amplifier circuit 21 or the output of the second amplifier circuit 22.

  The data storage chip 30 has a data storage unit 31 composed of a memory such as an EPROM, for example. The data storage unit 30 stores correction data according to sensitivity, offset, and offset temperature characteristics in the data storage unit 31. The correction data is output to the signal processing chip 20.

  The correction data is examined and stored for each pressure sensor after the sensor chip 10 is incorporated into the signal processing chip 20 and the data storage chip 30, that is, after the circuit of the pressure sensor is manufactured. The correction data is different for the first amplifier circuit 21 and the second amplifier circuit 22. FIG. 2 is a graph showing the relationship of the sensor output range to the pressure range to be detected. As shown in this figure, the allowable error is determined as a certain width with respect to the sensor characteristics. When the pressure is a low pressure lower than a predetermined value (8 MPa in the present figure), the allowable error is narrow and the pressure is predetermined. When the pressure is higher than the value, the tolerance is wider than that. That is, the tolerance on the low pressure side is more severe than that on the high pressure side. For this reason, the correction data of the first amplifier circuit 21 satisfies the condition that the tolerance is narrower in the low voltage range, and the correction data of the second amplifier circuit 22 is acceptable in the high voltage range. It is considered that the condition that the error width may be relatively wide is satisfied.

  When the correction data stored in the data storage chip 30 is output to the signal processing chip 20, the signal processing chip 20 corrects the sensitivity, the offset, and the offset temperature characteristic based on each received data. To be done. For example, the sensitivity is corrected by adjusting the value of the constant current I supplied to the sensor chip 10. Since specific methods for correcting sensitivity, offset, and offset temperature characteristics are known in the art, details are omitted here.

  Next, the operation of the pressure sensor configured as described above will be described.

  For example, when no pressure is applied to the sensing unit 11, no-pressure voltage is input to the amplifiers 21a, 21b, 22a, and 22b of the first and second amplifier circuits 21 and 22, respectively. When pressure is applied to the sensing unit 11, the midpoint potential of the Wheatstone bridge circuit (the potential at the points A and B) changes, and the amplifiers 21a and 22a and the amplifiers of the first and second amplifier circuits 21 and 22 are changed. Since the potentials of the inverting input terminals of 21b and 22b have different values, the output potentials of the amplifiers 21a and 21b and the output potentials of the amplifiers 21b and 22b have different values.

  In this case, for example, if the reference voltage Vref is 1.5V and the potentials of the inverting input terminals of the amplifiers 21b and 22b become 1.4V, the potentials of the non-inverting input terminals of the amplifiers 21b and 22b are also 1. Since the voltage is set to 4 V, a potential difference is generated between both ends of the resistor 21g and the resistor 22g, and a current flows from the voltage sources 21j and 22j toward the output terminals of the amplifiers 21b and 22b. Since this current also flows through the resistors 21f and 22f, the voltage at the output terminals of the amplifiers 21b and 22b becomes 1.3 V, for example, due to the voltage drop of the resistors 21f and 22f.

  On the other hand, if the potentials of the inverting input terminals of the amplifiers 21a and 22a are 1.6V, the potentials of the non-inverting input terminals of the amplifiers 21a and 22a are also 1.6V. As a result, current flows from the inverting input terminal side of the amplifiers 21a and 22a toward the output terminal side of the amplifiers 21b and 22b. Due to the influence of this current, the current also flows through the resistors 21d and 22d from the output terminal side of the amplifiers 21a and 22a toward the resistors 21e and 22e. Therefore, the voltage drop of the resistors 21d and 22d causes the output of the amplifiers 21a and 22a. The terminal voltage becomes 1.7V, for example.

  In this way, since the output potentials of the amplifiers 21a and 22a change, they are amplified by the inverting amplifier circuit composed of the resistors 21h and 21i and the amplifier 21c or the resistors 22h and 22i and the amplifier 22c. The output of this inverting amplifier circuit becomes the sensor output.

  At this time, both of the outputs of the first and second amplifier circuits 21 and 22 are input to the high and low voltage switching circuit 23. The high and low voltage switching circuit 23 includes the first and second amplifier circuits 21, Based on the output of any one of 22, the switching of which of the first and second amplifier circuits 21 and 22 is used as the sensor output is performed. For example, in the high pressure / low pressure switching circuit 23, the pressure applied to the sensing unit 11 is the boundary between the low pressure and the high pressure so that the output of the first amplifier circuit 21 is in the relationship between the pressure and the sensor output as shown in FIG. 3. 2, specifically, a potential corresponding to 8 MPa in FIG. 2 is used as a threshold value. For example, the switch circuit is switched when the output potential of the first amplifier circuit 21 becomes a value corresponding to the threshold value. . Therefore, when the output potential of the first amplifier circuit 21 is smaller than the value corresponding to the threshold value, the output of the first amplifier circuit 21 is adopted as the sensor output, and when the output potential is larger than the value, the output of the second amplifier circuit 22 is used. Adopted as sensor output.

  According to the pressure sensor configured as described above, the output of the first amplifier circuit 21 is adopted as the sensor output on the low pressure side where the tolerance is severe, and the second is adopted on the high pressure side where the tolerance is not relatively severe. The output of the amplifier circuit 22 is adopted as the sensor output. Therefore, it is only necessary to make an adjustment that satisfies the condition only on the low pressure side where the tolerance is severe, and it is possible to eliminate difficult adjustment on the high pressure side. As a result, it is possible to provide a pressure sensor that is highly accurate, has a good characteristic yield, and is easy to manufacture.

(Second Embodiment)
A second embodiment of the present invention will be described. The present embodiment provides a pressure sensor capable of improving accuracy with respect to the first embodiment.

  FIG. 4 is a circuit block diagram of the pressure sensor according to the present embodiment. As shown in this figure, the first amplifying circuit 21 used as the low-pressure side sensor output is provided with an offset correction unit 40 and a temperature sensor 50.

  As shown in FIG. 2, the offset correction unit 40 attempts to obtain an output potential at which the output potential of the first amplifier circuit 21 deviates from the allowable error when the allowable error width on the low voltage side is determined. The output potential is corrected so as to fall within the allowable error. For example, when the pressure assumed as the pressure detected by the pressure sensor is obtained, the sensor output corresponding to the assumed pressure can be seen from the graph of FIG. For this reason, the offset correction unit 40 receives the pressure assumed from the other ECU 60 or data necessary for assuming the pressure, and outputs the first amplification circuit for the sensor output corresponding to the assumed pressure. When the output potential of 21 deviates from the allowable error, it is stored as an offset, and the output potential of the first amplifier circuit 21 is corrected. For example, when the pressure sensor is applied to the detection of the exhaust pressure in the common rail, an engine ECU is assumed as the other ECU 60, and the fuel injection amount and the like can be grasped by the engine ECU. The exhaust pressure of the common rail is calculated, and the engine ECU may transmit the assumed exhaust pressure or data that can be used for calculating the exhaust pressure to the offset correction unit 40.

  The temperature sensor 50 detects the temperature so that the offset correction unit 40 can correct not only the offset but also the offset temperature characteristic. By transmitting data related to the temperature detected by the temperature sensor 50 to the offset correction unit 40, the offset temperature characteristic can also be corrected.

  As described above, the first correction circuit 21 on the low-voltage side, which is regarded as a strict tolerance, includes the offset correction unit 40 and the temperature sensor 50, so that higher accuracy can be achieved.

(Other embodiments)
In the above embodiment, the pressure sensor is configured by the three chips of the sensor chip 10, the signal processing chip 20, and the data storage chip 30, but these are merely examples. For example, the signal processing chip 20 and the data storage chip 30 are arranged as one chip. The pressure sensor may be constituted by two chips of the sensor chip 10 and the sensor chip 10, or all of the sensor chip 10, the signal processing chip 20, and the data storage chip 30 may be integrated into one chip.

  In the second embodiment, the example in which the offset correction unit 40 and the temperature sensor 50 are provided in the signal processing chip 20 has been described. However, the offset correction unit 40 and the temperature sensor 50 may be provided outside the signal processing chip 20.

  In the above embodiment, the output of the first amplifier circuit 21 and the second amplifier circuit 22 is switched between the low-voltage side and the high-voltage side to obtain a sensor output. The first amplifier circuit 21 may be used on the high voltage side, and the second amplifier circuit 22 may be used on the low voltage side.

  In the above embodiment, it is assumed that the output of the first amplifier circuit 21 and the second amplifier circuit 22 is switched between the low-voltage side and the high-voltage side to obtain a sensor output. May be used as sensor output. That is, in order to apply the pressure sensor having the above configuration to two different product standards, the output of the first amplifier circuit 21 is used as a sensor output for a product standard that requires high accuracy, and so high accuracy is required. For product standards that are not used, the output of the second amplifier circuit 22 may be used as the sensor output. In this case, the high- and low-voltage switching circuit 23 switches the output used in advance by the high- and low-voltage switching circuit 23 so that the output of which one of the first amplification circuit 21 and the second amplification circuit 22 is used can be switched in advance. I will go there.

  Further, in the above embodiment, the accuracy is divided into two stages of the low pressure side and the high pressure side. However, in order to divide the accuracy into three or more stages, a number of amplifier circuits corresponding to the number of stages may be provided. .

It is a circuit block diagram of the pressure sensor concerning a 1st embodiment of the present invention. It is a graph showing the relationship of the range of the sensor output with respect to the pressure range to detect. It is the graph which showed the relationship between a pressure and a sensor output. It is a circuit block diagram of the pressure sensor concerning a 2nd embodiment of the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Sensor chip, 11 ... Sensing part, 11a-11d ... Diffusion resistance, 20 ... Signal processing chip, 21 ... Amplifier circuit, 21a-21c ... Amplifier, 21d-21h ... Resistor, 21j ... Voltage source, 22 ... Amplifier circuit, Reference numerals 22a to 22c: amplifiers, 22d to 22h: resistors, 22j: voltage sources, 23: high and low voltage switching circuits, 30: data storage chips, 40: offset correction units, 50: temperature sensors, 60: other ECUs.

Claims (10)

A sensing unit (11) for generating an output corresponding to a change in pressure to be measured;
A first amplifier circuit (21) for amplifying and outputting the output of the sensing unit (11);
A second amplifier circuit (22) for amplifying and outputting the output of the sensing unit (11);
A switching circuit (23) for switching between the output of the first amplifier circuit (21) and the output of the second amplifier circuit (22) as a sensor output;
A data storage unit (31) for storing correction data of sensitivity, offset, and offset temperature characteristics in the first amplifier circuit (21) and the second amplifier circuit (22),
The output based on the correction based on the correction data of the first amplifier circuit (21) corresponds to the output having a narrower tolerance than the output based on the correction data based on the correction data of the second amplifier circuit (22). A pressure sensor. The switching circuit (23) is based on the output of either the first amplifier circuit (21) or the second amplifier circuit (22) until the pressure to be measured reaches a threshold value. The output of one amplifier circuit (21) is used as the sensor output, and when the pressure to be measured reaches a threshold value, the output of the second amplifier circuit (22) is used as the sensor output. The pressure sensor according to 1. The switching circuit (23) is based on the output of either the first amplifier circuit (21) or the second amplifier circuit (22) until the pressure to be measured reaches a threshold value. The output of the second amplifier circuit (22) is the sensor output, and the output of the first amplifier circuit (21) is the sensor output when the pressure to be measured reaches a threshold value. The pressure sensor according to 1. The switching circuit (23) switches the employed output in advance so that the output of only one of the first amplification circuit (21) and the second amplification circuit (22) is used as a sensor output. The pressure sensor according to claim 1. A sensor chip (10) including the sensing unit (11);
A signal processing chip (20) provided with the first amplifier circuit (21), the second amplifier circuit (22) and the switching circuit (23);
The pressure sensor according to any one of claims 1 to 4, comprising three chips of data storage chips (30) provided with the data storage section (31). A sensor chip (10) including the sensing unit (11);
The first amplifying circuit (21), the second amplifying circuit (22), and the switching circuit (23) are provided, and two chips of the data storing unit (31) are provided. The pressure sensor according to any one of claims 1 to 4, wherein: The sensing unit (11), the first amplifier circuit (21), the second amplifier circuit (22), the switching circuit (23), and the data storage unit (31) are provided in one chip. The pressure sensor according to any one of claims 1 to 4. The pressure sensor according to any one of claims 1 to 7, further comprising an offset correction unit (40) for performing offset correction of the first amplifier circuit (21). The pressure sensor according to claim 8, further comprising a temperature sensor (50) for transmitting data related to temperature to the offset correction unit (40). A sensing unit (11) for generating an output corresponding to a change in pressure to be measured;
A plurality of amplifier circuits (21, 22) for amplifying and outputting the output of the sensing unit (11);
A switching circuit (23) for switching which of the outputs of the plurality of amplifier circuits (21, 22) is a sensor output;
A data storage unit (31) for storing correction data of sensitivity, offset, and offset temperature characteristics in the plurality of amplifier circuits (21, 22),
The pressure sensor, wherein the outputs of the plurality of amplifier circuits (21) corrected based on the correction data correspond to different tolerance widths.

Images