JP2011153904A - Sensor-voltage processing circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sensor-voltage processing circuit, capable of properly removing a true signal voltage, in opposition to the fluctuations of a supply voltage. <P>SOLUTION: A piezoresistive element 23 of a combustion pressure sensor 20 is connected to a power source via a constant-current source 22. In the sensor voltage processing circuit 30, a grounded first capacitor 32 and a second capacitor 33, connected to the power source via a constant-voltage source 34, are connected through voltage preservation wiring 37. The capacity ratio between the first capacitor 32 and the second capacitor 33 is set so as to agree with the ratio between a reference preservation voltage which is substantially an intermediate value of an estimated fluctuation range of a preservation voltage Vk and a voltage, determined by subtracting the reference preservation voltage from the rated voltage of the power source. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a circuit for processing a sensor voltage. In particular, it extracts and amplifies the signal voltage from the sensor voltage in which the signal voltage that fluctuates at high speed is superimposed on the DC voltage (offset voltage) that fluctuates at a low speed and also follows the fluctuation of the power supply voltage. The present invention relates to a circuit that performs processing.

Patent Document 1 filed by the present applicant discloses a circuit for processing a sensor voltage output from a combustion pressure sensor installed in a combustion chamber of an internal combustion engine. The combustion pressure sensor incorporates a detection unit that utilizes a piezoresistance effect in which the resistance value varies with pressure. The sensor voltage output from the combustion pressure sensor is obtained by superimposing a voltage that varies depending on the change in the combustion pressure on a voltage that varies depending on the temperature of the detection unit. Since the temperature of the detector changes at a low speed, the voltage that depends on the temperature of the detector fluctuates at a low speed, and the combustion pressure changes at a high speed, so the voltage that depends on the combustion pressure changes at a high speed To do. The value of the DC voltage that fluctuates at a low speed depending on the temperature of the detection unit fluctuates following the fluctuation of the voltage of the power supply.
In order to detect the combustion pressure, the voltage that depends on the combustion pressure is superposed on the voltage that depends on the temperature of the detection unit, and the voltage that depends on the temperature of the detection unit is removed from the sensor voltage. It is necessary to take out the signal voltage and amplify it.
The above is an example, and the signal voltage is extracted from the sensor voltage in which the signal voltage that fluctuates at a high speed is superimposed on the DC voltage that fluctuates at a low speed and follows the fluctuation of the power supply voltage, and is amplified. There is a need in many cases.

If the bottom voltage of the sensor voltage in which the signal voltage that fluctuates at a high speed is superimposed on the DC voltage that fluctuates at a low speed, the bottom voltage corresponds to the DC voltage that fluctuates at a low speed. If the bottom voltage is subtracted from the sensor voltage, the signal voltage can be extracted and the signal voltage can be amplified.
In Patent Document 1, a bottom hold circuit that inputs a sensor voltage and stores the bottom voltage, and a storage voltage stored in the sensor voltage and the bottom hold circuit are input and a voltage obtained by amplifying the voltage difference between the two is output. A sensor voltage processing circuit comprising an operational amplifier is shown.
With reference to FIG. 2, the processing operation of the sensor voltage processing circuit of Patent Document 1 will be described. The thin solid line in FIG. 2A indicates the sensor voltage V1, the thick solid line indicates the DC voltage V2 that changes gradually, and the broken line indicates the storage voltage Vk. Further, the solid line in FIG. 2B indicates the signal voltage V3.

  As shown in FIG. 2, at the time A when the sensor voltage V1 becomes the bottom value, the sensor voltage V1 does not include the signal voltage V3 (is zero), and the sensor voltage V1 indicates the value of the DC voltage V2. The bottom hold circuit stores the sensor voltage V1 at this time as the storage voltage Vk. When the storage voltage Vk is updated every time the sensor voltage V1 becomes the bottom value, the storage voltage Vk closely matches the DC voltage V2 that changes gradually. The operational amplifier subtracts the storage voltage Vk from the sensor voltage V1, amplifies the voltage difference between the two, and outputs the amplified voltage difference. This is an amplified voltage obtained by amplifying the signal voltage V3. The signal voltage V3 calculated by (V1-Vk) is shown in FIG. The operational amplifier outputs a voltage obtained by amplifying the signal voltage V3 in FIG.

  The signal voltage V3 that has started increasing at time A then starts decreasing, and becomes zero again at time C. At time C, the sensor voltage V1 becomes the bottom value again. Similarly, at time E, the sensor voltage V1 becomes the bottom value again. In order to update the storage voltage Vk so as to coincide with the slowly changing DC voltage V2, it is necessary to update the storage voltage Vk every time the sensor voltage V1 becomes the bottom value.

At time C, the bottom value has decreased from the previous bottom value, and the bottom value at time C can be stored after time C by a normal bottom hold circuit. On the other hand, at the time E, the bottom value increases from the previous bottom value, and the normal bottom hold circuit cannot update the bottom value at the time E at the time E. After time E, the previous bottom value (in this case, the bottom value at time C) continues to be stored.
Therefore, in the bottom hold circuit of Patent Document 1, the storage voltage Vk is increased at a low speed as indicated by the broken line in FIG. Specifically, by providing a circuit for discharging the capacitor storing the voltage at a low speed, the storage voltage Vk is increased at a low speed. The rising speed of the storage voltage Vk is set to be slightly faster than the changing speed of the DC voltage that changes at a low speed.

  If the rising speed of the storage voltage Vk is slightly higher than the changing speed of the DC voltage, even when the DC voltage increases and the bottom value increases as in the period from the time C to the time E, the time before the time E increases. Thus, a time when the storage voltage Vk coincides with the sensor voltage is obtained. If this relationship is obtained, the storage voltage Vk stored in the bottom hold circuit decreases following the decrease of the sensor voltage after the time D when the storage voltage Vk matches the sensor voltage, and after the time E, the storage voltage Vk is stored at the time E. The voltage can be held. If the rising speed of the storage voltage Vk is made faster than the change speed of the DC voltage, the voltage stored in the bottom hold circuit is newly set even if the new bottom value is higher than the previous bottom value. The bottom value can be updated. However, the bottom hold circuit is a circuit for storing the bottom value. If the voltage stored in the bottom hold circuit is rapidly increased, the bottom value cannot be stored. In the circuit of Patent Document 1, the bottom hold circuit stores the bottom value by setting the relationship in which the rising speed of the storage voltage Vk is slightly faster than the change speed of the DC voltage (in this sense, the storage voltage Vk). When the new bottom value is higher than the previous bottom value, the bottom hold circuit updates the new bottom value (in this sense, the storage voltage Vk Ascending speed is set fast).

JP 2004-108896 A

  When the sensor is mounted on the vehicle, the voltage of the power source that supplies power to the sensor may fluctuate abruptly when power is supplied to the auxiliary machinery or when the power supply is stopped. In this case, the sensor voltage varies in proportion to the variation in the voltage of the power supply. FIG. 2 illustrates a case where the voltage of the power supply suddenly increases at time G. In this case, if the DC voltage V2 that fluctuates at a low speed increases, the signal voltage V3 that fluctuates at a rapid speed also increases. The meaning that the DC voltage V2 also increases here means that the value of the DC voltage V2 increases even if the environmental temperature of the sensor is constant, and the meaning that the amplitude of the signal voltage V3 increases means that the pressure or the like is detected. This means that the value of the signal voltage V3 increases even if the value of the target event is constant. When the voltage of the power source increases, the amplitude of the signal voltage V3 increases even if the fluctuation range of the detection target event such as pressure is constant.

  As described above, the bottom hold circuit of Patent Document 1 updates the storage voltage Vk even in a phase where the ambient temperature of the sensor rises and the DC voltage V2 rises (and hence the bottom value rises). I can go. However, as described above, if the storage voltage Vk is increased to a rapid speed, the bottom value cannot be stored. Therefore, the increase speed of the storage voltage Vk is slightly higher than the changing speed of the DC voltage V2 that fluctuates to a low speed. Is set. Therefore, when the bottom value suddenly rises because the power supply voltage suddenly rises, the storage voltage Vk of the bottom hold circuit cannot be updated to the bottom voltage after the power supply voltage rises. In order to be able to update to the bottom voltage after the power supply voltage rises, it is necessary to set the rising speed of the voltage stored in the bottom hold circuit to a rapid speed, but this does not allow the bottom voltage to be saved. . Therefore, as shown in FIG. 2A, when the voltage of the power source rises at time G, the storage voltage stored in the bottom hold circuit thereafter becomes the voltage Vk ′ indicated by the alternate long and short dash line, and the voltage before the power source voltage rises. The bottom value remains unchanged and is not updated to the bottom value after the power supply voltage rises. Therefore, even if the storage voltage Vk ′ is subtracted from the sensor voltage V1 by the operational amplifier, the truly necessary signal voltage V3 is not taken out, and as shown by the one-dot chain line in FIG. A value V3 ′ obtained by adding the increase ΔV of the DC voltage caused by the voltage fluctuation is extracted. The output voltage of the operational amplifier is not an amplified version of the true signal voltage, but an amplified version of the true signal voltage plus ΔV.

  In the above, the relationship of sensor voltage = bottom voltage + signal voltage is used to extract the true signal voltage. On the other hand, it can be said that there is a relationship of sensor voltage = peak voltage−signal voltage, and it is also possible to take out the signal voltage using this relationship. In this method, a peak hold circuit is used. When the peak hold circuit is used, when the power supply voltage drops, the peak voltage after the power supply voltage drop cannot be updated, and the peak voltage before the power supply voltage drop continues to be stored.

  The technology disclosed in this specification has been made in view of such circumstances, and its purpose is to supplement a DC voltage that fluctuates at a low speed by using a voltage storage circuit such as a bottom hold circuit or a peak hold circuit. When the DC voltage fluctuates due to voltage fluctuations of the power supply when subtracting it from the sensor voltage to extract a signal voltage that fluctuates at a rapid speed, the voltage stored in the voltage storage circuit is It is an object of the present invention to provide a voltage processing circuit capable of appropriately taking out a true signal voltage against voltage fluctuations of a power supply.

The technology disclosed in this specification extracts a signal voltage from a sensor voltage in which a signal voltage that fluctuates at a high speed is superimposed on a DC voltage that fluctuates at a low speed and also follows a voltage fluctuation of a power supply. The present invention relates to a sensor voltage processing circuit that amplifies the signal. This circuit includes a first capacitor, a second capacitor, a first operational amplifier, a second operational amplifier, and a backflow prevention element. The first operational amplifier, the first capacitor, and the second capacitor constitute a voltage storage circuit that stores the voltage and changes the stored voltage following the fluctuation of the power supply voltage.
One electrode of the first capacitor is grounded. The second capacitor is connected to a power supply voltage at which one electrode supplies power to the sensor. The other electrodes of the first capacitor and the second capacitor are connected to each other, and a voltage is stored in the wiring. The wiring connecting the other electrodes of the first capacitor and the second capacitor can be said to be a voltage storage wiring. The voltage stored in the voltage storage wiring is used as the storage voltage, and the approximate storage voltage fluctuation range assumed when the sensor is used is set as the reference storage voltage. In this case, the capacitance ratio between the first capacitor and the second capacitor is set to be a ratio between the reference storage voltage and a voltage obtained by subtracting the reference storage voltage from the rated voltage of the power source. One input terminal of the first operational amplifier is connected to the voltage storage wiring. The other input terminal of the first operational amplifier is connected to the output line of the sensor voltage. The first operational amplifier outputs, to the output terminal, a voltage that changes depending on the magnitude relationship between the storage voltage stored in the voltage storage wiring and the voltage output to the output line of the sensor voltage. For example, a high voltage is output while the sensor voltage is higher than the storage voltage, and a low voltage is output when the sensor voltage becomes equal to the storage voltage. The backflow prevention element is connected between the voltage storage wiring and the output terminal of the first operational amplifier, and allows only a current flow in one direction. The reverse current prohibition direction is switched depending on whether the voltage stored in the voltage storage wiring is the bottom value or the peak value. One input terminal of the second operational amplifier is connected to the voltage storage wiring. The other input terminal of the second operational amplifier is connected to the sensor voltage output line. The second operational amplifier outputs, to the output terminal, a voltage obtained by amplifying the voltage difference between the storage voltage stored in the voltage storage wiring and the sensor voltage.

  According to the above configuration, the voltage storage circuit is configured by the first operational amplifier, the backflow prevention element, the first capacitor, and the second capacitor, and the bottom voltage or the peak voltage of the sensor voltage is stored in the voltage storage wiring. For example, while the sensor voltage is higher than the storage voltage, the backflow prevention element prohibits charging and discharging of the first capacitor and the second capacitor and stores the voltage. On the other hand, when the sensor voltage matches the storage voltage, A bottom hold circuit is configured by charging or discharging the second capacitor. While the sensor voltage is lower than the storage voltage, the backflow prevention element prohibits charging and discharging of the first capacitor and the second capacitor to store the voltage. On the other hand, when the sensor voltage matches the storage voltage, the first capacitor and the second capacitor are stored. A peak hold circuit is configured by charging or discharging the capacitor.

The first capacitor and the second capacitor are connected in series between the power source and the grounding point, and the capacitance ratio between the first capacitor and the second capacitor is a voltage obtained by subtracting the reference storage voltage from the reference storage voltage and the rated voltage of the power source. When the ratio is set, the storage voltage stored in the voltage storage wiring fluctuates following the voltage fluctuation of the power supply.
The second operational amplifier outputs a voltage obtained by amplifying the voltage difference between the storage voltage that fluctuates following the voltage fluctuation of the power supply and the sensor voltage. In this way, according to this circuit, since the signal voltage is extracted using the storage voltage that fluctuates following the voltage fluctuation of the power supply, the true signal voltage is amplified even when the power supply voltage fluctuates. Output voltage.

  In one aspect of the technology disclosed in the present specification, a first voltage that outputs a high voltage to the output terminal when the sensor voltage is higher than the storage voltage, and outputs a low voltage to the output terminal when the sensor voltage is equal to or lower than the storage voltage. An operational amplifier is used. In this case, the backflow prevention element allows current to pass from the voltage storage wiring toward the output terminal of the first operational amplifier, and prohibits current from flowing from the output terminal of the first operational amplifier toward the voltage storage circuit. Insert in the direction.

  In the above configuration, when the sensor voltage is higher than the storage voltage, a voltage higher than the storage voltage is output to the output terminal of the first operational amplifier, but the backflow prevention element charges the first capacitor and the second capacitor. Ban. Since the voltage higher than the storage voltage is output to the output terminal of the first operational amplifier, the first capacitor and the second capacitor are not charged and discharged. When the sensor voltage is higher than the storage voltage, the voltage of the voltage storage wiring is kept constant.

When the sensor voltage is equal to or lower than the storage voltage, a voltage lower than the storage voltage is output to the output terminal of the first operational amplifier. Therefore, the first capacitor and the second capacitor are charged or discharged, and the voltage of the voltage storage wiring drops to a voltage equal to the sensor voltage. When the sensor voltage decreases below the storage voltage, the voltage of the voltage storage wiring decreases following the decrease in the sensor voltage.
According to the above configuration, the bottom value of the sensor voltage can be stored. The first capacitor and the second capacitor are connected in series between the power source and the grounding point, and the capacitance ratio between the first capacitor and the second capacitor is a reference storage voltage and a voltage obtained by subtracting the reference storage voltage from the rated voltage of the power source. Therefore, the storage voltage stored in the voltage storage wiring fluctuates following the fluctuation of the power supply voltage.

  In one aspect of the technology disclosed in the present specification, a first operational amplifier that outputs a high voltage to the output terminal when the sensor voltage is equal to or higher than the storage voltage, and outputs a low voltage to the output terminal when the sensor voltage is lower than the storage voltage. Is used. In this case, the backflow prevention element prohibits current from passing from the voltage storage wiring toward the output terminal of the first operational amplifier, and allows current to flow from the output terminal of the first operational amplifier toward the voltage storage circuit. Insert in the direction.

  In the above configuration, when the sensor voltage is equal to or higher than the storage voltage, a voltage equal to or higher than the storage voltage is output to the output terminal of the first operational amplifier, and the first capacitor and the second capacitor are discharged or charged. The voltage of the voltage storage wiring rises to a voltage equal to the sensor voltage. When the sensor voltage rises higher than the storage voltage, the voltage of the voltage storage wiring increases following the increase of the sensor voltage.

When the sensor voltage is less than the storage voltage, a voltage lower than the storage voltage is output to the output terminal of the first operational amplifier. However, the backflow prevention element prohibits the first capacitor and the second capacitor from being discharged and charged, and the voltage of the voltage storage wiring is maintained at a constant voltage.
According to the above configuration, the peak value of the sensor voltage can be stored. The first capacitor and the second capacitor are connected in series between the power source and the grounding point, and the capacitance ratio between the first capacitor and the second capacitor is a reference storage voltage and a voltage obtained by subtracting the reference storage voltage from the rated voltage of the power source. Therefore, the storage voltage stored in the voltage storage wiring varies following the variation of the power supply voltage.

In the technique disclosed in this specification, the DC voltage varies following the temperature of the sensor. In such a case, in the sensor, it is preferable that a sensor element for outputting a voltage including a signal voltage and an inverse characteristic element having a temperature characteristic opposite to the sensor element are connected in series. Moreover, a diode can be used as such a reverse characteristic element.
According to the above configuration, the temperature dependence of the DC voltage included in the sensor voltage can be reduced, so that the variation in the storage voltage is reduced. Therefore, since the difference between the storage voltage and the reference storage voltage can be reduced, a voltage obtained by amplifying the signal voltage can be output more appropriately.

  According to the technology disclosed in this specification, it is possible to store a voltage reflecting the fluctuation of the DC voltage caused by the fluctuation of the power supply voltage, and even if the power supply voltage fluctuates, a large malfunction is caused. Without taking out, a substantially true signal voltage can be extracted and amplified.

1 is a schematic diagram showing a combustion pressure measuring device according to Embodiment 1. FIG. FIG. 3 is a timing chart showing a voltage waveform processed by the combustion pressure measuring device of Embodiment 1 and a flag for engine control generated based on the signal voltage. FIG. FIG. 5 is a schematic diagram showing a combustion pressure measuring device according to a second embodiment. FIG. 6 is a schematic diagram illustrating a combustion pressure measuring device according to a third embodiment. FIG. 6 is a schematic diagram illustrating a combustion pressure measuring device according to a fourth embodiment. 10 is a graph showing a voltage waveform of an element with respect to the temperature of Example 4. FIG. 10 is a schematic diagram illustrating a combustion pressure measuring device according to a modification of the fourth embodiment.

The features of the embodiments of the present invention will be described below.
(Characteristic 1) It is determined whether or not the physical quantity indicated by the signal voltage is greater than or equal to a reference value depending on whether or not the amplified voltage output from the second operational amplifier is greater than or equal to the threshold voltage. The threshold voltage is varied according to the voltage of the power supply. Thereby, even if the voltage of the power supply fluctuates, it can be appropriately determined whether or not the physical quantity to be monitored is equal to or higher than the reference value.

A first embodiment in which the sensor voltage processing circuit disclosed in the present specification is applied to a combustion pressure measuring device for an in-vehicle internal combustion engine will be described with reference to FIGS. 1 and 2.
As shown in FIG. 1, the combustion pressure measuring device 10 includes a combustion pressure sensor 20 and a sensor voltage processing circuit 30 that processes a sensor voltage V <b> 1 output from the combustion pressure sensor 20.

  Although not shown, the combustion pressure sensor 20 is disposed so as to face the combustion chamber of the internal combustion engine. In the combustion pressure sensor 20, a diaphragm (not shown) is connected to the piezoresistive element 23. When the diaphragm bends due to the fluctuation of the pressure in the combustion chamber, a compressive stress acts on the piezoresistive element 23, and the resistance value of the piezoresistive element 23 changes according to the compressive stress. The resistance value of the piezoresistive element 23 varies depending on the environmental temperature.

The piezoresistive element 23 is connected to a power source (not shown) via a constant current source 22. This power source is powered from the battery of the vehicle, and normally the voltage value is maintained at a predetermined rated voltage, but by supplying or shutting off power from the battery to other accessories, etc. Temporarily, the rated voltage may increase or decrease. The constant current source 22 supplies a constant current regardless of the resistance value or the like of the piezoresistive element 23, and the current value of the constant current is proportional to the power supply voltage. The constant current source 22 is designed to perform a ratio operation described later. The combustion pressure sensor 20 outputs a voltage (sensor voltage) V <b> 1 on the upper end side of the piezoresistive element 23 to the sensor voltage processing circuit 30.
The sensor voltage V1 is determined by the resistance value of the piezoresistive element 23 and the energization current value, and has the following characteristics.
(1) Varies depending on the environmental temperature of the piezoresistive element 23.
(2) Varies depending on the pressure acting on the piezoresistive element 23.
(3) Since the environmental temperature of the piezoresistive element 23 changes to a low speed, the voltage V2 of (1) changes to a low speed.
(4) Since the pressure acting on the piezoresistive element 23 changes at a high speed, the voltage V3 of (2) changes at a high speed.
(5) The energization amount of the piezoresistive element 23 is proportional to the voltage of the power source.
From the above, the sensor voltage V1 varies at a low speed and changes to a DC voltage V2 that follows the power supply voltage fluctuation, and a signal that fluctuates at a high speed and follows the power supply voltage fluctuation. It can be said that the voltage V3 is a superimposed voltage.
The voltage of the power source is normally maintained at the rated voltage, but may temporarily increase or decrease as described above. For example, when the voltage of the power supply increases by α%, the constant current source 22 increases the current I supplied to the piezoresistive element 23 by α%. Therefore, even if the temperature and pressure in the combustion chamber do not change, the DC voltage V2 that depends on the temperature increases by α%, the signal voltage V3 that depends on the combustion pressure increases by α%, and the sensor output from the combustion pressure sensor 20 The voltage V1 also increases by α%.
The fact that various voltages fluctuate in proportion to the power supply voltage is called ratio operation. Sensors are required to perform a ratio operation. The processing circuit of the present embodiment subtracts the DC voltage V2 that changes at a low speed from the sensor voltage V1 that performs the ratio operation, and extracts the signal voltage V3 that performs the ratio operation. If the stored bottom voltage or peak voltage is kept constant against changes in the voltage of the power supply as in the prior art, the signal voltage V3 can be extracted using the stored voltage. The extracted signal voltage V3 does not perform a ratio operation.

  The sensor voltage processing circuit 30 removes the DC voltage V2 that varies depending on the temperature and the power supply voltage from the sensor voltage V1, and extracts and amplifies the signal voltage V3 that varies depending on the combustion pressure. The sensor voltage processing circuit 30 includes a bottom hold circuit 31 and a second operational amplifier 40.

  The bottom hold circuit 31 stores the bottom value of the sensor voltage V1 as the storage voltage Vk until the sensor voltage V1 becomes the bottom value again. As described above, the sensor voltage V1 is obtained by superimposing the signal voltage V3 depending on the combustion pressure on the DC voltage V2 depending on the temperature or the like. Therefore, when the signal voltage V3 becomes zero, the sensor voltage V1 As the value becomes the bottom value, the sensor voltage V1 at that time is equal to the DC voltage V2. Since the DC voltage V2 fluctuates at a low speed, the storage voltage Vk updated every time the sensor voltage V1 reaches the bottom is substantially equal to the DC voltage V2 that fluctuates at a low speed depending on the environmental temperature.

  The bottom hold circuit 31 includes a first capacitor 32, a second capacitor 33, a first operational amplifier 38, and a diode 39 as a backflow prevention element. One electrode of the first capacitor 32 (the lower electrode in FIG. 1) is grounded. One electrode of the second capacitor 33 (the upper electrode in FIG. 1) is connected to the constant voltage source 34. The other electrode of the first capacitor 32 (the upper electrode in the drawing of FIG. 1) and the other electrode of the second capacitor 33 (the lower electrode in the drawing of FIG. 1) are connected by a voltage storage wiring 37. The voltage storage wiring 37 stores a storage voltage Vk as will be described later. Assuming that the reference storage voltage is a substantially intermediate value of the fluctuation range of the storage voltage Vk assumed when the combustion pressure sensor 20 is used, the capacity ratio between the first capacitor 32 and the second capacitor 33 is the reference storage voltage and the power source. It is set to be a ratio with the voltage obtained by subtracting the reference storage voltage from the rated voltage. The constant voltage source 34 is connected to a power source, and the supply voltage of the constant voltage source 34 is equal to the voltage of the power source. Therefore, when the supply voltage of the power source increases by α%, the voltage of the constant voltage source 34 also increases by α%, and the constant voltage source 34 performs a ratio operation. A resistor 35 is connected to the second capacitor 33 in parallel.

  The output line 25 of the combustion pressure sensor 20 is branched into two, and one is connected to the non-inverting input terminal of the first operational amplifier 38. The voltage storage wiring 37 is connected to the inverting input terminal of the first operational amplifier 38 through the wiring. The diode 39 has an anode terminal connected to the voltage storage wiring 37 and a cathode terminal connected to the output terminal of the first operational amplifier 38. The first operational amplifier 38 functions as a comparator, and outputs the high voltage VH to the output terminal when the sensor voltage V1 is larger than the storage voltage Vk. The high voltage VH is equal to the voltage of the constant voltage source 34 and is higher than the storage voltage Vk. When the sensor voltage V1 is lower than or equal to the storage voltage Vk, the first operational amplifier 38 outputs the low voltage VL to the output terminal. The low voltage VL is lower than the storage voltage Vk. The voltage Vo at the output terminal of the first operational amplifier 38 is either the high voltage VH or the low voltage VL.

  The voltage storage wiring 37 is connected to the inverting input terminal of the second operational amplifier 40 via the output line 36 of the storage voltage Vk. The wiring branched from the output line 25 of the combustion pressure sensor 20 is connected to the non-inverting input terminal of the second operational amplifier 40. The second operational amplifier 40 amplifies the difference between the sensor voltage V1 of the combustion pressure sensor 20 input to the non-inverting input terminal and the storage voltage Vk of the bottom hold circuit 31 with a predetermined amplification degree, and the amplification result is a signal voltage. Output to the output terminal 41 as V3. The output voltage V3 of the output terminal 41 is not affected by the temperature in the combustion chamber, and increases or decreases according to the pressure in the combustion chamber. The second operational amplifier 40 is provided with a terminal 42 for setting the base voltage Vbb.

Next, a processing operation for storing the bottom value (DC voltage V2) of the sensor voltage as the storage voltage Vk in the bottom hold circuit 31 will be described with reference to FIGS.
In the bottom hold circuit 31, the output voltage of the first operational amplifier 38 when the sensor voltage V1 exceeds the storage voltage Vk (V1> Vk) and when the sensor voltage V1 is equal to the storage voltage Vk (V1 = Vk). Vo and the current-carrying state of the diode 39 are different.

  The first operational amplifier 38 functions as a comparator. When the sensor voltage V1 is larger than the storage voltage Vk, the output voltage Vo of the first operational amplifier 38 becomes the high voltage VH. Since the high voltage VH is higher than the storage voltage Vk, the first capacitor 32 and the second capacitor 33 are not discharged or charged. In addition, since the diode 39 is inserted in a direction prohibiting current from flowing from the output terminal of the first operational amplifier 38 toward the voltage storage line 37, the first capacitor 32 and the second capacitor 33 are discharged or charged. There is nothing. When the sensor voltage V1 is larger than the storage voltage Vk, charging / discharging of the first capacitor 32 and the second capacitor 33 is prohibited, and the voltage of the voltage storage line 37 is maintained at the storage voltage Vk.

  When the sensor voltage V1 is larger than the storage voltage Vk, the charged charge of the second capacitor 33 is actually discharged at a low speed through the resistor 35. As a result, the storage voltage of the voltage storage line 37 gradually increases. This causes a phenomenon that the storage voltage Vk gradually rises in FIG. This gradual rise is for updating the bottom voltage when the bottom voltage rises at a low speed, and is basically slow enough to say that the bottom voltage is preserved. The speed is lower than the speed when the bottom voltage rapidly increases due to the voltage fluctuation of the power supply.

  As shown in FIG. 2A, after time C, the storage voltage Vk of the bottom hold circuit 31 gradually increases. Therefore, as shown in time E, even when the next bottom voltage increases, time D when the sensor voltage V1 and the storage voltage Vk coincide with each other comes.

  When the storage voltage Vk = the sensor voltage V1, the output voltage Vo of the first operational amplifier 38 is switched to the low voltage VL. Since the low voltage VL is lower than the storage voltage Vk, the first capacitor 32 and the second capacitor 33 are charged and discharged via the diode 39 when the storage voltage Vk = sensor voltage V1. As a result, the circuit including the first operational amplifier 38 functions as a voltage follower. When storage voltage Vk = sensor voltage V1, the relationship of storage voltage Vk = sensor voltage V1 is maintained thereafter. After the time D when the storage voltage Vk = the sensor voltage V1, the storage voltage Vk also decreases following the decrease in the sensor voltage V1.

  When the sensor voltage V1 starts to rise again from the bottom value after the time E in FIG. 2A, the sensor voltage V1 becomes higher than the storage voltage Vk, so that charging / discharging of the first capacitor 32 and the second capacitor 33 is performed. Forbidden, the voltage of the voltage storage line 37 is maintained at the storage voltage Vk. In this way, the bottom hold circuit 31 updates the storage voltage Vk to a new bottom value every time the bottom value appears in the output voltage V1 of the combustion pressure sensor 20, and holds it as a new storage voltage Vk.

  The storage voltage Vk stored in this way is input to the inverting input terminal of the second operational amplifier 40. In the second operational amplifier 40, a voltage obtained by amplifying the signal voltage V3 (= V1-Vk) obtained by subtracting the storage voltage Vk from the sensor voltage V1 is extracted. Thereby, the signal voltage V3 from which the influence of the temperature-dependent DC voltage V2 included in the sensor voltage V1 of the combustion pressure sensor 20 is eliminated can be obtained. FIG. 2B shows the signal voltage V3 extracted in this way.

  FIG. 2C is a flag indicating whether the pressure in the combustion chamber is higher or lower than the reference pressure P, and by determining whether the signal voltage V3 in FIG. 2B is higher or lower than the threshold voltage. Is set. Prior to time G, the threshold voltage is the voltage Vb as shown in FIG. This flag is set to “1” indicating that the combustion pressure is higher than the reference pressure P when the signal voltage V3 is higher than the threshold voltage Vb, and when the signal voltage V3 is lower than the threshold voltage Vb1. “0” indicating that the combustion pressure is lower than the reference pressure P is set. In the internal combustion engine, engine control is executed based on this flag.

FIG. 2A illustrates a case where the voltage of the power source increases after time G, the supply current I from the constant current source 22 increases, and the voltage Vp of the constant voltage source 34 increases. In this case, even if the storage voltage Vk of the bottom hold circuit 31 is set to increase at a low speed by the resistor 35, the bottom voltage increases at a speed exceeding that. Therefore, according to the technique in which the storage voltage Vk of the bottom hold circuit 31 does not follow the voltage increase of the power supply as in the conventional technique, even if the sensor voltage V1 becomes the bottom value again after the voltage increase of the power supply, the bottom hold circuit 31 The storage voltage cannot be updated to a new bottom voltage.
In the present embodiment, as will be described below, if the voltage of the power supply increases, the storage voltage Vk also increases accordingly. For this reason, even when the bottom value of the sensor voltage V1 increases due to an increase in the voltage of the power supply, when the sensor voltage V1 reaches the bottom, the storage voltage of the bottom hold circuit 31 is updated to a new bottom voltage. be able to.

For example, it is assumed that the voltage of the power source increases by α% before and after the time G. In this case, as shown in Table 1, the voltage of the constant voltage source 34 also increases by α%, the current of the constant current source 22 also increases by α%, and the sensor voltage V1 also increases by α%. Since the capacitance ratio between the first capacitor 32 and the second capacitor 33 is set as described above, the voltage of each of the first capacitor 32 and the second capacitor 33 also increases by approximately α%. Since the voltage of the first capacitor 32 is the storage voltage Vk, the storage voltage Vk also increases by approximately α%. That is, almost all operate in a ratio manner.

In the above, the case where the sensor voltage V1 and the storage voltage Vk are the same and the voltage of the power supply rises while being discharged through the diode 39 has been described. However, the sensor voltage V1 is larger than the storage voltage Vk. Even when the power supply voltage rises in a state where charging / discharging of the first capacitor 32 and the second capacitor 33 is prohibited, the storage voltage Vk rises almost in proportion to the voltage rise of the constant voltage source 34. As described above, in this embodiment, when the sensor voltage V1 rises due to the rise in the power supply voltage, the storage voltage Vk stored in the voltage storage wiring 37 also increases at substantially the same rate.
In addition, when the voltage of a power supply falls, the sensor voltage V1 will also become low. The storage voltage Vk stored in the voltage storage wiring 37 of the bottom hold circuit 31 also decreases at the same rate. Regardless of whether the voltage of the power source rises or falls, the storage voltage Vk is almost ratio-operated.

  When the voltage of the power supply fluctuates, the current supplied from the constant current source 22 fluctuates and the sensor voltage V1 fluctuates. Both the DC voltage V2 and the signal voltage V3 change at the same rate as the change rate of the sensor voltage V1. At the same time, the storage voltage Vk varies following the voltage variation of the power supply. As a result, the storage voltage Vk fluctuates at substantially the same ratio as the fluctuation ratio of the sensor voltage V1, the DC voltage V2, and the signal voltage V3. The storage voltage Vk that varies following the power supply voltage is substantially equal to the DC voltage V2 that varies following the power supply voltage. The second operational amplifier 40 amplifies the voltage difference between the storage voltage Vk that changes following the fluctuation of the power supply voltage and the sensor voltage V1 that changes following the fluctuation of the power supply voltage, and outputs the amplified signal voltage V3. As a result, even when the power supply voltage fluctuates, the extracted signal voltage V3 has substantially the same value as the actual signal voltage, and can be appropriately extracted from the signal voltage V3 that does not include a DC component.

  For example, after time G in FIG. 2, the signal voltage V3 also increases by α%. Accordingly, the threshold voltage for setting the flag in FIG. 2C is also increased by α% after the time G and becomes (1 + α / 100) Vb. As a result, even after the timing G, the flag in FIG. 2C indicates whether the combustion pressure is higher or lower than the predetermined pressure P. Therefore, even if the supply voltage from the power source to the constant current source 22 fluctuates, the flag in FIG. 2C can appropriately indicate whether or not the pressure in the combustion chamber is higher than the reference pressure P. Engine control can be performed appropriately. If the threshold voltage operates as a ratio, the signal voltage V3 and a voltage obtained by amplifying the signal voltage also operate as a ratio. Therefore, it is possible to correctly detect the timing of the change over the reference pressure P against fluctuations in the power supply voltage. .

Next, Example 2 will be described with reference to FIG. The sensor voltage processing circuit 50 according to the second embodiment is a voltage processing circuit of the combustion pressure measuring device 11 of the in-vehicle internal combustion engine.
Although the sensor voltage processing circuit 30 of the first embodiment has the bottom hold circuit 31, the sensor voltage processing circuit 50 of the present embodiment has the peak hold circuit 51 that stores the peak value of the sensor voltage V1. This point is different from the first embodiment. The second operational amplifier 60 obtains a voltage obtained by amplifying the signal voltage by amplifying (peak voltage−sensor voltage). The obtained amplified voltage is obtained by inverting the magnitude relation of the signal voltage, but has a 1: 1 relationship with the signal voltage. By processing the amplified voltage, it is possible to perform processing depending on the signal voltage.

  The combustion pressure measuring device 11 includes a combustion pressure sensor 20 and a sensor voltage processing circuit 50 that processes a sensor voltage V1 output from the combustion pressure sensor 20. In this embodiment, a piezoresistive element 23 connected to a voltage source 24 that supplies a voltage of the same magnitude as that of a power source is grounded (not shown) via a constant current source 22.

  The sensor voltage processing circuit 50 includes a peak hold circuit 51 and a second operational amplifier 60. The peak hold circuit 51 is a circuit for storing the peak value of the sensor voltage V1 as the storage voltage Vk. The sensor voltage V1 of the combustion pressure sensor 20 is obtained by superimposing a signal voltage V3 that depends on the combustion pressure on a DC voltage V2 that depends on temperature and the like. When the signal voltage V3 becomes the maximum, the value of the sensor voltage V1 becomes a peak value, so that the fluctuation amount of the signal voltage V3 can be grasped from the difference between the peak value and the sensor voltage V1. Therefore, in this embodiment, in order to extract the signal voltage V3 from the sensor voltage V1, the difference between the peak value and the sensor voltage V1 is obtained.

  The peak hold circuit 51 includes a first capacitor 52, a second capacitor 53, a first operational amplifier 58, and a diode 59 as a backflow prevention element. The first capacitor 52 and the second capacitor 53 are connected by a voltage storage wiring 57. The first capacitor 52 is grounded. The second capacitor 53 is connected to the constant voltage source 54. A storage voltage Vk is stored in the voltage storage wiring 57. Assuming that the reference storage voltage is a substantially intermediate value of the fluctuation range of the storage voltage Vk assumed when the combustion pressure sensor 20 is actually used, the capacity ratio between the first capacitor 52 and the second capacitor 53 is the reference storage voltage. The ratio is set to a ratio with the voltage obtained by subtracting the reference storage voltage from the rated voltage of the power source. The constant voltage source 54 is connected to a power source, and the supply voltage of the constant voltage source 54 is equal to the supply voltage of the power source. Therefore, when the supply voltage of the power source decreases by α%, the voltage of the constant voltage source 54 also decreases by α%. A resistor 55 is connected to the first capacitor 52 in parallel.

The output line 25 of the combustion pressure sensor 20 is branched into two, one of which is connected to the non-inverting input terminal of the first operational amplifier 58. The inverting input terminal of the first operational amplifier 58 is connected to the voltage storage wiring 57 via the wiring. The diode 59 has a cathode terminal connected to the voltage storage wiring 57 via a wiring, and an anode terminal connected to the output terminal of the first operational amplifier 58 via the wiring.
The voltage storage wiring 57 is connected to the non-inverting input terminal of the second operational amplifier 60 via the output line 56 of the storage voltage Vk. The other branched from the output line 25 of the combustion pressure sensor 20 is connected to the inverting input terminal of the second operational amplifier 60. The second operational amplifier 60 amplifies the difference between the storage voltage Vk of the peak hold circuit 51 of the combustion pressure sensor 20 input to the non-inverting input terminal and the sensor voltage V1 with a predetermined amplification degree, and the amplification result is supplied to the terminal 61. The voltage is output as a voltage corresponding to the signal voltage V3. The output voltage V3 of the terminal 61 is not affected by the temperature in the combustion chamber, and increases or decreases according to the pressure in the combustion chamber. The second operational amplifier 60 is provided with a terminal 62 for setting the base voltage Vbb.

Next, the processing operation for storing the peak value of the sensor voltage V1 as the storage voltage Vk by the peak hold circuit 51 will be described.
In the peak hold circuit 51, the output voltage of the first operational amplifier 58 when the sensor voltage V1 is lower than the storage voltage Vk (V1 <Vk) and when the sensor voltage V1 is equal to the storage voltage Vk (V1 = Vk). Vo and the current-carrying state of the diode 39 are different.

  The first operational amplifier 58 functions as a comparator. When the sensor voltage V1 is smaller than the storage voltage Vk, the output voltage Vo of the first operational amplifier 58 becomes the low voltage VL. Since the low voltage VL is smaller than the storage voltage Vk, the first capacitor 52 and the second capacitor 53 are not charged or discharged. In addition, since the diode 59 is inserted in a direction prohibiting current from flowing from the voltage storage line 57 toward the output terminal of the first operational amplifier 58, the first capacitor 52 and the second capacitor 53 are charged or discharged. There is nothing. When the sensor voltage V1 is smaller than the storage voltage Vk, charging / discharging of the first capacitor 52 and the second capacitor 53 is prohibited, and the voltage of the voltage storage line 57 is maintained at the storage voltage Vk.

  When the sensor voltage V1 is larger than the storage voltage Vk, the charged electric charge of the first capacitor 52 is actually discharged at a low speed through the resistor 55. As a result, the storage voltage of the voltage storage line 57 gradually decreases. This gradual decrease is for updating the peak voltage when the peak voltage decreases at a low speed, and is basically at a low speed that it can be said that the peak voltage is preserved. The speed is lower than the speed when the peak voltage suddenly increases due to the voltage fluctuation of the power supply.

  When the storage voltage Vk = the sensor voltage V1, the output voltage Vo of the first operational amplifier 58 is switched to the high voltage VH. Since the high voltage VH is higher than the storage voltage Vk, when the storage voltage Vk = the sensor voltage V1, the first capacitor 52 and the second capacitor 53 are discharged and charged through the diode 59. As a result, the circuit including the first operational amplifier 58 functions as a voltage follower. When storage voltage Vk = sensor voltage V1, the relationship of storage voltage Vk = sensor voltage V1 is maintained thereafter. After the time when the storage voltage Vk = the sensor voltage V1, the storage voltage Vk also increases following the decrease in the sensor voltage V1.

  When the sensor voltage V1 starts to decrease again from the peak value, the sensor voltage V1 becomes lower than the storage voltage Vk, so that charging / discharging of the first capacitor 52 and the second capacitor 53 is prohibited, and the voltage of the voltage storage line 57 is stored. The voltage Vk is maintained. In this way, the peak hold circuit 51 updates the storage voltage Vk to a new peak value every time a peak value appears in the output voltage V1 of the combustion pressure sensor 20, and holds it as a new storage voltage Vk.

  The storage voltage Vk stored in this manner is input to the non-inverting input terminal of the second operational amplifier 40. Then, in the second operational amplifier 40, a voltage obtained by amplifying a voltage (= Vk−V1) obtained by subtracting the sensor voltage V1 from the storage voltage Vk is extracted. Since this voltage corresponds to the fluctuation of the signal voltage V3, it is possible to obtain the signal voltage V3 from which the influence of the temperature-dependent DC voltage V2 included in the sensor voltage V1 of the combustion pressure sensor 20 is eliminated.

When the power supply voltage decreases, the supply current I from the constant current source 22 decreases, and the voltage Vp of the constant voltage source 54 decreases. In this case, even if the storage voltage Vk of the peak hold circuit 51 is set to decrease at a low speed by the resistor 55, the peak voltage decreases at a speed exceeding that.
In the present embodiment, as will be described below, if the voltage of the power supply decreases, the storage voltage Vk also decreases accordingly. Therefore, even when the peak value of the sensor voltage V1 decreases due to the voltage drop of the power supply, the stored voltage of the peak hold circuit 51 is updated to a new peak voltage when the sensor voltage V1 reaches a peak. Can do.

Suppose that the voltage of the power supply is reduced by α%. In this case, the voltage of the constant voltage source 54 also decreases by α%, the current of the constant current source 22 also decreases by α%, and the sensor voltage V1 also decreases by α%. Since the first capacitor 52 and the second capacitor 53 are set to have a ratio of the reference storage voltage and the voltage obtained by subtracting the reference storage voltage from the rated voltage of the power supply, the first capacitor 52 and the second capacitor 53 are set. Each of the voltages also decreases by approximately α%. Since the voltage of the first capacitor 52 is the storage voltage Vk, the storage voltage Vk also decreases by approximately α%. That is, almost all operate in a ratio manner.
When the power supply voltage increases, the sensor voltage V1 also increases. The storage voltage Vk stored in the voltage storage wiring 57 of the peak hold circuit 51 also increases at substantially the same rate. Regardless of whether the voltage of the power source rises or falls, the storage voltage Vk is almost ratio-operated.

  When the voltage of the power supply fluctuates, the current supplied from the constant current source 22 fluctuates and the sensor voltage V1 fluctuates. Both the DC voltage V2 and the signal voltage V3 change at the same rate as the change rate of the sensor voltage V1. At the same time, the storage voltage Vk fluctuates following the fluctuation of the power supply voltage. As a result, the storage voltage Vk varies at substantially the same ratio as the sensor voltage V1, the DC voltage V2, and the signal voltage V3. The storage voltage Vk that varies following the power supply voltage is affected by the DC voltage V2 that varies following the power supply voltage variation. The second operational amplifier 60 outputs a voltage obtained by amplifying the voltage difference between the storage voltage Vk that changes following the voltage fluctuation of the power supply and the sensor voltage V1 that changes following the voltage fluctuation of the power supply. The value substantially corresponds to the signal voltage V3 not including the component.

Also in this embodiment, a flag indicating whether the combustion pressure used for engine control is higher or lower than the predetermined pressure P is set depending on whether or not the extracted voltage is equal to or lower than the threshold voltage. In this case, the threshold voltage is also changed following the voltage change of the power supply. Other configurations and operational effects are the same as those of the first embodiment.
As a modification of the present embodiment, although not shown, the inverting input terminal and the non-inverting input terminal of the second operational amplifier 60 may be interchanged.

Next, Example 3 will be described with reference to FIG. The sensor voltage processing circuit 70 according to the third embodiment is a voltage processing circuit of the combustion pressure measuring device 12 of the in-vehicle internal combustion engine.
As shown in FIG. 4, the combustion pressure measuring device 12 includes a combustion pressure sensor 20 and a sensor voltage processing circuit 70 that processes a sensor voltage V <b> 1 output from the combustion pressure sensor 20. The sensor voltage processing circuit 70 of this embodiment includes a bottom hold circuit 71 and a second operational amplifier 90. The configuration of the bottom hold circuit 71 of this embodiment is different from that of the bottom hold circuit 31 of the first embodiment. The combustion pressure sensor 20 and the constant current source 22 for supplying electric power to the combustion pressure sensor 20 are the same as those in the first embodiment.

  The bottom hold circuit 71 stores the bottom value of the sensor voltage V1 indicating the DC voltage V2 as the storage voltage Vk. The bottom hold circuit 71 includes a first capacitor 72, a second capacitor 73, a first operational amplifier 78, a MOS transistor 79 as a backflow prevention element, and a third operational amplifier 80. The first capacitor 72 and the second capacitor 73 are connected by a voltage storage wiring 77. The first capacitor 72 is grounded. The second capacitor 73 is connected to the constant voltage source 74. A storage voltage Vk is stored in the voltage storage wiring 77. Assuming that the reference storage voltage is a substantially intermediate value of the fluctuation range of the storage voltage Vk assumed when the combustion pressure sensor 20 is actually used, the magnitudes of the capacities of the first capacitor 72 and the second capacitor 73 are the reference storage voltage. And the ratio of the voltage obtained by subtracting the reference storage voltage from the rated voltage of the power supply. The constant voltage source 74 is connected to a power source and performs a ratio operation with respect to voltage fluctuations of the power source. A resistor 75 is connected in parallel to the second capacitor 73.

  The output line 25 of the combustion pressure sensor 20 branches into two, and one is connected to the non-inverting input terminal of the first operational amplifier 78. The inverting input terminal of the first operational amplifier 78 is connected to the voltage storage wiring 77 through a wiring. The MOS transistor 79 is an n-type MOS transistor, and has a gate terminal and a source terminal connected to the voltage storage wiring 77 through wiring, and a drain terminal connected to the output terminal of the first operational amplifier 78. .

  The voltage storage wiring 77 is connected to the non-inverting input terminal of the third operational amplifier 80 via the output line 76 of the storage voltage Vk. The output terminal of the third operational amplifier 80 is branched into two, one is connected to the inverting input terminal of the third operational amplifier, and the other is connected to the inverting input terminal of the second operational amplifier 90. The other branched from the output line 25 of the combustion pressure sensor 20 is connected to the non-inverting input terminal of the second operational amplifier. The second operational amplifier 90 amplifies the difference between the sensor voltage V1 of the combustion pressure sensor 20 input to the non-inverting input terminal and the storage voltage Vk of the bottom hold circuit 71 with a predetermined amplification degree, and the amplification result is output to the terminal 91. Is output as a signal voltage V3. The second operational amplifier 90 is provided with a terminal 92 for setting the base voltage Vbb. Since the second operational amplifier 90 of this embodiment has a lower impedance than the second operational amplifiers 40 and 60 of the first and second embodiments, the second operational amplifier 90 functions as a high impedance element between the voltage storage wiring 77 and the second operational amplifier 90. Three operational amplifiers 80 are interposed. As a result, the storage voltage Vk is held by the voltage storage wiring 77.

  In the bottom hold circuit 71, the first operational amplifier 78 and the output voltage when the sensor voltage V1 exceeds the storage voltage Vk (V1> Vk) and when the sensor voltage V1 is equal to the storage voltage Vk (V1 = Vk). And the conduction state of the MOS transistor 79 is different.

  The first operational amplifier 78 functions as a comparator. When the sensor voltage V1 is larger than the storage voltage Vk, the output voltage Vo of the first operational amplifier 78 becomes the high voltage VH. Since the high voltage VH is higher than the storage voltage Vk, the first capacitor 72 and the second capacitor 73 are not discharged or charged. Further, since the MOS transistor 79 is inserted in a direction prohibiting current from flowing from the output terminal of the first operational amplifier 78 toward the voltage storage line 77, the first capacitor 72 and the second capacitor 73 are discharged or charged. It never happens. When the sensor voltage V1 is larger than the storage voltage Vk, charging / discharging of the first capacitor 72 and the second capacitor 73 is prohibited, and the voltage of the voltage storage line 77 is maintained at the storage voltage Vk.

  When the sensor voltage V1 is larger than the storage voltage Vk, the charged charge of the second capacitor 73 is actually discharged at a low speed via the resistor 75. As a result, the storage voltage of the voltage storage line 77 gradually increases. This gradual rise is for updating the bottom voltage when the bottom voltage rises at a low speed, and is basically slow enough to say that the bottom voltage is preserved. The speed is lower than the speed when the bottom voltage rapidly increases due to the voltage fluctuation of the power supply.

  When the storage voltage Vk = the sensor voltage V1, the output voltage Vo of the first operational amplifier 78 is switched to the low voltage VL. Since the low voltage VL is lower than the storage voltage Vk, when the storage voltage Vk = the sensor voltage V1, the first capacitor 72 and the second capacitor 73 are charged and discharged via the MOS transistor 79. As a result, the circuit including the first operational amplifier 78 functions as a voltage follower. When storage voltage Vk = sensor voltage V1, the relationship of storage voltage Vk = sensor voltage V1 is maintained thereafter. After the time D when the storage voltage Vk = the sensor voltage V1, the storage voltage Vk also decreases following the decrease in the sensor voltage V1.

  Thereby, the bottom hold circuit 71 updates the storage voltage Vk to a new bottom value each time the bottom value appears in the output voltage V1 of the combustion pressure sensor 20, and holds the updated storage voltage Vk. Further, as described above, since the storage voltage Vk rises gently during storage, the storage voltage Vk is updated higher even when the bottom value is higher than the previous bottom value. be able to. Further, if the next bottom value decreases, the storage voltage Vk is updated low.

  The storage voltage Vk stored in this way is input to the inverting input terminal of the second operational amplifier 90 through the third operational amplifier 80. Then, in the second operational amplifier 90, a voltage (V1-Vk) obtained by subtracting the storage voltage Vk from the sensor voltage V1 is extracted as the signal voltage V3. The second operational amplifier 90 amplifies the signal voltage V3 and outputs it. Thereby, the signal voltage V3 from which the influence of the temperature-dependent DC voltage V2 included in the sensor voltage V1 of the combustion pressure sensor 20 is eliminated can be obtained.

When the voltage of the power supply rises, the supply current I from the constant current source 22 rises, and the voltage Vp of the constant voltage source 74 rises. In this case, even if the storage voltage Vk of the bottom hold circuit 71 is set so as to increase at a low speed by the resistor 75, the bottom voltage increases at a speed exceeding that.
In the present embodiment, as will be described below, if the voltage of the power supply increases, the storage voltage Vk also increases accordingly. For this reason, even when the bottom value of the sensor voltage V1 increases due to an increase in the voltage of the power supply, when the sensor voltage V1 reaches a peak, the storage voltage of the bottom hold circuit 71 is updated to a new bottom voltage. be able to.

Assume that the power supply voltage has increased by α%. In this case, the voltage of the constant voltage source 74 also increases by α%, the current of the constant current source 22 also increases by α%, and the sensor voltage V1 also increases by α%. Since the capacity ratio of the first capacitor 72 and the second capacitor 73 is set to be a ratio of the reference storage voltage and the voltage obtained by subtracting the reference storage voltage from the rated voltage of the power supply, the first capacitor 72 and the second capacitor 73 The voltage of each of the two capacitors 73 also increases by almost α%. Since the voltage of the first capacitor 72 is the storage voltage Vk, the storage voltage Vk also increases by approximately α%. That is, almost all operate in a ratio manner.
In addition, when the voltage of a power supply falls, the sensor voltage V1 will also become low. The storage voltage Vk stored in the voltage storage wiring 77 of the bottom hold circuit 71 also decreases at substantially the same rate. Regardless of whether the voltage of the power source rises or falls, the storage voltage Vk is almost ratio-operated.

  When the voltage of the power supply fluctuates, the current supplied from the constant current source 22 fluctuates and the sensor voltage V1 fluctuates. Both the DC voltage V2 and the signal voltage V3 vary at the same rate as the variation rate of the sensor voltage V1. At the same time, the storage voltage Vk changes following the change in the power supply voltage. As a result, the storage voltage Vk varies at substantially the same ratio as the sensor voltage V1, the DC voltage V2, and the signal voltage V3. The storage voltage Vk that varies following the power supply voltage is affected by the DC voltage V2 that varies following the power supply voltage. The second operational amplifier 90 outputs a voltage obtained by amplifying the voltage difference between the sensor voltage V1 that varies following the power supply voltage fluctuation and the storage voltage Vk that varies following the power supply voltage fluctuation. It becomes substantially equal to the signal voltage V3 not including the component.

  Also in this embodiment, a flag indicating whether the combustion pressure used for engine control is higher or lower than the predetermined pressure P is set depending on whether or not the extracted signal voltage V3 is equal to or lower than the threshold voltage. In this case, the threshold voltage is also changed following the voltage change of the power supply. Other configurations and operational effects are the same as those of the first embodiment.

  Next, Example 4 will be described with reference to FIGS. As shown in FIG. 5, in the combustion pressure measuring device 13 of the present embodiment, the combustion pressure sensor 26 connected to the sensor voltage processing circuit 30 is different from that of the first embodiment. Since the sensor voltage processing circuit 30 of the present embodiment is the same as the sensor voltage processing circuit 30 of the first embodiment, the illustration is omitted in FIG.

  In the combustion pressure sensor 26 according to the present embodiment, a piezoresistive element 23 that is a sensor element and a diode 27 that is a reverse characteristic element having reverse temperature characteristics are connected in series. The diode 27 has an anode terminal connected to the piezoresistive element 23 and a cathode terminal side grounded.

FIG. 5 shows the temperature characteristics of the voltage across the piezoresistive element 23 and the diode 27. As shown in FIG. 5, the temperature-dependent voltage Vx among the voltages across the piezoresistive element 23 increases as the temperature of the piezoresistive element 23 increases. In the first embodiment, the voltage Vx is the DC voltage V2 of the sensor voltage V1. Further, the temperature-dependent voltage Vy applied across the diode 27 decreases as the temperature increases. In this way, a diode 27 having a temperature characteristic opposite to that of the piezoresistive element 23 is connected in series to the piezoresistive element 23.
In the present embodiment, as shown in FIG. 5, the DC voltage V2 included in the sensor voltage V1 has a temperature-dependent voltage Vx applied across the piezoresistive element 23 and a temperature-dependent voltage applied across the diode 27. A value obtained by adding the voltage Vy. Therefore, the fluctuation range with respect to the temperature of the DC voltage V2 is smaller than the fluctuation range with respect to the temperature of the temperature-dependent voltage Vx of the piezoresistive element 23. Therefore, since the combustion pressure sensor 20 includes the diode 27, it is possible to reduce the fluctuation of the DC voltage V2 due to the temperature change as compared with the first embodiment. Therefore, since the fluctuation of the storage voltage Vk is reduced, the deviation between the storage voltage Vk and the reference storage voltage can be reduced. As a result, when the voltage of the power supply fluctuates, the first capacitor 32 and the second capacitor can perform the ratio operation with higher accuracy, and the storage voltage Vk can be operated with higher accuracy. As a result, the sensor voltage processing circuit 30 can extract the signal voltage V3 more appropriately.

If the fluctuation of the DC voltage V2 can be reduced and made almost constant, it is not necessary to store the bottom voltage, and the signal voltage V3 can be extracted by subtracting the constant DC voltage V2 from the sensor voltage V1. Conceivable. However, it is difficult to keep the DC voltage V2 constant due to variations occurring in the manufacturing process of the combustion pressure sensor 26, aging deterioration of the combustion pressure sensor 26, and the like. Therefore, it is necessary to update the bottom value of the sensor voltage V1 indicating the DC voltage V2 by the bottom hold circuit 31 described in the first embodiment. That is, by using the bottom hold circuit 31 and the combustion pressure sensor 26 of the present embodiment, the signal voltage V3 can be taken out more appropriately.
Such a combustion pressure sensor 26 may be used in place of the combustion pressure sensor 20 of the second and third embodiments.
(Modification of Example 4)

In Example 4, the anode terminal side of the diode 27 is connected to the piezoresistive element 23, and the cathode terminal side is grounded. However, as shown in FIG. 7, in the combustion pressure sensor 28 of the combustion pressure measuring device 14, the anode side of the diode 27 may be connected to the constant current source 22 and the cathode side may be connected to the piezoresistive element 23. Even in such a case, an effect equivalent to that of the fourth embodiment can be obtained.
Further, as an inverse characteristic element having a temperature characteristic opposite to that of the piezoresistive element 23, a resistor made of a metal oxide such as manganese, cobalt, or nickel may be used.
(Other examples)

The sensor voltage processing circuit 70 of the third embodiment includes a bottom hold circuit 71 having a MOS transistor 79 as a backflow prevention element. However, the invention disclosed in this specification is a peak having a MOS transistor as a backflow prevention element. You may apply to a sensor voltage processing circuit provided with a hold circuit. In that case, the gate terminal and source terminal of the MOS transistor are connected to the output terminal of the first operational amplifier, the drain terminal is connected to the voltage storage wiring, and a resistor is connected in parallel with the grounded first capacitor. The circuit configuration is appropriately changed as in the second embodiment.
In addition to the configuration of each of the embodiments described above, an output terminal for extracting the storage voltage Vk may be provided to extract the storage voltage Vk reflecting the DC voltage V2. Thereby, the temperature of the piezoresistive element can be detected.
In each of the above embodiments, the sensor voltage processing circuit is applied to the processing circuit of the combustion pressure sensor that detects the pressure in the combustion chamber of the internal combustion engine. However, the sensor voltage processing circuit may be applied to a circuit that processes the output value of other sensors. Good.

As mentioned above, although the specific example of the technique disclosed by this specification was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
In addition, the technical elements described in the present specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.

10, 11, 12, 13, 14: Combustion pressure measuring devices 20, 26, 28: Combustion pressure sensor 22: Constant current source 23: Piezoresistive element 25: Output lines 30, 50, 70: Sensor voltage processing circuits 31, 71 : Bottom hold circuits 32, 52, 72: first capacitors 33, 53, 73: second capacitors 34, 54, 74: constant voltage sources 35, 55, 75: resistors 37, 57, 77: voltage storage wires 38, 58 78: First operational amplifier 39, 59: Diodes 40, 60, 90: Second operational amplifier 41, 61, 91: Terminal 51: Peak hold circuit 79: MOS transistor 80: Third operational amplifier

Claims (5)

A circuit that extracts and amplifies the signal voltage from a sensor voltage in which a signal voltage that fluctuates at a high speed is superimposed on a DC voltage that fluctuates at a low speed and fluctuates in accordance with a voltage fluctuation of a power supply,
A first capacitor with one electrode grounded;
A second capacitor connected to a power source with one electrode feeding the sensor;
Voltage storage wiring connecting the other electrodes of the first capacitor and the second capacitor;
One input terminal is connected to the voltage storage wiring, and the other input terminal is connected to the output line of the sensor voltage, and the magnitude of the storage voltage stored in the voltage storage wiring and the sensor voltage is small or large. A first operational amplifier that outputs to the output terminal a voltage that varies depending on the relationship;
One end is connected to the voltage storage wiring, the other end is connected to the output terminal of the first operational amplifier, and a backflow prevention element that allows only a current flowing in one direction,
One input terminal is connected to the sensor voltage output line, and the other input terminal is connected to the voltage storage wiring, and outputs a voltage obtained by amplifying the voltage difference between the sensor voltage and the storage voltage. A second operational amplifier that outputs to the terminal,
The ratio of the reference storage voltage in which the capacitance ratio between the first capacitor and the second capacitor is approximately an intermediate value of the assumed fluctuation range of the storage voltage and the voltage obtained by subtracting the reference storage voltage from the rated voltage of the power supply A sensor voltage processing circuit characterized by being set to be The first operational amplifier outputs a high voltage to the output terminal when the sensor voltage is higher than the storage voltage, and outputs a low voltage to the output terminal when the sensor voltage is equal to or lower than the storage voltage.
2. The sensor voltage processing circuit according to claim 1, wherein the backflow prevention element is connected in a direction allowing a current from the voltage storage wiring toward an output terminal of the first operational amplifier. The first operational amplifier outputs a high voltage to the output terminal when the sensor voltage is equal to or higher than the storage voltage, and outputs a low voltage to the output terminal when the sensor voltage is less than the storage voltage.

2. The sensor voltage processing circuit according to claim 1, wherein the backflow prevention element is connected in a direction allowing a current from an output terminal of the first operational amplifier to the voltage storage wiring. The DC voltage fluctuates following the temperature of the sensor,
2. The sensor according to claim 1, wherein a sensor element for outputting a voltage including a signal voltage and an inverse characteristic element having a temperature characteristic opposite to the sensor element are connected in series. 4. The sensor voltage processing circuit according to any one of 3 above.   The sensor voltage processing circuit according to claim 4, wherein the inverse characteristic element is a diode.

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