JPH03231129A - Pressure sensor - Google Patents

Abstract

PURPOSE:To obtain a digital output corresponding to the pressure of fluid to be measured by outputting a signal having a duty ratio corresponding to the output of a strain gage. CONSTITUTION:A diaphragm part 1a is formed on a semiconductor substrate 1. One surface of the plate 1a is made to be the pressure receiving surface for a reference pressure, and the other surface is made to be the pressure receiving surface for a fluid source to be measured. A strain gage formed on the diaphragm 1a converts the pressure difference into an electric signal. The signal is supplied into a duty-ratio converting means 3. An oscillating means 2 supplies a square-wave signal in the reference duty ratio into the means 3. At this time, the signal from the means 2 is converted into the signal having the duty ratio corresponding to the output of the strain gage with the rectangular-wave generating circuit and a comparing circuit in the means 3. The signal is supplied into an output means 4. In the means 4, the output signal from the means 3 is converted into the digital signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pressure sensor for measuring fluid pressure, and more particularly to a pressure sensor using a strain gauge formed in a semiconductor single crystal substrate.

[Prior Art] In recent years, semiconductor pressure sensors that utilize the piezoresistance effect, in which the resistivity of a semiconductor crystal changes when an external force is applied to the semiconductor crystal, have been used in various fields including automobiles as small, lightweight, and highly sensitive pressure sensors. It is used in As a semiconductor pressure sensor of this type, a diffusion type semiconductor pressure sensor is known, in which a thin film diaphragm is processed and formed in the center of a semiconductor heavy crystal substrate such as silicon, and a diffused resistance layer is formed on this diaphragm to form a strain gauge. For example, a silicon pressure sensor using a diaphragm made of a silicon single crystal substrate is utilized. Fluid pressure is measured by detecting changes in diffusion resistance in response to strain caused by fluid pressure applied to the diaphragm, and a pair of strain gauges whose resistance increases and decreases with respect to fluid pressure are used. These two sets constitute a Wheatstone bridge, which is connected to a constant current or constant voltage power source to convert it into an electrical signal and measure fluid pressure.

Since the semiconductor pressure sensor mentioned above reacts sensitively to external heat and mechanical strain, it is constructed so as not to be affected by these. Techniques have been disclosed to reduce the impact.

Furthermore, a temperature compensation circuit is connected to compensate for nonlinear temperature characteristics of the semiconductor due to external environmental temperature changes including temperature changes of the fluid to be measured. For example, in the Wheatstone bridge for silicon pressure sensors, methods are used such as connecting a compensation resistor in series or parallel to the strain gauge, or giving temperature characteristics to the feedback resistor of an amplifier circuit composed of an operational amplifier. In addition, the special public official 59-4113
As described in Japanese Patent No. 4, there is also a technique in which a strain gauge in a pressure-insensitive section and a fixed resistor are connected in parallel and inserted in the feedback circuit of an output stage operational amplifier to perform temperature compensation.

[Problems to be Solved by the Invention] As mentioned above, in the conventional pressure sensor, a Wheatstone bridge including a gauge resistor is configured, and its output signal is amplified by an operational amplifier, so a temperature compensation circuit is essential. be.

Furthermore, since the output signal of the operational amplifier is an analog signal, analog-to-digital conversion is required in order to perform digital processing in a subsequent stage electronic control device equipped with a microcomputer, for example, and the signal is converted via an A/D conversion circuit. You will have to wear it.

Therefore, an object of the present invention is to provide a pressure sensor that outputs a signal that can be digitally processed by a microcomputer or the like without providing a special temperature compensation circuit.

[Means for Solving the Problems] In order to achieve the above object, the present invention, as shown in FIG. A semiconductor single-crystal substrate 1 on which a diaphragm portion 1a is formed as a pressure-receiving surface for the pressure of the fluid to be measured and deforms according to pressure fluctuations of the fluid to be measured, and a semiconductor single-crystal substrate! The pressure sensor is equipped with a strain gauge formed on a diaphragm portion 1a, and converts strain occurring in the diaphragm portion 1a into an electrical signal and outputs it. duty ratio converting means 3 which converts the output pulse signal into a signal having a duty ratio according to the output signal of the strain gauge based on the output pulse signal; and converting the output signal of the duty ratio converting means 3 into a digital signal according to the pressure of the fluid to be measured. and an output means 4 for outputting a signal.

In the above pressure sensor, the oscillation means 2 consists of an oscillation circuit that has a crystal oscillator and outputs a square wave signal, and the duty ratio conversion means 3 converts the square wave signal of the oscillation circuit into a triangular wave signal and outputs the triangular wave signal. It is preferable to include a circuit and a comparison circuit that compares the output signal of the triangular wave generation circuit with the output signal of the strain gauge and outputs a rectangular wave signal according to the comparison result.

Alternatively, in the above pressure sensor, the oscillation means 2 comprises an oscillation circuit having an operational amplifier and outputting a square wave signal,
The duty ratio conversion means 3 includes a triangular wave generating circuit that converts the square wave signal of the oscillation circuit into a triangular wave signal and outputs the triangular wave signal, and inputs the output signal of this triangular wave generating circuit to an operational amplifier, and outputs the output of the operational amplifier via a strain gauge. The output signal may be provided with a comparison circuit that returns the signal to the input and compares it with the output signal of the triangular wave generation circuit.

[Operation] In the pressure sensor configured as described above, a reference pressure is applied to one pressure receiving surface of the diaphragm portion 1a of the semiconductor single crystal substrate 1, and the measured fluid from the measured fluid source is applied to the other pressure receiving surface. Pressure is applied. These pressure differences cause strain in the diaphragm portion 1a including the strain gauge, and this strain is converted into an electrical signal by the strain gauge and supplied to the duty ratio converting means 3.

Further, the oscillation means 2 outputs a pulse signal of a predetermined frequency and supplies it to the duty ratio conversion means 3. and,
In the duty ratio conversion means 3, the output signal of the oscillation means 3 is converted into a signal having a duty ratio corresponding to the output signal of the strain gauge, and the signal is supplied to the output means 4. Thus, the output signal of the duty ratio converting means 3 is converted into a digital signal in the output means 4, and a signal corresponding to the pressure of the fluid to be measured is outputted from the output means 4.

[Embodiments] Hereinafter, preferred embodiments of the pressure sensor of the present invention will be described with reference to the drawings.

FIG. 2 shows an embodiment of the sensor element constituting the pressure sensor of the present invention, in which a silicon single crystal substrate is used as the semiconductor single crystal substrate of the present invention, and a silicon chip 11 having a square shape when viewed from the front is attached to a base 10. is supported by

A diaphragm portion 11a is formed in the center of the silicon chip 11 and is processed into a thin film having a thickness of several tens of μm. Two strain gauges of a diffused resistance layer are formed in this diaphragm portion 11a by diffusion of boron or the like. That is, as shown in FIG. 3, a diffused resistance, that is, a gauge resistance R5I, is formed at the periphery of the diaphragm portion 11a, and a gauge resistance R5I is formed at the center.
S2 is formed.

These gauge resistors R51 and R52 have a high gauge factor,
As described above, when pressure is applied to the diaphragm portion 11a, a positive resistance value change occurs in the gauge resistance R51, as shown in the following equations (1) and (2). R32 is placed at a position where a negative resistance value change occurs.

R51=R5to(1+α1 T+β+p)...
(1) R32=R32o(1+α, T-β2P)-(
2) However, R5I. , R32° is gauge resistance R5I.

Initial value of R32, α1. α2 is the temperature coefficient, β1. β2 represents the pressure coefficient, T represents the temperature, and P represents the pressure.

The gauge resistors R51 and RS2 are connected to the lead bins 13 and 14.1 shown in FIG.
5.

The silicon chip may be formed as shown in FIG. 4, but the gauge resistor RS1. It is necessary that R52 be arranged offset from each other. In FIG. 4, parts corresponding to those in FIG. 3 are indicated by adding 100 to the reference numerals in FIG. 3.

The silicon chip 11 configured as described above is supported by a pedestal 10a that is integrally formed with a glass base 10 having a linear expansion coefficient equivalent to that of the silicon chip 11. The lead bin 14 is connected to a constant voltage power supply VCC, the lead bin 15 is grounded GND, and the lead bin 14 is configured so that a voltage corresponding to a change in the resistivity of the gauge resistors R5I and RS2 is outputted via the lead bin 13.

The periphery of the base 10 and the flange portion of the cup-shaped case 16 are hermetically sealed to form a vacuum reference pressure chamber 17. A pressure port 10b formed approximately at the center of the base 10 is connected to a fluid source to be measured (not shown),
It is configured such that the fluid pressure to be measured is applied to the diaphragm portion 11a. Thus, one surface, that is, the surface of the diaphragm portion 11a of the silicon chip 11 is connected to the reference pressure chamber 1.
7 serves as a pressure receiving surface for the reference pressure, and the other surface, that is, the back surface serves as a pressure receiving surface for the fluid pressure to be measured.

FIG. 5 is an electric circuit diagram showing one embodiment of each means in the pressure sensor shown in FIG.
I and R32 are connected to a comparison circuit 40 constituting the duty ratio conversion means 3.

The oscillation means 2 includes an oscillation circuit 20 having a crystal resonator CR and outputting a square wave signal. In this oscillation circuit 20, a bias resistor R for starting and a capacitor C1 for frequency adjustment are connected to the input terminal of an inverter IVI, and a pressure terminal is fed back to the input terminal via a crystal oscillator CR, and a capacitor for temperature compensation is connected to the input terminal of the inverter IVI. C2 and inverter IV2 for waveform shaping
is connected to the input terminal of Note that the resistor R1 is connected to the constant voltage power supply VCC, and the capacitors C1 and C2 are connected to the ground GN.
It has been D. Then, from the oscillation circuit 20, for example, the sixth
A square wave signal with a duty ratio of 50% shown in Figure (a) is output.

The duty ratio conversion means 3 includes a triangular wave generation circuit 30 and a comparison circuit 40. The triangular wave generating circuit 30 consists of an integrating circuit consisting of a resistor R2 and a capacitor C3 connected to the output terminal of the inverter IV2, as shown in FIG. 6(a).
The square wave signal of the oscillation circuit 20 shown in FIG. 6 is converted into the triangular wave signal shown in FIG. 6(b). The comparison circuit 40 is an operational amplifier (
It has an operational amplifier (hereinafter referred to as an operational amplifier), and is configured such that a triangular wave signal from the triangular wave generating circuit 30 is input to its inverting input terminal. On the other hand, the voltage of the constant voltage power supply VCC is divided by the gauge resistors R31 and RS2, and the connection point between the two is connected to the non-inverting input terminal of the operational amplifier OP. The output terminal of the operational amplifier OP is connected to the constant voltage power supply Vcc via a resistor R3, and is also connected to the output terminal Vo.

The output terminal Vo is connected to the output means 4 of FIG. 1, where it is converted into a digital signal. For example, the output signal of the oscillation circuit 20 is frequency-divided to form a clock pulse of a predetermined frequency, and based on this clock pulse, the output signal of the output terminal Vo is digitally converted into the number of pulses of a predetermined gate time.

Note that the circuit elements constituting the electric circuit described above are mounted on a thick film resistance board (not shown), and are arranged on a printed wiring board (not shown) together with the sensor element shown in FIG. 2 to form a pressure sensor unit.

This pressure sensor unit is used, for example, to measure intake pipe pressure of an internal combustion engine.

To explain the operation of the above pressure sensor, the pressure port 10b
is connected to the source of the fluid to be measured, for example the intake pipe of an internal combustion engine,
Intake pipe pressure, ie, intake negative pressure, which is the fluid pressure to be measured, is transmitted to the diaphragm portion 11a of the silicon chip 11. When the intake negative pressure is transmitted to the back surface of the diaphragm portion 11a, stress corresponding to the pressure difference with the pressure in the reference pressure chamber 17 is generated in the gauge resistors R3I and R32 on the diaphragm portion 11a. In this embodiment, since the inside of the reference pressure chamber 17 is set to a vacuum, the stress corresponds to the absolute value of the intake negative pressure.

According to this stress, the resistivity of the gauge resistors R5I and RS2 changes due to the piezoresistance effect, and an output signal corresponding to the intake negative pressure is obtained from the output terminal V0 via the electric circuit shown in FIG.

Next, the operation of the electric circuit shown in FIG. 5 will be explained with reference to the waveform diagram shown in 'tSa diagram. In addition, (a) and (b) in Fig. 6
, (C) show the operating waveforms at points ①, ①, and @ in the circuit of FIG. 5, respectively. The square wave signal shown in FIG. 6(a) is output from the oscillation circuit 20, converted into the triangular wave signal shown in FIG. 6(b) by the triangular wave generating circuit 30, and inputted to the inverting input terminal of the operational amplifier OP of the comparator circuit 40. . Comparison circuit 4
0, the voltage of the constant voltage power supply VCC is divided according to the resistance values of the gauge resistors R5I and R52, and the voltage of the operational amplifier O
It is input to the non-inverting input terminal of P, and the threshold value Vs shown by the dashed line in FIG. 6(b) is set. As a result, the triangular wave signal of the triangular wave generating circuit 30 is applied to the gauge resistor R3I at the operational amplifier OP.

R32 is compared with the threshold value Vs corresponding to the signal shown in FIG.
A signal having a duty ratio corresponding to a change in 2 is output from the pressure terminal vO. The output signal from the output terminal vO is converted into a digital signal by the output means 4 shown in FIG. 1 and output.

FIG. 7 shows an electrical circuit diagram according to another embodiment of the present invention, which includes a square wave oscillation circuit 21 using an operational amplifier. That is, the oscillation circuit 21 has an operational amplifier OPI,
The voltage divided by the resistor R11 connected to the constant voltage power supply VCC and the grounded resistor R12 is applied to the operational amplifier OP.
It is input to the non-inverting input terminal of I. operational amplifier OPI
The output terminal of is fed back positively to the input terminal via a resistor R13, and is also fed negatively via an integrating circuit including a resistor R14 and a capacitor CI+. And operational amplifier OP
The output terminal of I is connected to a constant voltage power supply VCC via a resistor R15, and is also connected to a triangular wave generation circuit 31.

Similar to the embodiment shown in FIG. 5, the triangular wave generating circuit 31 is constituted by an integrating circuit consisting of a resistor R16 and a capacitor C12, and is connected to a comparator circuit 41. The comparison circuit 41 has an operational amplifier OP2 connected to the inverting input terminal of the triangular wave generation circuit 31, and a resistor R connected to the constant voltage power supply VCC.
17 and the grounded resistor R18 are connected to the non-inverting input terminal, and the gauge resistor R3I and the diode D1 are connected in parallel to the gauge resistor R32 and the diode D2, and the non-inverting input terminal is connected to the output terminal of the operational amplifier OP2. Positive feedback is provided to the input terminal. That is, a Schmitt trigger circuit is configured, and the threshold value is set according to the resistance values of the gauge resistors R3I and R52.

In the oscillation circuit 21, the voltage of the constant voltage power supply VCC is divided by resistors R11 and R12 and applied as a reference voltage to the non-inverting input terminal of the operational amplifier OP1, and the voltage is applied to the inverting input terminal via the resistor R14. The voltage of the capacitor C1l to be charged is applied. Capacitor C
As the charging of 1l progresses and becomes equal to or higher than the reference voltage, the output voltage of the operational amplifier oP1 changes to a negative value, is fed back positively, and the output voltage is instantaneously inverted to a negative value. As a result, the electric charge charged in the capacitor C1l is discharged via the resistor R14, and when the voltage becomes lower than the reference voltage, the output voltage becomes a positive value, and is returned to the original value by positive feedback. By repeating such operations, a square wave signal similar to that shown in Fig. @S (a) is output.

The output of the oscillation circuit 21 is converted into a triangular wave signal by the triangular wave generating circuit 31 as in the embodiment shown in FIG. The threshold value for the operational amplifier OP2 is determined by the resistors R17, R18 and the gauge resistors R3I, R52, and as mentioned above, when the gauge resistors RSt, RS2 fluctuate according to the pressure change of the fluid to be measured, the threshold level changes accordingly. changes. Then, it is converted into an output signal with a duty ratio corresponding to the gauge resistors R5I and R32, and further converted into a digital signal by the output means 4 and outputted as in the embodiment shown in FIG.

[Effects of the Invention] Since the present invention is configured as described above, it produces the effects described below.

That is, according to the pressure sensor of the present invention, the output signal of the strain gauge is converted into a signal having a duty ratio corresponding to the pressure of the fluid to be measured, and a digital output corresponding to the pressure of the fluid to be measured is obtained.
For example, the output of the pressure sensor can be used as is in an electronic control device composed of a microcomputer, and output errors caused by temperature changes can be easily processed. In particular, since a conventional pressure sensor using a Wheatstone bridge is amplified by an operational amplifier, a temperature compensation circuit is essential, whereas the present invention does not require an amplification effect by an operational amplifier, so a temperature compensation circuit is provided. Good output characteristics can be obtained without any problems.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the basic configuration of the pressure sensor of the present invention, Fig. 2 is a vertical sectional view of a sensor element in the pressure sensor of Fig. 1, Fig. 3 is a plan view of a silicon chip, and Fig. 4 is a plan view of another embodiment of the same silicon chip,
Figure 5 is an electrical circuit diagram of one embodiment of the pressure sensor, 1! S6
This figure is a waveform diagram of the output signal at each point in the electrical circuit diagram of FIG. 5, and FIG. 347 is an electrical circuit diagram of another embodiment of the pressure sensor of the present invention. 1...Semiconductor single crystal substrate. 1a...Diaphragm part, 10...Base. 10a... pedestal, 10b... pressure boat. 11...Silicon chip (semiconductor single crystal substrate) 11a
...Diaphragm section. 13.14.15...Lead pin. 17...Reference pressure chamber. 20.21...Oscillation circuit. 30.31... Triangular wave generation circuit, 40.41... Comparison circuit.

Claims (3)

[Claims] (1) One surface is a pressure-receiving surface for the reference pressure, the other surface is connected to a fluid source to be measured and is a pressure-receiving surface for the pressure of the fluid to be measured, forming a diaphragm portion that deforms according to pressure fluctuations in the fluid to be measured. A pressure sensor that includes a semiconductor single-crystal substrate and a strain gauge formed on the diaphragm portion of the semiconductor single-crystal substrate, and that converts strain occurring in the diaphragm portion into an electrical signal and outputs it. an oscillating means for outputting, a duty ratio converting means for converting the output pulse signal of the oscillating means into a signal having a duty ratio corresponding to the output signal of the strain gauge, and converting the output signal of the duty ratio converting means into a digital signal. and an output means for converting the pressure into the measured fluid and outputting a signal corresponding to the pressure of the fluid to be measured. (2) The oscillation means includes an oscillation circuit that has a crystal resonator and outputs a square wave signal, and the duty ratio conversion means converts the square wave signal of the oscillation circuit into a triangular wave signal and outputs the triangular wave signal. and a comparison circuit that compares the output signal of the triangular wave generation circuit and the output signal of the strain gauge and outputs a rectangular wave signal according to the comparison result. (3) The oscillation means includes an oscillation circuit that has an operational amplifier and outputs a square wave signal, and the duty ratio conversion means converts the square wave signal of the oscillation circuit into a triangular wave signal and outputs the triangular wave signal. , comprising a comparison circuit that inputs the output signal of the triangular wave generating circuit to an operational amplifier, returns the output of the operational amplifier to the input via the strain gauge, and compares it with the output signal of the triangular wave generating circuit. The pressure sensor according to claim 1.