JP3158800B2 - Acceleration sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor used in a vehicle airbag device or the like.

[0002]

2. Description of the Related Art Conventionally, as an acceleration sensor of this type, as shown in FIG.
And an impedance conversion circuit 3 provided with a field effect transistor (hereinafter referred to as FET) 2 for amplifying an output signal from the piezoelectric element 1, and a filter circuit for removing unnecessary components in the impedance-converted signal. includes a 4, which has an amplifier circuit 5 for amplifying a signal unnecessary components are removed are connected in series like configuration, the reference voltage generating circuit 6 for generating a reference voltage V _R based on the power supply voltage V _CC There are things. Then, a reference voltage V _{R, which} is a reference voltage in these operations, is applied to the filter circuit 4 and the amplification circuit 5 in the acceleration sensor, while the impedance conversion circuit 3
Is connected to a self-diagnosis signal circuit 7 for performing a failure diagnosis of the piezoelectric element 1.

Here, the impedance conversion circuit 3
With the filter circuit 4 is connected to the source side of the ground is of FET2 incorporated in, its drain
A power line is connected to the in side, and this FET2
Is supplied with a power supply voltage V _CC . The sensor output output from the amplification circuit 5 of the acceleration sensor is input to airbag control means (not shown) including a microcomputer.
The airbag control means instructs the in-vehicle airbag device (not shown) to perform an operation according to the input sensor output.

[0004]

[SUMMARY OF THE INVENTION Incidentally, the operating voltage of the impedance converter circuit 3 in the acceleration sensors and the conventional configuration, the power supply voltage V to the drain side of the FET2
_{Since CC} is supplied and the filter circuit 4 is connected to the ground side, it is always constant within the operating range even if the power supply voltage V _CC fluctuates. On the other hand, the reference voltage V _R generated by the reference voltage generation circuit 6 is
The power supply voltage V _CC fluctuates in accordance with the fluctuation or noise mixed from the power supply line. As a result, the filter circuit 4 and the amplifier circuit 5 operates the reference voltage V _R as a reference voltage, due to the operating voltage of the impedance converter circuit 3 is not changed similarly to the power supply voltage V _CC, fluctuations in the power supply voltage V _CC It will be amplified after picking up.

The present invention has been made in view of such inconvenience, and it is an object of the present invention to provide an acceleration sensor which is hardly affected by fluctuations in power supply voltage and noise from a power supply line. I have.

[0006]

An acceleration sensor according to the present invention comprises: a piezoelectric element; and an impedance conversion circuit provided with a field effect transistor for amplifying an output signal from the piezoelectric element. A filter circuit for removing an unnecessary component in the signal, an amplifier circuit for amplifying the signal from which the unnecessary component has been removed, and a reference voltage generating circuit for generating a reference voltage serving as an operation reference voltage of the filter circuit and the amplifier circuit. a acceleration sensor, a filter circuit is connected to the drain side of the FET transistor, and, together with a reference voltage is supplied via the load resistor to the drain side of the field effect transistor, wherein The piezoelectric element is
Connected to the gate of a field effect transistor,
The non-inverting input of the operational amplifier of the
A reference voltage, and the reference voltage is
It is characterized in that the reference voltage is the operation reference voltage of the filter circuit .

[0007]

According to the above configuration, since the reference voltage is supplied to the drain side of the FET to which the filter circuit is connected via the load resistance, the operating voltage of the impedance conversion circuit is changed by the fluctuation of the reference voltage. Will vary. Furthermore, the piezoelectric element
Connected to the gate of the field effect transistor, filter
The non-inverting input of the operational amplifier of the circuit is connected to the
Connected to the reference voltage and the reference
Since this is the circuit operation reference voltage, noise from the power supply
Noise can be eliminated.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit configuration diagram of an acceleration sensor according to the present embodiment, and FIG. 2 is a modification thereof. In FIGS. 1 and 2, the same or corresponding parts as those in FIG. 3 are denoted by the same reference numerals, and detailed description thereof will be omitted.

The acceleration sensor according to this embodiment has a piezoelectric element 1 for detecting acceleration, an impedance conversion circuit 3 provided with an FET 2 for amplifying an output signal from the piezoelectric element 1, a filter circuit 4, The amplifier circuit 5 and the amplifier circuit 5 are connected in series, and the filter circuit 4 is connected to the drain side of the FET 2. Further, the acceleration sensor, the reference voltage generating circuit for generating a reference voltage V _R based on the power supply voltage V _CC 6
And a self-diagnosis signal circuit 7 connected to the impedance conversion circuit 3 for diagnosing the failure of the piezoelectric element 1. The reference voltage V _R generated by the reference voltage generation circuit 6 is used as a reference voltage for operation. Circuit 4
And to the amplifying circuit 5, and is supplied to the drain side of the FET 2 via the load resistor R.

Therefore, by adopting such a configuration, when the reference voltage V _R fluctuates following the fluctuation of the power supply voltage V _CC or the intrusion of noise from the power supply line, the operating voltage of the FET 2 is also changed to the reference voltage. will vary while with the variation of the voltage V _R. And at this time,
Filter circuit 4 and the amplifier circuit 5 connected to the drain side of the FET2 also because the same reference voltage V _R and FET2 with each other to operate as the reference voltage, the filter circuit 4 and the amplifier circuit 5 is in the power voltage V _CC These Picking up and amplifying fluctuations will not occur.

[0012] In the acceleration sensor shown in FIG. 1, with grounding the FET2 upon via the feedback resistor R _1, to ground the leakage resistor R ₃ connected to the FET2 via a protective resistor R ₂ are, but not limited to this circuit configuration, for example, as shown in the modification of FIG. 2, it may be grounded in terms of connecting the feedback resistor R ₁ and the leak resistance R ₃ is Of course.

[0013]

As described above, according to the acceleration sensor of the present invention, the filter circuit is connected to the drain side of the FET constituting the impedance conversion circuit, and the reference voltage is supplied to the drain side of the FET. Therefore, the operating voltage of the impedance conversion circuit fluctuates while corresponding to the fluctuation of the reference voltage. Ma
In addition, the piezoelectric element contacts the gate of the field-effect transistor.
The non-inverting input of the operational amplifier of the filter circuit
Connected to the reference voltage via
Is the operating voltage of the filter circuit
Therefore, noise from the power supply can be removed. As a result, an effect is obtained that the acceleration sensor according to the present invention is less susceptible to fluctuations in the power supply voltage and the intrusion of noise from the power supply line.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of an acceleration sensor according to an embodiment.

FIG. 2 is a circuit configuration diagram of an acceleration sensor according to a modification.

FIG. 3 is a circuit configuration diagram of an acceleration sensor according to a conventional example.

[Explanation of symbols]

First piezoelectric element 2 FET (field effect transistor) 3 impedance conversion circuit 4 filter circuit 5 amplifier 6 a reference voltage generating circuit V _R reference voltage

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01P 15/09

Claims (1)

(57) [Claims] An impedance conversion circuit (3) provided with a piezoelectric element (1) and a field effect transistor (2) for amplifying an output signal from the piezoelectric element (1).
A filter circuit (4) for removing unnecessary components from the impedance-converted signal, an amplifier circuit (5) for amplifying the signal from which the unnecessary components have been removed, and a filter circuit (4) and an amplifier circuit (5). a acceleration sensor and a reference operation voltage becomes the reference voltage (V _R) reference voltage generating circuit for generating a (6), a filter circuit (4) is connected to the drain side of the FET transistor (2) and, and, together this reference voltage to the drain side via the load resistor (R) of the field-effect transistor (2) (V _R) is supplied
To the piezoelectric element (1) is the field-effect transistor
The non-inverting input of the operational amplifier of the filter circuit (4) is connected to the gate of (2).
Connected to the reference voltage (V _R ) via a resistor ;
The reference voltage (V _R) is the filter circuit (4)
An acceleration sensor characterized in that the operation reference voltage is equal to the reference voltage .