JP3321490B2 - Acceleration detection circuit - 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 for a safety device such as an air bag for ensuring safety at the time of a collision of an automobile, a device for improving riding comfort on a rough road, or a device for preventing camera shake from occurring. About

[0002]

2. Description of the Related Art Conventionally, various types of acceleration detection have been put to practical use. Among them, a piezoelectric acceleration sensor using piezoelectric ceramics has a simple structure and can be used at a high temperature, and thus is widely used for detecting vibration of various machines and detecting knocking of an automobile engine.

When the piezoelectric ceramic is used as an acceleration sensor, when an acceleration α is applied to the piezoelectric ceramic, a force F is applied to the piezoelectric ceramic, and a voltage V (charge Q) is generated at electrodes on both surfaces of the piezoelectric ceramic. ,
The acceleration α can be obtained. If this is expressed by a mathematical formula, F = K1 × α (1) V (Q) = K2 × F (2) Here, K1 and K2 are proportional constants.

FIG. 2 shows a conventional acceleration detection circuit using a piezoelectric acceleration sensor using this piezoelectric ceramic.
In a conventional acceleration detection circuit, a piezoelectric conversion resistor 2 is connected in parallel with a piezoelectric acceleration sensor 1, and an output is connected to an operational amplifier 4 constituting a buffer circuit. In the acceleration detection circuit shown in FIG. 2, the performance particularly in a low frequency range is determined by the capacitance and the piezoelectric conversion resistance 2 of the acceleration sensor 1 and the circuit constants constituting the input circuit of the operational amplifier 4 of the buffer circuit. .

In such an acceleration detection circuit, when the acceleration sensor 1 receives a vibration such as a hand shake, an alternating charge corresponding to the hand vibration is generated between the two electrodes of the piezoelectric ceramic of the acceleration sensor 1, and the voltage conversion is performed. After being output as an AC voltage to both ends of the resistor 2, the generated voltage is amplified and output via a buffer circuit. At this time, the output voltage due to vibration such as camera shake is a frequency corresponding to vibration equal to or higher than the frequency determined by the cutoff frequency on the low frequency side of the circuit constant determined by the capacitance of the acceleration sensor 1 and the resistance value of the voltage conversion resistor 2. Is output.

[0006]

When an acceleration sensor made of piezoelectric ceramics is used for a safety device such as an air bag or a device for improving riding comfort on a rough road, a required characteristic is about 0. It is required to be able to detect acceleration at a low frequency of up to 05 Hz, that is, to have high sensitivity up to the low frequency range. The acceleration detection circuit needs to increase the value of the capacitance of the capacitor connected in series with the cascade-connected circuit in order to be able to detect low-frequency acceleration. There is a problem that it takes a long time for the output of the acceleration detection circuit to stabilize and turn on to output a normal output value after the power is turned on because the oscillation voltage generated in the circuit interferes with each other. Was.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an acceleration detecting circuit which can output a normal output value in a shorter time when the power is turned on than in the prior art.

[0008]

In order to solve the above-mentioned problems, a piezoelectric acceleration sensor which generates an electric charge on an electrode surface in proportion to the acceleration when the acceleration is received, and a piezoelectric acceleration sensor In an acceleration detection circuit including a parallel circuit in which a voltage conversion resistor is connected in parallel, an operational amplifier circuit for amplifying a voltage generated in the parallel circuit, and a high-pass circuit connected to an output side of the operational amplifier circuit, The signal line and the ground side of the voltage conversion resistor inserted in parallel, and the resistor connected between the signal line side and the ground side of the high-pass circuit are simultaneously short-circuited for a predetermined time when the power is turned on. Is provided.

That is, the present invention provides a parallel circuit comprising a piezoelectric acceleration sensor for generating a voltage corresponding to the magnitude of acceleration, a voltage conversion resistor connected in parallel with the acceleration sensor, and An acceleration detection circuit comprising an amplification circuit connected in series, wherein both ends of a voltage conversion resistor connected in parallel to the acceleration sensor are short-circuited for a predetermined time by an analog switch driven by an initialization pulse generation circuit when power is turned on. An acceleration detection circuit characterized in that:

According to the present invention, there is provided a parallel acceleration circuit comprising a piezoelectric acceleration sensor for generating electric charges corresponding to the magnitude of acceleration, and a voltage conversion resistor connected in parallel with the acceleration sensor.
An acceleration detection circuit comprising an amplifier circuit connected in series with the parallel circuit and a high-pass circuit connected in series with the amplifier circuit, wherein both ends of a voltage conversion resistor connected in parallel to the acceleration sensor, An acceleration detection circuit, wherein both ends of a resistor are simultaneously short-circuited for a predetermined time by an analog switch connected to an initialization pulse generation circuit when power is turned on.

[0011]

The acceleration detecting circuit according to the present invention includes a parallel circuit connected between both ends of the output of the acceleration sensor and a resistance of the high-pass circuit for improving the sensitivity of the acceleration detecting circuit in a low frequency range. A circuit with a large time constant is configured with the connected capacitor, but when power is applied to the circuit, a long synchronized oscillation voltage is generated in the circuit and interferes with each other in the circuit. Therefore, when power is turned on, both ends of the voltage conversion resistor having a high resistance and the resistor of the high-pass circuit are short-circuited with a low resistance when the power is turned on, thereby reducing the time constant of the capacitor inserted in parallel or in series. That is, by short-circuiting for a predetermined time when the power is turned on, and after elapse of the predetermined time, the short-circuit is released, whereby the self-capacitance and the capacitor on the circuit are quickly charged and set to a reference value, and the output of the circuit is set. Can output a normal output value and be stabilized immediately.

[0012]

FIG. 1 shows an embodiment of an acceleration detecting circuit according to the present invention. When a vibration such as a camera shake is received, a voltage is generated across the piezoelectric acceleration sensor 1 according to the acceleration of the vibration, the piezoelectric characteristics of the acceleration sensor, and the shape and mass. A voltage conversion resistor 2 is connected in parallel to both ends of the piezoelectric acceleration sensor 1, one end being an output side and the other end being a ground terminal. One end of the voltage conversion resistor 2 is connected to a non-inverting input terminal of the operational amplifier 4. Further, both ends of the voltage conversion resistor 2 are connected to both ends of the analog switch 3 so as to be short-circuited when the analog switch 3 is turned on. When the short circuit is released after the lapse of time, the output V of the acceleration detection circuit is generated at the output terminal of the operational amplifier 4. The voltage conversion resistor 2 is used to stabilize the output voltage of the acceleration sensor. However, when the voltage conversion resistor 2 is not connected, an analog switch may be directly connected to both ends of the acceleration sensor.

In FIG. 1, the equivalent capacitance value of a piezoelectric acceleration sensor that generates electric charges according to acceleration is 100
In this embodiment, the resistance value of the voltage conversion resistor 2 connected to both ends is 20 MΩ. One end of the voltage conversion resistor 2 is connected to a non-inverting input terminal of the operational amplifier 4.
The operational amplifier 4 has an input resistor 5 connected to the inverting input terminal.
The input signal is amplified in a non-inverting manner by the feedback resistor 6. Further, both ends of the voltage conversion resistor 2 are also connected to both ends of the analog switch 3. The analog switch 3 forms an initializing pulse generation circuit by a Schmitt trigger circuit including a resistor 13, a capacitor 14, and a Schmitt inverter 15 that short-circuit the analog switch 3 for a predetermined time when the power is turned on. Further, both ends of the analog switch 3 are short-circuited for about 0.2 second to 1.0 second by a pulse signal from the initialization pulse generating circuit, and both ends of the voltage conversion resistor 2 are short-circuited when the power is turned on. This prevents long-period voltage fluctuations occurring in the circuit when the power is turned on. An output of the operational amplifier 4 is connected to a non-inverting input terminal of an operational amplifier 12 through a high-pass circuit including a capacitor 7 and a resistor 9 for blocking a drift voltage.

In this embodiment, the value of the capacitance of the capacitor 7 is 0.2 μF, and the value of the resistor 9 is 10 MΩ. The operational amplifier 12 amplifies the signal of the non-inverting input by the resistor 10 and the feedback resistor 11 connected to the inverting input terminal. Both ends of the resistor 9 constituting the high-pass circuit are connected to both ends of the analog switch 8. The analog switch 8 is activated by a pulse signal from the initialization pulse generating circuit when the power is turned on.
Is short-circuited at both ends of the resistor 9 for the same time as the time at which both ends of the voltage conversion resistor 2 are short-circuited.

An analog switch 3 for simultaneously short-circuiting both ends of the voltage conversion resistor 2 of the parallel circuit and a resistor 9 of the high-pass circuit shown in the embodiment of the present invention, and an analog switch 8
The initialization pulse generating circuit and the short-circuit analog switch for operating the circuit are shown in the embodiment, and can be configured by other circuit configurations. When it is desired that the voltage conversion resistor 2 operates at a lower frequency, the resistor having a value of 20 MΩ or more used in this embodiment may be used. On the other hand, the capacitor 7 and the resistor 9 of the high-pass circuit may be used. Similarly, a larger value may be used.

The overall low-frequency cutoff frequency of the acceleration detection circuit of the present invention is 0.2 Hz, and the low-frequency cutoff frequency is reduced by one digit as compared with a conventional acceleration detection circuit of this type. Was completed. Based on the present embodiment, the time required for the output signal of the acceleration detection circuit to stabilize after the power is turned on is greatly reduced to 1 second, compared to 15 seconds in the past, and the acceleration detection signal of the present invention is reduced. The validity of the circuit was fully confirmed.

[0017]

As described above, in the acceleration detection circuit according to the present invention, the voltage conversion resistor having a high resistance value and the signal line of the high-pass circuit connected between the signal line and the ground side in parallel with the acceleration sensor. By short-circuiting both ends of a resistor having a high resistance connected between the power supply and the ground for a predetermined time at the same time when the power is turned on, the self-capacitance of the acceleration sensor and the capacitor of the high-pass circuit are set to a reference value charge. The setting can be made quickly, and the output of the acceleration detection circuit can be quickly stabilized. Therefore, an acceleration detection circuit capable of outputting a normal output value quickly can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of an acceleration detection circuit according to the present invention.

FIG. 2 is a circuit diagram showing an outline of a conventional acceleration detection circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Acceleration sensor 2 Voltage conversion resistance 3,8 Analog switch 4,12 Operational amplifier 5,10 Input resistance 6,11 Feedback resistance 7 Capacitor 9,13 Resistance 14 Capacitor 15 Inverter with Schmitt

Claims (2)

(57) [Claims] 1. A parallel circuit comprising a piezoelectric acceleration sensor for generating a voltage corresponding to the magnitude of acceleration, a voltage conversion resistor connected in parallel with the acceleration sensor, and a cascade connection of the parallel circuit. In an acceleration detection circuit including an amplification circuit, both ends of a voltage conversion resistor connected in parallel to the acceleration sensor are short-circuited for a predetermined time by an analog switch driven by an initialization pulse generation circuit when power is turned on. An acceleration detection circuit, characterized in that: 2. A parallel circuit comprising a piezoelectric acceleration sensor for generating electric charge according to the magnitude of acceleration, a voltage conversion resistor connected in parallel with the acceleration sensor, and a cascade connection of the parallel circuit. In an acceleration detection circuit including an amplification circuit and a high-pass circuit connected in series with the amplification circuit, power is supplied to both ends of a voltage conversion resistor connected in parallel to the acceleration sensor and both ends of the resistance of the high-pass circuit. An acceleration detection circuit characterized in that the acceleration switch is configured to be simultaneously short-circuited for a predetermined time by an analog switch connected to the initialization pulse generation circuit.