JPH0694743A - Correcting circuit for acceleration sensor - Google Patents

Abstract

PURPOSE:To improve low frequency characteristics of a piezoelectric acceleration sensor by high frequency characteristics of a low-pass filter. CONSTITUTION:A correcting circuit for an acceleration sensor 1 to correct a detection signal to be output from the sensor 1 having high-pass filter characteristics comprises a low-pass filter 2 for receiving the signal from the sensor 1, and an adder 3 for adding the signal from the sensor 1 and an output signal from the filter 2, thereby outputting an output from the adder 3 as an acceleration signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor correction circuit for correcting and outputting a distorted detection output from an acceleration sensor using a piezoelectric element.

[0002]

2. Description of the Related Art Conventionally, when a rectangular wave acceleration is applied to an acceleration sensor, for example, a semiconductor acceleration sensor outputs a substantially rectangular wave acceleration signal as shown in FIG. On the other hand, an acceleration sensor using a piezoelectric element outputs an acceleration signal close to a differential waveform as shown in FIG. Further, when an acceleration signal that changes intricately like an acceleration waveform generated at the time of a vehicle collision acts on the acceleration sensor, the semiconductor type acceleration sensor accurately detects the acceleration change as shown in FIG. 7, for example. Although it outputs, an acceleration sensor using a piezoelectric element has a differential characteristic. Therefore, when an acceleration corresponding to the acceleration signal shown in FIG. 7 is received, the output waveform is changed when the acceleration changes as shown in FIG. The phenomenon that it changed greatly was occurring.

[0003]

That is, as described above, in the acceleration sensor using the piezoelectric element, there is a problem that the change in acceleration to be detected cannot be detected accurately with certainty. Was there.

Nevertheless, in particular, in recent years, especially in recent years, the piezoelectric acceleration sensor is used, paying attention to the great advantage that an acceleration sensor using a piezoelectric element can be manufactured at low cost as compared with a semiconductor acceleration sensor. The tendency has become noticeable.

The present invention has been made to solve the above problems, and an object thereof is to solve the above problems by improving the performance of a piezoelectric acceleration sensor.

[0006]

In an acceleration sensor correction circuit for correcting and outputting a detection signal output from an acceleration sensor having a high pass filter characteristic, a low pass filter for receiving the detection signal from the acceleration sensor, and the acceleration sensor. An addition circuit for adding a detection signal from the acceleration sensor and an output signal from the low-pass filter having a frequency characteristic that partially overlaps with the frequency characteristic of Output as a signal.

[0007]

According to the above construction, the frequency characteristic on the low frequency side of the acceleration sensor is improved by the frequency characteristic on the high frequency side of the low pass filter.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an embodiment according to the present invention will be described in detail with reference to FIGS. That is, 1 is a piezoelectric acceleration sensor, which is an ideal acceleration sensor 1a (sensor having flat characteristics over the entire frequency band), a capacitor 1b having a capacitance C0, and a resistance value R0 as shown in the equivalent circuit of FIG. Resistance 1c of an electric signal h when an external mechanical vibration acts as acceleration g (t).
(T) is output. The piezoelectric acceleration sensor 1
Is a high-pass filter (a frequency characteristic diagram is shown by a solid line 6 in FIG. 3) by the capacitor 1b and the resistor 1c, and as a result, outputs a waveform as described in FIGS. 6 and 8. That is, assuming that the output signal h (t) from the piezoelectric acceleration sensor 1 is T0 = C0.R0

[0009]

[Equation 1]

[0010] 2 is a low-pass filter (frequency characteristic diagram is shown by a chain line 5 in FIG. 3. Further, both the frequency characteristic diagram and the frequency characteristic diagram of the high-pass filter described above are set so as to partially overlap. (2) having a resistance value R1 and a capacitor 2b having a capacitance C1. The detection signal h (t) from the piezoelectric acceleration sensor 1 is input to the signal component extracted from the detection signal h (t). Based on this, a signal U (t) for correction is created. That is, assuming that the output signal U (t) from the low pass filter 2 is T0 = C1.R1.

[0011]

[Equation 2]

[0012] An adder circuit 3 receives the detection signal h (t) from the piezoelectric acceleration sensor 1 and the output signal U (t) from the low-pass filter 2 and corrects the adder signal V (t). Output as an acceleration signal.

[0013]

[Equation 3]

When the values of the capacitance C0 of the capacitor 1b and the resistance value R0 of the resistor 1c in the equivalent circuit of the piezoelectric acceleration sensor 1 are unknown, these two elements 1b, 1
It goes without saying that it is calculated from the theoretical relationship between the cutoff frequency f0 of the high-pass filter constituted by c and these two elements 1b and 1c. Further, in the figure, reference numeral 4 is an amplifier circuit that amplifies and outputs the output signal from the piezoelectric acceleration sensor 1.

Next, the operation of the above structure will be described with reference to FIG. When the acceleration g (t) acts on the piezoelectric acceleration sensor 1 from the outside, the high-pass filter function originally possessed by the piezoelectric acceleration sensor 1 causes the frequency characteristic 6 in FIG. 3 to act so that only high frequency components are output. It is supplied to the low-pass filter 2 and the adder circuit 3.
In the low pass filter 2, the supplied signal h
Of the frequency components of (t), only the frequency components indicated by the hatched lines 7 in FIG. 3 are extracted and output to the adder circuit 3.

The adder circuit 3 adds the signal component output from the piezoelectric acceleration sensor 1 having the frequency characteristic 6 and the signal component output from the low pass filter 2 and indicated by the hatched line 7 in FIG. As a result, as shown in FIG. 4, the frequency characteristic of the low-frequency side of the piezoelectric acceleration sensor 1 from the adding circuit 3 is improved from the solid line portion (6a portion) to the broken line 8.

[0017]

As described above, according to the present invention, in the acceleration sensor correction circuit for correcting and outputting the detection signal output from the acceleration sensor having the high pass filter characteristic, the low pass receiving the detection signal from the acceleration sensor. The adder circuit includes a filter and an adder circuit that has a frequency characteristic that partially overlaps the frequency characteristic of the acceleration sensor and that adds a detection signal from the acceleration sensor and an output signal from the low-pass filter. Since it is an acceleration sensor correction circuit that outputs the addition result from the acceleration signal as an acceleration signal, it is possible to improve the frequency characteristic on the low frequency side of the piezoelectric acceleration sensor, and it is possible to improve the detection accuracy. Is demonstrated.

[Brief description of drawings]

FIG. 1 is a circuit block explanatory diagram for explaining an embodiment according to the present invention.

FIG. 2 is a detailed circuit explanatory diagram of a circuit block shown in FIG.

FIG. 3 is a frequency characteristic diagram of a high pass filter and a low pass filter in FIG.

FIG. 4 is a frequency characteristic diagram improved by the present invention.

FIG. 5 is a characteristic explanatory view of a semiconductor type acceleration sensor for explaining a conventional example.

FIG. 6 is a characteristic explanatory diagram of a piezoelectric acceleration sensor for explaining a conventional example.

FIG. 7 is a characteristic explanatory diagram of a piezoelectric acceleration sensor for explaining a conventional example.

FIG. 8 is a characteristic explanatory view of a semiconductor type acceleration sensor for explaining a conventional example.

[Explanation of symbols]

 1 Piezoelectric acceleration sensor 2 Low pass filter 3 Adder circuit 4 Amplifier circuit

Claims (1)

[Claims] 1. An acceleration sensor correction circuit for correcting and outputting a detection signal output from an acceleration sensor (1) having a high pass filter characteristic, wherein a low pass filter (2) receives the detection signal from the acceleration sensor (1).
And an addition circuit (3) having a frequency characteristic that partially overlaps the frequency characteristic of the acceleration sensor (1) and adding the detection signal from the acceleration sensor and the output signal from the low pass filter (2). ) And outputting the addition result from the addition circuit as an acceleration signal.