JP2008151631A - Acceleration detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acceleration detector stably working even if it undergoes an impact other than acceleration. <P>SOLUTION: This acceleration detector is equipped with: an oscillating circuit 2 equipped with a first tuning-fork vibration element 20a; a resonant circuit 5 equipped with a second tuning-fork vibration element 20b to phase-shift an output signal outputted from the oscillating circuit 2 based on a resonance frequency determined by the vibration element 20b and a variable capacitance circuit 5b; a phase comparison circuit 7 for comparing the phase of an output signal from the oscillating circuit 2 with that of an output signal from the resonant circuit 5; an LPF 8 for turning a phase difference signal outputted from the comparison circuit 7 into a direct current; a differentiation circuit 9 differentiating an output from the LPF 8; and a DC servo circuit 11 feeding back a control voltage corresponding to the output of the LPF 8 to the capacitance circuit 5b. As to the vibration elements 20a and 20b, the extending direction of their respective vibration arms is made to coincide with an acceleration detecting direction, and the vibration elements 20a and 20b are disposed opposite to each other. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an acceleration detection device using a tuning fork type vibration element as a detection sensor.

In recent years, acceleration sensors that detect acceleration have been researched and developed for a wide range of applications such as next-generation automobiles, robots, and the space industry. As an acceleration sensor developed for consumer equipment, a MEMS (Micro Electro Mechanical Systems) sensor in which an acceleration detection mechanism is manufactured by a semiconductor process is well known.
On the other hand, for example, pressure sensors for measuring pressures of gases and liquids have been developed using tuning fork vibrators in addition to MEMS sensors.

FIG. 8 is a diagram showing a configuration of a conventional vibration sensor circuit disclosed in Patent Document 1. In FIG. A conventional sensor circuit 100 shown in FIG. 8 includes a sensor unit 101 and a drive circuit 102. The sensor unit 101 includes a vibrator 101a which is a sensor element, an amplifier 101b, and a rectifier circuit 101c. The vibrator 101a is, for example, a vibrator assembled with lead zirconium titanate (PZT).
The drive circuit 102 includes a voltage controlled oscillator 102a, an amplifier 102b, and a phase comparator 102c. In the sensor circuit 100 configured as described above, the vibrator 101 a of the sensor unit 101 is driven by the voltage controlled oscillator 102 a of the drive circuit unit 102.
Here, when the vibrator 101a receives physical stress (pressure), the resonance frequency of the vibrator 101a changes. When the resonance frequency of the vibrator 101a changes, the phase of the output signal output from the phase comparator 102c of the drive circuit 102 changes. Thus, the output signal of the voltage controlled oscillator 102a is controlled to coincide with the resonance frequency of the vibrator 101a, and the vibrator 101a vibrates at the resonance frequency corresponding to the stress. Therefore, the stress value received by the vibrator 101a can be detected by taking the output of the line 104 or 103 as a detection signal.
Japanese Utility Model Publication No. 62-155336

By the way, when the vibration sensor circuit 100 as described above is mounted on a moving object or the like as an acceleration sensor, if the resonance frequency of the vibrator 101a suddenly fluctuates due to an impact other than acceleration received when the moving object moves, the phase comparator 102c. The output signal of the signal fluctuates rapidly. However, since the vibration type sensor circuit 100 shown in FIG. 8 has a PLL control configuration that feeds back a phase comparison result based on the output of the vibrator 101a to the voltage controlled oscillator 102a, the output signal of the phase comparator 102c fluctuates rapidly. In this case, the voltage controlled oscillator 102a cannot follow the PLL control. As a result, the voltage controlled oscillator 102a may stop oscillating. For this reason, an acceleration detection device cannot be configured using the conventional vibration sensor circuit 100.
The present invention has been made in view of the above points, and an object of the present invention is to provide an acceleration detection device that operates stably even when subjected to an impact other than acceleration.

  In order to achieve the above object, an acceleration detection apparatus of the present invention includes an oscillation circuit including a first tuning fork type vibration element as a resonance element, a second tuning fork type vibration element, and a voltage-controlled variable capacitance circuit. A resonance circuit that shifts an output signal output from the oscillation circuit based on a resonance frequency determined by the second tuning-fork type vibration element and the voltage-controlled variable capacitance circuit; an output signal output from the oscillation circuit; A phase comparison circuit that compares the phase of the output signal output from the resonance circuit, a low-pass filter that converts the phase difference signal output from the phase comparison circuit into a direct current, and a differentiation that differentiates the output signal output from the low-pass filter A DC servo circuit that includes a circuit and a time constant circuit that feeds back a control voltage corresponding to an output signal after the low-pass filter to a voltage-controlled variable capacitance circuit; And the second tuning-fork type vibrating element has two vibrating arms arranged in parallel with each other, and a coupling portion for coupling one end in the extension direction of the two vibrating arms, and the first and second tuning-fork type The extension direction of each vibration arm of the vibration element is made to coincide with the acceleration detection direction, and the first and second tuning fork type vibration elements are arranged opposite to each other, and the output signal output from the differentiation circuit is used as the acceleration detection signal. It is characterized by outputting.

According to the present invention as described above, the output signal of the oscillation circuit including the first tuning fork type vibration element as a resonator and the first tuning fork type vibration element are arranged so as to face each other in the acceleration direction. The phase of the output signal of the resonance circuit provided with the vibration element is compared with a phase comparison circuit, and the phase comparison result is converted into a direct current by a low-pass filter and further differentiated by a differentiation circuit. This makes it possible to detect acceleration using the first tuning fork type vibration element provided as the resonator in the oscillation circuit and the second tuning fork type vibration element provided as the resonator in the resonance circuit.
Further, according to the present invention, since the voltage controlled oscillation circuit is not provided, the oscillation does not stop even when a strong impact other than acceleration is applied unlike the conventional vibration sensor circuit.

In addition, the acceleration detection device of the present invention is provided between the oscillation circuit and the phase comparison circuit, and between the resonance circuit and the phase comparison circuit, the first rectangularization circuit that outputs the rectangular output signal of the oscillation circuit. And a second rectangular circuit that outputs a rectangular output signal of the resonance circuit.
According to the present invention as described above, the first and second rectangularization circuits are provided in the previous stage of the phase comparison circuit, so that the phase comparison circuit can perform highly accurate phase comparison.

According to another aspect of the present invention, there is provided an acceleration detecting apparatus including a phase shift circuit that is provided between the oscillation circuit and the resonance circuit and shifts an output signal of the oscillation circuit.
According to the present invention as described above, one of the output signals branched and output from the oscillation circuit is phase-shifted by the phase-shift circuit in accordance with the phase characteristics of the phase-comparison circuit, so that the phase comparison circuit has a highly accurate phase. A comparison can be made.

In the acceleration detecting device of the present invention, the phase shift circuit is a 90 ° phase shift circuit.
According to the present invention, the phase difference output from the phase comparison circuit is shifted by 90 ° in accordance with the phase characteristic of the phase comparison circuit. The direction of acceleration can be detected by the signal.
The acceleration detecting apparatus of the present invention is characterized in that the first and second tuning fork type vibration elements are double tuning fork type vibration elements. According to the present invention, the stress sensitivity of the tuning fork type vibration element can be increased.

In the acceleration detecting device of the present invention, the DC servo circuit feeds back a control voltage corresponding to the output signal of the differentiating circuit to the voltage-controlled variable capacitance circuit.
According to the present invention as described above, it is possible to perform correction in consideration of the drift of the differentiation circuit.

The acceleration detecting device according to the present invention further includes a buffer amplifier circuit that buffers an output signal output from the differentiating circuit, and the DC servo circuit supplies a control voltage corresponding to the output signal of the buffer amplifier circuit to the voltage-controlled variable capacitance circuit. It is characterized by feeding back.
According to the present invention as described above, correction can be performed by taking into account the drift of the buffer amplifier circuit and the differential circuit.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing the configuration of the acceleration detection device according to the first embodiment of the present invention.
The acceleration detection apparatus 1 shown in FIG. 1 includes an oscillation circuit 2, a first rectangular circuit (waveform shaping circuit) 3, a 90 ° phase shift circuit 4, a resonance circuit 5, a variable capacitance circuit 5a, and a second rectangular circuit. (Waveform shaping circuit) 6, phase comparison circuit 7, low-pass filter (hereinafter referred to as LPF) 8, differentiation circuit 9, buffer amplifier circuit (hereinafter referred to as buffer amplifier) 10, and DC servo circuit (hereinafter referred to as DC servo circuit) ) 11.
The oscillation circuit 2 includes a first tuning-fork type crystal vibrating element (first tuning-fork type vibrating element) 20a. The first tuning-fork type crystal vibrating element 20a functions as a resonator and also functions as an acceleration detecting element that detects acceleration. The output signal of the oscillation circuit 2 is branched and input to the first rectangularization circuit 3 and the 90 ° phase shift circuit 4.

The first rectangularizing circuit 3 is constituted by a comparator, for example, and converts the output signal from the oscillation circuit 2 into a rectangular wave signal and outputs it.
The 90 ° phase shift circuit 4 shifts the phase of the output signal output from the oscillation circuit 2 by 90 °, and then outputs it to the resonance circuit 5. Although depending on the configuration of the 90 ° phase shift circuit 4, the signal waveform that can be phase shifted in the 90 ° phase shift circuit 4 is normally a sine wave, so that the oscillation circuit 2 has a sine waveform as the output signal waveform. It is desirable to construct a circuit.
The resonance circuit 5 includes a second tuning-fork type crystal vibrating element (second tuning-fork type vibrating element) 20b and a voltage-controlled variable capacitance circuit 5a. The second tuning-fork type crystal vibrating element 20b and the variable capacitance circuit are provided. Based on the resonance frequency determined by 5a, the output signal of the 90 ° phase shift circuit 4 is phase-shifted and output. The variable capacitance circuit 5a is composed of, for example, a varicap diode that is a voltage-controlled variable capacitance element.

The second rectangularization circuit 6 is also constituted by a comparator, for example, and converts the output signal from the resonance circuit 5 into a rectangular wave signal and outputs it.
For example, the phase comparison circuit 7 compares the phases of the output signal from the first rectangularization circuit 3 and the output signal from the second rectangularization circuit 6 and outputs the comparison result. At this time, the phase comparison circuit 7 performs phase comparison based on the phase difference of 90 ° and outputs the phase difference as a phase difference signal. Note that when phase comparison is performed in the phase comparison circuit 7, at least one of the waveforms of the input signals needs to be rectangular, and in this embodiment, the first and second rectangles are respectively provided in the preceding stage of the phase comparison circuit 7. However, at least one of them may be provided.
If the output waveform of the oscillation circuit 2 is a rectangular wave, the first and second rectangularization circuits 3 and 6 are not necessarily provided. However, since the signal waveform input to the 90 ° phase shift circuit 4 or the like normally needs to be a sine waveform, when the 90 ° phase shift circuit 4 is provided, the output waveform of the VCXO 2 is a sine waveform and the phase When input to the comparison circuit 7, it is desirable that the first and second rectangularization circuits 3 and 6 make it rectangular.
Furthermore, if the levels of the two signals input to the phase comparison circuit 7 do not match, the detection result includes a value based on the difference in signal level in addition to the phase difference between the two input signals, and an accurate acceleration detection result You may not be able to get
Therefore, in order to prevent the occurrence of such a problem, it is desirable that the first and second rectangularization circuits 3 and 6 make a rectangle (waveform shaping).
The LPF 8 converts the phase difference signal output from the phase comparison circuit 7 into a direct current and outputs it.
The differentiation circuit 9 differentiates and outputs the output signal from the LPF 8.

Here, the function of the differentiating circuit 9 will be described.
For example, when acceleration detection is performed using a tuning fork type crystal vibrating element or the like as an acceleration sensor as in the present embodiment, the acceleration value and the frequency displacement of the sensor frequency are in a proportional relationship. That is,
Acceleration ∝Δ sensor frequency (FM detection output)
Will satisfy the relationship.
However, in the present embodiment, since the phase comparison circuit 7 compares the phases of two frequencies obtained from the acceleration sensor, the phase detection circuit 7 can obtain the phase detection output Φ. The phase detection output Φ is equal to the integral value of the Δ sensor frequency. That is,
Phase detection output Φ = ∫ sensor frequency (FM detection output)
Will satisfy the relationship.
Therefore, the acceleration detection device of the present embodiment is provided with a differentiating circuit 9, and in the differentiating circuit 9, an acceleration value is obtained by differentiating the phase detection output Φ output as an output signal from the LPF 8. That is,
The relationship of FM detection = dΦ / dt 関係 acceleration is satisfied.

The signal differentiated by the differentiating circuit 9 is output as an acceleration detection signal Sα via the buffer amplifier 10. A part of the signal output from the differentiation circuit 9 is input to the DC servo circuit 11.
The DC servo circuit 11 is composed of, for example, a time constant circuit composed of a resistor R and a capacitor C, an operational amplifier OP, etc., and delays the output signal of the LPF 8 and feeds it back to the variable capacitance circuit 5a of the resonance circuit 5 as a control voltage Vcont. I have to.

FIG. 2 is a diagram schematically showing a configuration of first and second tuning-fork type crystal vibrating elements provided in the acceleration detection device of the present embodiment.
As shown in FIG. 2, the first and second tuning-fork type crystal vibrating elements 20a and 20b include two vibrating arms 21a and 21b arranged in parallel, and extensions of the two vibrating arms 21a and 21b. It comprises a coupling portion 22 for coupling one end in the direction. The coupling portions 22 of the first and second tuning-fork type crystal vibrating elements 20a and 20b are fixed to substrates (not shown) on which the tuning-fork type crystal vibrating elements 20a and 20b are respectively mounted. Each coupling portion 22 is a fixed portion connected to the substrate. At this time, as shown in FIG. 2, the extension directions of the vibrating arms 21a and 21b of the first tuning-fork type crystal vibrating element 20a and the vibrating arms 21a and 21b of the second tuning-fork type crystal vibrating element 20b are defined as the acceleration detection axis direction. And the free ends of the vibrating arms 21a and 21b of the first tuning-fork type quartz vibrating element 20a and the free ends of the vibrating arms 21a and 21b of the second tuning-fork type quartz vibrating element 20b are arranged to face each other. Alternatively, the coupling portion 22 of the first tuning-fork type crystal resonator element 20a and the coupling portion 22 of the second tuning-fork type crystal resonator element 20b are arranged to face each other. That is, the extending directions of the vibrating arm 21a and the vibrating arm 21b are opposite to each other between the tuning fork type crystal vibrating elements 20a and 20b.

In the first and second tuning-fork type crystal vibrating elements 20a and 20b configured in this way, when an AC voltage is applied to a drive electrode (not shown), the two vibrating arms 21a and 21b arranged in parallel are symmetrical as indicated by broken lines. Bends and vibrates. Then, for example, when the acceleration α in the direction of the arrow shown in FIG. 2 is applied in the state of bending vibration, the first tuning-fork type crystal vibrating element 20a apparently has an inertial force that is opposite to the direction of the acceleration α. As a result, the vibrating arms 21a and 21b of the tuning-fork type crystal vibrating element 20a are subjected to tensile stress that is pulled in a direction opposite to the acceleration α. In this case, the frequency of the first tuning-fork type crystal vibrating element 20a becomes high due to the influence of tensile stress. On the other hand, since the inertial force in the direction opposite to the direction of the acceleration α is apparently generated also in the second tuning-fork type crystal vibrating element 20b, the vibration arms 21a and 21b of the tuning-fork type crystal vibrating element 20b are coupled to each other due to this influence. A compressive stress that compresses in the direction of the portion 22 is received. In this case, the frequency of the second tuning-fork type crystal vibrating element 20b is lowered due to the influence of compressive stress.
Therefore, in the present embodiment, the acceleration detection signal Sα is obtained based on the frequency change that occurs when acceleration is applied to the first and second tuning-fork type crystal vibrating elements 20a, 20b.

Such tuning-fork type crystal vibrating elements 20a and 20b have a wide dynamic range (for example, ± 3 g to ± 400 g) and high linearity (for example, 0.05% FS) compared to conventional MEMS acceleration sensors. There is an advantage that the temperature sensitivity stability is good.
Since the acceleration detection axis direction and the extending direction of the vibrating arms 21a and 21b can be made coincident with each other, it is advantageous for reducing the height in the direction perpendicular to the acceleration detection axis direction (direction perpendicular to the substrate surface).
In FIG. 2, the concept of the bending vibration of the tuning fork type crystal vibrating elements 20a and 20b is shown by a broken line for easy understanding. However, in practice, the shape of the tuning fork type crystal vibrating element 20 is hardly displaced. It is.

Hereinafter, the operation of the acceleration detection device 1 of the present embodiment will be described based on the characteristics of the tuning fork type crystal resonator element described above.
FIG. 3 is a diagram showing the phase shift characteristics of the resonance circuit 5.
Here, in order to make the explanation of the operation easy to understand, the operations accompanying the acceleration detection of the first tuning-fork type crystal vibrating element 20a and the second tuning-fork type crystal vibrating element 20b will be described separately.
First, the operation accompanying the acceleration detection in the first tuning-fork type crystal vibrating element 20a will be described.
The phase shift characteristic of the resonance circuit 5 in the constant speed motion state is set to a characteristic as shown by a solid line in FIG. In this case, in the resonance circuit 5, when a signal of frequency A is input, the phase difference between the input signal and the output signal output from the resonance circuit 5 is “0”.
Here, acceleration motion is generated in the extending direction of the vibrating arms 21a and 21b of the first tuning-fork type quartz vibrating element 20a, and an inertial force in the compression direction is applied to the vibrating arms 21a and 21b of the first tuning-fork type quartz vibrating element 20a. To do. Then, the frequency of the first tuning-fork type crystal resonator element 20a is affected by the inertial force. When the frequency of the first tuning-fork type crystal vibrating element 20a is decreased from the frequency A to the frequency B, the frequency of the signal input to the resonance circuit 5 is decreased from A to B, so that the input signal and the resonance circuit 5 are output. ΔAB is obtained as a phase difference with the signal.

On the other hand, when an inertial force in the compression direction is applied to the vibrating arms 21a and 21b of the first tuning-fork type quartz vibrating element 20a, the second tuning-fork type quartz vibrating element 20b provided in the resonance circuit 5 vibrates. Since the inertia force in the pulling direction is applied to the arms 21a and 21b, the frequency of the second tuning-fork type crystal vibrating element 20b is increased by the influence of the inertia force. In this case, the phase shift characteristic of the resonance circuit 5 changes from the characteristic indicated by the solid line in FIG. 3 to the characteristic indicated by the broken line. That is, the characteristics are shifted to the high frequency side as a whole.
Therefore, when the frequency of the first tuning-fork type crystal vibrating element 20a is decreased from the frequency A to the frequency B, the phase shift characteristic of the resonance circuit 5 is also changed, so that the phase of the signal output from the resonance circuit 5 is ΔAB. The phase difference of ΔAB ′ is about twice as large as the above.
Therefore, in the acceleration detecting apparatus 1 of this embodiment, the phase of the output signal of the resonance circuit 5 and the output signal of the oscillation circuit 2 are compared by the phase comparison circuit 7 and the phase comparison result is converted to DC by the LPF 8. Further, by differentiating with the differentiating circuit 9, acceleration is obtained using the first tuning-fork type crystal vibrating element 20 a provided in the oscillation circuit 2 and the second tuning-fork type crystal vibrating element 20 b provided in the resonance circuit 5. Further, two acceleration detecting elements (first tuning fork type crystal vibrating element 20a and second tuning fork type crystal vibrating element 20b) are arranged so that their vibrating arms are opposite to each other. Thus, the acceleration detection sensitivity can be increased.

Further, in the present embodiment, since it can be configured without providing a voltage-controlled oscillation circuit as in the prior art, oscillation stops even when a strong impact other than acceleration is applied, as in a conventional vibration sensor circuit. There is no such thing.
Furthermore, in the present embodiment, the first and second tuning-fork type crystal vibrating elements 20a and 20b are arranged opposite to the acceleration detection direction, so that the phase comparison circuit 7 is compared with the case where there is one tuning-fork type crystal vibrating element. The level of the phase difference signal output from can be increased about twice. As a result, the acceleration detection sensitivity can be increased approximately twice.
Further, when the acceleration sensor is configured by using the tuning fork type crystal vibrating elements 20a and 20b as in the present embodiment, the dynamic range is wider than that of the conventional MEMS acceleration sensor, and the sensitivity temperature is high. There is also an advantage that stability is good.

Furthermore, in this embodiment, a control voltage corresponding to the output of the LPF 8 is fed back to the variable capacitance circuit 5 a provided in the resonance circuit 5 via the DC servo circuit 11. When there is no feedback control by the DC servo circuit 11 as described above, for example, when the oscillation frequency of the oscillation circuit 2 or the resonance frequency of the resonance circuit 5 is changed due to temperature drift, the phase difference is in spite of the acceleration being “0”. Will occur. Incidentally, even when the frequency of the first and second tuning-fork type crystal vibrating elements 20a and 20b drifts in the same manner, a phase difference occurs due to the difference in the circuit configuration of the VCXO 2 and the resonance circuit 5.
Therefore, in the present embodiment, a control voltage corresponding to the output of the LPF 8 is fed back to the variable capacitance circuit 5a of the resonance circuit 5 via the DC servo circuit 11, for example, the oscillation frequency of the transmission circuit 2 and the resonance circuit 5 The temperature drift of the resonance frequency was corrected. As a result, it is possible to detect acceleration with high accuracy without being affected by temperature drift or the like.
Further, in the present embodiment, since the oscillation frequency of the reference oscillation circuit 2 is not controlled, there is an advantage that the oscillation conditions and the like are stabilized.

FIG. 4 is a block diagram showing the configuration of the acceleration detection device according to the second embodiment of the present invention. The same blocks as those in the acceleration detection apparatus 1 shown in FIG.
In the acceleration detection device 1 shown in FIG. 1, the voltage corresponding to the output of the LPF 8 is fed back to the variable capacitance circuit 5a of the resonance circuit 5 via the DC servo circuit 11, whereas the acceleration detection shown in FIG. The apparatus 30 is different in that the output voltage of the differentiation circuit 9 is fed back to the variable capacitance circuit 5a of the resonance circuit 5 via the DC servo circuit 11.
With this configuration, even if a drift occurs in the voltage based on the output of the phase comparison circuit 7 regardless of the constant acceleration state due to the influence of the electrical characteristics of the differentiation circuit 9, it is possible to correct the drift.

  FIG. 5 is a block diagram showing a configuration of an acceleration detection apparatus according to the third embodiment of the present invention. The same blocks as those in the acceleration detection apparatus 1 shown in FIG. The acceleration detection device 31 shown in FIG. 5 is different in that the output voltage of the buffer amplifier 10 is fed back to the variable capacitance circuit 5a of the resonance circuit 5 via the DC servo circuit 11. With this configuration, even if a drift occurs in the voltage based on the output of the phase comparison circuit 7 regardless of the constant acceleration state due to the influence of the electrical characteristics of the differentiation circuit 9 and the buffer amplifier 10, it is possible to correct the drift. Therefore, a more accurate acceleration detection result can be obtained.

The configurations of the first and second tuning-fork type crystal vibrating elements 20a and 20b described so far are merely examples, and the tuning-fork type crystal vibrating element of the present invention is, for example, a double tuning fork type crystal vibrating element as shown in FIG. It is also possible to use children.
A double tuning fork type crystal vibrating element 23 shown in FIG. 6 includes two vibrating arms 21a and 21b arranged in parallel and a coupling portion 22a in which both ends of the extending directions of the two vibrating arms 21a and 21b are coupled. 22b. In this case, for example, only one of the coupling portions 22a and 22b is fixed to a substrate (not shown) on which the double tuning fork type crystal vibrating element 23 is mounted, and the other is a free end. good. The coupling portion 22a is a fixed portion that is connected to the substrate.
When the acceleration detecting device of the present embodiment is configured using the double tuning fork type crystal vibrating element 23, since the coupling portion 22b on the free end side functions as a weight, a large inertia force can be generated. Acceleration sensitivity can be increased compared to the type quartz resonator elements 20a and 20b.

In the present embodiment, the 90 ° phase shift circuit 4 is provided between the oscillation circuit 2 and the resonance circuit 5 as a phase shift circuit that shifts the sine wave signal output from the oscillation circuit 2. The phase shift circuit is not necessarily a 90 ° phase shift circuit. Further, depending on the characteristics of the phase comparison circuit 7, it is not always necessary to provide a phase shift circuit. However, a phase shift circuit is provided between the oscillation circuit 2 and the resonance circuit 5, and one of the output signals branched and output from the oscillation circuit 2 is phase-shifted in accordance with the phase characteristics of the phase comparison circuit 7. The phase comparison circuit 7 can reliably detect the phase difference between the output signals output from the first and second tuning-fork type crystal vibrating elements.
In particular, when the phase comparison circuit 7 is a 90 ° phase comparison circuit and a 90 ° phase shift circuit is provided as a phase shift circuit as in the present embodiment, the first and second tuning-fork type crystal vibrating elements in the phase comparison circuit 7 It becomes possible to detect the direction of acceleration from the phase difference of the output signals output from. That is, in FIG. 2, it is possible to detect whether the direction is the direction of the acceleration α or the direction opposite to the acceleration α.

That is, when the phase comparison circuit 7 is a 0 ° phase comparison circuit, the phase comparison circuit 7 can obtain an output result in which the phase difference becomes large in any situation where the acceleration increases or decreases from the constant speed state. Therefore, in this case, the direction of acceleration cannot be confirmed.
On the other hand, in the configuration in which the phase comparison circuit 7 is a 90 ° phase comparison circuit and the 90 ° phase shift circuit 4 is provided as in the present embodiment, the output result of the phase comparison circuit 7 is, for example, an acceleration from a constant speed state If so, a signal with a large phase difference is obtained, and if the vehicle is decelerated from a constant speed state, a signal with a small phase difference is obtained. Therefore, in this case, the direction of acceleration can be confirmed.
In the present embodiment, since the output signal waveform of the oscillation circuit 2 is a sine wave, the first rectangular circuit is provided in front of the phase comparison circuit 7. For example, the oscillation circuit 2 is connected to the sine wave signal. The first rectangular circuit 3 does not need to be provided as long as it is a two-output crystal oscillator with a rectangular wave signal.

FIG. 7 is a diagram showing a circuit configuration example of a two-output type crystal oscillator.
In the two-output type crystal oscillator shown in FIG. 7, the inverter circuit 40 is constituted by a series connection of three CMOS inverters IC11, IC12, and IC13.
In this case, first feedback resistors R11, R12, and R13 for self-bias are connected in parallel between the inputs and outputs of the CMOS inverters IC11, IC12, and IC13. Between the input of the CMOS inverter IC11 and the output of the CMOS inverter IC12, a series circuit in which the crystal resonator element 20, the variable capacitor TC, and the capacitor C11 are connected in series as the positive feedback circuit 41 is connected in parallel.
The connection point between the capacitor C11 and the variable capacitor TC is connected to the output of the CMOS inverter IC13, which is the output of the inverter circuit 40, via the second feedback resistor R14. A capacitor C12 is provided between the connection point between the capacitor C11 and the variable capacitor TC and the ground (GND). Further, a capacitor C13 for noise removal is connected to the output of the inverter circuit 40.

In the two-output type crystal oscillator configured as described above, a rectangular wave signal can be obtained from the CMOS inverter IC 13 of the inverter circuit 40.
Further, the rectangular wave signal output from the inverter circuit 40 is positively fed back to the input side of the inverter circuit 40 via the second feedback resistor R14, the variable capacitor TC, and the crystal resonator element 20. At this time, since the crystal resonator element 20 functions as a filter, a square wave signal positively fed back from the output side of the inverter circuit 40 to the input side of the inverter circuit 40 via the crystal resonator element 20 is spurious in the crystal resonator element 20. Ingredients are filtered.
Therefore, the feedback signal that was a rectangular wave on the output side of the inverter circuit 40 becomes a sine wave on the input side. Therefore, in this case, the two-output type crystal oscillator outputs a sine wave signal from the input side of the inverter circuit 40. In this way, it is possible to output a rectangular wave signal and a sine wave signal from one circuit.

It is the figure which showed the structure of the acceleration detection apparatus which concerns on the 1st Embodiment of this invention. It is the figure which showed the structure of the tuning fork type crystal vibrating element. It is the figure which showed the phase shift characteristic of the resonance circuit. It is the figure which showed the structure of the acceleration detection apparatus which concerns on the 2nd Embodiment of this invention. It is the figure which showed the structure of the acceleration detection apparatus which concerns on the 3rd Embodiment of this invention. It is the figure which showed the structure of the double tuning fork type crystal vibrating element. It is the figure which showed the circuit structural example of the 2 output type | mold crystal oscillator. It is the figure which showed the structure of the conventional vibration type sensor circuit.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Acceleration detection apparatus, 2 ... Oscillator circuit, 3 ... 1st rectangular circuit, 4 ... 90 degree phase shift circuit, 5 ... Resonance circuit, 5a ... Variable capacity circuit, 6 ... 2nd rectangular circuit, 7 ... Phase comparison circuit, 8 ... LPF, 9 ... differentiation circuit, 10 ... buffer amplifier, 11 ... DC servo circuit, 20a, 20b ... tuning fork type crystal vibrating element, 21a, 21b ... vibrating arm, 22 ... coupler, 23 ... double tuning fork Type quartz vibrating element, 30, 31 ... acceleration detecting device

Claims (7)

An oscillation circuit including a first tuning-fork type vibration element as a resonance element;
A second tuning fork type vibration element and a voltage control type variable capacitance circuit, and output from the oscillation circuit based on a resonance frequency determined by the second tuning fork type vibration element and the voltage control type variable capacitance circuit; A resonant circuit for phase shifting the output signal;
A phase comparison circuit for comparing the phase of the output signal output from the oscillation circuit and the output signal output from the resonance circuit;
A low-pass filter for converting the phase difference signal output from the phase comparison circuit into a direct current,
A differentiating circuit for differentiating an output signal output from the low-pass filter;
A DC servo circuit that includes a time constant circuit and feeds back a control voltage in accordance with an output signal after the low-pass filter to the voltage-controlled variable capacitance circuit;
The first and second tuning-fork type vibration elements each include two vibrating arms arranged in parallel, and a coupling portion that couples one end in the extension direction of the two vibrating arms. An output output from the differentiating circuit after the extending direction of each vibrating arm of the second tuning-fork type vibration element is made coincident with the acceleration detection direction and the first and second tuning-fork type vibration elements are arranged to face each other. An acceleration detection apparatus characterized by outputting a signal as an acceleration detection signal. A first rectangular circuit that is provided between the oscillation circuit and the phase comparison circuit and that outputs the rectangular output signal of the oscillation circuit;
The acceleration according to claim 1, further comprising: a second rectangularization circuit that is provided between the resonance circuit and the phase comparison circuit and that outputs an output signal of the resonance circuit by making it rectangular. Detection device.   The acceleration detecting apparatus according to claim 1, further comprising a phase shift circuit provided between the oscillation circuit and the resonance circuit and phase-shifting an output signal of the oscillation circuit.   The acceleration detection device according to claim 3, wherein the phase shift circuit is a 90 ° phase shift circuit.   The acceleration detecting device according to any one of claims 1 to 4, wherein the first and second tuning fork type vibration elements are double tuning fork type vibration elements.   6. The acceleration detecting apparatus according to claim 1, wherein the DC servo circuit feeds back a control voltage corresponding to an output signal of the differentiating circuit to the voltage-controlled variable capacitance circuit.   A buffer amplifier circuit for buffering an output signal output from the differentiating circuit; and the DC servo circuit feeds back a control voltage corresponding to the output signal of the buffer amplifier circuit to the voltage-controlled variable capacitance circuit. The acceleration detection device according to any one of claims 1 to 5.

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