JP2008190884A - Acceleration sensing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acceleration sensing device excellent in stability in temperature sensitivity. <P>SOLUTION: The acceleration sensing device comprises: an OSC 2 provided with the first tuning fork type quarts oscillator element 20a as a resonator; a VCXO 4 provided with the second tuning fork type quartz vibration element 20b as a resonator; a phase comparison circuit 3 for comparing the phase of the output signal output from the VCXO 4 and the phase of the reference signal output from the OSC 2; an LPF 5 for extracting the low-pass component of phase difference signal output from the phase comparison circuit 3; a differential circuit 6 for differentiating output signal from the LPF 5; and the DC servo circuit 8 for feeding back the control voltage to the VCXO 4 corresponding to the output signal of the LPF 5 provided with the time constant circuit. The output signal from the differential circuit 6 is output as the acceleration signal by arranging such that the first and the second tuning fork type quarts oscillator elements 20a, 20b are coincident with their acceleration detection axes but the acceleration detection directions of the first and the second tuning fork type quarts oscillator elements 20a, 20b are arranged in the reverse directions. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an acceleration detection device that detects acceleration using a piezoelectric vibration element.

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. 6 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. 6 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

Incidentally, the MEMS sensor manufactured by the semiconductor process as described above or the vibration type sensor circuit 100 shown in FIG. 6 has a drawback that an error occurs in the acceleration sensitivity due to the ambient temperature because the frequency-temperature characteristic is poor.
In addition, the MEMS sensor has a drawback in that the sensor is destroyed when a strong acceleration exceeding a specified value is applied.
The present invention has been made in view of the above-described points, and an object of the present invention is to provide an acceleration detection device having excellent temperature sensitivity stability. It is another object of the present invention to provide an acceleration detection device that is not destroyed even when strong acceleration is applied.

To achieve the above object, an oscillation circuit including a first stress sensitive element as a resonator, a voltage control type piezoelectric oscillation circuit including a second stress sensitive element as a resonator, and an output output from the oscillation circuit Output from the phase comparison circuit that compares the phase of the signal and the output signal output from the voltage-controlled piezoelectric oscillation circuit, the low-pass filter that extracts the low-frequency component of the phase difference signal output from the phase comparison circuit, and the low-pass filter And a DC servo circuit that feeds back a control voltage corresponding to the output signal of the low-pass filter to the voltage-controlled piezoelectric oscillation circuit. The first and second stress-sensitive elements have accelerations. A differential circuit in which the acceleration detection axis directions to be detected are made coincident and the acceleration detection directions to be detected in the first and second stress sensitive elements are opposite to each other. An output signal to output as an acceleration detection signal.
According to the present invention, the phase of the output signal of the oscillation circuit and the output signal of the voltage control type piezoelectric oscillation circuit are compared by the phase comparison circuit, the phase comparison result is converted into a direct current by the low-pass filter, and further, the differentiation circuit is used. By differentiating, acceleration can be detected using the first stress sensitive element provided in the oscillation circuit and the second stress sensitive element provided in the voltage control type piezoelectric oscillation circuit.
Further, since it can be configured without providing a voltage-controlled oscillation circuit as in the prior art, oscillation does not stop even when a strong impact other than acceleration is applied unlike the conventional vibration sensor circuit.

  In the acceleration detecting device of the present invention, the first and second stress sensitive elements are constituted by the first and second tuning fork type vibration elements, and the first and second tuning fork type vibration elements are respectively arranged in parallel. Two vibrating arms and a coupling portion for coupling one ends of the extending directions of the two vibrating arms, and the extending directions of the vibrating arms of the first and second tuning-fork type vibrating elements are defined as acceleration detection axis directions It is characterized by matching. According to the present invention, the tuning fork type vibration element can be used as the first and second stress sensitive elements for detecting acceleration.

  In the acceleration detecting device of the present invention, the first and second stress sensitive elements are constituted by first and second double tuning fork type vibration elements, and the first and second double tuning fork type vibration elements are respectively connected in parallel. It is a double tuning fork type vibration element having two arranged vibrating arms and a coupling part that couples both ends in the extending direction of the two vibrating arms, and either one of the coupling parts is a fixed end, and the other , And the extension direction of the two vibrating arms is arranged so as to coincide with the acceleration detection direction. According to the present invention as described above, since it is possible to use a double tuning fork type vibration element as the first and second stress sensitive elements for detecting acceleration, stress sensitivity can be improved as compared with the case where a tuning fork type vibration element is used. Can be increased.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of an acceleration detection device according to an embodiment of the present invention.
1 includes an oscillation circuit (hereinafter referred to as OSC (Oscillator)) 2, a phase comparison circuit 3, and a voltage controlled crystal oscillation circuit (hereinafter referred to as VCXO (Voltage Controlled Crystal Oscillator)) 4. , A low-pass filter (hereinafter referred to as LPF) 5, a differentiation circuit 6, a buffer amplifier circuit (hereinafter referred to as buffer amplifier) 7, and a DC servo circuit 8.
The OSC 2 includes, for example, a first tuning-fork type crystal vibrating element 20a as a first stress sensitive element, and oscillates at a predetermined frequency.
The phase comparison circuit 3 compares the phase of the output signal output from the OSC 2 with the phase of the output signal output from the VCXO 4 and outputs the comparison result.

The VCXO 4 includes a second tuning-fork type crystal vibrating element 20b having the same characteristics as the first tuning-fork type crystal vibrating element 20a as a second stress sensitive element. The second tuning-fork type crystal vibrating element 20b functions as a resonator of the VCXO 4 and also functions as an acceleration detecting element that detects acceleration. In the VCXO4, the output signal of the DC servo circuit 8 is applied as a control voltage Vcont to the variable capacitance diode of the VCXO4, thereby changing the load capacity of the oscillation loop so that the oscillation frequency of the output signal becomes constant. However, as will be described later, the DC servo circuit 8 includes a time constant circuit so that the frequency tracking speed of the VCXO 4 is slow.
The LPF 5 converts the phase difference signal output from the phase comparison circuit 3 into a direct current and outputs it. The output signal of the LPF 5 is output to the differentiation circuit 6 and a part thereof is also input to the DC servo circuit 8.

The differentiation circuit 6 differentiates and outputs the phase difference signal from the LPF 5.
Here, the function of the differentiating circuit 6 will be described.
For example, when performing acceleration detection 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, the relationship of acceleration ∝Δ sensor frequency (FM detection output) is satisfied.
However, in this embodiment, since the phase comparison circuit 3 compares the frequency obtained from the OSC 2 and the frequency obtained from the VCXO 4, the phase detection output Φ is obtained from the phase comparison circuit 3. . This phase detection output Φ is equal to the integral value of the Δ sensor frequency. That is, the relationship of phase detection output Φ = ∫ sensor frequency (FM detection output) is satisfied. Therefore, in the acceleration detection device of the present embodiment, the differentiation circuit 6 is provided after the LPF 5, and the differentiation value is obtained by differentiating the phase detection output Φ output from the LPF 5 in the differentiation circuit 6. That is, the relationship of FM detection = dΦ / dt∝acceleration is satisfied.

The DC servo circuit 8 is constituted by a time constant circuit including, for example, a resistor R and a capacitor C, an operational amplifier OP, and the like, and delays an output signal from the LPF 5 and feeds it back to the VCXO 4 as a control voltage Vcont.
In the acceleration detection device 1 of the present embodiment configured as described above, the phase comparison circuit 3 compares the phases of the output signal of the OSC 2 and the output signal of the VCXO 4, and the phase comparison result is converted into a direct current by the LPF 5 and further differentiated Differentiation by the circuit 6 makes it possible to detect acceleration using the first tuning-fork type crystal vibrating element 20a provided in the OSC2 and the second tuning-fork type crystal vibrating element 20b provided in the VCXO4. .

  Further, in the acceleration detection device 1 of the present embodiment, a control voltage corresponding to the output of the LPF 5 is fed back to the VCXO 4 via the DC servo circuit 8. When there is no feedback control by the DC servo circuit 8 as described above, for example, when the oscillation frequency of the OSC 2 or the resonance frequency of the VCXO 4 changes due to temperature drift, a phase difference occurs even though the acceleration is “0”. . Incidentally, even when the frequency of the first and second tuning-fork type crystal vibrating elements 20a and 20b drifts in the same manner, the difference between the circuit configurations of the OSC2 and the VCXO4, the first and second tuning-fork type crystal vibrating elements 20a, A phase difference occurs due to a difference in aging (aging) of 20b. Therefore, in the present embodiment, a control voltage corresponding to the output of the LPF 5 is fed back to the VCXO 4 via the DC servo circuit 8 so that, for example, the temperature drift of the resonance frequency of the VCXO 4 or OSC 2 is corrected. As a result, it is possible to detect the acceleration with high accuracy without the influence of the temperature drift or the like at a low cost without adding a temperature compensation circuit or the like to the OSC 2.

FIG. 2 is a diagram showing an example of the circuit configuration of the VCXO 4 described above.
The VCXO 4 shown in FIG. 2 includes a phase inverting amplifier (hereinafter referred to as a MOS inverter) IC1 as an oscillation circuit. Between the input and output of the MOS inverter IC1, a series circuit in which a feedback resistor R1 and a capacitor C1 for self-bias and a tuning fork type crystal resonator element 20b are connected in series is connected in parallel. Further, a capacitor C2 is connected between the connection point between the output terminal of the MOS inverter IC1 and the tuning fork type crystal vibrating element 20b and the ground (GND), and the connection point between the capacitor C1 and the tuning fork type crystal vibrating element 20b and the ground (GND). A variable capacitance diode D1 is connected between them. The variable capacitance diode D1 has an anode connected to the ground side and a cathode connected to the tuning fork type crystal vibrating element 20b.

  In the VCXO 4 configured as described above, an oscillation loop is configured by the tuning fork type crystal vibrating element 20b, the capacitors C1 and C2, and the variable capacitance diode D1. Therefore, by applying the control voltage Vcont to the cathode of the variable capacitance diode D1 constituting the oscillation loop via the resistor R2 to vary the capacitance of the variable capacitance diode D1, the load capacitance of the oscillation loop is changed to change the oscillation frequency. Is configured to be controllable so as to have a predetermined oscillation frequency. Further, the VCXO4 using such a MOS inverter IC1 has a rectangular output signal waveform.

FIG. 3 is a diagram schematically showing the configuration of the tuning fork type crystal vibrating elements 20a and 20b.
As shown in FIG. 3, the first and second tuning-fork type crystal vibrating elements 20a, 20b have the same acceleration detection axis direction for detecting acceleration, and the first and second tuning-fork type crystal vibrating elements 20a, It arrange | positions so that the acceleration detection direction detected in 20b may become reverse direction. That is, it includes two vibrating arms 21a and 21b arranged in parallel, and a coupling portion 22 that couples one end in the extending direction of the two vibrating arms 21a and 21b. 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. The coupling portion 22 is a fixed portion that is connected to the substrate. At this time, as shown in FIG. 3, 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 an acceleration α in the direction of the arrow shown in FIG. 3 is applied in the state of bending vibration, the inertial force in the direction opposite to the direction of the acceleration α is apparently applied to the first tuning-fork type crystal vibrating element 20a. 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 a frequency change that occurs when acceleration is applied to the first and second tuning-fork type crystal vibrating elements 20a, 20b.
In this case, the tuning fork type crystal resonator 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 the conventional MEMS acceleration sensor. There is an advantage that the temperature sensitivity stability is good. In addition, power consumption can be reduced. In addition, since the acceleration detection axis direction and the extending direction of the vibrating arms 21a and 21b can be matched, it is advantageous in reducing the height in the direction perpendicular to the acceleration detection axis direction (direction perpendicular to the substrate surface). In FIG. 3, 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. Therefore, in the acceleration detecting device 1 of the present embodiment, the element itself is not damaged even when a strong acceleration exceeding a specified value is applied.

In the present embodiment, the first and second tuning-fork type crystal vibrating elements 20a and 20b having the same performance are arranged opposite to the acceleration detection direction, so that compared with the case where there is one tuning-fork type crystal vibrating element. The level of the phase difference signal output from the phase comparison circuit 3 can be increased about twice. As a result, the acceleration detection sensitivity can be increased approximately twice.
For example, in the conventional vibration sensor circuit 100 shown in FIG. 6, it is conceivable to use the DC output (control voltage) of the phase comparator 102c of the drive circuit 102 as a stress value signal (acceleration signal). However, normally, an LC resonator or a CR resonator is used as the voltage controlled oscillator 102a, and the voltage controlled oscillator 102a having such a resonator has a large amount of frequency change with respect to the control voltage Vcont as shown in FIG. That is, the frequency sensitivity characteristic is high. For this reason, when the control voltage Vcont of the phase comparator 102c is used as the detection result of the stress value signal (acceleration signal) without using the resonance frequency as the detection result in the conventional vibration sensor circuit 100, the control voltage for the frequency change amount is used. A sensor with a small change amount of Vcont and high detection sensitivity cannot be realized.
On the other hand, in the acceleration detection device 1 of the present embodiment, the control voltage of the VCXO 4 is used as an acceleration signal. Since VCXO4 has a narrow frequency variable range for the control voltage compared to the VCO (frequency control sensitivity is low), the change in the output voltage (control voltage) of the LPF 5 with respect to the frequency change accompanying the acceleration operation is increased (high potential). ). As a result, a highly sensitive sensor can be realized with respect to acceleration changes.

In the present embodiment described so far, the tuning fork type crystal vibrating element 20 has been described as an example of the stress sensitive element. However, this is merely an example, and as the stress sensitive element, for example, a double tuning fork type crystal as shown in FIG. It is also possible to use a vibration element.
The double tuning fork type crystal vibrating element 23 shown in FIG. 5 includes two vibrating arms 21a and 21b arranged in parallel, and a coupling portion 22a in which both ends in the extending direction 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 set as a free end. do it.
When the acceleration detecting device of the present embodiment is configured using the double tuning fork type crystal vibrating element 23, the coupling portion 22b on the free end side functions as a weight, so that the acceleration sensitivity is higher than that of the tuning fork type crystal vibrating element 20 described above. be able to.
In the present embodiment, a tuning fork type vibration element has been described as an example of the stress sensitive element. However, this is only an example, and so-called AT-cut crystal vibration is used as long as the resonance frequency changes according to acceleration. Various piezoelectric vibration elements such as a child and a resonator can be applied as a stress sensitive element.

It is the figure which showed the structure of the acceleration detection apparatus which concerns on embodiment of this invention. It is the figure which showed an example of the circuit structure of VCXO. It is the figure which showed the structure of the tuning fork type crystal vibrating element. It is the figure which showed the frequency sensitivity characteristic of VCXO and VCO. It is the figure which showed the structure of the double tuning fork type crystal vibrating element. 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 ... Oscillation circuit, 3 ... Phase comparison circuit, 4 ... VCXO, 5 ... LPF, 6 ... Differentiation circuit, 7 ... Buffer amplifier, 8 ... DC servo circuit, 20 ... Tuning fork type crystal vibration element, 21a , 21b, each vibrating arm, 22, 22a, 22b, a coupling portion, 23, a double tuning fork type crystal vibrating element

Claims (3)

An oscillation circuit including a first stress sensitive element as a resonator;
A voltage-controlled piezoelectric oscillation circuit including a second stress-sensitive element as a resonator;
A phase comparison circuit for comparing the phase of the output signal output from the oscillation circuit and the output signal output from the voltage-controlled piezoelectric oscillation circuit;
A low pass filter for extracting a low frequency component of the phase difference signal output from the phase comparison circuit;
A differentiating circuit for differentiating an output signal output from the low-pass filter;
A DC servo circuit that feeds back a control voltage corresponding to the output signal of the low-pass filter to the voltage-controlled piezoelectric oscillation circuit,
The first and second stress sensitive elements are arranged so that the acceleration detection axis directions for detecting acceleration coincide with each other and the acceleration detection directions detected by the first and second stress sensitive elements are opposite to each other. Then, the acceleration detection device outputs the output signal of the differentiation circuit as an acceleration detection signal. The first and second stress sensitive elements are constituted by first and second tuning fork type vibration elements,
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. 2. The extending direction of each vibrating arm of the second tuning-fork type vibration element is made to coincide with the acceleration detection axis direction, and the first and second tuning-fork type vibration elements are arranged to face each other. Acceleration detection device.   The first and second stress sensitive elements are constituted by first and second double tuning fork type vibration elements, and the first and second double tuning fork type vibration elements are respectively arranged in parallel. A double tuning fork type vibration element having a vibrating arm and a coupling portion in which both ends in the extending direction of the two vibrating arms are coupled, one of the coupling portions being a fixed end and the other being a free end, 2. The acceleration detecting apparatus according to claim 1, wherein the extending direction of the two vibrating arms is made coincident with the acceleration detecting direction, and the first and second double tuning fork type vibrating elements are arranged to face each other.

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