JP2012156946A - Oscillation circuit and vibration type sensor using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oscillation circuit capable of realizing stable oscillation of the oscillation circuit by reducing the effect of parasitic resistance and parasitic capacitance of a vibrator on the resonance characteristic (Q value, gain, etc.), with improved measurement accuracy of a vibration type sensor, and to provide the vibration type sensor using the same.SOLUTION: A current voltage conversion circuit which converts an output current signal of an electrostatic drive type vibrator (fixed electrode 1 and vibrator 3) to a voltage signal includes a calculation amplifier 14 and a negative impedance conversion circuit 10 equipped with resistors 11, 12, and 13.

Description

  The present invention relates to an oscillation circuit that can improve the measurement accuracy of a vibration sensor by reducing the influence of parasitic resistance and capacitance of the vibrator, and a vibration sensor using the oscillation circuit.

  Various physical quantity measuring devices that measure physical quantities such as pressure using a vibration sensor have been proposed. For example, in the case of a vibration sensor using an electrostatic drive type vibrator, the physical quantity is measured based on the frequency of the vibrator that vibrates according to a change in electrostatic attraction force acting between the vibrator and the electrode. As a physical measurement device using a vibration sensor using such an electrostatic drive type vibrator, for example, there is one disclosed in Japanese Patent Application Laid-Open No. 2009-257807.

  FIG. 4 shows a basic configuration diagram of a vibration type sensor using a conventional electrostatic drive type vibrator. In the figure, a vibration sensor 102 includes a fixed electrode 1, a vibrator 3, a current-voltage conversion circuit 20, an absolute value circuit 30, a drive unit including an error amplifier 40 and an auto gain control circuit 50, a Schmitt. And a trigger 60. Here, the vibrator 3 is placed opposite to the fixed electrode 1 at a predetermined interval and has a natural frequency determined by its shape (for example, the shape of a beam).

  Further, the fixed electrode 1 to which the bias voltage Vb is applied, the electrostatic attraction force acting between the fixed electrode 1 and the vibrator 3, the vibrator 3, the current-voltage conversion circuit 20, the drive unit, and the fixed electrode of the self-excited signal Vi A self-excited circuit (positive feedback loop) that vibrates the vibrator 3 at the natural frequency is formed by a series of loops of feedback to 1.

JP 2009-257807 A

  In general, in the case of a vibration sensor using a vibrator such as a piezoelectric vibrator, it is known that an extremely high resolution, reproducibility, and stability can be obtained by increasing the Q value (resonance sharpness) of the vibrator. It has been. When the vibrator is viewed as an electric circuit element, the resonance characteristic is evaluated by a two-terminal vibrator, that is, a parallel circuit of a series circuit of an equivalent series resistance Rme, a series inductance Lme, and a series capacity Cme and a parallel capacity C0. it can.

  However, in practice, in the vibrator manufacturing process, it is inevitable that parasitic resistance and parasitic capacitance are formed due to the structure, and these deteriorate the resonance characteristics (Q value, gain, etc.) of the vibrator. There was a circumstance that the measurement accuracy of the vibration sensor was lowered.

For example, the parasitic resistance is represented as an equivalent circuit having parasitic resistances Rp1 and Rp2 as shown in FIG. At this time, when the Q value Q ₁₀ and the gain G ₁₀ are obtained for the voltage signal Vo that is the output of the current-voltage conversion circuit 20 of FIG.
(Equation 1)
Q ₁₀ = (Lme / Cme) ^1/2 / (Rme + Rp1 + Rp2) (1)
G ₁₀ = −Rf / (Rme + Rp1 + Rp2) (2)
Here, it is assumed that the resistance value of the feedback resistor 27 of the current-voltage conversion circuit 20 is Rf, and that the parallel capacitor C0 can be ignored as the parallel capacitor C0 >> the series capacitor Cme.

In the equations (1) and (2), compared to the ideal case where there is no parasitic resistance (Rp1 = Rp2 = 0), when the parasitic resistance is formed and Rp1 and Rp2 have finite values, the Q value Q it can be seen that the decrease in both ₁₀ and gain _{G 10.} Such a decrease in the Q value decreases the stability of oscillation, and in some cases, oscillation may not be possible. In addition, a decrease in gain causes a deterioration in the SN ratio (signal to noise ratio).

The present invention has been made in view of the above-described conventional circumstances, and can reduce the influence on the resonance characteristics (Q value, gain, etc.) due to the parasitic resistance and parasitic capacitance of the vibrator and realize stable oscillation. An object is to provide an oscillation circuit.
Another object of the present invention is to provide a vibration sensor using an oscillation circuit that can improve measurement accuracy.

  In order to solve the above problems, an oscillation circuit according to the present invention is an oscillation circuit including a vibrator and a current-voltage conversion circuit that converts an output current signal of the vibrator into a voltage signal, and the current The voltage conversion circuit is a negative impedance conversion circuit.

  In the above invention, the negative impedance converter circuit includes an operational amplifier, one end connected to one input terminal of the operational amplifier, the other end connected to the output terminal of the operational amplifier, and the vibration connected to the one end. A first circuit to which the output current signal of the child is input, a second circuit in which one end is connected to the other end of the first circuit, and the other end is connected to the other input terminal of the operational amplifier; And a third circuit connected to the other end of the second circuit and connected to the power supply potential at the other end.

  In the above invention, the first circuit, the second circuit, and the third circuit are each configured by a resistance element.

  In the invention described above, the first circuit and the second circuit are each configured by a resistance element, and the third circuit is configured by a capacitive element.

  In the above invention, the first circuit is constituted by a parallel circuit of a resistance element and a capacitive element, and the second circuit and the third circuit are each constituted by a resistance element.

  In the above invention, the vibrator is an electrostatic drive vibrator, a crystal vibrator, a surface acoustic wave vibrator, a silicon vibrator, or a ceramic vibrator.

  Furthermore, a physical quantity to be measured acts on the vibrator using the oscillation circuit.

  According to the oscillation circuit according to the present invention, the influence on the resonance characteristics (Q value, gain, etc.) due to the parasitic resistance and parasitic capacitance of the vibrator can be reduced or canceled, and stable oscillation of the oscillation circuit can be realized. In addition, an oscillation circuit that can improve the measurement accuracy of the vibration sensor can be provided. In addition, the measurement accuracy of the vibration sensor using the oscillation circuit can be improved.

It is a block diagram of the vibration type sensor using the oscillation circuit which concerns on one Example of this invention. It is explanatory drawing of the oscillation circuit used with the vibration type sensor of an Example. It is explanatory drawing of the oscillation circuit used with the vibration type sensor of a modification. It is a block diagram of the conventional vibration type sensor.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the drawings. In the following description, the vibrator used for the oscillation circuit is described as an electrostatic drive vibrator. However, the present invention is not limited to this, and the electrostatic drive vibrator may be replaced with another piezoelectric vibrator such as a quartz crystal vibrator. Even when the element is replaced with a child, a surface acoustic wave vibrator, a silicon vibrator, a ceramic vibrator, or the like, the same effect is obtained.

FIG. 1 is a configuration diagram of a vibration type sensor using an oscillation circuit according to an embodiment of the present invention. In the figure, the same reference numerals are given to the portions overlapping with FIG. 4 (conventional example).
In the figure, a vibration sensor 101 of this embodiment includes a fixed electrode 1, a vibrator 3, a negative impedance conversion circuit 10, an absolute value circuit 30, an error amplifier 40, and an auto gain control circuit 50. The driving unit and the Schmitt trigger 60 are provided. In the present embodiment, the vibrator referred to in the claims is an electrostatic drive vibrator, and corresponds to the fixed electrode 1 and the vibrator 3 in FIG.

  Here, the vibrator 3 is disposed to face the fixed electrode 1 at a predetermined interval. The vibrator 3 has a natural frequency determined by its shape (for example, the shape of a beam), and a self-excited circuit that vibrates the vibrator 3 at the natural frequency is formed. That is, the fixed electrode 1 to which the bias voltage Vb is applied, the electrostatic attractive force acting between the fixed electrode 1 and the vibrator 3, the vibrator 3, the negative impedance conversion circuit 10, the drive unit, and the self-excited signal Vi are fixed. A self-excited circuit (positive feedback loop) that vibrates the vibrator 3 at the natural frequency is formed by a series of loops of feedback to the electrode 1.

  The vibration operation of the vibrator 3 will be briefly described. A bias voltage Vb is applied between the fixed electrode 1 and the vibrator 3 via a resistor 73. The fixed electrode 1 is driven by a self-excited signal Vi. The frequency of the self-excited signal Vi matches the natural frequency of the vibrator 3. Since the voltage applied to the fixed electrode 1 is changed by the self-excited signal Vi, the vibrator 3 vibrates at a natural frequency according to a change in electrostatic attraction force acting between the fixed electrode 1 and the vibrator 3. . At this time, an electrostatic current flows from the fixed electrode 1 to the vibrator 3 via a capacitance formed between the fixed electrode 1 and the vibrator 3. This electrostatic current is output from the vibrator 3.

  The current signal io that is the output of the vibrator 3 is converted into a voltage signal Vo by the negative impedance conversion circuit 10. That is, in the conventional configuration (FIG. 5), the current / voltage conversion circuit 20 converts the current signal io to the voltage signal Vo, but in the configuration of this embodiment, the conversion is performed by the negative impedance conversion circuit 10. The effects obtained by replacing the conventional current-voltage conversion circuit 20 with the negative impedance conversion circuit 10 will be described later.

  The converted voltage signal Vo is input to the Schmitt trigger 60, the absolute value circuit 30, and the auto gain control circuit 50, respectively. The Schmitt trigger 60 generates a frequency signal obtained by shaping the waveform of the voltage signal Vo into a binary digital signal, as indicated by the signal waveform appended in the figure. The frequency signal is supplied to an arithmetic processing unit (not shown) of the physical quantity measuring device, and a physical quantity such as a pressure to be measured is obtained.

  The absolute value circuit 30 generates a DC voltage that matches the amplitude of the voltage signal Vo, and outputs this DC voltage to the error amplifier 40 as the absolute value signal Vabs. The error amplifier 40 amplifies an error (difference) with respect to the set voltage Vref of the absolute value signal Vabs, and outputs this to the auto gain control circuit 50 as an error signal Verr. The auto gain control circuit 50 generates a self-excited signal Vi in which the amplitude of the voltage signal Vo coincides with the set voltage Vref based on the voltage signal Vo and the error signal Verr, and outputs it to the fixed electrode 1.

  In the vibration type sensor 101 of the present embodiment, when a physical quantity such as pressure to be measured acts on the vibrator 3, the distortion of the vibrator 13 changes, and the natural frequency changes. That is, the natural frequency of the vibrator 3 changes according to a physical quantity such as pressure applied to the vibrator 3. Since the frequency of the voltage signal Vo matches the natural frequency of the vibrator 3, the physical quantity such as pressure can be known from the frequency of the voltage signal Vo.

  Next, an oscillation circuit used in the vibration type sensor of this embodiment will be described with reference to FIG. Here, FIG. 2 is an explanatory diagram of an oscillation circuit used in the vibration type sensor of the embodiment, and FIG. 2A is an equivalent circuit of an electrostatic drive type vibrator (fixed electrode 1 and vibrator 3 in FIG. 1). FIG. 2B is a circuit diagram of the negative impedance conversion circuit 10.

  As described above, when an electrostatically driven vibrator is viewed as an electric circuit element, an equivalent circuit for evaluating the resonance characteristics includes a series circuit of an equivalent series resistance Rme, a series inductance Lme, and a series capacitance Cme, and a parallel capacitance. It is represented by a parallel circuit with C0. In this embodiment, a case is assumed in which parasitic resistance is formed in the manufacturing process of the electrostatic drive type vibrator. In this case, as shown in FIG. 2A, the equivalent circuit has parasitic resistances Rp1 and Rp2 connected in series to the parallel circuit.

  In the present embodiment, the negative impedance conversion circuit 10 includes an operational amplifier 14 and resistors 11, 12 and 13. That is, the negative impedance conversion circuit 10 has an operational amplifier 14 and one end connected to one input terminal (−) of the operational amplifier 14 and the other end connected to the output terminal (node N2) of the operational amplifier 14 and one end. The first resistor 11 to which the current signal io, which is the output of the electrostatic drive type vibrator, is input to (node N1), one end is connected to the other end (node N2) of the first resistor 11, and the other end is an operational amplifier. 14, a second resistor 12 connected to the other input terminal (+), a third resistor 13 having one end connected to the other end (node N3) of the second resistor 12 and the other end connected to the power supply potential Vg. It is the structure provided with.

Here, if the resistance values of the first resistor 11, the second resistor 12, and the third resistor 13 are R1, R2, and R3, respectively, and the operational amplifier 14 is ideal, the input impedance Zi of the negative impedance conversion circuit 10 is assumed. Is as follows.
(Equation 2)
Zi = -R1 / R3 / R2 (3)
That is, when the negative impedance conversion circuit 10 is viewed from the input side, negative impedance (negative resistance) is observed.

At this time, when the Q value Q ₁ and the gain G ₁ are obtained for the voltage signal Vo that is the output of the negative impedance conversion circuit 10, the following expression is obtained.
(Equation 3)
Q ₁ = (Lme / Cme) ^1/2 / (Rme + Rp1 + Rp2 + Zi) (4)
G ₁ = Zi · (1 + R3 / R2) / (Rme + Rp1 + Rp2 + Zi) (5)
Here, as in the conventional case, it is assumed that the parallel capacitance C0 can be ignored as the parallel capacitance C0 >> the series capacitance Cme.

  First, comparing the conventional formula (1) with the formula (4) of the present embodiment with respect to the Q value, the input impedance Zi added in the denominator of the formula (4) is a negative value, and the increment due to the formation of the parasitic resistance It can be seen that Rp1 and Rp2 can be canceled by the input impedance Zi of the negative impedance conversion circuit 10.

  As described above, according to the oscillation circuit of the present embodiment, it is possible to suppress the decrease in the Q value due to the formation of the parasitic resistance (by increasing the Q value as compared with the prior art) and realize stable oscillation. Resolution can be realized. As a result, the measurement accuracy of the vibration sensor using the oscillation circuit can be improved.

  Further, when the conventional equation (2) and the equation (5) of the present embodiment are compared with respect to the gain, the input impedance Zi added in the denominator of the equation (5) is a negative value, and the increment Rp1 due to the formation of the parasitic resistance. And Rp2 can be canceled by the input impedance Zi of the negative impedance conversion circuit 10. At the same time, it can be seen that the gain can be increased by setting the resistance value ratio (R3 / R2) of the second resistor 12 and the third resistor 13 to a larger value.

As described above, according to the oscillation circuit of the present embodiment, it is possible to improve the SN ratio by suppressing a decrease in gain due to the formation of parasitic resistance (by increasing the gain as compared with the prior art). As a result, the SN ratio of the vibration sensor using the oscillation circuit can also be improved.
(Modification)

  Next, a modification will be described with reference to FIG. In this modified example, it is assumed that parasitic resistance and parasitic capacitance are formed in the manufacturing process of the electrostatic drive type vibrator, and the resonance characteristics (Q value, gain, etc.) of the oscillation circuit are affected. Here, FIG. 3 is an explanatory diagram of an oscillation circuit used in the vibration type sensor of the modification, FIG. 3A is an equivalent circuit of the electrostatic drive type vibrator (fixed electrode 1 and vibrator 3), and FIG. b) is a circuit diagram of a negative impedance conversion circuit. The configuration of the vibration type sensor is the same as the configuration of the embodiment (FIG. 1) except that the circuit configuration of the negative impedance conversion circuit shown in FIG. 2 (b) is replaced with FIG. 3 (b).

  When parasitic resistance and parasitic capacitance are formed in the manufacturing process of the electrostatic drive type vibrator, the equivalent circuit includes an equivalent series resistance Rme, a series inductance Lme, and a series capacitance Cme as shown in FIG. For the parallel circuit of the series circuit and the parallel capacitor C0, the parasitic resistors Rp1 and Rp2 are connected in series, and the parasitic capacitors Cp1 and Cp2 are connected in parallel, respectively.

  In this modification, the negative impedance conversion circuit includes an operational amplifier 25, resistors 21 to 23, and a capacitor 24. That is, the negative impedance conversion circuit has an operational amplifier 25, one end connected to one input terminal (−) of the operational amplifier 25, the other end connected to the output terminal (node N2) of the operational amplifier 25, and one end ( The node N1) is connected to the parallel circuit of the first resistor 21 and the capacitor 24 to which the current signal io, which is the output of the electrostatic drive vibrator, is input, and one end is connected to the other end (node N2) of the parallel circuit. Is connected to the other input terminal (+) of the operational amplifier 25, one end is connected to the other end (node N3) of the second resistor 22, and the other end is connected to the power supply potential Vg. 3 resistors 23. Here, the resistance values of the first resistor 21, the second resistor 22, and the third resistor 23 are R1, R2, and R2, respectively, and the capacitance value of the capacitor 24 is C4.

  Here, explanation based on the formula is omitted, but it can be considered in the same manner as in the embodiment. That is, when the negative impedance conversion circuit is viewed from the input side, the negative impedance is observed. Further, regarding the Q value and the gain, the increments Rp1 and Rp2 due to the formation of the parasitic resistance and the increments Cp1 and Cp2 due to the formation of the parasitic capacitance can be canceled or reduced by the input impedance Zi of the negative impedance conversion circuit.

  Therefore, according to the oscillation circuit of the present modification, it is possible to realize stable oscillation by suppressing a decrease in the Q value due to the formation of parasitic resistance and parasitic capacitance (increasing the Q value as compared with the prior art) High resolution can be achieved. As a result, the measurement accuracy of the vibration sensor using the oscillation circuit can be improved. In addition, it is possible to improve the SN ratio by suppressing a decrease in gain due to the formation of parasitic resistance and parasitic capacitance (by increasing the gain as compared with the prior art). As a result, the vibration sensor using the oscillation circuit can be improved. The S / N ratio can also be improved.

This modification is also applied to the case where the influence of parasitic capacitance in the manufacturing process of the electrostatic drive vibrator is relatively larger than the influence of parasitic resistance on the resonance characteristics (Q value, gain, etc.) of the oscillation circuit. By applying the example oscillation circuit, an equivalent effect can be obtained. That is, stable oscillation can be realized by suppressing a decrease in Q value due to the formation of parasitic capacitance, and high resolution can be realized. As a result, measurement accuracy of a vibration sensor using the oscillation circuit can be realized. Can be improved. In addition, it is possible to improve the SN ratio by suppressing a decrease in gain due to the formation of parasitic capacitance. As a result, the SN ratio of the vibration sensor using the oscillation circuit can also be improved.
(Other variations)

  The preferred embodiments and modifications of the present invention have been described above in detail. However, the oscillation circuit and the vibration sensor using the same according to the present invention are not limited to the above-described embodiments and modifications, and are claimed. Various modifications and changes can be made within the scope of the gist of the present invention described in the above.

  For example, as described above, the electrostatic drive type vibrator may be replaced with another piezoelectric vibrator. Examples of other piezoelectric vibrators include a quartz crystal vibrator, a surface acoustic wave vibrator (or a SAW (Surface Acoustic Wave) vibrator), a silicon vibrator, a ceramic vibrator, an end surface reflecting vibrator, or a bulk vibrator. is there. Even when these are replaced, the same effects as those of the embodiment and the modification can be obtained.

  Further, the vibrator is not limited to the piezoelectric vibrator but may be another vibrator. In the manufacturing process of the vibrator, in which parasitic resistance and parasitic capacitance are formed due to the structure, a negative impedance conversion circuit is added in the same manner as in the embodiment and the modified example, so that the Q due to the formation of parasitic resistance and parasitic capacitance is obtained. It is possible to suppress a decrease in value and gain.

  Further, the configuration of the negative impedance conversion circuit is not limited to the illustrated circuit configuration, and may be another circuit configuration. For example, a differential negative impedance conversion circuit as disclosed in Japanese Patent No. 3907633 can be used instead of an operational amplifier.

  Furthermore, the present invention is not limited to an oscillation circuit using a vibrator, and a configuration in which a negative impedance conversion circuit is added to another oscillation circuit such as an LC oscillation circuit is also conceivable. In the manufacturing process of each element constituting the oscillation circuit, a parasitic resistance or parasitic capacitance is structurally formed. By adding a negative impedance conversion circuit in the same manner as in the embodiment and the modification, parasitic resistance and parasitic capacitance are added. It is possible to suppress a decrease in Q value and gain due to the formation of a capacitor.

DESCRIPTION OF SYMBOLS 1 Fixed electrode 3 Oscillator 10 Negative impedance conversion circuit 14, 18, 25 Operational amplifier 11-13, 15, 16, 21-23, 73 Resistance 17, 24, 74 Capacitor 30 Absolute value circuit 40 Error amplifier 50 Auto gain control Circuit 60 Schmitt trigger 71, 72 Power supply 101 Vibrating sensor io Current signal Vo Voltage signal Vb Bias voltage Vref Setting voltage Verr Error signal Vi Self-excited signal Vg Power supply potential

Claims (7)

An oscillation circuit comprising a vibrator and a current-voltage conversion circuit that converts an output current signal of the vibrator into a voltage signal,
An oscillation circuit characterized in that the current-voltage conversion circuit is a negative impedance conversion circuit. The negative impedance converter circuit is
An operational amplifier;
A first circuit in which one end is connected to one input terminal of the operational amplifier, the other end is connected to an output terminal of the operational amplifier, and an output current signal of the vibrator is input to the one end;
A second circuit having one end connected to the other end of the first circuit and the other end connected to the other input terminal of the operational amplifier;
A third circuit having one end connected to the other end of the second circuit and the other end connected to a power supply potential;
An oscillation circuit comprising:   3. The oscillation circuit according to claim 2, wherein each of the first circuit, the second circuit, and the third circuit is configured by a resistance element.   3. The oscillation circuit according to claim 2, wherein each of the first circuit and the second circuit is configured by a resistance element, and the third circuit is configured by a capacitive element.   3. The oscillation circuit according to claim 2, wherein the first circuit is configured by a parallel circuit of a resistance element and a capacitive element, and the second circuit and the third circuit are each configured by a resistance element.   6. The vibrator according to claim 1, wherein the vibrator is an electrostatic drive vibrator, a crystal vibrator, a surface acoustic wave vibrator, a silicon vibrator, or a ceramic vibrator. Oscillation circuit. A vibration type sensor using the oscillation circuit according to claim 1, wherein a physical quantity to be measured acts on the vibrator.

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