JP2008241330A - Detection circuit of piezoelectric vibrator and gyro sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circuit which is a detection circuit of a piezoelectric vibrator and is stable to stray capacitance, and a gyro sensor having a scale factor whose temperature dependence is small. <P>SOLUTION: The detection circuit of the piezoelectric vibrator equipped with the piezoelectric vibrator 100 having vibration legs, and a current-voltage conversion circuit 2 for converting the output current from this piezoelectric vibrator into a voltage, has a current amplifier circuit 1 between the piezoelectric vibrator and the current-voltage conversion circuit. Consequently, the current-voltage conversion circuit sensitive to the stray capacitance, and the connection part between the piezoelectric vibrator and an IC being a spot where stray capacitance is the most easy to produce can be isolated by the current amplifier. Accordingly, the detection circuit which is hardly affected by the stray capacitance as a whole can be obtained, by using the current amplifier circuit whose sensitivity to the stray capacitance is low. Moreover, the gyro sensor having the scale factor whose temperature dependence is low can be provided by using this detection circuit for the gyro sensor, since the peak of the frequency characteristic of the gain of the detection circuit is suppressed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a detection circuit for a piezoelectric vibrator having a piezoelectric vibrator, a current amplifier circuit, and a current-voltage conversion circuit, and more particularly to stabilization of the operation of the detection circuit for stray capacitance.

  The present invention also relates to a gyro sensor having a low scale factor temperature dependency.

  Piezoelectric vibrators have been used in oscillation circuits of electronic devices, but in recent years, they are also widely used in various sensors such as acceleration sensors and gyro sensors.

  When the piezoelectric vibrator is used for a sensor application, the electronic circuit detects the influence of the physical quantity to be detected on the vibrator in the oscillation state. For example, in the case of a gyro sensor, the vibrating leg is bent by the application of Coriolis force due to rotation, thereby changing the charge amount of the electrode provided on the vibrating leg. This is converted into a voltage by a current-voltage conversion circuit, and the applied angular velocity is detected.

As an example of a detection circuit connected to a piezoelectric vibrator in a conventional gyro sensor, a configuration in which a differential amplifier circuit is connected to a current-voltage conversion circuit using an OP amplifier and a resistor as shown in FIG. It has been. In this configuration, since the common-mode noise can be canceled by the differential amplifier circuit, the SN ratio can be increased.
JP 11-44540 A (page 2-3)

  In this configuration, the SN ratio is governed by the feedback resistance value of the current-voltage conversion circuit. When the feedback resistance value is R, the thermal noise is proportional to √R, and the signal is proportional to R, so the SN ratio is proportional to √R. Therefore, the larger R is, the more advantageous the SN ratio.

  However, a problem arises when the feedback resistance of the current-voltage conversion circuit is increased. Since the LPF is composed of the feedback resistor and the stray capacitance C at the input end, and the phase is rotated, it becomes close to positive feedback and becomes unstable in the frequency region where the phase delay of the output of the OP amplifier becomes large. Depending on the size of the stray capacitance C, a peak occurs in the amplitude or oscillates due to frequency characteristics. In order to connect the piezoelectric vibrator and the current-voltage conversion circuit, it is necessary to route the electrode pads and wirings.

  Therefore, a large value is selected for the feedback resistance value so that no peak occurs in the frequency characteristics. However, the stray capacitance changes depending on the wiring layout, package structure, and the like, and is difficult to predict at the circuit design stage. Therefore, it is necessary to confirm the maximum value of the feedback resistor that operates stably by experimenting with several resistance values.

  In order to suppress this phenomenon, a method of performing phase compensation by adding a feedback capacitor in parallel to the feedback resistor is generally performed. This cancels the phase delay of the LPF formed by the feedback resistor and the stray capacitance by the phase advance of the HPF formed by the feedback resistor and the feedback capacitor.

  Although this method can improve the frequency characteristics of the current-voltage converter circuit, the optimum feedback capacitance value varies depending on the stray capacitance value, so the feedback capacitance value changes each time the wiring layout, package structure, etc. are changed. There was a need to adjust.

  The above matters become a serious problem in a gyro sensor using a piezoelectric vibrator. The peak in the frequency characteristics of the gain of the current-voltage converter circuit changes depending on the temperature characteristics of the elements that make up the circuit. , And the temperature dependence of the scale factor of the gyro sensor is degraded.

  The present invention has been made to solve the above-described problems caused by the prior art, and an object thereof is to provide a detection circuit that stably operates without the influence of stray capacitance.

  The present invention also relates to a gyro sensor having a low scale factor temperature dependency.

  In order to solve the above-described problems, the piezoelectric vibrator detection circuit according to the present invention includes a current amplifier circuit between the piezoelectric vibrator and the current-voltage conversion circuit.

  According to this configuration, the current amplifier functions to suppress the influence of the stray capacitance by separating the connection portion of the piezoelectric vibrator and the IC and the current-voltage conversion circuit that are most likely to generate stray capacitance and interposing the current amplifier circuit therebetween. The circuit will be in charge. Therefore, even if the current-voltage conversion circuit is sensitive to the input capacitance, it is not affected by the influence. By using a current amplifier circuit having low sensitivity to stray capacitance, a detection circuit that is less susceptible to stray capacitance as a whole can be configured.

  In the gyro sensor according to the present invention, the piezoelectric vibrator has a drive electrode and a Coriolis force detection electrode, and the detection circuit as described above is connected to the Coriolis force detection electrode.

  According to the present invention, even if the potential of the electrode of the piezoelectric vibrator fluctuates, it is not directly transmitted to the current-voltage conversion circuit, so that the peak in the frequency characteristic of the gain is unlikely to occur, and the detection circuit is not easily affected by stray capacitance There is an effect that can be configured.

  In addition, according to the present invention, there are effects that the in-phase component of noise is canceled, the SN ratio is improved, and the circuit can be miniaturized.

  Further, according to the present invention, since the current amplifier is composed of only the OP amplifier and the resistor, there is an effect that it is possible to realize a circuit having low waveform distortion and temperature dependency.

  In addition, according to the present invention, there is an effect that the influence on the vibration of the piezoelectric vibrator can be reduced by reducing the input impedance.

In addition, according to the present invention, there is an effect that the influence of the reference voltage fluctuation of current-voltage conversion can be suppressed and the accuracy of the output signal can be increased.

In addition, according to the present invention, it is difficult for a peak to appear in the frequency characteristic of the gain of the detection circuit, and the temperature dependency of the scale factor of the gyro sensor can be reduced.

Hereinafter, an optimal embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a circuit diagram showing a first embodiment of a detection circuit for a piezoelectric vibrator according to the present invention. The detection circuit has a piezoelectric vibrator 100, a current amplifier circuit 1, a current-voltage conversion circuit 2, and a differential amplifier circuit 3.

  The current amplifier circuit 1 includes an OP amplifier U111 and resistors R111 and R113. One end of the resistor R113 is connected to the output terminal of the OP amplifier U111, and the other end is connected to one end of the resistor R111. The other end of the resistor R111 is connected to the non-inverting input terminal of the OP amplifier U111. Further, the inverting input terminal and the output of the OP amplifier U111 are short-circuited to constitute a voltage follower. Another set of the same circuit is configured by the OP amplifier U112 and resistors R116 and R118, and the current amplifier circuit having the above configuration is connected to each of the two electrodes of the piezoelectric vibrator 100.

  The current-voltage conversion circuit 2 includes an OP amplifier U121 and a resistor R121. The resistor R121 is connected between the inverting input terminal and the output terminal of the OP amplifier U121. Another set of the same circuit is constituted by an OP amplifier U122 and a resistor R171, and one set is connected to each of two sets of outputs of the current amplifier circuit 1. A feedback capacitor may be added in parallel to the resistor R121 or R171 as is done in the current-voltage conversion circuit in the conventional detection circuit.

  The differential amplifier circuit 3 includes an OP amplifier U131 and resistors 131 to 134, and two inputs of the differential amplifier circuit are connected to two sets of outputs of the current-voltage conversion circuit, respectively. The differential amplifier circuit 3 may be in the form of an instrumentation amplifier. In this case, the symmetry of the circuit can be improved.

  Next, the operation of this circuit will be described. In the current amplifier circuit 1, if the voltages of the non-inverting input terminal and the inverting input terminal of the OP amplifier U111 are substantially equal, the potential difference applied to both ends of the resistor R111 and the resistor R113 is also approximately equal. Therefore, the ratio between the current flowing through the resistor R113 and the input current is the ratio of the resistor R111 and the resistor R113, and is given by R111 / R113.

Since both the current from R111 and the current from R113 flow into the next stage, the gain of the current amplifier circuit 1 can be expressed by (R111 + R113) / R113. This current flows into the current-voltage conversion circuit 2.

  In the current-voltage conversion circuit 2, the current supplied from the previous current amplifier circuit 1 is converted into a voltage by the resistor R121.

Therefore, the combined gain of the current amplifier circuit 1 and the current-voltage conversion circuit 2 is R121 ×
It is given by (R111 + R113) / R113.

  According to this configuration, the OP amplifier U111 (or U112) operates with a voltage follower, and thus operates stably up to near the unity gain frequency. The input impedance of the current amplifier circuit 1 is also constant up to near the unity gain frequency, and its value is approximately R111 (or R116). The frequency characteristic of the entire detection circuit is mainly determined by an LPF composed of R111 (or R116) and stray capacitance, and a frequency characteristic with a suppressed peak is obtained. Therefore, the effect of stray capacitance between the electrode of the piezoelectric vibrator 100 and the detection circuit can be suppressed, and there is an effect that a peak is hardly generated in the frequency characteristic of the gain.

Further, in this configuration, only an OP amplifier and a resistor are used, and since negative feedback is applied, there is an effect that waveform distortion can be reduced.

  Further, the inverting input terminal of the OP amplifier U121 (or U122) of the current-voltage conversion circuit 2 is easily affected by the stray capacitance, but it is not necessary to take this out of the IC, which is advantageous for suppressing the stray capacitance. .

  In addition, the piezoelectric vibrator is provided with two electrodes that output currents of opposite phase corresponding to the bending of the vibration legs during vibration, and has a differential amplifier circuit, and each of the two electrodes of the piezoelectric vibrator has a current amplifier. The circuit 1 and the current-voltage conversion circuit 2 are connected one by one to convert the current signal output from the two electrodes of the piezoelectric vibrator into a voltage signal, and then connect each output to the input terminal of the differential amplifier circuit By doing so, the in-phase component of noise can be canceled and the SN ratio can be improved.

  The current amplifier circuit 1 shown in FIG. 1 has a configuration in which the piezoelectric vibrator 100 is connected to the non-inverting input terminal of the OP amplifier U111 (or U112), but is inverted as in the second embodiment of FIG. A configuration of connecting to the input terminal may be adopted.

  The current amplifier circuit 1 according to the second embodiment illustrated in FIG. 2 includes an OP amplifier U211 and resistors R212 and R213. The resistor R212 is connected between the inverting input terminal and the output terminal of the OP amplifier U211, and the resistor R213 is connected between the non-inverting input terminal and the output terminal of the OP amplifier U211. Another set of the same circuit is constituted by an OP amplifier U212 and resistors R216 and R218. One set of the current amplifier circuit 1 having the above configuration is connected to each of the two electrodes of the piezoelectric vibrator 200.

  After the current amplifier circuit 1, a current-voltage conversion circuit 2 having an OP amplifier U221 (or U222), a resistor R221 (or 271), and a differential amplifier circuit 3 having an OP amplifier U231, resistors R231, R232, R233, and R234 Is connected. The operations of the current-voltage conversion circuit 2 and the differential amplifier circuit 3 are the same as those in FIG.

  Hereinafter, the operation of the current amplifier circuit 1 of this circuit will be described. An explanation will be given by taking a current amplifier composed of an OP amplifier U211 and resistors R212 and R213 as an example, but the operation of a current amplifier composed of an OP amplifier U212 and resistors R216 and R218 is exactly the same.

In the current amplifier circuit 1, if the voltages of the non-inverting input terminal and the inverting input terminal of the OP amplifier U211 are substantially equal, the potential difference applied to both ends of the resistor R213 is a value obtained by inverting that of the resistor R212. Therefore, the ratio between the current flowing through the resistor R213 and the input current is -1 times the ratio of the resistor R212 and the resistor R213, and is given by -R212 / R213.

  Since only the current from R213 flows into the next stage, the gain of the current amplifier circuit 1 can be expressed by -R212 / R213. This current flows into the current-voltage conversion circuit 2.

  Accordingly, in the embodiment of FIG. 2, the combined gain of the current amplifier circuit 1 and the current-voltage conversion circuit 2 is given by R221 × (−R212 / R213).

  In this circuit, a case where a stray capacitance is added to the inverting input terminal of the OP amplifier 211 is considered. First, the potential of the inverting input terminal fluctuates 90 degrees behind the input current.

Next, consider the potential at the non-inverting input terminal of the OP amplifier U211. The next-stage current-voltage conversion circuit 2 includes an OP amplifier U221 and a resistor R221. The potential of the input terminal is advanced by 90 degrees from the phase of the input current. Since the phase of the current input to the current-voltage conversion circuit 2 is inverted by the current amplifier circuit 1, the potential of the input terminal of the current-voltage conversion circuit 2 is 90 degrees with respect to the current output from the piezoelectric vibrator 200. It will be late.

  Therefore, the non-inverting input terminal of the OP amplifier U211 of the current amplifier circuit 1 fluctuates in the same phase as the inverting input terminal although it has a small amplitude. Thereby, the influence of the stray capacitance is suppressed, and as a result, the peak of the frequency characteristic of the gain can be suppressed as in the embodiment of FIG.

  Further, as in the embodiment of FIG. 1, the configuration uses only an OP amplifier and a resistor, and since negative feedback is applied, there is also an effect that waveform distortion can be reduced.

  Furthermore, this circuit has an effect that the input impedance can be lowered by the gain of the OP amplifier U211 as compared with the circuit of the embodiment of FIG. Accordingly, it is possible to suppress the fluctuation of the potential of the electrode of the piezoelectric vibrator 200, which is advantageous because the influence on the piezoelectric vibrator 200 is small.

  The third embodiment shown in FIG. 3 is a detection circuit having a differential current amplifier 4 and a current-voltage conversion circuit 2. The differential current amplifier circuit 4 of FIG. 3 has an OP amplifier U311 and resistors R311, R312 and R313. The resistor R312 is connected between the inverting input terminal and the output terminal of the OP amplifier U211. One end of the resistor R311 is connected to the non-inverting input terminal of the OP amplifier U311 and the other end is connected to one end of the resistor R313. The other end of the resistor R313 is connected to the output terminal of the OP amplifier U311.

  In the differential current amplifier circuit 4 having the above configuration, the inverting input terminal and the non-inverting input terminal of the OP amplifier U311 are input and connected to the two electrodes of the vibrator 300, respectively.

The output of the differential current amplifier circuit 4 is a connection point between the resistor R311 and the resistor R313, and this node is connected to the current-voltage conversion circuit 2.

  The operation of the differential current amplifier circuit 4 of FIG. 3 will be briefly described. The current flowing into the non-inverting input terminal of the OP amplifier U311 is i1, the current flowing into the inverting input terminal is i2, and the output current of the differential current amplifier circuit 4 is i0.

If the potentials of the non-inverting input terminal and the inverting input terminal of the OP amplifier U311 are substantially equal, R311 · i1 = R312 · i2 + R313 · (i0−i1) is established. Here, when R312 = R311 + R313, i0 = R312 / R313 · (i1-i2) is derived. Therefore, it can be seen that this circuit operates as a differential current amplifier having a gain of R312 / R313.

The differential current amplifier circuit 4 may be considered as a combination of the current amplifier circuit 1 of FIG. 1 and the current amplifier circuit 1 of FIG.

  Therefore, in the embodiment of FIG. 3, the combined gain of the differential current amplifier circuit 4 and the current-voltage conversion circuit 2 is given by −R321 × R312 / R313.

  This circuit has an advantage that the number of OP amplifiers is small and the circuit can be greatly reduced in size as compared with the circuits of the embodiments of FIGS. The function that required five OP amplifiers in the embodiment of FIGS. 1 and 2 can be realized by two OP amplifiers in the embodiment of FIG.

  The third embodiment shown in FIG. 4 is a detection circuit having a correction circuit 5 in addition to the differential current amplifier circuit 4 and the current-voltage conversion circuit 2.

The correction circuit of FIG. 4 includes a voltage follower configured by an OP amplifier U432, and a differential amplifier circuit configured by an OP amplifier U431 and resistors R431 to 434. The input of the voltage follower is connected to the inverting input terminal of the OP amplifier U411, and the output is connected to the non-inverting input terminal of the OP amplifier U421 of the current-voltage conversion circuit 2.

According to the correction circuit 5 having the above configuration, the potential serving as a reference for current-voltage conversion is the potential of the electrode of the piezoelectric vibrator 400, so that the effect of signal phase delay due to stray capacitance can be reduced. There is. However, since the electrode potential of the piezoelectric vibrator 400 is not DC, the fluctuation is corrected by the differential amplifier circuit of the OP amplifier U431.

  Although one differential current amplifier circuit 4 is used in FIG. 4, two current amplifier circuits 1 may be used as shown in FIGS. In that case, the correction circuit 5 is required for each of the two electrodes of the piezoelectric vibrator 400.

Further, when the fluctuation of the electrode potential of the piezoelectric vibrator is sufficiently smaller than the output voltage V0, there is no need for the differential amplifier circuit composed of the OP amplifier U431.

  In this case, the voltage follower composed of the OP amplifier U432 of the correction circuit 5 may be removed, and the electrode of the piezoelectric vibrator 400 and the non-inverting input terminal of the OP amplifier U421 of the current-voltage conversion circuit 2 may be directly connected.

The detection circuits of FIGS. 1 to 4 can suppress the peak of the frequency characteristic of the gain, so that the gain change due to the temperature change is small. Therefore, when the detection circuit of the present invention is used as a gyro sensor detection circuit, the temperature dependence of the scale factor of the gyro sensor can be reduced.

  Specifically, the piezoelectric vibrators 100, 200, 300, and 400 have an electrode for oscillation and a Coriolis force detection electrode, and a detection circuit is connected to the Coriolis force detection electrode. Thereby, the sensitivity of the scale factor with respect to the stray capacitance can be suppressed.

Since the detection circuit according to the present invention has low sensitivity to the stray capacitance, it is effective when the stray capacitance of the wiring or package is unknown.

  The gyro sensor using the detection circuit according to the present invention is suitable for a gyro sensor for a car navigation system in which the temperature dependence of the scale factor is small and the temperature is severely demanded.

  In addition, since the gyro sensor using the detection circuit according to the present invention has a small circuit scale, the gyro sensor is suitable for applications that require downsizing and cost reduction for camera shake correction.

1 is a diagram showing a first embodiment of a detection circuit according to the present invention. FIG. It is a figure which shows 2nd Embodiment of the detection circuit by this invention. It is a figure which shows the detection circuit using a differential current amplifier circuit in 3rd Embodiment by this invention. It is a figure which shows the detection circuit provided with the correction circuit in 4th Embodiment by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Current amplifier circuit 2 Current voltage conversion circuit 3 Differential amplifier circuit 4 Differential current amplifier circuit 5 Correction circuit 100, 200, 300, 400 Piezoelectric vibrator UX (X is a number) OP amplifier RY (Y is a number) Resistance

Claims (8)

In a piezoelectric vibrator detection circuit comprising a piezoelectric vibrator having a vibrating leg and a current-voltage conversion circuit that converts an output current from the piezoelectric vibrator into a voltage,
A detection circuit for a piezoelectric vibrator, wherein a current amplifier circuit is provided between the piezoelectric vibrator and the current-voltage conversion circuit. The piezoelectric vibration detection circuit according to claim 1,
Two electrodes that output currents in opposite phases corresponding to bending during vibration are provided on the vibration legs of the piezoelectric vibrator, and the current amplifier circuit and the current-voltage conversion circuit are connected to each of the two electrodes. And
Further, a differential amplifier circuit is provided, and the respective output terminals of the two sets of current-voltage conversion circuits are connected to the input terminals of the differential amplifier circuit. The piezoelectric vibrator detection circuit according to claim 1,
The current amplifier circuit short-circuits between the inverting input terminal and the output terminal of the OP amplifier,
Connect two resistors in series between the non-inverting input terminal and the output terminal,
A detection circuit for a piezoelectric vibrator, wherein a non-inverting input terminal is used as an input terminal, and a connection point between the two resistors connected in series is used as an output terminal. The piezoelectric vibrator detection circuit according to claim 1,
The current amplifier circuit connects resistors between the non-inverting input terminal and the output terminal of the OP amplifier and between the inverting input terminal and the output terminal, respectively.
A piezoelectric vibrator detection circuit comprising an inverting input terminal as an input terminal and a non-inverting input terminal as an output terminal. The piezoelectric vibrator detection circuit according to claim 1,
The current amplifier circuit is a differential current amplifier circuit, wherein an input terminal of the differential current amplifier circuit is connected to an electrode of the piezoelectric vibrator, and an output terminal is connected to an input terminal of the current-voltage conversion circuit. The piezoelectric vibrator detection circuit. In the detection circuit of the piezoelectric vibrator according to claim 5,
The differential current amplifier circuit has two resistors connected in series between a non-inverting input terminal and an output terminal of an OP amplifier,
Connect a resistor between the inverting input terminal and the output terminal,
A detection circuit for a piezoelectric vibrator, wherein the non-inverting input terminal and the inverting input terminal are used as input terminals, and a connection point between the two resistors connected in series is used as an output terminal. The piezoelectric vibrator detection circuit according to claim 1,
A detection circuit for a piezoelectric vibrator, wherein a correction circuit including a differential amplifier circuit is provided, and correction is performed so that the voltage of the electrode of the piezoelectric vibrator is set to a reference potential of the current-voltage conversion circuit. In a gyro sensor in which a driving electrode and a Coriolis force detection electrode are provided in a piezoelectric vibrator, and a detection circuit is connected to the Coriolis force detection electrode,
The gyro sensor according to claim 1, wherein the detection circuit has the configuration according to claim 1.

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