JP2006322818A - Angular velocity sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an angular velocity sensor for reducing the effect of detouring drive signals while preventing a vibrator from being upsized and a signal processing circuit from being complicated. <P>SOLUTION: This angular velocity sensor 80 comprises a vibrator 10 having a movable part 14 movable in two directions orthogonal to each other. An oscillation circuit 50 is connected to a drive electrode 22 and a monitor electrode 24 existing in the X direction of the movable part 14, the oscillation circuit 50 comprising a CV conversion circuit 52, a phase adjustment circuit 54, and an amplitude adjustment circuit 56. CV conversion circuits 60 and 62 are connected to detection electrodes 38 and 40 existing in the Y direction of the movable part 14 while connecting the conversion circuits 60 and 62 to an angular velocity signal processing circuit 64. In designing the vibrator 10, an electrostatic coupling capacitance Cc between the drive electrode 22 and the monitor electrode 24 is set to be equal to or less than 1/30 of detection capacitance of the monitor electrode 24. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an angular velocity sensor, and more particularly, for example, to a capacitance-type angular velocity sensor in which capacitance changes according to an applied angular velocity.

  FIG. 6 is a perspective view showing an example of a vibrator used in the angular velocity sensor as the background of the present invention. The vibrator 10 includes a substrate 12 formed of a single crystal silicon material or the like. A substantially rectangular movable portion 14 is formed on the substrate 12. Support beams 16 are formed to extend from four ends of the movable portion 14. The support beam 16 is bent and its tip is fixed to the substrate 12.

  A comb-like movable electrode 18 is formed on one side of the movable portion 14. A drive electrode 22 is formed to face the movable electrode 18. A fixed electrode 22 a extending from the drive electrode 22 so as to mesh with the movable electrode 18 is formed. A comb-shaped movable electrode 20 is formed on the side portion of the movable portion 14 where the movable electrode 18 is formed and the side portion facing away from the side portion. A monitor electrode 24 is formed to face the movable electrode 20. From the monitor electrode 24, a fixed electrode 24a extending so as to mesh with the movable electrode 20 is formed.

  Furthermore, movable electrodes 34 and 36 are respectively formed on the other side portions of the movable portion 14. The detection electrodes 38 and 40 are formed facing the movable electrodes 34 and 36. From these detection electrodes 38 and 40, fixed electrodes 38a and 40a extending so as to mesh with the movable electrodes 34 and 36 are formed.

  An oscillation circuit 50 is connected to the drive electrode 22 and the monitor electrode 24 as shown in FIG. The oscillation circuit 50 includes a CV conversion circuit 52 for converting a change in capacitance detected by the monitor electrode 24 into a voltage, and the CV conversion circuit 52 is connected to the monitor electrode 24. The output terminal of the CV conversion circuit 52 is connected to the phase adjustment circuit 54, and the phase adjustment circuit 54 is further connected to the amplitude adjustment circuit 56. The output terminal of the amplitude adjustment circuit 56 is connected to the drive electrode 22.

  Further, CV conversion circuits 60 and 62 are connected to the detection electrodes 38 and 40, respectively. In the CV conversion circuits 60 and 62, the change in capacitance detected by the detection electrodes 38 and 40 is converted into a voltage. Since the change in capacitance detected by the detection electrodes 38 and 40 corresponds to the angular velocity applied to the vibrator 10, the CV conversion circuits 60 and 62 output signals corresponding to the angular velocity. The signals output from these CV conversion circuits 60 and 62 are processed by the angular velocity signal processing circuit 64 and output as angular velocity signals.

  In the vibrator 10, when a drive signal is input to the drive electrode 22, the movable portion 14 vibrates in a direction connecting the drive electrode 22 and the monitor electrode 24 (X direction in FIG. 7). When the movable portion 14 vibrates, the facing area between the movable electrode 20 and the fixed electrode 24a changes, and the capacitance detected by the monitor electrode 24 changes. The capacitance change detected by the monitor electrode 24 is converted into a voltage by the CV conversion circuit 52. The signal converted into the voltage in this way is phase-adjusted by the phase adjustment circuit 54 and further amplitude-adjusted by the amplitude adjustment circuit 56, whereby a drive signal is generated. Then, this drive signal is input to the drive electrode 22. In this way, a closed loop oscillation circuit is formed, and the movable portion 14 is stably excited at the resonance frequency in the X direction.

  When an angular velocity is applied to the vibrator 12 around the axis orthogonal to the surface of the substrate 12 with the movable portion 14 being excited, the direction connecting the two detection electrodes 38 and 40 (Y direction in FIG. 7). Coriolis force acts on the movable portion 14 to vibrate the movable portion 14 in the Y direction. In the detection electrodes 38 and 40, a change in capacitance according to the displacement of the movable portion 14 caused by the Coriolis force is detected, and the change in capacitance is converted into a voltage signal by the CV conversion circuits 60 and 62. The detection signal converted into the voltage signal is converted into a DC voltage signal corresponding to the angular velocity in the angular velocity signal processing circuit 64 through, for example, differential amplification, synchronous detection, smoothing, amplification, and the like, and output as an angular velocity signal. The

  Here, as the CV conversion circuit 60, for example, a circuit including an operational amplifier 70 is used as shown in FIG. The detection electrode 38 of the vibrator 10 is connected to the inverting input terminal of the operational amplifier 70. Further, a feedback resistor 72 is connected between the output terminal and the inverting input terminal of the operational amplifier 70. The non-inverting input terminal of the operational amplifier 70 is grounded via the reference voltage source 74. Note that the movable portion 14 of the vibrator 10 used here is grounded via the support beam 16, but the movable portion 14 is not limited to being grounded as long as the voltage is different from that of the reference voltage source 74. Can be connected to a constant voltage source.

In the CV conversion circuit 60, since the reference voltage source 74 is connected to the non-inverting input terminal of the operational amplifier 70, the inverting input terminal is set to the same voltage as the reference voltage source 74 by an imaginary short. As a result, the fixed electrode 38 a of the vibrator 10 is biased to the voltage value set by the reference voltage source 74. Therefore, when the capacitance detected by the detection electrode 38 is C, the bias voltage to the fixed electrode 38a is Vb, the current flowing through the feedback resistor 72 is i, and the time is t, the movable electrode 34 and the fixed electrode 38a are configured. The amount of charge Q accumulated in the electrostatic capacitance is expressed by the following equation.
Q = CVb = it (1)
When the angular velocity is applied to the vibrator 10 and the capacitance C detected by the detection electrode 38 is changed by the vibration of the movable portion 14 due to the Coriolis force, the capacitance is accumulated in the capacitance formed by the movable electrode 34 and the fixed electrode 38a. The amount of charge Q to be changed also changes. At this time, since the bias voltage Vb is set by an imaginary short circuit of the operational amplifier 70, it does not change even if the capacitance changes. Therefore, the change ΔQ in the charge amount is expressed by the following equation.
ΔQ = ΔCVb (2)
The charge ΔQ released or attracted from the capacitance formed by the movable electrode 34 and the fixed electrode 38a of the vibrator 10 becomes a current Δi flowing through the feedback resistor 72. Therefore, the following equation holds.
ΔQ = Δit (3)
Here, the time t indicates the time when the capacitance changes. This is equal to the excitation frequency of the movable part 14. Due to the current Δi flowing through the feedback resistor 72, a voltage change ΔVo occurs at the output of the CV conversion circuit 60. Here, when the resistance value of the feedback resistor 72 is R, the output voltage change ΔVo is expressed by the following equation.
ΔVo = ΔiR (4)
From the expressions (2), (3) and (4), the following expression is derived.
ΔVo = ΔiR = ΔCVbR / t (5)
In this way, the change in capacitance detected by the detection electrode 38 is converted into a change in voltage. In the other CV conversion circuits 52 and 62, the capacitance change detected by the monitor electrode 24 and the detection electrode 40 is similarly converted into a voltage change (see Patent Document 1).

  In such a vibrator 10, when the electrostatic coupling capacitance between the drive electrode 22 and the monitor electrode 24 is large, the drive signal wraps around the signal obtained from the monitor electrode. If this wraparound drive signal is superimposed on the monitor signal as noise, the drive signal cannot be accurately controlled, and it becomes difficult to vibrate the movable portion 14 accurately at the resonance frequency.

Therefore, in order to reduce the influence of the electrostatic coupling capacitance between the drive electrode 22 and the monitor electrode 24, between the wire connected to the drive electrode 22 and the monitor electrode 24 and the wire connected to the detection electrodes 38 and 40. A technique for providing a blocking wire for electrically blocking these wires is disclosed (see Patent Document 2). This blocking wire is connected to a predetermined potential such as a ground potential, for example, and as shown by a dotted line in FIG. 7, the wire connecting the vibrator 10 and each circuit is electrically blocked.
Further, in a gyroscope using a tuning fork having a vibrating leg, a technique is disclosed in which a shielding portion for electrostatically shielding between electrodes is provided between a driving electrode and a detection electrode (patent) Reference 3).
Furthermore, a technique is disclosed in which means for reducing the influence of noise caused by electrostatic coupling capacitance is provided in a signal processing circuit (see Patent Document 4).

JP 2001-153659 A JP 2002-188924 A JP 2001-201348 A JP 2004-294405 A

  However, in the techniques of Patent Literature 2 and Patent Literature 3, it is necessary to separately provide a blocking wire, a shielding portion, and the like, and the vibrator itself becomes large. Further, the technique of Patent Document 4 has a problem that the signal processing circuit becomes complicated although the vibrator itself is not enlarged.

  Therefore, a main object of the present invention is to provide an angular velocity sensor that can reduce the influence of a sneak-in driving signal while preventing an increase in size of a vibrator and a complication of a signal processing circuit.

The present invention relates to at least one movable part movable in two orthogonal directions, at least one drive electrode to which a drive signal for vibrating the movable part in a predetermined drive direction is input, and At least one monitor electrode for monitoring a vibration state in a predetermined direction based on a change in capacitance, and at least one for detecting a vibration state of a movable part in a direction orthogonal to the driving direction based on the change in capacitance. Electrostatic coupling capacitance between drive electrode and monitor electrode in angular velocity sensor including vibrator having detection electrode and oscillation circuit for generating drive signal input to drive electrode from monitor signal obtained from monitor electrode The angular velocity sensor is characterized in that is 1/30 or less of the detection capacity of the monitor electrode.
In such an angular velocity sensor, the electrostatic coupling capacitance between the drive electrode and the monitor electrode should be 1/30 or less of the detection capacitance of the monitor electrode without providing an electrical shield between the drive electrode and the monitor electrode. Is preferred.

Even if it is impossible to completely eliminate the electrostatic coupling capacitance generated between the drive electrode and the monitor electrode of the vibrator, the present inventor has an adverse effect on the vibrator. Focused on giving Therefore, the relationship between the electrostatic coupling capacitance between the driving electrode and the monitor electrode and the driving signal stability is confirmed, and when the electrostatic coupling capacitance is 1/30 or less of the detection capacitance of the monitoring electrode, the driving signal stability is good. Thus, it was confirmed that the vibration state of the movable part was stabilized.
The electrode arrangement structure for the electrostatic coupling capacitance between the drive electrode and the monitor electrode to be 1/30 or less of the detection capacitance of the monitor electrode can be easily designed by simulation, and there are various patterns. Therefore, it is not limited to a specific electrode arrangement structure.

  According to this invention, by designing the electrode arrangement structure in the vibrator by simulation, the electrostatic coupling capacitance between the drive electrode and the monitor electrode can be reduced, and the vibrator in which the vibration state of the movable part is stable Can be obtained. Therefore, a detection signal corresponding to the angular velocity applied to the angular velocity sensor can be obtained, and the angular velocity can be accurately detected. In addition, it is not necessary to provide a separate wire or shield for the vibrator, and it is not necessary to add a special circuit to the signal processing circuit, thereby preventing an increase in the size of the vibrator and the complexity of the signal processing circuit. it can.

  The above object, other objects, features, and advantages of the present invention will become more apparent from the following description of the best mode for carrying out the invention with reference to the drawings.

  FIG. 1 is an illustrative view showing one example of an angular velocity sensor of the present invention. The angular velocity sensor 80 includes the vibrator 10 shown in FIG. Similarly to the circuit shown in FIG. 7, an oscillation circuit 50 including a CV conversion circuit 52, a phase adjustment circuit 54, and an amplitude adjustment circuit 56 is connected to the drive electrode 22 and the monitor electrode 24 of the vibrator 10. The detection electrodes 38 and 40 are connected to CV conversion circuits 60 and 62, respectively. The CV conversion circuits 60 and 62 are connected to an angular velocity signal processing circuit 64.

  In this angular velocity sensor 80, the shielding wire for electrically shielding the wire connecting the drive electrode 22 and the monitor electrode 24 and the oscillation circuit 50 as provided in the vibrator in the conventional angular velocity sensor is as follows. Not formed. The angular velocity signal processing circuit 64 is the same as the conventional angular velocity signal processing circuit in FIG.

  As described above, in this angular velocity sensor 80, since a shielding wire for shielding between the drive electrode 22 and the monitor electrode 24 is not provided, as indicated by a two-dot chain line in FIG. An electrostatic coupling capacitance Cc is formed between the drive electrode 22 and the monitor electrode 24. Here, the electrode arrangement structure of the fixed electrodes 22a, 24a, 38a, 40a connected to the drive electrode 22, the monitor electrode 24, the detection electrodes 38, 40, and the movable electrodes 18, 20, 34, 36 meshing with these electrodes. Is designed by simulation, and the electrode arrangement structure is designed so that the electrostatic coupling capacitance Cc between the drive electrode 22 and the monitor electrode 24 is 1/30 or less of the detection capacitance of the monitor electrode 24. The electrostatic coupling capacitance between the drive electrode 22 and the monitor electrode 24 can be easily designed by simulation. If the electrostatic coupling capacitance Cc is designed in this way, the electrode arrangement structure is not limited. Absent.

  Using such an angular velocity sensor 80, the drive voltage transient characteristics were measured. Further, as a comparative example, the drive voltage transient characteristics were measured using a vibrator in which the electrostatic coupling capacitance between the drive electrode and the monitor electrode was larger than 1/30 of the detection capacitance of the monitor electrode. The measurement results are shown in FIGS.

  FIG. 2 shows drive voltage transient characteristics when a vibrator having a capacitance Cc of 0 between the drive electrode and the monitor electrode is used. FIG. 3 shows drive voltage transient characteristics when using a vibrator in which the electrostatic coupling capacitance Cc between the drive electrode and the monitor electrode is 1/30 of the detection capacitance Cm of the monitor electrode. FIG. 4 shows drive voltage transient characteristics when using a vibrator in which the electrostatic coupling capacitance Cc between the drive electrode and the monitor electrode is 1/15 of the detection capacitance Cm of the monitor electrode. FIG. 5 shows drive voltage transient characteristics when using a vibrator in which the electrostatic coupling capacitance Cc between the drive electrode and the monitor electrode is 1 / 7.5 of the detection capacitance Cm of the monitor electrode.

  As can be seen from FIGS. 2 and 3, when the electrostatic coupling capacitance Cc between the drive electrode and the monitor electrode is 1/30 or less of the detection capacitance Cm of the monitor electrode, the drive voltage amplitude is stable. On the other hand, as can be seen from FIGS. 4 and 5, when the electrostatic coupling capacitance Cc between the drive electrode and the monitor electrode is larger than 1/30 of the detection capacitance Cm of the monitor electrode, the drive voltage amplitude becomes unstable. ing.

  Thus, by reducing the electrostatic coupling capacitance between the drive electrode and the monitor electrode, a stable drive signal can be obtained, and the movable portion 14 can be vibrated accurately at the resonance frequency. Therefore, when an angular velocity is applied to the angular velocity sensor 80, a signal corresponding to the angular velocity can be accurately obtained from the detection electrodes 38 and 40.

  Further, in this angular velocity sensor 80, it is not necessary to provide a separate wire or shielding member in order to reduce the influence of the sneak drive signal, and it is not necessary to add a special circuit to the signal processing circuit. Therefore, although the angular velocity can be accurately detected, it is possible to prevent the vibrator from being enlarged and the signal processing circuit from being complicated.

It is an illustration figure which shows an example of the angular velocity sensor of this invention. This is a drive voltage transient characteristic when a vibrator having an electrostatic coupling capacitance Cc of 0 between the drive electrode and the monitor electrode is used. This is a drive voltage transient characteristic when using a vibrator in which the electrostatic coupling capacitance Cc between the drive electrode and the monitor electrode is 1/30 of the detection capacitance Cm of the monitor electrode. This is a drive voltage transient characteristic when using a vibrator in which the electrostatic coupling capacitance Cc between the drive electrode and the monitor electrode is 1/15 of the detection capacitance Cm of the monitor electrode. This is a drive voltage transient characteristic when using a vibrator in which the electrostatic coupling capacitance Cc between the drive electrode and the monitor electrode is 1 / 7.5 of the detection capacitance Cm of the monitor electrode. It is a perspective view which shows an example of the vibrator | oscillator used for the angular velocity sensor used as the background of this invention. It is an illustration figure which shows an example of the conventional angular velocity sensor. It is a circuit diagram which shows an example of the CV conversion circuit used for the angular velocity sensor shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Vibrator 14 Movable part 22 Drive electrode 24 Monitor electrode 38,40 Detection electrode 50 Oscillation circuit 52 CV conversion circuit 54 Phase adjustment circuit 56 Amplitude adjustment circuit 60, 62 CV conversion circuit 64 Angular velocity signal processing circuit 80 Angular velocity sensor

Claims (2)

At least one movable part movable in two orthogonal directions, at least one drive electrode to which a drive signal for oscillating the movable part in a predetermined drive direction is input, and the predetermined of the movable part by the drive signal At least one monitor electrode for monitoring the vibration state in the direction based on the capacitance change, and at least one for detecting the vibration state of the movable part in a direction orthogonal to the drive direction based on the capacitance change. In an angular velocity sensor including a vibrator having two detection electrodes, and an oscillation circuit for generating a drive signal input to the drive electrode from a monitor signal obtained from the monitor electrode,
An angular velocity sensor characterized in that an electrostatic coupling capacitance between the drive electrode and the monitor electrode is 1/30 or less of a detection capacitance of the monitor electrode.   The electrostatic coupling capacitance between the drive electrode and the monitor electrode is set to 1/30 or less of the detection capacitance of the monitor electrode without providing an electrical shield between the drive electrode and the monitor electrode. The angular velocity sensor according to claim 1.

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