JP5286725B2 - Angular velocity sensor - Google Patents

Description

  The present invention relates to an angular velocity sensor used to prevent camera shake of a digital still camera or a video camera.

  This type of conventional angular velocity sensor has a configuration as shown in FIGS.

  FIG. 6 is a perspective view of a vibrator in a conventional angular velocity sensor, FIG. 7 is a circuit block diagram of the angular velocity sensor, and FIG. 8 is a circuit diagram of noise signal removing means in a detection circuit of the angular velocity sensor.

  6 to 8, reference numeral 1 denotes a vibrator formed of a piezoelectric tuning fork. As shown in FIG. 6, the vibrator 1 includes a drive electrode (not shown), a first detection electrode 2a, and a second detection electrode. A detection electrode 2b is provided. Reference numeral 3 denotes a drive circuit. The drive circuit 3 is composed of a drive means 4 and an oscillation means 5, and oscillation from the oscillation means 5 is transmitted to the vibrator 1 via the drive means 4 as shown in FIG. Input is made to a drive electrode (not shown). Reference numeral 6 denotes a detection circuit, which comprises a phase difference detection means 7, an amplification means 8 and a noise removal means 9, and an output generated from the detection electrode 2 in the vibrator 1 by the phase difference detection means 7. The phase difference of the signal is detected. The amplifying means 8 in the detecting circuit 6 amplifies the output signal from the phase difference detecting means 7, and the noise removing means 9 removes unnecessary noise frequency components from the output signal of the amplifying means 8 and outputs an angular velocity output. Output. The noise removing means 9 in the detection circuit 6 is configured by connecting a first low-pass filter 10 and a second low-pass filter 11 in series as shown in FIG.

  Next, the operation of the conventional angular velocity sensor configured as described above will be described.

  When an AC voltage is applied to a drive electrode (not shown) of the vibrator 1 in the angular velocity sensor, the vibrator 1 is driven to vibrate at a drive frequency in the X direction as shown in FIG. When an angular velocity is applied around the Z axis of the vibrator 1, the vibrator 1 vibrates at the detection frequency in the Y axis direction by Coriolis force. Then, the phase difference of the output signal composed of the charges generated from the first detection electrode 2a and the second detection electrode 2b by this vibration is detected by the phase difference detection means 7, and further amplified by the amplification means 8, thereby the angular velocity. Was detected.

  Further, when a digital still camera (not shown) equipped with an angular velocity sensor vibrates at about 10 Hz, which is a vibration frequency due to hand shaking of a person, the output signals are the first low-pass filter 10 and the second low-pass filter 11. Transmits almost all output signals without being attenuated by. That is, as shown in FIG. 9 and (Table 1), the gain of the output signal by the noise removing means 9 including the first low-pass filter 10 and the second low-pass filter 11 at 10 Hz is 0 dB.

As prior art document information relating to the invention of this application, for example, Patent Document 1 is known.
JP 2000-234934 A

  However, in the above-described conventional configuration, when a signal having a detuning frequency of about 500 Hz, which is the difference between the driving frequency of the vibrator 1 and the detection frequency, is input to the noise removing unit 9 as a noise component, As shown in (Table 1), since the gain at 500 Hz is -17 dB and noise component removal is small, an output signal is actually generated even though the angular velocity sensor is not loaded. It had the problem of end up.

  SUMMARY OF THE INVENTION The present invention solves the above-described conventional problems, and an object thereof is to provide an angular velocity sensor that can reliably remove a noise component having a detuning frequency that is a difference between a driving frequency of a vibrator and a detection frequency. Is.

  In order to achieve the above object, the present invention has the following configuration.

The invention according to claim 1 of the present invention includes a vibrator provided with a drive electrode and a detection electrode, a drive circuit that vibrates the vibrator by supplying a voltage to the drive electrode, and an angular velocity of the vibrator. A detection circuit provided with a noise removal means for converting a charge generated in the detection electrode by Coriolis force when loaded into an output signal and removing a noise signal of the output signal, and a noise removal means in the detection circuit Is configured by connecting a passive low-pass filter, an active low-pass filter, and a Chebyshev filter in series, and the active low-pass filter determines the frequency component that maximizes the resonance sharpness depending on the noise frequency generated by the Q characteristics of the Chebyshev filter. According to this configuration, noise removal Since a passive low-pass filter, an active low-pass filter, and a Chebyshev filter are connected in series, there is no loss such as phase delay due to frequency characteristics at 10 Hz, which is the vibration frequency of camera shake. In the harmonic frequency, since the attenuation factor by the Chebyshev filter is large, the noise component can be surely removed, and the frequency component having the maximum resonance sharpness depends on the noise frequency generated by the Q characteristic of the Chebyshev filter. Since it is removed by the active low-pass filter, it has an effect that the deterioration of the characteristics near the resonance point of the Chebyshev filter can be surely prevented.

As described above, the angular velocity sensor of the present invention includes a vibrator provided with a drive electrode and a detection electrode, a drive circuit that vibrates the vibrator by supplying a voltage to the drive electrode, and an angular velocity loaded on the vibrator. And a detection circuit provided with a noise removal means for removing the noise signal of the output signal, while converting the electric charge generated in the detection electrode by the Coriolis force into an output signal, and the noise removal means in the detection circuit A passive low-pass filter, an active low-pass filter, and a Chebyshev filter are connected in series, and the active low-pass filter uses the active low-pass filter for the frequency component that has the maximum resonance sharpness depending on the noise frequency generated by the Q characteristics of the Chebyshev filter. This configuration is designed to eliminate noise. Since a passive low-pass filter, an active low-pass filter, and a Chebyshev filter are connected in series, there is no loss such as phase lag due to frequency characteristics at 10 Hz, which is the vibration frequency of camera shake, and it is a noise component. At the detuned frequency, the attenuation factor by the Chebyshev filter is large, so that the noise component can be reliably removed, and the frequency component that maximizes the resonance sharpness depending on the noise frequency generated by the Q characteristic of the Chebyshev filter Since the active low-pass filter removes the characteristic, it is possible to reliably prevent deterioration of the characteristics in the vicinity of the resonance point of the Chebyshev filter.

  Hereinafter, an angular velocity sensor according to an embodiment of the present invention will be described with reference to the drawings.

  1 is a top view of a vibrator of an angular velocity sensor according to an embodiment of the present invention, FIG. 2 is a block diagram showing a drive circuit and a detection circuit in the angular velocity sensor, and FIG. 3 is a noise removing unit in the detection circuit of the angular velocity sensor. FIG.

  1 to 3, reference numeral 21 denotes a vibrator in which a piezoelectric thin film made of PZT is provided on the upper surface of a tuning fork-shaped silicon substrate. The vibrator 21 is provided with a drive electrode 22 and a detection electrode 23. A monitor electrode 25 is provided at the connection portion 24 in the vibrator 21. A drive circuit 26 is electrically connected to the drive electrode 22 in the vibrator 21 as shown in FIG. A detection circuit 27 includes a pair of amplifiers 28, a differential amplifier 29, a phase shifter 30, an inverting amplifier 31, a synchronous detector 32, a noise removing unit 33, and a smoothing circuit 39. It is comprised by. The pair of amplifiers 28 in the detection circuit 27 amplifies the output signals from the pair of detection electrodes 23 in the vibrator 21 and outputs them to the differential amplifier 29. The differential amplifier 29 in the detection circuit 27 differentially amplifies the output signal from the amplifier 28, and the phase shifter 30 delays the phase of the output signal from the differential amplifier 29 by 90 degrees. ing. Further, the inverting amplifier 31 in the detection circuit 27 inverts the output signal from the phase shifter 30 and inputs it to the synchronous detector 32. The synchronous detector 32 also receives an output signal from the phase shifter 30.

  Reference numeral 34 denotes a monitor circuit. The monitor circuit 34 inputs an output signal from the monitor electrode 25 in the vibrator 21 and inputs an output signal from the monitor circuit 34 to a detection clock 35. The synchronous detector 32 in the detection circuit 27 detects the output signal from the phase shifter 30 and the inverting amplifier 31 in accordance with the synchronous signal from the detection clock 35 and inputs it to the noise removing means 33. As shown in FIG. 3, the noise removing means 33 is configured by connecting a Butterworth filter comprising an active low-pass filter 36 and a passive low-pass filter 37, a non-inverting amplifier 40 and a Chebyshev filter 38 in series. It is what. Reference numeral 39 denotes a smoothing circuit. The smoothing circuit 39 smoothes the output signal from the Chebyshev filter 38 and outputs it.

  Next, the operation of the angular velocity sensor according to one embodiment of the present invention configured as described above will be described.

  When an AC voltage is applied to the drive electrode 22 in the vibrator 21, the vibrator 21 is driven to vibrate at a predetermined frequency in the direction of the arrow in FIG. In this state, when an angular velocity about the longitudinal direction of the vibrator 21 is applied to the vibrator 21, electric charges are generated in the piezoelectric thin film in the vibrator 21 due to the Coriolis force. Output signals having waveforms shown in FIGS. 4A and 4B are generated. Then, the output signal shown in FIG. 4C is input to the phase shifter 30 by differentially amplifying the output signal by the differential amplifier 29. The phase shifter 30 delays the phase by 90 degrees as shown in FIG. 4D, and the output signal is output as an inverted signal as shown in FIG. On the other hand, the electric charge generated from the monitor electrode 25 by the drive amplitude of the vibrator 21 is converted into the monitor voltage shown in FIG. 4 (f) by the monitor circuit 34, and further the detection shown in FIG. The clock output signal is input to the synchronous detector 32. The synchronous detector 32 detects the output signals from the phase shifter 30 and the inverting amplifier 31 in synchronization with the output signal from the detection clock 35, and outputs the output signal shown in FIG. The output signal from the synchronous detector 32 is subjected to noise removal by the noise signal removing means 33, smoothed by the smoothing circuit 39, and output as an angular velocity signal as shown in FIG. 4 (i).

  At this time, when a digital still camera (not shown) equipped with an angular velocity sensor vibrates at a vibration frequency of about 10 Hz, which is a vibration of a human hand, the active low-pass filter 36, the passive low-pass filter 37, and the Chebyshev filter 38 are included. Since the noise removing means 33 transmits almost all output signals, the gain at 10 Hz is 0 dB as shown in FIG. 5 and (Table 2).

  On the other hand, when a signal having a detuning frequency of about 500 Hz, which is the difference between the driving frequency of the vibrator 21 and the detection frequency, is input to the noise removing unit 33 as a noise component, The gain is -30 dB as shown in FIG. 5 and (Table 2). That is, in one embodiment of the present invention, the noise removing means 33 in the detection circuit 27 is configured by connecting a Butterworth filter composed of an active low-pass filter 36 and a passive low-pass filter 37 and a Chebyshev filter 38 in series. Therefore, there is no loss such as phase lag due to frequency characteristics at 10 Hz, which is the vibration frequency of camera shake, and the attenuation factor by the Chebyshev filter 38 is large at 500 Hz, which is a detuning frequency that is a noise component. The effect that the noise component can be surely removed is obtained.

  Here, considering the case where a noise signal of 180 Hz is added to the output signal due to the Q value of the Chebyshev filter 38, as shown in FIG. When 38 is 180 Hz, the resonance sharpness is maximum and increases by 2 dB. As a result, the noise signal increases with the Chebyshev filter 38 alone. On the other hand, since the attenuation factor of the active low-pass filter 36 near 180 Hz is −3.5 dB, the increase in the noise signal due to the characteristics of the Chebyshev filter 38 can be canceled out by the characteristics of the active low-pass filter 36.

  That is, in the angular velocity sensor according to the embodiment of the present invention, the Butterworth filter is composed of the passive low-pass filter 37 and the active low-pass filter 36, and the frequency component depending on the noise frequency generated by the Q characteristic of the Chebyshev filter 38 is active. Since the low-pass filter 36 is used for the removal, it is possible to reliably prevent the deterioration of the characteristics of the Chebyshev filter 38 in the vicinity of the resonance point.

  The angular velocity sensor according to the present invention has an effect of being able to provide an angular velocity sensor that can reliably remove a noise component composed of a detuning frequency that is a difference between a driving frequency of a vibrator and a detection frequency. In particular, it is useful as an angular velocity sensor used to prevent camera shake of a digital still camera or a video camera.

The top view of the vibrator of the angular velocity sensor in one embodiment of the present invention Block diagram showing drive circuit and detection circuit in the same angular velocity sensor Circuit diagram of noise removal means in detection circuit of same angular velocity sensor (A)-(i) Waveform diagram showing the operating state of the angular velocity sensor The figure which shows the frequency characteristic of the output signal in the same angular velocity sensor Perspective view of transducer in conventional angular velocity sensor Circuit block diagram for the same angular velocity sensor Circuit diagram of noise signal removal means in detection circuit of same angular velocity sensor The figure which shows the frequency characteristic of the output signal in the same angular velocity sensor

21 vibrator 22 drive electrode 23 detection electrode 26 drive circuit 27 detection circuit 33 noise removing means 36 active low-pass filter 37 passive low-pass filter 38 Chebyshev filter

Claims (1)

A vibrator provided with a drive electrode and a detection electrode, a drive circuit that vibrates the vibrator by supplying a voltage to the drive electrode, and generated at the detection electrode by Coriolis force when an angular velocity is applied to the vibrator And a detection circuit provided with a noise removal means for removing a noise signal of the output signal, and the noise removal means in the detection circuit includes a passive low-pass filter, an active low-pass filter, and a Chebyshev filter. An angular velocity sensor that is configured by connecting the two in series and that uses an active low-pass filter to remove the frequency component that has the maximum resonance sharpness depending on the noise frequency generated by the Q characteristics of the Chebyshev filter.

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