Vibratory gyro-sensor and vibratory gyro circuit

Disclosed herein is a vibratory gyro-sensor including a vibratory section, a synchronous detector which synchronously detects a detected signal from the vibratory section in timed relation to a timing signal for synchronous detection, and a timing signal output section which outputs the timing signal for synchronous detection. The timing signal output section has a low-pass filter, a comparator, and a first phase shifter. The vibration monitor signal as converted into the binary signal by the comparator and shifted in phase by the first phase shifter is used as the timing signal for synchronous detection.

BACKGROUND

The present disclosure relates to a vibratory gyro-sensor and a vibratory gyro circuit for use in a vibratory gyro-sensor.

Heretofore, vibratory gyro-sensors have widely been used as a sensor for detecting an angular velocity (see, for example, Japanese Patent Laid-Open No. 2006-105896 (Paragraphs [0026] through [0030], [0049]FIGS. 1,6) referred to as Patent Document 1 hereinafter).

As shown inFIG. 1of Patent Document 1, the vibratory gyro-sensor disclosed in Patent document 1 has a vibratory gyro31and a vibratory gyro circuit. The vibratory gyro31includes two piezoelectric elements33a,33bdisposed on a side surface of a vibrator32. The vibratory gyro circuit includes an adding circuit1, an oscillating circuit2, a differential amplifying circuit4, a synchronous detecting circuit5, a phase shifting circuit3, and a direct current amplifying circuit6.

The oscillating circuit2outputs a drive signal to the vibratory gyro31. The adding circuit1adds output signals from the two piezoelectric elements33a,33bof the vibratory gyro31and outputs the sum signal. The oscillating circuit2adjusts the amplitude and phase of the sum signal from the adding circuit1, and supplies the adjusted signal as the drive signal to the vibratory gyro31. The differential amplifying circuit4outputs a signal depending on the difference between the output signals from the two piezoelectric elements33a,33b. The synchronous detecting circuit5synchronously detects the signal output from the differential amplifying circuit4depending on a timing signal output from the phase shifting circuit3. The direct current amplifying circuit6amplifies the signal which is synchronously detected by the synchronous detecting circuit5and outputs the amplified signal.

As shown inFIG. 6of Patent Document 1, the phase shifting circuit3includes a phase shifting section (having an integrating circuit, an operational amplifier65, etc.) for shifting the phase of the output signal from the adding circuit1, and a comparator66for binarizing a signal output from the phase shifting section and outputting the binarized signal as the timing signal for the synchronous detecting circuit5. A signal used as a threshold value by the comparator66is generally represented by a reference voltage from a peripheral circuit.

SUMMARY

The signal output from the adding circuit1(hereinafter referred to as vibration monitor signal) is a sine-wave signal having a vibrational frequency component only under ideal conditions. Actually, however, since the impedance of the vibratory gyro31or the vibratory gyro circuit varies with time after the power supply is turned on, the low-frequency component of the vibration monitor signal may fluctuate.

If such a phenomenon occurs, then since the fixed reference potential is used as the threshold value for the comparator66, when the vibration monitor signal is binarized into a timing signal by the comparator66, the timing signal has an “H” interval and an “L” interval that are different from each other. When the timing signal is thus shifted, the synchronous detecting circuit5fails to accurately synchronously detect the signal output from the differential amplifying circuit4, thereby tending to add noise to an angular velocity signal.

Accordingly, it is desirable to provide a technology such as a vibratory gyro-sensor, and the like, which is capable of generating a timing signal for synchronous detection which has an “H” interval and an “L” interval that are substantially equal to each other even if the low-frequency component of a vibration monitor signal fluctuates.

A vibratory gyro-sensor according to an embodiment of the present disclosure includes a vibratory section, a synchronous detector, and a timing signal output section.

The synchronous detector synchronously detects a detected signal from the vibratory section in timed relation to a timing signal for synchronous detection.

The timing signal output section includes a low-pass filter, a comparator, and a first phase shifter.

The low-pass filter extracts a low-frequency component of a vibration monitor signal representative of a vibrating state of the vibrating section.

The comparator converts the vibration monitor signal into a binary signal using the low-frequency component of the vibration monitor signal which is extracted by the low-pass filter as a threshold value.

The first phase shifter shifts the phase of the vibration monitor signal.

The timing signal output section outputs the vibration monitor signal as converted into the binary signal by the comparator and shifted in phase by the first phase shifter, as the timing signal for synchronous detection.

In the vibratory gyro sensor, the comparator converts the vibration monitor signal into the binary signal using the low-frequency component of the vibration monitor signal which is extracted by the low-pass filter as the threshold value. Since the low-frequency component of the vibration monitor signal serves as the threshold value of the comparator, even if the low-frequency component of the vibration monitor signal varies due to a time-dependent change in the impedance of the vibratory section, for example, the threshold value of the comparator also varies in a manner to follow such variations of the vibration monitor signal. Therefore, even if the low-frequency component of the vibration monitor signal varies, the comparator can generate a binary signal having an “H” interval and an “L” interval that are substantially equal to each other. As a consequence, the synchronous detector can synchronously detect the detected signal at an appropriate timing, so that noise is prevented from being added to the angular velocity signal.

The first phase shifter may shift the phase of the vibration monitor signal after the vibration monitor signal is converted into the binary signal by the comparator. Alternatively, the first phase shifter may shift the phase of the vibration monitor signal before the vibration monitor signal is converted into the binary signal by the comparator.

If the first phase shifter shifts the phase of the vibration monitor signal before the vibration monitor signal is converted into the binary signal by the comparator, then the first phase shifter may be of a simple circuit arrangement for shifting the phase of analog signals. The vibratory gyro sensor may thus be reduced in cost.

If the first phase shifter shifts the phase of the vibration monitor signal after the vibration monitor signal is converted into the binary signal by the comparator, then the first phase shifter may include a phase comparator, a loop filter, a voltage-controlled oscillator, a frequency divider, and a timing generator.

The phase comparator outputs a phase difference signal depending on the phase difference between the vibration monitor signal is converted into the binary signal by the comparator and a comparison signal.

The loop filter smoothes the phase difference signal and outputs a frequency control signal.

The voltage-controlled oscillator outputs an oscillation signal having frequency characteristics depending on the frequency control signal.

The frequency divider outputs a frequency-divided signal produced by frequency-dividing the oscillation signal at a predetermined ratio as the comparison signal.

The timing generator inputs the oscillation signal and the frequency-divided signal and outputs the vibration monitor signal as converted into the binary signal and shifted in phase.

Since the first phase shifter is of a PLL (Phase Locked Loop) circuit arrangement, even if the frequency of the vibration monitor signal varies, it can accurately shift the phase of the binary signal in a manner to follow such variations of the frequency of the vibration monitor signal.

The vibratory gyro-sensor may further include a drive signal output section.

The drive signal output section includes a second phase shifter and an amplitude adjuster.

The second phase shifter shifts the phase of the vibration monitor signal.

The amplitude adjuster adjusts the amplitude of the vibration monitor signal.

The drive signal output section outputs the vibration monitor signal as shifted in phase by the second phase shifter and adjusted in amplitude by the amplitude adjuster, as the drive signal for the vibratory section.

In the vibratory gyro-sensor, the first phase shifter may shift the phase of the vibration monitor signal before the vibration monitor signal is converted into the binary signal by the comparator.

In this case, the second phase shifter may shift the phase of the vibration monitor signal before the vibration monitor signal is adjusted in amplitude by the amplitude adjuster.

The first phase shifter and the second phase shifter may be in the form of a single common phase shifter.

Since the single common phase shifter is used as the first phase shifter and the second phase shifter, the cost of the vibratory gyro-sensor is reduced.

In the vibratory gyro-sensor, the low-pass filter may have a cutoff frequency of 100 Hz or higher.

With the cutoff frequency of the low-pass filter being set to 100 Hz or higher, any phase delay of the signal which has passed through the low-pass filter, i.e., the signal serving as the comparator threshold value, is 1° or smaller at a frequency of 1 Hz or lower. Therefore, the signal which has passed through the low-pass filter, i.e., the signal serving as the comparator threshold value, can accurately follow variations of the low-frequency component of the vibration monitor signal. The comparator can thus generate a binary signal having an “H” interval and an “L” interval that are substantially equal to each other.

The low-pass filter may include a resistor and a capacitor. Alternatively, the low-pass filter may include a filter circuit including a switched capacitor.

A vibratory gyro circuit according to an embodiment of the present disclosure includes a synchronous detector and a timing signal output section.

The synchronous detector synchronously detects a detected signal from a vibratory section in timed relation to a timing signal for synchronous detection.

The timing signal output section includes a low-pass filter, a comparator, and a first phase shifter.

The low-pass filter extracts a low-frequency component of a vibration monitor signal representative of a vibrating state of the vibrating section.

The comparator converts the vibration monitor signal into a binary signal using the low-frequency component of the vibration monitor signal which is extracted by the low-pass filter as a threshold value.

The first phase shifter shifts the phase of the vibration monitor signal.

The timing signal output section outputs the vibration monitor signal as converted into the binary signal by the comparator and shifted in phase by the first phase shifter, as the timing signal for synchronous detection.

According to an embodiment of the present disclosure, as described above, even if the low-frequency component of the vibration monitor signal varies, the vibratory gyro-sensor can generate a timing signal for synchronous detector which has an “H” interval and an “L” interval that are substantially equal to each other.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

[Overall Arrangement and Details of a Vibratory Gyro-Sensor]

FIG. 1is a schematic perspective view of a vibratory section10of a vibratory gyro-sensor100according to a first embodiment of the present disclosure.FIG. 2is a wiring diagram of the vibratory section10and a vibratory gyro circuit20of the vibratory gyro-sensor.FIG. 3is a block diagram of the vibratory gyro circuit20.FIGS. 4A to 4Fare diagrams showing the waveforms of signals output when the vibratory gyro-sensor100operates.

As shown inFIGS. 1 through 3, the vibratory gyro-sensor100includes the vibratory section10and the vibratory gyro circuit20.

As shown inFIG. 1, the vibratory section10includes a vibrator11and a piezoelectric element14disposed on the vibrator11. The vibrator11has a beam12in the form of a rectangular parallelepiped which is elongate in one direction (Y-axis direction), and a base13which supports an end of the beam12.

The piezoelectric element14has a piezoelectric film15of lead zirconate titanate (PZT) disposed on an upper surface of the vibrator11. The piezoelectric element14also has a drive electrode16disposed on the piezoelectric film15centrally in a widthwise direction (X-axis direction) of the beam12, and a first detecting electrode17and a second detecting electrode18which are disposed one on each side of the drive electrode16in sandwiching relation to the drive electrode16.

As shown inFIGS. 2 and 3, the vibratory gyro circuit20includes an adder21, a subtractor22, a drive signal output section23(see the broken lines inFIG. 3), a timing signal output section24(see the broken lines inFIG. 3), a synchronous detector25, and a filter26. The vibratory gyro circuit20is in the form of an IC (Integrated Circuit) on a single semiconductor chip.

The adder21generates a sum signal of a first detected signal which is detected by the first detecting electrode17and a second detected signal which is detected by the second detecting electrode18, and outputs the generated sum signal as a vibration monitor signal representative of a vibrating state of the vibratory section10(seeFIG. 4B).

The subtractor22generates a differential signal between the first detected signal detected by the first detecting electrode17and the second detected signal detected by the second detecting electrode18, and outputs the generated differential signal as a detected signal of the vibratory section10(seeFIG. 4C).

The drive signal output section23adjusts the amplitude and phase of the vibration monitor signal, and outputs the vibration monitor signal with the adjusted amplitude and phase as a drive signal (seeFIGS. 4A and 4B). The drive signal output section23includes a second phase shifter27for shifting the phase of the vibration monitor signal by a certain shift (e.g., 90°), and an automatic gain controller28(AGC: Automatic Gain Control) (amplitude adjuster) for adjusting the amplitude of the vibration monitor signal to a constant amplitude. The drive signal output from the drive signal output section23is applied to the drive electrode16, which causes the vibrator11to oscillate by itself.

FIG. 5is a circuit diagram showing an example of the second phase shifter27.

As shown inFIG. 5, the second phase shifter27includes three resistors41,42,43each having a resistance value R, a capacitor44having an electrostatic capacitance C, and an operational amplifier45. The second phase shifter27has an input terminal connected to a positive feedback terminal of the operational amplifier45through the resistor41and also to a negative feedback terminal of the operational amplifier45through the resistor42. The capacitor44is connected between the positive feedback terminal of the operational amplifier45and ground (GND). The resistor43is connected between the negative feedback terminal of the operational amplifier45and an output terminal thereof.

The second phase shifter27shown inFIG. 5outputs a signal which is shifted in phase from its input signal (vibration monitor signal) by a phase shift (phase delay) expressed by the following equation (1):
Phase shift=tan−1−2RC/{(1−(RC)2}  (1)

When the drive signal is applied to the drive electrode16, the beam12of the vibrator11flexurally vibrates in a direction (Z-axis direction) perpendicular to the longitudinal direction (Y-axis direction) of the beam12. If no angular velocity is applied about a longitudinal central axis of the beam12, then the first detected signal detected by the first detecting electrode17and the second detected signal detected by the second detecting electrode18are equal in amplitude and phase to each other. Therefore, the output signal from the subtractor22, i.e., the detected signal of the vibratory section10, represents zero.

If an angular velocity is applied about a longitudinal central axis of the beam12while the beam12is flexurally vibrating, then a Coriolis force depending on the angular velocity is generated in a direction (X-axis direction) which is perpendicular to the longitudinal direction of the beam12and the flexurally vibrating direction. When the Coriolis force is generated, the beam12vibrates also in the X-axis direction, thereby producing a phase difference depending on the magnitude of the Coriolis force between the first detected signal and the second detected signal. The phase difference between the two detected signals causes the subtractor22to output a detected signal depending on the magnitude of the Coriolis force (the magnitude of the angular velocity) (seeFIG. 4C).

The detected signal of the vibratory section10output from the subtractor22is input to the synchronous detector25. The synchronous detector25synchronously detects the detected signal (seeFIG. 4E) in timed relation to a timing signal (seeFIG. 4D) for synchronous detection output from the timing signal output section24(first phase shifter31). The filter26smoothes the signal synchronously detected by the synchronous detector25into a gyro signal (angular velocity signal), and outputs the gyro signal (seeFIG. 4F).

The timing signal output section24binarizes the vibration monitor signal and shifts the phase of the vibration monitor signal. The timing signal output section24then outputs the vibration monitor signal which has been binarized and shifted in phase as a timing signal for synchronous detection. The timing signal output section24includes a low-pass filter29for extracting a low-frequency component of the vibration monitor signal, and a comparator30for converting the vibration monitor signal into a binary signal using the low-frequency component of the vibration monitor signal which is extracted by the low-pass filter29as a threshold value. The timing signal output section24also includes a first phase shifter31for shifting the phase of the binary signal output from the comparator30by a certain phase (e.g., 90°).

FIGS. 6A and 6Bare circuit diagrams showing examples of the low-pass filter29.

FIG. 6Ashows an example of low-pass filter29which includes a resistor51and a capacitor52.FIG. 6Bshows another example of low-pass filter29which is in the form of a filter circuit including a switched capacitor50.

In the example shown inFIG. 6A, the resistor51is connected between input and output terminals and has a resistance value R, and the capacitor52is connected between an output end of the resistor51and ground and has an electrostatic capacitance C. The low-pass filter29shown inFIG. 6Ahas a cutoff frequency fc expressed by the following equation (2):
fc=1/2πRC(2)

In the example shown inFIG. 6B, the low-pass filter29is of an arrangement which is generally referred to as a switched capacitance filter. The low-pass filter29includes, in addition to the switched capacitor50, an operational amplifier59and an output capacitor58.

The switched capacitor50includes an input capacitor53having an electrostatic capacitance Ci, a switch54connected between the input terminal and the input capacitor53, and a switch55connected between the input capacitor53and a negative feedback terminal of the operational amplifier59. The switched capacitor50also includes a switch56connected between an input end of the input capacitor53and ground and a switch57connected between an output end of the input capacitor53and ground.

The output capacitor58, which has an electrostatic capacitance Co, is connected between the output terminal of the operational amplifier59and the negative feedback terminal thereof. The operational amplifier59has its positive feedback terminal connected to ground or a reference potential.

The low-pass filter29shown inFIG. 6Bhas a cutoff frequency fc expressed by the following equation (3):
fc=Cifsw/2πCo(3)
where fsw represents a switching frequency.

FIG. 7is a block diagram showing an example of the first phase shifter31.FIGS. 8A, B, and C are diagrams showing the relationship between a signal A at a point A, a signal B at a point B, and an output signal from the first phase shifter31shown inFIG. 7.

As shown inFIG. 7, the first phase shifter31includes a phase comparator61, a loop filter62, a voltage-controlled oscillator (VCO)63, a first flip-flop64, a second flip-flop65, and an inverter66.

The phase comparator61uses the vibration monitor signal binarized by the comparator30as a reference signal. The phase comparator61outputs a phase difference signal depending on the phase difference between the reference signal and a comparison signal output from a Q output terminal of the first flip-flop64. The loop filter62smoothes the phase difference signal output from the phase comparator61and outputs a frequency control signal.

The voltage-controlled oscillator63outputs an oscillation signal of a rectangular waveform which has frequency characteristics depending on the frequency control signal output from the loop filter62.

Each of the first flip-flop64and the second flip-flop65is in the form of a D flip-flop. Each of the first flip-flop64and the second flip-flop65has a D input terminal, a CK (clock) input terminal, a Q output terminal, Q_output terminal (inverting output terminal), a CLR_(clear) output terminal, and PR_(preset) terminal. The symbol “_” means an inversion, which is represented by an overbar inFIG. 7.

The first flip-flop64serves to frequency-divide the oscillation signal, i.e., serves as a frequency divider. The second flip-flop65serves to generate the timing signal for synchronous detection, i.e., serves as a timing generator.

The Q output terminal of the first flip-flop64is connected to an input terminal of the phase comparator61. The Q_output terminal of the first flip-flop64is connected to the D input terminal thereof. The Q_output terminal of the first flip-flop64is connected to the D input terminal of the second flip-flop65. The voltage-controlled oscillator63has an output terminal connected to the CK input terminal of the second flip-flop65through the inverter66.

The oscillation signal output from the voltage-controlled oscillator63is input to the CK input terminal of the first flip-flop64. When the oscillation signal, which has a rectangular waveform, input to the CK input terminal of the first flip-flop64changes from a low level to a high level, the first flip-flop64changes the level of the signal output from the Q output terminal thereof to the level of the signal input to the D input terminal, i.e., the level of the output signal from the Q_output terminal. Otherwise, the first flip-flop64holds the level of the signal output from the Q output terminal thereof.

Therefore, the Q output terminal of the first flip-flop64outputs a frequency-divided signal representative of the oscillation signal, whose frequency is divided by 2, from the voltage-controlled oscillator63. The frequency-divided signal is input to the input terminal of the phase comparator61as a comparison signal of the phase comparator61.

The Q_output terminal of the first flip-flop64outputs a signal (inverted phase signal) whose phase is an inversion of the phase of the frequency-divided signal output from the Q output terminal. The inverted phase signal is input to the D input terminal of the first flip-flop64and the D input terminal of the second flip-flop65. The oscillation signal output from the voltage-controlled oscillator63is input to the CK input terminal of the second flip-flop65through the inverter66.

FIGS. 8A,8B, and8C show the waveform of a signal A at a point A inFIG. 7, the waveform of a signal B at a point B inFIG. 7, and the waveform of a signal output from the Q output terminal of the second flip-flop65.

The D input terminal of the second flip-flop65is supplied with the signal A whose waveform is shown inFIG. 8A. The CK input terminal of the second flip-flop65is supplied the signal B whose waveform is shown inFIG. 8B, i.e., the oscillation signal that has passed through the inverter66.

When the signal B input to the CK input terminal of the second flip-flop65changes from a low level to a high level, the second flip-flop65changes the level of the signal output from the Q output terminal thereof to the level of the signal A input to the D input terminal. Otherwise, the second flip-flop65holds the level of the signal output from the Q output terminal thereof.

Therefore, the Q output terminal of the second flip-flop65outputs a signal having a waveform shown inFIG. 8C. The signal output from the Q output terminal of the second flip-flop65has its phase delayed by 90° from the signal input to the first phase shifter31. The first phase shifter31thus delays the phase of the binary signal output from the comparator30by 90°.

Since the first phase shifter31shown inFIG. 7is of a PLL (Phase Locked Loop) circuit arrangement, even if the frequency of the vibration monitor signal varies, it can accurately shift the phase of the binary signal output from the comparator30in a manner to follow such variations of the frequency of the vibration monitor signal.

It has been described above that the frequency-dividing ratio is 2 and the phase shift is 90°. However, another frequency-dividing ratio and a phase shift other than 90° may be used. The first flip-flop64and the second flip-flop65may be replaced with a first frequency counter and a second frequency counter, respectively. Specifically, the first frequency counter may count the frequency of the oscillation signal output from the voltage-controlled oscillator63up to a desired count and generate a first count signal. The first count signal may be input to the input terminal of the phase comparator61. The second frequency counter may count the frequency of the oscillation signal output from the voltage-controlled oscillator63up to a desired count, using the binary signal as an enable signal, and generate a second count signal. The second count signal may be output as the timing signal for synchronous detection to the synchronous detector25.

Operation of the vibratory gyro-sensor100according to the first embodiment will be described below. First, a vibratory gyro circuit120(seeFIG. 9) according to a comparative example will be described below.

COMPARATIVE EXAMPLE

FIG. 9is a block diagram of the vibratory gyro circuit120according to the comparative example.

As shown inFIG. 9, the vibratory gyro circuit120according to the comparative example includes a phase shifter127, an automatic gain controller (AGC)128, a comparator130, a reference voltage supply129, a synchronous detector125, and a filter126.

The phase shifter127shifts the phase of a vibration monitor signal. The vibration monitor signal with the shifted phase is input to the automatic gain controller128, which adjusts the amplitude of the vibration monitor signal and outputs the vibration monitor signal with the adjusted amplitude as a drive signal. The vibration monitor signal with the shifted phase is also input to the comparator130. The comparator130converts the vibration monitor signal with the shifted phase into a binary signal using a signal supplied from the reference voltage source129as a threshold value. The binary signal output from the comparator130is input as a timing signal for synchronous detection to the synchronous detector125.

The synchronous detector125synchronously detects the detected signal in synchronism with the timing signal for synchronous detection. The filter126smoothes the signal which is synchronously detected by the synchronous detector125into a gyro signal (angular velocity signal), and outputs the gyro signal.

FIGS. 10A and 10Bare diagrams showing the relationship between the vibration monitor signal input to the comparator130and a threshold value for the comparator130(FIG. 10A), and a binary signal output from the comparator130(FIG. 10B) in the comparative example.FIG. 10Ashows an example in which the vibration monitor signal is shifted upwardly at the time the low-frequency component of the vibration monitor signal varies due to a time-dependent change in the impedance of the vibratory section10or the vibratory gyro circuit120.

In the comparative example shown inFIG. 9, the signal which serves as the threshold value for the comparator130is of a fixed value input from the reference voltage source129. If the vibration monitor signal is shifted upwardly at the time the low-frequency component of the vibration monitor signal varies due to a time-dependent change in the impedance of the vibratory section10or the vibratory gyro circuit120, as shown inFIG. 10A, the threshold value is shifted out of alignment with the center of the amplitude of the vibration monitor signal. Therefore, as shown inFIG. 10B, the duty ratio of the binary signal output from the comparator130is gradually shifted away from 50%. According to the comparative example, as a result, the synchronous detector125is unable to accurately synchronously detect the detected signal, so that noise tends to be added to the angular velocity signal.

Present Embodiment

The vibratory gyro-sensor100according to the present embodiment will be described below.

FIGS. 11A and 11Bshow the relationship between the vibration monitor signal input to the comparator30and the signal input to the comparator30which has passed through the low-pass filter29(the threshold value for the comparator30) (FIG. 11A), and the binary signal output from the comparator30(FIG. 11B) in the present embodiment.

FIG. 11Ashows an example in which the vibration monitor signal is shifted upwardly at the time the low-frequency component of the vibration monitor signal varies due to a time-dependent change in the impedance of the vibratory section10or the vibratory gyro circuit20.

According to the present embodiment, as described above, the comparator30converts the vibration monitor signal into a binary signal using the low-frequency component of the vibration monitor signal which is extracted by the low-pass filter29as a threshold value. Therefore, as shown inFIG. 11A, even if the vibration monitor signal is shifted upwardly at the time the low-frequency component of the vibration monitor signal input to the comparator30varies, the threshold value for the comparator30also varies in a manner to follow such variations in the low-frequency component of the vibration monitor signal.

Consequently, even when the low-frequency component of the vibration monitor signal varies, the comparator30can generate a binary signal having an “H” interval and an “L” interval that are substantially equal to each other, i.e., having a duty ratio of 50%, as shown inFIG. 11B. As a consequence, the synchronous detector25can synchronously detect the detected signal at an appropriate timing, so that noise is prevented from being added to the gyro signal (angular velocity signal).

According to the present embodiment, moreover, the vibratory gyro-sensor can be manufactured at a reduced cost because it is possible to generate a binary signal having an “H” interval and an “L” interval that are substantially equal to each other with a simple circuit arrangement.

According to the present embodiment, as described above, it is desirable for the comparator30to generate a binary signal having an “H” interval and an “L” interval that are substantially equal to each other, i.e., having a duty ratio of 50%. On the other hand, if the cutoff frequency of the low-pass filter29is not appropriate, then the vibration monitor signal input to the comparator30and the signal serving as the threshold value for the comparator30which has passed through the low-pass filter29are brought widely out of phase with each other. In such a case, the duty ratio of the output signal from the comparator30is shifted away from 50%, and it is not possible to generate a binary signal having an “H” interval and an “L” interval that are substantially equal to each other. Consequently, the low-pass filter29should its cutoff frequency fc set to an appropriate value.

Typically, the cutoff frequency fc of the low-pass filter29is set to 100 Hz or higher. With the cutoff frequency fc of the low-pass filter29being set to 100 Hz or higher, any phase delay of the signal which has passed through the low-pass filter29, i.e., the signal serving as the comparator threshold value, is 1° or smaller at a frequency of 1 Hz or lower. Therefore, when the cutoff frequency fc of the low-pass filter29is set to 100 Hz or higher, the phase difference between the vibration monitor signal input to the comparator30and the signal (whose frequency is 1 Hz or lower) which has passed through the low-pass filter29as the threshold value is 1° or smaller. The comparator30can thus generate a binary signal having an “H” interval and an “L” interval that are substantially equal to each other. If the cutoff frequency fc of the low-pass filter29is set to 1 kHz, then the phase difference between the vibration monitor signal and the signal (whose frequency is 1 Hz or lower) which has passed through the low-pass filter29is substantially zero.

If the low-pass filter29is of the circuit arrangement shown inFIG. 6A, then the cutoff frequency fc thereof may be set to 100 Hz or higher by setting the resistance R and the capacitance C to appropriate values. If the low-pass filter29is of the circuit arrangement shown inFIG. 6B, then the cutoff frequency fc thereof may be set to 100 Hz or higher by setting Ci, fsw, and Co to appropriate values. The cutoff frequency fc of the low-pass filter29is typically set to 1/10 or smaller of the drive frequency of the vibratory section10.

Second Embodiment

A second embodiment of the present disclosure will be described below. Those parts of the second embodiment and other modifications which are identical in structure and function to those of the first embodiment are denoted by identical reference characters, and will not be described in detail below or will be described briefly below.

FIG. 12is a block diagram of a vibratory gyro circuit70according to a second embodiment of the present disclosure.

According to the second embodiment, as shown in FIG.12, a phase shifter73is associated with the vibratory section10rather than the comparator30. The second embodiment is different from the first embodiment in that the phase shifter73shifts the phase of the vibration motor signal from the vibratory section10, and the comparator30binarizes the vibration motor signal with the shifted phase. The second embodiment is also different from the first embodiment in that the phase shifter73is shared by a timing signal output section72and a drive signal output section71.

As shown inFIG. 12, the vibratory gyro circuit70includes the drive signal output section71, the timing signal output section72, the synchronous detector25, and the filter26. The drive signal output section71includes a phase shifter73and the automatic gain controller28. The timing signal output section72includes the phase shifter73which it shares with the drive signal output section71, the low-pass filter29, and the comparator30.

The phase shifter73may be of the circuit arrangement shown inFIG. 5, i.e., a phase shifter for analog signals. The circuit arrangement shown inFIG. 5represents an example of the second phase shifter27according to the first embodiment.

The phase shifter73shifts the phase of the vibration monitor signal. The vibration monitor signal with the shifted phase is input to the automatic gain controller28, which adjusts the amplitude of the vibration monitor signal and outputs the vibration monitor signal with the adjusted amplitude as a drive signal. The vibration monitor signal with the shifted phase is also input to the comparator130. The comparator30converts the vibration monitor signal with the shifted phase into a binary signal using the vibration monitor signal which has passed through the low-pass filter29as a threshold value. The binary signal output from the comparator30is input as a timing signal for synchronous detection to the synchronous detector25.

The synchronous detector25synchronously detects the detected signal in synchronism with the timing signal for synchronous detection. The filter26smoothes the signal synchronously detected by the synchronous detector25into a gyro signal (angular velocity signal), and outputs the gyro signal.

According to the second embodiment, after the phase shifter73shifts the phase of the vibration monitor signal, the comparator30binarizes the vibration monitor signal. The second embodiment offers the same advantages as the first embodiment. Specifically, even when the low-frequency component of the vibration monitor signal varies, the comparator30can generate a binary signal having an “H” interval and an “L” interval that are substantially equal to each other. As a consequence, noise is prevented from being added to the gyro signal (angular velocity signal).

According to the second embodiment, the phase shifter73, which is of a simple circuit arrangement for shifting the phase of analog signals, can be used as a phase shifter in the timing signal output section72. Therefore, the cost of the vibratory gyro circuit70can be reduced. According to the second embodiment, furthermore, the vibratory gyro circuit70is made less costly because the single common phase shifter73is shared by the drive signal output section71and the timing signal output section72. However, the drive signal output section71and the timing signal output section72may not share the single common phase shifter73, but may have respective phase shifters which cause different phase shifts.

FIG. 13is a schematic perspective view showing another example of vibratory section, andFIG. 14is a wiring diagram of the vibratory section shown inFIG. 13and a vibratory gyro circuit.

As shown inFIGS. 13 and 14, a vibratory section9includes a vibration monitor electrode19on the piezoelectric film15disposed on the beam12of the vibrator11. The vibration monitor electrode19is positioned next to one end of the drive electrode16centrally in the widthwise direction (X-axis direction) of the beam12. As shown inFIG. 14, the vibration monitor signal is directly output from the vibration monitor electrode19. The vibratory section9shown inFIGS. 13 and 14is free of the adder21shown inFIG. 2. Otherwise, the vibratory section9shown inFIGS. 13 and 14is of the same structure as the vibratory section10shown inFIGS. 1 and 2.

The present disclosure contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2010-269772 filed in the Japan Patent Office on Dec. 2, 2010, the entire content of which is hereby incorporated by reference.