JP5561237B2 - Vibrator drive circuit - Google Patents

Description

  The present invention relates to a vibrator driving circuit used in a sensor circuit of a gyro sensor.

  Gyros that detect angular velocities required for GPS autonomous navigation, behavior stabilization control, camera shake correction control, etc. for electronic devices such as car navigation systems, vehicle stabilization control (VSC) systems, digital cameras, video cameras, and mobile phones A sensor is incorporated. A vibration type gyro sensor using a vibrator as a driving sensor element is used by vibrating a vibrator to a constant amplitude at a resonance frequency by a vibrator driving circuit (see, for example, Patent Document 1). This vibrator driving circuit includes an amplitude control circuit that automatically adjusts the loop gain based on a monitor signal corresponding to the state of driving vibration of the vibrator output from the gyro sensor. When an angular velocity is applied to the gyro sensor while the vibrator is vibrating, the sensor element for detection vibrates due to the Coriolis force.

Japanese Patent No. 2666505

  In recent years, vibrators having a high Q value (mechanical quality factor) are being used in order to reduce the size and size of the gyro sensor and obtain high sensitivity characteristics. A vibrator having a high Q value is different from the vibrator having a low Q value in material, vacuum sealing, and the like. In the case of a vibrator having a high Q value, the level of the monitor signal at the start of vibration is very weak, and a high SNR performance is required for the vibrator driving circuit in order to reliably vibrate the vibrator. In addition, since the resonance frequency of the vibrator varies, the level of the monitor signal may be further reduced. For this reason, a vibrator drive circuit cannot be configured with an operational amplifier having normal SNR performance. Furthermore, in a vibrator having a high Q value, there is a problem that the time (start-up time) from the start of driving to the stabilization of driving vibration becomes long.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a vibrator drive circuit that reliably activates a vibrator having a weak drive amplitude level at the start of vibration in a short time.

  The vibrator drive circuit according to the first aspect includes two types of drive signal generation means for generating a drive signal to be given to the vibrator. The steady drive signal generating means generates a steady drive signal for continuously vibrating the vibrator based on the monitor signal output according to the state of the drive vibration of the vibrator. The initial drive signal generating means includes an initial drive signal including a drive frequency at which continuous vibration is excited when a closed loop is formed by the vibrator and the steady drive signal generating means from the start of driving of the vibrator or after the start of driving. An initial drive signal is generated.

  The vibrator drive circuit sets a threshold value within a range of amplitude that can excite a continuous vibration when a closed loop is formed by the vibrator and the steady drive signal generating means. The amplitude detection means detects the amplitude of the drive vibration of the vibrator based on the monitor signal. The drive switching means selects the initial drive signal to drive the vibrator when the amplitude of the drive vibration detected by the amplitude detection means is less than the threshold value, and steady drive when the amplitude exceeds the threshold value. A signal is selected to drive the transducer.

  According to this means, when the vibrator is started, an initial drive signal including a drive frequency at which continuous vibration is excited can be used, so that the drive amplitude level at the start of vibration is weak regardless of variations in the resonance frequency. A simple vibrator (for example, a vibrator having a high Q value) can be reliably activated in a short time. Further, since a steady drive signal is used instead of the initial drive signal after the continuous vibration is excited, a stable vibration state with a constant vibration amplitude can be maintained.

The initial drive signal generation means selects an initial drive signal composed of white noise generated by the white noise generation means at the start of driving. The FFT operation means performs an FFT operation on the monitor signal when the vibrator is driven by the initial drive signal. The frequency selection unit selects a frequency having the maximum amplitude among the frequency components included in the monitor signal based on the result of the FFT operation, and the drive signal generation unit generates an initial drive signal having the selected frequency.

  The switching means selects the initial drive signal output from the drive signal generating means on the condition that a frequency component exceeding a predetermined determination level appears in the monitor signal based on the FFT calculation result. According to this means, the initial drive signal including a wide range of frequency components is applied to the vibrator for excitation, the frequency at which the drive vibration actually increases is selected, and the initial drive signal is subsequently given. The vibrator can be driven in a shorter time than the one to be updated.

According to the means described in claim 2 , the initial drive signal generation means is based on the amplitude of the drive vibration detected by the amplitude detection means when the vibrator is driven by the initial drive signals having different drive frequencies. Thus, a driving frequency closer to the resonance frequency of the vibrator to be driven is sequentially determined. As a result, the number of changes in the drive frequency of the initial drive signal can be reduced, and the vibrator can be started more reliably and the startup time can be further shortened.

According to the means described in claim 3 , the initial drive signal generating means drives the vibrator by the initial drive signal having the previous drive frequency f0, the current drive frequency f1, and the drive frequencies f0 and f1. If the detected amplitude is M0, M1 and the control coefficient is K (> 0),
Δf = K · (f1−f0) / (M1−M0)
f2 = f1 + Δf
Thus, the next drive frequency f2 is determined.

  In the vibrator, the gradient of the amplitude with respect to the frequency (= (M1-M0) / (f1-f0)) decreases as the distance from the resonance frequency increases. It has a frequency-amplitude characteristic that increases. Therefore, according to this means, the difference frequency Δf increases at a frequency far from the resonance frequency, and the difference frequency Δf decreases as the resonance frequency is approached. As a result, the startup time is shorter than when the value of the difference frequency Δf is fixed.

According to the means described in claim 4 , the initial drive signal generating means sequentially outputs the initial drive signal having the determined drive frequency f1 and the initial drive signal having the drive frequency f2 of f1 + Δf (Δf is a control constant), If the detected amplitude when the vibrator is driven by the initial drive signal having the drive frequencies f1 and f2 is M1 and M2, and the control coefficient is K (> 0),
f1 = f1 + K · (M2−M1)
Thus, the next drive frequency f1 is determined. According to this means, the drive frequency f1 is determined so as to approach the resonance frequency based on the frequency-amplitude characteristics of the vibrator described above. In addition, since the drive frequency can be updated by a relatively simple calculation that does not include division, the circuit scale is reduced and the processing load is reduced.

According to the means described in claim 5 , the initial drive signal generating means includes the nonvolatile storage means, and the drive frequency when the amplitude of the drive vibration detected by the amplitude detection means is equal to or greater than the threshold value is nonvolatile. The frequency stored in the non-volatile storage means at the start of driving the vibrator is set as the drive start frequency. Thereby, the update of the drive frequency is started from a frequency with a proven record of actual sustained vibration being excited, so that the startup time can be further shortened.

According to the means described in claim 6 , the steady drive signal generating means comprises an AGC circuit comprising an amplitude detection circuit for detecting the amplitude of the monitor signal and an amplitude control circuit, and the amplitude detection means is included in the AGC circuit. The circuit is shared with the amplitude detection circuit. This makes it possible to minimize the increase in circuit scale.

The block block diagram of the sensor circuit which shows the 1st Embodiment of this invention Diagram showing the relationship between the frequency and amplitude of the vibrator The block diagram of the initial stage drive signal generation circuit which shows the 2nd Embodiment of this invention FIG. 3 equivalent view showing a third embodiment of the present invention Configuration diagram of white noise generation circuit FIG. 3 equivalent view showing the fourth embodiment of the present invention Flow chart showing drive frequency calculation processing 2 equivalent diagram FIG. 7 equivalent view showing the fifth embodiment of the present invention FIG. 3 equivalent view showing the sixth embodiment of the present invention FIG. 3 equivalent view showing a seventh embodiment of the present invention FIG. 1 equivalent view showing an eighth embodiment of the present invention Block diagram of AGC circuit

In each embodiment, substantially the same parts are denoted by the same reference numerals and description thereof is omitted.
(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. 1 and 2.
FIG. 1 shows a block configuration of a sensor circuit that is applied to a car navigation system, a vehicle stabilization control (VSC) system, and the like and detects an angular velocity. An electrostatic drive / capacitance detection type micro gyro sensor is driven and vibrated in a first direction parallel to the substrate surface and detected in a second direction orthogonal to the first direction on a substrate formed of single crystal silicon or the like. The vibrator 1 is arranged so as to be. Although not shown, a drive electrode for driving and vibrating the vibrator 1 in the first direction around the vibrator 1 and a monitor electrode for monitoring the state of the drive vibration of the vibrator 1 are arranged around the vibrator 1. A pair of detection electrodes for detecting vibration in the second direction of the vibrator 1 are formed.

  The vibrator drive circuit 2 vibrates by applying an electrostatic force between the vibrator 1 and the drive electrode by applying a steady drive signal corresponding to the inherent resonance frequency of the vibrator 1 to the drive electrode in the steady drive state. The child 1 is driven to vibrate in the first direction. When an angular velocity centered on an axis perpendicular to the substrate surface is applied to the micro gyro sensor while the vibrator 1 is driven to vibrate, the vibrator 1 is detected and vibrated in the second direction by Coriolis force. The detection circuit 3 detects the angular velocity based on the change in capacitance between the vibrator 1 and the detection electrode due to the detection vibration. A specific configuration will be described below.

  The vibrator drive circuit 2 includes a steady drive signal generation circuit 4, an amplitude detection circuit 5, an initial drive signal generation circuit 6, and a drive switching circuit 7. The steady drive signal generation circuit 4 (steady drive signal generation means) is a steady drive signal that continuously vibrates the vibrator 1 based on the monitor signal output from the monitor electrode according to the drive vibration state of the vibrator 1. Is generated. The amplifier circuit 8 amplifies the monitor signal. An AGC (Automatic Gain Control) circuit 9 automatically adjusts the closed-loop gain so that the amplitude of the amplified monitor signal, that is, the vibration speed of the vibrator 1 becomes constant, in order to keep the sensitivity of the micro gyro sensor constant. As a result, the vibrator 1 in the steady drive state continues to vibrate in the first direction at the resonance frequency.

  As described above, the vibrator 1 having a high Q value has a very weak drive vibration level (monitor signal level) at the start of vibration. Further, since the resonance frequency of the vibrator 1 varies, the level of the monitor signal is further reduced according to the deviation between the drive frequency and the resonance frequency. Therefore, the initial drive signal generation circuit 6 (initial drive signal generation means) includes an initial drive signal including a drive frequency at which continuous vibration is excited when the vibrator 1 and the steady drive signal generation circuit 4 form a closed loop. Is generated. In this case, an initial drive signal including a drive frequency that can excite the continuous vibration from the start of driving is generated, and an initial drive that includes the drive frequency that can excite the continuous vibration by updating the drive frequency after the drive starts. In some cases, a signal is generated.

  The amplitude detection circuit 5 (amplitude detection means) detects the amplitude of the drive vibration of the vibrator 1 based on the amplified monitor signal. In the drive switching circuit 7 (drive switching means), the amplitude (detected amplitude) of the drive vibration detected by the amplitude detection circuit 5 is continuous when the vibrator 1 and the steady drive signal generation circuit 4 form a closed loop. A threshold value Mth within an amplitude range that can excite various vibrations is set. When the detected amplitude is less than the threshold value Mth, the drive switching circuit 7 selects the initial drive signal output from the initial drive signal generation circuit 6 and outputs it to the drive electrode of the vibrator 1 so that the detected amplitude is the threshold. When the value is equal to or greater than the value Mth, the steady drive signal output by the steady drive signal generation circuit 4 is selected and output to the drive electrode of the vibrator 1.

  The detection circuit 3 includes a binarization circuit 10, an amplification circuit 11, a synchronous detection circuit 12, and a filter circuit 13. The binarization circuit 10 generates a reference signal for synchronous detection by binarizing the monitor signal amplified by the amplifier circuit 8 with a comparator and shifting the phase by 90 °. The amplifier circuit 11 differentially amplifies the detection signals output from the detection electrodes and having opposite phases to each other. The synchronous detection circuit 12 synchronously detects the detection signal using the reference signal. As a result, the detection signal is full-wave rectified in synchronization with the reference signal. The filter circuit 13 is a low-pass filter composed of, for example, a CR filter, and outputs a desired angular velocity signal corresponding to the angular velocity by smoothing high frequency noise generated in the synchronous detection circuit 12.

Next, the operation and effect of this embodiment will be described.
FIG. 2 shows the relationship between the frequency and the amplitude of the vibrator 1. The amplitude of vibration becomes maximum when the vibrator 1 vibrates at the resonance frequency, and decreases as it deviates from the resonance frequency. The amplitude change rate, that is, the slope, with respect to the frequency change rate has a positive value in a frequency region lower than the resonance frequency and a negative value in a frequency region higher than the resonance frequency. The inclination decreases as the difference between the vibration frequency and the resonance frequency increases, except in the vicinity of the resonance frequency. The threshold value Mth shown in the figure is an amplitude capable of exciting a continuous vibration when a closed loop is formed by the vibrator 1 and the steady drive signal generation circuit 4 as described above.

  In the conventional vibrator driving circuit including only the steady driving signal generation circuit 4, the driving frequency at the start of driving is fixed to one frequency. For this reason, if the drive frequency is out of the frequency range from fa to fb shown in FIG. 2 due to variations in the resonance frequency of the vibrator 1, the vibrator 1 cannot be started or it takes a long time to start. .

  On the other hand, the vibrator drive circuit 2 according to the present embodiment switches the drive switching circuit 7 to the initial drive signal generation circuit 6 side at the start of driving when the ignition switch is turned on, for example. The initial drive signal output from the initial drive signal generation circuit 6 is a drive frequency (see FIG. 2) at which the drive vibration amplitude greater than or equal to the threshold value Mth is obtained at the start of drive or after the drive frequency is updated. Drive frequency within the range of fa to fb).

  As a result, it is possible to reliably start the vibrator 1 having a variation in resonance frequency due to manufacturing variation or the like in a short time. In particular, in the vibrator 1 having a high Q value, the amplitude level of the drive vibration at the start of vibration is weak, but in this embodiment, a higher amplitude level than that in the past can be obtained. An operational amplifier having SNR performance can be used. Further, after the continuous vibration is excited, the drive switching circuit 7 switches to the steady drive signal generation circuit 4 side, so that a stable vibration state with a constant vibration amplitude can be maintained.

(Second Embodiment)
The second embodiment will be described with reference to FIG. 3 showing a specific configuration of the initial drive signal generation circuit 6. The drive frequency holding circuit 21 includes a memory or a register that holds the value of the output drive frequency. The rectangular wave signal generating circuit 22 (driving signal generating means) reads the driving frequency held in the driving frequency holding circuit 21 at a predetermined cycle, and generates an initial driving signal composed of a rectangular wave having the driving frequency. The adding circuit 23 adds a predetermined difference frequency Δf to the driving frequency held in the driving frequency holding circuit 21 in the predetermined cycle. The drive frequency updated by the addition operation is held in the drive frequency holding circuit 21.

  The driving start frequency held in the driving frequency holding circuit 21 at the start of driving is set to the lowest resonance frequency or the highest resonance frequency within the range of variations in the resonance frequency of the vibrator 1. In the former case, the addition circuit 23 sequentially updates the initial drive signal by monotonically adding a predetermined difference frequency Δf (> 0) starting from the drive start frequency. In the latter case, the adding circuit 23 monotonously subtracts a predetermined difference frequency Δf (> 0) starting from the driving start frequency (in other words, monotonously adding the difference frequency Δf (<0)). Are updated sequentially.

  The initial drive signal generation circuit 6 stops its operation when the detected amplitude becomes equal to or greater than the threshold value Mth. In addition, this embodiment with improved start-up performance cannot normally occur, but the operation is also stopped when the drive frequency is added to the highest resonance frequency or subtracted to the lowest resonance frequency by updating the initial drive signal. To do. In this latter case, a lower drive start frequency or a higher drive start frequency may be reset in the drive frequency holding circuit 21 and the drive frequency update process may be repeated.

  The absolute value of the difference frequency Δf needs to be set to Δfw = | fb−fa | (see FIG. 2) or less. If it is set to be larger than Δfw, there is a possibility that it will jump over the drive frequency range in which the vibrator 1 can excite continuous vibration during the update. On the other hand, if the difference frequency Δf is too small, the time until the vibrator 1 is excited with continuous vibration, that is, the time from the start of driving to the stabilization of the driving vibration (start-up time) becomes long. Therefore, the difference frequency Δf is determined in consideration of these conditions.

  According to the present embodiment, the vibrator 1 can be reliably started up with the initial drive frequency suitable for excitation even when the manufacturing variation of the resonance frequency is large. Further, as described above, the startup time can be shortened as much as possible by appropriately determining the magnitude of the difference frequency Δf.

(Third embodiment)
A third embodiment will be described with reference to FIGS. 4 and 5. FIG. 4 shows a specific configuration of the initial drive signal generation circuit 6. As shown in FIG. 5, the white noise generating circuit 24 (white noise generating means) returns white noise (M-sequence signal) by returning ExOR between the output data of the shift register composed of the D flip-flop and the intermediate stage data. Is generated.

  The FFT operation circuit 25 (FFT operation means) is composed of a microcomputer, dedicated hardware, and the like, and performs an FFT operation on the monitor signal output from the amplifier circuit 8 (see FIG. 1). The frequency selection circuit 26 (frequency selection means) selects the frequency having the maximum amplitude among the frequency components included in the monitor signal based on the FFT calculation result. The rectangular wave signal generation circuit 22 generates an initial drive signal having a selected frequency.

  The switching circuit 27 (switching means) selects the initial drive signal output from the white noise generating circuit 24 at the start of driving, and when a frequency component exceeding a predetermined determination level appears in the monitor signal based on the FFT calculation result. The initial drive signal output from the rectangular wave signal generation circuit 22 is selected. The determination level is set to a value smaller than the threshold value Mth.

  According to this configuration, the initial drive signal generation circuit 6 supplies the vibrator 1 with an initial drive signal having a wide frequency component including the range of variation in the resonance frequency of the vibrator 1 at the start of driving. The drive vibration of the vibrator 1 gradually increases with this initial drive signal. In the present embodiment, when a frequency component exceeding the determination level appears, a rectangular wave signal having a large amplitude having a frequency having the maximum amplitude in the frequency, that is, the FFT calculation result, is given to the vibrator 1 as an initial drive signal. As a result, since the increase in drive vibration is accelerated, the time from the start of driving to switching to the steady drive signal, and thus the time to reach a stable steady drive state can be shortened.

(Fourth embodiment)
A fourth embodiment will be described with reference to FIGS. FIG. 6 shows a specific configuration of the initial drive signal generation circuit 6. The memory circuit 28 is configured by a memory or a register, and has an updated drive frequency f and a detected amplitude M when the vibrator 1 is driven with an initial drive signal having the drive frequency f for each predetermined period. Store in association with each other.

  The resonance frequency prediction circuit 29 is configured by a microcomputer, dedicated hardware, and the like, and is closer to the resonance frequency of the vibrator 1 based on the two most recent drive frequencies f and amplitude M stored in the storage circuit 28. The drive frequency is calculated sequentially. The calculated drive frequency is held in the drive frequency holding circuit 21. The rectangular wave signal generation circuit 22 reads the driving frequency held in the driving frequency holding circuit 21 and generates an initial driving signal composed of a rectangular wave having the driving frequency. After outputting for a predetermined period, the drive frequency f and the detected amplitude M are stored in the storage circuit 28 as described above.

  FIG. 7 is a flowchart showing a driving frequency calculation process performed by the initial driving signal generation circuit 6. The initial drive signal generation circuit 6 sets a drive start frequency to f1 used in the resonance frequency prediction circuit 29 and sets a difference initial value to Δf in step S1 immediately after the start of the arithmetic processing. The drive start frequency f1 here is the lowest resonance frequency or the highest resonance frequency within the range of variations in the resonance frequency of the vibrator 1, as described in the second embodiment.

  In step S2, the drive start frequency f1 is held in the drive frequency holding circuit 21, and the rectangular wave signal generation circuit 22 outputs an initial drive signal composed of a rectangular wave having the drive frequency f1 for a predetermined time (predetermined period). Thereafter, the initial drive signal generation circuit 6 inputs the detection amplitude M1 from the amplitude detection circuit 5 in step S3, and stores the drive frequency f1 and the detection amplitude M1 in the storage circuit 28. In subsequent step S4, it is determined whether or not the detected amplitude M1 is larger than a threshold value Mth. If the detected amplitude M1 is larger than the threshold value Mth (S4: YES), the drive switching circuit 7 switches from the initial drive signal to the steady drive signal, and the calculation process is terminated.

  On the other hand, when the detected amplitude M1 is equal to or less than the threshold value Mth (S4: NO), the resonance frequency prediction circuit 29 sets the difference frequency Δf (at this time) to the drive frequency f1 (the drive start frequency at this time) in step S5. Then, the difference frequency initial value) is added to obtain the drive frequency f2. The initial drive signal generation circuit 6 executes the same processing as in steps S2, S3, and S4 for the drive frequency f2 in subsequent steps S6, S7, and S8. That is, the detection amplitude M2 is input, and the drive frequency f2 and the detection amplitude M2 are stored in the storage circuit 28.

When the detected amplitude M2 is equal to or smaller than the threshold value Mth (S8: NO), the resonance frequency prediction circuit 29 calculates the difference frequency Δf by the equation (1) in step S9. Here, K (> 0) is a control coefficient. F1 corresponds to the previous drive frequency, and f2 corresponds to the current drive frequency. After using the drive frequencies f1 and f2 and the detected amplitudes M1 and M2 for the calculation, the current values f2 and M2 are set to the previous values f1 and M1 in preparation for the next calculation.
Δf = K · (f2−f1) / (M2−M1) (1)

Subsequently, the process proceeds to step S5 again, and the drive frequency f2 to be used next is calculated by equation (2).
f2 = f1 + Δf (2)
In this way, the processing of steps S5 to S9 is repeated, and when the detected amplitude M2 becomes larger than the threshold value Mth (S8: YES), the calculation processing is ended.

  FIG. 8 shows the relationship between the frequency and amplitude of the vibrator 1. As described above, the amplitude change rate, that is, the inclination with respect to the frequency change rate becomes smaller as the difference between the vibration frequency and the resonance frequency becomes larger except in the vicinity of the resonance frequency. Since the difference frequency Δf shown in the equation (1) is equal to (K / inclination), the smaller the inclination, the larger the difference frequency Δf, and the next drive frequency f2 is set to be accelerated toward the resonance frequency. Note that the difference frequency Δf increases even in the vicinity of the resonance frequency where the inclination becomes small, but the detected amplitude M2 becomes equal to or greater than the threshold value Mth before the drive frequency reaches the vicinity of the resonance frequency. The operation is stopped in the vicinity of the resonance frequency.

The difference frequency Δf is determined so that Equation (3) is established using Δfw shown in FIG. If this relationship is not satisfied, the next drive frequency f2 may jump over the drive frequency range in which continuous vibration can be excited. This adjustment may be performed by setting the control coefficient K.
f1 + Δf ≦ resonance frequency + Δfw / 2 (3)

  As described above, the initial drive signal generation circuit 6 according to the present embodiment vibrates based on the detected amplitudes M1 and M2 when the vibrator 1 is driven by the initial drive signals having different drive frequencies f1 and f2. A drive frequency closer to the resonance frequency of the child 1 is sequentially determined. As a result, the number of changes in the drive frequency of the initial drive signal can be reduced, and the vibrator 1 can be reliably started and its start-up time can be shortened. Furthermore, as shown in the equation (1), the difference frequency Δf increases as the drive frequency is further away from the resonance frequency, so that the startup time is further shortened.

(Fifth embodiment)
A fifth embodiment will be described with reference to FIG. Similar to the fourth embodiment, the initial drive signal generation circuit 6 of the present embodiment also has the configuration shown in FIG. The calculation method of the resonance frequency prediction circuit 29 is partially different from the fourth embodiment. In the flowchart shown in FIG. 9, the same steps as those shown in FIG.

In the present embodiment, the difference frequency Δf (> 0) is a control constant. The initial drive signal generation circuit 6 sets the drive start frequency to f1 in step S10 immediately after the start of the arithmetic processing. Thereafter, Steps S2 to S8 are executed to obtain detected amplitudes M1 and M2 when the vibrator 1 is driven by an initial drive signal having drive frequencies f1 and f2 (= f1 + Δf), respectively. The resonance frequency prediction circuit 29 calculates the drive frequency f1 by the equation (4) in step S11. Here, K (> 0) is a control coefficient.
f1 = f1 + K · (M2−M1) (4)

  When the drive frequency f1 is calculated, the initial drive signal generation circuit 6 acquires the detection amplitude M1 corresponding to the drive frequency f1 again in steps S2 and S3, and associates the drive frequency f1 with the detection amplitude M1 to store the memory circuit 28. To remember. If the detected amplitude M1 is less than or equal to the threshold value Mth (S4: NO), the process further proceeds to step S5, and the drive frequency f2 is calculated by the above-described equation (2). Δf used in equation (2) is a control constant. In subsequent steps S6 and S7, the detection amplitude M2 corresponding to the drive frequency f2 is acquired, and the drive frequency f2 and the detection amplitude M2 are associated with each other and stored in the storage circuit 28. When the detected amplitude M2 is less than or equal to the threshold value Mth (S8: NO), the process proceeds to step S11 again, and the drive frequency f1 is calculated by the equation (4).

  The initial drive signal generation circuit 6 according to the present embodiment also uses the resonance frequencies of the vibrator 1 based on the detected amplitudes M1 and M2 when the vibrator 1 is driven by initial drive signals having different drive frequencies f1 and f2. Close drive frequencies are determined sequentially. As a result, the drive frequency f1 is determined so as to approach the resonance frequency. Further, unlike the fourth embodiment, the drive frequency f1 is obtained by a relatively simple calculation that does not include division, so that the circuit scale can be reduced and the processing load is reduced.

(Sixth embodiment)
The initial drive signal generation circuit 6 of the sixth embodiment shown in FIG. 10 is different from the initial drive signal generation circuit 6 of the fourth embodiment and the fifth embodiment shown in FIG. The storage means) is added. When the initial drive signal generation circuit 6 determines YES in step S4 or step S8 in FIG. 7 or FIG. 9, the drive frequency f1 or f2 at that time is stored in the nonvolatile memory circuit 30.

  On the other hand, the initial drive signal generation circuit 6 reads the frequency stored in the nonvolatile memory circuit 30 and sets it as f1 as the drive start frequency in step S1 or step S10 when the drive of the vibrator 1 is started. According to the present embodiment, since the calculation of the drive frequency is started from a frequency with a proven record of actual sustained vibration, the startup time can be further shortened.

(Seventh embodiment)
A seventh embodiment will be described with reference to FIG. The initial drive signal generation circuit 6 of the present embodiment includes a white noise generation circuit 24 (see FIG. 5) that generates white noise (M-sequence signal). The white noise has a wide frequency component including a variation range of the resonance frequency of the vibrator 1. For this reason, when the vibrator 1 is given with white noise as an initial drive signal at the start of driving, the frequency component corresponding to the resonance frequency of the vibrator 1 gradually increases. When the detected amplitude is equal to or greater than the threshold value Mth, the drive switching circuit 7 selects the steady drive signal instead of the initial drive signal and drives the vibrator 1, so that the initial drive signal generation circuit 6 stops its operation. According to the present embodiment, the vibrator 1 can be excited without changing the drive frequency, and the configuration of the initial drive signal generation circuit 6 can be simplified.

(Eighth embodiment)
An eighth embodiment applicable to each of the above-described embodiments will be described with reference to FIGS. FIG. 12 shows a block configuration of the sensor circuit, and FIG. 13 shows a block configuration of the AGC circuit. The vibrator drive circuit 31 has a circuit configuration in which the amplitude detection circuit 5 shown in FIG. 1 is shared with the amplitude detection circuit 32 included in the AGC circuit 9.

  The AGC circuit 9 includes an amplitude detection circuit 32 and an amplitude control circuit 33. Of these, the amplitude detection circuit 32 includes a rectification circuit 34 and a smoothing circuit 35 that rectifies and smoothes the monitor signal amplified by the amplification circuit 8, and outputs a detection amplitude corresponding to the magnitude of the drive amplitude. This detected amplitude is used for determination of switching from the initial drive signal to the steady drive signal and generation of the steady drive signal in the drive switching circuit 7. Therefore, the amplitude detection circuit 32 in the AGC circuit 9 needs to be always operated regardless of before and after the switching of the drive switching circuit 7.

  On the other hand, the amplitude control circuit 33 includes a phase shifter 36, a comparison circuit 37, and a drive voltage adjustment circuit 38. When a drive signal is applied to the drive electrode of the vibrator 1 to vibrate, a phase difference of about 90 ° occurs between the drive signal and the monitor signal output from the monitor electrode. Therefore, the phase shifter 36 shifts the phase of the output signal of the amplifier circuit 8 by about 90 ° so that the phases of the monitor signal and the drive signal match.

  The comparison circuit 37 compares the detected amplitude with the target amplitude and outputs a difference between the two amplitudes. The drive voltage adjustment circuit 38 generates a drive signal synchronized with the phase-shifted monitor signal output from the phase shifter 36. At that time, the gain adjustment when generating the drive signal is performed based on the amplitude difference output from the comparison circuit 37 so that the amplitude of the drive vibration of the vibrator 1 becomes equal to the target amplitude. As a result, the vibrator 1 is excited so that the amplitude of the drive vibration is constant. According to this embodiment, since the amplitude detection circuit 5 (see FIG. 1) and the amplitude detection circuit 32 included in the AGC circuit 9 can be shared, it is possible to minimize an increase in circuit scale. .

(Other embodiments)
As mentioned above, although preferred embodiment of this invention was described, this invention is not limited to embodiment mentioned above, A various deformation | transformation and expansion | extension can be performed within the range which does not deviate from the summary of invention.
The present invention can be generally applied to a vibration type gyro sensor regardless of a vibration system.
The drive signal generating means is not limited to the rectangular wave signal generating circuit 22 and may be composed of a sine wave signal generating circuit or the like.

  The second and third embodiments also include the nonvolatile memory circuit 30 as in the sixth embodiment, and the drive frequency when the detected amplitude is equal to or greater than the threshold value Mth is stored in the nonvolatile memory circuit 30. The frequency stored in the nonvolatile memory circuit 30 at the start of driving of the vibrator 1 may be set as the drive start frequency. In the third embodiment, the white noise generation circuit 24 may be used at the first activation, and the frequency stored in the nonvolatile memory circuit 30 may be activated as the drive start frequency at the second and subsequent activations.

  The white noise generating means is not limited to the circuit shown in FIG. 5, and any white noise or pseudo white noise including a resonance frequency component of the vibrator 1 may be used.

  In the drawings, 1 is a vibrator, 2 and 31 are vibrator drive circuits, 4 is a steady drive signal generation circuit (steady drive signal generation means), 5 is an amplitude detection circuit (amplitude detection means), and 6 is an initial drive signal generation circuit. (Initial drive signal generation means), 7 is a drive switching circuit (drive switching means), 9 is an AGC circuit, 22 is a rectangular wave signal generation circuit (drive signal generation means), and 24 is a white noise generation circuit (white noise generation means). , 25 is an FFT operation circuit (FFT operation means), 26 is a frequency selection circuit (frequency selection means), 27 is a switching circuit (switching means), 30 is a nonvolatile memory circuit (nonvolatile memory means), and 32 is an amplitude detection circuit. 33 are amplitude control circuits.

Claims (6)

A steady drive signal generating means for generating a steady drive signal for continuously vibrating the vibrator based on a monitor signal output according to the state of drive vibration of the vibrator;
Amplitude detecting means for detecting the amplitude of the drive vibration of the vibrator based on the monitor signal;
When the closed loop is formed by the vibrator and the steady drive signal generating means, an initial drive signal is generated so that a drive frequency at which a continuous vibration is excited is included from the start of driving of the vibrator or after the start of driving. Initial drive signal generating means for
The initial drive signal is selected when the amplitude of the drive vibration detected by the amplitude detection means is less than a threshold value set within an amplitude range in which continuous vibration can be excited when the closed loop is formed. Driving the vibrator, and when it becomes equal to or greater than the threshold value, a drive switching means for driving the vibrator by selecting the steady drive signal ,
The initial drive signal generating means includes
White noise generating means for generating an initial drive signal composed of white noise;
FFT calculation means for performing FFT calculation on the monitor signal;
Frequency selection means for selecting a frequency having a maximum amplitude among frequency components included in the monitor signal based on the calculation result of the FFT;
Drive signal generating means for generating an initial drive signal having the selected frequency;
An initial drive signal output from the white noise generating means is selected at the start of driving, and the drive signal is generated on the condition that a frequency component exceeding a predetermined determination level appears in the monitor signal based on the calculation result of the FFT A vibrator drive circuit comprising switching means for selecting an initial drive signal output from the means . A steady drive signal generating means for generating a steady drive signal for continuously vibrating the vibrator based on a monitor signal output according to the state of drive vibration of the vibrator;
Amplitude detecting means for detecting the amplitude of the drive vibration of the vibrator based on the monitor signal;
When the closed loop is formed by the vibrator and the steady drive signal generating means, an initial drive signal is generated so that a drive frequency at which a continuous vibration is excited is included from the start of driving of the vibrator or after the start of driving. Initial drive signal generating means for
The initial drive signal is selected when the amplitude of the drive vibration detected by the amplitude detection means is less than a threshold value set within an amplitude range in which continuous vibration can be excited when the closed loop is formed. Driving the vibrator, and when it becomes equal to or greater than the threshold value, a drive switching means for driving the vibrator by selecting the steady drive signal,
The initial drive signal generation means is configured to resonate a vibrator to be driven based on the amplitude of the drive vibration detected by the amplitude detection means when the vibrator is driven by initial drive signals having different drive frequencies. A vibrator driving circuit characterized by sequentially determining a driving frequency closer to the frequency . The initial drive signal generating means sets the detected amplitude when the vibrator is driven by the initial drive signal having the previous drive frequency f0, the current drive frequency f1, and the drive frequencies f0, f1 to M0, M1, If the control coefficient is K (> 0),
Δf = K · (f1−f0) / (M1−M0)
f2 = f1 + Δf
The vibrator driving circuit according to claim 2 , wherein the next driving frequency f2 is determined by The initial drive signal generating means sequentially outputs an initial drive signal having a determined drive frequency f1 and an initial drive signal having a drive frequency f2 of f1 + Δf (Δf is a control constant), and an initial drive having the drive frequencies f1 and f2. If the detected amplitude when the vibrator is driven by a signal is M1, M2, and the control coefficient is K (> 0),
f1 = f1 + K · (M2−M1)
The vibrator driving circuit according to claim 2, wherein the next driving frequency f1 is determined by The initial drive signal generating means includes nonvolatile storage means, and stores the drive frequency when the amplitude of the drive vibration detected by the amplitude detection means is equal to or greater than the threshold value in the nonvolatile storage means, 5. The vibrator driving circuit according to claim 1, wherein a frequency stored in the non-volatile storage unit is set as a driving start frequency when driving of the vibrator is started. 6. A steady drive signal generating means for generating a steady drive signal for continuously vibrating the vibrator based on a monitor signal output according to the state of drive vibration of the vibrator;
Amplitude detecting means for detecting the amplitude of the drive vibration of the vibrator based on the monitor signal;
When the closed loop is formed by the vibrator and the steady drive signal generating means, an initial drive signal is generated so that a drive frequency at which a continuous vibration is excited is included from the start of driving of the vibrator or after the start of driving. Initial drive signal generating means for
The initial drive signal is selected when the amplitude of the drive vibration detected by the amplitude detection means is less than a threshold value set within an amplitude range in which continuous vibration can be excited when the closed loop is formed. Driving the vibrator, and when it becomes equal to or greater than the threshold value, a drive switching means for driving the vibrator by selecting the steady drive signal,
The steady drive signal generating means includes an AGC circuit including an amplitude detection circuit and an amplitude control circuit for detecting the amplitude of the monitor signal,
The vibrator driving circuit , wherein the amplitude detecting means is a circuit shared with an amplitude detecting circuit included in the AGC circuit.

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