Gyro sensor

Abstract

This gyro sensor comprises a vibrator, a plurality of electrodes, and a control unit. The plurality of electrodes include a drive electrode and a detection electrode. The drive electrode has applied thereto a drive signal for driving and vibrating the vibrator. The detection electrode outputs a detection signal generated by vibration of the vibrator. The control unit comprises a drive circuit unit, a detection circuit unit, and a mode switching unit. The drive circuit unit generates the drive signal. The detection circuit unit generates an angular velocity signal from the detection signal. The mode switching unit switches operation modes of the drive circuit unit and the detection circuit unit. The mode switching unit switches, on the basis of the detection signal inputted to the detection circuit unit, the operation mode to a sleep mode or an active mode.

Description

Gyro sensor

[0001] The present disclosure generally relates to a gyro sensor, and more particularly to a gyro sensor whose operation mode can be switched between an active mode and a sleep mode.

[0002] The inertial force sensor described in Patent Document 1 includes a first sensor element that is an acceleration sensor, a second sensor element that is an angular velocity sensor, a first signal processing unit, a second signal processing unit, and a power control unit. The first signal processing unit obtains the acceleration applied to the first sensor element based on the output signal of the first sensor element. The second signal processing unit obtains the angular velocity applied to the second sensor element based on the output signal of the second sensor element. The power control unit switches the operation mode of the second signal processing unit between a normal power mode (active mode) and a power saving mode (sleep mode) based on the acceleration obtained by the first signal processing unit.

[0003] International Publication No. 2013 / 125200

[0004] In Patent Document 1, the operation mode of the second signal processing unit that processes the output signal of the angular velocity sensor is switched using the acceleration obtained from the output signal of the acceleration sensor. Therefore, in Patent Document 1, it is necessary to provide an acceleration sensor in order to switch the operation mode of the angular velocity sensor. For this reason, Patent Document 1 has a problem that the inertial force sensor becomes large-sized and the power consumption increases.

[0005] A gyro sensor according to one aspect of the present disclosure comprises a vibrator, a plurality of electrodes, and a control unit. The plurality of electrodes are arranged facing the vibrator and form capacitance with the vibrator. The control unit is connected to the plurality of electrodes. The plurality of electrodes include a drive electrode and a detection electrode. A drive signal is applied to the drive electrode to drive the vibrator to vibrate. The detection electrode outputs a detection signal generated by the vibration of the vibrator. The control unit comprises a drive control unit, a detection circuit unit, and a mode switching unit. The drive circuit unit generates the drive signal. The detection circuit unit generates an angular velocity signal from the detection signal. The mode switching unit switches the operating modes of the drive circuit unit and the detection circuit unit. The mode switching unit switches the operating mode to sleep mode or active mode based on the detection signal input to the detection circuit unit.

[0006] This disclosure has the effect of providing a gyro sensor that is miniaturized and power-efficient.

[0007] Figure 1 is a block diagram of a gyro sensor according to Embodiment 1. Figure 2 is a block diagram showing the main parts of the gyro sensor. Figure 3 is an explanatory diagram illustrating the operation of the gyro sensor. Figure 4 is a block diagram of a gyro sensor according to Embodiment 2. Figure 5 is an explanatory diagram illustrating the operation of the gyro sensor. Figure 6 is a block diagram of a gyro sensor according to Embodiment 3.

[0008] (Embodiment 1) Hereinafter, the gyro sensor 1 according to Embodiment 1 will be described with reference to the drawings.

[0009] (Overview) As shown in Figure 1, the gyro sensor 1 according to Embodiment 1 comprises a vibrator 10, a plurality of electrodes 2, and a control unit 3. The plurality of electrodes 2 are arranged facing the vibrator 10 and form capacitance with the vibrator 10. The control unit 3 is connected to the plurality of electrodes 2. The plurality of electrodes 2 include a drive electrode 21 and a detection electrode 22. A drive signal D1 is applied to the drive electrode 21 to drive the vibrator 10. The detection electrode 22 outputs a detection signal S1 generated by the vibration (detection vibration) of the vibrator 10. The control unit 3 comprises a drive circuit unit 31, a detection circuit unit 32, and a mode switching unit 33. The drive circuit unit 31 generates the drive signal D1. The detection circuit unit 32 generates an angular velocity signal from the detection signal S1. The mode switching unit 33 switches the operating modes of the drive circuit unit 31 and the detection circuit unit 32. The mode switching unit 33 switches the operating mode to sleep mode or active mode based on the detection signal S1 input to the detection circuit unit 32.

[0010] This configuration allows the operating mode to be switched based on the detection signal S1 of the sensor elements (vibrator 10 and multiple electrodes 2). Therefore, since the operating mode can be switched without using the detection signal of the acceleration sensor, the acceleration sensor can be omitted. As a result, the gyro sensor 1 can be made smaller and more power-efficient by eliminating the acceleration sensor.

[0011] (Details) The gyro sensor 1 according to Embodiment 1 will be described in more detail below.

[0012] (1) As shown in the overall configuration diagram 1, the gyro sensor 1 comprises an oscillator 10, a plurality of electrodes 2 (six in Figure 1), and a control unit 3. The gyro sensor 1 automatically and selectively switches between active mode and sleep mode, as described later.

[0013] (1-1) The oscillator and the plurality of electrode oscillators 10 are formed from a material including, for example, single-crystal silicon or polycrystalline silicon. The shape of the oscillator 10 is, for example, disc-shaped.

[0014] Multiple electrodes 2 are positioned facing the vibrator 10. More specifically, the multiple electrodes 2 are positioned around the vibrator 10, with a gap between them and the vibrator 10. Each of the multiple electrodes 2 has a facing surface that faces the vibrator 10.

[0015] The plurality of electrodes 2 in Embodiment 1 include two drive electrodes 21, two detection electrodes 22, and two monitor electrodes 23.

[0016] In Figure 1, the two drive electrodes 21 are shown adjacent to each other, but it is preferable that the two drive electrodes 21 are positioned on opposite sides of the center of the vibrator 10. That is, it is preferable that the vibrator 10 is positioned between the two drive electrodes 21. Similarly, it is preferable that the two detection electrodes 22 are positioned on opposite sides of the center of the vibrator 10, and the two monitor electrodes 23 are positioned on opposite sides of the center of the vibrator 10.

[0017] When distinguishing between the two drive electrodes 21, they shall be referred to as the first drive electrode 21a and the second drive electrode 21b. Similarly, when distinguishing between the two detection electrodes 22, they shall be referred to as the first detection electrode 22a and the second detection electrode 22b. Furthermore, when distinguishing between the two monitor electrodes 23, they shall be referred to as the first monitor electrode 23a and the second monitor electrode 23b.

[0018] Two drive electrodes 21 are subjected to drive signals D1 that are out of phase with respect to each other. The drive signal D1 is a voltage signal. The frequency of the drive signal D1 matches the resonant frequency of the oscillator 10. When two drive signals D1 that are out of phase with respect to each other are applied to the two drive electrodes 21, the oscillator 10 vibrates (expands and contracts) periodically due to the electrostatic force between the oscillator 10 and the two drive electrodes 21. This vibration is referred to as drive vibration in this disclosure.

[0019] The two detection electrodes 22 face the vibrator 10 in a direction perpendicular to the direction of the drive vibration of the vibrator 10. The two monitor electrodes 23 face the vibrator 10 in a direction perpendicular to the direction of the drive vibration of the vibrator 10.

[0020] When the vibrator 10 vibrates, the distance between the vibrator 10 and the two monitor electrodes 23 changes, and the capacitance between the vibrator 10 and the two monitor electrodes 23 changes. As a result, the two monitor electrodes 23 output two monitor signals M1 that are in opposite phase to each other, corresponding to the change in capacitance. The monitor signals M1 are current signals.

[0021] The monitor signal M1 is an AC signal. The frequency of the monitor signal M1 matches the resonant frequency of the oscillator 10. The components corresponding to the driving vibration of the oscillator 10 contained in the two monitor signals M1 output from the two monitor electrodes 23 are out of phase with each other.

[0022] When the vibrator 10 is being driven and vibrating, if an angular velocity is applied to the vibrator 10, the vibrator 10 resonates and vibrates (detects vibration) due to the Coriolis force. Then, in accordance with the angular velocity applied to the vibrator 10, the distance between the vibrator 10 and the two detection electrodes 22 changes, and the capacitance between the vibrator 10 and the two detection electrodes 22 changes. The two detection electrodes 22 output two detection signals S1 that are out of phase with each other in response to the change in capacitance. The detection signal S1 is a signal corresponding to the magnitude of the angular velocity applied to the vibrator 10. The detection signal S1 is a modulated signal.

[0023] The frequency (peak frequency) of the detection signal S1 is equal to the frequency of the drive signal D1. In this disclosure, "equal" is not limited to being exactly equal, but also includes cases where they differ within a range that does not cause practical problems. For example, if the difference between the frequency of the detection signal S1 and the frequency of the drive signal D1 is within the range of 0.2% or less of either value, the frequencies of the detection signal S1 and the drive signal D1 may be considered "equal" and the disclosure may be applied accordingly.

[0024] (1-2) Control Unit The control unit 3 drives the vibrator 10 to vibrate and outputs a signal (angular velocity signal) relating to the angular velocity applied to the vibrator 10 during the drive vibration.

[0025] The control unit 3 comprises a drive circuit unit 31, a detection circuit unit 32, and a mode switching unit 33.

[0026] (1-2-1) Drive Circuit The drive circuit 31 is connected to two drive electrodes 21 and two monitor electrodes 23. The drive circuit 31 drives the vibrator 10 to vibrate by applying two drive signals D1 (self-excitement signals) or two auxiliary signals H1 (auxiliary signals) that are out of phase to each other to the two drive electrodes 21 of the vibrator 10. The drive circuit 31 selectively applies the drive signals D1 and auxiliary signals H1 to the drive electrodes 21 according to the operating mode of the gyro sensor 1. That is, the drive circuit 31 switches between self-excited driving, which applies a self-excitement signal (drive signal D1) to the vibrator 10, and externally excited driving, which applies an externally excited signal (auxiliary signal H1) to the vibrator 10, according to the operating mode of the gyro sensor 1.

[0027] Furthermore, the drive circuit 31 generates two drive signals D1, which are in opposite phases, from two monitor signals M1, which are in opposite phases, output from the two monitor electrodes 23 of the vibrator 10.

[0028] The drive circuit section 31 includes a TIA (Transimpedance Amplifier) ​​circuit 40, an AGC (Automatic Gain Control) circuit 41, an oscillator 42, a storage unit 43, a selector 44, a buffer 45, a third determination unit 46, and a differential amplifier 47.

[0029] (1-2-1-1) TIA Circuit The TIA circuit 40 has two input terminals and two output terminals. The two input terminals of the TIA circuit 40 are connected to two monitor electrodes 23. The two output terminals of the TIA circuit 40 are connected to two input terminals of the AGC circuit 41. The TIA circuit 40 converts two monitor signals M1, which are out of phase and output from the two monitor electrodes 23, from current signals to voltage signals, and outputs the two converted monitor signals M2 (voltage signals) to the two input terminals of the AGC circuit 41.

[0030] (1-2-1-2) AGC Circuit The AGC circuit 41 has two input terminals and one output terminal. The two input terminals of the AGC circuit 41 are connected to the two output terminals of the TIA circuit 40. The output terminal of the AGC circuit 41 is connected to the first input terminal of the selector 44, which will be described later. Based on at least one of the two monitor signals M2 (voltage signals) output from the two output terminals of the TIA circuit 40, the AGC circuit 41 generates a drive signal D1 with the same frequency as the monitor signal M2. At that time, the AGC circuit 41 corrects the drive signal D1 so that the amplitude is between a predetermined upper limit and a predetermined lower limit. The AGC circuit 41 outputs the generated drive signal D1 to the selector 44.

[0031] (1-2-1-3) Oscillator The oscillator 42 generates a voltage signal of a predetermined frequency by oscillating at a predetermined frequency, and outputs the generated voltage signal of the predetermined frequency as an auxiliary signal H1. More specifically, the oscillator 42 oscillates at the same frequency as the drive signal D1 stored in the memory unit 43, which is the predetermined frequency. The memory unit 43 stores the frequency of the drive signal D1 applied to the drive electrode 21 in the most recent active mode, as described later. As a result, the oscillator 42 outputs an auxiliary signal H1 with the same frequency as the frequency stored in the memory unit 43. The output terminal of the oscillator 42 is connected to the second input terminal of the selector 44. The oscillator 42 outputs the generated auxiliary signal H1 to the second input terminal of the selector 44.

[0032] (1-2-1-4) The memory unit 43 stores the frequency of the drive signal D1 output from the AGC circuit 41 to the selector 44. More specifically, the memory unit 43 stores the frequency of the drive signal D1 output from the AGC circuit 41 to the selector 44 each time the gyro sensor 1 enters active mode. When the gyro sensor 1 enters sleep mode, the memory unit 43 controls the oscillator 42 so that its oscillation frequency becomes the same as the frequency stored in the most recent active mode immediately before entering sleep mode (i.e., the frequency of the drive signal D1 in the most recent active mode immediately before entering sleep mode).

[0033] More specifically, as shown in Figure 2, the storage unit 43 comprises a control register 50, a phase comparator 51, a smoothing filter 52, and a determination unit 53.

[0034] Each time the system enters active mode, the control register 50 stores the frequency of the drive signal D1 output from the AGC circuit 41 to the selector 44. When the system enters sleep mode, the control register 50 controls the oscillation frequency of the oscillator 42 so that the oscillation frequency of the oscillator 42 (a predetermined frequency) becomes the same as the frequency stored in the most recent active mode immediately preceding the entry into sleep mode.

[0035] The phase comparator 51 has a first input terminal, a second input terminal, and an output terminal. The first input terminal of the phase comparator 51 is connected to the output terminal of the AGC circuit 41, and the drive signal D1 (self-excited signal) output from the AGC circuit 41 is input to it. The second input terminal of the phase comparator 51 is connected to the oscillator 42, and the auxiliary signal H1 (externally excited signal) output from the oscillator 42 is input to it. The output terminal of the phase comparator 51 is connected to the determination unit 53 via a smoothing filter 52.

[0036] The phase comparator 51 calculates the difference ΔV1 between the self-excited signal (drive signal D1) input to the first input terminal and the externally excited signal (auxiliary signal H1) input to the second input terminal, and outputs the calculated difference ΔV1 from the output terminal.

[0037] The smoothing filter 52 smooths the output signal (difference ΔV1) from the phase comparator 51 and outputs the smoothed difference ΔV2 to the determination unit 53. This difference ΔV2 corresponds to the phase difference between the self-excited signal and the externally excited signal.

[0038] The determination unit 53 calculates the absolute value ΔV3 of the peak value of the difference ΔV2 and determines whether the calculated absolute value ΔV3 is less than the threshold ΔVa (i.e., ΔV3 < ΔVa).

[0039] Based on the determination result of the determination unit 53, the control register 50 adjusts the oscillation frequency of the oscillator 42 so that the absolute value ΔV3 is less than the threshold ΔVa. More specifically, if the determination unit 53 determines that the absolute value ΔV3 is not less than the threshold ΔVa, the control register 50 controls the oscillation frequency of the oscillator 42 so that the absolute value ΔV3 is less than the threshold ΔVa. On the other hand, if the determination unit 53 determines that the absolute value ΔV3 is less than the threshold ΔVa, the control register 50 maintains the oscillation frequency of the oscillator 42 at the current frequency.

[0040] In the memory unit 43, each time the gyro sensor 1 switches to active mode, the control register 50 stores the frequency of the drive signal D1 output from the AGC circuit 41. Then, when the gyro sensor 1 switches from active mode to sleep mode, the control register 50 initializes the oscillation frequency of the oscillator 42 based on the frequency of the drive signal D1 stored in the control register 50 during the most recent active mode immediately preceding the sleep mode. Then, the control register 50 adjusts the initialized oscillation frequency (i.e., the oscillation frequency of the oscillator 42) based on the determination result of the determination unit 53. By performing this initial setting and adjustment, the control register 50 controls the oscillation frequency of the oscillator 42 so that, in sleep mode, the oscillation frequency of the oscillator 42 stabilizes at the same frequency as the frequency of the drive signal D1 during the most recent active mode immediately preceding the sleep mode.

[0041] (1-2-1-5) Third determination unit The third determination unit 46 determines whether the amplitude of the drive signal D1 output from the AGC circuit 41 is stable. More specifically, the third determination unit 46 acquires the output signals of the TIA circuit 40 (i.e., two monitor signals M2a and M2b that are out of phase with respect to each other) via the AGC circuit 41. The third determination unit 46 calculates the absolute value ΔM of the difference between the peak value of monitor signal M2a and the peak value of monitor signal M2b. If the absolute value ΔM is greater than the threshold ΔMa, the third determination unit 46 determines that the amplitude of the drive signal D1 output from the AGC circuit 41 is stable. On the other hand, if the absolute value ΔM is less than or equal to the threshold ΔMa, the third determination unit 46 determines that the amplitude of the drive signal D1 output from the AGC circuit 41 is not stable.

[0042] Based on the determination result of the third determination unit 46, the selector 44 is switched and controlled. More specifically, when the third determination unit 46 determines that the amplitude of the drive signal D1 output from the AGC circuit 41 is stable, the third determination unit 46 switches and controls the selector 44 so that the drive circuit unit 31 performs self-excited driving (that is, the output signal of the selector 44 becomes the drive signal D1). On the other hand, when the third determination unit 46 determines that the amplitude of the drive signal D1 output from the AGC circuit 41 is not stable, the third determination unit 46 switches and controls the selector 44 so that the drive circuit unit 31 performs externally-excited driving (that is, the output signal of the selector 44 becomes the auxiliary signal H1).

[0043] (1-2-1-6) Selector The selector 44 has two input terminals (a first input terminal and a second input terminal) and two output terminals (a first output terminal and a second output terminal). The first input terminal of the selector is connected to the output terminal of the AGC circuit 41, and the drive signal D1 (self-excited signal) output from the AGC circuit 41 is input. The second input terminal of the selector 44 is connected to the output terminal of the oscillator 42, and the auxiliary signal H1 (externally-excited signal) output from the oscillator 42 is input. The two output terminals of the selector 44 are connected to the two drive electrodes 21 via the buffer 45. Further, the selector 44 is connected to the third determination unit 46.

[0044] Based on the determination result of the third determination unit 46, the selector 44 selects one of the drive signal D1 input to the first input terminal and the auxiliary signal H1 input to the second input terminal. Then, the selector 44 generates two signals having the same frequency as the selected signal and opposite phases to each other, and outputs the two generated signals from the two output terminals of the selector 44. The two signals output from the two output terminals of the selector 44 are output to the two drive electrodes 21 via the buffer 45.

[0045] More specifically, if the third determination unit 46 determines that the amplitude of the drive signal D1 output from the AGC circuit 41 is unstable, the selector 44 selects the auxiliary signal H1 output from the oscillator 42, generates two auxiliary signals H1 with the same frequency as the selected auxiliary signal H1 but in opposite phases, and outputs the two generated auxiliary signals H1 from the two output terminals of the selector 44. As a result, the vibrator 10 is driven to vibrate by the auxiliary signals H1. On the other hand, if the third determination unit 46 determines that the amplitude of the drive signal D1 output from the AGC circuit 41 is stable, the selector 44 selects the drive signal D1 output from the AGC circuit 41, generates two drive signals D1 with the same frequency as the selected drive signal D1 but in opposite phases, and outputs the two generated drive signals D1 from the two drive electrodes 21 of the selector 44. As a result, the vibrator 10 is driven to vibrate by the drive signals D1.

[0046] In Embodiment 1, the drive of the drive circuit section 31 when the selector 44 outputs a drive signal D1 (self-excited signal) may be described as self-excited drive, and the drive of the drive circuit section 31 when the selector 44 outputs an auxiliary signal H1 (externally excited signal) may be described as externally excited drive.

[0047] (1-2-1-7) Buffer 45 is connected between the selector 44 and the two drive electrodes 21. Buffer 45 corrects the signal strength of each of the two signals output from the selector 44, which are out of phase, and outputs the two corrected signals to the two drive electrodes 21.

[0048] (1-2-1-8) Differential Amplifier The differential amplifier 47 has two input terminals and an output terminal. The two input terminals of the differential amplifier 47 are connected to the two output terminals of the TIA circuit 40. Two monitor signals (voltage signals) M2 with opposite phases to each other output from the two output terminals of the TIA circuit 40 are input to the two input terminals of the differential amplifier 47. The output terminal of the differential amplifier 47 is connected to the demodulation circuit 61. The differential amplifier 47 takes the difference between the two monitor signals M2 input to the two input terminals, amplifies it, and outputs the amplified monitor signal M3 to the demodulation circuit 61. Since the monitor signal M3 has the same frequency as the drive signal D1 output from the AGC circuit 41, it is the same signal as the drive signal D1.

[0049] (1-2-1-9) Oscillation Loop Circuit The TIA circuit 40, AGC circuit 41, selector 44, and buffer 45 constitute an oscillation loop circuit 48. That is, the oscillation loop circuit 48 includes the TIA circuit 40, AGC circuit 41, selector 44, and buffer 45. The oscillation loop circuit 48 generates two drive signals D1 (self-excitation signals) with opposite phases to each other from the two monitor electrodes 23 with opposite phases output from the two monitor electrodes 23, and outputs the generated drive signal D1 from the buffer 45.

[0050] (1-2-2) Detection Circuit Section The detection circuit section 32 detects the angular velocity applied to the vibrator 10 based on two detection signals S1 with opposite phases output from the two detection electrodes 22 of the vibrator 10.

[0051] The detection circuit section 32 includes a TIA circuit 60, a demodulation circuit 61, a low-pass filter 62, an AD (analog-digital) converter 63, an output circuit 64, a first determination section 65, and a second determination section 66.

[0052] (1-2-2-1) Current-Voltage Conversion Circuit As shown in Figure 4, the TIA circuit 60 has two input terminals 60a and 60b and two output terminals 60c and 60d. The two input terminals 60a and 60b of the TIA circuit 60 are connected to two detection electrodes 22 via signal paths L1a and L1b, and two detection signals S1 that are in opposite phases to each other are input to them. The two output terminals 60c and 60d of the TIA circuit 60 are connected to two input terminals of the demodulation circuit 61 via signal paths L2a and L2b. The TIA circuit 60 converts the two detection signals S1 output from the two detection electrodes 22 from current signals to voltage signals, and outputs the two detection signals S2 that are in opposite phases to each other from the two output terminals of the TIA circuit 60.

[0053] (1-2-2-2) Demodulation Circuit The demodulation circuit 61 has two input terminals and two output terminals. The two input terminals of the demodulation circuit 61 are connected to the two output terminals of the TIA circuit 60. The demodulation circuit 61 is, for example, a detection circuit. The demodulation circuit 61 demodulates each of the two detection signals S2 output from the TIA circuit 60 using the monitor signal M3 (i.e., drive signal D1) from the differential amplifier 47. Through this demodulation, the demodulation circuit 61 generates a demodulated signal S3 from the two detection signals S2 output from the TIA circuit 60. The demodulation circuit 61 demodulates based on amplitude and phase.

[0054] (1-2-2-3) Low-pass filter The low-pass filter 62 has two input terminals and two output terminals. The two input terminals of the low-pass filter 62 are connected to the two output terminals of the demodulation circuit 61. The two output terminals of the low-pass filter 62 are connected to the two input terminals of the AD converter 63. The low-pass filter 62 removes high-frequency components from each of the two demodulated signals S3 output from the demodulation circuit 61 and outputs the two demodulated signals S4, which are out of phase with respect to each other, to the AD converter 63.

[0055] (1-2-2-4) AD Converter The AD converter 63 has two input terminals and one output terminal. The two input terminals of the AD converter 63 are connected to the two output terminals of the low-pass filter 62. The output terminal of the AD converter 63 is connected to the output circuit 64. The AD converter 63 receives an auxiliary signal H1 from the oscillator 42 (i.e., a signal with the same frequency as the drive signal D1). The AD converter 63 converts the difference signal of the two demodulated signals S4 that are out of phase output from the low-pass filter 62 from an analog signal to a digital signal using the auxiliary signal H1 from the oscillator 42, and outputs the converted demodulated signal S5 to the output circuit 64.

[0056] (1-2-2-5) Output Circuit The input terminal of the output circuit 64 is connected to the output terminal of the AD converter 63. Based on the demodulated signal S5 output from the AD converter 63, the output circuit 64 generates an angular velocity signal representing the angular velocity of the oscillator 10.

[0057] (1-2-2-6) First determination unit The first determination unit 65 determines whether the oscillator 10 has remained stationary for a certain period of time based on the angular velocity signal output from the output circuit 64 in the active mode (first determination). The above "stationary state of the oscillator 10" refers to a state in which the angular velocity applied to the oscillator 10 is less than a certain value, and can be considered as if no angular velocity is applied to the oscillator 10. Furthermore, the state in which the angular velocity is less than a certain value means, for example, that the absolute value of the peak value of the angular velocity signal is less than a certain value. In addition, the "angular velocity signal output from the output circuit 64" used by the first determination unit 65 in its determination is an example of the detection signal S1 input from the detection electrode 22 to the detection circuit unit 32.

[0058] More specifically, the first determination unit 65 determines the angular velocity applied to the oscillator 10 based on the angular velocity signal. The first determination unit 65 then determines that the oscillator 10 has remained stationary for a certain period of time if the determined angular velocity remains below a certain value for a certain period of time. On the other hand, if the determined angular velocity is not below a certain value, or if the determined angular velocity does not remain below a certain value for a certain period of time, the first determination unit 65 determines that the oscillator 10 has not remained stationary for a certain period of time. However, in sleep mode, the first determination unit 65 stops and does not perform the first determination. Thus, in sleep mode, the control unit 3 stops the first determination unit 65 and does not operate it.

[0059] (1-2-2-7) Second determination unit The second determination unit 66 acquires two detection signals S2a and S2b, which are out of phase with respect to each other, from the signal paths L1a and L1b between the TIA circuit 60 and the demodulation circuit 61 in sleep mode. The two detection signals S2a and S2b are signals obtained by the TIA circuit 60 by converting two detection signals S1 into IV (current-voltage). Based on the two acquired detection signals S2a and S2b, the second determination unit 66 determines whether or not angular velocity has been applied to the oscillator 10 (second determination). The "two detection signals S2a and S2b" used by the second determination unit 66 in its determination are an example of the detection signal S1 input from the detection electrode 22 to the detection circuit unit 32.

[0060] More specifically, the second determination unit 66 determines the peak values ​​of the detection signals S2a and S2b, and calculates the absolute value ΔS2 of the difference between the peak value of detection signal S2a and the peak value of detection signal S2b. The second determination unit 66 then determines that angular velocity has been applied to the oscillator 10 if the absolute value ΔS2 is greater than the threshold ΔSa (ΔS2 > ΔSa). On the other hand, the second determination unit 66 determines that no angular velocity has been applied to the oscillator 10 if the absolute value ΔS2 is less than or equal to the threshold ΔSa (ΔSa ≥ ΔS2). In active mode, the second determination unit 66 does not perform a determination (second determination) because the first determination unit 65 is in operation.

[0061] (1-2-3) Mode switching unit The mode switching unit 33 switches the operating mode of the gyro sensor 1 to active mode or sleep mode based on the determination results of the first determination unit 65 and the second determination unit 66, respectively.

[0062] Here, switching the operating mode of the gyro sensor 1 means switching the operating modes of the drive circuit 31 and the detection circuit 32.

[0063] Furthermore, the active mode is a mode in which all the circuits of the gyro sensor 1 are operated to detect the angular velocity applied to the oscillator 10. The sleep mode is a mode in which only the minimum number of circuits of the gyro sensor 1 that are capable of detecting only the application of angular velocity to the oscillator 10 are operated, and the remaining circuits are stopped.

[0064] Furthermore, "operating only the minimum necessary circuits" means turning on the power only to the minimum necessary circuits. Also, "stopping the remaining circuits" means turning off the power to the remaining circuits. Therefore, in sleep mode, the power consumption of the gyro sensor 1 can be reduced because the power to the remaining circuits is turned off. In other words, sleep mode is a mode that reduces the power consumption of the gyro sensor 1. The minimum necessary circuits are the mode switching unit 33, memory unit 43, oscillator 42, selector 44, buffer 45, TIA circuit 60, and second determination unit 66. The remaining circuits are the TIA circuit 40, AGC circuit 41, third determination unit 46, differential amplifier 47, demodulation circuit 61, low-pass filter 62, AD converter 63, output circuit 64, and first determination unit 65.

[0065] In Embodiment 1, the example shows that the remaining circuits are stopped in sleep mode, but it is sufficient that at least the AGC circuit 41 among the multiple circuits provided by the gyro sensor 1 is stopped. In other words, sleep mode is a mode in which at least the AGC circuit 41 is stopped.

[0066] In active mode, the mode switching unit 33 operates all of the circuits of the gyro sensor 1 by turning on the power to all of them. In active mode, the mode switching unit 33 also switches the operating mode of the gyro sensor 1 based on the determination result of the first determination unit 65. More specifically, in active mode, when the first determination unit 65 determines that the oscillator 10 has remained stationary for a certain period of time, the mode switching unit 33 switches the operating mode of the gyro sensor 1 from active mode to sleep mode by operating only the minimum number of circuits and stopping the remaining circuits.

[0067] In sleep mode, the first determination unit 65 stops, so the mode switching unit 33 switches the operating mode of the gyro sensor 1 based on the determination result of the second determination unit 66. More specifically, in sleep mode, when the second determination unit 66 determines that angular velocity has been applied to the vibrator 10, the mode switching unit 33 switches the operating mode of the gyro sensor 1 from sleep mode to active mode.

[0068] (2) The operation of the gyro sensor 1 will be explained with reference to the operation diagram 3.

[0069] First, we assume that the operating mode of the gyro sensor 1 is active mode AM1. In active mode AM1, the mode switching unit 33 turns on the power to all circuits of the gyro sensor 1 and operates all of the above circuits. In active mode AM1, when angular velocity is applied to the vibrating transducer 10, a detection signal S1 corresponding to the magnitude of the angular velocity is input from the detection electrode 22 to the detection circuit unit 32. The detection circuit unit 32 then obtains an angular velocity signal from the input detection signal S1.

[0070] Furthermore, in active mode, the third determination unit 46 determines whether the amplitude of the drive signal D1 output from the AGC circuit 41 of the drive circuit unit 31 is stable, and the drive circuit unit 31 switches its drive mode between self-excited drive and externally excited drive based on the determination result of the third determination unit 46. More specifically, if the third determination unit 46 determines that the amplitude of the drive signal D1 output from the AGC circuit 41 is not stable, the drive circuit unit 31 is externally excited, and if the third determination unit 46 determines that the amplitude of the drive signal D1 output from the AGC circuit 41 is stable, the drive circuit unit 31 is self-excited. More specifically, for a while (a certain period of time) after switching from sleep mode SM1 to active mode AM1, the amplitude of the drive signal D1 output from the AGC circuit 41 is usually not stable, so the drive circuit unit 31 is externally excited. After a certain period of time has elapsed, the amplitude of the drive signal D1 output from the AGC circuit 41 stabilizes, and the drive circuit 31 switches from externally excited drive to self-excited drive. When the drive circuit 31 is self-excited, the vibrator 10 vibrates according to the drive signal D1, and when the drive circuit 31 is externally excited, the vibrator 10 vibrates according to the auxiliary signal H1.

[0071] Furthermore, in active mode AM1, when the third determination unit 46 determines that the amplitude of the drive signal D1 output from the AGC circuit 41 is stable, the memory unit 43 stores the frequency of the drive signal D1 at that time in the memory unit 43.

[0072] In addition, in active mode AM1, the oscillator 42 adjusts the frequency of the auxiliary signal H1 by referring to the drive signal D1.

[0073] In active mode AM1, the first determination unit 65 determines whether the oscillator 10 has remained stationary for a certain period of time based on the detection signal S1 (more specifically, the angular velocity signal output from the output circuit 64) input from the detection electrode 22 to the detection circuit unit 32. When the first determination unit 65 determines that the oscillator 10 has remained stationary for a certain period of time, the mode switching unit 33 operates only the minimum number of circuits among the multiple circuits of the gyro sensor 1 and stops the remaining circuits. As a result, the mode switching unit 33 switches the operating mode of the gyro sensor 1 from active mode AM1 to sleep mode SM1. This switching reduces the power consumption of the gyro sensor 1.

[0074] In sleep mode SM1, the AGC circuit 41 of the drive circuit unit 31 is stopped and the oscillator 42 is operating, so the selector 44 automatically switches the drive method of the drive circuit unit 31 from self-excited drive to externally excited drive. As a result, the vibrator 10 is driven and vibrates by the externally excited signal (auxiliary signal H1).

[0075] At that time (when switching from active mode AM1 to sleep mode SM1), the oscillator 42 oscillates an auxiliary signal H1 with the same frequency as the drive signal D1 in the most recent active mode immediately before entering sleep mode, based on the frequency of the drive signal D1 stored in the memory unit 43 in the most recent active mode immediately before entering sleep mode (i.e., the frequency of the drive signal D1 in the most recent active mode immediately before entering sleep mode). This auxiliary signal H1 is applied to the vibrator 10 via the drive electrode 21, and the vibrator 10 is driven and vibrates by the auxiliary signal H1. This reduces the degradation of the characteristics of the gyro sensor 1 in sleep mode.

[0076] Furthermore, in sleep mode SM1, the first determination unit 65 is stopped and the second determination unit 66 is operating, so the second determination unit 66 performs the determination process. More specifically, the second determination unit 66 determines whether or not angular velocity has been applied to the oscillator 10 based on the detection signal S1 (more specifically, the detection signal S2 obtained from the signal paths L2a and L2b between the TIA circuit 60 and the demodulation circuit 61) input from the detection electrode 22 to the detection circuit unit 32. When the second determination unit 66 determines that angular velocity has been applied to the oscillator 10, the mode switching unit 33 switches the operating mode of the gyro sensor 1 from sleep mode SM1 to active mode AM1 by operating all the circuits of the gyro sensor 1.

[0077] Then, when the operating mode of the gyro sensor 1 switches from sleep mode SM1 to active mode AM1, the gyro sensor 1 repeats the operation of the active mode as described above.

[0078] (3) The gyro sensor 1 according to the first embodiment comprises a vibrator 10, a plurality of electrodes 2, and a control unit 3. The plurality of electrodes 2 are arranged facing the vibrator 10 and form capacitance with the vibrator 10. The control unit 3 is connected to the plurality of electrodes 2. The plurality of electrodes 2 include a drive electrode 21 and a detection electrode 22. A drive signal D1 is applied to the drive electrode 21 to drive the vibrator 10. The detection electrode 22 outputs a detection signal S1 generated by the vibration of the vibrator 10. The control unit 3 comprises a drive circuit unit 31, a detection circuit unit 32, and a mode switching unit 33. The drive circuit unit 31 generates the drive signal D1. The detection circuit unit 32 generates an angular velocity signal from the detection signal S1. The mode switching unit 33 switches the operating modes of the drive circuit unit 31 and the detection circuit unit 32. The mode switching unit 33 switches the operating mode to sleep mode SM1 or active mode AM1 based on the detection signal S1 input to the detection circuit unit 32.

[0079] With this configuration, the operating modes of the drive circuit 31 and the detection circuit 32 can be switched based on the detection signal S1 of the sensor elements (vibrator 10 and multiple electrodes 2). Therefore, since the operating mode can be switched without using the detection signal of the acceleration sensor, the acceleration sensor can be omitted. As a result, the gyro sensor 1 can be made smaller and more power-efficient by eliminating the acceleration sensor.

[0080] Furthermore, in the gyro sensor 1 according to Embodiment 1, the plurality of electrodes 2 include a monitor electrode 23. The monitor electrode 23 outputs a monitor signal M1 generated by the driving vibration of the vibrator 10. The drive circuit 31 includes an oscillation loop circuit 48 and an oscillator 42. The oscillation loop circuit 48 generates a drive signal D1 based on the monitor signal M1. The oscillator 42 generates an auxiliary signal H1 for driving vibration of the oscillator. The drive electrode 21 is selectively to which the drive signal D1 and the auxiliary signal H1 are applied. When the operating mode switches from active mode AM1 to sleep mode SM1, the auxiliary signal H1 is applied to the drive electrode 21, and the vibrator 10 is driven to vibrate by the auxiliary signal H1. When the operating mode switches from sleep mode SM1 to active mode AM1, the drive signal D1 is applied to the drive electrode 21, and the vibrator 10 is driven to vibrate by the drive signal D1.

[0081] With this configuration, in sleep mode SM1, the oscillator 10 can be driven to vibrate by the auxiliary signal H1. In other words, the oscillator 10 can be externally excited to vibrate. Therefore, in sleep mode SM1, the oscillation loop circuit 48 that generates the drive signal D1 can be stopped. As a result, the current consumption in sleep mode SM1 can be reduced.

[0082] Furthermore, in the gyro sensor 1 according to Embodiment 1, the drive circuit unit 31 includes a memory unit 43. The memory unit 43 stores the frequency of the drive signal D1 in the immediately preceding active mode AM1. When the operating mode switches from active mode AM1 to sleep mode SM1, the frequency of the auxiliary signal H1 is set to the frequency of the drive signal D1 stored in the memory unit 43.

[0083] This configuration allows the frequency of the auxiliary signal H1 in sleep mode SM1 to be set to the same frequency as the drive signal D1 in the most recent active mode AM1 just before entering sleep mode. This suppresses the degradation of the gyro sensor 1's characteristics in sleep mode SM1. Furthermore, it enables a rapid transition from sleep mode SM1 to active mode AM1.

[0084] (4) Modifications of Embodiment 1 are listed below. The modifications described below can be combined and applied as appropriate.

[0085] (4-1) Modification 1 In Embodiment 1, when the second determination unit 66 determines that angular velocity has been applied to the vibrator 10, the operating mode of the gyro sensor 1 is switched from sleep mode SM1 to active mode AM1. However, the gyro sensor 1 may be automatically switched from sleep mode SM1 to active mode AM1 after a certain period of time has elapsed since the gyro sensor 1 entered sleep mode SM1. In this case, the mode switching unit 33 determines, for example, whether a certain period of time has elapsed since the gyro sensor entered sleep mode SM1. Modification 1 can also achieve the same effects as Embodiment 1.

[0086] (4-2) Modification 2 In Embodiment 1, in active mode AM1, the mode switching unit 33 switches the gyro sensor 1 from active mode AM1 to sleep mode SM1 based on the determination result of the first determination unit 65. However, in active mode AM1, the mode switching unit 33 may switch the operating mode from active mode AM1 to sleep mode SM1 based on the determination result of the second determination unit 66 instead of the first determination unit 65.

[0087] More specifically, in Modification 2, the second determination unit 66 determines, in active mode AM1, whether the oscillator 10 has remained stationary for a certain period of time based on detection signals S2a and S2b obtained from signal paths L1a and L1b. That is, the second determination unit 66 makes the same determination as the first determination of the first determination unit 65 based on detection signals S2a and S2b obtained from signal paths L2a and L2b. Then, in active mode AM1, the mode switching unit 33 switches the gyro sensor 1 from active mode AM1 to sleep mode SM1 based on the determination result of the sixth determination of the second determination unit 66, instead of the determination result of the first determination unit 65. Modification 21 can also achieve the same effects as in Embodiment 1.

[0088] (Embodiment 2) The gyro sensor 1 according to Embodiment 2 will be described with reference to Figures 4 and 5.

[0089] (1) As shown in the configuration diagram 4, the gyro sensor 1 according to Embodiment 2 is configured similarly to the gyro sensor 1 according to Embodiment 1, except that the second determination unit 66 is removed, and it further includes a first injection unit 67 and a fourth determination unit 68, a detection feedback circuit unit 70 and a QCFB (Quadrature Cancellation feedback) circuit unit 80.

[0090] In the gyro sensor 1, among the detection signals S1 output from the detection electrode 22, the signals that are in phase with the drive signal D1 are fed back to the vibrator 10 through the detection feedback circuit 70.

[0091] In the gyro sensor 1, among the detection signals S1 output from the detection electrode 22, signals with a predetermined phase different from the phase of the drive signal D1 are fed back to the oscillator 10 through the QCFB circuit section 80. Among the detection signals S1, signals with a predetermined phase different from the phase of the drive signal D1 are also called quadrature signals or unwanted signals. The phase difference between the drive signal D1 and the quadrature signal is, for example, 90 degrees. In the following explanation, the case where the phase difference between the drive signal D1 and the quadrature signal is 90 degrees will be explained as an example. However, the phase difference is not limited to 90 degrees.

[0092] (1-1) The plurality of electrodes 2 of the plurality of electrodes embodiment 2 further includes a first detection feedback electrode 24a and a second detection feedback electrode 24b, two first QCFB electrodes 25a and 25b, and two second QCFB electrodes 26a and 26b, in addition to the plurality of electrodes 2 of embodiment 1.

[0093] (1-2) First injection unit and fourth determination unit The detection circuit unit 32 of Embodiment 2 is configured similarly to the detection circuit unit 32 of Embodiment 1, except that the second determination unit 66 is omitted and the first injection unit 67 and the fourth determination unit 68 are added.

[0094] The first injection unit 67 generates a first test signal 92a and a second test signal 92b. The first test signal 92a is in phase with the second test signal 92b.

[0095] The above statement that "the two signals are in phase" means that when the sign of one signal is positive, the sign of the other signal is also positive, and when the sign of one signal is negative, the sign of the other signal is also negative. Two signals that are in phase may have different amplitudes. In Embodiment 2, the first test signal 92a is the same signal as the second test signal 92b. That is, the first test signal 92a is in perfect agreement with the second test signal 92b. The amplitude of the first test signal 92a is equal to the amplitude of the second test signal 92b. The frequencies of the first test signal 92a and the second test signal 92b are, for example, between 1 MHz and 10 MHz. As an example, the waveforms of the first test signal 92a and the second test signal 92b are square waves. The waveforms of the first test signal 92a and the second test signal 92b may also be sine waves.

[0096] The first injection unit 67 is connected to signal paths L1a and L1b in the preceding stage of the TIA circuit 60. Signal path L1a is a signal path that connects one of the two detection electrodes 22 to the first input terminal 60a of the TIA circuit 60, and the first detection signal S1a from the one detection electrode 22 flows through it. Signal path L1b is a signal path that connects the other of the two detection electrodes 22 to the second input terminal 60b of the TIA circuit 60, and the second detection signal S1b from the other detection electrode 22 flows through it.

[0097] The first injection unit 67 is connected to the signal path L1a. The first injection unit 67 outputs a first test signal 92a to the signal path L1a. This generates a first sum signal 93a, which is obtained by adding the first test signal 92a to the first detection signal S1a. The first sum signal 93a is input to the first input terminal 60a of the TIA circuit 60. The TIA circuit 60 converts the first sum signal 93a input to the first input terminal 60a from a current signal to a voltage signal, and outputs the converted first conversion signal 94a from the first output terminal 60c.

[0098] The first injection unit 67 is connected to the signal path L1b. The first injection unit 67 outputs a second test signal 92b to the signal path L1b. This generates a second sum signal 93b, which is obtained by adding the second test signal 92b to the second detection signal S1b. The second sum signal 93b is input to the second input terminal 60b of the TIA circuit 60. The TIA circuit 60 converts the second sum signal 93b input to the second input terminal 60b from a current signal to a voltage signal, and outputs the converted second conversion signal 94b from the second output terminal 60d.

[0099] Since the signal paths L1a and L1b are connected to the TIA circuit 60, the connection between the first injection unit 67 and the signal paths L1a and L1b can be made simple. Specifically, without using an adder, the first injection unit 67 can be connected to the signal paths L1a and L1b to perform addition of the first detection signal S1a and the first test signal 92a, and addition of the second detection signal S1b and the second test signal 92b.

[0100] The fourth determination unit 68 is connected to signal paths L2a and L2b. The fourth determination unit 68 acquires the first conversion signal 94a and the second conversion signal 94b via the signal paths L2a and L2b. The first conversion signal 94a and the second conversion signal 94b acquired by the fourth determination unit 68 are voltage signals.

[0101] The fourth determination unit 68 determines whether the oscillator 10 is vibrating freely based on the first conversion signal 94a and the second conversion signal 94b in sleep mode (fourth determination). More specifically, the fourth determination unit 68 obtains the peak values ​​of the first conversion signal 94a and the second conversion signal 94b, and calculates the absolute value ΔS3 of the sum of the peak values ​​of the first conversion signal 94a and the second conversion signal 94b. The fourth determination unit 68 then determines that the oscillator 10 is vibrating freely if the absolute value ΔS3 is greater than the threshold ΔSc (ΔS3 > ΔSc). On the other hand, the fourth determination unit 68 determines that the oscillator 10 is not vibrating freely if the absolute value ΔS3 is less than or equal to the threshold ΔSc (ΔSc ≥ ΔS3). In active mode, the fourth determination unit 68 does not perform the determination (fourth determination) because the first determination unit 65 is in operation.

[0102] In Embodiment 2, the fourth determination unit 68 performs the determination in sleep mode, as described later. In Embodiment 2, as described later, in sleep mode, the drive circuit unit 31 stops driving and does not perform self-excited or externally excited driving, so the vibrator 10 does not vibrate. For this reason, it is not possible to detect the angular velocity applied to the vibrator 10 in sleep mode. For this reason, in Embodiment 2, instead of detecting the angular velocity applied to the vibrator 10 in sleep mode, the fourth determination unit 68 determines whether or not the vibrator 10 has vibrated freely.

[0103] (1-3) Detection Feedback Circuit The detection feedback circuit 70 generates a first FTR (Force-to-Rebalance) signal 97a and a second FTR signal 97b to suppress the driving vibration of the vibrator 10 based on the detection signal S1 (more specifically, the demodulated signal S5 output from the AD converter 63), and applies the generated first FTR signal 97a and second FTR signal 97b to the first detection feedback electrode 24a and the second detection feedback electrode 24b.

[0104] The detection feedback circuit section 70 includes an FTR control circuit 71, a DA (digital-analog) converter 72, a low-pass filter 73, a modulation circuit 74, a voltage buffer 75, a second injection section 76, and a fifth determination section 77.

[0105] (1-3-1) FTR Control Circuit The FTR control circuit 71 generates digital control signals 95, which are the basis for the first FTR signal 97a and the second FTR signal 97b, based on the demodulated signal S5 output from the AD converter 63. The FTR control circuit 71 outputs the generated control signals 95 to the DA converter 72.

[0106] (1-3-2) DA Converter The DA converter 72 has one input terminal and two output terminals (a first output terminal and a second output terminal). The input terminal of the DA converter 72 is connected to the FTR control circuit 71, and a control signal 95 from the FTR control circuit 71 is input to it. The two output terminals of the DA converter 72 are connected to the two input terminals of the low-pass filter 73. The DA converter 72 also receives an auxiliary signal H1 output from the oscillator 42 (i.e., a signal having the same frequency as the drive signal D1).

[0107] The DA converter 72 performs a DA (digital-to-analog) conversion on the control signal 95 input to the input terminal, and generates a first control signal 95a and a second control signal 95b from the DA-converted control signal 95, which have the same frequency as the drive signal D1 but are out of phase with each other. More specifically, the DA converter 72 uses an auxiliary signal H1 from the oscillator 42 (a signal with the same frequency as the drive signal D1) to modulate the DA-converted control signal 95 to generate the first control signal 95a. The DA converter 72 also uses the auxiliary signal H1 from the oscillator 42 to modulate the DA-converted control signal 95 to generate the second control signal 95b.

[0108] The DA converter 72 outputs the generated first control signal 95a from its first output terminal to the first input terminal of the modulation circuit 74 via the low-pass filter 73. The DA converter 72 also outputs the generated second control signal 95b from its second output terminal to the first input terminal of the modulation circuit 74 via the low-pass filter 73.

[0109] (1-3-3) Low-pass filter The low-pass filter 73 has two input terminals (a first input terminal and a second input terminal) and two output terminals (a first output terminal and a second output terminal). The two input terminals of the low-pass filter 73 are connected to the two output terminals of the DA converter 72. The first input terminal of the low-pass filter 73 receives a first control signal 95a. The second input terminal of the low-pass filter 73 receives a second control signal 95b. The two output terminals of the low-pass filter 73 are connected to the two input terminals of the modulation circuit 74.

[0110] The low-pass filter 73 removes high-frequency components from the first control signal 95a input to the first input terminal, and outputs the removed first control signal 95a from the first output terminal to the first input terminal of the modulation circuit 74. The low-pass filter 73 also removes high-frequency components from the second control signal 95b input to the second input terminal, and outputs the removed second control signal 95b from the second output terminal to the second input terminal of the modulation circuit 74.

[0111] (1-3-4) Modulation Circuit The modulation circuit 74 has two input terminals and two output terminals. The two input terminals of the modulation circuit 74 are connected to the two output terminals of the low-pass filter 73. The modulation circuit 74 is, for example, a detection circuit. The modulation circuit 74 modulates the filtered first control signal 95a and the second control signal 95b output from the two output terminals of the low-pass filter 73 using the monitor signal M3 from the differential amplifier 47 (i.e., a signal with the same frequency as the drive signal D1). As a result, the modulation circuit 74 generates a first modulated control signal 96a by modulating the filtered first control signal 95a input to the first input terminal to a signal in phase with the drive signal D1, and outputs the generated first modulated control signal 96a to the first input terminal of the voltage buffer 75. Furthermore, the modulation circuit 74 generates a second modulated control signal 96b by modulating the filtered second control signal 95b input to the second input terminal to a signal in opposite phase to the drive signal D1, and outputs the generated second modulated control signal 96b to the first input terminal of the voltage buffer 75. The first modulated control signal 96a and the second modulated control signal 96b are signals in opposite phase to each other.

[0112] The modulation circuit 74 applies the generated first modulation control signal 96a and second modulation control signal 96b to the first detection feedback electrode 24a and second detection feedback electrode 24b via the voltage buffer 75.

[0113] (1-3-5) Voltage buffer The voltage buffer 75 corrects the modulation control signals 96a and 96b output from the modulation circuit 74 and outputs the corrected FTR signals 97a and 97b.

[0114] The voltage buffer 75 includes two input terminals (first input terminal 75a and second input terminal 75b), two output terminals (first output terminal 75c and second output terminal 75d), and a reference voltage terminal 75e. The two input terminals 75a and 75b are connected to the two output terminals of the modulation circuit 74, and two modulation control signals 96a and 96b, which are out of phase with respect to each other, are input to them. The two output terminals 75c and 75d are connected to two detection feedback electrodes 24a and 24b via signal paths L3a and L3b.

[0115] The voltage buffer 75 generates a voltage (first FTR signal 97a in Figure 4) corresponding to the difference voltage between the reference voltage input to the reference voltage terminal 75e and the first voltage input to the first input terminal 75a (first modulation control signal 96a in Figure 4), and outputs the generated voltage from the first output terminal 75c. The voltage buffer 75 generates a voltage (second FTR signal 97b in Figure 4) corresponding to the difference voltage between the reference voltage input to the reference voltage terminal 75e and the second voltage input to the second input terminal 75b (second modulation control signal 96b in Figure 4), and outputs the generated voltage from the second output terminal 75d. The first FTR signal 97a and the second FTR signal 97b output from the voltage buffer 75 are applied to the first detection feedback electrode 24a and the second detection feedback electrode 24b.

[0116] By applying voltage (first FTR signal 97a and second FTR signal 97b) to the first detection feedback electrode 24a and the second detection feedback electrode 24b, the resonant vibration (detected vibration) of the oscillator 10 corresponding to the angular velocity of the oscillator 10 is suppressed. As a result, the amplitude of each angular velocity component of the first detection signal S1a and the second detection signal S1b becomes smaller relative to the magnitude of the angular velocity of the oscillator 10. Therefore, the gyro sensor 1 becomes capable of detecting larger angular velocities. In other words, the dynamic range of the gyro sensor 1 is widened.

[0117] Thus, the first FTR signal 97a and the second FTR signal 97b are signals for controlling (suppressing) the change in capacitance between the first detection electrode 22a and the second detection electrode 22b and the oscillator 10, which occurs when angular velocity is applied to the oscillator 10.

[0118] (1-3-6) The second injection unit 76 generates a third test signal 98a and a fourth test signal 98b. The third test signal 98a is in phase with the fourth test signal 98b.

[0119] In this embodiment, the third test signal 98a is the same signal as the fourth test signal 98b. That is, the third test signal 98a is a perfect match with the fourth test signal 98b. The amplitude of the third test signal 98a is equal to the amplitude of the fourth test signal 98b.

[0120] The frequencies of the third test signal 98a and the fourth test signal 98b are, for example, between 1 MHz and 10 MHz.

[0121] As an example, the waveforms of the third test signal 98a and the fourth test signal 98b are square waves. However, the waveforms of the third test signal 98a and the fourth test signal 98b may also be sine waves.

[0122] The second injection unit 76 is connected to the reference voltage terminal 75e of the voltage buffer 75. The second injection unit 76 inputs the third test signal 98a (or the fourth test signal 98b) to the reference voltage terminal 75e. In other words, the second injection unit 76 applies the third test signal 98a (or the fourth test signal 98b) as a reference voltage to the reference voltage terminal 75e. More specifically, the second injection unit 76 applies a signal to the reference voltage terminal 75e that is the sum of the DC voltage and the third test signal 98a (or the fourth test signal 98b).

[0123] As a result, the first output terminal 75c of the voltage buffer 75 outputs a first FTR signal 97a, which corresponds to the difference voltage between the third test signal 98a and the first voltage (first modulation control signal 96a) input to the first input terminal 75a. In addition, the second output terminal 75d of the voltage buffer 75 outputs a second FTR signal 97b, which corresponds to the difference voltage between the fourth test signal 98b and the second voltage (second modulation control signal 96b) input to the second input terminal 75b.

[0124] The first FTR signal 97a is applied to the first detection feedback electrode 24a, and the second FTR signal 97b is applied to the second detection feedback electrode 24b. Here, the oscillator 10 is positioned between the first detection feedback electrode 24a and the second detection feedback electrode 24b (see Figure 4), and the third test signal 98a is in phase with the fourth test signal 98b. Therefore, the third test signal 98a and the fourth test signal 98b cancel each other out in the oscillator 10, reducing their influence on the operation of the oscillator 10. More specifically, the third test signal 98a is in perfect agreement with the fourth test signal 98b. Therefore, the third test signal 98a and the fourth test signal 98b completely cancel each other out in the oscillator 10, and have almost no influence on the operation of the oscillator 10.

[0125] As described above, the second injection unit 76 applies the third test signal 98a (or the fourth test signal 98b) to the reference voltage terminal 75e of the voltage buffer 75. Therefore, compared to the case where the control unit 3 does not have a voltage buffer 75, the circuit for injecting (outputting) the third test signal 98a and the fourth test signal 98b can be configured on a smaller scale. For example, a circuit for injecting (outputting) the third test signal 98a and the fourth test signal 98b can be configured without using an adder. In addition, the number of branch wires in the circuit between the FTR control circuit 71 and the first detection feedback electrode 24a and the second detection feedback electrode 24b can be reduced, so noise generated in this circuit can be reduced. Therefore, the influence of noise on the operation of the gyro sensor 1 can be reduced.

[0126] (1-3-7) The fifth determination unit 77 is connected to signal paths L3a and L3b. The fifth determination unit 77 is connected to signal paths L3a and L3b downstream of the voltage buffer 75.

[0127] The fifth determination unit 77 acquires at least one (both in Embodiment 2) of the first FTR signal 97a and the second FTR signal 97b via signal paths L3a and L3b. The first FTR signal 97a and the second FTR signal 97b acquired by the fifth determination unit 77 are, for example, voltage signals.

[0128] The fifth determination unit 77 determines whether the oscillator 10 is vibrating freely based on the first FTR signal 97a and the second FTR signal 97b in sleep mode (fifth determination). More specifically, the fifth determination unit 77 calculates the peak values ​​of the first FTR signal 97a and the second FTR signal 97b, and calculates the absolute value ΔS4 of the sum of the peak values ​​of the first FTR signal 97a and the second FTR signal 97b. The fifth determination unit 77 then determines that the oscillator 10 is vibrating freely if the absolute value ΔS4 is greater than the threshold ΔSd (ΔS4 > ΔSd). On the other hand, the fifth determination unit 77 determines that the oscillator 10 is not vibrating freely if the absolute value ΔS4 is less than or equal to the threshold ΔSd (ΔSd ≥ ΔS4). In active mode, the fifth determination unit 77 does not perform the determination (fifth determination) because the first determination unit 65 is in operation.

[0129] In Embodiment 2, the fifth determination unit 77 performs the determination in sleep mode. As described later, in sleep mode, the drive circuit unit 31 stops driving and does not perform self-excited or externally excited driving, so the vibrator 10 does not vibrate. For this reason, it is not possible to detect the angular velocity applied to the vibrator 10 in sleep mode. For this reason, in Embodiment 2, instead of detecting the angular velocity applied to the vibrator 10 in sleep mode, the fifth determination unit 77 determines whether or not the vibrator 10 has vibrated freely.

[0130] (1-4) QCFB circuit section The QCFB circuit section 80 includes phase shifters 81, 82, demodulation circuit 83, low-pass filter 84, AD converter 85, QCFB control circuit 86, DA converters 87, 89, and amplifiers 88, 90.

[0131] (1-4-1) Phase shifter The phase shifter 81 shifts the phase of the monitor signal M3 (a signal having the same frequency as the drive signal D1) output from the differential amplifier 47 and outputs it to the local oscillator terminal of the demodulation circuit 83. More specifically, the phase shifter 81 shifts the phase of the monitor signal M3 from the differential amplifier 47 by -45 degrees and outputs it to the local oscillator terminal of the demodulation circuit 83, which will be described later.

[0132] (1-4-2) Demodulation Circuit The demodulation circuit 83 has two input terminals, a local oscillator terminal, and two output terminals. The local oscillator terminal of the demodulation circuit 83 is connected to the output terminal of the differential amplifier 47 via a phase shifter 81, and the monitor signal M3 output from the differential amplifier 47 is input via the phase shifter 81. The phase shifter 81 shifts the monitor signal M3 output from the differential amplifier 47 by -45 degrees and inputs it to the local oscillator terminal of the demodulation circuit 83. The two input terminals of the demodulation circuit 83 are connected to the signal paths L2a and L2b between the TIA circuit 60 and the demodulation circuit 61 via a phase shifter 82. The first conversion signal 94a and the second conversion signal 94b output from the two output terminals of the TIA circuit 60 are input to the two input terminals of the demodulation circuit 83 via the phase shifter 82. The phase shifter 82 shifts the phase of the first conversion signal 94a and the second conversion signal 94b by 45 degrees and inputs them to the two input terminals of the demodulation circuit 83. The two output terminals of the demodulation circuit 83 are connected to the two input terminals of the AD converter 85 via a low-pass filter 84.

[0133] The demodulation circuit 83 uses the signal (monitor signal M3) input to the local oscillator terminal of the demodulation circuit 83 to demodulate the first conversion signal 94a and the second conversion signal 94b, which have been shifted by 45 degrees and input to the two input terminals of the demodulation circuit 83. As a result, the demodulation circuit 83 generates two demodulated signals S6 in each of the first conversion signal 94a and the second conversion signal 94b, which have been shifted by 454 degrees and input to the two input terminals of the demodulation circuit 83, by demodulating signal components that are in a different phase from the monitor signal M3 (i.e., a signal with the same frequency as the drive signal D1). The two demodulated signals S6 are signals that are out of phase with each other. The demodulation circuit 83 outputs the two generated demodulated signals S6 to the two input terminals of the AD converter 85 via the low-pass filter 84. The low-pass filter 84 removes high-frequency components (first test signal 92a and second test signal 92b) from the two demodulated signals S6 output from the two output terminals of the demodulation circuit 83, and outputs the two demodulated signals ST7, which are out of phase with respect to each other after filtering, to the two input terminals of the AD converter 85.

[0134] (1-4-3) AD Converter The AD converter 85 has two input terminals and one output terminal. The two input terminals of the AD converter 85 are connected to the two output terminals of the demodulation circuit 83 via a low-pass filter 84, and two filtered demodulated signals S7 are input. The output terminal of the AD converter 85 is connected to the QCFB control circuit 86. The AD converter 85 receives an auxiliary signal H1 (a signal with the same frequency as the drive signal D1) from the oscillator 42.

[0135] The AD converter 85 generates a difference signal by taking the difference between the two demodulated signals S7 that are out of phase and output from the low-pass filter 84, demodulates the difference signal using the auxiliary signal H1 from the oscillator 42, converts the demodulated signal from an analog signal to a digital signal, and outputs the demodulated signal S8 in digital format to the QCFB control circuit 86.

[0136] (1-4-4) QCFB Control Circuit The QCFB control circuit 86 generates a first signal 100 and a second signal 101 based on the demodulated signal S8. The first signal 100 is a signal (digital signal) for generating a first quadrature signal 104 to be applied to the two first QCFB electrodes 25a and 25b. The second signal 101 is a signal (digital signal) for generating a second quadrature signal 105 to be applied to the two second QCFB electrodes 26a and 26b.

[0137] The QCFB control circuit 86 applies the first signal 100 to the first QCFB electrodes 25a and 25b via the DA converter 87 and amplifier 88. The QCFB control circuit 86 also applies the second signal 101 to the second QCFB electrodes 26a and 26b via the DA converter 89 and amplifier 90.

[0138] (1-4-5) DA Converter The DA converter 87 has an input terminal and an output terminal. The input terminal of the DA converter 87 is connected to the QCFB control circuit 86 and the first signal 100 is input to it. The output terminal of the DA converter 87 is connected to the input terminal of the amplifier 88. The DA converter 87 converts the first signal 100 input to the input terminal of the DA converter 87 from a digital signal to an analog signal (first voltage signal 102), and outputs the converted first voltage signal 102 from the output terminal of the DA converter 87 to the input terminal of the amplifier 88.

[0139] The DA converter 89 has an input terminal and an output terminal. The input terminal of the DA converter 89 is connected to the QCFB control circuit 86, and the second signal 101 is input to it. The output terminal of the DA converter 89 is connected to the input terminal of the amplifier 90. The DA converter 89 converts the second signal 101 input to the input terminal from a digital signal to an analog signal (second voltage signal 103), and outputs the converted second voltage signal 103 from the output terminal of the DA converter 89 to the input terminal of the amplifier 90.

[0140] (1-4-6) Amplifier The amplifier 88 has an input terminal and an output terminal. The input terminal of the amplifier 88 is connected to the output terminal of the DA converter 87, and a first voltage signal 102 is input to it. The output terminal of the amplifier 88 is connected to two first QCFB electrodes 25a and 25b. The amplifier 88 amplifies the first voltage signal 102 input to the input terminal of the amplifier 88, and applies the amplified first quadrature signal 104 to the two first QCFB electrodes 25a and 25b.

[0141] The amplifier 90 has an input terminal and an output terminal. The input terminal of the amplifier 90 is connected to the output terminal of the DA converter 89, and a second voltage signal 103 is input to it. The output terminal of the amplifier 90 is connected to two second QCFB electrodes 26a and 26b. The amplifier 90 amplifies the second voltage signal 103 input to the input terminal of the amplifier 90 and applies the amplified second quadrature signal 105 to the two second QCFB electrodes 26a and 26b.

[0142] The first quadrature signal 104 output from the QCFB circuit 80 is applied to the two first QCFB electrodes 25a and 25b, and the second quadrature signal 105 output from the QCFB circuit 80 is applied to the two second QCFB electrodes 26a and 26b, thereby suppressing the second-mode motion of the oscillator 10. This second-mode motion is the cause of the detection signal S1 containing signal components (quadrature signals) with different phases.

[0143] (1-5) Mode switching unit The mode switching unit 33 of the second embodiment switches the operating mode of the gyro sensor 1 to active mode or sleep mode based on the determination results of the first determination unit 65, the fourth determination unit 68, and the fifth determination unit 77.

[0144] The active mode of Embodiment 2 is similar to the active mode of Embodiment 1 in that all circuits of the gyro sensor 1 operate to detect the angular velocity applied to the oscillator 10.

[0145] Furthermore, the sleep mode of Embodiment 2, like the sleep mode of Embodiment 1, is a mode in which only the minimum number of circuits capable of detecting only the free vibration of the oscillator 10 among the multiple circuits provided by the gyro sensor 1 are operated, and the remaining circuits are stopped. However, in the sleep mode of Embodiment 2, the minimum number of circuits is the mode switching unit 33, the TIA circuit 60, the first injection unit 67, the fourth determination unit 68, the voltage buffer 75, the second injection unit 76, and the fifth determination unit 77. The remaining circuits are the entirety of the drive circuit unit 31, the entirety of the QCFB circuit unit 80, the demodulation circuit 61, the low-pass filter 62, the AD converter 63, the output circuit 64, the first determination unit 65, the FTR control circuit 71, the DA converter 72, the low-pass filter 73, and the modulation circuit 74. In the sleep mode of Embodiment 2, all circuits in the drive circuit unit 31 are stopped, so the drive circuit unit 31 stops driving and does not perform self-excited driving or externally excited driving.

[0146] In Embodiment 2, the example shows that the remaining circuits are stopped in sleep mode, but it is sufficient that at least the AGC circuit 41 among the multiple circuits provided by the gyro sensor 1 is stopped. In other words, sleep mode is a mode in which at least the AGC circuit 41 is stopped.

[0147] In Embodiment 2, the mode switching unit 33 operates in the same way as the mode switching unit 33 in Embodiment 1 in active mode, switching the operating mode of the gyro sensor 1 from active mode to sleep mode.

[0148] Furthermore, the mode switching unit 33 of Embodiment 2 operates similarly except that, in sleep mode, the first determination unit 65 stops, and therefore the operating mode of the gyro sensor 1 is switched based on the determination results of the fourth determination unit 68 and the fifth determination unit 77. More specifically, in sleep mode, when both the fourth determination unit 68 and the fifth determination unit 77 determine that the vibrator 10 has vibrated freely, the mode switching unit 33 of Embodiment 2 switches the operating mode of the gyro sensor 1 from sleep mode to active mode.

[0149] (2) The operation of the gyro sensor 1 of Embodiment 2 will be described with reference to the operation diagram 5. In the following description, the differences from the operation of the gyro sensor 1 of Embodiment 1 will be explained, and the explanation of parts that are the same as the operation of the gyro sensor 1 of Embodiment 1 may be omitted.

[0150] First, we assume that the operating mode of the gyro sensor 1 is active mode AM1. The operation of the gyro sensor 1 in active mode AM1 is the same as the operation in active mode AM1 of Embodiment 1, so we will omit the explanation.

[0151] In the active mode of Embodiment 2, similar to the active mode AM1 of Embodiment 1, when the first determination unit 65 determines that the oscillator 10 has remained stationary for a certain period of time, the mode switching unit 33 switches the operating mode of the gyro sensor 1 from active mode AM1 to sleep mode SM1 by operating only the minimum number of circuits among the multiple circuits of the gyro sensor 1 and stopping the remaining circuits. At this time, in sleep mode SM1 of Embodiment 2, all the circuits of the drive circuit unit 31 are included in the remaining circuits, so the drive circuit unit 31 stops driving and does not perform self-excited or externally excited driving.

[0152] The operation of the gyro sensor 1 in sleep mode SM1 of Embodiment 2 is the same as that of sleep mode SM1 of Embodiment 1, except that the fourth determination unit 68 and the fifth determination unit 77 determine whether or not the vibrator 10 is vibrating freely (fourth determination and fifth determination).

[0153] In the sleep mode SM1 of Embodiment 2, when both the fourth determination unit 68 and the fifth determination unit 77 determine that the vibrator 10 is vibrating freely, the mode switching unit 33 switches the operating mode of the gyro sensor 1 from sleep mode SM1 to active mode AM1, similar to the case of the sleep mode in Embodiment 1. Once the operating mode of the gyro sensor 1 switches from sleep mode SM1 to active mode AM1, the gyro sensor 1 repeats the operation of active mode AM1 as described above.

[0154] (3) The gyro sensor 1 according to the second embodiment further comprises a detection feedback circuit section 70. The detection feedback circuit section 70 generates FTR signals 97a and 97b that suppress the detected vibration of the oscillator 10 based on the detection signal S1. The plurality of electrodes 2 further include detection feedback electrodes 24a and 24b to which the FTR signals 97a and 97b are applied. The mode switching section 33 switches the operating mode from sleep mode SM1 to active mode AM1 based on at least one of the FTR signals 97a and 97b and the detection signal S1.

[0155] With this configuration, in addition to the detection signal S1 of the sensor element (vibrator 10 and multiple electrodes 2), FTR signals 97a and 97b can be used as trigger signals for switching the operating mode. That is, the operating mode can be switched by utilizing the free vibration applied to the vibrator 10 during sleep mode SM1 (i.e., the change in electrode capacitance of the sensor element). In this case as well, power saving and miniaturization of the gyro sensor 1 can be achieved.

[0156] Furthermore, in the gyro sensor 1 according to Embodiment 2, the detection circuit unit 32 includes a TIA circuit 60, a demodulation circuit 61, and an output circuit 64. The TIA circuit 60 receives a detection signal S1 from the detection electrode 22. The demodulation circuit 61 is connected downstream of the TIA circuit 60. The output circuit 64 is connected downstream of the demodulation circuit 61 and determines the angular velocity applied to the oscillator 10 based on the detection signal S1. The mode switching unit 33 switches the operating mode from sleep mode SM1 to active mode AM1 based on the detection signal S1 (i.e., converted signals 94a, 94b) obtained from the signal paths L2a, L2b between the TIA circuit 60 and the demodulation circuit 61.

[0157] With this configuration, the detection signals S1a and S1b (i.e., converted signals 94a and 94b) obtained from the signal paths L2a and L2b between the TIA circuit 60 and the demodulation circuit 61 inside the detection circuit unit 32 can be used as the detection signal (S1, trigger signal) for switching the operating mode. As a result, in sleep mode SM1, the circuits from the demodulation circuit 61 to the output circuit 64 among the circuits constituting the detection circuit unit 32 can be stopped, contributing to power saving.

[0158] Furthermore, in the gyro sensor 1 according to Embodiment 2, the plurality of electrodes 2 include a first detection feedback electrode 24a and a second detection feedback electrode 24b. The detection feedback circuit section 70 includes a voltage buffer 75. The voltage buffer 75 is connected to the first detection feedback electrode 24a and the second detection feedback electrode 24b. The voltage buffer 75 outputs a first FTR signal 97a as the FTR signal to the first detection feedback electrode 24a, and outputs a second FTR signal 97b, which is in the opposite phase to the first FTR signal 97a, to the second detection feedback electrode 24b as the FTR signal. The mode switching section 33 switches the operating mode from sleep mode SM1 to active mode AM1 based on the first FTR signal 97a and the second FTR signal 97b. The first FTR signal 97a is obtained from the signal path L3a between the first detection feedback electrode 24a and the voltage buffer 75. The second FTR signal 97b is obtained from the signal path L3b between the second detection feedback electrode 24b and the voltage buffer 75.

[0159] With this configuration, the FTR signals 97a and 97b for switching the operating mode can be used, and as trigger signals, the first FTR signal 97a obtained from the signal path L3a between the first detection feedback electrode 24a and the voltage buffer 75, and the second FTR signal 97b obtained from the signal path L3b between the second detection feedback electrode 24b and the voltage buffer 75 can be used.

[0160] (4) Modifications of Embodiment 2 are listed below. The modifications described below can be combined and applied as appropriate.

[0161] (4-1) Modification 1 In Embodiment 2, when both the fourth determination unit 68 and the fifth determination unit 77 determine that the vibrator 10 is vibrating freely, the mode switching unit 33 switches the operating mode of the gyro sensor 1 from sleep mode SM1 to active mode AM1. However, when at least one of the fourth determination unit 68 and the fifth determination unit 77 determines that the vibrator 10 is vibrating freely, the mode switching unit 33 may switch the operating mode of the gyro sensor 1 from sleep mode SM1 to active mode AM1.

[0162] (4-2) Modification 2 In Embodiment 2, in sleep mode SM1, the drive circuit unit 31 is stopped, and the fourth determination unit 68 and the fifth determination unit 77 determine whether or not the vibrator 10 is vibrating freely. However, in Embodiment 2 as well as in Embodiment 1, the drive circuit unit 31 may be externally driven in sleep mode SM1, and the fourth determination unit 68 may be made to detect the angular velocity applied to the vibrator 10, similar to the second determination unit 66 in Embodiment 1. In this case, if the fourth determination unit 68 determines that angular velocity has been applied to the vibrator 10 in sleep mode SM1, the mode switching unit 33 switches the operating mode of the gyro sensor 1 from sleep mode SM1 to active mode AM1.

[0163] (Embodiment 3) The gyro sensor 1 according to Embodiment 3 will be described with reference to Figure 6.

[0164] (1) As shown in the configuration diagram 6, the gyro sensor 1 according to Embodiment 3 differs from the gyro sensor 1 according to Embodiment 2 in that the detection circuit section 32 further includes a current buffer 69. In the following description, the same components as in Embodiment 2 are denoted by the same reference numerals and their descriptions are omitted, while the description may focus on components that differ from Embodiment 2.

[0165] (1-1) Current Buffer The current buffer 69 is connected between the two detection electrodes 22a and 22b and the TIA circuit 60. The current buffer 69 has two input terminals and two output terminals. The two input terminals of the current buffer 69 are connected to the two detection electrodes 22a and 22b via signal paths L1a and L1b. The two output terminals of the current buffer 69 are connected to the two input terminals of the TIA circuit 60 via signal paths L4a and L4b.

[0166] The current buffer 69 amplifies the two summation signals 93a and 93b, described later, input to the two input terminals, and outputs the two amplified signals 104a and 104b from the two output terminals to the two input terminals of the TIA circuit 60. Therefore, the signal component in the two summation signals 93a and 93b that corresponds to the magnitude of the angular velocity of the oscillator 10 is amplified by the current buffer 69. This improves the accuracy of angular velocity detection in the output circuit 64.

[0167] (1-2) The first injection unit 67 is connected to the signal paths L1a and L1b. The first injection unit 67 is connected to the signal paths L1a and L1b in front of the current buffer 69. The first injection unit 67 injects (outputs) the first test signal 92a and the second test signal 92b into the signal paths L1a and L1b. In other words, the first injection unit 67 injects the first test signal 92a into the signal path L1a between the first detection electrode 22a and the current buffer 69, and injects the second test signal 92b into the signal path L1b between the second detection electrode 22b and the current buffer 69.

[0168] (1-3) Fourth determination unit The fourth determination unit 68 acquires two amplified signals 104a and 104b via signal paths L4a and L4b in sleep mode. That is, the fourth determination unit 68 acquires two amplified signals 104a and 104b from two signal paths L4a and L4b between the current buffer 69 and the TIA circuit 60. Based on the acquired amplified signals 104a and 104b, the fourth determination unit 68 determines whether the oscillator 10 has vibrated freely or not, similar to the fourth determination unit 68 of Embodiment 2 (fourth determination).

[0169] Furthermore, the in-phase first test signal 92a and the second test signal 92b cancel each other out in the TIA circuit 60. The fourth determination unit 68 can then obtain the amplified signals 104a and 104b from the signal paths L4a and L4b prior to the TIA circuit 60. In other words, the fourth determination unit 68 can obtain the first summation signal 93a and the second summation signal 93b before the first test signal 92a and the second test signal 92b are reduced in the TIA circuit 60. Thus, the possibility of the TIA circuit 60 interfering with the fourth determination of the fourth determination unit 68 can be reduced.

[0170] (2) The operation of the gyro sensor 1 in the third embodiment is the same as the operation of the gyro sensor 1 in the second embodiment, so the explanation will be omitted.

[0171] (3) Effect Embodiment 3: In the gyro sensor 1, the plurality of electrodes 2 include a detection electrode 22, a first detection electrode 22a and a second detection electrode 22b. The first detection electrode 22a outputs a first detection signal S1a (detection signal). The second detection electrode 22b is located on the opposite side of the oscillator 10 from the first detection electrode 22a and outputs a second detection signal S1b (detection signal). The detection circuit 32 includes a current buffer 69 and a TIA circuit 60. The current buffer 69 is connected to the first detection electrode 22a and the second detection electrode 22b. The TIA circuit 60 is connected downstream of the current buffer 69. The mode switching unit 33 switches the operating mode from sleep mode SM1 to active mode AM1 based on the first detection signal S1a (i.e., amplified signal 104a) and the second detection signal S1b (i.e., amplified signal 104b) obtained from the signal paths L4a and L4b between the current buffer 69 and the TIA circuit 60.

[0172] With this configuration, the detection signals S1a and S1b (i.e., amplified signals 104a and 104b) obtained from the signal paths L4a and L4b between the current buffer 69 and the TIA circuit 60 inside the detection circuit unit 32 can be used as the detection signal S1 (trigger signal) for switching the operating mode.

[0173] (Summary) Based on the embodiments described above, the following embodiments are disclosed.

[0174] The gyro sensor (1) according to the first embodiment comprises an oscillator (10), a plurality of electrodes (2), and a control unit (3). The plurality of electrodes (2) are arranged facing the oscillator (10) and form capacitance with the oscillator (10). The control unit (3) is connected to the plurality of electrodes (2). The plurality of electrodes (2) include a drive electrode (21) and a detection electrode (22). A drive signal (D1) is applied to the drive electrode (21) to drive the oscillator (10) to vibrate. The detection electrode (22) outputs a detection signal (S1) generated by the vibration of the oscillator (10). The control unit (3) comprises a drive circuit unit (31), a detection circuit unit (32), and a mode switching unit (33). The drive circuit unit (31) generates the drive signal (D1). The detection circuit unit (32) generates an angular velocity signal from the detection signal (S1). The mode switching unit (33) switches the operating modes of the drive circuit unit (31) and the detection circuit unit (32). Based on the detection signal (S1) input to the detection circuit unit (32), the mode switching unit (33) switches the operating mode to sleep mode (SM1) or active mode (AM1).

[0175] With this configuration, the operating modes of the drive circuit (31) and the detection circuit (32) can be switched based on the detection signal (S1) of the sensor elements (vibrator (10) and multiple electrodes (2)). Therefore, since the operating mode can be switched without using the detection signal of the acceleration sensor, the acceleration sensor can be omitted. As a result, the gyro sensor (1) can be made smaller and more power-efficient by eliminating the acceleration sensor.

[0176] In the gyro sensor (1) according to the second embodiment, the plurality of electrodes (2) include a monitor electrode (23) as in the first embodiment. The monitor electrode (23) outputs a monitor signal (M1) generated by the driving vibration of the oscillator (10). The drive circuit (31) includes an oscillation loop circuit (48) and an oscillator (42). The oscillation loop circuit (48) generates a drive signal (D1) based on the monitor signal (M1). The oscillator (42) generates an auxiliary signal (H1) for driving vibration of the oscillator. The drive electrode (21) is selectively to which the drive signal (D1) and the auxiliary signal (H1) are applied. When the operating mode switches from active mode (AM1) to sleep mode (SM1), the auxiliary signal (H1) is applied to the drive electrode (21), and the oscillator (10) is driven to vibrate by the auxiliary signal (H1). When the operating mode switches from sleep mode (SM1) to active mode (AM1), a drive signal (D1) is applied to the drive electrode (21), and the vibrator (10) vibrates according to the drive signal (D1).

[0177] With this configuration, in sleep mode (SM1), the oscillator (10) can be driven to vibrate by the auxiliary signal (H1). In other words, the oscillator (10) can be externally excited to vibrate. Therefore, in sleep mode (SM1), the oscillation loop circuit (48) that generates the drive signal (D1) can be stopped. As a result, the current consumption in sleep mode (SM1) can be reduced.

[0178] In the third embodiment of the gyro sensor (1), in the first or second embodiment, the drive circuit unit (31) includes a memory unit (43). The memory unit (43) stores the frequency of the drive signal (D1) in the immediately preceding active mode (AM1). When the operating mode switches from active mode (AM1) to sleep mode (SM1), the frequency of the auxiliary signal (H1) is set to the frequency of the drive signal (D1) stored in the memory unit (43).

[0179] This configuration allows the frequency of the auxiliary signal (H1) in sleep mode (SM1) to be set to the same frequency as the drive signal (D1) in the most recent active mode (AM1) just before entering sleep mode. This suppresses the degradation of the gyro sensor (1) characteristics in sleep mode (SM1). Furthermore, it enables a rapid transition from sleep mode (SM1) to active mode (AM1).

[0180] The gyro sensor (1) according to the fourth embodiment further comprises a detection feedback circuit (70) in any one of the first to third embodiments. The detection feedback circuit (70) generates first FTR signals (97a, 97b) that suppress the detected vibration of the oscillator (10) based on the detection signal (S1). The plurality of electrodes (2) further include first detection feedback electrodes (24a, 24b) to which the first FTR signals (97a, 97b) are applied. The mode switching unit (33) switches the operating mode from sleep mode (SM1) to active mode (AM1) based on at least one of the first FTR signals (97a, 97b) and the detection signal (S1).

[0181] With this configuration, in addition to the detection signal (S1) of the sensor element (vibrator (10) and multiple electrodes (2)), a first FTR signal (97a, 97b) can be used as a trigger signal for switching the operating mode. That is, the operating mode can be switched by utilizing the free vibration applied to the angular velocity sensor during sleep mode (SM1) (i.e., the change in electrode capacitance of the angular velocity sensor). In this case as well, power saving and miniaturization of the gyro sensor (1) can be achieved.

[0182] In the fifth embodiment of the gyro sensor (1), in any one of the first to fourth embodiments, the detection circuit unit (32) includes a TIA circuit (60), a demodulation circuit (61), and an output circuit (64). The TIA circuit (60) receives a detection signal (S1) from the detection electrode (22). The demodulation circuit (61) is connected downstream of the TIA circuit (60). The output circuit (64) is connected downstream of the demodulation circuit (61) and determines the angular velocity applied to the oscillator (10) based on the detection signal (S1). The mode switching unit (33) switches the operating mode from sleep mode (SM1) to active mode (AM1) based on the detection signal (S2) obtained from the signal path (L2a, L2b) between the TIA circuit (60) and the demodulation circuit (61).

[0183] With this configuration, the detection signal (S1, trigger signal) obtained from the signal path (L2a, L2b) between the TIA circuit (60) and the demodulation circuit (61) inside the detection circuit unit (32) (i.e., the converted signals 94a, 94b) can be used as the detection signal (S1, trigger signal) for switching the operating mode. As a result, in sleep mode (SM1), the circuits from the demodulation circuit (61) to the output circuit (64) among the circuits constituting the detection circuit unit (32) can be stopped, contributing to power saving.

[0184] In the gyro sensor (1) according to the sixth embodiment, in any one of the first to fifth embodiments, the plurality of electrodes (2) include a detection electrode (22), a first detection electrode (22a), and a second detection electrode (22b). The first detection electrode (22a) outputs a first detection signal (S1a) as a detection signal (S1). The second detection electrode (22b) is located on the opposite side of the oscillator (10) from the first detection electrode (22a) and outputs a second detection signal (S1b) as a detection signal (S1). The detection circuit (32) includes a current buffer (69) and a TIA circuit (60). The current buffer (69) is connected to the first detection electrode (22a) and the second detection electrode (22b). The TIA circuit (60) is connected downstream of the current buffer (69). The mode switching unit (33) switches the operating mode from sleep mode (SM1) to active mode (AM1) based on the first detection signal (amplified signal 104a) and the second detection signal (amplified signal 104b) obtained from the signal path (L4a, L4b) between the current buffer (69) and the TIA circuit (60).

[0185] With this configuration, the detection signal (S1) (trigger signal) for switching the operating mode can be the detection signal (L4a, L4b) obtained from the signal path (L4a, L4b) between the current buffer (69) and the TIA circuit (60) inside the detection circuit unit (32) (amplification signals 104a, 104b).

[0186] In the gyro sensor (1) according to the seventh embodiment, in the fourth embodiment, the plurality of electrodes (2) further include a second detection feedback electrode (24b). The detection feedback circuit (70) includes a voltage buffer (75). The voltage buffer (75) is connected to the first detection feedback electrode (24a) and the second detection feedback electrode (24b). The voltage buffer (75) outputs a second FTR signal (97b) which is in the opposite phase to the first FTR signal (97a) to the second detection feedback electrode (24b). The mode switching unit (33) switches the operating mode from sleep mode (SM1) to active mode (AM1) based on the first FTR signal (97a) and the second FTR signal (97b). The first FTR signal (97a) is obtained from the signal path (L3a) between the first detection feedback electrode (24a) and the voltage buffer (75). The second FTR signal (97b) is obtained from the signal path (L3b) between the second detection feedback electrode (24b) and the voltage buffer (75).

[0187] With this configuration, the first FTR signal (97a) obtained from the signal path (L3a) between the first detection feedback electrode (24a) and the voltage buffer (75), and the second FTR signal (97b) obtained from the signal path (L3b) between the second detection feedback electrode (24b) and the voltage buffer (75) can be used as FTR signals (97a, 97b, trigger signal) for switching the operating mode.

[0188] 1 Gyro sensor 2 Electrode 3 Control unit 10 Vibrator 21 Drive electrode 22 Detection electrode 23 Monitor electrode 24a First detection feedback electrode (detection feedback electrode) 24b Second detection feedback electrode (detection feedback electrode) 31 Drive circuit section 32 Detection circuit section 33 Mode switching section 42 Oscillator 43 Memory section 48 Oscillator loop circuit 60 TIA circuit 61 Demodulation circuit 64 Output circuit 69 Current buffer 70 Detection feedback circuit section 75 Voltage buffer 94a, 94b Conversion signal (detection signal) 97a First FTR signal (FTR signal) 97b Second FTR signal (FTR signal) S1 Detection signal 104a Amplification signal (first detection signal) 104b Amplification signal (second detection signal) AM1 Active mode D1 Drive signal H1 Auxiliary signal L1a, L1b, L2a, L2b, L3a, L3b, L4a, L4b signal path SM1 sleep mode

Claims

1. A gyro sensor comprising: a vibrator; a plurality of electrodes arranged opposite the vibrator and forming capacitance with the vibrator; and a control unit connected to the plurality of electrodes, wherein the plurality of electrodes include a drive electrode to which a drive signal is applied for driving vibration of the vibrator; and a detection electrode that outputs a detection signal generated by the vibration of the vibrator; the control unit comprises a drive circuit unit that generates the drive signal; a detection circuit unit that generates an angular velocity signal from the detection signal; and a mode switching unit that switches the operating mode of the drive circuit unit and the detection circuit unit, wherein the mode switching unit switches the operating mode to sleep mode or active mode based on the detection signal input to the detection circuit unit.

2. The plurality of electrodes include a monitor electrode that outputs a monitor signal generated by the drive vibration of the vibrator, the drive circuit includes an oscillation loop circuit that generates the drive signal based on the monitor signal, and an oscillator that generates an auxiliary signal for driving the vibrator, the drive electrode is selectively to which the drive signal and the auxiliary signal are applied, when the operating mode switches from the active mode to the sleep mode, the auxiliary signal is applied to the drive electrode and the vibrator is driven and vibrated by the auxiliary signal, and when the operating mode switches from the sleep mode to the active mode, the drive signal is applied to the drive electrode and the vibrator is driven and vibrated by the drive signal, the gyro sensor according to claim 1.

3. The drive circuit unit includes a storage unit that stores the frequency of the drive signal in the immediately preceding active mode, and when the operating mode switches from the active mode to the sleep mode, the frequency of the auxiliary signal is set to the frequency of the drive signal stored in the storage unit, the gyro sensor according to claim 2.

4. A gyro sensor according to any one of claims 1 to 3, further comprising a detection feedback circuit that generates a first FTR (Force-to-Rebalance) signal for suppressing the detected vibration of the oscillator based on the detection signal, wherein the plurality of electrodes further include a first detection feedback electrode to which the first FTR signal is applied, and the mode switching unit switches the operating mode from the sleep mode to the active mode based on at least one of the first FTR signal and the detection signal.

5. The detection circuit unit comprises a TIA (Transimpedance Amplifier) ​​circuit to which the detection signal from the detection electrode is input; a demodulation circuit connected downstream of the TIA circuit; and an output circuit connected downstream of the demodulation circuit to determine the angular velocity applied to the oscillator based on the detection signal, wherein the mode switching unit switches the operating mode from the sleep mode to the active mode based on the detection signal obtained from the signal path between the TIA circuit and the demodulation circuit, according to any one of claims 1 to 3.

6. The plurality of electrodes include a first detection electrode and a second detection electrode, the detection electrode, the first detection electrode outputs a first detection signal as the detection signal, the second detection electrode is positioned on the side of the oscillator opposite to the first detection electrode and outputs a second detection signal as the detection signal, the detection circuit unit comprises a current buffer connected to the first detection electrode and the second detection electrode, and a TIA (Transimpedance Amplifier) ​​circuit connected downstream of the current buffer, and the mode switching unit switches the operating mode from the sleep mode to the active mode based on the first detection signal and the second detection signal obtained from the signal path between the current buffer and the TIA circuit, the gyro sensor according to any one of claims 1 to 3.

7. The gyro sensor according to claim 4, wherein the plurality of electrodes further include a second detection feedback electrode, the detection feedback circuit unit comprises a voltage buffer connected to the first detection feedback electrode and the second detection feedback electrode, the voltage buffer outputs a second FTR signal in opposite phase to the first FTR signal to the second detection feedback electrode, and the mode switching unit switches the operating mode from the sleep mode to the active mode based on the first FTR signal obtained from the signal path between the first detection feedback electrode and the voltage buffer, and the second FTR signal obtained from the signal path between the second detection feedback electrode and the voltage buffer.

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