JP2015125054A - Capacitance detection circuit, and angular velocity sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a voltage higher than conventional voltage to be applied to a vibrator, making it possible to increase the vibration amplitude of the vibrator.SOLUTION: A capacitance detection circuit 7 is configured so as to include: a C-V conversion circuit 8 composed of a full differential amplifier 11 and feedback capacitors Cf1, Cf2; an input common mode feedback circuit 9, having a reference voltage input terminal 14, for controlling an average voltage of the inverted input terminal and non-inverting input terminal of the full differential amplifier 11 to a voltage to be inputted to the reference voltage input terminal 14; and a reference voltage generation circuit 10 for outputting a reference voltage signal varying at a higher frequency than a resonance frequency of a vibrator 4, to the reference voltage input terminal 14. It is thereby made possible to apply a high voltage to the vibrator 4, and hence to increase a vibration amplitude of the vibrator.

Description

  The present invention relates to a capacitance detection circuit and an angular velocity sensor.

  Conventionally, by vibrating the vibrator in a predetermined vibration direction, when an angular velocity is applied from the outside, Coriolis force is generated in the direction perpendicular to the vibration direction of the vibrator, and the vibrator is detected perpendicular to the vibration direction. An angular velocity sensor that detects the amount of displacement in the direction and measures the angular velocity is known (for example, Patent Documents 1 and 2).

  This type of conventional angular velocity sensor has a configuration as shown in FIG. That is, the conventional angular velocity sensor 100 includes a vibrator 101, a pair of driving capacitors 102 and 103, a pair of detection capacitors 104 and 105, a driving circuit 110, a carrier signal generation circuit 120, and an input common mode feedback. The circuit 140 and the CV conversion circuit 130 are included.

  The driving capacitors 102 and 103 are each composed of a movable electrode provided on the vibrator 101 and a fixed electrode facing the movable electrode, and are connected in series via the vibrator 101. The drive circuit 110 applies drive signals Vdp and Vdn whose polarities are inverted to each other to the fixed electrodes of the pair of drive capacitors 102 and 103, thereby causing the drive capacitors 102 and 103 to have different sizes of static electricity. A force is generated to vibrate the vibrator 101 in a predetermined vibration direction (X direction). For example, the drive signals Vdp and Vdn are generated as sine wave signals having a frequency that matches the resonance frequency (about 5 kHz) of the vibrator 101.

  The detection capacitors 104 and 105 are capacitors that detect displacement of the vibrator 101 in the detection direction (Y direction) due to Coriolis force, and each includes a movable electrode provided on the vibrator 101 and a fixed electrode facing the movable electrode. And connected in series via the vibrator 101. The CV conversion circuit 130 includes a fully differential amplifier 131 connected to the fixed electrodes of the detection capacitors 104 and 105, and a feedback capacitor having the same capacitance provided in each of the two feedback paths of the fully differential amplifier 131. 133 and 134, and switches 135 and 136 for resetting the electric charge stored in the feedback capacitors 133 and 134. A predetermined reference voltage Vref is connected to the output common mode terminal 132 that determines the output reference voltage of the fully-differential amplifier 131. The fully-differential amplifier 131 receives each feedback capacitor from each of the non-inverting output terminal and the inverting output terminal. Output signals Vop and Von having the reference voltage Vref as the center voltage are output in accordance with the charges accumulated in 133 and 134. The reference voltage Vref is set to the center voltage (Vdd / 2) of the power supply voltage Vdd of the angular velocity sensor 100, for example.

  The input common mode feedback circuit 140 is provided on the input side of the CV conversion circuit 130, and includes an amplifier 141, monitoring capacitors 142 and 143, and buffer capacitors 144 and 145. The input common mode feedback circuit 140 is a circuit that controls the average value of the input voltages of the inverting input terminal and the non-inverting input terminal of the fully-differential amplifier 131 provided in the CV conversion circuit 130 to be the reference voltage Vref. . However, since the non-inverting input terminal and the inverting input terminal of the fully differential amplifier 131 of the CV conversion circuit 130 have the same voltage due to a virtual short circuit, the input common mode feedback circuit 140 includes the inverting input terminal of the fully differential amplifier 131 and Control is performed so that each of the non-inverting input terminals becomes the reference voltage Vref. Therefore, the fixed electrodes of the detection capacitors 104 and 105 are always held at the reference voltage Vref.

  In the angular velocity sensor 100 configured as described above, when the vibrator 101 is displaced in the Y direction by the Coriolis force, the capacitances of the detection capacitors 104 and 105 change. That is, when the capacitance of one detection capacitor 104 increases, the capacitance of the other detection capacitor 105 decreases. Along with this change in capacitance, charges are transferred from the detection capacitors 104 and 105 to the CV conversion circuit 130. At this time, some charges transferred from the detection capacitors 104 and 105 are absorbed by the input common mode feedback circuit 140, and the feedback capacitors 133 and 134 of the CV conversion circuit 130 correspond to the change in capacitance. Charge is accumulated. That is, one feedback capacitor 133 stores a charge corresponding to the capacitance change of the detection capacitor 104, and the other feedback capacitor 134 stores a charge corresponding to the capacitance change of the detection capacitor 105. Is done. Therefore, the CV conversion circuit 130 outputs the output signals Vop and Von having the reference voltage Vref as the center voltage based on the charges accumulated in the hoodback capacitors 133 and 134.

  In the conventional angular velocity sensor 100, the carrier signal generation circuit 120 is provided so that Tr noise generated by the fully differential amplifier 131 of the CV conversion circuit 130, kT / C noise, and the like can be removed by a low-pass filter on the rear stage side. Applies a carrier signal SIG having a higher frequency (for example, about 200 kHz) than the vibration frequency (resonance frequency) of the vibrator 101 to the vibrator 101. As a result, the charge signals output from the detection capacitors 104 and 105 are modulated by the carrier signal SIG, so that the output signals Vop and Von of the CV conversion circuit 130 also become high-frequency signals. Therefore, the noise generated in the CV conversion circuit 130 is included in the high frequency components of the output signals Vop and Von, and the noise can be satisfactorily removed by a low-pass filter or the like at the subsequent stage.

JP2011-137777A JP 2008-102091 A

  However, when a high-frequency carrier signal is applied to the vibrator 101 as in the above prior art, the vibration amplitude when the drive circuit 110 drives the vibrator 101 in the vibration direction (X direction) is limited by the carrier signal. There is a problem that the vibration amplitude of the vibrator 101 cannot be increased.

  FIG. 5 is a diagram showing a conventional carrier signal SIG and drive signals Vdp and Vdn. For example, the carrier signal generation circuit 120 applies a carrier signal SIG having an amplitude matching the power supply voltage Vdd to the vibrator 101 as shown in FIG. This carrier signal SIG is a rectangular wave signal having a frequency (for example, 200 kHz) sufficiently higher than the resonance frequency (for example, 5 kHz) of the vibrator 101. Even when such a high-frequency carrier signal SIG is applied, the vibrator 101 does not vibrate in the vibration direction (X direction) following the carrier signal SIG. This is because, from the viewpoint of the drive circuit 110, it is equivalent to the average value of the carrier signal SIG being applied to the vibrator 101, that is, assuming that the duty of the carrier signal SIG is 50%, half of the vibration amplitude (Vdd). This is because it becomes equivalent to the case where a direct current of the voltage (Vdd / 2) is applied.

  As shown in FIG. 5B, the drive circuit 110 generates an electrostatic force in the drive capacitors 102 and 103 in a state where the average voltage (Vdd / 2) of the carrier signal SIG is applied to the vibrator 101. Drive signals Vdp and Vdn are generated. That is, the drive circuit 110 generates drive signals Vdp and Vdn having an oscillation amplitude of the average voltage (Vdd / 2) of the carrier signal SIG and applies the drive signals to the fixed electrodes of the drive capacitors 102 and 103, respectively. As a result, in the period TA, the electrostatic force generated in the driving capacitor 103 is larger than the electrostatic force generated in the driving capacitor 102, and the vibrator 101 is attracted to the fixed electrode side of the driving capacitor 103. In the period TB, the electrostatic force generated in the driving capacitor 102 is larger than the electrostatic force generated in the driving capacitor 103, and the vibrator 101 is attracted to the fixed electrode side of the driving capacitor 102. In this way, the vibrator 101 vibrates in the vibration direction.

  Since the electrostatic force generated in each of the driving capacitors 102 and 103 is proportional to the square of the potential difference between the movable electrode and the fixed electrode, it is maximum when the drive signals Vdp and Vdn as shown in FIG. 5B are applied. However, only an electrostatic force corresponding to the square of the half of the potential difference of the power supply voltage Vdd can be generated between the movable electrode and the fixed electrode. Therefore, the conventional angular velocity sensor 100 has a small electrostatic force generated to vibrate the vibrator 101 and cannot increase the vibration amplitude of the vibrator 101.

  Therefore, the present invention has been made to solve the above-described conventional problems, and is a capacitance that can increase the vibration amplitude of the vibrator by applying a higher voltage to the vibrator than before. An object of the present invention is to provide a detection circuit and an angular velocity sensor.

  In order to achieve the above object, the present invention first adopts as a solution means that two detection capacitors with variable capacitance are connected in series via a vibrator, and are adapted to the displacement of the vibrator. A capacitance detection circuit for detecting capacitance based on a charge signal output from each of the two detection capacitors, wherein the capacitances of the two detection capacitors are changed. A feedback capacitor is connected between the inverting input terminal and the non-inverting output terminal of the fully differential amplifier, and between the non-inverting input terminal and the inverting output terminal of the fully differential amplifier. The charge corresponding to the charge signal output from one of the capacitors for detection is accumulated in the feedback capacitor connected to the inverting input terminal, and from the other detection capacitor. A CV conversion circuit that outputs a pair of output signals corresponding to the capacitances of the two detection capacitors by accumulating charges corresponding to the input charge signal in a feedback capacitor connected to a non-inverting input terminal; An input common mode feedback circuit having a reference voltage input terminal and controlling an average voltage of the inverting input terminal and the non-inverting input terminal of the fully differential amplifier to a voltage input to the reference voltage input terminal; and And a reference voltage generation circuit that generates a reference voltage signal that changes at a frequency higher than the resonance frequency and outputs the reference voltage signal to the reference voltage input terminal.

  In the configuration of the capacitance detection circuit, the fully differential amplifier has an output reference voltage terminal that determines a center voltage of the output signal, and the reference voltage generation circuit converts the reference voltage signal to the output reference. It is more preferable to employ a configuration that further outputs to the voltage terminal.

  The second aspect of the present invention adopts as a solution means an angular velocity sensor configured to vibrate, and a pair of vibrators that are held at a predetermined voltage and that vibrate the vibrators in a predetermined vibration direction. Applying drive signals whose polarities are reversed to each of the drive capacitor and the pair of drive capacitors, an electrostatic force is generated in the pair of drive capacitors to vibrate the vibrator in the vibration direction. And a pair of detection capacitors that change capacitance according to displacement of the vibrator in a detection direction orthogonal to the vibration direction, and a fully differential amplifier. A feedback capacitor is connected between each of the inverting input terminal and the non-inverting output terminal and between the non-inverting input terminal and the inverting output terminal. The charge corresponding to the charge signal output from one of the sensors is stored in a feedback capacitor connected to the inverting input terminal, and the charge corresponding to the charge signal output from the other detection capacitor is stored. A CV conversion circuit that outputs a pair of output signals corresponding to the capacitance of the pair of detection capacitors by storing in a feedback capacitor connected to a non-inverting input terminal; and a reference voltage input terminal, An input common mode feedback circuit that controls the average voltage of the inverting input terminal and the non-inverting input terminal of the fully-differential amplifier to a voltage input to the reference voltage input terminal, and a reference that changes at a frequency higher than the resonance frequency of the vibrator A reference voltage generation circuit for generating a voltage signal and outputting the reference voltage signal to the reference voltage input terminal; and Certain pressure to the structure and a voltage holding circuit for holding the predetermined voltage.

  In the configuration of the angular velocity sensor, the fully-differential amplifier has an output reference voltage terminal that determines a center voltage of the output signal, and the reference voltage generation circuit sends the reference voltage signal to the output reference voltage terminal. It is more preferable to adopt a configuration that further outputs.

  Furthermore, in the configuration of the angular velocity sensor, a configuration in which the vibration amplitude of the drive signal is the predetermined voltage held by the voltage holding circuit may be adopted.

  According to the present invention, since a higher voltage can be applied to the vibrator than before without reducing the noise reduction effect, the vibration amplitude of the vibrator can be increased.

It is a circuit diagram which shows one structural example of the angular velocity sensor which concerns on this invention. It is a figure which shows an example of the drive signal produced | generated by a drive circuit. It is a timing chart which shows the operation example of each part in an electrostatic capacitance detection circuit. It is a figure which shows the structural example of the conventional angular velocity sensor. It is a figure which shows the conventional carrier signal and drive signal.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In addition, in each embodiment demonstrated below, the same code | symbol is attached | subjected to the member which is mutually common, and the overlapping description about them is abbreviate | omitted.

  FIG. 1 is a circuit diagram showing a configuration example of an angular velocity sensor 1 according to the present invention. The angular velocity sensor 1 includes a sensor unit 2 formed by a MEMS (Micro Electro Mechanical Systems) structure and a signal processing unit 3 formed as an ASIC (Application Specific Integrated Circuit). The sensor unit 2 and the signal processing unit 3 is a configuration formed and packaged on one substrate such as a silicon substrate.

  The sensor unit 2 includes a vibrator 4 that is supported on a substrate by a spring structure or the like and is capable of vibration displacement in the X direction (vibration direction) and the Y direction (detection direction) orthogonal to each other. The sensor unit 2 also includes a pair of driving capacitors C1 and C2 for vibrating the vibrator 4 in the X direction and a pair of amplitude detecting capacitors C3 and C4 for detecting the vibration amplitude of the vibrator 4 in the X direction. And a pair of detection capacitors C5 and C6 for detecting the displacement of the vibrator 4 in the Y direction. Each of the driving capacitors C1 and C2 includes a movable electrode provided on the vibrator 4 and a fixed electrode provided on the substrate so as to face the movable electrode, and is connected in series with the vibrator 4 interposed therebetween. . Similarly, the amplitude detection capacitors C3 and C4 are each composed of a movable electrode provided on the vibrator 4 and a fixed electrode provided on the substrate so as to face the movable electrode. It is a connected configuration. The same applies to the detection capacitors C5 and C6. Each of the detection capacitors C5 and C6 includes a movable electrode provided on the vibrator 4 and a fixed electrode provided on the substrate so as to face the movable electrode. It is a connected configuration.

  The signal processing unit 3 includes a drive circuit 5 that vibrates the vibrator 4 in the X direction, a voltage holding circuit 6 that holds the voltage of the vibrator 4 at a predetermined voltage, and a detection that detects displacement of the vibrator 4 in the Y direction. And a capacitance detection circuit 7 connected to the fixed electrodes of the capacitors C5 and C6, for detecting the capacitance of the detection capacitors C5 and C6 and outputting a signal corresponding to the displacement of the vibrator 4 in the Y direction.

  The voltage holding circuit 6 holds the vibrator 4 in a constant state at the power supply voltage Vdd by applying the power supply voltage Vdd of the angular velocity sensor 1 to the vibrator 4, for example. The drive circuit 5 applies drive signals Vdp and Vdn whose polarities are inverted to the fixed electrodes of the pair of drive capacitors C1 and C2, respectively, and vibrates the vibrator 4 in the X direction. When the vibrator 4 vibrates in the X direction, the capacitances of the amplitude detection capacitors C3 and C4 change. For example, when the capacitance of one amplitude detection capacitor C3 increases, the capacitance of the other amplitude detection capacitor C4 decreases. The drive circuit 5 generates the drive signals Vdp and Vdn while detecting the vibration amplitude in the X direction of the vibrator 4 based on the capacitance change of the vibration detection capacitors C3 and C4.

  FIG. 2 is a diagram illustrating an example of drive signals Vdp and Vdn applied to the drive capacitors C1 and C2 by the drive circuit 5. The drive signals Vdp and Vdn are, for example, sine wave signals having a frequency that matches the resonance frequency (for example, 5 kHz) of the vibrator 4 and are signals whose polarities are inverted. These drive signals Vdp and Vdn are periodically switched in magnitude relation, for example, with the voltage (power supply voltage Vdd) of the vibrator 4 held by the voltage holding circuit 6 as the vibration amplitude. The drive circuit 5 applies the drive signal Vdp to the fixed electrode of one drive capacitor C1, and applies the drive signal Vdn to the fixed electrode of the other drive capacitor C2. Accordingly, the electrostatic force acting between the movable electrode and the fixed electrode of the driving capacitor C1 during the period of the timings T0 to T1 shown in FIG. 2 is the electrostatic force acting between the movable electrode and the fixed electrode of the driving capacitor C2. The vibrator 4 is attracted to the fixed electrode of the driving capacitor C2 and displaced. In addition, during the period from timing T1 to T2, the electrostatic force acting between the movable electrode and the fixed electrode of the driving capacitor C1 is larger than the electrostatic force acting between the movable electrode and the fixed electrode of the driving capacitor C2, The vibrator 4 is attracted to the fixed electrode of the driving capacitor C1 and displaced. Accordingly, the vibrator 4 vibrates in the X direction at the resonance frequency. At this time, an electrostatic force proportional to the square of the power supply voltage Vdd is generated at the maximum in each of the driving capacitors C1 and C2, and therefore the vibrator 4 can be vibrated in the X direction with a larger electrostatic force than before. The vibration amplitude of 4 can be increased.

  When the vibrator 4 is vibrating in the X direction, if an angular velocity is applied to the angular velocity sensor 1, a Coriolis force that displaces the vibrator 4 in the Y direction is applied according to the magnitude of the angular velocity. This Coriolis force is proportional to the velocity of the vibrator 4 in the X direction. If the vibration frequency of the vibrator 4 is the same, the greater the vibration amplitude of the vibrator 4, the greater the speed at which the vibrator 4 moves in the X direction, so the Coriolis force acting on the vibrator 4 increases. When the angular velocity is applied, the amount of displacement of the vibrator 4 in the Y direction can be increased. Therefore, since the angular velocity sensor 1 of the present embodiment can increase the vibration amplitude of the vibrator 4 as compared with the conventional one, the Coriolis force displacement of the vibrator 4 becomes larger than before, and the sensitivity when detecting the angular velocity. Will improve.

  The detection capacitors C5 and C6 are capacitors that detect the displacement of the vibrator 4 in the Y direction due to the Coriolis force, and are capacitors having the same capacitance when the Coriolis force is not acting. When the vibrator 4 is displaced in the Y direction by the Coriolis force, the distance between the movable electrode and the fixed electrode in each of the detection capacitors C5 and C6 changes, and thereby the capacitance changes. For example, when the capacitance of one detection capacitor C5 increases, the capacitance of the other detection capacitor C6 decreases. Conversely, when the capacitance of one detection capacitor C5 decreases, the capacitance of the other detection capacitor C6 increases. The detection capacitors C5 and C6 detect the amount of displacement of the vibrator 4 in the Y direction by such a change in capacitance. The detection capacitors C5 and C6 output charge signals corresponding to the respective capacitances.

  The capacitance detection circuit 7 includes a CV conversion circuit 8 connected to the fixed electrodes of the detection capacitors C5 and C6, and an input common mode feedback provided between the detection capacitors C5 and C6 and the CV conversion circuit 8. A circuit 9 and a reference voltage generation circuit 10 are provided.

  The CV conversion circuit 8 includes a fully differential amplifier 11 connected to the fixed electrodes of the detection capacitors C5 and C6, and a feedback capacitor having the same capacitance provided in each of the two feedback paths of the fully differential amplifier 11. Cf1 and Cf2 and switches SW1 and SW2 connected in parallel with the feedback capacitors Cf1 and Cf2 in order to reset the charges accumulated in the feedback capacitors Cf1 and Cf2, respectively. The inverting input terminal of the fully differential amplifier 11 is connected to the fixed electrode of the detection capacitor C5, and the non-inverting input terminal is connected to the fixed electrode of the detection capacitor C6. A feedback capacitor Cf1 and a switch SW1 are connected in parallel between the inverting input terminal and the non-inverting output terminal, and a feedback capacitor Cf2 and a switch SW2 are connected in parallel between the non-inverting input terminal and the inverting output terminal. The The reference voltage Vc generated by the reference voltage generation circuit 10 is input to an output common mode terminal (output reference voltage terminal) 12 that determines the output reference voltage of the fully differential amplifier 11. Output signals Vop and Von having the reference voltage Vc as the center voltage are output from the non-inverting output terminal and the inverting output terminal, respectively, according to the charges accumulated in the feedback capacitors Cf1 and Cf2. In such a CV conversion circuit 8, since the inverting input terminal and the non-inverting input terminal of the fully differential amplifier 11 are virtually short-circuited, the input voltage Vip of the inverting input terminal and the input voltage Vin of the non-inverting input terminal are mutually connected. Operates to have the same voltage.

  The CV conversion circuit 8 temporarily turns on the switches SW1 and SW2 to reset the accumulated charges of the feedback capacitors Cf1 and Cf2, and then turns off the switches SW1 and SW2 to be output from the detection capacitors C5 and C6, respectively. Charges corresponding to the charge signals are accumulated in the feedback capacitors Cf1 and Cf2, and output signals Vop and Von corresponding to these charges are output. At this time, if one of the detection capacitors C5 and C6 increases in capacitance, the other capacitance decreases. Therefore, the output signals Vop and Von correspond to the displacement of the vibrator 4 in the Y direction. Are output as a pair of differential signals. Therefore, if a differential signal Vout (= Vop−Von) between the output signals Vop and Von is calculated in a subsequent circuit (not shown), common mode noise included in the output signals Vop and Von can be removed.

  The input common mode feedback circuit 9 includes an amplifier 13, monitoring capacitors Ca and Cb, and buffer capacitors Cc and Cd. The non-inverting input terminal (reference voltage input terminal) 14 of the amplifier 13 includes a reference voltage generation circuit 10. The generated reference voltage Vc is input. The input common mode feedback circuit 9 detects the average values of the input voltages Vip and Vin of the inverting input terminal and the non-inverting input terminal of the fully differential amplifier 11 by the monitoring capacitors Ca and Cb, and the average value is the reference voltage. It is a circuit that controls to be Vc. However, since the input voltages Vip and Vin become the same voltage due to the virtual short circuit of the fully differential amplifier 11 as described above, the input common mode feedback circuit 9 outputs the input voltages Vip and Vin from the reference voltage generation circuit 10. It operates so as to match the reference voltage Vc.

  The reference voltage generation circuit 10 is a circuit that generates a reference voltage Vc to be output to the CV conversion circuit 8 and the input common mode feedback circuit 9. The reference voltage generation circuit 10 modulates the reference voltage Vc at a frequency (for example, 200 kHz) higher than the resonance frequency of the vibrator 4, and the modulated signal (reference voltage signal) is converted into the CV conversion circuit 8 and the input common mode feedback circuit. Output to 9.

  FIG. 3 is a timing chart illustrating an operation example of each unit in the capacitance detection circuit 7. FIG. 3A is a diagram illustrating an example of the reference voltage Vc generated by the reference voltage generation circuit 10. As shown in FIG. 3A, the reference voltage generation circuit 10 sets the reference voltage Vc to a first voltage (Vdd / 2) and a second voltage (3 * Vdd / 4) higher than the first voltage. ) And a third voltage (Vdd / 4) that is lower than the first voltage. That is, the reference voltage Vc is Vdd / 2 in the period from the timing T10 to T11, the reference voltage Vc is 3 * Vdd / 4 in the period from the timing T11 to T12, and the reference voltage Vc is Vdd / 4 in the period from the timing T12 to T13. It becomes. After timing T13, the reference voltage Vc becomes Vdd / 2 again, and the same change is repeated. When the reference voltage Vc thus modulated is input to the amplifier 13 of the input common mode feedback circuit 9, the input voltages Vip and Vin of the CV conversion circuit 8 change following the reference voltage Vc. When such a reference voltage Vc is input to the output common mode terminal 12 of the fully differential amplifier 11, the output signals Vop and Von output from the CV conversion circuit 8 are also modulated by the reference signal Vc.

  Hereinafter, the operation of each part in the capacitance detection circuit 7 will be described. It is assumed that a constant Coriolis force acts on the vibrator 4 during the periods T10 to T13. As shown in FIG. 3B, the switches SW1 and SW2 of the CV conversion circuit 8 are temporarily turned on when the reference voltage Vc is the first voltage (Vdd / 2), and are fed to the feedback capacitors Cf1 and Cf2. Reset accumulated charge. At this time, since a voltage of Vdd / 2 is applied between the movable electrode and the fixed electrode of the detection capacitors C5 and C6, a charge corresponding to the applied voltage (Vdd / 2) is applied to the detection capacitors C5 and C6. Is accumulated. For example, if the capacitance of the detection capacitor C5 is (C + ΔC), the charge Q11 accumulated in the detection capacitor C5 is Q11 = (C + ΔC) * (Vdd / 2). Here, ΔC is a change in capacitance due to the displacement of the vibrator 4 in the Y direction by the Coriolis force. At this time, since the capacitance of the detection capacitor C6 is (C−ΔC), the charge Q21 accumulated in the detection capacitor C6 is Q21 = (C−ΔC) * (Vdd / 2).

  Thereafter, the switches SW1 and SW2 are turned off, and when the reference voltage Vc rises to the second voltage (3 * Vdd / 4) at the timing T11, the potential difference between both ends of the detection capacitors C5 and C6 changes to Vdd / 4. . At this time, the charge Q12 accumulated in the detection capacitor C5 is Q12 = (C + ΔC) * (Vdd / 4), and the amount of charge (Q12−Q11) transferred from the detection capacitor C5 to the capacitance detection circuit 7 is , (Q12−Q11) = − (C + ΔC) * (Vdd / 4). On the other hand, the charge Q22 stored in the detection capacitor C6 is Q22 = (C−ΔC) * (Vdd / 4), and the amount of charge transferred from the detection capacitor C6 to the capacitance detection circuit 7 (Q22−Q21). ) Is (Q22−Q21) = − (C−ΔC) * (Vdd / 4).

  In the input common mode feedback circuit 9, the monitoring capacitors Ca and Cb monitor the input voltages Vip and Vin. When charges are transferred from the detection capacitors C5 and C6, the input voltages Vip and Vin are used as reference voltages. In order to hold at Vc (= 3 * Vdd / 4), some of the charges transferred from the detection capacitors C5 and C6 are absorbed by the buffer capacitors Cc and Cd. That is, the buffer capacitor Cc absorbs a part of the charge (−C * Vdd / 4) in the charge amount (Q12−Q11) = − (C + ΔC) * (Vdd / 4) transferred from the detection capacitor C5. To do. Further, the buffer capacitor Cd receives a part of the charge (-C * Vdd / 4) in the charge amount (Q22−Q21) = − (C−ΔC) * (Vdd / 4) transferred from the detection capacitor C6. Absorb. The charge of Q3 = −ΔC * (Vdd / 4) is transferred and accumulated in the feedback capacitor Cf1 of the CV conversion circuit 8, and the charge of Q4 = ΔC * (Vdd / 4) is transferred to the feedback capacitor Cf2. Accumulated. As a result, the output signal Vop output from the CV conversion circuit 8 during the period of the timing T11 to T12 when the reference voltage Vc becomes the second voltage (3 * Vdd / 4) is as shown in FIG. It becomes higher than the reference voltage Vc (= 3 * Vdd / 4), and the output signal Von becomes lower than the reference voltage Vc.

  Next, when the reference voltage Vc decreases to the third voltage (Vdd / 4) at timing T12, the potential difference between both ends of the detection capacitors C5 and C6 changes to 3 * Vdd / 4. At this time, the charge Q13 stored in the detection capacitor C5 is Q13 = (C + ΔC) * (3 * Vdd / 4), and the amount of charge (Q13−Q12) transferred from the detection capacitor C5 to the capacitance detection circuit 7 ) Is (Q13−Q12) = (C + ΔC) * (Vdd / 2). On the other hand, the charge Q23 accumulated in the detection capacitor C6 is Q23 = (C−ΔC) * (3 * Vdd / 4), and the amount of charge transferred from the detection capacitor C6 to the capacitance detection circuit 7 (Q23 −Q22) becomes (Q23−Q22) = (C−ΔC) * (Vdd / 2).

  In the input common mode feedback circuit 9, as described above, the monitoring capacitors Ca and Cb monitor the input voltages Vip and Vin, and when charges are transferred from the detection capacitors C5 and C6, the input voltages Vip , Vin is held at the reference voltage Vc (= Vdd / 4), part of the charges transferred from the detection capacitors C5 and C6 are absorbed by the buffer capacitors Cc and Cd. At this time, the buffer capacitor Cc absorbs a part of the charge (C * Vdd / 2) in the charge amount (Q13−Q12) = (C + ΔC) * (Vdd / 2) transferred from the detection capacitor C5. . The buffer capacitor Cd absorbs a part of the charge (C * Vdd / 2) out of the charge amount (Q23−Q22) = (C−ΔC) * (Vdd / 2) transferred from the detection capacitor C6. . Since the charge of Q5 = ΔC * (Vdd / 2) is transferred to the feedback capacitor Cf1 of the CV conversion circuit 8, the accumulated charge (Q3 + Q5) of the feedback capacitor Cf1 is (Q3 + Q5) = ΔC * (Vdd / 4) It becomes. Since the charge of Q6 = −ΔC * (Vdd / 2) is transferred to the feedback capacitor Cf2, the accumulated charge (Q4 + Q6) of the feedback capacitor Cf2 becomes (Q4 + Q6) = − ΔC * (Vdd / 4). As a result, during the period from the timing T12 to T13 when the reference voltage Vc becomes the third voltage (Vdd / 4), the output signal Vop output from the CV conversion circuit 8 is the reference voltage as shown in FIG. It becomes lower than Vc (= Vdd / 4), and the output signal Von becomes higher than the reference voltage Vc.

  Therefore, the output signals Vop and Von of the CV conversion circuit 8 are signals obtained by adding a signal component corresponding to the displacement of the vibrator 4 in the Y direction to the reference voltage Vc modulated by the reference voltage generation circuit 10. Since the output signals Vop and Von are high-frequency signals sufficiently higher than the resonance frequency of the vibrator 4, Tr noise and kT / C noise generated in the fully differential amplifier 11 of the CV conversion circuit 8 are also output signal Vop. , Von are included in the high-frequency component, and if a low-pass filter or the like is provided in a subsequent circuit (not shown), such a noise component can be satisfactorily removed.

  As described above, when the differential signal Vout (= Vop−Von) between the output signals Vop and Von is calculated in the subsequent circuit, as shown in FIG. 3D, the period of the timing T11 to T12 and the period of the timing T12 to T13 Since the polarity of the difference signal Vout is switched, a signal based on the displacement of the vibrator 4 in the Y direction can be obtained by demodulating it.

  In the above, the reference voltage generation circuit 10 sets the reference voltage Vc to the first voltage (Vdd / 2), the second voltage (3 * Vdd / 4) higher than the first voltage, Although the case of changing to the three values of the third voltage (Vdd / 4) lower than the voltage of 1 has been exemplified, the present invention is not limited to this. For example, the reference voltage generation circuit 10 changes the reference voltage Vc into a binary value of a first voltage (for example, 3 * Vdd / 4) and a second voltage (for example, Vdd / 4) lower than the first voltage. As the rectangular wave signal to be generated, a high-frequency reference voltage signal may be generated.

  In the above, the reference voltage Vc output from the reference voltage generation circuit 10 is not only input to the reference voltage input terminal 14 of the input common mode feedback circuit 9, but also the output of the fully differential amplifier 11 in the CV conversion circuit 8. Although the case where it inputs also to the common mode terminal 12 was illustrated, it is not restricted to this. For example, the reference voltage Vc output from the reference voltage generation circuit 10 is input only to the reference voltage input terminal 14 of the input common mode feedback circuit 9 and is applied to the output common mode terminal 12 of the fully differential amplifier 11 in the CV conversion circuit 8. May be configured to receive a constant reference voltage Vref (for example, Vdd / 2) as in the prior art.

  However, when the output common mode terminal 12 is always held at a constant reference voltage Vref, a potential difference is generated between the input side and the output side of the fully-differential amplifier 11, and the electric charge corresponding to the potential difference is fed back to the feedback capacitor Cf1. , Cf2. At this time, when the electrostatic capacitances of the feedback capacitors Cf1 and Cf2 are not the same due to factors such as manufacturing variations, the accumulated charges vary, so that errors due to the capacitance mismatch are included in the output signals Vop and Von. In order to reduce such an error, a high-frequency reference voltage signal output from the reference voltage generation circuit 10 is converted into a reference voltage input terminal 14 of the input common mode feedback circuit 9 and CV conversion as in the above-described configuration. It is preferable to employ a configuration in which the circuit 8 is input to both the output common mode terminal 12 of the fully-differential amplifier 11.

  As described above, in the angular velocity sensor 1 of the present embodiment, the voltage holding circuit 6 holds the vibrator 4 at a constant voltage, and the drive circuit 5 controls the vibrator 4 with respect to the pair of driving capacitors C1 and C2. By applying drive signals Vdp and Vdn that are sine wave signals that coincide with the resonance frequency and have opposite polarities, a difference in electrostatic force is caused between the pair of drive capacitors C1 and C2, and the vibrator 4 is Vibrate in the X direction. At this time, the drive circuit 5 generates drive signals Vdp and Vdn whose amplitude is the voltage applied to the vibrator 4 and applies it to the drive capacitors C1 and C2. Therefore, as described above, for example, if the voltage holding circuit 6 keeps the voltage of the vibrator 4 constant at the power supply voltage Vdd of the angular velocity sensor 1, the driving circuit 5 is connected to the movable electrodes of the driving capacitors C1 and C2. Since the maximum power supply voltage Vdd of the angular velocity sensor 1 can be applied between the fixed electrodes, the electrostatic force generated in each of the driving capacitors C1 and C2 can be made larger than before, and the vibration amplitude of the vibrator 4 can be increased. Can be made larger than before. As a result, the vibration speed when the vibrator 4 vibrates in the X direction increases, and the Coriolis force generated according to the angular speed also increases. Therefore, the amount of displacement of the vibrator 4 in the Y direction can be increased, and the angular speed Measurement sensitivity is improved.

  In addition, the angular velocity sensor 1 of the present embodiment employs the above-described configuration, and a pair of detection capacitors C5 and C6 that change the capacitance as the vibrator 4 is displaced in the Y direction orthogonal to the X direction. A CV conversion circuit 8 that outputs a pair of output signals Vop and Von corresponding to the amount of displacement of the vibrator 4 in the Y direction by detecting the capacitance of the pair of detection capacitors C5 and C6, and a reference voltage An input common mode feedback circuit having an input terminal 14 and controlling the average voltage of the inverting input terminal and the non-inverting input terminal of the fully-differential amplifier 11 provided in the CV conversion circuit 8 to a voltage input to the reference voltage input terminal 14 9 and a reference voltage signal that changes at a frequency higher than the resonance frequency of the vibrator 4, and the reference voltage signal is input to the reference voltage input terminal of the input common mode feedback circuit 9. A configuration including a reference voltage generating circuit 10 for outputting to 4. According to such a configuration, since the inverting input terminal and the non-inverting input terminal of the fully differential amplifier 11 provided in the CV conversion circuit 8 are modulated by the reference voltage signal, the output signals Vop and Von of the CV conversion circuit 8 are used. Can be output as a high-frequency signal higher than the resonance frequency of the vibrator 4. Therefore, it is possible to satisfactorily remove Tr noise, kT / C noise, and the like generated in the fully differential amplifier 11 of the CV conversion circuit 8 using a low-pass filter on the rear stage side.

  That is, the angular velocity sensor 1 of the present embodiment modulates the low frequency signal output from the sensor unit 2 into a high frequency signal in the capacitance detection circuit 7, so that the sensor unit 2 needs to apply the high frequency signal to the vibrator 4. There is no. As a result, the drive circuit 5 and the voltage holding circuit 6 can apply a high voltage to vibrate the vibrator 4 in the X direction, and the vibration amplitude of the vibrator 4 can be increased. Therefore, the angular velocity sensor 1 of the present embodiment has a configuration in which a large vibration amplitude can be ensured by applying a higher voltage to the vibrator 4 than in the past while adopting a configuration that can satisfactorily reduce noise. Yes.

  As mentioned above, although one Embodiment regarding this invention was described, this invention is not limited to the content mentioned above, A various modification is applicable. For example, although the case where the voltage holding circuit 6 holds the voltage of the vibrator 4 at the power supply voltage Vdd of the angular velocity sensor 1 is illustrated in the above embodiment, the present invention is not limited to this. For example, the voltage holding circuit 6 includes boosting means such as a charge pump that boosts the power supply voltage Vdd of the angular velocity sensor 1 and applies a voltage higher than the power supply voltage Vdd boosted by the boosting means to the vibrator 4. good. Since the voltage applied to the vibrator 4 may be a DC voltage, the load current is small, and a voltage higher than the power supply voltage Vdd can be obtained relatively easily by using a boosting means such as a charge pump. The drive circuit 5 can further increase the vibration amplitude of the vibrator 4 by generating the drive signals Vdp and Vdn having the voltages boosted by the boosting means and applying them to the drive capacitors C1 and C2. There are advantages.

  Further, the capacitance detection circuit 7 in the above embodiment is not limited to the angular velocity sensor 1 but can be applied to a capacitance type sensor that detects a physical quantity other than the angular velocity, such as an acceleration sensor. That is, the above-described capacitance detection circuit 7 is configured to generate a high-frequency signal that can satisfactorily remove noise with a low-pass filter or the like, and therefore, even when applied to a capacitance-type sensor other than an angular velocity sensor. The suppression effect is exhibited well.

  DESCRIPTION OF SYMBOLS 1 ... Angular velocity sensor, 4 ... Vibrator, 5 ... Drive circuit, 6 ... Voltage holding circuit, 7 ... Electrostatic capacitance detection circuit, 8 ... CV conversion circuit, 9 ... Input common mode feedback circuit, 10 ... Reference voltage generation circuit, DESCRIPTION OF SYMBOLS 11 ... Fully differential amplifier, 12 ... Output common mode terminal (output reference voltage terminal), 14 ... Reference voltage input terminal, C1, C2 ... Driving capacitor, C5, C6 ... Detection capacitor, Cf1, Cf2 ... Feedback capacitor

Claims (5)

Two detection capacitors with variable capacitance are connected in series via a vibrator, and the two detection capacitors change in capacitance according to the displacement of the vibrator. A capacitance detection circuit for detecting capacitance based on a charge signal output from each of the
A feedback capacitor is connected between the inverting input terminal and the non-inverting output terminal and between the non-inverting input terminal and the inverting output terminal of the fully differential amplifier; The charge corresponding to the charge signal output from one of the two detection capacitors is accumulated in the feedback capacitor connected to the inverting input terminal, and the charge signal output from the other detection capacitor A CV conversion circuit that outputs a pair of output signals corresponding to the capacitances of the two detection capacitors by accumulating the stored charge in a feedback capacitor connected to a non-inverting input terminal;
An input common mode feedback circuit having a reference voltage input terminal and controlling an average voltage of the inverting input terminal and the non-inverting input terminal of the fully differential amplifier to a voltage input to the reference voltage input terminal;
A reference voltage generation circuit that generates a reference voltage signal that changes at a frequency higher than a resonance frequency of the vibrator, and outputs the reference voltage signal to the reference voltage input terminal;
A capacitance detection circuit comprising: The fully differential amplifier has an output reference voltage terminal that determines a center voltage of the output signal,
The capacitance detection circuit according to claim 1, wherein the reference voltage generation circuit outputs the reference voltage signal to the output reference voltage terminal. A vibrator configured to be vibrated and maintained at a predetermined voltage;
A pair of driving capacitors for vibrating the vibrator in a predetermined vibration direction;
A drive circuit that applies a drive signal whose polarities are reversed to each of the pair of drive capacitors, and generates an electrostatic force for causing the pair of drive capacitors to vibrate the vibrator in the vibration direction;
A pair of detection capacitors that change capacitance as the vibrator is displaced in a detection direction orthogonal to the vibration direction;
A feedback capacitor is connected between the inverting input terminal and the non-inverting output terminal and between the non-inverting input terminal and the inverting output terminal. The charge corresponding to the charge signal output from one of the detection capacitors is accumulated in the feedback capacitor connected to the inverting input terminal, and the charge signal output from the other detection capacitor A CV conversion circuit that outputs a pair of output signals corresponding to the capacitances of the pair of detection capacitors by storing the accumulated charge in a feedback capacitor connected to a non-inverting input terminal;
An input common mode feedback circuit having a reference voltage input terminal and controlling an average voltage of the inverting input terminal and the non-inverting input terminal of the fully differential amplifier to a voltage input to the reference voltage input terminal;
A reference voltage generation circuit that generates a reference voltage signal that changes at a frequency higher than a resonance frequency of the vibrator, and outputs the reference voltage signal to the reference voltage input terminal;
A voltage holding circuit for holding the voltage of the vibrator at the predetermined voltage;
An angular velocity sensor comprising: The fully differential amplifier has an output reference voltage terminal that determines a center voltage of the output signal,
The angular velocity sensor according to claim 3, wherein the reference voltage generation circuit outputs the reference voltage signal to the output reference voltage terminal.   The angular velocity sensor according to claim 3 or 4, wherein the vibration amplitude of the drive signal is the predetermined voltage held by the voltage holding circuit.

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