JP6056636B2 - Sensor device - Google Patents

Description

  The present invention relates to a sensor device configured by, for example, MEMS (Micro Electro Mechanical Systems) or the like and detecting accelerations in three axis directions orthogonal to each other.

  Conventionally, a capacitance sensor is known in which a pair of fixed electrodes is provided with a movable electrode movable in a uniaxial direction, and two variable capacitors are formed between each fixed electrode and the movable electrode ( For example, Patent Document 1). In this type of capacitance sensor, when an external force (acceleration) acts in one axial direction in which the movable electrode can move, the movable electrode is displaced between the two fixed electrodes accordingly, and the electrostatic capacity of the two variable capacitors is increased. Change the capacity. In order to detect a change in the capacitance of these variable capacitors, for example, Patent Document 1 is configured to apply a charge voltage whose polarity is inverted at a constant period to a pair of fixed electrodes.

  When such a charge voltage is applied, a potential difference is generated between the two variable capacitors, and thus an electrostatic force is generated to attract the movable electrode in each of the two variable capacitors. However, when a movable electrode is disposed between a pair of fixed electrodes, electrostatic forces generated in each variable capacitor are canceled by attracting the movable electrodes in opposite directions. For this reason, the electrostatic force acting on the movable electrode is canceled, and the movable electrode is displaced between the two fixed electrodes only when an external force is applied.

JP 2004-294077 A

  In recent years, it has been desired that one sensor device is provided with the above-described capacitance sensors in three axial directions orthogonal to each other, and the measurement results in these three axial directions are output. For example, when forming a capacitive sensor in a triaxial direction with a MEMS structure in one sensor device, two fixed electrodes are sandwiched between one movable electrode in two directions of the X axis and the Y axis, as described above. Since it can be arranged, a capacitance sensor including two variable capacitors can be configured. However, in the Z-axis direction orthogonal to the X-axis and the Y-axis, it is difficult to dispose two fixed electrodes with one movable electrode interposed therebetween.

  FIG. 14 is a diagram illustrating a configuration example of a capacitance sensor that detects acceleration in the Z-axis direction. As shown in FIG. 14A, the electrostatic capacitance sensor that detects the acceleration in the Z-axis direction has a movable electrode 16 disposed opposite to the fixed electrode 17 formed on the surface of the semiconductor substrate 91. It is supported so as to be movable in the Z-axis direction (vertical direction) in a state where it floats at a predetermined interval (about several μm) from 17. That is, the movable electrode 16 is configured such that the peripheral side surface thereof is supported by a large number of springs 93 extending from the inner surface of the support column 92 erected around the fixed electrode 17. A cap 94 is placed around the movable electrode 16 to seal the operation space of the movable electrode 16. In such a configuration, since the distance between the movable electrode 16 and the cap 94 becomes excessive, the fixed electrode constituting the variable capacitor cannot be provided on the lower surface side of the cap 94. For this reason, in the capacitance sensor that detects the acceleration in the Z-axis direction, only one variable capacitor formed by the movable electrode 16 and the fixed electrode 17 can be formed.

  Therefore, in the case of a capacitance sensor that detects acceleration in the Z-axis direction, for example, as shown in an equivalent circuit shown in FIG. 14B, in addition to the variable capacitor CZ1, a capacitor CZ2 having a fixed capacitance is used, for example, the semiconductor substrate 91 or the like. Are separately formed and connected in series. Thereby, it becomes possible to detect a change in the capacitance of the variable capacitor CZ1 by a method similar to that for the other two axes.

  However, on the other hand, the Z-axis electrostatic capacity sensor configured as shown in FIG. 14B, when a charge voltage is applied to the two terminals Z1 and Z2, the movable electrode 16 of the variable capacitor CZ1. An electrostatic force attracting each other is generated between the movable electrode 16 and the fixed electrode 17, and the movable electrode 16 moves toward the fixed electrode 17 by the electrostatic force. In other words, since there is no other variable capacitor in the Z-axis capacitance sensor that cancels out the electrostatic force generated in the variable capacitor CZ1, the movable electrode 16 is displaced by the electrostatic force generated by the application of the charge voltage. Therefore, it becomes impossible to detect only a change in capacitance due to an external force (acceleration).

  In order to prevent this, after applying a charge voltage to the terminals Z1 and Z2, the electrostatic force acting on the movable electrode 16 and the tensile force by the spring 93 are equalized, and the displacement of the movable electrode 16 due to the electrostatic force is reduced. It is necessary to wait until the light converges to a certain value and stabilizes before measurement. Therefore, for example, as shown in FIG. 15 (a), when the capacitance change in each of the XYZ triaxial capacitance sensors is detected by one CV conversion circuit 106, the three axes cannot be measured simultaneously. As shown in FIG. 15B, after performing the measurement of the X axis and the measurement of the Y axis in order, before starting the measurement of the Z axis, a charge voltage is applied to the Z axis to It is necessary to perform processing for stabilization. However, if the processing for stabilizing the Z-axis capacitance is performed after the measurement of the X-axis and the measurement of the Y-axis is completed, it takes a long time to complete the measurement of all three axes. In addition, there is a problem that the average power consumption in the sensor device increases as the measurement time increases.

  In order to solve the above-described problems, an object of the present invention is to provide a sensor device that can shorten the time required for measurement of all three axes and reduce power consumption.

  In order to achieve the above object, a sensor device according to the present invention is provided with a pair of fixed electrodes sandwiching a movable electrode movable in a first axial direction, and the two connected in series by each fixed electrode and the movable electrode. A pair of fixed electrodes are arranged across a first capacitance sensor configured by two variable capacitors and a movable electrode movable in a second axial direction orthogonal to the first axial direction, and each fixed electrode A second capacitance sensor comprising two variable capacitors connected in series by a movable electrode and a movable electrode, a movable electrode movable in a third axial direction orthogonal to the first and second axial directions, and A third capacitance sensor configured by connecting in series a variable capacitance capacitor constituted by a fixed electrode disposed opposite to the movable electrode and a capacitance invariant capacitor comprising a pair of fixed electrodes; First One of the first to third capacitance sensors is applied by sequentially applying charge voltages of opposite phases to the fixed electrodes at both ends of each of the third to third capacitance sensors in a time-sharing manner. A control circuit that selects a capacitance sensor and sequentially shifts to the measurement mode, and the control circuit has both ends of the third capacitance sensor when the first or second capacitance sensor is in the measurement mode. By applying a driving voltage having a phase opposite to that of the charge voltage to the fixed electrode, a change in capacitance due to the electrostatic force of the variable capacitor in the third capacitance sensor is stabilized. It is the structure to do.

  Further, in the sensor device, the control circuit has a fixed period around a predetermined reference voltage with respect to the fixed electrodes at both ends of the capacitance sensor in the measurement mode among the first to third capacitance sensors. When a charge voltage whose polarity is inverted with a constant voltage width is applied and the first or second capacitance sensor is in the measurement mode, a charge is applied to the fixed electrodes at both ends of the third capacitance sensor. A configuration may be adopted in which a driving voltage having the same period as the voltage and oscillating with a constant voltage width in the same polarity direction from the reference voltage is applied.

  In this case, the sensor device includes a CV conversion circuit that outputs a signal corresponding to the capacitance change of the variable capacitor in each of the first to third capacitance sensors, and the first to third capacitance sensors. And a sampling circuit that samples and outputs the signal output of the CV conversion circuit at a predetermined timing when each is in the measurement mode. The sampling circuit is measured by the first or second capacitance sensor. In the mode, after the polarity of the charge voltage applied to the fixed electrodes at both ends of the first or second capacitance sensor is inverted, the signal output of the CV conversion circuit is sampled and output, thereby driving It is more preferable to adopt a configuration characterized in that the charge movement from the third capacitance sensor due to the voltage is canceled and output. Arbitrariness.

  According to the present invention, when the first or second capacitance sensor is in the measurement mode, the capacitance change due to the electrostatic force of the variable capacitance capacitor in the third capacitance sensor is stabilized. Therefore, when the measurement in the first or second axial direction is completed, the third capacitance sensor can be promptly shifted to the measurement mode and measurement in the third axial direction can be started. Therefore, the time required for measurement of all three axes is shorter than before, and the power consumption can be suppressed.

It is a block diagram which shows the notional structure of a sensor device. It is a figure which shows an example of the specific circuit structure of a sensor device. It is a figure which shows the sequence of control operation | movement by a control circuit. It is a figure which shows the voltage applied to the both ends of the electrostatic capacity sensor of XYZ 3-axis. It is a figure which shows the charge voltage applied to an electrostatic capacitance sensor at the time of a measurement mode. It is a figure which shows the 1st charge transfer in a measurement mode. It is a figure which shows the 2nd electric charge movement in measurement mode. It is a figure which shows the 3rd charge transfer in a measurement mode. It is a figure which shows the drive voltage applied for a capacity | capacitance stabilization process. It is a figure which shows the 1st charge transfer in a capacity | capacitance stabilization process. It is a figure which shows the 2nd electric charge movement in a capacity | capacitance stabilization process. It is a figure which shows the 3rd electric charge movement in a capacity | capacitance stabilization process. It is a figure which shows an example of the other circuit structure of a sensor device. It is a figure which shows the example of 1 structure of the electrostatic capacitance sensor which detects the acceleration of a Z-axis direction. It is a figure which shows the conventional measuring method by the electrostatic capacity sensor of XYZ 3-axis.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the embodiments described below, members that are common to each other are denoted by the same reference numerals, and redundant descriptions thereof are omitted.

  FIG. 1 is a block diagram showing a conceptual configuration of a sensor device 1 according to an embodiment of the present invention. The sensor device 1 includes a sensor unit 2 configured to detect accelerations in three axial directions orthogonal to each other on the X axis, the Y axis, and the Z axis, and a CV conversion circuit 6 that performs CV conversion on the output from the sensor unit 2. A sampling circuit 7 that samples and outputs an output signal of the CV conversion circuit 6 at a predetermined timing, and a control circuit 8.

  The sensor unit 2 includes a first capacitance sensor 3 that detects acceleration in the X-axis direction, a second capacitance sensor 4 that detects acceleration in the Y-axis direction, and a first capacitance sensor that detects acceleration in the Z-axis direction. 3 capacitance sensors 5. These capacitance sensors 3, 4, and 5 are formed on the surface of the semiconductor substrate by, for example, a MEMS structure. The X-axis capacitance sensor 3 is provided with a pair of fixed electrodes 11 and 12 with a movable electrode 10 movable in the X-axis direction parallel to the surface of the semiconductor substrate, for example, and movable with the fixed electrodes 11 and 12. In this configuration, two variable capacitors CX1 and CX2 connected in series with the electrode 10 are formed. Similarly, the Y-axis capacitance sensor 4 is, for example, parallel to the surface of the semiconductor substrate and a pair of fixed electrodes 14 and 15 sandwiching a movable electrode 13 movable in the Y-axis direction orthogonal to the X-axis. , And two variable capacitors CY1 and CY2 connected in series by the fixed electrodes 14 and 15 and the movable electrode 13 are formed. On the other hand, the Z-axis capacitance sensor 5 includes, for example, a movable electrode 16 that can move in the Z-axis direction perpendicular to the surface of the semiconductor substrate, and a fixed electrode 17 that is disposed to face the movable electrode 16. The capacitor CZ1 formed by the above and a capacitor CZ2 of constant capacitance formed by the fixed electrodes 18 and 19 provided on the semiconductor substrate or the like are connected in series. The variable capacitor CZ1 constituting the Z-axis capacitance sensor 5 is the same as the structure shown in FIG.

  In these capacitance sensors 3, 4 and 5, when an external force (acceleration) acts in a direction in which the movable electrodes 10, 13, 16 can move, the movable electrodes 10, 13, 16 are displaced accordingly. The capacitances of the variable capacitors CX1, CX2, CY1, CY2, and CZ1 are each changed. Then, the middle point of the two capacitors connected in series in each of the capacitance sensors 3, 4, 5 is connected to the CV conversion circuit 6, and the signal accompanying the change in capacitance is converted to CV as a single output from the sensor unit 2. Output to circuit 6.

  The control circuit 8 sequentially applies a predetermined charge voltage to each of the three capacitance sensors 3, 4, and 5 in a time-sharing manner, so that the three capacitance sensors 3, 4, and 5 This is a circuit that selects one of the capacitance sensors and sequentially shifts to the measurement mode, and controls the operation of the CV conversion circuit 6 and the sampling circuit 7.

  FIG. 2 is a diagram illustrating an example of a specific circuit configuration of the sensor device 1. As shown in FIG. 2, the CV conversion circuit 6 of this embodiment includes an operational amplifier 20. An output terminal from the sensor unit 2 is connected to the inverting input terminal of the operational amplifier 20. A feedback capacitor Cf and a switch Sf are connected in parallel between the inverting input terminal and the output terminal of the operational amplifier 20. The switch Sf is for discharging the electric charge accumulated in the capacitor Cf, and is on / off controlled by the control circuit 8 described above. On the other hand, the non-inverting input terminal of the operational amplifier 20 is connected to the reference voltage Vref. Since the operational amplifier 20 operates so that the potential Vin of the inverting input terminal is equal to the potential Vip of the non-inverting input terminal, the potential Vin of the inverting input terminal is held at a predetermined reference voltage Vref.

  Such a CV conversion circuit 6 is configured such that when each capacitance sensor 3, 4, 5 provided in the sensor unit 2 is in the measurement mode, if the acceleration acts and the capacitance of the variable capacitor changes, Charges that move due to the change in capacitance are accumulated in the feedback capacitor Cf, and an output signal Vo corresponding to the change in capacitance is output from the output terminal of the operational amplifier 20.

  The sampling circuit 7 of this embodiment employs an output correlated double sampling circuit. The sampling circuit 7 includes capacitors Ca and Cb and switches Sa and Sb for sampling and outputting the output signal Vo of the CV conversion circuit 6. One end of the capacitor Ca is connected to the output terminal of the operational amplifier 20 in the CV conversion circuit 6, and the other end is connected to one end of the switch Sb. One end of the switch Sa is connected between the capacitor Ca and the switch Sb, and the other end of the switch Sa is connected to the reference voltage Vref. The other end of the switch Sb is an output terminal Vout of the sampling circuit 7, and the output terminal Vout is connected to the reference voltage Vref via the capacitor Cb.

  Such a sampling circuit 7 first samples the output signal Vo from the CV conversion circuit 6 in the capacitor Ca by closing the switch Sa with the switch Sb opened. Then, the switch Sa is opened with the switch Sb opened, and the second sampling of the output signal Vo from the CV conversion circuit 6 is performed in the capacitor Ca. After sampling twice with the capacitor Ca in this way, the switch Sb is closed to output an output signal Vout corresponding to the amount of charge accumulated in the capacitor Ca. Thereby, the sampling circuit 7 can output the output signal Vout in which the offset voltage of the operational amplifier 20 in the CV conversion circuit 6 and kT / C noise are canceled. The switches Sa and Sb in the sampling circuit 7 are on / off controlled by the control circuit 8 described above.

  In the sensor unit 2, a plurality of switches SXa that are alternatively closed to apply a charge voltage to both ends X1, X2 of the two variable capacitors CX1, CX2 in the X-axis capacitance sensor 3. , SXb, SXc are provided. Similarly, a plurality of switches SYa, SYb, SYc that are alternatively closed are provided at both ends Y1, Y2 of the two variable capacitors CY1, CY2 in the Y-axis capacitance sensor 4. Furthermore, a plurality of switches SZa, SZb, and SZc that are alternatively closed are provided at both ends Z1 and Z2 of the variable capacitor CZ1 and the capacitor CZ2 that does not change the capacitance in the Z-axis capacitance sensor 5. ing. Each switch provided at both ends of each of the capacitance sensors 3, 4 and 5 has one of three values, that is, a reference voltage Vref and a predetermined voltage Vc higher than the reference voltage Vref as shown in FIG. Either a voltage VH that is higher than the reference voltage Vref or a voltage VL that is lower than the reference voltage Vref by a predetermined voltage Vc is connected. For example, when Vc = Vref, VH = 2 · Vref and VL = 0. Each switch is controlled to be turned on and off by the control circuit 8, and during the measurement mode, a charge voltage that is sequentially switched by three values of Vref, VH, and VL is applied to both ends of each of the capacitance sensors 3, 4, and 5.

  Next, control by the control circuit 8 will be described. FIG. 3 is a diagram showing a sequence of control operations by the control circuit 8. As shown in FIG. 3A, when the control circuit 8 measures the acceleration of each axis in order as the measurement timing of the XYZ three axes, first, as shown in FIG. The capacitance sensor 3 on the axis is shifted to the measurement mode, and a variable voltage corresponding to the acceleration in the X-axis direction is applied by applying charge voltages having opposite phases to both ends X1, X2 of the X-axis capacitance sensor 3. The capacitance change of the capacitors CX1 and CX2 is measured. At this time, the other Y-axis and Z-axis capacitance sensors 4 and 5 are in the non-measurement mode. When the measurement of the X axis is completed, the control circuit 8 next causes the Y axis capacitance sensor 4 to enter the measurement mode at timing T1, and the opposite ends of the Y axis Y1 and Y2 of the Y axis capacitance sensor 4 are opposite to each other. The change in the capacitance of the variable capacitors CY1 and CY2 corresponding to the acceleration in the Y-axis direction is measured by applying the charge voltage. At this time, the other X-axis and Z-axis capacitance sensors 3 and 5 are in the non-measurement mode. When the measurement of the Y-axis is further completed, the control circuit 8 next causes the Z-axis capacitance sensor 5 to enter the measurement mode at the timing T2 and reverses both ends Z1, Z2 of the Z-axis capacitance sensor 5 to each other. A change in the capacitance of the variable capacitor CZ1 corresponding to the acceleration in the Z-axis direction is measured by applying a phase charge voltage. At this time, the other X-axis and Y-axis capacitance sensors 3 and 4 are in the non-measurement mode.

  As described above, the period in which the electrostatic sensors 3, 4 and 5 in the XYZ three axes sequentially shift to the measurement mode is the operation period of the sensor device 1. The timing at which this operation period starts has a fixed period in the sensor device 1. For example, when the measurement of the Z axis is completed at timing T3, the time until the start timing of the next operation period is reached. It becomes a rest period. During the suspension period, the power consumption can be reduced by cutting off the power supply to the sensor unit 2, the CV conversion circuit 6, and the sampling circuit 7.

  When the X-axis and Y-axis capacitance sensors 3 and 4 are in the measurement mode during the operation period, the control circuit 8 performs a capacitance stabilization process on the Z-axis capacitance sensor 5 in advance. This capacitance stabilization processing generates an electrostatic force on the variable capacitor CZ1 of the Z-axis capacitance sensor 5, and the displacement of the movable electrode 16 due to the electrostatic force is previously measured during the measurement of the X-axis and the Y-axis. This is a process to be stabilized. That is, the control circuit 8 moves the movable electrode 16 toward the fixed electrode 17 in advance in the Z-axis capacitance sensor 5 when the X-axis and Y-axis capacitance sensors 3 and 4 are in the measurement mode. Accordingly, a drive voltage having a pattern different from the charge voltage and having opposite phases is applied to both ends Z1 and Z2 of the Z-axis capacitance sensor 5. As a result, the electrostatic capacitance of the Z-axis variable capacitor CZ1 gradually changes from the initial value C0 in a state where no electrostatic force is generated at the timing T0, as shown in FIG. 3B. . In parallel with the measurement of the X-axis and the Y-axis, the movement of the Z-axis movable electrode 16 can be converged early, and the timing T2 when the Z-axis capacitance sensor 5 shifts to the measurement mode. In this case, the electrostatic capacity of the Z-axis variable capacitor CZ1 can be stabilized at a constant value Cd that does not change due to electrostatic force. Therefore, when the measurement mode of the Y-axis capacitance sensor 4 ends at the timing T2, the Z-axis capacitance sensor 5 can be immediately shifted to the measurement mode and measurement of the Z-axis can be started. Therefore, the time required for measurement of all XYZ three axes can be shortened. In addition, since the suspension period can be extended accordingly, the power consumption of the sensor device 1 can be reduced.

  FIG. 4 is a diagram illustrating voltages applied to both ends of the XYZ triaxial capacitance sensors 3, 4, and 5 when the sensor device 1 is in an operation period. As described above, the X-axis capacitance sensor 3 is in the measurement mode between the timings T0 and T1. At this time, the control circuit 8 performs on / off control of the plurality of switches SXa, SXb, SXc connected to the X-axis capacitance sensor 3, thereby making reference to both ends X 1, X 2 of the capacitance sensor 3. A charge voltage having a waveform whose polarity is inverted with a constant period and a constant voltage width (Vc) around the voltage Vref is applied. That is, the control circuit 8 first applies the same reference voltage Vref to the two terminals X1 and X2 with the switch SXb closed, and secondly applies the voltage VH to one terminal X1 with the switch SXa closed. The voltage VL is applied to the other terminal X2. Third, the switch SXb is closed again and the same reference voltage Vref is applied to the two terminals X1 and X2. Fourth, the switch SXc is closed and the voltage VL is applied to one terminal X1, and the other terminal X2 is applied. A voltage VH is applied. By performing these first to fourth on / off controls, the control circuit 8 applies a charge voltage for one cycle to both ends X1 and X2 of the capacitance sensor 3. The control circuit 8 applies the charge voltage as described above for a plurality of periods (four periods in the example of FIG. 4) when the X-axis capacitance sensor 3 is in the measurement mode. Therefore, when the X-axis capacitance sensor 3 is in the measurement mode, a voltage indicated by a solid line in FIG. 4 is applied to one terminal X1, and a voltage indicated by a broken line is applied to the other terminal X2. The same applies when the Y-axis capacitance sensor 4 is in the measurement mode at the timings T1 to T2 and when the Z-axis capacitance sensor 5 is in the measurement mode at the timings T2 to T3. A charge voltage is applied. When the X-axis and Y-axis capacitance sensors 3 and 4 are in the non-measurement mode, the reference voltage Vref is applied as shown in FIG.

  In addition, when the X-axis and Y-axis capacitance sensors 3 and 4 are in the measurement mode, the drive voltages applied to both ends Z1 and Z2 of the Z-axis capacitance sensor 5 are as shown in FIG. The waveform oscillates from the voltage Vref with a constant voltage width (Vc) in the same polarity direction. At this time, the control circuit 8 alternately turns on and off two switches SZa and SZb among the plurality of switches SZa, SZb, and SZc connected to the Z-axis capacitance sensor 5 to thereby change the capacitance sensor. 5 is applied with a driving voltage at which the reference voltage Vref and the voltage VH are alternately switched, and a driving voltage at which the reference voltage Vref and the low voltage VL are alternately switched is applied to the other terminal Z2. .

  Next, the operation when the sensor device 1 is in the operation period will be described. First, an operation for detecting a change in capacitance according to acceleration when each of the capacitance sensors 3, 4, 5 is in the measurement mode will be described. FIG. 5 is a diagram illustrating one cycle Ts of the charge voltage applied to the two terminals X1 and X2 when the X-axis capacitance sensor 3 is in the measurement mode. As shown in FIG. 5, one period Ts of the charge voltage includes a first section Ta, a second section Tb, a third section Tc, and a fourth section Td.

  The control circuit 8 sets the charge voltage applied to both ends X1 and X2 of the X-axis capacitance sensor 3 to the reference voltage Vref in the first section Ta. At this time, since the potential Vin between the two variable capacitors CX1 and CX2 in the X-axis capacitance sensor 3 is also the reference voltage Vref, no charge accumulation occurs in the two variable capacitors CX1 and CX2. In addition, the control circuit 8 discharges the charge of the feedback capacitor Cf by closing the switch Sf of the CV conversion circuit 6 in the first section Ta. Further, the control circuit 8 closes the switch Sa of the sampling circuit 7 and opens the switch Sb. As a result, if the operational amplifier 20 has an offset voltage, a charge corresponding to the offset voltage can be stored in the capacitor Ca.

  When the control circuit 8 makes a transition from the first section Ta to the second section Tb, the control circuit 8 opens the switch Sf of the CV conversion circuit 6 and uses the charge voltage applied to one terminal X1 of the capacitance sensor 3 as a reference. The voltage Vref is switched to the voltage VH, and the charge voltage applied to the other terminal X2 is switched from the reference voltage Vref to the voltage VL. FIG. 6 is a diagram illustrating charge transfer when transitioning from the first section Ta to the second section Tb. As shown in FIG. 6, when the transition is made from the first section Ta to the second section Tb, charges are accumulated in the variable capacitors CX1 and CX2, respectively. At this time, it is assumed that acceleration in the X-axis direction is acting, the capacitance C of the variable capacitor CX1 changes to C + ΔC, and the capacitance C of the variable capacitor CX2 changes to C−ΔC. . In this case, the charge amount Q = (C + ΔC) Vc is accumulated in the variable capacitor CX1, and the charge amount Q = − (C−ΔC) Vc is accumulated in the variable capacitor CX2. The charge amount Q = −2ΔCVc is accumulated in the feedback capacitor Cf of the CV conversion circuit 6 due to the charge movement that occurs at this time. As a result, the output signal Vo of the operational amplifier 20 becomes Vo = −2ΔCVc / Cf + Vref, and a potential difference −2ΔCVc / Cf is generated at both ends of the capacitor Ca of the sampling circuit 7, and the charge Qa corresponding to this potential difference is accumulated in the capacitor Ca. Is done. Cf is the capacitance of the feedback capacitor Cf.

  Next, when the control circuit 8 makes a transition from the second section Tb to the third section Tc, first, the switch Sa of the sampling circuit 7 is opened, and the charge Qa accumulated in the capacitor Ca is stored. Thereafter, the charge voltage applied to both ends X1 and X2 of the capacitance sensor 3 is switched again to the reference voltage Vref. FIG. 7 is a diagram illustrating the charge transfer when transitioning from the second section Tb to the third section Tc. When both ends X1 and X2 of the capacitance sensor 3 return to the reference voltage Vref again in the third section Tc, charge transfer for setting the charges accumulated in the two variable capacitors CX1 and CX2 to zero in the second section Tb. Happens. That is, as shown in FIG. 7, the charge amounts Q of the two variable capacitors CX1 and CX2 are both 0, and the charge amount Q of the feedback capacitor Cf is also 0. As a result, the output signal Vo of the operational amplifier 20 is Vo = Vref. A potential Va = 2ΔCVc / Cf + Vref corresponding to the charge Qa stored in the capacitor Ca appears at the node a on the output side of the capacitor Ca in the sampling circuit 7.

  Next, when the control circuit 8 makes a transition from the third section Tc to the fourth section Td, the control circuit 8 switches the charge voltage applied to one terminal X1 of the capacitance sensor 3 from the reference voltage Vref to the voltage VL, and the other terminal. The charge voltage applied to X2 is switched from the reference voltage Vref to the voltage VH. FIG. 8 is a diagram illustrating the charge transfer when the transition is from the third section Tc to the fourth section Td. As shown in FIG. 8, when the transition is made from the third section Tc to the fourth section Td, charges are again accumulated in the two variable capacitors CX1 and CX2. That is, the charge amount Q = − (C + ΔC) Vc is accumulated in the variable capacitor CX1, and the charge amount Q = (C−ΔC) Vc is accumulated in the variable capacitor CX2. The charge amount Q = 2ΔCVc is accumulated in the feedback capacitor Cf of the CV conversion circuit 6 due to the charge movement that occurs at this time. As a result, the output signal Vo of the operational amplifier 20 is Vo = 2ΔCVc / Cf + Vref. At this time, the output side node a of the capacitor Ca in the sampling circuit 7 has a potential difference corresponding to the electric charge Qa stored in the capacitor Ca with respect to the output signal Vo. Therefore, the potential Va of the output side node a is Va. = 4ΔCVc / Cf + Vref. Accordingly, in the fourth section Td, the signal component corresponding to the change ΔC in the capacitances of the variable capacitors CX1 and CX2 included in the potential Va is amplified twice as much as the signal component in the third section Tc. The signal is highly sensitive.

  The control circuit 8 samples the output signal Vo output from the CV conversion circuit 6 in the fourth section Td with the capacitor Ca of the sampling circuit 7, and then closes the switch Sb to thereby output the output signal Vout from the sampling circuit 7. Output. At this time, since the charge accumulation in the capacitor Cb is performed by closing the switch Sb, the output signal Vout becomes a potential corresponding to the charge accumulation amount of the capacitor Cb. Then, by repeating the operation from the first section Ta to the fourth section Td a plurality of times while the electric charge is accumulated in the capacitor Cb, the output signal Vout gradually becomes the output side node a in the fourth section Td described above. The potential Va approaches 4ΔCVc / Cf + Vref. As a result, the output signal Vout finally becomes the average value of the potential Va appearing at the output side node a in the fourth section Td each time the operation of the first section Ta to the fourth section Td is repeated a plurality of times. Will be output as. Such an output signal Vout is a signal in which the offset voltage of the operational amplifier 20 is canceled.

  When the X-axis capacitance sensor 3 is in the measurement mode, the operation from the first section Ta to the fourth section Td as described above is output from the sampling circuit 7 by repeating a plurality of periods (for example, four periods). By reading the output signal Vout with a subsequent circuit, the X-axis acceleration can be calculated. In the above description, the operation when the X-axis capacitance sensor 3 is in the measurement mode has been described. However, even when the Y-axis and Z-axis capacitance sensors 4 and 5 are in the measurement mode, It is the same. However, since the Z-axis capacitance sensor 5 has only one variable capacitor CZ1, the charge Q accumulated in the feedback capacitor Cf in the second section Tb becomes −ΔCVc, and the feedback capacitor in the fourth section Td. The difference is that the charge Q accumulated in Cf becomes ΔCVc.

  Next, an operation of capacitance stabilization processing performed on the Z-axis capacitance sensor 5 when the X-axis and Y-axis capacitance sensors 3 and 4 are in the measurement mode will be described. FIG. 9 shows one cycle Ts of drive voltage applied to the two terminals Z1 and Z2 of the Z-axis capacitance sensor 5 when the X-axis or Y-axis capacitance sensors 3 and 4 are in the measurement mode. FIG. As shown in FIG. 9, one period Ts of the drive voltage is the same as one period Ts of the charge voltage, and the same first period Ta, second period Tb, third period Tc, and fourth period Td as the charge voltage. It consists of. That is, the duty of the drive voltage is equal to the duty of the charge voltage.

  The control circuit 8 sets the drive voltage applied to both ends Z1 and Z2 of the Z-axis capacitance sensor 5 in the first section Ta to the reference voltage Vref. At this time, no charge accumulation occurs in the two capacitors CZ1 and CZ2 in the Z-axis capacitance sensor 5.

  When transitioning from the first section Ta to the second section Tb, the control circuit 8 switches the drive voltage applied to one terminal Z1 of the Z-axis capacitance sensor 5 from the reference voltage Vref to the voltage VH, The charge voltage applied to the terminal Z2 is switched from the reference voltage Vref to the voltage VL. FIG. 10 is a diagram illustrating the charge transfer when transitioning from the first section Ta to the second section Tb. As shown in FIG. 10, when the transition from the first section Ta to the second section Tb is performed, charges are accumulated in the variable capacitor CZ1 and the capacitor CZ2 in the Z-axis capacitance sensor 5, respectively. At this time, it is assumed that acceleration in the Z-axis direction is acting, and the capacitance C of the variable capacitor CZ1 is changed to C + ΔC. In this case, the charge amount Q = (C + ΔC) Vc is stored in the variable capacitor CZ1, and the charge amount Q = −CVc is stored in the fixed capacitor CZ2. The charge amount Q = −ΔCVc is accumulated in the feedback capacitor Cf of the CV conversion circuit 6 due to the charge movement that occurs at this time. As a result, the output signal Vo of the operational amplifier 20 becomes Vo = −ΔCVc / Cf + Vref, and a potential difference −ΔCVc / Cf is generated at both ends of the capacitor Ca of the sampling circuit 7, and a charge Qz corresponding to this potential difference is accumulated in the capacitor Ca. Is done. At this time, since a potential difference is generated between the movable electrode 16 and the fixed electrode 17 of the variable capacitor CZ1, an electrostatic force is generated, and the movable electrode 16 moves toward the fixed electrode 17.

  Next, when transitioning from the second section Tb to the third section Tc, the control circuit 8 switches the drive voltage applied to both ends Z1, Z2 of the Z-axis capacitance sensor 5 to the reference voltage Vref again. FIG. 11 is a diagram illustrating the charge transfer when transitioning from the second section Tb to the third section Tc. When both ends Z1 and Z2 of the capacitance sensor 5 return to the reference voltage Vref again in the third section Tc, charge transfer for setting the charges accumulated in the two capacitors CZ1 and CZ2 to zero occurs in the second section Tb. . That is, as shown in FIG. 11, the charge amount Q of the variable capacitor CZ1 and the fixed capacitor CZ2 is both 0, and the charge amount Q of the feedback capacitor Cf is also 0. As a result, the output signal Vo of the operational amplifier 20 is Vo = Vref. The potential Va = ΔCVc / Cf + Vref obtained by adding the potential (ΔCVc / Cf) corresponding to the electric charge Qz accumulated in the capacitor Ca to the potential of Vo = Vref at the node a on the output side of the capacitor Ca in the sampling circuit 7. appear.

  Next, when transitioning from the third section Tc to the fourth section Td, the control circuit 8 switches the drive voltage applied to one terminal Z1 of the Z-axis capacitance sensor 5 from the reference voltage Vref to the voltage VH again. The charge voltage applied to the other terminal Z2 is switched from the reference voltage Vref to the voltage VL again. At this time, since a potential difference is generated again between the movable electrode 16 and the fixed electrode 17 of the variable capacitor CZ1, an electrostatic force is generated, and the movable electrode 16 moves toward the fixed electrode 17. FIG. 12 is a diagram illustrating the charge transfer when transitioning from the third section Tc to the fourth section Td. As shown in FIG. 12, when the transition is made from the third section Tc to the fourth section Td, charges are accumulated again in each of the variable capacitor CZ1 and the capacitor CZ2. That is, the charge amount Q = (C + ΔC) Vc is accumulated in the variable capacitor CZ1, and the charge amount Q = −CVc is accumulated in the capacitor CZ2 having a fixed capacitance. Then, the feedback capacitor Cf of the CV conversion circuit 6 becomes the charge amount Q = −ΔCVc, and as a result, the output signal Vo of the operational amplifier 20 becomes Vo = −ΔCVc / Cf + Vref again. At this time, the output side node a of the capacitor Ca in the sampling circuit 7 has a potential difference (ΔCVc / Cf) corresponding to the charge Qz stored in the capacitor Ca with respect to the output signal Vo. The potential Va is Va = Vref. That is, in the fourth section Td, the influence of applying the drive voltage shown in FIG. 9 to the Z-axis capacitance sensor 5 is removed.

  Therefore, when the X-axis or Y-axis capacitance sensors 3 and 4 are in the measurement mode, the Z-axis is obtained by closing the switch Sb of the sampling circuit 7 and extracting the output signal Vout in the fourth section Td as described above. It is possible to obtain an output signal Vout in which the influence of the drive voltage applied to the capacitance sensor 5 is canceled. Therefore, without affecting the X-axis or Y-axis measurement result in the measurement mode, the electrostatic capacitance is previously applied to the variable capacitor CZ1 of the Z-axis capacitance sensor 5 in parallel with the X-axis or Y-axis measurement operation. Force can be generated, and when the measurement of the X-axis and the Y-axis is completed, the Z-axis capacitance sensor 5 can be promptly shifted to the measurement mode and the measurement of the Z-axis can be started early. .

  As described above, in the sensor device 1, the control circuit 8 sequentially applies a predetermined charge voltage in time division to each of the XYZ triaxial capacitance sensors 3, 4, 5. One capacitance sensor is selected from the three capacitance sensors 3, 4, and 5, and the mode is sequentially shifted to the measurement mode. The X-axis or Y-axis capacitance sensors 3 and 4 are in the measurement mode. In order to move the movable electrode 16 toward the fixed electrode 17 with respect to the Z-axis capacitance sensor 5, a driving voltage having a pattern different from the charge voltage is applied. Therefore, the capacitance of the variable capacitor CZ1 in the Z-axis capacitance sensor 5 can be stabilized during the measurement of the X-axis or the Y-axis. As a result, when the measurement of the X-axis and the Y-axis is completed, the Z-axis capacitance sensor 5 can be shifted to the measurement mode more quickly than before, so that the time required for the measurement of all three axes can be shortened. . Note that the Z-axis capacity stabilization process is started during the X-axis or Y-axis measurement even if the Z-axis capacity stabilization process is not completed when the X-axis and Y-axis measurements are completed. Therefore, there is no change in that the Z-axis capacitance sensor 5 can be shifted to the measurement mode earlier than in the prior art.

(Modification)
As mentioned above, although several embodiment regarding this invention was described, this invention is not limited to the thing of the content mentioned above, A various modification is applicable. Hereinafter, some modified examples will be described.

  First, FIG. 13 is a diagram illustrating an example of another circuit configuration of the sensor device 1. As shown in FIG. 13, the CV conversion circuit 6 in this circuit configuration includes a fully differential operational amplifier 20a. The output terminal from the sensor unit 2 is connected to the inverting input terminal of the fully differential operational amplifier 20a. A feedback capacitor Cf1 and a switch Sf1 are connected in parallel between the inverting input terminal and the non-inverting output terminal of the fully differential operational amplifier 20a. The switch Sf1 is for discharging the electric charge accumulated in the capacitor Cf1, and is on / off controlled by the control circuit 8 described above. On the other hand, a capacitor 30 is connected to the non-inverting input terminal of the fully differential operational amplifier 20a. The capacitance of the capacitor 30 is designed in advance so as to be equal to the total capacitance of the sensor unit 2 when viewed from the output terminal of the sensor unit 2. A feedback capacitor Cf2 and a switch Sf2 are connected in parallel between the non-inverting input terminal and the inverting output terminal of the fully differential operational amplifier 20a. Capacitor Cf2 has the same capacity as capacitor Cf1. The switch Sf2 is for discharging the electric charge accumulated in the capacitor Cf2, and is turned on / off by the control circuit 8 described above at the same timing as the switch Sf1. The fully differential operational amplifier 20a operates so that the potential Vin of the inverting input terminal is equal to the potential Vip of the non-inverting input terminal. However, these potentials Vip and Vin are reduced by an input common mode feedback circuit (not shown). Control is made to be equal to each other at a predetermined reference voltage Vref. The sampling circuit 7 has the configuration described in the above embodiment provided in each of the non-inverting output terminal and the inverting output terminal of the fully differential operational amplifier 20a.

  Such a CV conversion circuit 6 is configured such that when each capacitance sensor 3, 4, 5 provided in the sensor unit 2 is in the measurement mode, if the acceleration acts and the capacitance of the variable capacitor changes, Charges corresponding to the amount of charge moving due to the capacitance change are accumulated in the feedback capacitors Cf1 and Cf2, and differential output signals Vop and Von corresponding to the capacitance change ΔC are output. Further, such a CV conversion circuit 6 can cancel the disturbance noise by the differential output of the fully differential operational amplifier 20 when charges due to the disturbance noise are injected into each of the sensor unit 2 and the capacitor 30. There is an advantage that you can. The present invention can also be applied to a circuit configuration as shown in FIG. 13, and there is no change in the operational effects described in the above embodiment.

  Secondly, in the above-described embodiment, the case where the sensor device 1 measures acceleration is illustrated, but the measurement target of the sensor device 1 is not necessarily limited to acceleration, for example, it measures angular velocity. It is also possible to measure pressure.

  Thirdly, in the above embodiment, the case where the output correlated double sampling circuit is adopted as the sampling circuit 7 is exemplified, but a sampling circuit having a configuration other than the above may be adopted.

  1: sensor device, 2: sensor unit, 3, 4, 5: capacitance sensor, 6: CV conversion circuit, 7: sampling circuit, 8: control circuit

Claims (3)

A first capacitance sensor in which a pair of fixed electrodes is provided with a movable electrode movable in the first axial direction, and two variable capacitors are connected in series by each fixed electrode and the movable electrode. When,
A pair of fixed electrodes is disposed with a movable electrode movable in a second axial direction orthogonal to the first axial direction, and two variable capacitance capacitors connected in series by each fixed electrode and movable electrode constitute A second capacitance sensor to be
A variable capacitor constituted by a movable electrode movable in a third axial direction orthogonal to the first and second axial directions, and a fixed electrode disposed opposite to the movable electrode, and a pair of fixed electrodes A third capacitance sensor configured by connecting in series a capacitance invariant capacitor,
The first to third capacitance sensors are sequentially applied to the fixed electrodes at both ends of each of the first to third capacitance sensors in a time-division manner. A control circuit for selecting one of the capacitance sensors and sequentially shifting to the measurement mode;
With
When the first or second capacitance sensor is in the measurement mode, the control circuit drives the fixed electrodes at both ends of the third capacitance sensor in opposite phases different from the charge voltage. A sensor device characterized by stabilizing a change in capacitance due to an electrostatic force of a variable capacitor in the third capacitance sensor by applying a voltage.   The control circuit has a constant period and a constant voltage width around a predetermined reference voltage with respect to the fixed electrodes at both ends of the capacitance sensor in the measurement mode among the first to third capacitance sensors. When a charge voltage whose polarity is reversed is applied and the first or second capacitance sensor is in the measurement mode, the charge voltage is applied to the fixed electrodes at both ends of the third capacitance sensor. 2. The sensor device according to claim 1, wherein a driving voltage having the same cycle and oscillating with a constant voltage width in the same polarity direction from the reference voltage is applied. A CV conversion circuit that outputs a signal corresponding to a capacitance change of a variable capacitor in each of the first to third capacitance sensors;
A sampling circuit that samples and outputs a signal output of the CV conversion circuit at a predetermined timing when each of the first to third capacitance sensors is in a measurement mode;
Further comprising
The sampling circuit reverses the polarity of the charge voltage applied to the fixed electrodes at both ends of the first or second capacitance sensor when the first or second capacitance sensor is in a measurement mode. 3. After that, by sampling and outputting the signal output of the CV conversion circuit, charge movement from the third capacitance sensor due to the drive voltage is canceled and output. The described sensor device.

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