JP6545611B2 - Inertial detection device - Google Patents

Description

  The present invention relates to inertial detection technology.

  An inertial sensor (hereinafter sometimes referred to as an inertial detection device) is a sensor that detects a physical quantity such as the acceleration or angular velocity of an object. The inertial sensor can observe the state of the object such as the pressure applied to the substance, the fluctuation of the angular velocity, and the tilt angle. Inertial sensors are used in various applications such as control of vehicles such as cars, attitude control and attitude detection of unmanned airplanes and remote control robots, observation of sound waves and seismic waves, acquisition of maintenance information of old infrastructure, provision of smart phones, etc. It is used.

  There is a capacitive detection type as a detection principle of the inertial sensor. In the capacitive detection type, a physical quantity is detected based on a change in capacitance between electrodes constituting an inertial body of a sensor element. Applications of the capacitive detection type inertial sensor are expanding because the MEMS structure can be realized as a MEMS sensor in a small size and at low cost. The sensor element has a manufacturing advantage because a substance such as silicon is used and the affinity with the detection circuit is high.

  As a method for improving detection accuracy in an inertial sensor, there is a method in which an inertial body of a sensor element is servo-controlled. This servo control is control for applying a servo force to the inertial body in order to control this displacement when the inertial body is displaced in the inertial coordinate system with a change in physical quantity. In other words, this servo control is control for applying a servo voltage from the circuit unit to the inertial body to apply a servo force to bring the inertial body into a suitable vibration state.

  Japanese Patent No. 3804242 (Patent Document 1) is given as a prior art example of a capacitive detection type and servo control type inertial sensor. Patent Document 1 describes that a physical quantity detection device includes a signal processing circuit that outputs a feedback voltage, a carrier wave signal generation unit, and the like.

Patent No. 3804242

  A system including an inertial sensor is required to reduce the operating voltage in order to realize low power consumption and the like. For example, in the case of a power supply voltage of an inertial sensor for automobiles, it has been lowered to 12V, 5V and 3.3V. In systems where electrostatic force is used to generate force, the electrostatic force that can be generated is proportional to the square of the applied voltage. In the above system, when the operating voltage for driving the inertial body is small, for example, when the operating voltage is reduced as compared with the conventional case, the servo force that can be generated based on the operating voltage is reduced. If the servo force decreases, the detection accuracy decreases. Therefore, in the above system, it is important to efficiently generate the necessary force using a limited operating voltage.

  The detection accuracy depends on the magnitude of displacement of the inertial body, but the servo voltage and servo force of servo control are required according to the magnitude of the displacement. The servo voltage is generated using the power supply voltage of the system, but when the power supply voltage is low, the servo voltage that can be generated is low and the servo force is small. As a result, the signal-to-noise ratio (S / N) decreases, the dynamic range narrows, and it is difficult to improve the detection accuracy. In order to generate a high servo voltage using a low power supply voltage, it is necessary to provide a high voltage generation circuit or the like. However, the high voltage generation circuit has a large element size and power consumption. Therefore, a system including the inertial sensor has a large circuit area and power consumption, is expensive, and is difficult to apply to an application requiring small size and low power consumption.

  An object of the present invention is to provide a technology capable of efficiently generating a servo force even with a low power supply voltage and realizing improvement in detection accuracy and suppression of deterioration with respect to an inertial sensor of a capacitance detection type and a servo control system. is there.

  A representative embodiment of the present invention is an inertial detection device characterized by having the following configuration. An inertial detection device according to one embodiment includes a sensor element including an inertial body, a first electrode provided on the inertial body, and a second electrode having a pair of the first electrode and a second electrode. A second signal having a frequency peak overlapping the first frequency peak of the first frequency in the first signal input to the first electrode is input to the second electrode to servo-control the inertial body .

  According to a representative embodiment of the present invention, servo force can be efficiently generated even with a low power supply voltage for capacitive sensors and servo control inertial sensors, and detection accuracy is improved and deterioration is suppressed. realizable.

It is a figure which shows the structure of the inertial detection apparatus of Embodiment 1 of this invention. In Embodiment 1, it is a figure which shows the capacity | capacitance regarding the sense mass of a sensor element, the structure of an electrode, and schematic structure of a circuit. FIG. 7 is a diagram showing a servo force at displacement of a sense mass in the first embodiment. FIG. 6 is a diagram showing a carrier wave, servo control signals before and after modulation, and servo force in the first embodiment. It is a figure shown about improvement of a signal noise ratio by Embodiment 1 and a comparative example. FIG. 2 is a diagram showing a configuration of a mounting module in the first embodiment. FIG. 7 is a diagram showing a spectrum of a waveform in the first embodiment. It is a figure which shows the servo force with respect to an operating voltage by Embodiment 1 and a comparative example. FIG. 10 is a diagram showing a servo force with respect to an operating voltage in the case of using a voltage higher than the power supply voltage in the first embodiment and the comparative example. It is a figure which shows each signal and servo force in the example in the case of using a voltage higher than a power supply voltage, and in the case of waveform rounding in Embodiment 1 and a comparative example. It is a figure which shows each signal and servo force in the example in the case of using the voltage higher than a power supply voltage, and when there is no waveform rounding off by Embodiment 1 and a comparative example. FIG. 7 is a diagram of phase delay in the modulation circuit in the first embodiment. FIG. 7 is a diagram for the case where there is a waveform rounding in the first embodiment. FIG. 2 is a diagram showing a configuration of a sensor element and a circuit unit in the first embodiment. FIG. 2 is a diagram showing a configuration of an analog circuit of a circuit portion in Embodiment 1; FIG. 7 is a diagram showing a configuration of a modulation circuit on the Coriolis detection side of the circuit unit in the first embodiment. FIG. 7 is a diagram showing a configuration of a modulation circuit on a drive side of a circuit portion in the first embodiment. FIG. 7 is a diagram showing a configuration of a DAC on the Coriolis detection side of the circuit unit in the first embodiment. FIG. 8 is a diagram showing an example of a MEMS mounting structure of a sensor element in the first embodiment. It is a figure which shows the structure of a sensor element and a circuit part in the inertia detection apparatus of Embodiment 2 of this invention. FIG. 16 is a diagram showing a spectrum of a waveform in a second embodiment. FIG. 16 is a diagram illustrating an example of a MEMS mounting structure of a sensor element in a second embodiment. It is a figure which shows the structure of a sensor element and a circuit part in the inertia detection apparatus of Embodiment 3 of this invention. In Embodiment 3, it is a figure which shows the example of a MEMS mounting structure of a sensor element. It is a figure which shows the structure of the inertial sensor of a comparative example. It is a figure which shows the waveform and servo force regarding servo control in a comparative example.

  Hereinafter, embodiments of the present invention will be described in detail based on the drawings. Note that, in all the drawings for describing the embodiment, the same reference numeral is attached to the same part in principle, and the repeated description thereof will be omitted.

[Comparative example]
We will supplement the aforementioned issues. Servo control and the like of the inertial sensor of the comparative example with respect to the first embodiment will be described with reference to FIGS. The inertial sensor of the comparative example is an angular velocity sensor of a capacitance detection type and a single axis servo control type.

  FIG. 25 shows a functional block configuration of an inertial sensor of a comparative example. The inertial sensor is provided with a sensor element SE and a circuit unit at a base portion. The sensor element SE has a frame FR and a sense mass SM as an inertial body. The frame FR and the sense mass SM are provided with capacities for servo control and detection. The capacitance is constituted by an electrode pair. The frame FR can be displaced (referred to as x) in the first axial direction (referred to as the X direction). The sense mass SM can be displaced (referred to as y) in the second axial direction (referred to as the Y direction) with respect to the frame FR. The X direction and the Y direction are orthogonal to each other. The inertial sensor measures the angular velocity by measuring the displacement y of the sense mass SM in the circuit unit. The servo control used in this inertial sensor consists of two controls. The first control is control for holding the motion of the frame FR in a constant vibration state. The second control is control for holding the sense mass SM in the initial position.

  The circuit unit includes a first circuit unit that performs servo control and detection on the frame FR, a second circuit unit that performs servo control and detection on the sense mass SM, and a carrier wave generation circuit 250 that applies the carrier wave C0 to the frame FR and the sense mass SM. including. The first circuit unit includes a first high voltage generation circuit 251. The first high voltage generation circuit 251 generates and outputs a first voltage V1 by boosting from the power supply voltage V0 based on the input of the power supply voltage V0. V1> V0. The power supply voltage V0 is supplied from a system in which the inertial sensor is mounted. The second circuit unit includes a second high voltage generation circuit 252. The second high voltage generation circuit 252 generates and outputs the second voltage V2 by boosting based on the input of the power supply voltage V0. V2> V0.

  In this inertial sensor, a carrier C0 is applied to the sensor element SE in order to detect a change in capacitance of the sensor element SE. Carrier wave C0 is used for capacitive voltage conversion. Carrier wave generation circuit 250 generates carrier wave C0 based on power supply voltage V0, and applies the same to frame FR and sense mass SM.

  In the motion control of the frame FR, the displacement x of the frame FR is detected as a detection voltage Vsx from the capacitance Csx which is a detection capacitance by the first circuit unit. The analog circuit in the first circuit unit obtains the detection voltage Vsx based on capacitance-voltage conversion from the capacitance value of the capacitance Csx. The control circuit generates a signal for controlling the vibration state of the frame FR based on the detected voltage Vsx, and outputs the signal to a DAC (digital-to-analog converter). The DAC generates an analog voltage for servo control based on the signal and applies it as a servo voltage Vfx of a servo control signal to a capacity Cfx which is a servo capacity. At this time, the DAC generates a servo voltage Vfx based on the first voltage V1.

  In the motion control of the sense mass SM, the displacement y of the sense mass SM is detected as the detection voltage Vsy from the capacitance Csy which is the detection capacitance by the second circuit unit. The analog circuit in the second circuit unit differentially detects the capacitance value of the capacitor Csy as a detection voltage Vsy by capacitance-voltage conversion. The control circuit generates a signal for controlling the state of the sense mass SM based on the detected voltage Vsy, and outputs the signal to the DAC. The DAC generates an analog voltage for servo control based on a signal from the control circuit, and applies it as a servo voltage Vfy of a servo control signal to a capacity Cfy which is a servo capacity. At this time, the DAC generates the servo voltage Vfy based on the second voltage V2.

  FIG. 26 shows waveforms and servo forces of respective signals in the comparative example of FIG. (A) of FIG. 26 shows the voltage Vcom of the carrier wave C0. In addition, this waveform shows the state which approached the triangular wave by waveform rounding based on a square wave. A method of applying a carrier wave by an inertial sensor is known in the art. FIG. 26B shows the servo voltage Vfy of the servo control signal for the sense mass SM, which corresponds to the output signal of the DAC in the second circuit unit. There is a phase inversion relationship between the positive voltage Vfyp and the negative voltage Vfyn in the servo voltage Vfy. (C) of FIG. 26 shows the servo force Fs on the sense mass SM. The dashed line shows the effective servo force. As a result of applying both the voltage Vcom of (a) and the servo voltage Vfy of (b) to the sense mass SM, a servo force Fs such as (c) is generated.

  The displacement y of the sense mass SM is described as y = 2 mvΩ, where the magnitude of the angular velocity is Ω, the velocity of the frame FR is v, and the mass of the sense mass SM is m. By increasing the velocity v, the output can be increased for an angular velocity input of the same size. In order to increase the velocity v, it is necessary to increase the displacement x of the frame FR. However, when the power supply voltage V0 of the system is low, for example, reduced compared to the prior art, the force that can be generated is reduced. Therefore, the speed x can not but be reduced.

  Therefore, in the comparative example, the first high voltage generation circuit 251 is used for the first circuit portion including the DAC that generates the servo voltage Vfx to be applied to the frame FR. The first high voltage generation circuit 251 generates a first voltage V1 which is higher than the low power supply voltage V0, and generates a servo voltage Vfx by using the first voltage V1. As a result, the displacement x of the frame FR can be increased, and accordingly, the displacement y of the sense mass SM can be increased, whereby the detection accuracy can be improved.

  However, when the displacement y of the sense mass SM increases, the force required for servo control to suppress the displacement y and approach the stationary state also increases. That is, a high voltage is also required for the servo voltage Vfy to be applied from the DAC of the second circuit unit to the capacitance Cfy. For this reason, in the comparative example, it is necessary to use the second high voltage generation circuit 252 in the second circuit section in order to increase the servo voltage Vfy more than the conventional one. The second high voltage generation circuit 252 generates a second voltage V2 which is a voltage higher than the low power supply voltage V0, and generates a servo voltage Vfy by the DAC using the second voltage V2.

  Therefore, in the comparative example, the provision of the first high voltage generation circuit 251 and the second high voltage generation circuit 252 is required as the two systems of high voltage generation circuits. The high voltage generation circuit includes a booster circuit. The size of an element such as a transistor that constitutes the booster circuit is large. Therefore, a large circuit area is required to mount each high voltage generation circuit. As a result, the inertial sensor of the comparative example and the system thereof increase the circuit area and the power consumption.

  When the servo voltage Vfy is generated using the low power supply voltage V0 without using the second high voltage generation circuit 252, the servo force is insufficient. As a result, the control loop does not form a complete closed loop, and signal component leakage occurs. As a result, the signal-to-noise ratio (S / N) or the dynamic range is degraded, leading to a decrease in detection accuracy.

Embodiment 1
The inertial detection system according to the first embodiment of the present invention will be described with reference to FIGS. The inertia detection device according to the first embodiment is an angular velocity sensor of a capacitance detection type and a single axis servo control type.

[(1-1) Inertial sensor_functional block]
FIG. 1 shows a functional block configuration of the inertial detection system of the first embodiment. The inertial detection device according to the first embodiment of FIG. 1 is different from the configuration of the comparative example of FIG. 25 in that it has modulation circuit 13 and second circuit unit 12 has a second high voltage generation circuit. There is no point. In the first embodiment, the method of using carrier wave C0 is different, and the waveform of servo voltage Vfy of the servo control signal applied to sensor element 2 is different.

  The inertial detection device according to the first embodiment roughly includes, as components, a base portion 1, a sensor element 2, and a circuit portion. The base unit 1 is provided with a sensor element 2 and a circuit unit. The sensor element 2 has a frame 3 and a sense mass 4 as an inertial body. Frame 3 is the first square, and sense square 4 is the second square. The frame 3 is connected to the base 1 via a spring or the like, and displacement x is possible in the X direction which is the first axial direction. The sense mass 4 is connected to the frame 3 via a spring or the like, and displacement y is possible in the Y direction which is the second axial direction with respect to the frame 3.

  It has a frame 3 and a sense mass 4 in order to detect the displacement x in the X direction and the displacement y in the Y direction in the inertial body. The frame 3 and the sense mass 4 are respectively provided with servo capacitance and detection capacitance as capacitance. Their capacity is constituted by electrode pairs. The electrode pair is connected to the circuit unit. As a single-axis servo control method, servo control regarding displacement y in the Y direction is performed on the sense mass 4 of the sensor element 2. The angular velocity sensor detects the angular velocity using the Coriolis force applied to the vibrating inertial body. In the capacitive type, a change in capacitance between the electrodes due to the displacement of the inertial body is detected. The frame 3 is a drive side corresponding to the displacement x in the first axial direction (X direction), and the sense mass 4 is a Coriolis detection side corresponding to the displacement y in the second axial direction (Y direction).

  In the inertial detection system according to the first embodiment, when an angular velocity is applied to the sensor element 2 in a state in which the frame 3 is maintained in a constant vibration state in the X direction, the sense mass 4 is Y in the same plane as the vibration of the frame 3. The direction is displaced relative to the frame 3. The inertial sensor measures the angular velocity by measuring the displacement y of the sense mass 4 in the circuit unit. The servo control used in this inertial sensor consists of two controls. The first control is control for holding the motion of the frame 3 in a constant vibration state. In the first control, as a control target of the displacement x, a predetermined vibration frequency and vibration amplitude are set. The second control is control for holding the sense mass 4 in the initial position. The initial position is the relative position of the sense mass 4 to the frame 3 when the angular velocity is zero. The second control is a stationary state at the initial position as a control target of the displacement y.

  The circuit unit includes a carrier wave generating circuit 10, a first circuit unit 11, a second circuit unit 12, and a modulation circuit 13. The power supply voltage V0 of the system on which the inertial sensor is mounted is input to the circuit unit.

  Carrier wave generation circuit 10 generates carrier wave C0 based on power supply voltage V0, and applies carrier wave C0 to frame 3 and sense mass 4 of sensor element 2 in common. The first circuit unit 11 performs servo control and detection on the frame 3. The second circuit unit 12 performs servo control and detection on the sense mass SM. Carrier wave generation circuit 10 generates carrier wave C 0 in accordance with carrier wave control signal Sc from control circuit 52.

  The first circuit unit 11 includes an analog circuit 41, a control circuit 51, a DAC 31, and a first high voltage generation circuit 21. The first high voltage generation circuit 21 receives the power supply voltage V0, generates a first voltage V1 by boosting, and outputs the first voltage V1. V1> V0.

  The frame 3 and the sense mass 4 are provided with capacities for servo control and detection. The frame 3 has a capacity Cfx, which is a servo capacity for servo control, and a capacity Csx, which is a detection capacity for detection. These capacitors are connected to the first circuit unit 11. An electrode constituting the capacitor Csx is connected to the analog circuit 41. An electrode forming the capacitor Cfx is connected to the DAC 31.

  The sense mass 4 has a positive side capacitance Cfyp and a negative side capacitance Cfyn as a capacitance Cfy which is a servo capacitance for servo control, and a positive side capacitance Csyp as a capacitance Csy which is a detection capacitance for detection. And a negative side capacitance Csyn. These four capacitors are connected to the second circuit unit 12. The electrodes constituting the capacitance Csy {Csyp, Csyn} are connected to the analog circuit 42. The electrodes constituting the capacitors Cfy {Cfyp, Cfyn} are connected to the modulator 132 of the modulation circuit 13.

  In the motion control of the frame 3, the displacement x of the frame 3 is detected by the first circuit unit 11 as a detection voltage Vsx from the capacitance Csx which is a detection capacitance. The analog circuit 41 detects the detection voltage Vsx from the capacitance value of the capacitance Csx based on capacitance voltage conversion. The detected voltage Vsx represents a displacement x.

  The control circuit 51 generates a digital signal for controlling the vibration state of the frame 3 based on the detection voltage Vsx, and outputs the digital signal to the DAC 31. The DAC 31 generates an analog voltage for servo control based on the digital signal, and outputs it as a servo voltage Vfx of the servo control signal. At this time, the DAC 31 generates the servo voltage Vfx based on the first voltage V1. The servo voltage Vfx is applied to an electrode of a capacity Cfx which is a servo capacity.

  The second circuit unit 12 includes an analog circuit 42, a control circuit 52, a DAC 32, and a logic circuit 53. In the motion control of the sense mass 4, the displacement y of the sense mass 4 is detected by the second circuit unit 12 from the capacitances Csy {Csyp, Csyn} which are detection capacitances. The analog circuit 42 differentially detects the capacitance value of the capacitor Csy as a detection voltage Vsy {Vsyp, Vsyn} by capacitance-voltage conversion. The detection voltage Vsy represents a displacement y.

  The control circuit 52 generates a signal SV for controlling the state of the sense mass 4 based on the detection voltage Vsy, and outputs the signal SV to the DAC 32. The signal SV is a signal for controlling the DAC 32 for servo control. The DAC 32 includes a positive DAC and a negative DAC. The DAC 32 generates an analog voltage for servo control based on the signal SV from the control circuit 52. At this time, the DAC 32 generates the analog voltage based on the power supply voltage V0, and outputs the analog voltage to the modulation circuit 13 as the output signal DA {DAp, DAn}. The output signals DA {DAp, DAn} are, in other words, servo control signals before modulation.

  The modulation circuit 13 is a circuit that generates a servo control signal unique to the first embodiment. The modulation circuit 13 includes an inverter, a delay unit 131, and a modulator 132. The modulation circuit 13 receives the carrier wave C0 from the carrier wave generation circuit 10, inverts the phase of the voltage Vcom of the carrier wave C0 with an inverter, and inputs the signal to the delay device 131. The delay 132 is a circuit that provides an appropriate delay to the carrier C0 for appropriate modulation. The delay unit 131 appropriately delays the inverted signal of the carrier wave C0 based on the delay control signal Sd from the control circuit 52, and outputs the delayed signal as the carrier wave delayed signal Vd. Appropriate delays will be discussed later. The carrier delay signal Vd is input to the modulator 132.

  The modulation circuit 13 receives the output signal DA {DAp, DAn} from the DAC 32, and modulates the analog voltage of the output signal DA {DAp, DAn} using the carrier C0. At this time, the modulator 132 modulates the analog voltage of the output signal DA {DAp, DAn} with the carrier delay signal Vd. Modulator 132 includes a positive modulator and a negative modulator. The modulator 132 outputs the signal of the analog voltage after modulation as the servo voltage Vfy {Vfyp, Vfyn} of the servo control signal. The servo voltage Vfy is applied to an electrode constituting a capacitance Cfy which is a servo capacitance of the sense mass 4. The positive side output signal DAp is modulated by the positive side modulator, output as the positive side servo voltage Vfyp, and applied to the electrode of the positive side capacitor Cfyp. The negative side output signal DAn is modulated by the negative side modulator, outputted as the negative side servo voltage Vfyn, and applied to the electrode of the negative side capacitance Cfyn.

  The control circuit 52 outputs a signal OP1 based on the detection voltage Vsy in the analog circuit 42 to the logic circuit 53. The logic circuit 53 is a circuit that performs predetermined logic processing, performs processing including calculation of angular velocity based on the signal OP1, and outputs an output signal OP2 including angular velocity detection information as a result to the outside. The angular velocity output is expressed as the magnitude of the servo force applied by the control of the sense mass 4. The logic circuit 53 is, in other words, an angular velocity output unit.

  The modulation circuit 13 has a function of monitoring the carrier wave C0 and the servo voltage Vfy. Using this function, the waveform of each signal can be confirmed, whereby the waveform of each signal can be adjusted. The delay unit 131 has its delay amount controlled in accordance with the delay control signal Sd from the control circuit 52. The delay amount is variable depending on the setting for the control circuit 52. The control circuit 52 may have a function of realizing user setting including setting of the delay amount.

[(1-2) Configuration of capacitance and electrode of sensor element, circuit configuration]
FIG. 2 shows the capacitance of the sense mass 4 of the sensor element 2, the configuration of the electrodes, and the schematic configuration of the circuit for detection of the displacement y of the sense mass 4 and servo control. The sense mass 4 is an electrode on the Coriolis detection side, and is a first electrode to which the carrier wave C0 is applied. In the sense mass 4, as the four capacitances, capacitances Cfy {Cfyp, Cfyn}, which are servo capacitances, and capacitances Csy {Csyp, Csyn}, which are detection capacitances, are provided.

  The capacitance Cfy is composed of a positive capacitance Cfyp and a negative capacitance Cfyn. The positive side capacitance Cfyp is constituted by an electrode pair, one of the electrodes is the sense mass 4 which is the first electrode, and the other electrode is the electrode Dfyp which is the second electrode. The electrode Dfyp is a positive servo electrode. Similarly, the negative side capacitance Cfyn is configured as an electrode pair by the sense mass 4 which is the first electrode and the electrode Dfyn which is the second electrode. The electrode Dfyn is a negative servo electrode. The positive voltage Vfyp is applied to the positive electrode Dfyp, and the negative voltage Vfyn is applied to the negative electrode Dfyn.

  The capacitance Csy consists of a positive capacitance Csyp and a negative capacitance Csyn. The positive side capacitance Csyp is constituted by an electrode pair, one of which is the sense mass 4 which is the first electrode, and the other one of which is the electrode Dsyp which is the third electrode. The electrode Dsyp is a positive side detection electrode. Similarly, the negative side capacitance Csyn is configured as an electrode pair by the sense mass 4 which is the first electrode and the electrode Dsyn which is the third electrode. The electrode Dsyn is a negative side detection electrode. The positive voltage Vsyp is detected from the positive electrode Dsyp, and the negative voltage Vsyn is detected from the negative electrode Dsyn.

  The sense mass 4 which is the first electrode is connected to the carrier generation circuit 10 which is the first circuit through the frame 3. A carrier wave C0 is applied to the sense mass 4 as a first signal. Electrodes Dfy {Dfyp, Dfyn}, which are the second electrodes, are connected to the modulation circuit 13. A third electrode Dsy {Dsyp, Dsyn} is connected to the analog circuit 42. As a detection circuit which is a third circuit, the analog circuit 42 detects the detection voltage Vsy from the third electrode as a detection signal which is a third signal. The control circuit 52 outputs a signal OP1 based on the detection signal. The third signal is a signal having a frequency according to the vibration and displacement y of the sense mass 4.

  As a servo control circuit which is a second circuit, the control circuit 52 generates a signal SV for servo control from a detection signal of the detection voltage Vsy, and outputs the signal SV to the DAC 32. The DAC 32 generates an analog voltage for servo control from the signal SV based on the power supply voltage V0 and outputs it as an output signal DA. The modulation circuit 13 modulates the output signal DA with the carrier wave C0 and outputs it as the servo voltage Vfy of the modulated servo control signal. The servo voltage Vfy is applied as a second signal to the electrodes Dfy {Dfyp, Dfyn} which is the second electrode.

  The servo force Fs generated by the above servo control is applied to the displacement y in the Y direction of the sense mass 4 to maintain the sense mass 4 at the initial position. The voltage Vcom of the carrier wave 0, which is a first signal to the first electrode, is a signal having a first frequency peak, which will be described later. On the other hand, the servo voltage Vfy which is a second signal to the second electrode is a signal having a frequency peak overlapping with the first frequency peak of the first signal.

[(1-3) Displacement, servo force]
FIG. 3 shows the state of displacement y in the Y direction and the servo force Fs acting at that time when an inertial force is applied to the sense mass 4 of FIG. FIG. 3A shows the servo force Fs in the state of being displaced to the positive side (up in FIG. 3) as the displacement y of the sense mass 4. This servo force is a force in the direction (lower in FIG. 3) in which it tries to return the sense mass 4 to the initial position of displacement y (indicated by a broken line). An alternate long and short dash line indicates the center position of the sense mass 4. FIG. 3B shows the servo force in the state of being displaced to the negative side (downward in FIG. 3) as the displacement y of the sense mass 4. This servo force is a force in a direction (upward in FIG. 3) to return the sense mass 4 to the initial position.

On the servo control side, Vp = (Vfyp−Vcom) if the voltage across the positive side capacitor Cfyp is Vp, and Vn = (Vfyn−Vcom) if the voltage across the negative side capacitor Cfyn is Vn . The servo force Fs is proportional to (Vp ² −Vn ² ). That is described in Fsα ^{(Vp 2} -Vn 2).

[(1-4) Carrier wave, servo control signal, servo force]
FIG. 4 shows each signal and servo force related to servo control in the first embodiment. (A) of FIG. 4 shows the voltage Vcom of the carrier wave C0. Note that FIG. 4 shows a state where there is a waveform rounding. The waveform at the time of generation of the carrier wave C0 is a rectangular wave, but in general, the actual waveform approaches a triangular wave as illustrated because of the influence of the waveform becoming dull in circuit propagation. The oscillation frequency Fcom of the carrier C0 has to be set to at least twice the frequency of frame 3. In a conventional angular velocity sensor, this vibration frequency is set to a frequency sufficiently larger than the frequency of the frame. In the first embodiment, the vibration frequency Fcom is set to a frequency eight times the frequency of the frame 3.

  In the voltage Vcom of the carrier wave C0, the potential at the low level is the ground potential Vgnd, and the potential at the high level is the power supply voltage potential Vdd. Power supply voltage potential Vdd is a potential corresponding to the maximum voltage level of power supply voltage V0. The amplitude Vpp of the voltage Vcom is (Vdd-Vgnd).

  The voltage value of the output of the capacitance voltage conversion circuit in the analog circuit 42 is CVout, the capacitance fluctuation is ΔC, and the capacitance for determining the gain of the capacitance voltage conversion circuit is Cg. In that case, CVout = Vpp × ΔC / Cg is described. CVout is proportional to the amplitude Vpp of the carrier C0. Therefore, as for the amplitude Vpp, it is desirable to use all of the power supply voltage V0, that is, the maximum amplitude and voltage level. Therefore, in the first embodiment, the amplitude Vpp of the carrier wave C0 is defined using the maximum voltage level of the power supply voltage V0. Carrier wave generation circuit 10 generates carrier wave C0 having amplitude Vpp corresponding to the maximum voltage level of power supply voltage V0. As a modification, it is also possible to use other than the maximum voltage level of the power supply voltage V0 as the amplitude Vpp of the carrier wave C0.

  (B) of FIG. 4 shows a voltage waveform of an output signal DA {DAp, DAn} of the DAC 32, which is a servo control signal before modulation. This voltage waveform is a signal having a frequency corresponding to the vibration state of frame 3 based on the detection voltage Vsx. The output signal DA has a phase inversion relationship between the positive side output signal DAp and the negative side output signal DAn. Here, p represents the positive side and n represents the negative side.

  The output signal DA is as follows. The displacement y of the sense mass 4 is detected in the analog circuit 42 through the electrode Dsy of the capacitance Csy. The analog circuit 42 detects a capacitance value corresponding to the displacement y as a voltage value by performing capacitance-voltage conversion from the voltage Vsy {Vsyp, Vsyn}. The control circuit 52 appropriately controls the gain, the delay, and the phase based on the detection signal of the analog circuit 42 in order to control the displacement y to be zero. The control circuit 52 outputs a signal SV under the control to the DAC 32. The DAC 32 uses an analog voltage generated by DA conversion from the signal SV as an output signal DA. The DAC 32 appropriately controls the output signal DA by inverting the phase on the positive side and the negative side. In the waveform of the output signal DA, a sine wave is assumed as a physical quantity input of the sensor element 2. In the case of the first embodiment, both the error component and the angular velocity component are modulated at the same frequency as the vibration of the frame 3. Therefore, the frequency and amplitude of this sine wave reflect the vibration state of frame 3.

  FIG. 4C shows the waveform of the servo voltage Vfy of the servo control signal after modulation. The servo voltages Vfy {Vfyp, Vfyn} are voltages obtained by modulating the analog voltage which is the output signals DA {DAp, DAn} by the modulation circuit 13 with the carrier delay signal Vd. The servo voltage Vfy is a signal having modulation of the carrier wave C0. In this modulation, when the value of the voltage Vcom is High (for example, time t1), an output (for example, about 0.5) corresponding to the value (for example, about 0.75) of the DC component of the output signal DA is obtained. Do. Further, in this modulation, when the value of the voltage Vcom is low (for example, time t2), the output {Vfyp, Vfyn} is obtained by inverting the phase of the DC component of the output signal DA in the positive and negative directions. The voltage Vfyp on the positive side and the voltage Vfyn on the negative side have respective DC levels symmetrical with respect to the DC component of the output signal, and have a phase inversion relationship. As described above, it is important that the modulation circuit 13 modulates the servo control signal using the carrier wave C0. Detailed characteristics of the servo voltage Vfy will be described later.

  (D) of FIG. 4 shows the servo force Fs generated based on the servo voltage Vfy of (c) of FIG. 4 as an effective servo force. The maximum servo force that can be generated when the maximum servo voltage that can be generated is common to the first embodiment and the comparative example will be described in comparison. First, as shown in FIG. 26C, in the comparative example, the frequency (f1) of the voltage Vcom of the carrier wave C0 remains in the servo force Fs. Therefore, in the comparative example, the effective servo force that can be generated is relatively small.

  On the other hand, in the first embodiment, the voltage Vcom of the carrier wave C0 is used to modulate the analog voltage of the output signal DA of the DAC 32, as shown in (d) of FIG. Therefore, the vibration component of the voltage Vcom can be removed by taking the difference from the voltage Vcom. As a result, in the first embodiment, only the sine wave component which is originally required remains in the servo force Fs of (d) of FIG. 4, and as a result, the effective servo force of the maximum efficiency can be generated. The servo force Fs is larger than the servo force Fs of the comparative example.

  When the maximum servo force can be generated as in the first embodiment, it is not necessary to use a high voltage power supply or a high voltage generation circuit as a servo voltage generation means. That is, in the first embodiment, a high voltage is unnecessary as the power supply voltage V0, and a relatively low voltage is applicable. Further, the second high voltage generation circuit 252 for generating a high voltage from a low voltage as the power supply voltage V0 is unnecessary. Alternatively, even in the case of using a high voltage power supply, the same effect can be obtained at a lower voltage than in the prior art. That is, in the first embodiment, highly efficient servo control is possible. Thus, in the first embodiment, the circuit area for mounting can be reduced, and low power consumption can be realized. Further, in the first embodiment, an S / N and a dynamic range can be secured, and an inexpensive system can be realized without sacrificing detection accuracy.

[(1-5) Improvement of signal noise ratio]
The improvement of the S / N in the first embodiment with respect to the comparative example will be described with reference to FIG. FIG. 5A shows the S / N in the first embodiment, and FIG. 5B shows the S / N in the comparative example. (A) shows the input physical quantity displacement, (b) shows the servo control displacement, (c) shows the resolution, and (d) shows the detection circuit. As in (a), it is assumed that the input physical quantity displacement is the same 100 in both Embodiment 1 and the comparative example. As in (b), in the first embodiment, as a result of obtaining the maximum servo force, it is assumed that the amplitude can be suppressed to 20 and in the comparative example, it can be suppressed to only 60. Under this assumption, the maximum input range is set so that the servo control displacement of the comparative example can be completely resolved. In that case, if the gradation of the analog circuit is 16 bits, as shown in (c), the resolution becomes 60/2 ^16. In this case, as shown in (d), in the comparative example, in the case of the signal of the displacement of the input physical quantity of (a) or more, the detection circuit is saturated. On the other hand, in the first embodiment, the detection circuit is not saturated even if the signal is more than that, and the input physical quantity can be increased up to three times as much.

  For this reason, the S / N when the thermal noise of the circuit is assumed to be 10 LSB is 30 in the first embodiment and 10 in the comparative example. Therefore, the adoption of the first embodiment can improve the S / N by three times over the comparative example. The above S / N is just an example, and since the magnitude of the servo force can be designed according to the MEMS structure of the sensor element, there is a possibility that the S / N can be improved by three times or more. Under the present circumstances, although the modulation circuit 13 is required as an excellent point of Embodiment 1, there exists a point which can make the voltage used for servo control not be the same as the voltage of a conventional system.

[(1-6) Module]
FIG. 6 shows chip arrangement, wiring, and the like as the configuration of the module 100 mounted in the inertial detection system of the first embodiment of FIG. This module 100 is a MEMS angular velocity sensor module. FIG. 6A shows the configuration of the main surface of the module 100, and FIG. 6B shows the configuration of the side surface. The main surface corresponds to a plane having an X direction and a Y direction. The module 100 includes a circuit chip 101 and a sensor chip 102. The sensor chip 102 is stacked on the circuit chip 101. The circuit chip 101 corresponds to the base unit 1 of FIG. 1, and the circuit unit is mounted by LSI or the like. The sensor element 2 of FIG. 1 is mounted on the sensor chip 102 by MEMS. The circuit chip 101 and the sensor chip 102 are electrically connected by wire bonds 104 to the bonding pad 103 at a plurality of locations on the outer peripheral portion. The bonding pads 103 connected by the wire bonds 104 are arranged such that the physical distance is short. This has the effect of minimizing the parasitic component due to the wire bond 104 and preventing failure due to an unexpected delay.

[(1-7) spectrum]
FIG. 7 shows the spectrum of each signal of the module 100 of FIG. In FIG. 6, the bonding pad 103 at a position indicated by the probe p1 is probed, and the waveform is observed. The portion indicated by the probe p1 corresponds to a portion to which the voltage Vcom of the carrier C0 is applied. The location of the probe p1 is observed in time series by an oscilloscope or the like. Then, the voltage Vcom of the carrier wave C0 as shown in FIG. 4A is confirmed. The portion indicated by the probe p2 corresponds to a portion to which the output signal DA of the servo control signal before modulation is applied. When this portion is observed, the waveform of the output signal DAp on the positive side of the output signal DA as shown in (b) of FIG. 4 is confirmed. The portion indicated by the probe p3 corresponds to a portion to which the servo voltage Vfy of the servo control signal after modulation is applied. When this portion is observed, the waveform of the voltage Vfyp on the positive side of the servo voltage Vfy as shown in (c) of FIG. 4 is confirmed.

  If these waveforms are subjected to frequency spectrum analysis, a spectrum as shown in FIG. 7 is obtained. In FIG. 7, the horizontal axis is frequency, the vertical axis is spectrum, and has spectra SP1 to SP3. A spectrum SP1 indicated by a dotted line is a spectrum of the voltage Vcom of the carrier C0 of (a) of FIG. 4 corresponding to the probe p1. The spectrum SP1 has a first frequency peak identified at the first frequency FS1. The first frequency FS1 of the first frequency peak corresponds to the vibration frequency Fcom of the voltage Vcom of (a) of FIG.

  A spectrum SP2 indicated by a thin solid line is a spectrum of the positive side output signal DAp of FIG. 4B corresponding to the probe p2. The spectrum SP2 has a second frequency peak identified at the second frequency FS1. The second frequency FS2 is lower than the first frequency FS1. The second frequency FS2 of the second frequency peak corresponds to the vibration frequency Ff of the frame 3 in (b) of FIG. The oscillation frequency Ff of frame 3 is lower than the oscillation frequency Fcom of the carrier C0 (Ff <Fcom).

  A spectrum SP3 indicated by a thick solid line is a spectrum of the voltage Vfyp on the positive side of the servo voltage Vfy of the servo control signal after the modulation of (c) of FIG. 4 corresponding to the probe p3. In the spectrum SP3, the frequency peak 701 and the frequency peak 702 are confirmed at two frequencies of the first frequency FS1 and the second frequency FS2. These two frequencies correspond to the oscillation frequency Ff of frame 3 and the oscillation frequency Fcom of the carrier C0. The frequency peak 701 at the first frequency FS1 of the spectrum SP3 has an overlap with the first frequency peak of the spectrum SP1. The frequency peak 702 at the second frequency FS2 of the spectrum SP3 has an overlap with the second frequency peak of the spectrum SP2. Thus, spectrum SP3 has two frequency peaks as a characteristic component. The reason is that the modulation circuit 13 modulates the waveform of the output signal DA having the oscillation frequency Ff with the carrier C0 having the oscillation frequency Fcom.

  In the module 100, using the monitor function of the modulation circuit 13, the voltage Vcom of the carrier C0, the servo voltage Vfy, and the like can be observed. As a result, as shown in FIG. 7, it can be confirmed that a characteristic component is possessed as a spectrum analysis result. As described above, the servo voltage Vfy applied to the sense mass 4 in the first embodiment is a waveform having two frequency peaks corresponding to the first frequency peak and the second frequency peak. Note that these spectra show an ideal state, and there is a possibility that the actual spectrum may include noise components and harmonic components based on rectangular waves, but the characteristics for which the above features are observed are lost. I can not do it.

[(1-8) Servo Force-Operating Voltage_ (1)]
FIG. 8 shows the servo force with respect to the operating voltage in the quantitative comparison with the comparative example, regarding the effect of the first embodiment. The solid line in FIG. 8 indicates the first embodiment, and the broken line indicates the comparative example. FIG. 8A shows a graph in which changes in the generated servo force Fs are plotted when the servo voltage Vfy is changed with a constant carrier wave C0. This is the case where the amplitude of the voltage Vcom is fixed to 1 as the constant carrier C0. As the servo voltage Vfy, the magnitude of the positive-side voltage Vfyp (the same applies to the voltage Vfyn) is changed in the range of 0-1. The case where the magnitudes of the voltage Vcom and the voltage Vfyp are 1 corresponds to the case of using the maximum voltage level of the power supply voltage V0. The maximum value of the servo force Fs of the comparative example is about 0.15 [au], and the maximum value of the servo force Fs of the first embodiment is about 0.6 [au]. The first embodiment has a characteristic that the servo force Fs linearly increases with respect to the voltage Vfyp. In the first embodiment, a servo force Fs that is four times larger than that of the comparative example can be obtained. The first embodiment has these two advantages.

  (B) of FIG. 8 shows a graph in which the change of the servo force Fs is plotted when the voltage Vcom of the carrier wave C0 is changed at a constant servo voltage Vfy. This is the case where the positive voltage Vfyp is fixed to 1 as the constant servo voltage Vfy. This is the case where the amplitude of the voltage Vcom is changed in the range of 0-1. The amplitude of the signal at the time of capacitance detection is proportional to the voltage Vcom. Therefore, it is natural to use 1, which is the maximum value, basically as the amplitude of the voltage Vcom. In the comparative example, as the voltage Vcom is smaller, a larger servo force Fs can be obtained. Therefore, in order to obtain a large servo force Fs, the voltage Vcom must be reduced within a reasonable range. In the comparative example, there is a trade-off between the servo force Fs, the capacity detection accuracy, the S / N, and the like.

  On the other hand, in the first embodiment, since the servo force Fs is proportional to the voltage Vcom, the voltage Vcom of the carrier C0 can be set to 1, which is the maximum value. This means that the maximum servo force Fs can be obtained, and the maximum signal strength or maximum capacity detection accuracy and S / N can be obtained. That is, in the first embodiment, there is an advantage that the tradeoff between the servo force Fs of the comparative example and the capacity detection accuracy or the like can be eliminated.

[(1-8) Servo Force-Operating Voltage_ (2)]
FIG. 9 shows the relationship between the servo power and the operating voltage in the case where a voltage (referred to as Vh) higher than the power supply voltage V0 is used as the servo voltage Vfy, as compared with the first embodiment and the comparative example. The horizontal axis shows the case where the amplitude of the voltage Vcom of the carrier wave C0 is fixed to 1 and the positive side voltage Vfyp is changed in the range of 0-4. A case where a voltage Vh higher than the power supply voltage V0 can be used as the servo voltage Vfy will be described with reference to FIG.

  Vfyp = 4 means that the voltage Vh corresponding to the high voltage power supply four times the power supply voltage V0 is used to generate the servo voltage Vfy. The crossover of the servo force Fs that can be generated in the first embodiment and the comparative example is when Vfyp / Vcom = 2, that is, when the voltage Vh which is twice the power supply voltage V0 is used. An area of (Vfyp / Vcom) <2 is a first area, and an area other than this is a second area. In the first region, the larger servo force Fs can be obtained in the first embodiment than in the entire region, and in the second region, the larger servo force Fs can be obtained in the entire region.

  If the voltage Vh of the second region is used as the servo voltage Vfy when the servo force Fs is made as large as possible, a comparative example should be selected. However, when the servo force Fs is sufficient and the linear characteristic of the servo force Fs with respect to the servo voltage Vfy in FIG. 8B is regarded as important, Embodiment 1 can be applied to either the first region or the second region. Should be selected. These choices depend on the system design.

[(1-8) Servo Force-Operating Voltage_ (3)]
FIG. 10 is a waveform example of each signal in the case of (Vfyp / Vcom) = 4, where the voltage Vh of FIG. 9 can be used, as compared with the embodiment 1 of (A) and the comparison example of (B) Shown by comparison. (A) shows the voltage Vcom of the carrier wave C0, (b) shows the servo voltage Vfy, and (c) shows the servo force Fs. FIG. 10 shows the case where there is a waveform rounding. In the first embodiment, the effective servo force Fs indicated by the broken line is smaller than that of the comparative example. This can be understood from the characteristic that a larger servo force Fs is obtained as the voltage Vcom is smaller in the comparative example of FIG. 9B. When the magnitude of the voltage Vcom can be ignored with respect to the magnitude of the servo voltage Vfy, a larger servo force Fs can be obtained in the comparative example.

  On the other hand, the first embodiment is effective when the DC components of the voltage Vcom and the servo voltage Vfy are close to each other, but if they are separated, the servo force that can be generated is reduced. This is the reason why the effective servo force Fs is reduced in FIG. As described above, Embodiment 1 is effectively applied when the low power supply voltage V0 is used and the direct current components of the voltage Vcom and the servo voltage Vfy are close to each other.

[(1-8) Servo Force-Operating Voltage_ (4)]
FIG. 11 is a graph similar to FIG. 10 but showing the case where there is no waveform rounding. The carrier C0 is an ideal square wave.

[(1-9) Carrier phase delay]
FIG. 12 is an explanatory diagram for supplementarily describing the phase delay of the voltage Vcom of the carrier wave C0 in the delay unit 131 of the modulation circuit 13 described above. The above-mentioned "appropriate delay" refers to the optimum delay amount for exactly aligning the phase with the voltage Vcom of the carrier C0 with respect to the servo voltage Vfy. (A) shows a rectangular wave without waveform rounding as the voltage Vcom of the carrier wave C0. (B) shows the servo voltages Vfy {Vfyp, Vfyn} after modulation. (C) shows a graph of servo force with respect to the phase delay amount (unit: [radian]) of voltage Vcom.

  As to whether or not this phase delay amount is appropriate, servo voltage Vfy and voltage Vcom are actually observed in advance at the design and manufacturing stages, and it is confirmed that they are appropriate and adjusted so as to be appropriate. When the phase delay amount is appropriate, that is, when the voltage Vcom and the servo voltage Vfy are in phase, the servo force Fs can be generated with high efficiency. Further, in order to enable confirmation and adjustment of this phase delay even after manufacturing, the modulation circuit 13 has a function including a circuit capable of monitoring the voltage Vcom, the servo voltage Vfy, and the like as described above. The delay unit 131 has a function for adjusting this phase delay amount. The phase delay amount of the delay unit 131 can be set based on the delay control signal Sd from the control circuit 52. The control circuit 52 can set the phase delay amount.

  Further, the impedance of the modulation circuit 13 and the driving force of the DAC 32 are designed such that the servo voltage Vfy appropriately swings. These depend on the parasitic capacitance of the wiring and the like. Therefore, the mounting of the inertial sensor is appropriately devised like the module 100.

  The detection accuracy in the case where there is a phase shift between the voltage Vcom and the servo voltage Vfy will be described with reference to FIG. A delay 1201 indicates a delay corresponding to a phase shift between the voltage Vcom of (a) and the servo voltage Vfy of (b). The phase 1202 is 2π and indicates one cycle of the voltage Vcom. The solid line in (c) indicates the servo force of the first embodiment. When the phase delay is 0, the optimum delay amount is obtained, and 1 [au] is obtained as the servo force Fs. When the phase delay is π (180 degrees), the positive voltage Vfyp and the negative voltage Vfyn are inverted. The servo force Fs obtained in that case is equal to the servo force Fs when the delay 1201 is zero. Therefore, in the first embodiment, the phase delay is desirably 0, and π (180 degrees) is also acceptable.

  The broken line indicates the servo force of the comparative example. In the comparative example, only 0.25 servo force Fs can be obtained at the maximum. The conditions for phase delay for obtaining a servo force Fs larger than that of the comparative example in the first embodiment are as follows. That is, assuming that the phase delay amount is D, 0 ≦ D <(3π / 8 + nπ), or (5π / 8 + nπ) <D <(11π / 8 + nπ), or (11π / 8 + nπ) <D <(2π + nπ), It is. This is calculated in the case where the carrier wave C0 is an ideal rectangular wave, but the same holds true even when there is a waveform rounding.

[(1-10) waveform rounding]
FIG. 13 is an explanatory view for supplementarily explaining that the predetermined effect of the first embodiment is realized even when there is a waveform rounding as shown in FIG. 10 and the like. FIG. 13 shows an example in which only the voltage Vcom of the carrier wave C0 is passed through a second-order low-pass filter to make it approach a triangular wave from a rectangular wave. The cutoff frequency Fc of the low pass filter is set to Fc = 20. (A) shows the relationship of the servo force to the cutoff frequency Fc and the relationship of the phase delay to the cutoff frequency Fc. (B) shows the case where there is a waveform rounding of Fc = 20 as the voltage Vcom of the carrier wave C0. (C) shows the servo force Fs in the case corresponding to (b).

  As an appropriate delay, the phase delay amount D = 0.72 [rad] in the case of Fc = 20 is applied. As a result, as compared with the case of the rectangular wave as shown in FIG. 11, the optimum state is as shown in FIG. When the voltage Vcom and the servo voltage Vfy have the same waveform rounding, if they are set to different waveform rounds, the generated servo force becomes smaller. In the first embodiment, when the voltage Vcom, the servo voltage Vfy, or both of them have a waveform rounding, an appropriate phase delay amount is applied in the modulation circuit 13 as in the above example. The appropriate amount of delay is a value that can be plotted as a phase delay when a Bode diagram is created. Thereby, in the first embodiment, as described above, a preferable effect can be obtained such that the servo force Fs can be generated with high efficiency with respect to the low power supply voltage V0.

[(1-11) Circuit part]
FIG. 14 shows the configuration of the sensor element 2 and the circuit part in the module 100 of FIG. In order to detect the angular velocity, the module 100 detects the displacement x of the first axis of the frame 3 on the drive side of the inertial body of the sensor element 2 and the Y direction of the second axis of the sense mass 4 on the Coriolis detection side. Detect the displacement y of Correspondingly, the sensor element 2 has two detection capacitances and servo capacitances on the drive side and the Coriolis detection side, and the circuit unit has two detection potentials and a servo control circuit.

  The sensor element 2 is a component mounted by MEMS described later, but is represented by an equivalent circuit in FIG. The sensor element 2 has a capacitance Csx {Csxp, Csxn} which is a detection capacitance provided in the frame 3 which is a driving side, and a capacitance Cfx {Cfxp, Cfxn} which is a servo capacitance. The capacitance Csx is a complementary capacitance for detecting the displacement x, and has a positive side capacitance Csxp and a negative side capacitance Csxn. The capacitance Cfx is a complementary capacitance for servo control of the displacement x, and has a positive side capacitance Cfxp and a negative side capacitance Cfxn. The sensor element 2 has a capacitance Csy {Csyp, Csyn} which is a detection capacitance provided in the sense mass 4 which is the Coriolis detection side, and a capacitance Cfy {Cfyp, Cfyn} which is a servo capacitance. The capacitance Csy is a complementary capacitance for detecting the displacement y, and has a positive side capacitance Csyp and a negative side capacitance Csyn. The capacitance Cfy is a capacitance for servo control of the displacement y, and has a positive capacitance Cfyp and a negative capacitance Cfyn.

  Each of these capacitances has a complementary relationship, and is constituted by an electrode pair as in FIG. For example, in the detection capacitance on the drive side, the positive side capacitance Csxp is composed of the positive side electrode Dsxp and the frame 3, and the negative side capacitance Csxn is composed of the negative side electrode Dsxn and the frame 3. Similarly, in the servo capacitance, the positive side capacitance Cfxp is configured by the positive side electrode Dfxp and the frame 3, and the negative side capacitance Cfxn is configured by the negative side electrode Dfxn and the frame 3. The frame 3 corresponds to the aforementioned first electrode.

  A total of eight capacitances on the drive side and the Coriolis detection side of the sensor element 2 are electrically connected to each other as one electrode of the electrode pair of each capacitance is shown as a node 1401. In other words, the frame 3 and the sense mass 4 which are the first electrodes are commonly connected. The voltage Vcom of the carrier wave C0 is commonly applied to these capacities.

  The circuit unit includes two systems of detection circuits, two systems of servo control circuits, a carrier wave generation circuit 10, a control circuit 52, and a logic circuit 53. The two-system detection circuit includes an analog circuit 42x that detects a voltage from the detection capacitance on the drive side, and an analog circuit 42y that detects a voltage from the detection capacitance on the Coriolis detection side. It has DAC32x and modulation circuit 13x for applying servo voltage to the drive side servo capacity as a servo control circuit of two systems, DAC32y and modulation circuit 13y for applying servo voltage to the servo capacity on the Coriolis detection side. .

  The detection electrodes {Dsxp, Dsxn} of the drive side detection capacitances {Csxp, Csxn} are connected to the analog circuit 42x on the drive side. The detection electrodes {Dsyp, Dsyn} of the detection capacitances {Csyp, Csyn} on the Coriolis detection side are connected to the analog circuit 42y on the Coriolis detection side. The servo electrodes {Dfxp, Dfxn} of the drive side servo capacitances {Cfxp, Cfxn} are connected to the drive side modulation circuit 13x. The servo electrodes {Dfyp, Dfyn} of the servo capacitances {Cfyp, Cfyn} on the Coriolis detection side are connected to the modulation circuit 13y on the Coriolis detection side.

  The servo voltages Vfy {Vfyp, Vfyn} from the modulation circuit 13y are applied to the servo electrodes {Dfyp, Dfyn} of the servo capacitances {Cfyp, Cfyn} on the Coriolis detection side. The positive voltage Vfyp is applied to the positive electrode Dfyp, and the negative voltage Vfyn is applied to the negative electrode Dfyn. From the detection electrodes {Dsyp, Dsyn} of the detection capacitance {Csyp, Csyn} on the Coriolis detection side, the detection voltage Vsy {Vsyp, Vsyn} of the detection signal is detected by the capacitance voltage conversion circuit in the analog circuit 42y. A positive voltage Vsyp (indicating a positive displacement signal) is detected from the positive electrode Dsyp, and a negative voltage Vsyn (indicating a negative displacement signal) is detected from the negative electrode Dsyn.

  The analog circuit 42x detects the displacement x as a detection voltage Vsx from the detection capacitance on the drive side, and outputs a digital signal corresponding thereto as an output signal ADx. The analog circuit 42y detects the displacement y as a detection voltage Vsy from the detection capacitance on the Coriolis detection side, and outputs a digital signal corresponding thereto as an output signal ADy.

  FIG. 15 shows the internal configuration of the analog circuits 42x and 42y. The analog circuit 42x includes a capacitance-voltage conversion circuit 421x (indicated by "CVC"), an amplifier 422x, an ADC (analog-digital converter) 423x, and the like. The capacitance voltage conversion circuit 421 includes circuits on the positive side and the negative side. Similarly, in the analog circuit 42y, a capacitance-voltage conversion circuit 421y, an amplifier 422y, an ADC 423y, and the like are included.

  For example, the capacitance-voltage conversion circuit 421y of the analog circuit 42y receives the detection voltage Vsy {Vsyp, Vsyn}, converts the capacitance value into a voltage value by capacitance-voltage conversion, and outputs the analog voltage signal CVy1 {CVy1p, CVy1n as a result thereof. Output}. For example, the circuit on the positive side receives the voltage Vsyp, which is a displacement signal on the positive side, and outputs an analog voltage signal CVy1p on the positive side. The amplifier 422y receives the analog voltage signal CVy1, differentially amplifies it, and outputs it as an analog voltage signal CVy2. The ADC 423 y receives the analog voltage signal CVy 2, performs AD conversion with positive and negative differentials, and outputs the resultant digital signal as an output signal ADy. The analog circuit 42x has a similar configuration.

  General components of the analog circuits 42x and 42y are applicable, and may be sample-and-hold circuits based on clocks or continuous circuits. Also, the gain of each circuit may be designed to optimize the system, and is not limited to a specific gain or scheme. As a modification, when a sufficient gain can be obtained by the output of the capacitance-voltage conversion circuit, the amplifier can be omitted. Further, the capacitance voltage conversion circuit may have a circuit configuration in which the output is not a complementary positive / negative signal but a single signal, or may be a circuit configuration for differentially amplifying the detection voltage of the input.

  In FIG. 14, the control circuit 52 receives output signals ADx and ADy of the analog circuits 42x and 42y, generates signals SVx and SVy for servo control based on those output signals, and outputs them to DACs 32x and 32y. Do. The control circuit 52 performs appropriate control on the DACs 32x and 32y. Further, the control circuit 52 performs appropriate control on the carrier wave generation circuit 10 and the modulation circuits 13x and 13y.

  Control circuit 52 outputs a signal SVx {SVxp, SVxn} which is a digital signal for control to DAC 32x. The signal SVx is composed of a positive side signal SVxp and a negative side signal SVxn. Control circuit 52 outputs signal SVy {SVyp, SVyn} which is a digital signal for control to DAC 32y. The signal SVy is composed of a positive side signal SVyp and a negative side signal SVyn.

  Further, the control circuit 52 outputs the delay control signal Sd to the modulation circuit 13y on the Coriolis detection side. The delay control signal Sd is a signal for setting an appropriate delay to the servo voltage Vfy. The control circuit 52 also outputs the modulation control signal CKm to the drive modulation circuit 13x. The modulation control signal CKm is a signal for appropriately controlling modulation of servo control on the drive side. Further, control circuit 52 outputs carrier control signal Sc to carrier generation circuit 10. Carrier wave control signal Sc is a signal for controlling the generation of carrier wave C0 in carrier wave generation circuit 10.

  The control circuit 52 performs control such as low frequency noise removal by synchronous detection, generation of a signal SV for servo control by a PID controller, amplification by a gain circuit, DC offset removal by a difference circuit, and the like. The control circuit 52 also controls the generation of the delay control signal Sd, the modulation control signal CKm, and the carrier control signal Sc, and the like.

  The control circuit 52 outputs a signal OP1 based on the output signals ADx and ADy to the logic circuit 53. The logic circuit 53 performs logic processing including calculation of angular velocity using the signal OP1, and outputs an output signal OP2 including angular velocity detection information to the outside.

  The DAC 32x generates an output signal DAx {DAxp, DAxn} of an analog voltage for servo control on the drive side by DA conversion of the signal SVx. The DAC 32 y generates an output signal DAy {DAyp, DAyn} of an analog voltage for servo control on the Coriolis detection side by DA conversion of the signal SVy. The DACs 32x and 32y include positive and negative DACs, respectively. For example, the positive-side DAC of the DAC 32 y receives the positive-side signal SVyp, performs DA conversion, and outputs the resultant positive-side output signal DAyp. The DAC 32y on the Coriolis detection side has the same configuration as the DAC 32 of FIG. 1, and the output signal DAy {DAyp, DAyn} of the analog voltage corresponds to the above-mentioned output signal DA {DAp, DAn}.

  Carrier wave generation circuit 10 generates voltage Vcom of carrier wave C0 based on power supply voltage V0 and according to carrier wave control signal Sc from control circuit 52, and on node 1401 of the first electrode of sensor element 2 and on the Coriolis detection side. It outputs to the modulation circuit 13y.

  The modulation circuit 13y on the Coriolis detection side has the same configuration as that of the modulation circuit 13 of FIG. The modulation circuit 13y appropriately modulates the output signal DAy {DAyp, DAyn} of the analog voltage from the DAC 32y at the timing according to the delay control signal Sd using the voltage Vcom of the carrier wave C0. Thus, the modulation circuit 13y outputs servo voltages Vfy {Vfyp, Vfyn} which are signals after modulation. The servo voltage Vfy is applied to electrodes {Dfyp, Dfyn} that constitute a servo capacitance on the Coriolis detection side of the sensor element 2.

  The modulation circuit 13x on the drive side modulates the output signal DAx {DAxp, DAxn} of the analog voltage from the DAC 32x in accordance with the modulation control signal CKm, and outputs servo voltage Vfx {Vfxp, Vfxn} which is a signal after modulation. The servo voltage Vfx is applied to the electrodes {Dfxp, Dfxn} which constitute the servo capacitance on the drive side of the sensor element 2.

  In addition, as a modification, when increasing a measurement axis according to a use, the form which increased the module 100 to plurality, and the form which increases the sensor element 2 to plural and is shared by one circuit part are also possible. In the shared mode, the circuit unit uses an appropriate switching circuit or switching signal.

[(1-12) Modulation circuit]
FIG. 16A shows a detailed configuration of the modulation circuit 13y on the Coriolis detection side. In this modulation circuit 13y, the modulator 132 in FIG. 1 is configured using switches 135 {SW: SW1, SW2, SW3, SW3, SW4} which are analog switch elements. Each switch 135 has an input "SWin", an output "SWout" and a control input "CK". The input side of the output signal DAy {DAyp, DAyn} of the DAC 32 y is connected to the input side of the switch 135. At the output side of the switch 135, an output line of the servo voltage Vfy {Vfyp, Vfyn} is connected. The first switch SW1 is provided between the positive input line and the negative output line. The second switch SW2 is provided between the negative input line and the positive output line. The third switch SW3 is provided between the negative input line and the negative output line. The fourth switch SW4 is provided between the positive input line and the positive output line.

  The delay device 131 receives the voltage Vcom of the carrier C0 as shown in FIG. 4A and the delay control signal Sd. Delay device 131 generates an appropriate delay with respect to voltage Vcom at a timing based on delay control signal Sd, and the resulting carrier wave delayed signal Vd is input to the control input "CK" of each switch 135 {SW1 to SW4}. give. The carrier wave delayed signal Vd is input to the first switch SW1 and the second switch SW2 as a signal whose phase is inverted by the inverter, and is not inverted for the third switch SW3 and the fourth switch SW4. A signal is input.

  Each switch 135 operates to switch whether or not to output the value of the input “SWin” as the value of the output “SWout” according to the value {High, Low} of the carrier delay signal Vd of the control input “CK”. . When the value of the carrier wave delayed signal Vd is High, the third switch SW3 and the fourth switch SW4 are outputs, and the first switch SW1 and the second switch SW2 have a value of Low (No output). Therefore, as the servo voltage Vfy which is the output of the modulation circuit 13y, the signal DAyn on the negative side is output as the voltage Vfyn on the negative side, and the signal DAyp on the positive side is output as the voltage Vfyp on the positive side. When the value of the carrier wave delay signal Vd is Low, the positive and negative values are inverted and output as the output servo voltage Vfy.

  In the first embodiment, as described above, voltage Vcom of carrier wave C0 has amplitude Vpp {ground potential Vgnd to power supply voltage potential Vdd} corresponding to the maximum voltage level of power supply voltage V0. When the voltage Vcom, which is an analog voltage, thus takes on two values of the power supply voltage potential Vdd and the ground potential Vgnd, the voltage Vcom can be processed in the same manner as the logic in the modulation circuit 13y. Therefore, control of the switch 135 of the modulation circuit 13y is simplified, and can be realized by a simple and small-scale circuit.

  FIG. 16B shows a detailed configuration of the switch 135. The circuit of the switch 135 is arranged such that one PMOS element 1601 and one NMOS element 1602 are connected to their respective sources and drains. The control line (control input “CK”) is connected to the gate of the NMOS element 1602, and the inversion information of the control line is connected to the gate of the PMOS element 1601. With such a configuration of switch 135, an analog voltage level from ground potential Vgnd to power supply voltage potential Vdd can be output without voltage drop. In the output "SWout" of the switch 135, an on resistance (not shown) is appropriately designed to drive the servo capacitance.

  FIG. 17 shows the detailed configuration of the drive side modulation circuit 13x. The modulation circuit 13x differs from the modulation circuit 13y in that there is no delay unit 131, and the modulation control signal CKm is used as a control input "CK" to the switches 135 {SW1 to SW4} without delay. The level of the output signal DAx which is the input of the modulation circuit 13x is such that the upper potential is the potential Vddh, and the potential Vddh is a potential higher than the upper potential Vdd of the input of the modulation circuit 13y (Vddh> Vdd). The switch 135 is appropriately designed to allow input of a voltage signal having this potential Vddh. Specifically, in the MOS transistor used for the switch 135, a type having a thicker oxide film than usual and resistant to high pressure is selected.

[(1-13) DAC]
FIG. 18A shows a detailed configuration of the DAC 32y on the Coriolis detection side. The DAC 32 y includes a decoder 321, an analog voltage selection circuit 322, and a drive circuit 323. The signal SVy {SVyp, SVyn} from the control circuit 52 is input to the decoder 321. The decoder 321 decodes the signal SVy to generate a selection control signal SEL {SELp, SELn} which is the resultant signal, and outputs the selection control signal SEL {SELp, SELn} to the analog voltage selection circuit 322. The selection control signal SEL is a signal for selecting from the switch 325 in the analog voltage selection circuit 322, and includes a positive side signal SELp and a negative side signal SELn. The symbol [0: m] in the selection control signal SEL is a symbol in which m + 1 lines are omitted.

  The analog voltage selection circuit 322 includes a plurality of resistors 324 and a plurality of switches 325. The plurality of resistors 324 form a series connected string. The low side electric potential REFL and the high side electric potential REFH in the reference voltage of the string can be arbitrarily designed, but in the first embodiment, they are the ground electric potential Vgnd and the power supply voltage electric potential Vdd. A switch 325 is located at the tap position for the string. There are m + 1 pieces of switches 325 indicated by numbers [0] to [m]. The switch 325 has an input "in", positive and negative outputs "outp" and "outn", and a control input "ck".

  The switch 325 switches whether to output the input value or not in accordance with the value of the selection control signal SEL of the control input “ck”. It is possible to select which switch 325 is used to output or not according to the value {Hign, Low} for each number in the selection control signal SEL {SELp, SELn}. The positive side signal SELp can select the positive side output “outp”, and the negative side signal SELn can select the negative side output “outn”. Assuming that the selection number of the positive side signal SELp is kp and the selection number of the negative side signal SELn is kn, a relationship of kp + kn = m is established between the selection number kp and the selection number kn. That is, in the analog voltage selection circuit 322, the positive voltage value and the negative voltage value are in a complementary relationship within the range of the reference voltage of the string with the selection value of the selection control signal SEL as the center, The selected voltage signal is generated and output.

  The positive side output "outp" of the switch 325 is connected to the positive side circuit of the drive circuit 323, and the negative side output "outn" of the switch 325 is connected to the negative side circuit of the drive circuit 323 There is. The drive circuit 323 amplifies the voltage signal selected by the analog voltage selection circuit 322 in the positive and negative directions, and outputs the amplified signal as an output signal DAy {DAyp, DAyn}.

  As described above, a desired voltage can be selected and output as the output of the analog voltage selection circuit 322. It is important that the analog voltage selection circuit 322 is a circuit that can select and output a desired analog voltage by changing the tap position according to the selection control signal SEL. In addition, in order to adjust the output impedance of the DAC 32y, various circuit configurations other than FIG. 18 are applicable.

  FIG. 18B shows a circuit configuration of the switch 325. The circuit of the switch 325 includes a first switch sw1 and a second switch sw2. With respect to the voltage of the input "in" of the switch 325, whether it is the output of the first switch sw1 and the second switch sw2 according to the selection number {kp, kn} of the selection control signal SEL {SELp, SELn} of the control input "ck" Is selected. The result of this selection is the positive side output "outp" and the negative side output "outn". The voltage of the input “in” of the switch 325 is input to the input “in1” of the first switch sw1 and the input “in2” of the second switch sw2. The positive side signal SELp is input to the control input "ck1" of the first switch sw1, and the negative side signal SELn is input to the control input "ck2" of the second switch sw2. The output of the first switch sw1 is a positive output "outp", and the output of the second switch sw2 is a negative output "outn". For example, the first switch sw1 of the switch 325 selected by the selection number kp of the positive side signal SELp is turned on, and the voltage of the input “in1” is output as the positive side output “outp”.

  Although not illustrated, the drive side DAC 32x differs from the Coriolis detection side DAC 32y in the following points. The DAC 32x uses a potential Vddh higher than the power supply voltage potential Vdd, which is the high-side potential REFH of the reference voltage of the analog voltage selection circuit 322 of the DAC 32y, as the high-side potential of the reference voltage of the analog voltage selection circuit. The switches and drive circuits in the analog voltage selection circuit are circuits corresponding to the reference voltage of the potential Vddh. Specifically, as a MOS transistor used for the circuit, a type having a thicker oxide film than usual and resistant to high pressure is selected.

[(1-14) sensor element_MEMS structure]
FIG. 19 shows an example of the MEMS mounting structure of the sensor element 2 of the module 100. This sensor element 2 is an angular velocity sensor element having a mass which is a single inertial body. The sensor element 2 is configured using a comb-shaped electrode. This sensor element 2 has a total of eight capacitances {Cfx {Cfxp, Cfxn}, Cfy {Cfyp, Cfyn}, Csx {Csxp, Csxn}, Csy {Csyp}, shown in FIG. , Csyn}} is provided as an electrode pair of MEMS. As the electrode pair, electrodes {{Dfxp1, Dfxp2, Dfxn1, Dfxn2}, {Dfyp, Dfyn}, {Dsxp1, Dsxp2, Dsxn1, Dsxn2}, {Dsyp, Dsyn}} are shown.

  The electrode 190 has a substantially rectangular shape, and is connected to the spring 1901 at four points on the outer periphery. The electrodes {Dfxp1, Dsxp1, Dsxn1, Dfxn1} on the driving side are arranged on one side of the outer periphery of the electrode 190, and the electrodes {Dfxp2, Dsxp2, Dsxn2, Dfxn2} on the driving side are arranged on the other side of the outer periphery. It is arranged. In addition, the spring 1902 is connected to the spring 1902 at four points on the inner periphery of the electrode 190, and the Coriolis detection electrodes {Dfyp, Dfyn, Dsyp, Dsyn} are disposed via the spring 1902. For example, one electrode Dfxp of the above-mentioned capacitance Cfxp is formed of two electrode parts of the electrode Dfxp1 and the electrode Dfxp2, and the electrode parts are arranged at positions separated through the electrode 190 and are electrically connected . The same applies to electrodes of other capacities.

[(1-15) effects, etc.]
As described above, according to the MEMS angular velocity sensor which is the inertial detection device of the capacitance detection type and servo control system of the first embodiment, the servo force can be efficiently generated even at a low power supply voltage, and detection accuracy is It is possible to realize improvement and suppression of deterioration. The inertia detection device according to the first embodiment modulates the output signal of the DAC using the carrier wave C0, and performs servo control of the sensor element 2 using the servo voltage after the modulation. As a result, even with the low power supply voltage V0, the servo force Fs can be generated at the maximum efficiency, and the required maximum servo voltage can be reduced. As a result, in the first embodiment, the detection accuracy can be improved or maintained. In the first embodiment, the high voltage generation circuit can be reduced as compared with the prior art such as the comparative example, so that the circuit area and the power consumption can be reduced, and a small and low cost inertial sensor and system can be realized.

  The inertial detection device according to the first embodiment can be particularly suitably applied when the system to which the inertial sensor is applied is a system that wants to realize low power consumption with a low power supply voltage. The system can detect physical quantities with low power consumption and high sensitivity, and can mount an inertial sensor in a space-saving manner. The applicable system is applicable to various applications described in the background art. The inertia detection device according to the first embodiment is similarly applicable to an acceleration sensor and all other physical quantity sensors of electrostatic capacitance type and servo control type.

Second Embodiment
The inertia detection device according to the second embodiment will be described with reference to FIGS. The basic configuration of the second embodiment is the same as that of the first embodiment, and the components different from the first embodiment in the second embodiment will be described below. The inertia detection device according to the second embodiment is an acceleration sensor of a capacitance detection type and a single axis servo control type.

[(2-1) Circuit part]
FIG. 20 shows the configuration of the sensor element 2 and the circuit section in the module 200 of the implementation of the inertial detection system of the second embodiment. The overview of the module 200 is similar to that of the module 100 of FIG. The sensor element 2 has one system of detection capacitance and servo capacitance for detection of acceleration in one axis. The circuit unit has one system of analog circuit 42z, DAC 32z, modulation circuit 13z, etc., correspondingly.

  The sensor element 2 is an acceleration sensor element and has a mass of one inertial body. The sensor element 2 has a total of four capacities as a detection capacity and a servo capacity for detecting a displacement in the direction of a predetermined one axis. As detection capacitances, there are complementary positive side capacitance Csp and negative side capacitance Csn, and as servo capacitances, there are complementary positive side capacitance Cfp and negative side capacitance Cfn. The positive side capacitance Csp of the detection capacitance is composed of the positive side electrode Dsp and the first electrode, and the negative side capacitance Csn is composed of the negative side electrode Dsn and the first electrode. The positive side capacitance Cfp of the servo capacitance is composed of the positive side electrode Dfp and the first electrode, and the negative side capacitance Cfn is composed of the negative side electrode Dfn and the first electrode. The first electrode is an electrode that constitutes the mass of the inertial body. At the node 2001, the first electrodes constituting the respective capacitors are electrically connected, and the voltage Vcom of the carrier wave C0 is commonly applied.

  The circuit unit includes an analog circuit 42z, a DAC 32z, a modulation circuit 13z, a carrier wave generation circuit 10, a control circuit 52, and a logic circuit 53. The analog circuit 42z is connected to the electrodes {Dsp, Dsn} of the detection capacitances {Csp, Csn} of the sensor element 2, and detects the detection voltage Vs {Vsp, Vsn} from these electrodes. The configuration in the analog circuit 42z is the same as the configuration in FIG. 15, and includes a capacitance-voltage conversion circuit, an amplifier, an ADC, and the like. The analog circuit 42z obtains a voltage signal representing displacement from the detection voltage Vs by capacitance-voltage conversion. The analog circuit 42z outputs, as an output signal AD, a digital signal obtained by differential AD conversion from the amplified voltage value.

  The control circuit 52 performs appropriate control on the DAC 32z, etc., as in the first embodiment, based on the output signal AD from the analog circuit 42z. Control circuit 52 generates and outputs signal SV {SVp, SVn} for controlling DAC 32z based on output signal AD. Further, the control circuit 52 outputs the delay control signal Sd to the modulation circuit 13z, and outputs the carrier control signal Sc to the carrier generation circuit 10.

  Carrier wave generation circuit 10 generates voltage Vcom of carrier wave C0 based on power supply voltage V0 and according to carrier wave control signal Sc from control circuit 52, and outputs it to node 2001 of the first electrode of sensor element 2 and modulation circuit 13z. Do.

  The DAC 32 z generates an analog voltage by DA conversion of the signal SV, and outputs it as an output signal DA {DAp, DAn}. The modulation circuit 13z has a configuration similar to that of the modulation circuit 13y of the first embodiment. The modulation circuit 13z modulates the output signal DA {DAp, DAn} from the DAC 32z with the carrier wave C0 according to the timing of the delay control signal Sd, and outputs a servo voltage Vf {Vfp, Vfn} after modulation. The servo voltage Vf is applied to electrodes {Dfp, Dfn} of the servo capacitance.

  The control circuit 52 outputs a signal OP1 based on the output signal AD to the logic circuit 53. The logic circuit 53 performs processing including calculation of acceleration based on the signal OP1, and outputs an output signal OP2 including acceleration detection information to the outside. The logic circuit 53 is, in other words, an acceleration detection unit.

[(2-2) Spectrum]
FIG. 21 shows the spectrum of the waveform in the second embodiment. As in the first embodiment, the waveform is observed by probing a predetermined pad of the module 200. The spectrum SP1 shows the spectrum of the waveform of the voltage V0 of the carrier C0 corresponding to the above-mentioned probe p1. The spectrum SP2 shows the spectrum of the waveform of the servo voltage Vfp after modulation, which corresponds to the aforementioned probe p2.

  The spectrum SP1 has a first frequency peak at a first frequency FS1. The first frequency FS1 corresponds to the vibration frequency Fcom of the inertial body. The spectrum SP2 also has a frequency peak 2101 overlapping the first frequency peak of the spectrum SP1 at the first frequency FS1. The spectrum SP2 also has a frequency peak 2102 smaller than the frequency peak 2101 at the input acceleration frequency Fsig, which is a frequency smaller than the first frequency FS1.

  The input acceleration frequency Fsig is either at very low frequency or at DC level. Of course, if the input acceleration is direct current, Fsig = 0, and no clear frequency peak is observed. Further, when the input acceleration is zero, there is a possibility that the frequency peak 2101 overlapping with the first frequency peak of the spectrum SP1 is not observed in the spectrum SP2. As illustrated, it can be said that the frequency peak 2101 overlapping with the spectrum SP1 is observed in the spectrum SP2 only when acceleration is applied.

[(2-3) Sensor Element_MEMS Structure]
FIG. 22 shows an example of the MEMS mounting structure of the sensor element 2 in the second embodiment. This sensor element 2 has an electrode 220 which constitutes a mass which is one inertial body, corresponding to detection and servo control of a predetermined one axis. And in the electrode 220, the electrode pair {Dfp, Dfn, Dsp, Dsn} which comprises four capacity | capacitances {Cfp, Cfn, Csp, Csn} of FIG. 20 is eight electrode parts {Dfp1, Dfp2, Dfn1, It is provided as Dfn2, Dsp1, Dsp2, Dsn1, Dsn2}.

  The electrode 220 has a substantially rectangular shape and has a minute movable part having a beam structure. Four places on the outer periphery of the electrode 220 are connected to the spring 2201. Electrode portions {Dfp1, Dfn1, Dsp1, Dsn1} are disposed on one side of the outer periphery of the electrode 220, and electrode portions {Dfp2, Dfn2, Dsp2, Dsn2} are disposed on the other side of the outer periphery . For example, the electrode Dfp constituting the capacitor Cfp is constituted of the electrode portion Dfp1 and the electrode portion Dfp2, and they are arranged at positions separated through the electrode 220 and electrically connected. The same is true for other capacities.

[(2-4) effects, etc.]
According to the MEMS acceleration sensor, which is an inertial detection device of a capacitance detection type and a servo control system according to the second embodiment, as in the first embodiment, the servo force can be efficiently generated even at a low power supply voltage. It is possible to realize improvement in accuracy and suppression of deterioration.

Third Embodiment
The inertia detection device according to the third embodiment will be described with reference to FIGS. The inertia detection device of the third embodiment is a modification of the angular velocity sensor of the first embodiment.

[(3-1) Circuit part]
FIG. 23 shows the configuration of the sensor element 2 and the circuit section in the module 300 of the inertial sensor implementation of the third embodiment. In the third embodiment, the sensor element 2 has a first inertial body 5A and a second inertial body 5B as two masses which are two inertial bodies. Each inertial body is comprised of a frame 3 and a sense mass 4 as in the first embodiment. The circuit unit includes a circuit 231 and a circuit 232 as two systems of circuits for detecting and servo-controlling these two inertial bodies. The configuration of one inertial body in units is the same as that of the first embodiment.

  In the first inertial body 5A and the second inertial body 5B, the respective capacitances and electrode pairs in FIG. 14 are the capacitances and electrode pairs on the first inertial body 5A side and the capacitances and electrodes on the second inertial body 5B side in FIG. It is divided into pairs. For example, the first inertial body 5A has a total of eight capacitances {CfxpA, CfxnA, CfypA, CfynA, CsxpA, CsxnA, CsypA, CsynA} and an electrode pair constituting those capacitances. For example, a capacity Cfyp, which is a positive side servo capacity on the Coriolis detection side, is configured by a set of a capacity CfypA on the first inertial body 5A side and a capacity CfypB on the second inertial body 5B side. The circuit unit detects the difference from the set of capacitances.

  The circuit portion includes a circuit 231, a circuit 232, and a logic circuit 53. The internal configuration of the circuit 231 and the circuit 232 is the same as that of the circuit portion in FIG. 14 of the first embodiment except the logic circuit 53. The circuit 231 performs detection and servo control on the capacity of the first inertial body 5A. The circuit 231 applies a voltage of a servo control signal to the second electrode of the first inertial body 5A, and detects a voltage from the third electrode of the first inertial body 5A. The circuit 232 performs detection and servo control on the capacity of the second inertial body 5B. The circuit 232 applies a voltage of a servo control signal to the second electrode of the second inertial body 5B, and detects a voltage from the third electrode of the second inertial body 5B.

  Circuit 231 includes carrier generation circuit 10, and circuit 232 does not include carrier generation circuit 10. The carrier wave generation circuit 10 of the circuit 231 commonly applies the carrier wave C0 to the node 2301 of the first inertial body 5A and the node 2302 of the second inertial body 5B. The control circuit in the circuit 231 outputs a signal OP1A including the detected voltage from the first inertial body 5A. The control circuit in the circuit 231 outputs a signal OP1B including the detected voltage from the second inertial body 5B. The logic circuit 53 performs processing including calculation of angular velocity using the signal OP1A from the circuit 231 and the signal OP1B from the circuit 232, and outputs an output signal OP2 including angular velocity detection information to the outside.

[(3-2) Sensor Element_MEMS Structure]
FIG. 24 shows an example of the MEMS mounting structure of the sensor element 2 of the third embodiment. This sensor element 2 has two electrodes 241 and 242 corresponding to two frames, corresponding to the first inertial body 5A and the second inertial body 5B which are two inertial bodies in FIG. These electrodes 241 and 242 work in opposite directions to each other. In the circuit section, a signal relating to angular velocity detection is obtained by taking the difference between the signals of these electrodes 241 and 242.

  The electrodes 241 and 242 have substantially the same structure as the electrode 190 in FIG. 19 of the first embodiment. The electrodes 241 and 242 are first electrodes, to which the voltage Vcom of the carrier C0 is applied. In the electrodes 241 and 242, eight capacitances {Cfx {Cfxp, Cfxn}, Cfy {Cfyp, Cfyn}, Csx {Csxp, Csxn}, Csy {Csyp, Csyn}} involved in servo control and detection of two axes are The electrode pair which comprises those capacity | capacitances is provided as an electrode part to show in figure. That is, the electrode parts {{Dfxp1, Dfxp2, Dfxp3, Dfxp4, Dfxn1, Dfxn2, Dfxn3, Dfxn4}, {DfypA, DfynA, DfypB, DfynB}, {Dsxp1, Dsxp2, Dsxn3, Dsxn4, Dxxx, xcxx, xcx , {DsypA, DsynA, DsypB, DsynB}}. In the electrode 241, electrode portions {Dfxp1, Dsxp1, Dsxn1, Dfxn1} are disposed on one side of the outer periphery, and electrode portions {Dfxp2, Dsxp2, Dsxn2, Dfxn2} are disposed on the other side. On the inner periphery of the electrode 241, electrode parts {DsypA, DfypA, DfynA, DsynA} are disposed. In the electrode 242, electrode parts {Dfxn3, Dsxn3, Dsxp3, Dfxp3} are arranged on one side of the outer periphery, and electrode parts {Dfxn4, Dsxn4, Dsxp4, Dfxp4} are arranged on the other side. On the inner periphery of the electrode 241, electrode parts {DsynB, DfynB, DfypB, DsypB} are disposed.

  For example, an electrode constituting a positive side capacitance Csyp, which is a detection capacitance on the Coriolis detection side, is constituted by two electrode portions of an electrode portion DsypA on the electrode 241 side and an electrode portion DsypB on the electrode 242 side. The electrode parts are disposed at different positions through the electrode 241 and the electrode 242 and are electrically connected. The same is true for other capacities.

[(3-3) effects, etc.]
According to the MEMS angular velocity sensor which is an inertial detection device of the capacitance detection type and the servo control system of the third embodiment, as in the first embodiment, the servo force can be efficiently generated even at a low power supply voltage It is possible to realize improvement in accuracy and suppression of deterioration. In the third embodiment, the configuration of performing detection by difference using two inertial bodies has an effect of doubling the signal and doubling the S / N with respect to the first embodiment, and high detection accuracy Can be realized.

  As mentioned above, although this invention was concretely demonstrated based on embodiment, this invention is not limited to the said embodiment, It can change variously in the range which does not deviate from the summary.

  DESCRIPTION OF SYMBOLS 1 ... base part, 2 ... sensor element, 3 ... frame, 4 ... sense mass, 10 ... carrier generation circuit, 11 ... first circuit part, 12 ... second circuit part, 13 ... modulation circuit, 21 ... first high voltage generation Circuits 31, 32 ... DAC, 41, 42 ... Analog circuits, 51, 52 ... Control circuits, 53 ... Logic circuits, 131 ... Delays, 132 ... Modulators.

Claims (11)

An inertial detection device,
A sensor element including an inertial body,
A first electrode provided on the inertial body;
A second electrode that constitutes a capacitance in pairs with the first electrode;
Equipped with
A second signal having a frequency peak which is overlapping with the first frequency peak of the first frequency of the first signal input to said first electrode, is input to the second electrode, the inertial body servos,
A first circuit for outputting the first signal to the first electrode;
A second circuit for outputting the second signal to the second electrode;
A modulation circuit,
Equipped with
The second signal is a signal having modulation by the first frequency,
The second circuit generates an analog voltage output signal for outputting the second signal,
The modulation circuit generates the second signal by modulating the analog voltage output signal using the first signal.
Inertial detection device. In the inertial detection device according to claim 1 ,
The first circuit generates a carrier wave based on a rectangular wave as the first signal,
Inertial detection device. In the inertial detection device according to claim 1 ,
And a third circuit configured to detect a capacitance value of the capacitor as a voltage value from a third electrode that constitutes a capacitor in a pair with the first electrode.
The second circuit generates an analog voltage output signal for outputting the second signal based on the voltage value detected by the third circuit.
Inertial detection device. In the inertial detection device according to claim 1 ,
The first circuit generates the first signal based on a power supply voltage.
The second circuit generates the analog voltage output signal based on the power supply voltage.
Inertial detection device. In the inertial detection device according to claim 1 ,
The modulation circuit includes a modulator that modulates the analog voltage output signal,
The modulator comprises a plurality of switches,
Inertial detection device. In the inertial detection device according to claim 1 ,
The modulation circuit includes a delay that delays the first signal, and performs the modulation using the first signal delayed by the delay.
Inertial detection device. In the inertial detection device according to claim 1,
Said first circuit for outputting the first signal to the first electrode,
It said second circuit for outputting said second signal to said second electrode,
A third circuit for detecting a capacitance value of the capacitor as a voltage value from a third electrode which constitutes a capacitor in a pair with the first electrode;
Equipped with
The inertial body has a first mass capable of displacement in a first direction and a second mass capable of displacement in a second direction,
The first circuit outputs the first signal in common to the first electrodes constituting the first mass and the second mass,
The second circuit outputs the second signal to the second electrode constituting the servo capacitance of the second mass,
The third circuit detects the voltage value from the third electrode constituting the detection capacitance of the second mass, and detects an angular velocity applied to the inertial body based on the voltage value.
Inertial detection device. In the inertial detection device according to claim 1,
Said first circuit for outputting the first signal to the first electrode,
It said second circuit for outputting said second signal to said second electrode,
A third circuit for detecting a capacitance value of the capacitor as a voltage value from a third electrode which constitutes a capacitor in a pair with the first electrode;
Equipped with
The inertial body has a mass that can be displaced in a predetermined direction,
The first circuit outputs the first signal in common to the first electrodes constituting the mass,
The second circuit outputs the second signal to the second electrode constituting the servo capacitance of the mass,
The third circuit detects the voltage value from the third electrode constituting the detection capacitance of the mass, and detects an acceleration applied to the inertial body based on the voltage value.
Inertial detection device. An inertial detection device,
Servos said sensor element by a servo control signal having a frequency peak which is overlapping with the first frequency peak of the first frequency in a carrier wave input into the sensor element,
A first circuit for outputting the carrier wave to a first electrode of the sensor element;
A second circuit for outputting the servo control signal to a second electrode of the sensor element;
A modulation circuit,
Equipped with
The servo control signal is a signal having modulation by the first frequency,
The second circuit generates an analog voltage output signal for outputting the servo control signal,
The modulation circuit generates the servo control signal by modulating the analog voltage output signal using the carrier wave.
Inertial detection device. In the inertial detection device according to claim 9 ,
The servo control signal driving an inertial body of the sensor element has a frequency peak at a second frequency lower than the first frequency.
Inertial detection device. In the inertial detection device according to claim 9 ,
The analog voltage output signal generated by the digital-to-analog converter based on the detection signal from the inertial body of the sensor element has a second frequency peak at a second frequency lower than the first frequency,
The servo control signal for driving the inertial body is a signal obtained by modulating the analog voltage output signal using the carrier wave, and has a frequency peak overlapping with the second frequency peak.
Inertial detection device.