JP2001153659A - Angular velocituy sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an angular velocity sensor using a sensor element having an electrostatic capacity varied depending on an applied angular velocity, which has high detection precision with little dispersion of sensitivity and is manufacturable at a low cost. SOLUTION: This angular velocity sensor 50 comprises a sensor element 10 having an output end part 38 whose electrostatic capacity is varied depending on an applied angular velocity. An electrostatic capacity detecting circuit 52 consisting of an operational amplifier 54, a feedback resistance 56 and a reference voltage source 58 is connected to the output end 38 of the sensor element 10. The output end of the electrostatic capacity detecting circuit 52 for applying the voltage equal to the reference voltage source 58 to the output end 38 of the sensor element 10 as bias voltage by the imaginary short circuit of the operational amplifier 54 is connected to an AC amplifier 60, and further connected to a synchronous wave detecting circuit 62 and a low pass filter 64.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an angular velocity sensor, and more particularly to, for example, a capacitance type angular velocity sensor whose capacitance changes according to an applied angular velocity.

[0002]

2. Description of the Related Art FIG. 5 is a perspective view showing an example of a sensor element used in a conventional angular velocity sensor. Sensor element 1
0 includes a substrate 12 formed of a single crystal silicon material or the like. A substantially rectangular vibrator 14 is formed on the substrate 12. Support beams 16 extend from four ends of the vibrator 14. The support beam 16 is bent, and its tip is fixed to the substrate 12.

[0003] Comb-shaped driving movable electrodes 18 and 20 are formed at one opposing end of the vibrator 14, respectively.
Input terminals 22 and 24 are formed to face the movable electrodes 18 and 20 for driving. From the input ends 22 and 24, comb-shaped fixed electrodes 26 and 28 for driving are formed to extend, and are arranged so as to mesh with the movable electrodes 18 and 20 for driving. The driving movable electrode 18 and the driving fixed electrode 26 form one driving electrode 30, and the driving movable electrode 20 and the driving fixed electrode 28 form the other driving electrode 32. In order to input a drive signal to these drive electrodes 30 and 32, an input terminal 2
2, 24 are used.

Further, detection movable electrodes 34 and 36 are formed at the other facing end of the vibrator 14. Opposite to the movable electrodes for detection 34, 36, the output terminals 38,
40 are formed. From the output ends 38 and 40, detection fixed electrodes 42 and 44 are formed to extend so as to mesh with the detection movable electrodes 34 and 36, respectively. The detection movable electrode 34 and the detection fixed electrode 42 form one detection electrode 46, and the detection movable electrode 36 and the detection fixed electrode 44 form the other detection electrode 48. Output terminals 38 and 40 are used to output detection signals from these detection electrodes 46 and 48.

In this sensor element 10, input terminals 22, 2
4 by applying an AC voltage to the driving movable electrode 1.
8 and the driving fixed electrode 26 and the driving movable electrode 2
An electrostatic force is generated between 0 and the driving fixed electrode 28, and the vibrator 14 vibrates in a direction connecting the input terminals 22 and 24 by the electrostatic force. When an angular velocity about an axis perpendicular to the surface of the substrate 12 is applied while the vibrator 14 is vibrating, a direction perpendicular to the vibration direction of the vibrator 14, that is, a direction connecting the output ends 38 and 40 is applied. Generates a Coriolis force. Due to this Coriolis force, the vibrator 14 causes the output end 3
Vibrates in the direction connecting 8,40. As a result, the distance between the detection movable electrode 34 and the detection fixed electrode 42 and the distance between the detection movable electrode 36 and the detection fixed electrode 44 change, and the capacitance of the detection electrodes 46 and 48 changes. Changes.
Such a change in capacitance corresponds to a change in vibration of the vibrator 14 due to Coriolis force.
By measuring the change in the capacitance at 48, the applied angular velocity can be detected.

In order to detect such a change in the capacitance of the detection electrodes 46 and 48, the driving AC power supply 1 is connected to the input terminal 22, for example, as shown in FIG. Further, the capacitance detection circuit 2 is connected to the output terminal 38. Here, the capacitance detection circuit 2 includes the JFET 3, and the output terminal 38 is connected to the gate of the JFET 3. The gate of JFET 3 is connected to JF
Connected to the source of ET3. Further, the source of the JFET 3 is grounded via the source resistor 5, and the drain is connected to the power supply voltage Vdd. Here, the gate resistance 4 is
High resistance that hardly passes current, approximately 10MΩ ~
1 GΩ. The vibrator 14 is grounded via a support beam 16. In the capacitance detection circuit 1, when the power supply voltage Vdd is connected to the drain of the JFET 3, the source voltage Vs generated by the source resistance 5 and the drain current Id is also applied to the gate of the JFET 3 by the gate resistance 4, It becomes the self-bias voltage Vb of the detection electrode 46.

FIG. 7 shows the principle of detecting a change in the capacitance of the detection electrode 46 of the sensor element 10 by the capacitance detection circuit 2. The gate of the JFET 3 usually has a high input impedance and hardly any current input / output. on the other hand,
Due to the gate resistance 4, JFET3
Charge is allowed to flow in. As a result, the gate of the JFET 3 is biased to the same voltage as the source voltage Vs after a certain time has elapsed since the power-on. However, the gate resistor 4 has a high resistance, and the entrance and exit of electric charges are restricted.

When a bias voltage Vb is applied to the capacitance C of the detection electrode 46 of the sensor element 10, a charge Q represented by the following equation is accumulated in the capacitance. Q = CVb (1) Here, when the angular velocity is applied, Coriolis force acts, and when the capacitance changes, the inflow and outflow of the charge are restricted. The quantity cannot follow quickly. Therefore, since the charge amount is held in the initial state, the gate voltage is reduced as shown in the following equation so that the equation (1) is satisfied, for example, the gate voltage Vb decreases as the capacitance C increases. Change. Q = ΔCΔVb = constant (2) When the gate voltage changes, the drain current Id flowing through the JFET 3 changes. Thus, as shown in the following equation,
The source voltage Vs of JFET3 changes. ΔVs = ΔIdRs (3) Here, Rs is a resistance value of the source resistor 5.

In this manner, a change in capacitance is converted into a change in voltage. From equations (1) to (3), it can be seen that the sensitivity of the sensor can be increased by increasing the amount of charge initially accumulated. It can be seen that the bias voltage Vb should be increased.

In order to detect the angular velocity applied to the sensor element 10, the voltage converted from the capacitance by the capacitance detection circuit 2 is applied to the AC amplifier 6 as shown in FIG. It is amplified until. Then, the output of the AC amplifier 6 is synchronously detected by the synchronous detection circuit 7 in accordance with the vibration frequency of the vibrator. Further, the output of the synchronous detection circuit 7 becomes a sensor output via the low-pass filter 8, and is output as a DC voltage corresponding to the angular velocity applied to the sensor element 10.

[0011]

However, in such an angular velocity sensor, the individual difference in the drain current of the JFET is very large, and the self-bias voltage greatly varies. For this reason, the bias voltage applied to the detection electrode varies, causing a variation in the sensitivity of the sensor.

Further, when the angular velocity is detected by using two detection electrodes, there is a problem that the sensitivity of each detection electrode varies due to the individual difference of the JFET, thereby deteriorating the angular velocity detection accuracy of the sensor. Also, with respect to a change in capacitance caused by unnecessary external vibration, there is a problem that the in-phase should be removed, but a residual signal remains due to a sensitivity difference between the two output terminals, thereby deteriorating detection accuracy. Was.
In order to solve such a problem, it is necessary to separately prepare a circuit for adjusting the sensitivity difference, which leads to an increase in cost.

SUMMARY OF THE INVENTION It is, therefore, a primary object of the present invention to provide an angular velocity sensor that has small sensitivity variations, high detection accuracy, and can be manufactured at low cost.

[0014]

According to the present invention, there is provided a sensor element whose capacitance changes according to an applied angular velocity;
In an angular velocity sensor including a capacitance detection circuit for detecting a change in capacitance of a sensor element, the capacitance detection circuit includes: an operational amplifier having an output terminal of the sensor element connected to the inverting input terminal; Includes a feedback resistor connected between the output terminal and the inverting input terminal, and a reference voltage source connected to the non-inverting input terminal of the operational amplifier, and is equal to the reference voltage source at the output terminal of the sensor element due to the imaginary short circuit of the operational amplifier. Characterized in that a voltage is applied.
It is an angular velocity sensor. In such an angular velocity sensor, a sensor element having two output terminals that perform a differential operation in which one capacitance increases when the other capacitance decreases can be used. A capacitance detection circuit is connected to each of the two output terminals. At this time,
In the capacitance detection circuits connected to the two output terminals of the sensor element, the non-inverting input terminals of the operational amplifiers included in the respective capacitance detection circuits can be connected to a common reference voltage source. Further, in the capacitance detecting circuits connected to the two output terminals of the sensor element, different reference voltage sources can be connected to the non-inverting input terminals of the operational amplifiers included in the respective capacitance detecting circuits. In this case, the voltage of the reference voltage source can be adjusted.

Since the voltage equal to the reference voltage source is applied to the output terminal of the sensor element due to the imaginary short circuit of the operational amplifier, the variation in the bias voltage applied to the output terminal of the sensor element can be suppressed. Therefore, when the capacitance at the output terminal portion of the sensor element changes, the amount of charge accumulated in the capacitance changes, and the current flowing through the feedback resistor connected to the operational amplifier changes accordingly. As a result, the output voltage of the operational amplifier changes, and a change in the capacitance at the output end of the sensor element is converted into a change in the output voltage. In the case of using a sensor element having two output terminals that perform differential operation, a reference voltage due to an imaginary short of an operational amplifier is applied to the two output terminals, and it is possible to suppress variation in detection of a change in capacitance of each output terminal. it can.
At this time, by connecting the non-inverting input terminal of the operational amplifier connected to the two output terminals to a common reference voltage source,
The same bias voltage can be applied to the two output terminals. Further, if an adjustable reference voltage source is connected to the non-inverting input terminal of the operational amplifier connected to the two output terminals, the voltage applied to the two output terminals is changed by adjusting the voltage of the reference voltage source. Thus, the variation in the initial value of the capacitance can be corrected.

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments of the present invention with reference to the drawings.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an illustrative view showing one example of an angular velocity sensor according to the present invention. The angular velocity sensor 50 uses the sensor element 10 shown in FIG. A drive AC power supply 51 is connected to the input terminal 22 of the sensor element 10. Further, the output end 38 of the sensor element 10 is connected to a capacitance detection circuit 52 as shown in FIG. The capacitance detection circuit 52 includes an operational amplifier 54. The output terminal 38 of the sensor element 10 is connected to the inverting input terminal of the operational amplifier 54.
Is connected. Further, a feedback resistor 56 is connected between the output terminal and the inverting input terminal of the operational amplifier 54. Also,
The non-inverting input terminal of the operational amplifier 54 is grounded via the reference voltage source 58. Although the vibrator 14 of the sensor element 10 used here is grounded via the support beam 16, the vibrator 14 is not limited to ground as long as the voltage is different from that of the reference voltage source 58. Can be connected to a constant voltage source. The input stage of the operational amplifier 54 may be any of a bipolar, a JFET, and a CMOS, but preferably has a small bias current.

In the capacitance detecting circuit 52, since the reference voltage source 58 is connected to the non-inverting input terminal of the operational amplifier 54, the inverting input terminal is set to the same voltage as the reference voltage source 58 by imaginary short. . Thus, the detection fixed electrode 42 of the sensor element 10 is biased to the voltage value set by the reference voltage source 58. Therefore, the capacitance of the detection electrode 46 is C, and the detection fixed electrode 4 is
Assuming that the bias voltage to 2 is Vb, the current is i, and the time is t, the charge amount Q accumulated in the detection electrode 46 is expressed by the following equation. Q = CVb = it (4) An angular velocity is applied to the sensor element 10, and the capacitance C of the detection electrode 46 is generated by the vibration of the vibrator 14 due to the Coriolis force.
Changes, the amount of charge Q stored in the detection electrode 46 also changes. At this time, since the bias voltage Vb is set by the imaginary short of the operational amplifier 54, it does not change even if the capacitance changes. Therefore, the change ΔQ in the charge amount is expressed by the following equation. ΔQ = ΔCVb (5) The electric charge ΔQ released or sucked from the detection electrode 46 of the sensor element 10 becomes a current Δi flowing through the feedback resistor 56. Therefore, the following equation holds. ΔQ = Δit (6) Here, the time t indicates a time when the capacitance changes. This is equal to the excitation frequency of the vibrator 14 for a vibration-type sensor element. Due to the current Δi flowing through the feedback resistor 56, a voltage change ΔVo is output to the output of the capacitance detection circuit 50.
Occurs. Here, assuming that the resistance value of the feedback resistor 56 is R, the output voltage change ΔVo is expressed by the following equation. ΔVo = ΔiR (7) From the equations (5), (6) and (7), the following equation is derived. ΔVo = ΔiR = ΔCVbR / t (8) In this way, a change in capacitance of the detection electrode 46 is converted into a change in voltage. From equation (8), the bias voltage Vb,
In other words, it is understood that as the set value of the reference voltage source 58 is increased and the resistance value of the feedback resistor 56 is increased, the output voltage change of the capacitance detection circuit 50, that is, the sensitivity of the sensor is increased. Specifically, it is desirable that the resistance value of the feedback resistor 56 be 10 kΩ or more.

The output of the capacitance detecting circuit 50 is amplified to an appropriate signal level by an AC amplifier 60, and detected by a synchronous detecting circuit 62 in synchronization with the excitation frequency of the vibrator 14. After that, it becomes a sensor output via the low-pass filter 64 and is output as a DC voltage corresponding to the angular velocity applied to the sensor element 10.

In the angular velocity sensor 50, the sensor element 1
The bias voltage Vb applied to the zero detection electrode 46 is
Since it is determined by the reference voltage source 58 connected to the non-inverting input terminal of the operational amplifier 54, the bias voltage can be set freely without being affected by the initial capacitance and impedance of the sensor element 10. Thereby, variation in sensor sensitivity can be suppressed.

FIG. 3 shows an example in which two detection electrodes 46 and 48 of the sensor element 10 are used. In this angular velocity sensor 50, two output terminals 3 of the sensor element 10
8 and 40, the capacitance detection circuits 52a and 52
b is connected. At this time, the capacitance detection circuits 52a,
The non-inverting input terminals of the operational amplifiers 54a and 54b used for 52b are connected to a common reference voltage source 58. Therefore, the voltage of the reference voltage source 58 is applied to the two detection electrodes 46 and 48 as the bias voltage Vb due to the imaginary short of the operational amplifiers 54a and 54b. The two capacitance detection circuits 52a and 52b are connected to AC amplifiers 60a and 60b, respectively. Furthermore, these A
The C amplifiers 60a and 60b are connected to a differential amplifier circuit 66. Then, the differential amplifier circuit 66 is connected to the synchronous detection circuit 62, and the synchronous detection circuit 62 is connected to the low-pass filter 64.

In the angular velocity sensor 50, when the vibrator 14 vibrates in the direction connecting the output terminals 38, 40 by Coriolis force, the capacitances of the two detection electrodes 46, 48 change in reverse. That is, when the capacitance of one detection electrode 46 increases, the capacitance of the other detection electrode 48 decreases. Conversely, when the capacitance of one detection electrode 46 decreases, the capacitance of the other detection electrode 48 increases. Due to such a change in the capacitance, the amount of charge accumulated in the detection electrodes 46 and 48 changes, and the output voltages Vo1 and Vo2 of the capacitance detection circuits 52a and 52b change. At this time, since the output of the sensor element 10 performs a differential operation, Vo2 decreases as Vo1 increases, and Vo2 increases as Vo1 decreases.

The output V of the capacitance detecting circuits 52a and 52b
The signals o1 and Vo2 are amplified to appropriate signal levels by the AC amplifiers 60a and 60b, and are subjected to subtraction processing by the differential amplifier circuit 66. Therefore, when the angular velocity is not applied to the sensor element 10, since the capacitances of the detection electrodes 46 and 48 are equal, the output voltages Vo1 and Vo2 of the capacitance detection circuits 52a and 52b are also equal, and the differential amplifier 66 Output is 0
Becomes However, when an angular velocity is applied to the sensor element 10, the output of the sensor element 10 performs a differential operation as described above, so that a signal is output from the differential amplifier circuit 66. At this time, since the bias voltages Vb applied to the detection electrodes 46, 48 are equal, the two detection electrodes 46, 4
The sensitivities of 8 are almost equal. When the capacitances of the detection electrodes 46 and 48 change in phase due to unnecessary external vibration, the in-phase component is removed by subtraction processing, and unnecessary signal components due to external vibration are removed. .

The signal from which unnecessary signal components have been removed by the differential amplifier circuit 66 is sent to the synchronous detection circuit 62 by the oscillator 14.
Is synchronously detected by the excitation frequency of After that, it becomes a sensor output via the low-pass filter 64 and is output as a DC voltage corresponding to the angular velocity applied to the sensor element 10.

As described above, by using the two detection electrodes 46 and 48 of the sensor element 10, unnecessary signal components due to external vibrations are removed, and the angular velocity can be accurately detected. At this time, since the same bias voltage Vb is applied to the two detection electrodes 46 and 48 of the sensor element 10, the sensitivities of the detection electrodes 46 and 48 can be made substantially equal. The signal can be reduced, and the detection accuracy can be improved. Further, since the difference in sensitivity between the two detection electrodes 46 and 48 can be reduced, there is no need to prepare another circuit for adjusting the difference in sensitivity, and the angular velocity sensor 50 can be manufactured at low cost. .

When the two detection electrodes 46 and 48 of the sensor element 10 are used, as shown in FIG.
Operational amplifier 5 of two capacitance detection circuits 52a and 52b
4a and 54b have different reference voltage sources 58a and 5b, respectively.
8b may be connected. These reference voltage sources 58a, 5
The voltage of 8b is adjustable. In this case, different bias voltages Vb1 and Vb2 are applied to the two detection electrodes 46 and 48 of the sensor element 10, respectively. Although the detection electrodes 46 and 48 of the sensor element 10 are manufactured so as to be substantially equal, it is actually impossible to make them completely equal, and the initial capacitance is slightly different. When the initial capacitance of the sensor element 10 varies, the sensor sensitivity varies as shown in Expression (8). However, in this angular velocity sensor 50, the bias voltages Vb1,
Since Vb2 can be adjusted individually, the sensitivity of the two detection electrodes 46 and 48 can be made substantially equal by adjusting the bias voltages Vb1 and Vb2 according to the variation in the initial capacitance. Therefore, the detection electrodes 46, 4
The difference signal due to the sensitivity difference of No. 8 can be reduced, and the detection accuracy can be improved.

[0027]

According to the present invention, the voltage of the reference voltage source can be applied as a bias voltage to the sensor element by utilizing the imaginary short circuit of the operational amplifier of the capacitance detection circuit. The variation in sensor sensitivity can be suppressed without being affected by the impedance or the like. When two detection electrodes of the sensor element are used, the same reference voltage power supply is used, so that the bias voltage to the detection electrodes can be equalized, and the sensitivity variation of the detection electrodes can be reduced. it can. Thus, unnecessary signals due to external vibrations can be removed, and the detection accuracy can be improved. Further, since the sensitivity difference between the two detection electrodes can be reduced, another circuit for adjusting the sensitivity difference becomes unnecessary, and the angular velocity sensor can be manufactured at low cost. Further, when there is a difference between the initial capacities of the two detection electrodes of the sensor element, the sensitivity of the detection electrodes is adjusted by connecting a voltage-adjustable reference voltage source to the operational amplifiers connected to the respective detection electrodes. The difference signal due to the difference can be reduced, and the detection accuracy can be improved.

[Brief description of the drawings]

FIG. 1 is an illustrative view showing one example of an angular velocity sensor of the present invention;

FIG. 2 is an illustrative view for explaining an operation of a capacitance detection circuit used in the angular velocity sensor shown in FIG. 1;

FIG. 3 is an illustrative view showing another example of the angular velocity sensor of the present invention;

FIG. 4 is an illustrative view showing a capacitance detection circuit used in another example of the angular velocity sensor of the present invention.

FIG. 5 is a perspective view showing a sensor element used in the present invention and a conventional angular velocity sensor.

FIG. 6 is an illustrative view showing one example of a conventional angular velocity sensor;

FIG. 7 is an illustrative view for explaining the operation of a capacitance detection circuit used in the conventional angular velocity sensor shown in FIG. 6;

[Explanation of symbols]

 Reference Signs List 10 sensor element 14 vibrator 46, 48 detection electrode 50 angular velocity sensor 52 capacitance detection circuit 54 operational amplifier 56 feedback resistor 58 reference voltage source

Claims (4)

[Claims] 1. An angular velocity sensor comprising: a sensor element whose capacitance changes according to an applied angular velocity; and a capacitance detection circuit for detecting a change in capacitance of the sensor element. The capacitance detection circuit includes an operational amplifier having an output terminal of the sensor element connected to an inverting input terminal, a feedback resistor connected between an output terminal and an inverting input terminal of the operational amplifier, and a non-inverting input terminal of the operational amplifier. A reference voltage source connected thereto, wherein a voltage equal to the reference voltage source is applied to the output terminal of the sensor element by an imaginary short of the operational amplifier. 2. The sensor element has two output terminals that perform a differential operation in which one capacitance increases and the other capacitance decreases, and the static output is provided to each of the two output terminals. The angular velocity sensor according to claim 1, wherein a capacitance detection circuit is connected. 3. The reference voltage source, wherein a non-inverting input terminal of the operational amplifier included in each of the capacitance detection circuits is common to the capacitance detection circuits connected to two output terminals of the sensor element. The angular velocity sensor according to claim 2, wherein the angular velocity sensor is connected to the sensor. 4. The capacitance detection circuit connected to two output terminals of the sensor element, wherein the non-inverting input terminal of the operational amplifier included in each of the capacitance detection circuits has a different reference voltage source. Is connected, and the voltage of the reference voltage source is adjustable.
2. The angular velocity sensor according to 1.