JP6314813B2 - Acceleration sensor - Google Patents

Description

  The present invention relates to an acceleration sensor that detects acceleration based on a change in capacitance when acceleration is applied.

  Conventionally, when adjusting the sensitivity of an acceleration sensor that can measure high acceleration, it is difficult to apply high acceleration, which is the maximum acceleration in the measurement range, to the acceleration sensor. A method for adjusting the sensitivity is generally known.

  For example, Patent Document 1 proposes a method of adjusting sensitivity of an acceleration sensor by providing an adjustment capacitance in the acceleration sensor and trimming the adjustment capacitance.

JP 2000-346865 A

  However, in the method of adjusting sensitivity by applying acceleration that can be applied to an acceleration sensor capable of measuring high acceleration, if the applied acceleration at the time of sensitivity adjustment is small, the output value of the acceleration sensor is buried in noise generated for some reason. There is a possibility that. That is, the noise value becomes larger than the output value of the acceleration sensor, and the noise is output from the acceleration sensor. For this reason, there is a problem that the sensitivity adjustment of the output value cannot be performed or the error of the sensitivity adjustment becomes large.

  An object of the present invention is to provide an acceleration sensor capable of adjusting sensitivity without applying high acceleration.

  In order to achieve the above object, in the invention described in claim 1, the fixed electrode (12, 15), the movable electrode (11, 14) formed to be displaceable with respect to the fixed electrode (12, 15), When the acceleration is applied to the movable electrodes (11, 14), a change in electrostatic capacitance between the fixed electrodes (12, 15) and the movable electrodes (11, 14) corresponding to the acceleration is detected. The sensing part (10) which performs is provided.

  The sensing unit (10) includes an operational amplifier (21) and a feedback capacitor (23) connected between the input and output terminals of the operational amplifier (21). Based on the feedback capacitance value of the feedback capacitor (23), A CV conversion unit (20) that converts the detected change in capacitance into a voltage signal is provided.

  Further, a sensitivity adjustment unit (30) having a sensitivity adjustment value for adjusting the sensitivity and inputting the voltage signal from the CV conversion unit (20) and adjusting the sensitivity of the voltage signal based on the sensitivity adjustment value is provided. I have.

  The CV conversion unit (20) has a capacitance value that is smaller than the feedback capacitance value of the feedback capacitor (23) and has a sensitivity adjustment capacitance value that can be adjusted, and the operational amplifier (21). A sensitivity adjustment capacitor (24) connected in parallel with the feedback capacitor (23) is provided between the input and output terminals, and either one of the feedback capacitor (23) and the sensitivity adjustment capacitor (24) is an operational amplifier (21 The connection state can be switched so as to be connected to.

  The sensitivity adjustment value of the sensitivity adjustment unit (30) is the value in the first connection state in which the sensitivity adjustment capacitor (24) is connected to the operational amplifier (21) in a state where no acceleration is applied to the movable electrodes (11, 14). The first sensitivity adjustment in which the voltage difference between the voltage signal and the voltage signal in the second connection state in which the feedback capacitor (23) is connected to the operational amplifier (21) is acquired, and the feedback capacitance value based on the voltage difference Is applied to the movable electrodes (11, 14) after the second sensitivity adjustment, in which the sensitivity adjustment capacitance value is adjusted so that the difference between the sensitivity adjustment capacitance value and the sensitivity adjustment capacitance value is a predetermined magnification. And the third sensitivity adjustment in which the sensitivity adjustment value is adjusted based on the voltage signal in the first connection state.

  According to this, when the sensitivity adjustment value is adjusted, the sensitivity adjustment capacitance (24) having a sensitivity adjustment capacitance value smaller than the feedback capacitance value is switched, and the sensitivity adjustment is performed so that the capacitance value has a predetermined magnification with respect to the feedback capacitance value. The capacity value is adjusted. For this reason, even if a small acceleration is applied to the movable electrodes (11, 14), a large voltage signal can be obtained by the CV conversion unit (20). Therefore, the sensitivity adjustment value can be adjusted based on the voltage signal. Become. Therefore, the sensitivity adjustment value can be adjusted without applying high acceleration to the sensing unit (10).

  In addition, the code | symbol in the bracket | parenthesis of each means described in this column and the claim shows the correspondence with the specific means as described in embodiment mentioned later.

It is the figure which showed the structure of the acceleration sensor which concerns on 1st Embodiment of this invention. It is the figure which showed the structure of the CV conversion part which concerns on 2nd Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals in the drawings.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. The acceleration sensor according to the present embodiment is a capacitive sensor device that detects acceleration applied to a sensing unit. The acceleration sensor is mounted on a vehicle and used to detect a vehicle collision.

  As shown in FIG. 1, the acceleration sensor includes a sensing unit 10, a CV conversion unit 20, and a sensitivity adjustment unit 30.

  The sensing unit 10 is a detecting unit that detects an acceleration received by the sensing unit 10 when the vehicle collides as an acceleration. Specifically, the sensing unit 10 includes a first capacitor 13 in which the movable electrode 11 and the fixed electrode 12 are arranged to face each other, and a second capacitor 16 in which the movable electrode 14 and the fixed electrode 15 are arranged to face each other in series. Connected to and configured.

  Here, the movable electrodes 11 and 14 and the fixed electrodes 12 and 15 are, for example, a part of a beam structure formed in the semiconductor layer of the SOI substrate, and are formed as comb-teeth electrodes. The movable electrode 11 is formed to be displaceable with respect to the fixed electrode 12, and the movable electrode 14 is formed to be displaceable with respect to the fixed electrode 15.

  And the sensing part 10 detects the change of the electrostatic capacitance between the fixed electrodes 12 and 15 and the movable electrodes 11 and 14 according to the said acceleration by applying an acceleration to the movable electrodes 11 and 14. FIG. For example, when the capacitance between the movable electrode 11 and the fixed electrode 12 increases by ΔC due to the application of acceleration, the capacitance between the movable electrode 14 and the fixed electrode 15 decreases by ΔC.

  As described above, the movable electrodes 11 and 14 and the fixed electrodes 12 and 15 perform a symmetrical operation with the application of acceleration to cause a symmetrical capacitance change. Therefore, by periodically applying signals (carrier waves) that are inverted with respect to the fixed electrodes 12 and 15, electrostatic capacitances (differential capacitances) in the capacitors 13 and 16 according to the displacement of the movable electrodes 11 and 14, respectively. ) Is output to the CV conversion unit 20.

  The acceleration sensor according to the present embodiment detects a vehicle collision, and the acceleration at the time of the collision is, for example, 480G. Therefore, the sensing unit 10 is configured to detect an acceleration of about 500G.

  The CV conversion unit 20 converts a change in capacitance input from the sensing unit 10 into a voltage signal. The CV conversion unit 20 includes an operational amplifier 21, a switch 22, a feedback capacitor 23, and a sensitivity adjustment capacitor 24.

  The operational amplifier 21 has movable electrodes 11 and 14 connected to an inverting input terminal, and a feedback capacitor 23 and a sensitivity adjustment capacitor 24 connected in parallel via a switch 22 between the inverting input terminal and the output terminal. . The non-inverting input terminal of the operational amplifier 21 receives an intermediate voltage Vdd / 2 (for example, 2.5 V) that is a half voltage of a voltage Vdd (for example, 5 V) applied as a carrier wave.

  The switch 22 can switch the connection state so that one of the feedback capacitor 23 and the sensitivity adjustment capacitor 24 is connected between the input and output terminals of the operational amplifier 21. Specifically, the switch 22 is switched so that the operational amplifier 21 and the sensitivity adjustment capacitor 24 are connected by a signal from a control signal generation circuit (not shown) when the sensitivity adjustment unit 30 adjusts the sensitivity. On the other hand, the switch 22 is switched to connect the operational amplifier 21 and the feedback capacitor 23 by the control signal generation circuit after the sensitivity adjustment of the sensitivity adjustment unit 30, that is, before the acceleration sensor is shipped as a product.

  The sensitivity adjustment capacitor 24 is connected between the input and output terminals of the operational amplifier 21 when the sensitivity adjustment unit 30 adjusts the sensitivity. The sensitivity adjustment capacitance 24 has a sensitivity adjustment capacitance value (Ca) that is smaller than the feedback capacitance value (Cf) of the feedback capacitance 23 and is configured such that the capacitance value can be adjusted. Specifically, the sensitivity adjustment capacitor 24 is configured by connecting a plurality of adjustment capacitors 24a in parallel. Further, a switch 24b is connected in series to each adjustment capacitor 24a and is driven by the control signal generation circuit described above. That is, the sensitivity adjustment capacity value (Ca) of the sensitivity adjustment capacity 24 is changed by controlling each switch 24b.

  One of the plurality of adjustment capacitors 24 a is always connected to the switch 22. The plurality of adjustment capacitors 24a are formed so as to have different capacitance values. From the viewpoint of finely adjusting the capacitance value, the capacitance value of the adjustment capacitor 24a connected to the switch 24b is preferably sufficiently smaller than the capacitance value of the adjustment capacitor 24a not connected to the switch 24b.

  In the above configuration, the CV conversion unit 20 converts the change in capacitance detected by the sensing unit 10 based on the feedback capacitance value of the feedback capacitance 23 into a voltage signal, and the voltage signal is converted to the sensitivity adjustment unit 30. Output to.

  The sensitivity adjustment unit 30 receives the voltage signal from the CV conversion unit 20 and adjusts the sensitivity of the voltage signal. Therefore, the sensitivity adjustment unit 30 has a sensitivity adjustment value for adjusting the sensitivity, and includes an operational amplifier, a resistor, and the like (not shown) for adjusting the sensitivity of the voltage signal based on the sensitivity adjustment value. Yes. The sensitivity adjustment value is an amplification factor (gain) for the voltage signal. The sensitivity adjustment unit 30 outputs the sensitivity-adjusted voltage signal to the outside as an output signal (Vout). The above is the overall configuration of the acceleration sensor according to the present embodiment.

  Next, a sensitivity adjustment method of the sensitivity adjustment unit 30 will be described. First, the acceleration sensor having the configuration shown in FIG. 1 is manufactured. The acceleration sensor is installed in a sensitivity adjustment device (not shown), and the switch 22 is connected to the sensitivity adjustment capacitor 24 by a control signal generation circuit provided in the sensitivity adjustment device.

  Thereafter, preparations for sensitivity adjustment are made according to the following procedure. First, as procedure 1 (first sensitivity adjustment), the voltage signal in the first connection state in which the sensitivity adjustment capacitor 24 is connected to the operational amplifier 21 in a state where no acceleration is applied to the movable electrodes 11 and 14, and feedback to the operational amplifier 21. A voltage difference from the voltage signal in the second connection state to which the capacitor 23 is connected is acquired. This voltage difference includes an error in the capacitance difference between the feedback capacitance value of the feedback capacitor 23 and the sensitivity adjustment capacitance value of the sensitivity adjustment capacitor 24.

  The CV conversion unit 20 is manufactured so that the feedback capacitance value of the feedback capacitor 23 is, for example, 10 times the sensitivity adjustment capacitance value of the sensitivity adjustment capacitor 24. However, a manufacturing error is included in the voltage difference. ing. Therefore, the feedback capacitance value and the sensitivity adjustment capacitance value are not at a predetermined magnification (for example, 10 times).

  Subsequently, as procedure 2 (second sensitivity adjustment), the sensitivity is set so that the feedback capacitance value becomes a capacitance difference of a predetermined magnification (for example, 10 times) with respect to the sensitivity adjustment capacitance value based on the voltage difference acquired in procedure 1. Adjust the adjustment capacity value. That is, ON / OFF of each switch 24b of the sensitivity adjustment capacitor 24 is controlled by the control signal generation circuit of the sensitivity adjustment device.

  Then, as a procedure 3, the voltage difference between the voltage signal in the first connection state and the voltage signal in the second connection state after adjusting the sensitivity adjustment capacitance value is acquired. Thereby, the capacitance difference between the feedback capacitance value and the sensitivity adjustment capacitance value is acquired.

  Thereafter, procedure 2 and procedure 3 are repeated as procedure 4. That is, the voltage difference (capacitance difference) between the voltage signal in the first connection state and the voltage signal in the second connection state is obtained again, and the switch 24b is switched so that the voltage difference is within a predetermined error range. The sensitivity adjustment capacity value of the sensitivity adjustment capacity 24 is adjusted. Note that step 2 and step 3 may be repeated a predetermined number of times in advance. Thereby, the precision of the magnification of the sensitivity adjustment capacitance value with respect to the feedback capacitance value can be improved. The above steps 1 to 4 correspond to preparation for sensitivity adjustment.

  Next, as procedure 5 (third sensitivity adjustment), the sensitivity adjustment value is adjusted based on the voltage signal in the first connection state in a state where acceleration is applied to the movable electrodes 11 and 14. At the time of the adjustment, the switch 22 of the CV conversion unit 20 is connected to the sensitivity adjustment capacitor 24, so that a large output can be obtained with a small acceleration. Therefore, for example, the acceleration sensor is tilted so that acceleration is applied to the gravity of the earth, in other words, the movable electrodes 11 and 14. As a result, a high output equivalent to that obtained when high acceleration is applied is obtained. In this state, the sensitivity adjustment value (gain) of the sensitivity adjustment unit 30 is adjusted.

  After the adjustment of the sensitivity adjustment value, the connection of the switch 22 is switched to the feedback capacitor 23 by the control signal generation circuit. Thereby, the acceleration sensor operates as a product.

  As described above, in the present embodiment, when adjusting the sensitivity adjustment value of the sensitivity adjustment unit 30, the sensitivity adjustment capacitor 24 having a sensitivity adjustment capacitance value smaller than the feedback capacitance value is switched, and the feedback capacitance value has a predetermined magnification. A feature is that the sensitivity adjustment capacitance value can be adjusted so as to be the capacitance value. With this configuration, even if a small acceleration is applied to the movable electrodes 11 and 14, a large voltage signal can be obtained by the CV conversion unit 20. For this reason, S / N with respect to noise increases, it is not necessary to apply high acceleration to the acceleration sensor, and the sensitivity adjustment value in a high range can be adjusted based on the voltage signal.

  In addition, the collision of a vehicle equipped with an acceleration sensor can be several hundred G, and it is very difficult to adjust sensitivity by applying such high acceleration. However, the acceleration sensor according to the present embodiment can perform sensitivity adjustment in a high acceleration range without applying a high acceleration of several hundred G.

(Second Embodiment)
In the present embodiment, parts different from the first embodiment will be described. As shown in FIG. 2, the feedback capacitance 23 has a feedback capacitance value set by a combination of m adjustment capacitors 23a (Cs) having the same capacitance value. Similarly, the sensitivity adjustment capacitor 24 has a sensitivity adjustment capacitor value set by a combination of n adjustment capacitors 24c (Cs) having the same capacitance value.

  That is, the capacitance value of the adjustment capacitor 23a of the feedback capacitor 23 and the capacitance value of the adjustment capacitor 24c of the sensitivity adjustment capacitor 24 are the same value, and the feedback capacitor 23 and the sensitivity adjustment capacitor 24 are the adjustment capacitors 23a, Each of 24c is configured by being combined in different integer multiples.

  When this is expressed by a mathematical expression, the feedback capacitance value of the feedback capacitor 23 is Cf = m × Cs, and the sensitivity adjustment capacitance value of the sensitivity adjustment capacitor 24 is Ca = n × Cs. Further, since the adjustment capacitors 23a and 24c are formed to have the same capacitance value, the error components (Δ) of the adjustment capacitors 23a and 24c are all the same. For this reason, as shown in the following Equation 1, the error component (Δ) included in each of the adjustment capacitors 23a and 24c can be canceled when adjusting the magnification of the sensitivity adjustment capacitance value with respect to the feedback capacitance value.

  Therefore, by configuring the feedback capacitor 23 and the sensitivity adjustment capacitor 24 with a plurality of adjustment capacitors 23a and 24c having the same capacitance value, in step 2 (second sensitivity adjustment), the sensitivity adjustment capacitance value with respect to the feedback capacitance value is set. The accuracy of magnification adjustment can be improved.

(Other embodiments)
The configuration of the acceleration sensor shown in each of the above embodiments is an example, and is not limited to the configuration shown above, and may be another configuration that can realize the present invention. For example, when adjusting the sensitivity adjustment capacity value, it is not necessary to repeat the procedure 2 and the procedure 3, and the procedure 2 and the procedure 3 may be performed once.

  Further, the acceleration sensor is not limited to being mounted on a vehicle. Therefore, the acceleration sensor may be used in other devices that need to detect acceleration. Similarly, the acceleration sensor may be used for detecting acceleration other than collision.

DESCRIPTION OF SYMBOLS 10 Sensing part 11, 14 Movable electrode 12, 15 Fixed electrode 20 CV conversion part 21 Operational amplifier 23 Feedback capacity 24 Sensitivity adjustment capacity 30 Sensitivity adjustment part

Claims (5)

A fixed electrode (12, 15); and a movable electrode (11, 14) formed to be displaceable with respect to the fixed electrode (12, 15). The movable electrode (11, 14) is accelerated. A sensing unit (10) for detecting a change in capacitance between the fixed electrode (12, 15) and the movable electrode (11, 14) according to the acceleration by being applied;
An operational amplifier (21), and a feedback capacitor (23) connected between input and output terminals of the operational amplifier (21), and the sensing unit (10) based on a feedback capacitance value of the feedback capacitor (23) A CV conversion unit (20) that converts the change in capacitance detected in step 1 into a voltage signal;
A sensitivity adjustment unit (30) having a sensitivity adjustment value for adjusting the sensitivity, inputs the voltage signal from the CV conversion unit (20), and adjusts the sensitivity of the voltage signal based on the sensitivity adjustment value. )When,
With
The CV conversion unit (20) has a capacitance value that is smaller than the feedback capacitance value of the feedback capacitance (23) and has a sensitivity adjustment capacitance value that can be adjusted, and the operational amplifier (21 ) Has a sensitivity adjustment capacitor (24) connected in parallel to the feedback capacitor (23) between the input and output terminals, and is either one of the feedback capacitor (23) and the sensitivity adjustment capacitor (24). The connection state can be switched so that one is connected to the operational amplifier (21).
The sensitivity adjustment value of the sensitivity adjustment unit (30) is:
The voltage signal in the first connection state in which the sensitivity adjustment capacitor (24) is connected to the operational amplifier (21) in a state where the acceleration is not applied to the movable electrodes (11, 14), and the operational amplifier (21). A first sensitivity adjustment in which a voltage difference between the voltage signal and the voltage signal in a second connection state in which the feedback capacitor (23) is connected to is acquired;
A second sensitivity adjustment in which the sensitivity adjustment capacitance value is adjusted so that the feedback capacitance value becomes a capacitance difference of a predetermined magnification with respect to the sensitivity adjustment capacitance value based on the voltage difference;
After the second sensitivity adjustment, the sensitivity adjustment value is adjusted based on the voltage signal in the first connection state in a state where the acceleration is applied to the movable electrodes (11, 14). Adjustment,
An acceleration sensor characterized by being set by   The said feedback capacity | capacitance (23) and the said sensitivity adjustment capacity | capacitance (24) are comprised by the combination of the several capacity | capacitance for adjustment (23a, 24c) which is the same capacity | capacitance value. Acceleration sensor.   The sensitivity adjustment value of the sensitivity adjustment unit (30) is obtained by performing the first sensitivity adjustment and the second sensitivity adjustment after the voltage signal in the first connection state and the second connection state. A voltage difference with the voltage signal is acquired, and the first sensitivity adjustment and the second sensitivity adjustment are repeatedly performed so that the voltage difference is within a predetermined range. The acceleration sensor according to claim 1 or 2.   The acceleration sensor according to any one of claims 1 to 3, wherein the sensing unit (10) detects an acceleration received by the sensing unit (10) during a collision as the acceleration.   The acceleration sensor according to claim 1, wherein the acceleration sensor is mounted on a vehicle.

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