JPH05188083A - Variable electrostatic capacity type semiconductor acceleration sensor - Google Patents

Abstract

PURPOSE:To enable the execution of constantly stable sensor action by detecting electrical attraction between a movable electrode and a fixed electrode with a detecting circuit, and earthing both electrodes with a switching circuit, thereby letting the charge of both electrodes escape to release them automatically. CONSTITUTION:An oscillating circuit 12 with a variable electrostatic capacity type acceleration sensor 11 integrated therein, a frequency divider 13 for dividing the oscillation frequency, and a first and a second transistor circuits Tr1, Tr2 for earthing a movable electrode and a fixed electrode in the sensor 11 to the ground 14 are controlled by a microcomputer 15. The computer 15 receives the input of oscillation frequency from the circuit 12 through the frequency divider 13, and judges the attracted state of the movable and fixed electrodes when this input is stopped. The computer 15 then turns on the circuits Tr1, Tr2 so as to let the charge of both electrodes escape to the ground 14, and thus both electrodes are separated from each other in an instant. Constantly stable sensor action can be thereby maintained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor acceleration sensor used for detecting the acceleration of an automobile or for a small seismic device, and more particularly to an electrostatic capacitance having an improved maintenance performance of a sensor sensitive section. The present invention relates to a variable semiconductor acceleration sensor.

[0002]

2. Description of the Related Art Generally, in a capacitance type semiconductor acceleration sensor, as shown in FIG. 2, a weight portion 22 and a supporting frame 23 around the weight portion 22 are formed in a central portion of a substrate 21 by etching. A pair of beam portions 24, 2 which are parallel to the weight portion 22.
4 is elastically supported in a cantilever state via 4 to be movable in the plane direction. Further, as shown in FIG. 3, a movable electrode 25 is disposed on one surface of the weight portion 22 in the movable direction, and faces the movable electrode 25. A fixed electrode 27 is provided on the substrate 26 to form an electrode portion for measuring acceleration.

The capacitance-changing type semiconductor acceleration sensor 28 having such a structure is capable of detecting a change in capacitance between the movable electrode 25 and the fixed electrode 27 when the weight portion 22 moves due to acceleration. Is used to calculate the applied acceleration.

In this case, there is known a sensor in which a change in the capacitance obtained by the capacitance-changing type semiconductor acceleration sensor 28 described above is captured as an oscillation frequency, and is configured as a capacitor of an oscillation circuit.

[0005]

However, in order to detect this electrostatic capacitance, a voltage is usually applied to the electrode portion for measuring the electrostatic capacitance. However, because of this voltage, the electrodes are separated by several microns. There is a problem that electrostatic attraction is generated and both electrodes easily perform an adsorption operation, and when this adsorption phenomenon occurs, the movement of the weight portion stops and the sensor operation stops.

Therefore, the present invention provides a capacitance-changing type semiconductor acceleration sensor capable of immediately separating and returning to a normal state even if an adsorption phenomenon occurs in the electrode parts separated by several microns of the sensor sensitive part. To aim.

[0007]

SUMMARY OF THE INVENTION The present invention is a capacitance-changing type semiconductor acceleration sensor which obtains acceleration by electrically detecting a change in capacitance between a movable electrode and a fixed electrode. A switch circuit that connects each of the movable electrode and the fixed electrode to the ground, a detection circuit that detects that the movable electrode and the fixed electrode are electrically adsorbed, and the detection circuit detects the adsorption of both electrodes. In this case, the semiconductor acceleration sensor of the electrostatic capacitance change type is equipped with a control means for controlling the connection of both electrodes to the ground by turning on the switch circuit.

[0008]

According to the present invention, when the movable electrode is attracted to the fixed electrode due to the electrostatic attractive force during the acceleration measurement to cause the adsorption phenomenon, the detection circuit detects that the electrode is electrically adsorbed, and The detection data is input to the control means, and based on this, the control means turns on the switch circuit to control the connection of both electrodes to the ground, allowing the electric charge applied to both electrodes to escape to the ground and separate the both electrodes. ..

[0009]

As a result, even if an adsorption phenomenon occurs on both electrodes, both electrodes can be immediately returned to the normal separated state and automatically restored. As a result, the separation operation of the adsorbed electrodes does not have to be troublesome, and the recovery operation is automatically performed, so that the reliable and stable optimum sensor operation can always be maintained.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows a block diagram of a control circuit of a capacitance-changing type semiconductor acceleration sensor. This figure shows an oscillation circuit 12 incorporating a capacitance-changing type semiconductor acceleration sensor 11 and an oscillation frequency of this oscillation circuit 12. Frequency divider 13 for frequency processing
A first transistor circuit Tr1 and a second transistor circuit Tr2 which connect the movable electrode and the fixed electrode provided inside the sensor 11 to the ground 14, and a microcomputer 15 which controls and manages these circuit devices.
Composed of and.

The capacitance change type semiconductor acceleration sensor 11 described above is constructed in the same manner as the conventional sensor shown in FIGS. 2 and 3, and has a movable electrode when the weight portion moves due to acceleration. The sensor 11 calculates acceleration by detecting a change in electrostatic capacitance between fixed electrodes.
The sensor 11 is configured as a capacitor of the oscillation circuit 12 by catching the change in the capacitance obtained in step 1 as the oscillation frequency.

Further, the frequency divider 13 is the oscillator circuit 12 described above.
The oscillating frequency obtained in step 1 is divided into values that can be discriminated by the microcomputer 15, and the microcomputer 15
Output to.

The above-mentioned microcomputer 15 is provided with an adsorption releasing function for immediately and automatically recovering the adsorption phenomenon in which the movable electrode is adsorbed to the fixed electrode. This microcomputer 15 is supplied from the oscillation circuit 12 via the frequency divider 13. When the oscillation frequency is input and the input of the oscillation frequency is stopped, it is determined that the movable electrode serving as the sensor sensitive portion is electrically attracted to the fixed electrode and the movement of the weight portion is stopped, thereby causing an adsorption phenomenon. And when it is determined that this adsorption phenomenon occurs,
The microcomputer 15 includes a first transistor circuit T
By turning on r1 and the second transistor circuit Tr2, the charge of both electrodes in the adsorbed state is transferred to both transistor circuits Tr2.
It escapes to the ground 14 via 1 and Tr2 and instantly separates both electrodes. In addition, this microcomputer 15
Stores and corrects an error of input / output data for each circuit device.

In the capacitance-changing type semiconductor acceleration sensor 11 constructed as above, the oscillation circuit 12 normally changes the capacitance between the movable electrode and the fixed electrode when the weight portion moves due to acceleration. The frequency is output from the frequency divider 13 as the oscillation frequency, is then divided into a predetermined value, and then is input to the microcomputer 15, and the acceleration applied to the sensor 11 is obtained.

At the time of this acceleration measurement, when an attraction phenomenon occurs in which the movable electrode unexpectedly attracts the fixed electrode due to electrostatic attraction,
Based on this adsorption data, the microcomputer 15 turns on the first transistor circuit Tr1 and the second transistor circuit Tr2 to release the electric charge of both electrodes in the adsorbed state to the ground 14, and to restore the space between both electrodes as the sensor sensitive section. Immediately, the separation operation is performed to the normal separation state of several microns. After the separating operation, the microcomputer 15 turns off both the transistor circuits Tr1 and Tr2 to restart the oscillation operation which allows the movement of the movable electrode integrated with the weight portion of the sensor.

As described above, even if an adsorption phenomenon occurs on both electrodes inside the sensor incorporated in the oscillation circuit, both electrodes can be immediately returned to the normal separated state and automatically restored. As a result, the separating operation of the adsorbed electrodes does not have to be troublesome, and the sensor operation is automatically restored so that the optimum sensor operation can always be maintained, and reliable and stable sensor operation can be executed.

In the correspondence between the present invention and the configuration of the above-described embodiment, the switch circuit of the present invention is the first embodiment of the present invention.
Transistor circuit Tr1 and second transistor circuit Tr
2 and so on. Similarly, the detection circuit is the oscillation circuit 12
, And the frequency divider 13 and the microcomputer 13, and the control means corresponds to the microcomputer 15, but the present invention is not limited to the configuration of the above-described embodiment.

[Brief description of drawings]

FIG. 1 is a block diagram of a control circuit of a capacitance change type semiconductor acceleration sensor according to the present invention.

FIG. 2 is an enlarged perspective view of a main part of a conventional electrostatic capacitance change type semiconductor acceleration sensor.

FIG. 3 is a vertical cross-sectional view of a main part showing a conventional capacitance change type semiconductor acceleration sensor.

[Explanation of symbols]

 11 ... Capacitance change type semiconductor acceleration sensor 12 ... Oscillation circuit 14 ... Ground 15 ... Microcomputer Tr1, Tr2 ... Transistor circuit

Claims (1)

[Claims] 1. A capacitance-changing type semiconductor acceleration sensor for electrically detecting a change in capacitance between a movable electrode and a fixed electrode to obtain an acceleration, wherein: A switch circuit that connects each to the ground, a detection circuit that detects that the movable electrode and the fixed electrode are electrically adsorbed, and a switch circuit that is turned on when the detection circuit detects the adsorption of both electrodes. Then, a capacitance change type semiconductor acceleration sensor having a control means for connecting and controlling both electrodes to the ground.