JPH05249141A - Failure detection circuit of semiconductor acceleration sensor - Google Patents

Abstract

PURPOSE:To obtain a failure detection circuit of a semiconductor acceleration sensor which can positively detect failure by connecting the output of an acceleration signal to the ground positively when a beam part of the semiconductor acceleration sensor is damaged. CONSTITUTION:In a semiconductor acceleration sensor, a semiconductor substrate is formed by supporting a movable part 2 at the center using a beam part 3 with elasticity for a surrounding support part 1 by etching, a strain gauge 4 is provided at the beam part 3, a bridge circuit 7 is formed by resistors R1 and R2 by utilizing the strain gauge 4, and then the output of the bridge circuit 7 is taken out as an acceleration signal through an amplification circuit. Then. the resistors R1 and R2 for compensating temperature are provided between the bridge circuit 7 and the amplification circuit, the resistors are connected to a comparator CO1 through diodes D1 and D2, and then the comparator CO1 is connected to the output side of the amplification circuit. thus abnormally increasing voltage at the input side of the amplification circuit by the provision of the resistors for compensating temperature when the beam part 3 is damaged and there is no signal from the bridge circuit 7 and forcing the output of the amplification circuit to be connected to the ground level by detection using the comparator CO1.

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 example, for detecting the acceleration of an automobile, and for detecting the disconnection due to breakage of a beam portion constituting the sensor. The invention relates to a failure detection circuit for a semiconductor acceleration sensor.

[0002]

2. Description of the Related Art As shown in FIG. 2, the above-mentioned semiconductor acceleration sensor has a supporting portion 1 around which a semiconductor substrate is etched.
On the other hand, the central movable portion 2 is formed by being supported by the beam portion 3 having elasticity, and when the movable portion 2 is displaced by acceleration, the beam portion 3 is formed.
Is distorted, strain gauges 4 ... Are formed on the beam portion 3, and the strain amount is taken out by the strain gauges 4 ... In the figure, reference numerals 5 and 6 denote upper and lower plates, which protect the support part 1, the movable part 2 and the beam part 3 described above, but do not hinder the movement of the movable part 2 and the beam part 3.

As shown in FIG. 3, a circuit for extracting the strain amount of the strain gauges 4 ... As an acceleration signal forms a bridge circuit 7 by the above-mentioned four strain gauges 4 ... The output signal is the operational amplifier OP1, OP2, OP
The output amplified in 3 is used as the acceleration signal. The resistors R1 and R2 are for temperature compensation, and either one of them is provided.

The semiconductor acceleration sensor constructed as described above has the advantages of being lightweight and small in size, but has a problem of being vulnerable to an impact, and the beam 3 may be damaged when an impact is applied. When the beam portion 3 is damaged in this way, the strain gauge 4
... and its wiring are cut, so normally V of the acceleration signal
Although the cc level is designed to drop to the GND level, if the internal voltages of the operational amplifiers OP1, OP2, and OP3 described above are delicately balanced, the output will be balanced between the Vcc level and the GND level to output a signal. Output, G
It may happen that the ND level does not fall. In such a case, since the semiconductor acceleration sensor outputs an acceleration signal, even if the beam 3 is damaged and fails as described above, the failure is not noticed. ..

[0005]

SUMMARY OF THE INVENTION According to the present invention, when a beam portion of a semiconductor acceleration sensor is damaged, the output of an acceleration signal surely drops to GND, and the failure can be reliably detected. The purpose of the present invention is to provide a failure detection circuit.

[0006]

A semiconductor substrate is formed by etching with a beam portion having elasticity supporting a central movable portion with respect to a surrounding support portion, and a strain gauge is provided on the beam portion. A semiconductor acceleration sensor in which a gauge is used to form a bridge circuit with a resistor, and the output of this bridge circuit is taken out as an acceleration signal via an amplifier circuit. When the bridge circuit is damaged, A circuit for outputting a high voltage is provided on the input side of the amplifier circuit, the circuit is connected to a comparator via a diode, and the comparator compares with a reference value,
This comparison output is a failure detection circuit for a semiconductor acceleration sensor, which is connected to the output side of the amplifier circuit.

[0007]

The failure detecting circuit for a semiconductor acceleration sensor according to the present invention is a circuit for outputting a voltage higher than that in a normal state of the bridge circuit. For example, when a resistor for temperature compensation is interposed between the bridge circuit and the amplifier circuit, Is damaged and strain gauge 4
.. and its wiring are disconnected, the output of the bridge circuit output terminal on the side where the temperature compensating resistor is interposed becomes several tens of times higher than the output of the normal acceleration signal, so the comparator outputs this abnormal output. When detected, the output of this comparator becomes GND level, and when this is connected to the output side of the amplifier circuit that amplifies the output of the bridge circuit, the output of the amplifier circuit is forcibly dropped to the GND level, and as a result, the semiconductor acceleration sensor If the beam part of the sensor is damaged, the output of the sensor will be GN
It becomes D level, and the failure can be detected when it becomes GND level.

[0008]

As a result of the above, according to the present invention, even if the bridge circuit constituted by the strain gauge of the semiconductor acceleration sensor fails and the voltage is balanced inside the amplifier circuit, Since this can be surely lowered to the GND level, the failure can be surely detected, and an erroneous acceleration signal can be prevented from being output.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the drawings. The drawing shows a semiconductor acceleration sensor, and the configuration of this semiconductor acceleration sensor is configured as shown in FIG. 2, so a detailed description thereof will be omitted.

FIG. 1 shows a circuit structure of a semiconductor acceleration sensor, and parts having the same functions as those of the circuit structure shown in FIG. 3 are designated by the same reference numerals. That is, the strain cage 4
Form a bridge circuit 7, and either one of the resistors R1 and R2 for temperature compensation is interposed. Further, the output terminals 8 and 9 of the above-mentioned bridge circuit 7 are input to the plus side terminals of the corresponding operational amplifiers OP1 and OP2, respectively.
These output terminals 8 and 9 are diodes D1 and D, respectively.
2 is input to the negative side terminal of the comparator CO1 and the reference voltage set by dividing Vcc by the resistors R3 and R4 is input to the positive side terminal of the comparator CO1. Operational amplifier O
It is connected to the output side of P3.

The reference voltage of the above-mentioned comparator CO1 is set to be larger than the value for detecting the acceleration signal. For example, when this acceleration sensor targets 1 G or less, the above-mentioned bridge circuit is caused by a change in acceleration equivalent to 1 G. If the output difference between the output terminals 8 and 9 of 7 is about 10 mV, the reference voltage is set to be larger than this.

For example, when the temperature compensating resistor R1 side is connected and the beam portion 3 (see FIG. 2) of the acceleration sensor is damaged in this state, the strain gauges 4 ... (See FIG. 2) and their wiring are cut. Then, the input side of the operational amplifier OP1 is the resistor R1.
Is present, the voltage is pulled to the Vcc side and the voltage rises to several tens of times of the normal level (about 10 mV described above), while the other operational amplifier OP2 input side floats in the air (assuming that the resistor R2 is not connected). Eventually, it becomes the GND level.

Since a high voltage is input to the above-mentioned comparator CO1 via the diode D1, the output of this comparator CO1 becomes the GND level when this voltage is higher than the reference voltage, and the output of the operational amplifier OP3 at the final stage. Is forced to drop to the GND level, and even if the voltage becomes unstable inside each of the operational amplifiers OP1, OP2, OP3, the acceleration signal is not erroneously output.

When the temperature compensating resistor 2 side is used, the input side of the operational amplifier OP2 has a high voltage and the input side of the operational amplifier OP1 has the GND level, so that the same operation as described above is performed.

As described above, according to the above-described embodiment, the bridge circuit 7 constituted by the strain gauges 4 of the semiconductor acceleration sensor fails, and the operational amplifiers OP1, OP2, O are provided.
Even if the voltage is balanced inside P3, it can be surely dropped to the GND level by the output of the comparator CO1, so that the failure can be surely detected and an erroneous acceleration signal can be output. It can be prevented.

In the correspondence between the configuration of the present invention and the embodiment, the amplifier circuit of the present invention corresponds to the operational amplifiers OP1, OP2 and OP3 of the embodiment. Similarly, when the bridge circuit is damaged, the bridge circuit The circuit that outputs a higher voltage than the normal state is the resistors R1 and R2 for temperature compensation.
However, the present invention is not limited to the configuration of the embodiment.

[Brief description of drawings]

FIG. 1 is a failure detection circuit diagram of a semiconductor acceleration sensor.

FIG. 2 is a perspective view of a partially cutaway external view of a semiconductor acceleration sensor.

FIG. 3 is a circuit diagram of a conventional semiconductor acceleration sensor.

[Explanation of symbols]

 1 ... Supporting part 2 ... Movable part 3 ... Beam part 4 ... Strain gauge 7 ... Bridge circuit OP1, OP2, OP3 ... Operational amplifier R1, R2 ... Resistor D1, D2 ... Diode CO1 ... Comparator

Claims (1)

[Claims] 1. A semiconductor substrate is formed by etching with a beam portion having elasticity supporting a central movable portion with respect to a surrounding support portion, and a strain gauge is provided on the beam portion, and the strain gauge is used. A semiconductor acceleration sensor that forms a bridge circuit with a resistor and outputs the output of this bridge circuit as an acceleration signal via an amplifier circuit, and when the bridge circuit is damaged, outputs a voltage higher than that of the bridge circuit under normal conditions. A semiconductor device in which the circuit for connecting to the input side of the amplifier circuit is connected to the comparator via a diode, the comparator is compared with a reference value, and the comparison output is connected to the output side of the amplifier circuit. Accelerometer failure detection circuit.