JPH087692Y2 - Sensor signal processing circuit - Google Patents

Description

[Detailed description of the device]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a processing circuit for a signal given from a sensor or the like.

[0002]

2. Description of the Related Art Generally, an output signal of an amplifier circuit is regulated by its power supply voltage. Therefore, a signal processing circuit performs processing such as unipolarizing and amplifying the signal to greatly amplify only a necessary portion of the output signal of the sensor and accurately process it. For example, in an airbag device or the like that protects an occupant when a vehicle collides, an acceleration sensor is provided in the vehicle to inflate the airbag when the deceleration of the vehicle exceeds a predetermined value. In this device, in order to detect the deceleration of the vehicle with high accuracy, a signal processing circuit is used that amplifies a portion corresponding to acceleration and greatly amplifies a portion corresponding to deceleration in the output signal of the acceleration sensor.

FIG. 3 exemplifies a configuration of a sensor signal processing circuit as a premise of the present invention. The sensor unit 1 is, for example, an acceleration sensor, and resistors R11 to R14 forming a bridge according to the detected acceleration. The resistance value of (for example, a piezo element) is configured to change, and a voltage corresponding to the acceleration is generated between the output terminals.

Reference numeral 2 denotes a differential amplification section for amplifying the output signal of the sensor section 1, which is composed of operational amplifiers 21 and 22 and resistors R21 to R24. When the ratio of the resistance value of the resistor R22 to the resistance R21 is n times, the resistance R
The ratio of the resistance value of the resistor R24 to 23 is also set to n times. The output signal of the differential amplifier 2 is given to the inverting amplifier 3 via the capacitor C. That is, the DC component of the output signal of the differential amplifier 2 is the capacitor C.
Only the AC component included in the output signal of the differential amplifying section 2 is given to the inverting amplifying section 3.

The inverting amplification section 3 is composed of an operational amplifier 31 and resistors R31 and R32, and the output signal of the differential amplification section 2 given through the capacitor C is
It is inverted and amplified with reference to a reference voltage Vref (power supply voltage Vcc, for example, 5 V is divided by resistors R1 and R2 to be 2 V, for example). And, in the above-mentioned differential amplifier 2,
The output signal of the inverting amplifier 3 is given as its reference voltage, and when the output signal of the differential amplifier 2 increases, the output signal of the inverting amplifier 3 decreases and the output of the differential amplifier 2 increases. The negative feedback loop is formed so as to suppress the increase of the signal.

Next, the output signal of the inverting amplifier 3 is given to an offset adder 4 which is composed of an operational amplifier 41 and resistors R41 to R43. Then, the reference voltage Vref is also applied to the offset addition section 4, whereby the offset addition section 4 adds the offset voltage Vcc to the output signal from the inverting amplification section 3,
The result is inverted with reference to the reference voltage Vref. The range of the output voltage Vo of the offset addition unit 4 is 0V to the power supply voltage Vcc (for example, 5V).
Therefore, the output voltage Vo during the period in which the result of addition and inversion is negative is 0 V, and thus only the voltage corresponding to deceleration in the output signal of the acceleration sensor 1 is added to the offset addition unit. 4 and output signal from the acceleration sensor 1 is 0 (at this time, the voltage on the output side of the differential amplifier 2 and the voltage on the input side of the inverting amplifier 3 are both Vref (the example shown in FIG. 3). In this case, the resistance value of the resistors R43 and R42 is appropriately set so that the output voltage Vo output from the offset addition unit 4 becomes 0.5 V, for example, when the DC voltage is equal to 2 V). As a result, the output signal from the acceleration sensor 1 becomes 0
And the time when the output side of the offset adder 4 is disconnected.

As described above, the inverting amplification unit 3 outputs the output signal of the inverting amplification unit 3 in terms of direct current (when the output signal from the sensor 1 is 0, it becomes Vref (DC 2V in this case)).
Via the negative feedback loop as a reference voltage to the input side of the differential amplification section 2, and for AC, it amplifies the AC signal given from the differential amplification section 2. And has a function of sending it to the offset addition section 4. Then, in this case, a part of the amplified AC signal is returned to the differential amplification section 2 side through the negative feedback loop,
By forming a loop circuit between the differential amplification section 2 and the inverting amplification section 3 in this way, the CR time constant of the input impedance to the inverting amplification section 3 including the capacitor C and the resistor R31 is It is possible to make the value larger than the actual CR value of the capacitor C and the resistor R31,
The capacitor C and the resistor R31 having such small capacitance and resistance can be used.

As described above, in the circuit shown in FIG. 3, the output side of the differential amplifying section 2 and the input side of the inverting amplifying section 3 are galvanically separated by the capacitor C, and the reference voltage Vre is set.
f (here, 2 V DC) is given to the differential amplification section 2 side through the inverting amplification section 3. Therefore, the potentials of and on both ends of the capacitor C are both equal to Vref in terms of direct current. Therefore, the AC component of the signal output from the sensor unit 1 is constantly added to the capacitor C (that is, the polarity of the AC voltage applied to both ends of the capacitor C changes alternately), and Therefore, as the capacitor C, only a non-polar one can be used, and a polar capacitor (for example, a capacitor having a large capacity and a low cost such as an electrolytic capacitor or a tantalum capacitor) cannot be used. It was

Further, there is an unbalanced voltage in the sensor unit 1 itself (for example, even when there is no AC signal corresponding to acceleration, a DC voltage appears due to variations in the sensor element (resistive element)),
Further, since the operational amplifier also has an offset voltage (these DC voltages are caused by variations in the elements, and their polarities and sizes are not constant), there is a potential of several tens of mV (for example, between them) (for example, There is a potential difference of about 0.02 V). This potential difference is usually the above-mentioned capacitor C
The output signal Vo from the final stage (offset adder 4) is not affected because it is cut by, but when the capacitor C is short-circuited, this potential difference is amplified by the operational amplifier in the subsequent stage (for example, amplified to about 2V). , Will affect the output signal Vo.

In a system using such a sensor, a failure of the sensor is detected, and when the failure is detected, fail-safe is considered so as to prevent abnormal movement (for example, to prevent malfunction of the airbag). However, it is determined whether the amplified output signal is due to the output signal from the sensor unit 1 or due to a short circuit of the capacitor C (that is, if the output signal from the sensor unit causes an instantaneous change. However, in the case of a failure such as a short circuit of the capacitor, it is determined by keeping the output signal all the time), and it takes 1-2 seconds. On the other hand, in a system (for example, an airbag system) that needs to make a judgment (for example, a judgment such as a collision) within several tens of milliseconds based on the sensor signal, the judgment is made when the sensor failure is checked as described above. There is also a problem in that the time to perform is insufficient (that is, there is no time to determine whether or not the output signal is due to a failure), which may cause a malfunction of the system.

[0011]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an erroneous signal generated at the time of sensor failure (in this case, when the capacitor C is short-circuited) is sent to the sensor side as a system. The function of positively outputting in the direction that does not cause malfunction of the capacitor (that is, the output signal at the time of capacitor short circuit has a fail-safe, for example, when the output signal Vo increases due to the sensor signal at the time of collision, the capacitor C By positively lowering the output signal Vo at the time of the short circuit), it is possible to instantaneously determine whether the output signal from the sensor unit or the output signal based on the short-circuit failure of the capacitor to prevent the malfunction of the system. In addition, the polar capacitor as described above can be used as the capacitor.

[0012]

In order to solve such a problem, according to the present invention, a first operational amplifier circuit to which a sensor signal is input, and a capacitor and a resistor on the output side of the first operational amplifier circuit are provided. A sensor signal processing circuit having a second operational amplifier circuit connected via an input impedance consisting of, the output side of which is feedback-connected to the input side of the first operational amplifier circuit, A sensor signal processing circuit is provided in which a resistor is connected between an input side of the second operational amplifier circuit to which the input impedance is connected and a power supply line having a predetermined potential.

[0013]

According to the above structure, since the resistor is connected between the input side of the second operational amplifier circuit and the power supply line, the DC potential on the input side of the second operational amplifier circuit becomes A value deviating from the DC potential on the output side of the first operational amplifier circuit (that is, a state in which the DC potential on both ends of the capacitor is out of balance), and when this causes a short circuit in the capacitor, an abnormal signal is positively output. Output to the safe side (to the fail safe side). Furthermore, a polar capacitor can be used as the capacitor by handling a sensor signal in a range that does not exceed the DC potential difference between both ends of the capacitor.

[0014]

FIG. 1 shows a sensor signal processing circuit as one embodiment of the present invention, and FIG. 2 shows a sensor signal processing circuit as another embodiment of the present invention, both of which are shown in FIG.
The same reference numerals are used for the portions corresponding to the circuit of FIG. The sensor unit 1 and the offset addition unit 4 shown in FIG. 3 are not shown in FIGS. 1 and 2.

The one shown in FIG. 1 is characterized in that a resistor R33 is connected between the inverting input terminal side of the operational amplifier 31 in the inverting amplifier section 3 and the ground, while the one shown in FIG. The operational amplifier 3
A feature is that a resistor R34 is connected between the inverting input terminal side of 1 and the power supply Vcc (for example, 5 V). Thus, as will be described later, when the capacitor C is short-circuited, the output signal of the inverting amplification section 3 (output signal of the operational amplifier 31) in the embodiment shown in FIG. In the embodiment shown in FIG. 2, the output signal of the inverting amplifier 3 rises from 2V which is the normal voltage to 2.75V. Which of the embodiments is adopted depends on the fail-safe of the system that receives this signal (whether the side where the output signal Vo from the offset adder 4 increases is the safe side or the output signal Vo is
Will be decided depending on whether the side that decreases will be the safe side).

That is, in the embodiment shown in FIG. 1, the inverting input terminal side of the operational amplifier 31 functions as an adder,
In the normal time when there is no output signal from the sensor unit, the potential acts so as to be equal to Vref (1V in this case). The output side of the operational amplifier 31 has the potential Vr.
In this case it will be 2V, so that it will be equal to ef (1V). Further, since each operational amplifier of the differential amplifier 2 uses the output of the operational amplifier 31 of the inverting amplifier 3 as a reference, the potential on the output side of the differential amplifier 2 also becomes 2V. In the circuit of FIG. 1, the resistance values of the resistors R31, R32 and R33 are all set to 1 megohm, for example. By connecting the resistor R33 between the point and the ground as described above, the potential is kept at 2 V in the normal state when there is no output signal from the sensor unit, as in the case of FIG. The potential is set to 1V. In this way, a potential difference of 1 V is generated between and between both ends of the capacitor C. Therefore, if a sensor signal in a range not exceeding the AC signal of 1 V or more is handled, the capacitor C is always positive on the side, Therefore, a polar capacitor can be used. The DC potential difference (1V) existing between both ends of the capacitor C in the normal state is cut by the capacitor C and does not affect the output signal Vo side (the output voltage of the inverting amplification unit 3 is the normal voltage as described above). The output voltage Vo (offset voltage) from the offset adder 4 is set to 0.5 V, for example. However, when the capacitor C is short-circuited, it is based on the potential difference existing between both ends of the capacitor C. The current flows from this side to the side (that is, the current flowing into the side becomes twice as much as in the normal state (flows from the output side of the operational amplifier 31 and the output side (that is, side) of the operational amplifier 31), and the potential of the output side of the operational amplifier 31 becomes higher. And the Vref (1
The difference from V) is half that of normal operation, and the operational amplifier 3
The potential on the output side of 1 drops to 1.5V. At this time, the potential at the point also drops to 1.5V, and the potential at the point remains 1V. In this way, when the capacitor is short-circuited, the potential on the output side of the operational amplifier 31 decreases to 1.5V, so that the inverted output signal Vo output from the offset adder 4 rises to, for example, 2 to 3V or more. Therefore, the embodiment shown in FIG.
The side where o rises is the safe side (that is, the output signal Vo
(For example, the collision determination for the operation of the airbag is performed) by the decrease of (1).

On the other hand, in the embodiment shown in FIG. 2, the operational amplifier 3 is operated under normal conditions when there is no output signal from the sensor section.
The potential on the side of the inverting input terminal of 1 is Vref (in this case, 3.
5V). In addition, the operational amplifier 31
The output side of is also 2V so that its potential is equal to Vref (3.5V). Further, similarly to the case of FIG. 1, the potential on the output side of the differential amplifier 2 is also 2V. In the circuit of FIG. 2, the resistances of the resistors R31, R32 and R34 are all set to 1 megohm, for example. Thus, in this embodiment, the resistor R34
Is connected between the above point and the power supply Vcc (for example, 5V), the above potential is 2 V in the normal state when there is no output signal from the sensor unit.
The potential is kept at V and the above potential is set to 3.5V. Also in this case, a potential difference of 1.5 V is generated between and on both ends of the capacitor C. Therefore, if a sensor signal in a range not exceeding an AC signal equal to or more than this potential difference is handled, the capacitor C is always positive on the side. Therefore, a polar capacitor can be used.

In a normal state, as in the case of FIG. 1, the DC potential difference (1.5 V) existing between both ends of the capacitor C is cut by the capacitor C and affects the output signal Vo side. However, when the capacitor C is short-circuited, a current flows out from the side to the side based on the potential difference existing between both ends of the capacitor (that is, the current flowing out from the side is twice as much as that at the normal time (compared with the output side of the operational amplifier 31). It flows out to the output side (that is, side) of the operational amplifier 22, and the difference between the Vref (3.5 V) and the potential on the output side of the operational amplifier 31 is 1/2 of the normal state.
Therefore, the potential on the output side of the operational amplifier 31 is 2.75.
Rise to V. At this time, the potential at that point is also 2.75.
It rises to V and the potential at that point remains at 3.5V.
In this way, the potential on the output side of the operational amplifier 31 rises to 2.75 V when the capacitor is short-circuited,
Inverted output signal Vo output from the offset adder 4
Drops to almost 0V. Therefore, the embodiment shown in FIG. 2 is applied to the case where the side where the output signal Vo decreases is the safety side (that is, the collision determination for the airbag operation is performed by the increase of the output signal Vo).

In this way, when the capacitor is short-circuited, the abnormal signal is positively output to the safe side (to the fail-safe side) so that the output signal is based on the short-circuit failure of the capacitor. It is possible to make an instantaneous determination, and it is possible to reliably prevent the occurrence of a system malfunction.

[0020]

According to the present invention, the signal generated when the capacitor for cutting the DC component from the sensor signal has a short circuit failure can be positively output in a direction (fail-safe side) that does not cause the system to malfunction. In addition, a polar capacitor having a large capacity and low cost can be used as the capacitor.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a sensor signal processing circuit as one embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a sensor signal processing circuit as another embodiment of the present invention.

FIG. 3 is a diagram illustrating a configuration of a sensor signal processing circuit as a premise of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Sensor part 2 ... Differential amplification part 3 ... Inversion amplification part 4 ... Offset addition part 21, 22, 31, 41 ... Operational amplifier

Claims (1)

[Scope of utility model registration request] 1. A first operational amplifier circuit to which a sensor signal is input to one input side, and a reference voltage connected to one input side
And a second operational amplifier circuit which is the output of the first operational amplifier is connected to the other input side of said second operational amplifier circuit through an input impedance comprising a capacitor and a resistor, said The output side of the second operational amplifier circuit is the input impedance
The other input side of the second operational amplifier circuit to which the sense amplifier is connected.
To the second operation via the first resistor.
The output side of the voltage amplifying circuit other of the first operational amplifier
In the sensor signal processing circuit is fed back as a reference voltage to the input side of the square, the between the power supply line having a second input side and a predetermined potential of the second operational amplifier circuit the input impedance is connected 2 A sensor signal processing circuit , wherein the resistance of the sensor signal is connected.