JPH10239180A - Sensor circuit and adjusting method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To compensate for the temperature coefficient of sensor sensitivity without sacrificing the sensor sensitivity. SOLUTION: In the sensor circuit provided with a plurality of resistor circuits RR1, RR2 for dividing a reference voltage Vcc, a constant current source CC receiving the voltage Vref divided by the plurality of resistor circuits RR1, RR2, a sensor S having a positive temperature coefficient of sensitivity being fed with a current from the constant current source CC based on the divided voltage Vref, and a compensation resistor circuit RK to be connected in parallel with the sensor S, a least one of the plurality of resistor circuits RR1, RR2 is provided with a voltage division parallel circuit R12 comprising a voltage division variable resistor R1 having resistance variable in the increasing direction of the divided voltage Vref, and a voltage division resistor R2 connected in parallel with the voltage division variable resistor R1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensor circuit connected to sensors such as a pressure sensor and an acceleration sensor.

[0002]

2. Description of the Related Art Conventionally, as a sensor circuit of this kind, FIG.
There are the following. This is a constant current source CC composed of a plurality of voltage dividing resistors R1 and R2 for dividing the reference voltage Vcc and an operational amplifier to which the divided voltage Vref divided by the plurality of voltage dividing resistors R1 and R2 is input. A sensor S of a resistance circuit supplied from the constant current source CC based on the divided voltage Vref and having a positive temperature coefficient of sensitivity, and a compensating resistor R3 connected in parallel to the sensor S.

[0003]

In the above-mentioned conventional sensor circuit, even if the resistance value of the sensor S increases with the temperature and the sensor sensitivity increases, the resistance value of the sensor S increases. Accordingly, a current flows through the compensating resistor R3 connected in parallel to the sensor S, so that the current flowing through the sensor S decreases, so that a change in sensor sensitivity due to a temperature rise can be compensated. By changing the resistance value of the resistor R3, the current flowing through the sensor S can be adjusted according to the sensitivity temperature coefficient of the sensor S.

However, when the resistance value of the compensating resistor R3 is small, the resistance value of the parallel circuit RS including the compensating resistor R3 and the sensor S decreases, and both ends of the parallel circuit RS which is the output voltage of the sensor S are reduced. There has been a problem that the voltage is reduced and the sensor sensitivity is reduced.

The present invention has been made in view of the above points, and an object of the present invention is to provide a sensor circuit capable of compensating a temperature coefficient of sensitivity of a sensor without lowering the sensitivity of the sensor, and an adjustment thereof. It is to provide a method.

[0006]

In order to solve the above-mentioned problems, the invention according to the first aspect of the present invention comprises a plurality of voltage dividing resistor circuits for dividing a reference voltage and a plurality of voltage dividing resistor circuits. A constant current source to which the divided voltage is input, a sensor fed from the constant current source based on the divided voltage and having a sensitivity temperature coefficient of a positive sign, and a compensation resistor circuit that can be connected in parallel to the sensor, In at least one of the plurality of voltage dividing resistor circuits, the voltage dividing variable resistor whose resistance value can change in the increasing direction of the divided voltage and a voltage dividing resistor connected in parallel to the voltage dividing variable resistor are provided. The configuration is such that a voltage-dividing parallel circuit composed of a voltage resistor is provided.

According to a second aspect of the present invention, in the first aspect of the present invention, the resistance value of the grounding variable resistor can change in an increasing direction, and the grounding variable resistor has a film shape. The configuration is made up of resistors.

According to a third aspect of the present invention, there is provided an operational amplifier for inputting an input voltage to a non-inverting input terminal, and a sensor connected between an output terminal and an inverting input terminal of the operational amplifier and having a positive temperature coefficient of sensitivity. A grounding resistor circuit connected between the inverting input terminal of the operational amplifier and the ground, and a compensating resistor circuit that can be connected in parallel to the sensor, wherein the grounding resistor circuit has a resistance value of A grounding parallel circuit including a grounding variable resistor that can change in the increasing direction and a grounding resistor connected in parallel to the grounding variable resistor is provided.

According to a fourth aspect of the present invention, in the second aspect of the invention, the grounding variable resistor is formed of a film resistor.

According to a fifth aspect of the present invention, there is provided an adjusting method, comprising: a plurality of voltage dividing resistor circuits for dividing a reference voltage; and a constant current source to which the divided voltage divided by the plurality of voltage dividing resistor circuits is input. And a sensor fed from a constant current source based on the divided voltage and having a sensitivity temperature coefficient of a positive sign, and a compensating resistor circuit that can be connected in parallel to the sensor, and at least one of the plurality of voltage dividing resistor circuits. One is provided with a voltage-dividing parallel circuit including a voltage-dividing variable resistor made of a film-like resistor whose resistance value can change in the direction in which the divided voltage increases and a voltage-dividing resistor connected in parallel to the voltage-dividing variable resistor. And adjusting the resistance value of the voltage dividing variable resistor by trimming.

According to a sixth aspect of the present invention, there is provided an adjustment method, comprising: an operational amplifier for inputting an input voltage to a non-inverting input terminal; and a positive temperature coefficient of sensitivity connected between the output terminal and the inverting input terminal of the operational amplifier. And a grounded resistor circuit connected between the inverting input terminal of the operational amplifier and the ground,
A compensating resistance circuit that can be connected in parallel to the sensor,
The grounding resistance circuit is a method for adjusting a sensor circuit provided with a grounding parallel circuit including a grounding variable resistor whose resistance value can change in an increasing direction and a grounding resistor connected in parallel to the grounding variable resistor. Thus, the resistance value of the ground variable resistor is changed by trimming.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIG. This sensor circuit comprises sensors S,
Compensation resistance circuit RK, operational amplifier Op, first voltage division resistance circuit RR1, second voltage division resistance circuit RR2, grounding resistance circuit RR
3 is configured.

The sensor S includes first to fourth piezoresistors r.
This is a bridge circuit consisting of 1, r2, r3, r4. This sensor S
Detects a physical change due to pressure, acceleration, or the like as a change in resistance value. The sensor S includes a connection point between the first and second piezoresistors r1, r2 and a third and fourth piezoresistors r3, r
4, a compensating resistor circuit RK is connected in parallel to form a parallel circuit 10. The compensation resistance circuit RK is a so-called film resistance which is a film resistance.
Even if the sensitivity temperature coefficient of the sensor S has the maximum possible value, it has a small resistance value capable of compensating the temperature characteristic of the sensitivity of the sensor S.

The operational amplifier Op is used as a constant current source CC and has a non-inverting input terminal connected to a reference voltage V.
The divided voltage Vref obtained by dividing cc by the first and second voltage dividing resistance circuits RR1 and RR2 is input. This operational amplifier Op
Has an inverted input terminal connected to the connection point of the second and third piezoresistors r2 and r3 of the sensor S, and an output terminal connected to the sensor S
Are connected to the connection point of the first and fourth piezoresistors r1 and r4. Therefore, the operational amplifier Op supplies power to the sensor S according to the input divided voltage Vref.

The second voltage-dividing resistor circuit RR2 includes a voltage-dividing variable resistor R1 composed of a so-called thick film resistor and a voltage-dividing parallel circuit composed of a voltage-dividing resistor R2 connected in parallel with the voltage-dividing variable resistor R1. The circuit is R12. As will be described in detail later, the resistance value of the voltage dividing variable resistor R1 increases due to trimming. That is, the divided voltage Vre of the operational amplifier Op
The resistance value changes in the increasing direction of f.

One end of the ground resistance circuit RR3 has a sensor S
Is connected to the connection point of the second and third piezo resistors r2 and r3, and is connected between the inverting input terminal of the operational amplifier Op and the ground.

Next, an adjustment procedure for compensating the temperature characteristic of the sensor sensitivity will be described. First, the sensitivity temperature coefficient of the sensor S is measured, and based on the measurement result, the resistance value of the compensation resistor circuit RK that can compensate for the temperature characteristics of the sensor sensitivity is calculated. Next, as shown in FIG. 2 (a), the compensation resistor circuit RK bridged between the conductors X is partially cut out along the lateral direction by laser trimming as shown in FIG. 2 (b). By increasing the resistance value of the compensating resistance circuit RK, the value is adjusted to the above-described calculated value. The resistance value of the voltage dividing resistor R2 for obtaining the maximum output value Voutmax of the operational amplifier Op and the initial resistance value of the voltage dividing variable resistor R2 will be described later in detail. Next, by increasing the resistance value of the voltage dividing variable resistor R2 by laser trimming in the same manner as when increasing the resistance value of the compensation resistance circuit RK,
Increase the divided voltage Vref. Thus, the voltage across the parallel circuit 10, which is the voltage across the sensor S, is adjusted to be the maximum output value Voutmax that can be output from the operational amplifier Op.

When the measured temperature coefficient of sensitivity is substantially zero or has a negative sign, the compensation resistor circuit bridged between the conductors X as shown in FIG. The RK is cut along the lateral direction by laser trimming as shown in FIG. When the temperature coefficient of sensitivity has the maximum possible value, the resistance value of the compensation resistance circuit RK is kept as it is, and the voltage division for the voltage division is performed in the same manner as when the compensation resistance circuit RK is disconnected. Disconnect the variable resistor R2.

Next, the maximum output value Voutmax of the operational amplifier Op
The resistance value of the voltage dividing resistor R2 for obtaining the following will be described.
The resistance value of the voltage dividing resistor R2 is set to a value satisfying the expression (1). Note that the resistance value of the first voltage dividing resistor circuit RR1 is R
₁ , the resistance value of the voltage dividing resistor R2 is R ₂ , the resistance value of the compensation resistance circuit RK is R ₃ , and the resistance value of the sensor S is R ₄ .

Voutmax = Vcc × R ₂ × R ₄ / (R ₃ × (R ₁ + R ₂ )) (1) Next, the initial resistance value of the voltage dividing variable resistor R 1 will be described. The initial resistance value of the voltage dividing variable resistor R1 is set to a value that satisfies the expression (2). Note that the initial resistance value of dividing the variable resistor R1 and the R _5.

Voutmax = Vcc × R ₂ × R ₅ × R ₄ / ((R ₁ × (R ₂ + R ₅ )) + R ₂ × R ₅ ) × R ₃ ) (2) In such a sensor circuit, By increasing the resistance value of the variable resistor R1 for voltage division, the divided voltage Vref is increased, so that the current value to the sensor S fed from the operational amplifier Op is increased based on the divided voltage Vref, and the compensation resistor circuit RK has a small resistance value and a compensation resistor circuit RK and sensor
Even if the resistance of the parallel circuit 10 composed of S decreases, the sensor S
The output voltage Vout of the parallel circuit 10 does not decrease. Therefore, the sensitivity temperature coefficient of the sensor S can be compensated without lowering the sensor sensitivity.

Further, a voltage dividing variable resistor R1 composed of a film resistor is used.
Since the resistance value is increased by trimming, the work of increasing the resistance value is not required.

Next, a second embodiment of the present invention will be described below with reference to FIG. Note that elements having substantially the same functions as those in the first embodiment are denoted by the same reference numerals, and only differences from the first embodiment will be described. In the first embodiment, the parallel circuit including the variable resistor whose resistance value can change in the increasing direction of the divided voltage Vref and the resistor connected in parallel to the variable resistor is the first voltage dividing resistor circuit RR1. In the present embodiment, the configuration is a ground resistance circuit RR3.

More specifically, the grounding resistor circuit RR3 is a grounding parallel circuit R34 comprising a grounding variable resistor R3 made of a thick film resistor and a grounding parallel connection resistor R4 connected in parallel to the grounding variable resistor R3. I have. The resistance value of the grounding variable resistor R3 increases by trimming, similarly to the voltage dividing variable resistor R1. That is, the resistance value changes in the increasing direction of the divided voltage Vref of the operational amplifier Op.

The adjustment procedure for compensating the temperature characteristic of the sensor sensitivity is performed in the same manner as in the first embodiment.
First, the sensitivity temperature coefficient of the sensor S is measured, and based on the measurement result, the resistance value of the compensation resistor circuit RK that can compensate for the temperature characteristics of the sensor sensitivity is calculated. Next, the compensation resistor circuit
The resistance value of RK is adjusted to the above-mentioned calculated value by increasing by laser trimming. Next, the divided voltage Vref is increased by increasing the resistance value of the voltage dividing variable resistor R2 by laser trimming in the same manner as when increasing the resistance value of the compensation resistance circuit RK. Thus, the voltage across the parallel circuit 10, which is the voltage across the sensor S, is adjusted to be the maximum output value Voutmax that can be output from the operational amplifier Op.

When the measured temperature coefficient of sensitivity is substantially zero or has a negative sign, the compensation resistor circuit
RK is disconnected by laser trimming. If the sensitivity temperature coefficient has the maximum possible value, the resistance value of the compensation resistance circuit RK is left as it is, and the voltage dividing variable resistor R2 is disconnected.

In such a sensor circuit, the divided voltage V is increased by increasing the resistance of the grounding variable resistor R3.
Since ref increases, the current value to the sensor S supplied from the operational amplifier Op increases based on the divided voltage Vref, and the resistance value of the compensation resistance circuit RK is small, and the compensation resistance circuit RK includes the compensation resistance circuit RK and the sensor S. Even if the resistance value of the parallel circuit 10 decreases, the voltage across the parallel circuit 10, which is the output voltage Vout of the sensor S, does not decrease. Therefore, the sensitivity temperature coefficient of the sensor S can be compensated without lowering the sensor sensitivity.

A grounding variable resistor R1 composed of a film resistor
Since the resistance value is increased by trimming, the work of increasing the resistance value is not required.

In the first and second embodiments, each of the voltage dividing variable resistor R1 and the grounding variable resistor RR3 is a thick film resistor. However, for example, when the resistance value can be easily increased. May not be a thick film resistor.

In the first embodiment, the divided voltage Vre is increased by increasing the resistance value of the variable resistor R1 for voltage division of the parallel circuit 12 for voltage division which is the second resistance circuit for voltage division RR2.
Although f is configured to increase, the first voltage-dividing resistor circuit RR1 includes a voltage-dividing variable resistor whose resistance value can change in a decreasing direction and a voltage-dividing resistor connected in parallel with the voltage-dividing variable resistor. By providing a parallel circuit for voltage division,
The configuration may be such that the divided voltage Vref increases.

In the first embodiment, the divided voltage V is increased by increasing the resistance value of the variable voltage dividing resistor R1 of the voltage dividing parallel circuit R12 which is the second voltage dividing resistor circuit RR2.
Although ref is increased, the first voltage-dividing resistor circuit RR1 also includes a voltage-dividing variable resistor having a variable resistance value and a voltage-dividing resistor connected in parallel to the voltage-dividing variable resistor. A parallel circuit is provided, and first and second voltage dividing resistors RR are provided.
1, the divided voltage Vref may be increased by appropriately changing the resistance values of the variable resistors for voltage division provided in RR2.

In the first embodiment, the reference voltage Vcc
Is divided by two voltage dividing resistance circuits RR1 and RR, but the number of voltage dividing resistance circuits is not limited to two.

Further, in the first embodiment, the constant current source CC
Although it is the operational amplifier Op, it need not be the operational amplifier Op.

In the first embodiment, the second voltage-dividing resistor circuit RR2 itself is a voltage-dividing parallel circuit R12. However, as a part of the second voltage-dividing resistor circuit RR2, May be provided.

In the second embodiment, the resistance circuit for grounding is used.
RR3 itself is the grounding parallel circuit R34,
A grounding parallel circuit 34 may be provided as a part of the grounding resistance circuit RR2.

[0036]

According to the first aspect of the present invention, by changing the resistance value of the variable resistor for voltage division in the direction of increasing the divided voltage, the current supplied to the sensor from the constant current source based on the divided voltage is supplied to the sensor. Since the resistance value of the compensating resistor circuit is small because the value increases, even if the resistance value of the parallel circuit including the compensating resistor circuit and the sensor decreases, the voltage across the parallel circuit, which is the output voltage of the sensor, decreases. Never. Therefore, the sensitivity temperature coefficient of the sensor can be compensated without lowering the sensor sensitivity.

According to a second aspect of the present invention, in addition to the effect of the first aspect of the present invention, the voltage dividing variable resistor composed of a film-shaped resistor increases the resistance value by trimming. No more hassle.

According to the third aspect of the present invention, since the divided voltage is increased by increasing the resistance value of the grounding variable resistor, the current value to the sensor fed from the constant current source based on the divided voltage is increased. Even if the resistance value of the compensation resistor circuit is small and the resistance value of the parallel circuit composed of the compensation resistor circuit and the sensor is reduced, the voltage across the parallel circuit, which is the output voltage of the sensor, will not decrease. Absent. Therefore, the sensitivity temperature coefficient of the sensor can be compensated without lowering the sensor sensitivity.

According to a fourth aspect of the present invention, in addition to the effects of the third aspect of the present invention, the resistance value of the grounding variable resistor formed of a film-shaped resistor is increased by trimming. No more hassle.

According to the adjusting method of the invention described in claim 5,
By changing the resistance value of the variable resistor for voltage division in the increasing direction by trimming, the divided voltage increases, so the current value to the sensor supplied from the constant current source based on the divided voltage increases, and the compensation voltage increases. Even if the resistance value of the resistance circuit is small and the resistance value of the parallel circuit including the compensation resistance circuit and the sensor decreases, the voltage across the parallel circuit, which is the output voltage of the sensor, does not decrease. Therefore, the sensitivity temperature coefficient of the sensor can be compensated without lowering the sensor sensitivity.
Since the resistance value is increased by trimming, the work of increasing the resistance value is not required.

According to the adjusting method of the invention described in claim 6,
Since the divided voltage is increased by changing the resistance value of the grounding variable resistor in the increasing direction by trimming, the current value to the sensor supplied from the constant current source based on the divided voltage is increased, and the compensation voltage is increased. Even if the resistance value of the resistance circuit is small and the resistance value of the parallel circuit including the compensation resistance circuit and the sensor decreases, the voltage across the parallel circuit, which is the output voltage of the sensor, does not decrease. Therefore, the sensitivity temperature coefficient of the sensor can be compensated without lowering the sensor sensitivity.
Since the resistance value is increased by trimming, the work of increasing the resistance value is not required.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a first embodiment of the present invention.

FIG. 2 is a plan view showing a state in which the resistance value of the compensating resistor is increased.

FIG. 3 is a plan view showing a state in which the compensating resistor is disconnected.

FIG. 4 is a circuit diagram of a second embodiment of the present invention.

FIG. 5 is a circuit diagram of a conventional example.

[Explanation of symbols]

 S Sensor Op Operational amplifier CC Constant current source R1 Variable resistor for voltage divider R2 Variable resistor for voltage divider R3 Variable resistor for ground R4 Ground resistor RK Compensation resistor circuit RR1 First voltage divider resistor circuit RR2 Second voltage divider resistor circuit RR3 Ground resistor Circuit R12 Parallel circuit for voltage division R34 Parallel circuit for grounding Vcc Reference voltage Vref Voltage division

Claims (6)

[Claims] A plurality of voltage dividing resistor circuits for dividing a reference voltage, a constant current source to which a divided voltage divided by the plurality of voltage dividing resistor circuits is input, and a constant current source based on the divided voltage. A sensor circuit comprising: a sensor supplied from a current source and having a positive-sign sensitivity temperature coefficient; and a compensating resistor circuit that can be connected in parallel to the sensor, wherein at least one of the plurality of voltage dividing resistor circuits is A sensor circuit comprising: a variable resistor for voltage division whose resistance value can change in a direction of increasing the divided voltage; and a parallel circuit for voltage division comprising a voltage dividing resistor connected in parallel to the variable resistor for voltage division. 2. The sensor according to claim 1, wherein the resistance value of the grounding variable resistor can change in an increasing direction, and the grounding variable resistor is formed of a film resistance. circuit. 3. An operational amplifier for inputting an input voltage to a non-inverting input terminal, a sensor connected between an output terminal and an inverting input terminal of the operational amplifier and having a positive temperature coefficient of sensitivity, and an inverting input terminal of the operational amplifier. And a compensation resistor circuit that can be connected in parallel to the sensor, wherein the ground resistor circuit has a resistance value that can change in an increasing direction. A sensor circuit, comprising: a grounding parallel circuit including a grounding variable resistor and a grounding resistor connected in parallel to the grounding variable resistor. 4. The sensor circuit according to claim 2, wherein said grounding variable resistor comprises a film-shaped resistor. 5. A plurality of voltage dividing resistor circuits for dividing a reference voltage, a constant current source to which the divided voltage divided by the plurality of voltage dividing resistor circuits is input, and a constant current source based on the divided voltage. A sensor having a sensitivity temperature coefficient of a positive sign supplied from a current source, and a compensating resistor circuit which can be connected in parallel to the sensor; at least one of the plurality of voltage dividing resistor circuits has a A method of adjusting a sensor circuit provided with a voltage-dividing variable resistor made of a film-like resistor whose resistance value can change in an increasing direction and a voltage-dividing parallel circuit including a voltage-dividing resistor connected in parallel to the voltage-dividing variable resistor. And adjusting the resistance value of the variable resistor for voltage division by trimming. 6. An operational amplifier for inputting an input voltage to a non-inverting input terminal, a sensor connected between an output terminal of the operational amplifier and an inverting input terminal and having a positive temperature coefficient of sensitivity;
A grounding resistor circuit connected between the inverting input terminal of the operational amplifier and ground; and a compensating resistor circuit that can be connected in parallel to the sensor, wherein the grounding resistor circuit has a ground whose resistance value can change in an increasing direction. A method of adjusting a sensor circuit provided with a grounding parallel circuit comprising a grounding variable resistor and a grounding resistor connected in parallel to the grounding variable resistor, wherein the resistance value of the grounding variable resistor is changed by trimming. A method for adjusting a sensor circuit, comprising: