JPH0534224A - Transducer circuit and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a highly accurate output by simple adjustment and to obtain a large dynamic range with a low-cost circuit constitution. CONSTITUTION:A sensor 12, wherein the resistance value is changed in response to the change in an object to be measured, is provided. An offset adjusting resistor 32 adjusts the offset potential of the output of a circuit. Operational amplifiers 20 and 22 amplify the outputs of the above described sensor 12. A span adjusting resistor 40 adjusts the amplification factor of the operational amplifier 22 in conformity with the measuring range. These parts are provided. The output of the sensor 12 is connected to the side of the non-inverted input of the operational amplifier 20. The offset adjusting resistor 32 is connected to the side of the inverted input of the operational amplifier 20. Under the reference state when the offset adjusting resistor 32 is adjusted, the adjustment is performed so that the output voltage value of the sensor 12 becomes approximately equal to the output voltage of the above described amplifier 22.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transducer for converting a mechanical quantity into an electric signal and taking it out, and a method for manufacturing the transducer.

[0002]

2. Description of the Related Art Conventionally, for example, a circuit used for a pressure sensor has a diffused resistor on a sensor chip 1 composed of a semiconductor diaphragm, as disclosed in Japanese Patent Laid-Open No. 61-77735 and FIG. To form a bridge,
The sensor chip 1 is deformed by pressure and the output voltage is changed by changing the resistance value of the resistor, the sensor power source 3 connected to the sensor 2, the plurality of operational amplifiers 4,
It includes a span adjustment (amplification degree adjustment) resistor 5, an offset adjustment resistor 6, and the like.

In the adjustment during the assembly of this circuit, normally, the offset voltage is adjusted to 0 V by operating the offset adjusting resistor 6 at atmospheric pressure. Next, the span adjustment resistor 5 is moved to match the predetermined span with the measurement range. At this time, since the offset voltage fluctuates due to the span adjustment, the offset adjusting resistor 6 is adjusted again, and further, the span voltage moves due to the offset voltage adjusting. Therefore, the span adjusting resistor 5 is further moved to perform the adjustment. . Then, this was repeated to gradually adjust to a predetermined position. Then, this resistance value adjustment has been performed by function trimming of a variable resistor or a resistor.

[0004]

In the case of the above-mentioned conventional technique, the circuit adjustment requires two kinds of adjustments, that is, the zero point or offset adjustment and the span adjustment which is the amplification degree adjustment as described above. For such measurements, adjustment by the asymptotic method as described above was indispensable. However, the number of adjustments cannot be increased indefinitely, and the above-mentioned adjustment has a problem that it is difficult to obtain a highly accurate circuit. Furthermore, fine adjustment of the variable resistor is difficult. On the other hand, in the case of function trimming, there is a contradictory problem that the number of defective products increases and the number of adjustments increases if the trimming amount is small unless the trimming amount is made small, since it is not possible to reverse. In addition, since the adjustment is delicate and complicated, it is difficult to automate the adjustment process, and the cost is high.

The present invention has been made in view of the above-mentioned problems of the prior art, and an accurate output can be obtained by a simple adjustment.
It is an object of the present invention to provide a transducer circuit which can have a large dynamic range with an inexpensive circuit configuration and a manufacturing method thereof.

[0006]

According to the present invention, there is provided a sensor having a resistance value fluctuating in response to a change of an object to be measured, and an offset adjusting resistor for adjusting an offset potential of an output of this circuit, and the sensor. An operational amplifier for amplifying the output of
A span adjustment resistor for adjusting the amplification degree of this operational amplifier is provided according to the measurement range, the output of the sensor is connected to the non-inverting input side of the operational amplifier, and the offset adjustment resistor is connected to the inverting input of the operational amplifier. The output voltage value of the sensor and the output voltage value of the operational amplifier to which the span adjustment resistor is connected are adjusted to be substantially equal in the reference state when the offset adjustment resistor is adjusted. It is a transducer circuit.

Further, according to the present invention, an offset adjusting resistor for adjusting the offset potential of this circuit is mounted with a sensor having a resistance value which fluctuates according to the change of the object to be measured, and an amplifier for amplifying the output voltage of the sensor. , A span adjustment resistor for adjusting the amplification degree of this amplifier is provided according to the measurement range, and the offset adjustment resistor is adjusted so that the output voltage value of the sensor and the output voltage value of the amplifier become substantially equal. After the setting, it is a method of manufacturing a transducer circuit in which the span adjustment resistor is adjusted to set a predetermined amplification degree.

[0008]

In the transducer circuit of the present invention, the output voltage of the sensor and the output voltage of the amplifier of this circuit are adjusted to be substantially equal in a predetermined state, so that the offset potential does not change even if the span adjustment is performed. .

[0009]

Embodiments of the present invention will be described below with reference to the drawings. 1, 2 and 3 show a first embodiment of the present invention, the transducer circuit of this embodiment is
This is a circuit for a pressure sensor, and as shown in FIG. 1, a sensor chip 12 is connected in series to a sensor power supply 10. This sensor chip 12 has resistors 13, 14, 1 whose resistance value changes with pressure in a bridge shape on the surface of the semiconductor chip.
5 and 16 are formed. This sensor chip 1
The two output terminals 17 and 18 are connected to the non-inverting input terminals of the operational amplifiers 20 and 22, respectively.

A power supply terminal 24, an output terminal 26, and a ground terminal 28, which are connected to an external circuit, are formed in this circuit. The power supply terminal 24 has a resistor 30, a variable resistor 32, and a resistor. 34 are connected in series, and the resistor 34
Is connected to the ground terminal 28. The slider of the variable resistor 32 is connected to the inverting input terminal of the operational amplifier 20 via the resistor 36. A resistor 38 is connected to the operational amplifier 20, and its output is output via the variable resistor 40 and the temperature sensitive resistor 45 connected in series to the output terminal 26.
It is connected to the. The intersection of the variable resistor 40 and the temperature sensitive resistor 45 is connected to the inverting input terminal of the operational amplifier 22, and the output of the operational amplifier 22 is connected to the output terminal 26 together with the temperature sensitive resistor 45. Operational amplifier 20, 22
Together form a non-inverting amplifier circuit.

Regarding the sensor chip 12 of this embodiment,
It will be described in detail with reference to FIG. Sensor chip 1 of this embodiment
2 is a diffusion resistor 13, 14, on the surface of the semiconductor chip,
15 and 16 are formed, and are provided so that pressure is applied to the semiconductor surface and each resistor is deformed to change the resistance value. Although the resistance values of the resistors 13, 14, 15 and 16 are formed to be substantially equal to each other, a slight error remains, so that the output of the output terminals 17 and 18 becomes equal in the reference state. , 42, 43, 44 are provided in the same step as the above resistors. This resistor 41
The resistance values of ~ 44 are smaller than those of the resistor 13 and the like by about 2 to 3 digits. The resistors 41 to 44 are arranged so that, when the constant current source 10 and the sensor chip 12 are connected to each other, the potentials of the output terminals 17 and 18 become equal in a predetermined reference state, for example, in an unloaded state. Any of the terminals ~ 44 are selected and connected by wire bonding.

A resistor 46 is connected in parallel with the resistor 16 assembled in the bridge. The resistor 46 has a resistance value of about two digits larger than that of the resistor 16 and has a temperature coefficient of 100 PPm / degree, which means that the temperature coefficient of the resistor 16 and the like is several thousand PPm / degree. It is a small one. In addition, the terminal 2 is connected in series with the resistor 16 and the resistor 46.
A resistor 48 is connected to the 8 side. The resistor 48 is
The resistance value is smaller than that of the resistor 16 by about two digits, and the temperature coefficient is similar to that of the resistor 46. This resistor 46, 48
Is a resistor for adjustment, and the resistor 1 of the sensor chip 12
It is provided at a shift of 3 to 16.

Next, the operation and operation of the transducer circuit of this embodiment will be described. This sensor chip 12
When the pressure is detected, the resistance values of the resistors 14 and 16 increase, and the resistance values of the resistors 13 and 15 decrease,
Since the voltage V2 at the output terminal 17 decreases and the voltage V1 at the output terminal 18 increases, the bridge output voltage V0 increases by the difference between both fluctuations, and is expressed as V0 = V1-V2. here,
A reference state is a state where V0 = 0 in the no-load state.

The resistance value of the variable resistor 32 connected to the inverting input terminal of the operational amplifier 20 is VR1, and the resistance value between the slider of the variable resistor 32 and the resistor 34 is VR.
Assuming that 1 L and the resistance values of the resistors 30 and 34 are R1 and R2, respectively, the potential V3 of the slider of the variable resistor 32, which serves as a reference of the voltage applied to the inverting input side of the operational amplifier 20, is V3 = (R2 + VR1L ) / (R1 + R2 + VR1) Vcc (1) Then, in the reference state of V1−V2 = 0, V1 = V2 (2), and at this time, the variable resistor 32 is adjusted so that the above V3 becomes substantially equal to V1 and V2, and the offset adjustment is performed. . Therefore, the resistor 30, the variable resistor 32, the resistor 34
The respective resistance values R1, VR1 and R2 of the above must be set so as to satisfy the above conditions. Also, V1−
V3 = ΔV1, V2-V3 = ΔV2, and resistors 36 and 38
When the output voltage of the operational amplifier 20 is V4, the resistance values of R3 and R4 are V4−V3 = (1 + R4 / R3) ΔV2 (3). Here, R3 is set to be much larger than R4,
By setting the voltage amplification degree of the non-inverting amplifier circuit including the operational amplifier 20 to 1, the sensor chip 12 and the variable resistor 3
The influence of the impedance fluctuation of No. 2 is excluded.

If the resistance value of the variable resistor 40 is VR2, the resistance value of the temperature sensitive resistor 45 is Rt, the output voltage of the operational amplifier 22 is V5, and V5−V3 = ΔV5, then ΔV5 = ΔV1− (Rt / VR2) · (R4 / R3) ΔV2 + (ΔV1−ΔV2) Rt / VR2 (4) Here, Rt and R3 are set almost equal,
If the resistance value within the adjustable range of VR2 and R4 are set to be substantially equal, the equation (4) becomes ΔV5 = (ΔV1−ΔV2) (1 + Rt / VR2) = V0 (1 + Rt / VR2) (5) . Therefore, (1 + Rt / VR2) is the voltage amplification factor that amplifies the sensor output. Further, since the voltage amplification degree is usually about 30 to 100, substantially Rt / VR2 becomes the voltage amplification degree, and the span adjustment is performed by adjusting VR2. Further, the temperature sensitive resistor 45 is provided for span voltage temperature compensation.

Therefore, the adjusting method in the reference state of the circuit of this embodiment is as shown in the flow chart of FIG.
First, the terminals of the resistors 41 to 44 are selected so as to approximately satisfy V0 = V1-V2 = 0, and wire bonding is performed with the output side of the constant current source 10. After that, the resistance values of V1 and V2 and the resistances 13 to 16 of the bridge are measured in each state of the maximum compensation temperature of 80 ° C. and the minimum compensation temperature of −30 ° C. Then, the insertion positions of the resistors 46 and 48 and the respective resistance values are calculated so that V1 and V2 are exactly equal. Also, the resistors 46 and 48 are
Since the temperature coefficient is as described above, the sensor chip 1
Compensation calculation of the offset voltage temperature characteristic of 2 is also performed. Then, the resistors 46 and 48 selected by these calculations
Is attached to the specified place.

After accurately setting V0 = V1-V2 = 0,
V1 and V2 are measured, the variable resistor 32 is adjusted to adjust the offset, and V3 is set to be substantially equal to V1 and V2. The actual offset adjustment in the reference state is V
1 = V2, V1 = V2 = V5 (6) The voltage V5 of the output terminal 26 is changed to the variable resistor 32.
By moving and setting, V1, V2, and V5 are set to be substantially equal to V3. Here, the fact that V5 does not match V3 and becomes approximately equal is actually the case when the sensor 12
This is because an offset voltage is generated between the output terminals of the above and between the inverting and non-inverting input terminals of the operational amplifiers 20 and 22, and an adjustment error appears. Also, at this time, V3 and V4
Are almost equal. After that, VR2 is moved to perform span adjustment to set a desired amplification degree. As mentioned above,
In the circuit of this embodiment, the voltage amplification degree and the offset voltage are independent of each other in the reference state, and the offset adjustment and the span adjustment can be performed independently.

According to the pressure sensor circuit of this embodiment,
In the reference state, the sensor output V0 is set to 0 and the circuit offset adjustment is performed so as to substantially satisfy the above expression (7). Therefore, even if the variable resistor 40 is adjusted thereafter and the span adjustment is performed, the offset voltage is adjusted. There is no fluctuation, and accurate circuit adjustment is possible.

Next, a second embodiment of the present invention will be described with reference to FIG.
A description will be given based on FIG. Here, the same members as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted. This embodiment is a magnetic sensor circuit, and the sensor chip 50 is
Magnetoresistive elements 51, 52, 53, 54 as shown in FIG.
Are formed on a glass or ceramic substrate with their orientations changed, and a variable resistor 56 is provided between the bridge and the constant current source 10.

In the magnetoresistive elements 51 to 54, aluminum thin film electrodes 58 and 60 are formed in a substrate shape, and a magnetic thin film 62 of permalloy or the like is formed in a zigzag shape between them. A wide portion 64 is provided at one end of the magnetic thin film 62, and a portion of the wide portion 64 is laser-trimmed to form a cut portion 66, as described later.

Also in the magnetic sensor circuit of this embodiment, the variable resistor 56 is adjusted so that the bridge output voltage V0 = V1-V2 = 0 of the sensor chip 50 in the reference state where the magnetism is 0, and then the magnetism is adjusted. The resistance values of the resistance elements 51 to 54 are measured, laser cutting is performed to form a cutout portion 66 in one magnetoresistive element to increase the resistance value, and V is almost accurately measured.
Adjust so that 1 = V2. At this time, if necessary,
The magnetoresistive elements on the other adjacent sides are further laser-trimmed. After this, similarly to the first embodiment, V1, V2, and each magnetoresistive element are measured under predetermined conditions. Then, the resistors 46 and 48 are selected so that the resistors 46 and 48 having a predetermined value are attached, and V0 = V1−V2 = accurately.
It is adjusted to be 0. After that, the same adjustment as that of the above-described embodiment is performed.

Also in this embodiment, as in the first embodiment, the bridge output voltage V0 of the sensor chip 50 is set to 0 in the reference state, and the offset of the circuit is adjusted so as to satisfy the above expression (6). Therefore, even if the span adjustment is performed thereafter, the offset voltage does not fluctuate, and accurate circuit adjustment is possible.

The present invention is not limited to the above embodiment, and various resistance value adjustments may be performed by laser function trimming using a printing resistor or a diffusion resistor. The bridge may have a sensor on two sides and a resistive element on the other two sides, or may be a half bridge of a resistor and a sensor. Further, in the present invention, the reference state is
It may be adjusted not only at 0 point but also under the environment of a predetermined pressure and strength of magnetism, etc. In order to make the dynamic range as wide as possible in an arbitrary pressure measurement range when using an operational amplifier with a single power supply. Alternatively, the reference state may be set to a predetermined intermediate pressure value or the like, offset adjustment may be performed so as to satisfy the above equation (6), and then span adjustment may be performed. Further, the sensor power supply 10 determines the temperature coefficient of the temperature sensitive resistor 45 as
By installing as follows, even if it is a constant current power supply,
It may be a constant voltage power supply. That is, in the case of a constant current power supply, the temperature coefficient of the temperature sensitive resistor 45 is set so as to compensate the total temperature characteristic of the temperature characteristic of the resistor of the sensor chip 12 and the temperature characteristic of the pressure resistance change of the resistor. Set. Further, in the case of a constant voltage power supply, the temperature coefficient of the temperature sensitive resistor 45 may be set so as to compensate only the temperature characteristic of the pressure resistance change of the resistor of the sensor chip 12.

[0024]

In the transducer circuit of the present invention, the offset voltage is adjusted by setting the output voltage value of the sensor and the output voltage value of the amplifier to be equal in the reference state. Therefore, the amplification degree is adjusted thereafter. However, there is no fluctuation in the offset voltage, and accurate circuit adjustment is possible. Therefore, a highly accurate transducer can be provided at low cost. In addition, the dynamic range can be effectively used even with an inexpensive amplifier such as a single power supply operational amplifier,
A wide range of measurement is possible with an inexpensive transducer circuit.

Further, in the method of manufacturing the transducer circuit according to the present invention, in the reference state, the offset adjustment is performed so that the output value of the sensor and the output voltage value of the amplifier are substantially equal to each other, and then the span adjustment which is the amplification degree adjustment is performed. Therefore, the offset voltage does not change during the amplification degree adjustment, and a highly accurate sensor circuit can be manufactured. Further, since the adjustment work is not cyclic, the manufacturing process can be automated, the number of manufacturing steps and the cost can be greatly reduced, and an inexpensive and highly accurate transducer circuit can be provided.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a pressure sensor circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a sensor chip of this example.

FIG. 3 is a flow chart showing an adjustment process at the time of manufacturing the pressure sensor circuit of this embodiment.

FIG. 4 is a circuit diagram of a sensor chip of a pressure sensor circuit according to a second embodiment of the present invention.

FIG. 5 is a plan view of a magnetoresistive element of this example.

FIG. 6 is a circuit diagram of a conventional pressure sensor circuit.

[Explanation of symbols]

10 Sensor power supply 12,50 sensor chip 20,22 Operational amplifier 32,40 variable resistors

Claims (2)

[Claims] 1. An offset adjusting resistor for adjusting an offset potential of an output of the circuit, which has a sensor whose resistance value changes in response to a change of an object to be measured, and one or more for amplifying the output of the sensor. In the transducer circuit provided with the operational amplifier and the span adjusting resistor for adjusting the amplification degree of the operational amplifier according to the measurement range, the sensor output is connected to the non-inverting input side of the operational amplifier to perform the offset adjustment. A resistor is connected to the inverting input side of the operational amplifier, and in a predetermined reference state, the output voltage value of the sensor and the output voltage value of the operational amplifier to which the span adjustment resistor is connected are substantially equal to each other. A transducer circuit comprising an offset adjustment resistor adjusted. 2. An offset adjustment resistor for adjusting the offset potential of this circuit, a sensor having a resistance value that fluctuates in response to a change in an object to be measured, an amplifier for amplifying the output voltage of the sensor, and a measurement range. In the method of manufacturing a transducer circuit having a span adjusting resistor for adjusting the amplification factor of the amplifier, the output voltage value of the sensor and the output voltage value of the amplifier are made substantially equal by adjusting the offset adjusting resistor. After the above setting, the span adjusting resistor is adjusted to set a predetermined amplification degree, and a method of manufacturing a transducer circuit.