JP2948958B2 - Transducer circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transducer circuit for converting a physical quantity such as pressure or magnetism into an electric signal and extracting it.

[0002]

2. Description of the Related Art Conventionally, for example, a circuit used for a pressure sensor, as shown in FIG. 5, has a constant current power supply 12 connected to a power supply terminal 10, and a semiconductor using a piezoresistive effect. The pressure sensors 14 are connected in series. Resistors 16 and 18 are connected to the semiconductor pressure sensor 14 in parallel and series, respectively, with the resistor of the sensor 14 for offset adjustment and offset temperature compensation. The offset temperature compensation means that the output is linear at the upper limit (c) and the lower limit (d) of the operating temperature range as shown by straight lines c and d, respectively, with respect to the pressure-output characteristic at room temperature indicated by a broken line e in FIG. c,
This is to compensate for the parallel movement like d. Further, in parallel with the sensor 14, a bypass resistor 20 for span (a measurement range and corresponding to an amplification degree) temperature compensation.
Is connected. The span temperature compensation is to compensate for the change in the slope of the pressure-output characteristic shown in FIG. 4 due to the temperature change, and to make the straight lines c and d in FIG. 4 parallel to the broken line e. It is to be. Accordingly, when the offset temperature compensation and the span temperature compensation are completely performed, the straight lines c and d in FIG. 4 overlap the broken line e.

The output of the sensor 14 is connected to a non-inverting input terminal of a pair of operational amplifiers 22, and a variable resistor 24 for span adjustment is connected to the inverting input terminals of the operational amplifier 22. The output of each operational amplifier 22 is input to an operational amplifier 26, amplified, and output to an output terminal 28. An offset adjusting variable resistor 30 is connected to a non-inverting input terminal of the operational amplifier 26.

Further, in the same circuit arrangement as described above, a constant voltage power supply is used as a drive power supply for the sensor, and the output of the sensor is similarly amplified and output by an operational amplifier, and a diffusion resistor for temperature compensation is offset by an offset. There is also a transducer circuit provided in parallel with each variable resistor for adjustment and span adjustment.

[0006]

In the former case of the prior art, since a constant current power supply 12 is used, there is a voltage drop due to a resistor in the constant current power supply 12, and a low voltage power supply is used. There is a drawback that you can not. Further, when the driving power supply is replaced with a constant voltage power supply in this circuit, the span temperature compensation range becomes as large as 1500 to 3000 ppm / degree, and there is also a problem that it is not possible to compensate accurately only by inserting a temperature compensation resistor in the circuit. This is because the temperature coefficient of the diffusion resistor of the semiconductor pressure sensor 14 changes depending on the impurity concentration, as shown in FIG. This change is represented by the change in the temperature coefficient of the resistance value of the resistor shown by the curve in FIG.
In the case of driving with a constant current power supply, a + b in FIG. 3 acts as the span temperature coefficient, and in the case of driving with a constant voltage power supply, This is because b becomes the span temperature coefficient. Furthermore, in the case of driving with a constant voltage power supply, the resistance value of the bypass resistor 20 must be reduced, which reduces the current flowing through the sensor 14 and lowers the sensitivity, which is not practical.

In the latter case of the prior art, there is a correlation between the span adjustment and the span temperature compensation. If one of the two is adjusted, the other adjustment value will be out of order, and the other adjustment must be performed again. In addition, there is a problem that it is necessary to cyclically adjust and set a predetermined adjustment value, and there is a disadvantage that the adjustment takes time and accuracy is poor.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the related art, and it is an object of the present invention to provide a transducer circuit whose temperature is accurately compensated regardless of the type of driving power supply.

[0009]

According to the present invention, there is provided a sensor connected to a drive power supply, an amplifier connected to the output of the sensor, a variable resistor for adjusting the offset of the sensor output,
A variable resistor for span adjustment, wherein the variable resistor for span adjustment and the temperature-sensitive resistor are cascaded, and the resistance value at a predetermined temperature of the temperature-sensitive resistor including the temperature-sensitive resistor is included. A temperature compensating resistor circuit having an equal resistance value and a temperature coefficient whose temperature coefficient is substantially equal to the temperature coefficient of the circuit including the span adjustment variable resistor and the sensor and whose sign is opposite to that of the span adjustment variable resistor, And a transducer circuit provided in cascade with a variable resistor.

[0010]

According to the transducer circuit of the present invention, the temperature dependency of the resistance value of the sensor and the variable resistor for span adjustment is canceled by the temperature compensation resistor circuit having the opposite temperature characteristic, and the temperature compensation range is large. Also enables accurate measurement.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a pressure sensor circuit according to a first embodiment of the present invention. A semiconductor pressure sensor 34 is connected in series to a drive power supply 32 which is a constant voltage power supply or a constant current power supply. It consists of a diffusion resistor formed by diffusing impurities on the surface.
36, 37 and 38 are connected to the bridge. A resistor 40 is connected in parallel with the resistor 38, and a resistor 42 is connected in series with the resistor 37. Resistor 4
Reference numerals 0 and 42 denote resistors for offset adjustment of the sensor output and offset temperature compensation. Output terminals 44 and 4 of sensor 34
5 is connected to the non-inverting input terminals of a pair of operational amplifiers 46 and 48, respectively. One or more resistors 40 and 42 can be attached to each of the resistors of the sensor 34 at arbitrary locations for performing offset adjustment and offset temperature compensation.

This circuit is provided between a positive power supply terminal 50 and a negative power supply terminal 52, and the resistor 36 and the resistor 42 of the sensor 34 are connected to the negative power supply terminal 52. Positive power supply terminal 50 and negative power supply terminal 5
2, a resistor 54, a variable resistor 56, and a resistor 58 are connected in series. The variable resistor 56 is
The variable resistor for offset adjustment, the slider of which is connected to the inverting input terminal of the operational amplifier 46 via the resistor 60. The output of the operational amplifier 46 is connected to an inverting input terminal of the operational amplifier 48 via a span adjusting variable resistor 62 and to one side of a resistor circuit 64. The other side of the resistor circuit 64 is connected to the output of the operational amplifier 48 and to the output terminal 68 of the pressure sensor circuit of this embodiment.

A fixed resistor 72 having a very small temperature coefficient is connected in series with the temperature-sensitive resistor 70 to the resistor circuit 64. A fixed resistor 72 having a metal film resistor is connected in parallel with the resistors 70 and 72. Unit 74 is connected. The resistance value of the resistor circuit 64 is equal to the resistance value of the temperature-sensitive resistor 70 at room temperature (for example, 25 ° C.), and the temperature coefficient is the temperature coefficient of the circuit including the span adjustment variable resistor 62 and the sensor 34. The resistors 72 and 74 are selected so that the absolute values are equal and the signs are opposite. Resistance value setting method of the resistor 72 and 74, the resistance value of the resistor 72 Rs, the resistance value of the resistor 74 Rp, the resistance value of the temperature-sensitive resistor 70 When _{Rt, R t = R 25 (} 1 + αt ) (1) t = T−T ₂₅ , T is the operating temperature, T ₂₅ is 25 ° C., α is the temperature coefficient of the temperature sensitive resistor 70, and R ₂₅ is the resistance value of the temperature sensitive resistor 70 at 25 ° C. It is. , Then, the resistance value r _t of the resistance circuit 64 is expressed as follows. the temperature coefficient of _{r t = r 25 (1 +} βt) ... (2) β is determined temperature-sensitive resistor 64, thus -β is a temperature coefficient of a circuit including the span adjusting variable resistor 62 and the sensor 34. Further, as described above, since r ₂₅ = R ₂₅ (3), _rt = (R _t + R _s ) R _p / (R _t + R _s + R _p ) (4) r ₂₅ = (R ₂₅ + R _s ) R _p / (R _t + R _s + R _p ) = R ₂₅ (5) Therefore, R _p = R ₂₅ (R ₂₅ + R _s ) / R _s (6) From (4) and (6), (R _t + R _s) ) R ₂₅ (R ₂₅ + R _s ) = R ₂₅ R _s (1 + βt) ｛R _t + R _S + R ₂₅ (R ₂₅ + R _s ) / R _s ｝ This is arranged (R _t + R _s ) (R ₂₅ −R _{s βt) = R 25 (1} + βt) (R 25 + R s) Therefore, _{Rt = R 25 (1 + βt} ) (R 25 + R s) / (R 25 -R s βt) -R s ... (7) (1), ( According to 7), R ₂₅ (1 + αt) = R ₂₅ (1 + βt) (R ₂₅ + R _s ) / (R ₂₅ −R _s β _t ) −R _s By rearranging these, β _t R _s ² + R ₂₅ β _t (2 + αt) R _s + R ₂₅ ^{2 (β-α) t =} 0 than ^{_{R s 2 + R 25 (2}} + αt) R s + R 25 2 (β-α) / β = 0 R s> 0 than R _s = ^{[{(2 + αt) 2 -4} (β −α) / β｝ ^1/2 − (2+ [alpha] t)] R _25/2 = ^{[{1 + αt + α 2 t} 2/4 + (α-β) / β} 1/2 - (1 + αt / 2) ] ^{_{R 25 1 >> αt >> α 2}} t 2 / 4,1 >> From (α-β) / (2β), R _s ≒ [{1 + αt / 2 + (α-β) / (2β)}-(1 + αt / 2)] R ₂₅ = ｛(α-β) / (2β) ｝ R ₂₅ … (8) From (6) and (8), R _p = [R ₂₅ ｛R ₂₅ + (α-β) / (2β) R ₂₅ ｝] / [｛(α-β) / (2β) ｝ R ₂₅ ] = ｛(α + β) / (α-β)｝ R ₂₅ (9) Equations (8) and (9) are the resistance values of the resistors 72 and 74. Here, the temperature coefficients of the resistors 72 and 74 are relatively small and can be ignored.

The pressure sensor circuit of this embodiment has a sensor 3
4 is adjusted so that the output voltages of the output terminals 44 and 45 and the output voltage of the operational amplifier 48 become equal, and then the variable resistor 62 for span adjustment is adjusted. Adjust to the desired span. The operation of the pressure sensor of this embodiment is such that the sensor 34 made of a semiconductor diaphragm is deformed when pressure is applied,
Is detected as a change in resistance value, is output as an output difference between output terminals 36 and 37, is amplified to a set amplification degree via operational amplifiers 46 and 48, and is output from an output terminal 68. Is output. Needless to say, the positions of the span adjustment variable resistor 62 and the resistor circuit 64 may be reversed.

According to the pressure sensor circuit of this embodiment, the variable resistor 6 is connected in series with the span adjusting variable resistor 62.
2 and a resistor circuit 64 having a temperature coefficient that cancels out the temperature characteristics of the circuit including the sensor 34,
Span temperature compensation can be performed reliably, and the drive power supply 3
Even in a circuit having a large temperature coefficient in terms of circuit characteristics, as in the case of connecting directly to a constant-voltage power supply, that is, a power supply, it is possible to surely eliminate fluctuations in span due to temperature changes.
Further, since the offset adjustment, span adjustment, offset temperature compensation, and span temperature compensation are independent of each other and do not affect each other, the adjustment and compensation work can be completed at once.

Next, a second embodiment of the present invention will be described with reference to FIG. Here, the same members as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. In this embodiment, the output terminals 44 and 45 of the sensor 34 are connected to the non-inverting input terminals of the operational amplifiers 80 and 82, respectively.
The slider of the offset adjusting variable resistor 56 is connected to the non-inverting input terminal of the operational amplifier 84. The output of the operational amplifier 84 is connected to the inverting input terminal of the operational amplifier 80, and the variable resistor 8
6. It is connected to the inverting input terminal of the operational amplifier 82 via the resistor 88. Outputs of the operational amplifiers 80 and 82 are connected to inverting and non-inverting input terminals of an operational amplifier 92 via resistors 90 and 91, respectively. The resistor circuit 64 is connected between the inverting input terminal of the operational amplifier 92 and the output. The resistor circuit 64 has the same configuration as that of the first embodiment, and has a resistance value set in a similar manner. The variable resistor for span adjustment and the resistor circuit 64 may be directly or indirectly cascaded, and may be arranged at a position where predetermined span adjustment and span temperature compensation are possible.

According to this embodiment, the accuracy is high, the amplification degree can be increased, and the resistor circuit 64 acts so as to eliminate the temperature characteristic of the whole circuit. In addition, the temperature characteristics can be improved.

The transducer circuit of the present invention can be used for span temperature compensation of various sensor circuits such as a magnetic sensor in which a magnetoresistive element is assembled in a bridge, a humidity sensor, and the like, in addition to the pressure sensor. Also, the span adjustment variable resistor and the temperature sensitive resistor may be directly or indirectly cascaded.

[0019]

According to the transducer circuit of the present invention, a temperature-sensitive resistor is connected in cascade to a variable resistor for span adjustment, and the above-mentioned temperature-sensitive resistor is equal to a resistance value of the temperature-sensitive resistor at a predetermined temperature. A temperature compensation resistor circuit having a resistance value and a temperature coefficient whose absolute value is equal to the temperature coefficient of the circuit including the span adjustment variable resistor and the sensor and has the opposite sign to that of the span adjustment variable resistor. Since the resistors are connected in cascade with the resistor, the span adjustment and the span temperature compensation can be adjusted independently, and do not affect each other. Therefore, the adjustment and compensation work is completed at once. Furthermore, temperature compensation of the entire circuit can be performed,
Even when the temperature coefficient of a sensor or the like is large and its variation is large, temperature compensation can be reliably performed for each of them, and a highly accurate sensor circuit can be obtained. Furthermore, even if a constant-voltage power supply is used as the drive power supply, significant temperature compensation can be reliably performed. Even in an operation environment using a low-voltage power supply, the use of the constant-voltage power supply allows the voltage at the power supply itself to be increased. It is possible to provide a high-precision sensor circuit at a low cost without waste of the descent.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram of a second embodiment of the transducer circuit of the present invention.

FIG. 3 is a graph showing a relationship between an impurity of a semiconductor diffusion resistor and a temperature coefficient.

FIG. 4 is a graph showing fluctuations in pressure and output of the pressure sensor circuit due to temperature.

FIG. 5 is a circuit diagram of a conventional pressure sensor circuit.

[Explanation of symbols]

 Reference Signs List 32 Drive power supply 34 Sensor 46, 48, 80, 82, 84, 92 Operational amplifier 64 Resistor circuit 70 Temperature sensitive resistor 56 Variable resistor for offset adjustment 62, 86 Variable resistor for span adjustment

Claims (1)

(57) [Claims] 1. A sensor for electrically detecting a predetermined physical quantity, a drive power supply for operating the sensor, an amplifier connected to the output of the sensor, a variable resistor for offset adjustment of the sensor output, and a span adjustment. And a resistance value at a predetermined temperature of the temperature-sensitive resistor including the temperature-sensitive resistor, wherein the variable resistor for span adjustment and the temperature-sensitive resistor are cascade-connected. A temperature compensation resistor circuit having a resistance value equal to the temperature coefficient of which the temperature coefficient is substantially equal to the temperature coefficient of the circuit including the span adjustment variable resistor and the sensor and the sign of which is opposite to that of the circuit is A transducer circuit characterized by being provided in cascade connection with an adjusting variable resistor.