JPS61246618A - Resistance-type conversion device - Google Patents

Abstract

PURPOSE:To enable the highly accurate detection of a physical quantity to be measured, by providing a pair of gage resistances whose resistance values change differentially according to the physical quantity to be measured and a compensation signal generating means. CONSTITUTION:Resistance value detecting circuits 21 and 22 detect resistance values of paired gage resistances 15 and 16 and deliver outputs Ea and Eb respectively. A difference detecting circuit 27 receiving said outputs Ea and Eb operates a difference voltage Ef (Ea-Eb) and delivers same. Meanwhile, a compensation signal generating circuit 23 forms and delivers a compensation signal Ec based on an output Ed of an error amplifier 24. An output circuit 28 delivers a signal based on a difference between the output of the difference detecting circuit 27 delivered when the compensation signal Ec is ON, and the output of the circuit 27 delivered when the signal Ec is OFF. An effect produced by fluctuations of ambient temperature is thereby compensated effectively, and thus a physical quantity to be measured can be detected with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a resistance conversion device using a gauge resistor whose resistance value changes depending on a physical quantity to be measured such as pressure or differential pressure.

<Conventional technology> Generally, in a resistive converter, a high concentration impurity (poron) is diffused onto a pressure receiving diaphragm made of a single crystal semiconductor such as silicon to form a gauge resistance, and the pressure applied to both sides of the pressure receiving diaphragm is reduced. A stress based on the difference is applied to the gauge resistor, and the change in the resistance value of the gauge resistor due to the piezoresistance effect is made to correspond to the pressure difference, that is, the physical quantity to be measured.

Then, two or four gauge resistors are provided on the pressure-receiving diaphragm to form a half bridge or full bridge, and a signal representing the physical quantity to be measured is obtained.

<Problems to be Solved by the Invention> By the way, in this type of resistance converter, the gauge resistance has a large temperature dependence, so there is a drawback that the output fluctuates due to the influence of changes in ambient temperature.

Therefore, in general, a temperature sensing element such as a thermistor, a posistor, or a transistor is used to control the power supply voltage of the bridge according to the concentration change to compensate for the output fluctuation. In order to perform accurate compensation using this method, it is necessary to match the temperature characteristics of the gauge resistance and the temperature characteristics of the compensation temperature sensing element. However, it is not easy to match these, and highly accurate compensation is not possible. It was difficult.

The present invention aims to realize a resistive converter that can effectively compensate for the effects of changes in ambient temperature and can detect physical quantities to be measured with high accuracy.

Means for Solving Problems〉 The present invention provides a system in which the output voltages of the voltage supply circuits are commonly applied,
A pair of resistance value detection circuits that detect the resistance values of a pair of gauge resistors whose resistance values differentially change depending on the physical quantity to be measured, and a difference between the outputs of these pair of resistance value detection circuits, that is, a pair of gauge resistors. a difference detection circuit that obtains a difference signal based on the difference in resistance value of the voltage supply circuit; a compensation signal generation circuit that generates a compensation signal by turning on and off a voltage proportional to the output voltage of the voltage supply circuit; and a pair of resistance value detection circuits. means for controlling the voltage supply circuit so that a value obtained by subtracting the compensation signal from the sum of the outputs, that is, the sum of the resistance values of a pair of gauge resistors becomes constant; The present invention is characterized in that it includes an output circuit that obtains an output signal based on the difference between the output of the difference detection circuit and the output of the difference detection circuit when the compensation signal is off.

Function> The present invention combines a signal based on the sum of the outputs of a pair of resistance value detection circuits, that is, the sum of the resistance values of a pair of gauge resistors, and a compensation signal that turns on and off a voltage proportional to the output voltage of a voltage supply circuit. Ill the voltage supply circuit so that the difference is constant.
III, and by obtaining an output signal based on the difference between the output of the difference detection circuit when the compensation signal is on and the output of the difference detection circuit when the compensation signal is off, By selecting the value, the temperature coefficient term of the gauge resistance is effectively removed.

<Example> FIG. 1 is a connection diagram showing an example of the present invention, and FIG. 2 is a configuration explanatory diagram showing an example of a detector used in the device of the present invention.
A) is a cross-sectional view, and (b) is a perspective view. In both figures,
10 is a detector, and 20 is a signal processing circuit.

In the detector 10, a single crystal semiconductor substrate 1 such as silicon
A pressure receiving diaphragm 12 is formed in the center of the pressure receiving diaphragm 1 by etching, which is sensitive to the difference between a reference pressure Po (for example, atmospheric pressure) and a measured pressure PM.

A fixed portion 13 around the substrate 11 is joined to a base 14 . The pressure-receiving diaphragm 12 is provided with gauge resistors 15, 16 using diffusion technology.

The gauge resistors 15 and 16 have a stress σ corresponding to the measured pressure PM.
1. σ2 acts, and the resistance value RNI of the gauge resistor 15 and the resistance value RM2 of the gauge resistor 16 are given by the following equations.

RMt=Rot (1+αti) × (1+π1σ1 (1+β1t)) ... (1) RMz-Ro2 (1+α2j) × (1+π2σ2 (1+β2t)) ... (2) However, Ro+, RO2: Resistance at I quasi-temperature to Value α electric, α2: Temperature coefficient π1 of resistance value ROl e RO2. π22l! Piezoresistance coefficient β1 at quasi-temperature to. β2: Temperature coefficient of piezoresistance coefficient π1°π2 t: m quasi-temperature 1. Note that the gauge resistors 15 and 16 are formed on the same substrate 11, and their temperature coefficients are α1-α2-α and β1-β2-, respectively.
It is possible to match the kneading properties that can be considered as β. Also π
Goose σ1. For π2σ2, for example, /(1
00) plane in the [1101 direction] Gauge resistance 15.16
If they are placed at right angles to each other, π1σ+−I+−π2σ2
−πσ. In this way, the resistance value of one of the gauge resistors 15 and 16 increases and the resistance value of the other decreases depending on the measured pressure Pi acting on the pressure receiving diaphragm.

In the signal processing circuit 20, 21 and 22 are resistance value detection circuits, 23 is a compensation signal generation circuit, 24 is an error amplifier,
25 is an arithmetic circuit, 26 is a reference voltage source, 27 is a difference detection circuit, 28 is an output circuit, and 29 is a control circuit. The resistance value detection circuit 21 has an operational amplifier 1!21a, a gauge resistor 15 is connected to the feedback circuit of 21a, and a resistance value R is connected to the input circuit of 21a.
The resistors 21b of a are connected to each other. The resistance value detection circuit 22 has a circuit 122a, a gauge resistor 16 is connected to the return port of 22a, and a resistor 22b having a resistance value Rb is connected to the input circuit. The output Ed of the error amplifier 24 is commonly applied to the inputs of the resistance value detection circuits 21 and 22. Therefore, the gauge resistor 15 receives a current of Ed/Ra, and the gauge resistor 16 receives a current of Ed/Ra.
A current I2 called Rb flows. The compensation signal generation circuit 23 is
Voltage dividing resistor 23a and error amplification! A switch 23b that turns on and off the voltage obtained by dividing the output Ed of 24 using a voltage dividing resistor 1123a, and a buffer ? It consists of an amplifier 23c. The switch 23b is driven by a constant cycle pulse P1 from the liIJw circuit 29. The arithmetic circuit 25 includes arithmetic resistors 25b, 25C, and 2 having the same resistance value as the operational amplifier 125a.
5d and 25e, the sum of the outputs Ea, l:b of the resistance value detection circuit 21.22 and the output EC of the compensation signal generation circuit 23 is calculated and added to the input terminal (-) of the error amplifier 24. The reference voltage source 2 is connected to the input terminal (+) of the error amplifier 24.
A constant voltage Er is applied from 6 to 6. Difference detection circuit 27
is an operational resistor 27b having the same resistance value as the operational amplifier 27a.
, 27c, 27d, and 27e, and calculates the difference (Ea - Eb) between the output Ea of the resistance value detection circuit 21 and the output Eb of the resistance value detection circuit 22. The output circuit 28 includes a sample hold circuit 28C made up of a switch 28a and a capacitor 28b, and a sample hold circuit 28f made up of a switch 28d and a capacitor 28e.
It consists of a circuit 28g that calculates the difference between the outputs of the sample and hold circuits 280 and 28f. The sample and hold circuit 28c holds the output Ef of the difference detection circuit 27 when the switch 28a is driven by the sampling pulse P2 from the control circuit 29 and the compensation voltage EC is on.

In the sample and hold circuit 28f, the switch 28d is driven by the sampling pulse P3 from the control circuit 29, and holds the output Ef2 of the difference detection circuit 27 when the compensation voltage EC is off.

In the device of the present invention configured in this way, the outputs Ea and Eb of the resistance value detection circuits 21 and 22 are as follows: Ea = -Ed -
RM + /Ra = (3) 1:b --Ed
-RM2/Rt) (4), and the output EO of the arithmetic circuit 25 is as shown in the following equation.

Ee −−(Ea +l:b +EC) (5) Moreover, the output EC of the compensation signal generation circuit 23 is connected to the voltage dividing resistor 2
If the voltage division ratio of 3b is -, it becomes sEd when the switch 23b is on, and zero when it is off. Then, the error amplifier 24 determines that the output Ee of the arithmetic circuit 25 is the reference voltage Er.
Since the voltage Ed supplied to the resistance value detection circuit 21.22, that is, the current 1++T2 flowing through the gauge resistor 15.16, is controlled so that the output Ed+ of the error amplifier 24 and the switch 23 when the switch 23b is on is equal to
The output Ed2 of the error amplifier 24 when b is off is Ra
-Rb, each is given by the following formula.

Ed + -Ra Er/ (RM l +R
M2-IRa)...(6) Ed2-Ra l:r/(RM++RM
2)...(A) Therefore, when the switch 23b is on, the difference detection circuit 27
The voltage Ef+ obtained at the output terminal of , and the voltage E obtained at the output terminal of the difference detection circuit 27 when the switch 23b is off.
fa is as shown in the following equations.

Ef + −(RM l −RM2 )
Ed + /Ra-Er (RM I-RM
2 )/(RM I+RM 2 -rs Ra
)...(8) Efz=(RM+-RMz)Ed2/Ra=Er
(RM + RM2) / (RM +
+RM 2 )... (9) These Ef+ and Efz are applied to the output circuit 28 and held in sample and hold circuits 28c and 28f, respectively. The output port W128 is a sample hold circuit 28c,
The difference between the voltages held at 28f is calculated and an output voltage EO expressed by the following equation is output.

1: o −Er l −Ef 2 = −I Ra (RM l −RM 2 ) Er/
(RM + +RM2) (RM嘗+RH2-s
Ra >... (10) (10) formula (1), (2
) formula and set Ro+=Ro2-Ro, EO-ytats Ra (1+βt)Er/k +
(1+2Ro at /k t )...(11) However, since k I = 2R□ -ta Ra, the voltage dividing resistor is set so that β-α・2RO/ satisfies *...(12) When the voltage division ratio - of 1123c is am, the output voltage Eo is Eo -k πcyEr ・ (13)
However, k - I Ra /k 1 is obtained, and the α and β terms of the temperature coefficient can be effectively removed, and a signal representing the measured pressure PM can be obtained with high accuracy without being influenced by temperature fluctuations. .

and the impurity concentration and temperature coefficient α of the gauge resistance.

In the impurity concentration range of 101 to 1020, the relationship with β is α>0, β×O, so by selecting the dividing voltage ratio n of the voltage dividing resistor 23, the relationship in equation (12) can be easily established. can be satisfied.

Note that if the initial resistance value Rot of the gauge resistor 15 and the initial resistance WiRO2 of the gauge resistor 16 are not equal, the resistance value Ra of either the resistor 21b or the resistor 22b,
Rb may be adjusted to satisfy RaRo+-RbRoz-0'' (14).

FIG. 3 is a connection diagram showing another embodiment of the device of the present invention.

In the embodiment of the third factor, the difference from the embodiment of FIG. )
This is the point that I added to this. In this case the voltage dividing resistor 28
When the division ratio of n is n, the output Ed of the error amplifier 24 is
+ and Ed2 are given by the following equation.

Ed + = (Er-nEo)Ra/ (RM
+ +RM2 1 Ra ) ... - (15) Ed 2- (Er -n EO) / (RM + +RM 2 ) ... (16) Therefore, the output voltage EO is EO-k π (7E r/ (l +nkπcy)・・
・(17) The larger the stress σ, the higher the rate of increase in the output voltage EO, making the input-output relationship non-linear. - The nonlinearity between the measured pressure PM PM and the stress σ is caused by the thicker PH (if σ
Since the increase rate of σ tends to decrease, by adjusting the partial pressure ratio n of the partial pressure resistor 28n, the measured pressure PM
The effects of nonlinearity can be compensated for. This 1m is PH
Output voltage E corresponding to the measured pressure Pn1mPM2*PMz, which has a relationship of 2-(PMl+PM3)/2
O+ * EO21EO3 becomes EO2-(Eo 1+E
This can be easily done by determining the voltage dividing ratio n of the voltage dividing resistor 28n so that it becomes 0/2.

Although the error amplification 824 is used as a means for controlling the voltage Ed supplied to the resistance value detection circuits 21 and 22, the 11-minute circuit 30 may be used as shown in FIG. In FIG. 4, the integrating circuit 30 consists of an operational amplifier 130a, a capacitor 30b connected to its feedback circuit, and two resistors 30c and 30d of equal resistance. The input terminal (-) of the operational amplifier 30a is connected to the operational circuit 2.
5 is applied via a resistor 30d, and a negative reference voltage Er is applied via a resistor 30c.

In this case, Ea +Eb +n Eo -Ec -Er -0...
- Ed is controlled so that (18). If the resistor 25d and the resistor 25f are variable resistors, the voltage dividing resistor 23a,
28n can also be omitted.

<Effects of the Invention> As explained above, in the present invention, the term of the temperature coefficient can be effectively removed, so that a resistive conversion device that can measure the physical quantity to be measured with high accuracy without being affected by temperature fluctuations can be used. It will be done.

[Brief explanation of the drawing]

FIG. 1 is an electrical connection diagram showing one embodiment of the present invention, FIG. 2 is a configuration explanatory diagram showing an example of a detector used in the present invention, and FIG.
4 and 4 are electrical connection diagrams showing other embodiments of the present invention. 10...Detector 11...Single crystal semiconductor substrate 12...Pressure diaphragm section 15.16...Gauge resistor 20...Signal processing Circuit 21.22...Resistance value detection circuit 23...
-Compensation signal generation circuit 24...Error amplifier 25...Arithmetic circuit 26...Reference voltage source 27...Difference detection circuit 28... Output circuit 29...Control circuit 30...Integrator circuit yP, Figure 2 (A) (B)

Claims (2)

[Claims] (1) A pair of gauge resistors whose resistance value differentially changes according to the physical quantity to be measured, a pair of resistance value detection circuits that respectively detect the resistance values of the pair of gauge resistors, and a pair of resistance value detection circuits that respectively detect the resistance values of the pair of gauge resistors. a voltage supply circuit that applies an output voltage to the circuit;
a compensation signal generation circuit that generates a compensation signal by turning on and off a voltage proportional to the output voltage of the voltage supply circuit; a difference detection circuit that obtains a signal based on the difference between the outputs of the pair of resistance value detection circuits; means for controlling the voltage supply circuit so that a value obtained by subtracting the compensation signal from a signal based on the sum of the outputs of the resistance value detection circuit of the circuit is constant; and means for controlling the difference detection circuit when the compensation signal is on. A resistive conversion device comprising: an output circuit that obtains an output signal based on a difference between the output and the output of the difference detection circuit when the compensation signal is off. (2) A pair of gauge resistors whose resistance value differentially changes according to the physical quantity to be measured, a pair of resistance value detection circuits that respectively detect the resistance values of the pair of gauge resistors, and a pair of resistance value detection circuits that respectively detect the resistance values of the pair of gauge resistors. a voltage supply circuit that applies an output voltage to the circuit;
a compensation signal generation circuit that generates a compensation signal by turning on and off a voltage proportional to the output voltage of the voltage supply circuit; a difference detection circuit that obtains a signal based on the difference between the outputs of the pair of resistance value detection circuits; an output circuit that obtains an output signal based on the difference between the output of the difference detection circuit when the signal is on and the output of the difference detection circuit when the compensation signal is off; and the output of the pair of resistance value detection circuits. and means for controlling the voltage supply circuit so that a value obtained by adding and subtracting a signal based on the sum of , a signal proportional to the output signal, and the compensation signal is constant.