JPS61246617A - 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 voltage generating means so as to compensate an effect produced by fluctuations of ambient temperature. CONSTITUTION:A current IS is supplied from a current source 21 to a series circuit of paired gage resistances 15 and 16 through the intermediary of a current detecting resistance 22. Subsequently, the opposite-end voltages Ea and Eb of the gage resistances 15 and 16 and the opposite-end voltage Ec of a current detection resistance 22 are supplied to detection amplifiers 23a, 23b and 23c respectively. An arithmetic circuit 24 conducts the operation of the formula by using voltages E1 and E2 outputted from the amplifiers 23a and 23b and a compensation voltage E3 outputted from the amplifier 23c. An effect produced by fluctuations of ambient temperature is compensated effectively thereby, 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 resistance type converter, a high concentration impurity (boron) 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 compensate for output fluctuations by adjusting the bridge power supply voltage IIJi[IL in response to temperature changes. 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 effectively compensates for the effects of changes in ambient concentration,
The object of the present invention is to realize a resistive conversion device that can detect physical quantities to be measured with high precision.

Means for Solving the Problems> The present invention provides a pair of gauge resistors whose resistance value differentially changes depending on the physical quantity to be measured, and a measuring voltage proportional to the resistance value of one of the pair of gauge resistors. a circuit for obtaining a measurement voltage E2 proportional to E1 and the resistance value of the other; a circuit for obtaining a compensation voltage unrelated to the physical quantity to be measured; and a circuit for obtaining the measurement voltage E+
, E2 and the compensation voltage E3, substantially (EI E2 (El + E2 ) (El + E2 - E co )
This method is characterized by performing calculations to obtain a signal corresponding to the physical quantity to be measured.

Effects> The present invention makes it possible to effectively eliminate the influence of ambient temperature by simply selecting the value of the compensation voltage by performing the above calculation.

<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 MIN of the present invention.
(A) is an IFi plane view, and (B) is a perspective view. In both figures, 10 is a detector and 20 is a signal processing circuit.

In the detection 110, 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 . Gauge resistors 15 and 16 are provided on the pressure receiving diaphragm 12 by diffusion technology, ion implantation, or the like. The gauge resistance 15.16 has a stress σ1 corresponding to the measured pressure PM.
．． σ2 acts, and the resistance value RMI of the gauge resistor 15 and the resistance value RM2 of the gauge resistor 16 are given by the following equations.

Rr++=Ro+(1+α+i) × (1+π1σ1 (1+β1t)) ・・・(1) Rr+2=Ro2 (1+αai) ×(1+π2σ2 (1+β2t)) ・・・(2) However, Ro I+ Ro 2 ”Resistance at reference temperature to Et3 Value α blind, α2 Temperature coefficient π of two resistors 11 Ro1, Ro2, π2: Piezoresistance coefficient β at reference temperature tol, β2: Piezoresistance coefficient π.

Temperature coefficient t of π2: Humidity change from group Ql'aW1 io Note that the gauge resistors 15 and 16 are formed on the same substrate 11, and the temperature coefficients are α1-α2-α and β1-β2-, respectively.
It is possible to align the retention properties that can be regarded as β @also π
1σ1. Regarding π2σ2, for example, silicon (10
0) in the [1101 direction] Gauge resistance 15.16
are placed at right angles to each other, then π1σ嘗−−π2σ2−π
It can be σ. In this way, gauge resistance 1
5°16, one resistance value increases and the other resistance value decreases due to the measured pressure PM acting on the pressure receiving diaphragm.

In the signal processing circuit 20, 21 is a current source, 22 is a current detection resistor with a resistance value of RC, and 23a.

23b and 23c are each a detection amplifier, 24 is an arithmetic circuit,
25 is a reference voltage source. A current is from a current source 21 is supplied to a series circuit of gauge resistors 15° and 16 through a 2m detection resistor 22. and gauge resistance 15.1
6 and the voltage EC across the current detection resistor 22 are detected by the detection amplifiers 23a, 23b, 2, respectively.
3c to the input terminal of the arithmetic circuit 24.

Further, a reference voltage E' from a reference voltage source 25 is applied to the input terminal of the arithmetic circuit 24.

In the device of the present invention configured in this way, the current source 21
The output current of the IS1S1 detector 23a.

The gains of 23b and 23c are AI, A2゜A3, respectively.
Then, the measurement voltages E+ and Ea obtained at the output terminals of the detection amplifiers 123a and 23b and the compensation voltage E3 obtained at the output terminal of the detection amplifier 21230 are given by the following equations, respectively.

EI-At Ea...
(3) Ea -A2 Eb...
(4) E3-As Ec =
(5) The arithmetic circuit 24 performs the following calculation using the measured voltages E+, Ea, the compensation voltage E3, and the reference voltage Er from the reference voltage IN23, and outputs the output voltage EO.

Eo −Er E3 (EI Ea )/
((El+E2) (El+E2 E3
) )...(6) Therefore, by substituting (3), (4), and (5) into equation (6), A
If I-A2, Eo is Eo -Er A3 RC(RM I -RM
2 )/((RM + +RM 2 )
(AI RM eyes + A2 RM 2 -A3 R
C) )... (7) becomes. Substituting equations (1) and (2) into equation (7), ROt
=RO2-RO, then Eo-πσErAsRc(1+βt)/l+(1+αt2Δ+Ro/l+)...(8) However, since @I+-(2A+ROA3RC), β-α2A+Ro/l+...(9) -1 value, that is, the current detection resistor 22 so as to satisfy
resistance (lIRc or the gain A3 of the sense amplifier 23C)
, the output voltage EO is Eo = lπσE r
・＜10) However, Zen-A3RC
/II, the α and β terms of the temperature coefficient can be effectively removed, and the measured pressure P can be measured with high accuracy without being affected by temperature fluctuations.
A signal representing M is obtained.

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

The relationship of β is that in the range of impurity concentration from 101 m to 10'°, α>O and β 0, so the relationship of equation (9) is as follows: resistance 1 m of the current detection resistor 22 Rc or detection amplification! 2
It can be satisfied by choosing a gain A3 of 3c.

Note that if the initial resistance value Ro+ of the gauge resistor 15 and the initial resistance value RO2 of the gauge resistor 16 are not equal, the amplification 1
Gain AI of either W23a or 24b, A2
It is sufficient to satisfy AI Ro I - A2 RO2=O"<11> using amb. Also, since the voltage Ec across the current detection resistor 22 is constant, the voltage obtained by dividing the reference voltage E" can be used as the compensation voltage E3, and the current detection resistor 22 can be omitted.However, when the current detection resistor 22 is used, the influence of fluctuations in the current ls flowing through the gauge resistor 15.16 It has the advantage of not being affected by current I.
! 21 is simplified, and instead of a current source,
A voltage source can also be used.

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

The embodiment shown in FIG. 3 differs from the embodiment shown in FIG. 1 in that a subtraction circuit 26 is provided, and the output voltage E
The voltage Er obtained by dividing o by the voltage divider 27 is subtracted, and (Er
-Er) is added to the arithmetic circuit 24. In this case, if the voltage division ratio of the voltage divider 27 is n, the output E4 of the subtraction circuit 26 is given by the following equation.

Ea −ErnEo −(12) Therefore, the output voltage Eo is Eo=−πσEr / (1−n ti π(7)...
・(13) The larger the stress σ, the higher the rate of increase in the output voltage Eo, making the input-output relationship non-linear. On the other hand, the pressure to be measured P
The nonlinearity between M and stress σ increases as Pr+ increases.
Since the increase rate of
The effects of nonlinearity can be compensated for. This adjustment is
Output voltage E corresponding to the measured pressure P M l *PMa and PNa having the relationship of 2-(PM ++ pH3)/2.

+ * EO2 * EO3 is Eo 2- (Eo +
+E.

This can be easily done by determining the voltage dividing ratio n of the voltage dividing resistor 27 so that it becomes 3)/2.

Note that the arithmetic circuit 24 may be configured by combining analog adders/subtracters, multipliers, and dividers, or the outputs of the detection amplifiers 23a, 23b, 23c, etc. may be converted into digital amounts by an A/D converter. It may also be configured so that the microcomputer performs a digital operation corresponding to equation (7).

<Effects of the Invention> As explained above, in the present invention, since the temperature coefficient term can be effectively removed, a resistive converter that can measure the physical quantity to be measured with high accuracy without being affected by fluctuations in l1r1 is provided. can get.

[Brief explanation of drawings]

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.
The figure is an electrical connection diagram showing another embodiment of the present invention. 10...Detector 11...Single crystal semiconductor substrate 12...Pressure diaphragm section 15.16-...Gauge resistor 20...Signal processing Circuit 21---・-Electric*s! 22...Resistors 23a, 23b, 23c for current detection...Detection amplifier 24...Arithmetic circuit 25...Reference voltage source 26...・Subtraction circuit 27... Voltage divider M2 circle (a) (b)

Claims (1)

[Claims] A pair of gauge resistors whose resistance value differentially changes according to the physical quantity to be measured, and a measurement voltage E_1 proportional to the resistance value of one gauge resistor and proportional to the resistance value of the other gauge resistor. a circuit for obtaining the measured voltage E_2, a circuit for obtaining the compensation voltage E_3 unrelated to the physical quantity to be measured, and a circuit for obtaining the measured voltage E_1.
, E_2 and compensation voltage E_3, substantially (E_1-E_2)/[(E_1+E_2)(E_1+
E_2-E_3)] and an arithmetic circuit that outputs a signal according to a physical quantity to be measured.