JP2940321B2 - Temperature compensation device for operational amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature characteristic correction device for automatically correcting a temperature characteristic of an operational amplifier used in a measurement control field or the like.

[0002]

2. Description of the Related Art An amplification characteristic of an operational amplifier changes due to a change in ambient temperature or the like. As a general method for correcting the amplification characteristic due to such a temperature change, correction data is measured in advance, In some cases, correction is performed using the correction data.

That is, prior to the actual measurement, the ambient temperature is changed, and 0 V and a reference voltage are input for each temperature.
The offset correction value is calculated at the time of inputting 0 V, and the gain correction value is calculated at the time of inputting the reference voltage. The calculated correction value corrects the analog input to be actually measured.

[0004]

However, in such a conventional example, in order to obtain correction data prior to actual measurement of an object to be measured, many measurements must be performed by changing the ambient temperature. However, there is a drawback in that it is not possible to correct an error in measurement data due to a secular change of a resistance value after the start of actual measurement of a measurement target.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and it is an object of the present invention to provide an operational amplifier which can reduce the number of measurements for obtaining correction data and can cope with errors in measurement data due to aging of a resistance value. It is an object to provide a temperature characteristic correction device.

[0006]

In order to achieve the above-mentioned object, the present invention is configured as follows.

That is, according to the present invention, there is provided a first switching means for switching and outputting either an analog input to be measured or a reference voltage input by a high-precision resistor for amplification factor correction, and an output from the first switching means. A first operational amplifier, an output of the first operational amplifier, a second switching means for switching and outputting any of 0 V for variable resistance magnification correction or a reference voltage for variable resistance magnification correction, and an output of the second switching means. A second operational amplifier provided, and third switching means for switching and connecting any one of a plurality of feedback resistors to the second operational amplifier;
An A / D converter for A / D converting the output of the second operational amplifier, and switching of each of the switching means are controlled, and correction data of the temperature characteristic of the operational amplifier is calculated based on the output of the A / D converter. Control means.

[0008]

According to the above arrangement, by providing a reference input to each operational amplifier through the switching means as necessary, the control means can calculate the correction data. It is not necessary to perform a large number of measurements by changing the ambient temperature in order to obtain correction data prior to measurement, and if errors occur in the measurement data due to aging of the resistance value, etc. By providing a reference input to the operational amplifier via the switching means and calculating the correction data, it is possible to easily cope with the operational amplifier.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings.

Embodiment 1 FIG. FIG. 1 is a configuration diagram of one embodiment of the present invention. A temperature characteristic correction device of this embodiment includes a high precision resistor R00, R01, R02 for correcting an analog input or an amplification factor to be measured.
A first multiplexer 1 as first switching means for switching and outputting any one of the reference voltage inputs of the first and second operational amplifiers; a first operational amplifier 2 to which the output of the first multiplexer 1 is provided;
The output of the first operational amplifier 2 is set to 0 for variable resistance magnification correction.
Second multiplexer 3 as second switching means for switching and outputting either V or a reference voltage for variable resistance magnification correction
And the second to which the output of the second multiplexer 3 is given.
An operational amplifier 4, a third multiplexer 5 as third switching means for switching and connecting any one of the plurality of feedback resistors R1 to R4 to the second operational amplifier 4, and an A for performing A / D conversion of an output of the second operational amplifier 4 A / D converter 6 and switching of each of multiplexers 1, 3, 5 are controlled.
A CPU 7 is provided as control means for calculating correction data of the temperature characteristics of the operational amplifier based on the output of the D converter 6 as described later.

The first multiplexer 1 is provided with an analog input to be measured between the inputs A and B, and a power source 8 (when a strain gauge is connected to the analog input) between the inputs C and D.
Precision resistors hardly influenced by the temperature of the strain gauge and the same power supply) and the amplification factor for correcting R 00, R01, R02
Are connected, and the input A is connected to the input B1, the input B is connected to the input A1, the input C is connected to the input D1, and the input D is connected to the input C1.

The first operational amplifier 2 is a differential amplifier, and differentially amplifies the output from the first multiplexer 1.

The second multiplexer 3 receives an output of the first operational amplifier 2 at an input A2, a reference voltage for variable resistance magnification correction at an input B2, and 0 V for variable resistance magnification correction at an input C2. , And switches and outputs one of them.

One input of the second operational amplifier 4 is a resistor R
5 is connected to the output side of the second multiplexer 3, and between the resistor R5 and one of the inputs, the third multiplexer 5 is connected. It is connected to the D converter 6.

The third multiplexer 5 has inputs A3, B
3, C3 and D3 are connected to the output of the second operational amplifier 4 via feedback resistors R1 to R4, respectively.

The output of the A / D converter 6 is provided to a CPU 7, which calculates correction data as described later, corrects actual measurement data based on the calculated correction data, and The CPU 7 controls switching of each of the multiplexers 1, 3, and 5.

Next, calculation of correction data by the correction device having the above configuration will be described. (A) First, the output of the second multiplexer 3 is input to the input C
2, that is, fixed to 0 V for variable resistance magnification correction, and this 0 V is applied to one input of the second operational amplifier 4. Then, the output of the third multiplexer 5 is input to inputs A3, B3,
C3, D3 sequentially switched to sequentially capture the output _{V c2A3, V c2B3, V c2c3} , V c2D3 the A / D converter 6 at that time. It is assumed that the variable resistance magnification when switching to the input A3 is 1.

(B) Next, the output of the second multiplexer 3 is fixed to the input B2, that is, the reference voltage for variable resistance magnification correction, and the output of the third multiplexer 5 is changed to the input A3 as described above. B3, C3 and D3 are sequentially switched, and the outputs V _B2A3 , V _B2B3 and V of the A / D converter 6 at that time are
_B2c3 and _VB2D3 are sequentially fetched.

As described above, 0 V and the reference voltage are switched and applied to one input of the second operational amplifier 4 via the second multiplexer 3, and the feedback resistors R 1 to R 4 are switched by the third multiplexer 5 in accordance with each of them. A / D
The outputs V _c2A3 , V _c2B3 , V _c2c3 , V _c2D3 ,
When the calibration data H _{A3 to} H _D3 of each variable resistance magnification is calculated from V _B2A3 , V _B2B3 , V _B2c3 , V _B2D3 , the following equations (1) to
(4).

H _A3 = (reference voltage) / (V _B2A3 −V _c2A3 ) (1) H _B3 = {(V _B2A3 −V _c2A3 ) / (V _B2B3 −V _c2B3 )} × 1 (2) H _{C3 = {(V B2A3 -V c2A3)} / (V B2C3 -V c2C3)} × m ... (3) H D3 = {(V B2A3 -V c2A3) / (V B2D3 -V c2D3)} × n ... (4) Here, l, m, and n are arbitrary variable magnifications.

(C) Next, the output of the second multiplexer 3 is fixed to the input A2, that is, the output of the first operational amplifier 2, and the output of the first multiplexer 1 is connected to a high-precision resistor for amplification factor correction. R is switched between the connected inputs C and C1 and between inputs D and D1, respectively. Then, in each switching state, the output of the third multiplexer 5 is sequentially switched to the inputs A3, B3, C3, and D3,
The following A / D converter outputs for l, m, and n are fetched.

(1) When the output of the first multiplexer 1 is set between the inputs C and C1. A) The output of the A / D converter 6 when the variable magnification is _1. b) A when the variable magnification is 1. / output V _CC1B3 c of D converter 6) variable magnification m times the output V _CC1D3 (2 output V _CC1C3 d) a variable magnification n times the a / D converter 6 when the the a / D converter 6 when the) first multiplexer When the output of 1 is between the inputs D and D1 a) The output of the A / D converter 6 when the variable magnification is 1 × V _DD1A3 b) The output of the A / D converter 6 when the variable magnification is 1 × V _DD1B3 c ) Output of A / D converter 6 when variable magnification is m times V _DD1C3 d) Output of A / D converter 6 when variable magnification is n times V _DD1D3 Output of A / D converter 6 sequentially taken in this way V _CC1A3 , V _CC1B3 , V _CC1C3 , V _CC1D3 , V _DD1A3 ,
When the correction data of the operational amplifier other than the correction of the variable resistance magnification is calculated for each variable resistance magnification from V _DD1B3 , V _DD1C3 , and V _DD1D3 , the following equations (5) to (8) are obtained.

H _CDA3 = V / (V _CC1A3 −V _DD1A3 ) (5) H _CDB3 = V / (V _CC1B3 −V _DD1B3 ) (6) H _CDC3 = V / (V _CC1C3 −V _DD1C3 ) (7) H _CDD3 = V / (V _CC1D3 −V _DD1D3 ) (8) Here, V is a reference voltage V (= V _CC1 −V _DD1 ) to be output by the high-precision resistor R for amplification factor correction.

Based on the correction data (1) to (8) calculated as described above, an analog input value to be actually measured is corrected as follows.

That is, in the measurement of the analog input to be actually measured, the output of the first multiplexer 1 is switched between the inputs A and A1 and between the inputs B and B1, and the A / D converter 6 at that time is switched. Output of V _AA1 , V
_{If BB1} , the analog input value is calculated by the following equations (9) to (12) based on the correction data.

(A) Variable magnification 1 time Analog input value = (V _AA1 −V _BB1 ) × H _CDA3 (9) (b) Variable magnification 1 × Analog input value = (V _AA1 −V _BB1 ) × H _B3 × _{H CDB3 ... (10) (c} ) a variable magnification m multiplied analog input value _{= (V AA1 -V BB1) ×} H C3 × H CDC3 ... (11) (d) a variable magnification n times the analog input value = (V _AA1 -V _BB1 ) × H _D3 × H _CDD3 (12) The correction of the operational amplifier is performed as described above.

In this embodiment, the CPU 7 controls each of the multiplexers 1, 3, and 5 as required by an instruction from an external setting means (not shown) to correct the correction data (1) to (8) as described above. Is calculated. After that, the actual analog input of the measurement target is measured, and the CPU 7 calculates the analog input value according to the above-described correction formulas (9) to (12). That is, the temperature characteristic of the operational amplifier is corrected.

Therefore, it is not necessary to perform a large number of measurements by changing the ambient temperature in order to obtain correction data prior to the actual measurement, as in the conventional example. Even in the case where an error occurs in the data, the correction data (1) to (8) can be easily handled by newly calculating the correction data.

As another embodiment of the present invention, the correction data (1) to (8) are calculated at regular time intervals or
A temperature sensor may be provided to perform the measurement every time a certain temperature change occurs.

Further, the offset characteristic of the strain gauge can be calculated by connecting the analog input of the present invention to the output of the strain gauge, setting the load of the strain gauge to 0 and increasing the temperature in that state. it can.

[0031]

As described above, according to the present invention, it is possible to calculate correction data as needed by giving a reference input to each operational amplifier via the switching means. As in the conventional example, in order to obtain correction data prior to actual measurement, it is not necessary to perform a large number of measurements by changing the ambient temperature, and errors occur in the measurement data due to aging of the resistance value and the like. In such a case, it can be easily handled.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

[Explanation of symbols]

1, 3, 5 First, second, and third multiplexers (switching means) 2, 4 First and second operational amplifiers 6 A / D converters 7 CPU (control means) R 00 to R02 High-precision resistors R1 to R4 Feedback resistors

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H03F 1/30

Claims (1)

(57) [Claims] 1. A first switching means for switching and outputting either an analog input to be measured or a reference voltage input by a high-precision resistor for amplification factor correction, and a first operational amplifier to which an output of the first switching means is provided. Output of the first operational amplifier, 0V for variable resistance magnification correction
Or a second switching means for switching and outputting any one of the reference voltages for variable resistance magnification correction; a second operational amplifier to which the output of the second switching means is applied; and a second feedback amplifier for the second operational amplifier. Third switching means for switching connection between the A / D converter, an A / D converter for A / D converting the output of the second operational amplifier, and controlling the switching of each of the switching means,
Control means for calculating correction data of the temperature characteristic of the operational amplifier based on the output of the D converter. A temperature characteristic correcting device for the operational amplifier, comprising: