JP2003042870A - Temperature characteristics correcting circuit apparatus for sensor and sensor temperature characteristics correcting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a temperature characteristics correcting circuit apparatus for a sensor capable of highly accurately correcting the temperature characteristic of the sensor. SOLUTION: The state of connection of a plurality of resistive elements 31-38 for variably setting the amplification factor of a voltage amplifier by a plurality of analogue switches 42(1)-42(5) is changed at a TCS adjusting circuit 25 to perform adjustment so as to lower the temperature coefficient of sensitivity of a bridge circuit 22 as much as possible. The state of connection of a plurality of resistive elements 28 for variably setting the amplification factor of the voltage amplifier by a plurality of analogue switches 29 is changed at a sensitivity adjusting circuit 24 to adjust the sensitivity of a pressure sensor 21.

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 circuit for a sensor, which corrects the temperature characteristic of a sensor provided with a sensor unit constituted by connecting a plurality of resistance elements in a bridge in order to detect a target physical quantity. The present invention relates to a device and a temperature characteristic correction method for a sensor.

[0002]

2. Description of the Related Art FIG. 4 shows a structural example of a semiconductor sensor having a bridge circuit. The bridge circuit 1 is configured by connecting four piezoresistive elements 2 in a bridge connection. The current Iin is supplied to the terminal 1a of the bridge circuit 1 by the current mirror circuit 3 and the terminal 1 located on the diagonal line of the terminal 1a.
b is connected to ground. Current mirror circuit 3
The reference power source 4 (voltage V1), operational amplifier 5,
The I / V conversion circuit 8 including the transistor 6 and the resistor 7 (resistance value R1) is connected, and the current Iin supplied to the bridge circuit 1 has a value corresponding to the voltage V1 of the reference power supply 4. There is.

The terminal 1a of the bridge circuit 1 is connected to the ground via a resistor 9 (resistance value R2),
The terminals 1c and 1d are respectively connected to two input terminals of an operational amplifier 10 which constitutes a voltage amplifier circuit. And
When the bridge circuit 1 outputs a voltage according to the pressure (target physical quantity) applied from the outside between the terminals 1c and 1d, the operational amplifier 10 amplifies and outputs the voltage. The above constitutes the pressure sensor 11.

By the way, such a pressure sensor 11 has a predetermined sensitivity temperature coefficient (TCS). Here, FIG.
Shows the degree of change of the output voltage Vo with respect to the applied pressure P, that is, the sensitivity of the sensor. Therefore, the sensitivity of the sensor increases as the inclination of the straight line in FIG. 5 increases.
The sensitivity temperature coefficient indicates the rate at which the sensitivity of the sensor changes according to temperature. Then, at the manufacturing stage, in order to eliminate the temperature dependence of the sensor as much as possible, the sensitivity temperature coefficient TCS of each sensor is trimmed so as to be as small as possible.

Assuming that the temperature coefficient of sensitivity of the pressure sensor 11 is TCSa and the temperature coefficient of sensitivity of the bridge circuit 1 portion including the resistor 9 (R2) is TCSb, the relationship between the two is expressed by equation (1). . TCSa = TCSb-TCR.RB / (R2 + RB) (1) where TCR is a resistance element 2 which constitutes the bridge circuit 1.
It is assumed that there is no temperature characteristic in the resistance values of (7) and (9) and the current Iin. That is, by properly selecting the resistance value R2 of the resistor 9 from the equation (1), the pressure sensor 1
The sensitivity temperature coefficient TCSa of 1 can be adjusted so as to approach zero.

[0006]

However, since the bridge circuit 1 is generally formed by a diffused resistor, the TCR can take only a positive value. Therefore, when the adjustment is performed based on the equation (1), there is a problem that the correction can be performed only when the TCSb has a positive value.

Further, in order to adjust the resistance value R2, as shown in FIG. 6, the resistor 9 is replaced by a plurality of resistors 9 (1), 9 (2),
9 (3), ... (Resistance values R2-1, R2-2, R2-3 ...,) are replaced by parallel circuits, and switches 12 (1), 12 (2), 12 ( 3), ... Can be connected to selectively close one of the switches 12. However, in such a configuration, a current also flows through the closed switch 12, so that the conduction resistance of the switch 12 causes an error, which may deteriorate the accuracy of the sensor.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a temperature characteristic correction circuit device for a sensor capable of correcting the temperature characteristic of a sensor with higher accuracy.
Another object of the present invention is to provide a temperature characteristic correction method for a sensor.

[0009]

According to another aspect of the present invention, there is provided a sensor temperature characteristic correction circuit device according to claim 1, wherein in a sensitivity adjusting circuit for adjusting the sensitivity of the sensor, a plurality of switching elements connect a plurality of resistance elements. And the voltage amplification factor of the voltage amplifier circuit configured by using the operational amplifier is variably set. Further, in the sensitivity temperature coefficient adjusting circuit for adjusting the sensitivity temperature coefficient of the sensor, a plurality of switching elements are used to switch the connection state of a plurality of resistance elements having resistance temperature coefficients that are different from each other, and are configured using an operational amplifier. The voltage amplification factor of the voltage amplification circuit is variably set.

That is, in the sensitivity temperature coefficient adjusting circuit, when the set of input resistance and feedback resistance connected to the operational amplifier has the resistance temperature coefficients TCRi and TCRf, the respective resistance values Ri (T ), Rf (T)
Is Ri (T) = Ri (0) · (1 + TCRi · T) (2) Rf (T) = Rf (0) · (1 + TCRf · T) (3) However, Ri (0) and Rf (0) are the input resistance value and the feedback resistance value at the reference temperature, and T is the temperature difference from the reference temperature.

Then, the gain G of the voltage amplifier circuit formed by the operational amplifier is expressed by the equation (4). G = Rf (T) / Ri (T) = Rf (0) / Ri (0) {1+ (TCRf-TCRi) .T} (4) However, the lower part of the expression (4) is an approximate expression. In addition, TCRf <
It is assumed that <1, TCRi << 1. That is, (4)
The term (TCRf-TCRi) in the equation represents the gain temperature coefficient of the voltage amplifier circuit, and the gain temperature coefficient is
Depending on the magnitude relationship between TCRf and TCRi, TCRf> TCRi → gain temperature coefficient: positive TCRf = TCRi → gain temperature coefficient: 0 TCRf <TCRi → gain temperature coefficient: negative.

Therefore, the gain temperature coefficient of the voltage amplifier circuit in the sensitivity temperature coefficient adjusting circuit can take either positive or negative value, and regardless of whether the sensitivity temperature coefficient of the sensor shows a positive or negative value, Adjustment can be performed in the sensitivity temperature coefficient adjustment circuit so that the temperature coefficient becomes as small as possible.

Further, if the resistance temperature coefficient is adjusted in the sensitivity temperature coefficient adjusting circuit, the amplification factor of the voltage amplifying circuit also changes. Therefore, the sensitivity adjusting circuit side should be adjusted so that the voltage amplification factor becomes appropriate in total. To do. Therefore, the sensitivity of the sensor and the temperature coefficient of resistance can be satisfactorily adjusted. And when switching the connection of the resistance element when adjusting,
Since both are performed using the switching element connected in series to the input terminal of the operational amplifier, almost no current flows through the switching element in the conductive state. Therefore, even if the conduction resistance of the switching element is large, the resistance value does not affect the adjustment, so that the adjustment can be performed with high accuracy.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a pressure sensor will be described below with reference to FIGS. FIG. 1 is a diagram showing an electrical configuration of the pressure sensor 21. The pressure sensor 21 is the pressure sensor 11 shown in FIG.
Bridge circuit (sensor unit) corresponding to the bridge circuit 1
22, a current mirror circuit 3, and a current source 23 corresponding to the I / V conversion circuit 8, as well as a sensitivity adjustment circuit 24 and a TCS.
An adjusting circuit (sensitivity temperature coefficient adjusting circuit) 25 is provided.

The sensitivity adjusting circuit 24 is composed of an operational amplifier 26 and a resistor 28 as a differential amplifier. That is, the non-inverting input terminal of the operational amplifier 26 is connected to the terminal 22d of the bridge circuit 22, and the output terminal is connected to the bridge circuit 22 via the plurality of resistance elements 28 connected in series and the operational amplifier 43 as a buffer. Terminal 2
2c is connected. An analog switch (switching element) 29 is provided at each common connection point of the resistor elements 28.
Of the analog switch 29, and the other end of each analog switch 29 is commonly connected to the inverting input terminal of the operational amplifier 26. Each resistance element 28 is composed of a polysilicon resistance (poly).

On the other hand, the TCS adjusting circuit 25 is configured as an inverting amplifier by the operational amplifier 30 and the resistors 31 to 38. That is, the reference voltage Vref is applied to the non-inverting input terminal of the operational amplifier 30.
Operational amplifier 2 that configures the output terminal and the sensitivity adjustment circuit 24
Three series resistance circuits 39 to 41 composed of resistance elements 31 to 38 are connected in parallel with the output terminal of No. 6. The series resistance circuits 39, 40, 41 are respectively connected to the resistance element 3
1 to 33, 34 to 36, 37 and 38.

The inverting input terminal of the operational amplifier 30 has five analog switches (switching elements) 42.
One ends of (1) to 42 (5) are connected, and the other ends of these analog switches 42 are connected to the series resistance circuits 39 to 4 respectively.
1 is connected to each common connection point. That is, the analog switch 42 (1) is the resistance elements 32 and 33, the analog switch 42 (2) is the resistance elements 31 and 32, the analog switch 42 (3) is the resistance elements 37 and 38, and the analog switch 42 (4) is the resistance element. 34 and 35 and the analog switch 42 (5) are connected to a common connection point of the resistance elements 35 and 36.

The resistance elements 31, 32, 35 to 38 are composed of polysilicon resistors, and the resistance element 33
And 34 are constituted by diffused resistors (p +). The temperature coefficient of resistance of the polysilicon resistor is 800 ppm /
The temperature coefficient of diffusion resistance is 1200 ppm / ° C. The resistance values of the resistance elements 31 and 36 are 1 kΩ, the resistance values of the resistance elements 32 and 35 are 9 kΩ, and the resistance values of the other resistance elements are 10 kΩ.

Next, the operation of this embodiment will be described with reference to FIGS. 2 and 3. FIG. 2 shows the configuration of a general non-inverting amplifier circuit, but as described above, the gain G of the voltage amplifier circuit is expressed by equation (4). Then, in this embodiment, the analog switches 42 (1) to 42 (5) are used.
The input resistance Ri of the operational amplifier 30 depends on the selected state of
Alternatively, one of the feedback resistors Rf may be a series circuit of two resistance elements. Hereinafter, how the temperature coefficient of resistance in this case is expressed will be considered.

As shown in FIG. 3, it is assumed that the resistance values of two resistance elements connected in series are R1 and R2, and the temperature coefficients of resistance are TCR1 and TCR2. In this case, the respective resistance values R1 (T) and R2 (T) reflecting the resistance temperature coefficient
Is R1 (T) = R1 · (1 + TCR1 · T) (5) R2 (T) = R2 · (1 + TCR2 · T) (6)

Therefore, the combined resistance value of the two is given by equation (7). R1 + R2 = R1 * (1 + TCR1 * T) + R2 * (1 + TCR2 * T) = (R1 + R2) * (1+ (R1 * TCR1 + R2 * TCR2) * T / (R1 + R2)) (7) From the expression (7), the combined resistance The temperature coefficient TCR is expressed by equation (8). TCR = (R1 * TCR1 + R2 * TCR2) / (R1 + R2) ... (8) From this equation (8), if the resistance values R1 and R2 are selected as appropriate, the temperature coefficient TCR of the combined resistance becomes the resistance temperature coefficient TCR.
It can be set to a value between 1 and TCR2.

Hereinafter, when any one of the analog switches 42 (1) to 42 (5) of the TCS adjusting circuit 25 is switched to the ON state, the gain G of the voltage amplifying circuit is obtained.
(Predetermined room temperature) and how its temperature coefficient TCS is determined will be described.

<Analog switch 42 (1): ON> In this case, the input resistance Ri = 10 kΩ and the feedback resistance Rf = 10.
Since kΩ, the gain G = 1. Since the temperature coefficient TCRi of the input resistance is 800 ppm / ° C and the temperature coefficient TCRf of the feedback resistance is 1200 ppm / ° C,
The gain temperature coefficient TCS of the voltage amplifier circuit is TCS = 1200-800 = 400 (ppm / ° C.).

<Analog switch 42 (2): ON> In this case, the input resistance Ri = 1 kΩ and the feedback resistance Rf = 19 k
Ω, the gain G = 19. The temperature coefficient TCRi of the input resistance is 800 ppm / ° C. and the temperature coefficient TCRf of the feedback resistance is TCRf = (800 · 9 + 1200 · 10) / (9 + 10) = 1010 (ppm / ° C.), so the gain temperature coefficient TCS is , TCS = 1010−800 = 210 (ppm / ° C.).

<Analog Switch 42 (3): ON> In this case, the input resistance Ri = 10 kΩ and the feedback resistance Rf = 10.
Since kΩ, the gain G = 1. And TC
Since Ri = TCRf, the gain temperature coefficient TCS = 0,
Becomes

<Analog Switch 42 (4): ON> In this case, since the input resistance Ri and the feedback resistance Rf are switched when the analog switch 42 (2) is turned on, the gain G is 1/19. And the gain temperature coefficient TCS
Is TCS = 800-1010 = -210 (ppm /
℃).

<Analog Switch 42 (5): ON> In this case, since the input resistance Ri and the feedback resistance Rf are switched when the analog switch 42 (1) is turned on, the gain G = 1. The gain temperature coefficient TCS is equal to TC
S = 800-1200 = −400 (ppm / ° C.).

As described above, when any one of the analog switches 42 (1) to 42 (5) of the TCS adjusting circuit 25 is turned on, the gain temperature coefficient TCS becomes 40.
0ppm / ° C, 210ppm / ° C, 0, -210ppm
/ ° C, -400ppm / ° C can be changed.
Therefore, for example, the sensitivity temperature coefficient of the bridge circuit 22 is ±
± 100ppm if it varies to 500ppm / ℃
It can be adjusted to within / ° C.

However, in this case, the gain G at room temperature of the voltage amplifier also changes in the range of 19,1,1 / 19.
The change amount of the gain is adjusted by switching the analog switch 29 of the sensitivity adjusting circuit 24 at the previous stage. Since the resistance elements 28 of the sensitivity adjustment circuit 24 are all polysilicon resistors, the gain temperature coefficient is always "0".

Next, the actual adjustment procedure will be described.
First, the operator turns on the analog switch 42 (3) of the TCS adjusting circuit 25 to set the gain temperature coefficient to "0". At this adjustment stage, the analog switch 42
In order to selectively turn on (1) to 42 (5), a latch memory or the like for outputting data is provided to the control terminals of these analog switches 42 (1) to 42 (5), and the latches are provided. Switching is done by supplying data to the memory.

Then, the sensitivity temperature coefficient of the bridge circuit 22 is measured with the gain temperature coefficient of the TCS adjusting circuit 25 set to "0". That is, it is measured how the sensitivity of the bridge circuit 22 changes when the temperature is changed. Next, in order to set the gain temperature coefficient in the TCS adjustment circuit 25 so as to cancel the measured sensitivity of the bridge circuit 22, the analog switch 42
Any one of (1) to 42 (5) is selectively turned on.

Then, the analog switch 29 of the sensitivity adjusting circuit 24 is selected so as to adjust the gain amount added corresponding to the gain temperature coefficient of the selected TCS adjusting circuit 25. After the adjustment work, one of the analog switches 29 and 42 is constantly turned on (when the power is turned on), so that data is written in the EPROM (memory cell). Then, the corresponding analog switches 29, 42
ON data is supplied from the EPROM to the control terminal of.

As a premise for performing the above adjustment work,
The resistive elements 31 to 38 used in the TCS adjustment circuit 25 include
It goes without saying that a circuit having a resistance temperature coefficient larger than the assumed temperature coefficient of sensitivity of the bridge circuit 22 is required.

As described above, according to this embodiment, in the TCS adjustment circuit 25, the plurality of analog switches 42 are
(1) to 42 (5), the connection state of the plurality of resistance elements 31 to 38 that variably sets the amplification factor of the voltage amplification circuit is switched, and the sensitivity temperature coefficient of the bridge circuit 22 is adjusted to be as small as possible. In the sensitivity adjustment circuit 24, the sensitivity of the pressure sensor 21 is adjusted by switching the connection state of the resistance elements 28 that variably set the voltage amplification factor of the voltage amplification circuit by using the analog switches 29.

That is, since the gain temperature coefficient of the voltage amplification circuit in the TCS adjustment circuit can take either positive or negative value,
Regardless of whether the sensitivity temperature coefficient of the bridge circuit 22 shows a positive or negative value, the temperature coefficient can be adjusted to be as small as possible. Then, when the temperature coefficient of resistance is adjusted in the TCS adjusting circuit 25, the voltage amplification factor also changes, so that the voltage amplification factor on the side of the sensitivity adjusting circuit 24 is the pressure sensor 2.
1 Adjust so that the total is appropriate. Therefore, the sensitivity of the pressure sensor 21 and the temperature coefficient of resistance can be adjusted well.

The resistance elements 28, 3 for adjustment
The connection switching of 1 to 38 is performed by the operational amplifiers 26 and 30
Analog switch 28 connected in series to the input terminal of
Since it is performed by using 42, almost no current flows through the analog switches 28, 42 which have become conductive. Therefore,
Even if the conduction resistance is large, the resistance value does not affect the adjustment, so that the adjustment can be performed with high accuracy.

The present invention is not limited to the embodiments described above and shown in the drawings, and the following modifications or expansions are possible. Resistance temperature coefficient and resistance value of the resistance element,
The number of switching elements in the sensitivity adjustment circuit 24 and the TCS adjustment circuit 25 may be set appropriately. Sensitivity adjustment circuit 24
The connection order of the TCS adjusting circuit 25 and the TCS adjusting circuit 25 may be exchanged.
The connection form of the resistance element and the analog switch in the sensitivity temperature coefficient adjusting circuit may be the same as that of the resistance element 28 and the analog switch 29 of the sensitivity adjusting circuit 24, for example. A FET may be used as the switching element.
The resistance element used in the sensitivity temperature coefficient adjusting circuit is not limited to the polysilicon resistance and the diffusion resistance, and any element having a different resistance temperature coefficient may be used. The present invention is not limited to the pressure sensor, but may be applied to other acceleration sensors or the like.

[Brief description of drawings]

FIG. 1 is a diagram showing an electrical configuration of an embodiment of the present invention applied to a pressure sensor.

FIG. 2 is a diagram illustrating a gain when elements having different resistance temperature coefficients are used for an input resistance and a feedback resistance in a general configuration of a non-inverting amplifier circuit.

FIG. 3 is a diagram illustrating a temperature coefficient of resistance when elements having different temperature coefficients of resistance are connected in series.

FIG. 4 is a view corresponding to FIG. 1 showing a conventional technique.

FIG. 5 is a diagram illustrating a sensitivity temperature coefficient of a sensor.

6 is a diagram showing a state in which a resistor 9 in FIG. 5 is replaced with a parallel circuit of a plurality of elements.

[Explanation of symbols]

21 is a pressure sensor, 22 is a bridge circuit (sensor section),
24 is a sensitivity adjustment circuit, 25 is a TCS adjustment circuit (sensitivity temperature coefficient adjustment circuit), 26 is an operational amplifier, 28 is a resistance element,
Reference numeral 29 is an analog switch (switching element), 30 is an operational amplifier, 31 to 38 are resistance elements, and 42 is an analog switch (switching element).

Claims (2)

[Claims] 1. A circuit that amplifies an output voltage of a sensor unit configured by connecting a plurality of resistance elements in a bridge to detect a target physical quantity and corrects a temperature characteristic of a sensor that outputs a sensor signal. A sensitivity adjustment circuit for adjusting the sensitivity of the sensor and a sensitivity temperature coefficient adjustment circuit for adjusting the sensitivity temperature coefficient of the sensor.The sensitivity adjustment circuit includes an operational amplifier, an input resistance and a feedback to the operational amplifier. A plurality of resistance elements connected as resistors to variably set the voltage amplification factor and a plurality of resistance elements connected in series to the input terminal of the operational amplifier in order to switch the connection state of the plurality of resistance elements to the operational amplifier. The sensitivity temperature coefficient adjusting circuit is configured by including a switching element, and the sensitivity temperature coefficient adjusting circuit includes an operational amplifier, and an input resistance and a feedback resistance in the operational amplifier. A plurality of resistance elements for variably setting the voltage amplification factor of the operational amplifier having at least a part of different resistance temperature coefficients, and for switching the connection state of the plurality of resistance elements to the operational amplifier, A temperature characteristic correction circuit device for a sensor, comprising: a plurality of switching elements connected in series to an input terminal of the operational amplifier. 2. A method of amplifying an output voltage of a sensor unit configured by connecting a plurality of resistance elements in a bridge to detect a target physical quantity and correcting the temperature characteristic of the sensor output as a sensor signal. Then, in any one of the two voltage amplification circuits connected in series to the sensor unit, at least a part of the resistors is different due to the plurality of switching elements connected in series to the input terminal of the operational amplifier. The voltage amplification factor is variably set by switching the connection state of a plurality of resistance elements having a temperature coefficient, and the sensitivity temperature coefficient of the sensor unit is adjusted to be as small as possible. On the other hand, the voltage amplification factor can be adjusted by switching the connection state of the resistance elements with the switching elements connected in series to the input terminal of the operational amplifier. Set, the temperature characteristic correction method of the sensor, characterized in that to adjust the sensitivity of the sensor.