JPH0273104A - Temperature compensating circuit for semiconductor sensor - Google Patents

Abstract

PURPOSE:To suppress curvature of a temperature characteristic at the zero point of a bridge output voltage to reduce the number of elements by adjusting resistances in accordance with the zero-point output voltage of a bridge and its temperature characteristic. CONSTITUTION:The differential output voltage of the bridge has the impedance converted by operational amplifiers OP2 and OP3 and is amplified by a differential amplifier consisting of an operational amplifier OP1 and resistances R1 to R4 and RA. A positive temperature dependency is provided to the degree of amplification by the positive temperature dependency of the resistance RA to compensate the output voltage of the bridge. At such a time, adjustment is performed y the resistance R4. The circuit consisting of an operational amplifier OP4 and resistances R5 to R8 inverts and amplifies the difference between a power supply voltage Vcc and the voltage divided by resistances R5 and R6. The value of a resistance R7 is selected to compensate the temperature characteristic of the bridge zero-point output voltage, and simultaneously, values of resistances R5 and R6 are changed to adjust the pressure sensor output level.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a circuit for temperature compensation of a semiconductor sensor, such as a pressure sensor equipped with a strain gauge formed on a semiconductor pressure-sensitive diaphragm. The present invention relates to a temperature compensation circuit for a semiconductor sensor that can achieve temperature compensation with a small number of resistors with high accuracy.

[Conventional technology]

In general, a pressure sensor equipped with a semiconductor pressure-sensitive diaphragm has a zero point temperature characteristic due to a difference in temperature characteristics between strain gauges, and a sensitivity temperature characteristic due to the temperature dependence of the piezoresistance coefficient of the strain gauge. Particularly when used in applications requiring high precision over a wide temperature range, it is essential to compensate for these two temperature characteristics. FIG. 3 shows an example of a conventional circuit for compensating the zero point temperature characteristic and sensitivity temperature characteristic in this type of semiconductor pressure sensor. The strain gauges Rgl-Rg4 are formed by diffusion on a silicon pressure-sensitive diaphragm and are positioned on the diaphragm such that when pressure is applied to the diaphragm, a voltage signal is generated between the bridge output terminals AB. This voltage signal is applied to operational amplifier OP2. The impedance is converted by a buffer configured by OP3, and further amplified by a differential amplifier configured by an operational amplifier OPI, resistors R1 to R4, and a large temperature-dependent resistor RA,
Output. The voltage signal generated between the bridge output terminals AB changes depending on the amount of pressure applied to the silicon diaphragm, and the relationship between this voltage and pressure, that is, the sensitivity is -3.
It has a negative temperature characteristic of 000 to -1000 ppm/"C. This negative temperature characteristic of sensitivity is
This is compensated for by connecting a parallel resistor consisting of a resistor RA and a resistor R4, which have a positive temperature dependence, as a feedback resistor. On the other hand, a zero point temperature characteristic compensation circuit is constituted by the operational amplifier OP4, the resistors R5 to RIO, and the resistors RB and RC having large temperature dependence. The output terminal C of this circuit is a resistor R
3 to the non-inverting input terminal of the operational amplifier OPI, whereby the output voltage Vd of the zero point temperature characteristic compensation circuit is added to the amplified bridge output voltage. In this case, temperature compensation at the zero point is performed by adjusting the values of the resistors R8 and R9 in accordance with the temperature characteristics of the bridge output voltage when the pressure applied to the silicon diaphragm is zero. At the same time, by adjusting the values of the resistors R5 and R6, the output level can be adjusted to a predetermined value. Furthermore, as a temperature compensation circuit of this type, there exists Japanese Patent Laid-Open No. 59-153117, which is an earlier application filed by the present applicant. FIG. 5 shows an example of a temperature compensation circuit for a pressure sensor constructed using the circuit of the prior application, in which a resistor R11 is connected in parallel to the resistors RB and R8 in FIG. 3, and a resistor RC. A resistor R12 is added in parallel to R9. In this case, the zero point temperature characteristics can be compensated by selecting the values of the resistors R8, R9, R11, and R12.

[Problem to be solved by the invention]

In the temperature compensation circuit of the pressure sensor shown in FIG. 3, the bridge output voltage amplification circuit and the zero point temperature characteristic compensation circuit are relatively independent, making adjustment easy. However, the output voltage Vd of the zero point temperature characteristic compensation circuit is influenced by the temperature characteristic of the resistor RA for sensitivity characteristic compensation by passing through the operational amplifier OP1, and the temperature characteristic of the resistor RA is affected by the temperature characteristic due to the resistors RB and RC. By combining the gates, a second-order temperature characteristic, that is, a curve in the temperature characteristic is produced. This curve in temperature characteristics is as shown in FIG. 4, and there is a problem in that the accuracy is particularly poor near the upper limit Th and lower limit Tf of the operating temperature range. In addition, in the circuit shown in FIG. 5, the resistors R8, R9, and R11°R
By selecting a value of 12, it is possible to compensate for the curve in the temperature characteristic at the zero point of the sensor output voltage and make it a flat characteristic. It is necessary to add two more resistors,
Therefore, there was a problem in that the number of elements increased and it was difficult to make the circuit compact. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a temperature compensation circuit for a semiconductor pressure sensor that can eliminate the above-mentioned problems, suppress the bending of the temperature characteristics at the zero point of the bridge output voltage, and can be configured with a small number of elements. .

[Means to solve the problem]

In order to solve the above problems, the present invention provides an inventive circuit that includes:
"A bridge circuit that includes a strain gauge formed on a semiconductor diaphragm, and an operational amplifier that amplifies the output voltage of this bridge circuit. a first operational amplifier connected to a large first resistor; an output terminal of the second operational amplifier is connected to a non-inverting input terminal of the first operational amplifier via a second resistor; A voltage obtained by dividing the power supply voltage by a resistor is applied to the non-inverting input terminal of the second operational amplifier, and the first voltage is applied between the inverting input terminal of the second operational amplifier and a predetermined potential. It is assumed that a third resistor having the same or almost equal temperature dependence as the resistor is provided with an adjustable resistor between the inverting input terminal and the output terminal so as to compensate for the zero point temperature characteristic.

[For use]

According to the configuration of the present invention, first, the sensitivity temperature characteristic of the output voltage of the bridge circuit including the strain gauge formed on the semiconductor diaphragm is the same as that of the conventionally known circuit.
compensated by a feedback resistor circuit of the first operational amplifier, which includes a first resistor with a high temperature dependence, while a feedback resistor of the second operational amplifier and a power supply voltage divider resistor, which are identical to or equal to said first resistor. In a zero-point temperature characteristic compensation circuit composed of a third resistor having approximately equal temperature dependence, the temperature characteristic of the zero-point output voltage is adjusted by adjusting the resistance according to the zero-point output voltage of the bridge and its temperature characteristics. has a flat characteristic with no bending.

【Example】

FIG. 1 shows a first embodiment of a temperature compensation circuit for a semiconductor pressure sensor to which the present invention is applied. Strain gauges Rg1 to Rg4 are formed by diffusion on a silicon pressure-sensitive diaphragm, and are positioned on the diaphragm such that applying pressure to the diaphragm generates a voltage signal between differential output terminals A and B of the bridge. . The differential output terminal A is connected to a non-inverting input terminal of an operational amplifier OP2 which acts as a buffer, and the differential output terminal B is connected to a non-inverting input terminal of an operational amplifier OP3 which also acts as a buffer. Furthermore, the output terminal of the operational amplifier OP2 is connected to the non-inverting input terminal of the operational amplifier OPI via a resistor R1,
The output terminal of the operational amplifier OP3 is connected to the inverting input terminal of the operational amplifier 2SOP1 via a resistor R2. The output terminal F of the operational amplifier OPI is the output terminal of this pressure sensor, and a resistor RA and a resistor R4, which have a large positive temperature dependence, are connected between the output terminal and the inverting input terminal of the amplifier ○P1. connected in parallel. As this resistor RA, a diffused resistor formed outside the diaphragm portion of the silicon chip, a thermistor, or the like is applied. On the other hand, a resistor RB having the same or approximately the same temperature dependence as the resistor RA is connected between the power supply terminal E and the inverting input terminal of the operational amplifier OP4. Also, power terminal E and ground terminal G
Resistors R5 and R6 are connected in series between R
The connection point between the resistor R6 and the resistor R6 is connected to the non-inverting input terminal of the operational amplifier OP4. A resistor R7 is connected between the output terminal C of the operational amplifier OP4 and the inverting input terminal of this amplifier OP4.
is connected, and the output terminal C is connected to the non-inverting input terminal of the operational amplifier OPI via a resistor R3. The present invention will be described in detail with the above configuration. The differential output voltage of the bridge is determined by operational amplifier OP2. The impedance is converted by a buffer made up of OP3, and further amplified by a differential amplifier made up of an operational amplifier OPI and resistors R1 to R4 and RA. Here, the output voltage signal of the bridge due to pressurization is -3000 to -1000 ppm/
Although it has a negative temperature characteristic of "C", it is compensated for by making the amplification degree of the differential amplifier have a positive temperature dependence due to the positive temperature dependence of the resistor RA.Resistor R4 is an adjustment resistor for this purpose. Also, the sensitivity of this pressure sensor is determined by the resistance R.
It is adjusted by equally raising and lowering the values of 1 and R2. The circuit consisting of operational amplifier OP4 and resistors R5, R6, R7, and RB inverts and amplifies the difference between the power supply voltage VCC and the voltage divided by resistors R5 and R6.The value of resistor R7 must be selected. This circuit compensates for the temperature characteristics of the bridge zero point output voltage, that is, the temperature characteristics of the output voltage when the diaphragm is not pressurized, and at the same time adjusts the pressure sensor output level by changing the values of resistors R5 and R6. It is. Here - R1-R2 for boat fishing, and R1. R2(R3, R
4, RA, and this example also follows. In this way, the pressure sensor output voltage Vout when no pressure is applied is expressed by the following equation (1). Here, Vino is the zero point output voltage of the bridge. I will do it again. When the zero point output voltage of the bridge and its temperature characteristics are zero,
The first term on the right side of equation (3) is zero. Therefore, for temperature compensation, the second term on the right side needs to be a constant value regardless of the temperature. In other words, substituting 2(2) into equation (1) and transforming it gives 2R
3・(R5+R6) RB (RA+R4)
Since the resistors RA and RB have the same temperature dependence, RA/RB in equation (4) has a constant value regardless of temperature. Therefore, in order to satisfy equation (4), it is assumed that the resistors RA and RB have the same temperature dependence. The zero-point output voltage of the bridge and its temperature characteristics often vary on both sides of the positive and negative sides around zero, and this example also follows this, where RAoRBo is the resistance RA at the reference temperature (for example, 25°C). ,R
This is the BO value. By selecting a value for the resistor R7 that satisfies equation (6), the zero point temperature characteristics can be compensated for. In this case, Vou
L = const, and the zero point output voltage of the pressure sensor V
The slope and curve of the out temperature characteristics are all zero, making it possible to realize completely flat characteristics. Next, when the first term on the right side of equation (3) has a positive temperature characteristic, increase the values of resistors R5 and R1, or decrease the value of R5R6, and increase the temperature of the second term on the right side of equation (3). Compensate by giving the characteristic a negative tendency. Conversely, if the first term on the right side has a negative temperature characteristic, reduce the values of resistors R5 and R7, or increase the value of R5-R6, and then compensate by giving it a positive tendency. FIG. 2 shows a second embodiment in which the present invention is applied, in which the connection point of the resistor RB in the first embodiment (FIG. 1) is changed from the power terminal E to the ground terminal G. With this circuit, the potential V of the output terminal C of the operational amplifier OP4
d becomes more than Vcc/2, and as a result, the amplified bridge output voltage at the output terminal F of the pressure sensor is Vcc
A large potential of /2 or more is added and output. This method can be applied when it is desired to set the zero point of the pressure sensor output to a high level. Note that the compensation of temperature characteristics has the same effect as the first embodiment.

【Effect of the invention】

According to the present invention, there is a bridge circuit including strain gauges Rgl to Rg4 formed on a semiconductor diaphragm, and the output of the bridge circuit is given to its two input terminals via a resistor RLR2, and A first feedback resistor circuit RA, R4 including a first resistor RA with large temperature dependence is connected between its inverting input terminal and output terminal F.
A temperature compensation circuit for a semiconductor pressure sensor, comprising: an operational amplifier OPI; a third resistor having the same or almost equal temperature dependence as the first resistor RA; The resistor RB and the resistor R7, which is a feedback resistor and whose other end is connected to the output terminal C, are both connected to its own inverting input terminal, and the power supply voltage Vcc is divided by the resistors R5 and R6. The output Vd of the second operational amplifier OP4, which is connected so that the applied voltage is applied to its non-inverting input terminal, is connected to the non-inverting input terminal of the first operational amplifier OPI via a second resistor R3. Therefore, when the zero point output voltage of the bridge and its temperature characteristic are zero, by selecting the value of resistor R7 to satisfy the condition of equation (6), the zero point temperature characteristic of the sensor output voltage Vout can be changed. It becomes possible to have flat characteristics without bending. If the zero point output voltage of the bridge and its temperature characteristics deviate from zero, select the values of resistors R5 to R7 and use the formula (3
) By making the slope of the temperature characteristic of the first term on the right side of (2) cancel out the slope of the temperature characteristic of the second term on the right side of (3), the slope of the zero point temperature characteristic of the sensor output voltage Vout becomes zero. Adjustments are made so that It is a value. Further, the number of resistances of a circuit to which the present invention is applied is shown in FIG. Both the embodiments in Figure 2 have 9 resistors (however, not including strain gauges), and the embodiment in Figure 5, which has the same function, has 1 resistor.
This is 6 fewer pieces compared to the 5 pieces used. Therefore, it becomes possible to realize a more compact circuit. It goes without saying that this circuit can be applied not only to the temperature characteristics of semiconductor pressure sensors, but also to other applications that require compensation for the temperature characteristics of zero point and sensitivity.

[Brief explanation of the drawing]

1 and 2 are diagrams showing different embodiments of a temperature compensation circuit for a semiconductor sensor to which the present invention is applied, FIG. 3 is a diagram showing a conventionally known temperature compensation circuit for a semiconductor sensor, and FIG. The figure is a diagram showing an example of the zero-point temperature characteristic of the sensor output voltage when the circuit shown in Fig. 3 is applied, and Fig. 5 is a diagram showing another example of the conventionally known temperature compensation circuit for semiconductor sensors. be. Rgl~Rg4: Diffused strain gauge, R1-R7: Resistor,
RA, RB: Resistance with large positive temperature dependence, OP
1 to OP4: Operational amplifier, Vcc: Power supply voltage, Vou
t: sensor output voltage, Gnd: ground potential, Vd: operational amplifier OP4 output voltage, A-C1B-G: terminal. L Th temperature Figure 4

Claims (1)

[Claims] A bridge circuit including a strain gauge formed on a semiconductor diaphragm, and an operational amplifier for amplifying the output voltage of this bridge circuit, between an inverting input terminal and an output terminal of this amplifier. a first operational amplifier in which a large temperature-dependent first resistor is connected to the output terminal of the second operational amplifier; A voltage obtained by dividing the power supply voltage by a resistor is applied to the non-inverting input terminal of the second operational amplifier, and a voltage is applied between the inverting input terminal of the second operational amplifier and a predetermined potential. A third resistor having the same or almost equal temperature dependence as the first resistor is connected, and an adjustable resistor is connected between the inverting input terminal and the output terminal to compensate for the temperature characteristics at the zero point. A temperature compensation circuit for a semiconductor sensor, characterized by: