JP2610736B2 - Amplification compensation circuit of semiconductor pressure sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor pressure sensor element having a resistance bridge circuit formed of a pressure-sensitive gauge resistor (piezoresistive element) formed on a silicon diaphragm, and an output signal from the sensor element. The present invention relates to an amplification compensation circuit of a semiconductor pressure sensor which is suitable as a so-called integrated pressure sensor amplification compensation circuit in which a bipolar linear IC (integrated circuit) for amplifying a signal is integrated on the same semiconductor chip.

[0002]

2. Description of the Related Art For example, a pressure sensor used in an environment having a large temperature change, such as a semiconductor pressure sensor used as an electric component of an automobile, is required to be able to measure the pressure with high accuracy in a wide temperature range. You. The semiconductor pressure sensor includes, as a sensor element, a resistance bridge circuit including a pressure-sensitive gauge resistor formed on a silicon diaphragm. However, since the sensitivity and the zero point of the sensor element fluctuate depending on the temperature, when used in an environment where the temperature change is large, a compensation circuit is usually provided to compensate for the fluctuation of the output of the sensor element due to the temperature. Is provided.

FIG. 6 is a circuit diagram showing a compensating circuit for compensating a variation in the output of a conventional semiconductor pressure sensor element due to temperature. Each of the resistors Ra, Rb, Rc, and Rd is a pressure-sensitive gauge resistor (piezoresistive element) formed on a silicon diaphragm, and forms a resistor bridge circuit. Conventionally, an external resistor R is connected between input terminals 1 and 2 of a bridge circuit constituted by pressure-sensitive gauge resistors Ra, Rb, Rc, and Rd.
By connecting _L, and the compensate for variations in sensitivity due to temperature, the input terminal 1 and the output terminal 3 (or, the output terminal 4) by connecting an external resistor R _P between, the zero point due to temperature Variations are compensated.

That is, the pressure-sensitive gauge resistors Ra, Rb, Rc, and Rd formed on the silicon diaphragm have a positive temperature coefficient of about 1000 to 3000 ppm / ° C. On the other hand, the external resistors _RP and _RL are ordinary resistance elements, and their temperature coefficients are as small as about 100 ppm / ° C. Therefore, the external resistance temperature coefficient than the pressure sensitive gauge resistors is small R _P, R
By connecting _L as shown in FIG. 6, the temperature coefficient of the combined resistance value can be reduced.

More specifically, when a bridge circuit composed of a pressure-sensitive gauge resistor is driven by a constant current, an offset voltage is generated due to an unbalance of the resistors constituting the bridge circuit. This is caused by an output terminal of the bridge circuit. It can be considered that there is a pseudo resistor between them. Then, it can be said that the output voltage from the resistance bridge circuit changes depending on the temperature because the resistance value of the pseudo resistor changes depending on the temperature. The temperature characteristics of the pressure sensor element can be compensated by connecting the external resistors _RP and _RL so as to cancel the pseudo temperature coefficient of the resistor.

More specifically, the resistance values of the resistors R _P and R _L are determined as follows.

[0007] Sensitivity compensation resistor R _L First, the resistance value when the temperature of the resistive bridge circuit is low R _bl
And the resistance value R _bh when the span (sensitivity) _Sl and the temperature are high
And measuring the span S _h. Then, the value of the sensitivity compensation resistor _RL is determined by the following equation (1).

[0008]

R _L = (R _bh × S _l −R _bl × S _h ) / (S _h −S _l )

By determining the resistance value of the external resistor _RL in this way, it is possible to compensate for a change in sensitivity due to the temperature of the sensor element.

[0010] resistor R _P generally for zero compensation, the temperature coefficient of resistance is a, if the pseudo resistance temperature is present between the output terminals when the t ₁ and R _01, the temperature t The resistance value R _{1 at a} temperature higher than ₁ by t ° C. is R ₁ = R ₀₁ (1 + at).

If it is assumed that the output voltage V ₀ from the bridge circuit does not change even if the temperature changes, the pseudo resistance R ₀₁ when the temperature is t ₁ and the pseudo resistance R ₀₁ when the temperature is t ₂ It suffices if R ₀₂ is the same. That is, each of the resistors Ra, Rb, Rc, Rd, _RL , and R when the temperature is t _1.
P and the respective resistances Ra and R when the temperature is t _{2.
b, Rc, Rd, R L} , by solving the equation of the combined resistance value R _P for the resistance R _P, it is possible to calculate the value of the resistor R _P. In fact, there is no change in the zero point is linear, with temperature, by determining the resistance value of the thus resistor R _P, practically compensates for variations in the zero point due to temperature with sufficient accuracy that Can be.

FIG. 7 is a circuit diagram showing an amplification compensation circuit of a conventional semiconductor pressure sensor. An operational amplifier AMP is provided in the semiconductor pressure sensor element 5 constituted by a pressure-sensitive gauge resistor.
1 is supplied with a predetermined current.
As before, the resistance R _P in the sensor element 5 to compensate for variations in the resistance R _L and zero to compensate for variations in sensitivity due to temperature
Is connected. Further, fine adjustment resistors R ₁₁ and R ₁₂ of a resistance bridge circuit are connected to the sensor element 5.
The signal output from the sensor element 5 is amplified by the operational amplifiers AMP2 and AMP3 and output from the output terminals 7 and 8.

Such an amplification compensating circuit of a semiconductor pressure sensor utilizes the difference between the temperature characteristics of a pressure-sensitive gauge resistor and the temperature characteristics of an external resistor to compensate for the temperature characteristics of a sensor element. There is an advantage that the temperature fluctuation of the pressure sensor element can be easily compensated and adjusted with high accuracy without requiring a special temperature sensing element and an active element as a compensation element. For this reason, this kind of amplification compensation circuit is widely adopted.

By the way, usually, in order to set the resistance value of an external resistor according to the characteristics of the sensor element, a thick film printed resistance circuit is used as the external resistor, and the resistance value of the thick film resistor is set for each sensor. Adjusted (trimmed). For a typical semiconductor pressure sensor, the resistance value as the external resistor R _P is 3
A high resistance of 00 kΩ to 15 MΩ is required, and an external resistance R
_{As L} , a resistor having a resistance value of 15 kΩ to 100 kΩ is required. Conventionally, thick film resistor circuits are usually used as external resistors R _P and _RL , and thick film resistors having several types of sheet resistance values are formed by printing and firing in accordance with each resistor. .

[0015]

However, the conventional amplification compensation circuit for a semiconductor pressure sensor has the following problems. That is, recently, in response to a demand for downsizing the pressure sensor, an integrated pressure sensor in which a sensor element and an amplifier section (including a temperature compensation and adjustment section) are integrally formed on the same chip has been developed. In such an integrated pressure sensor, a large area is required for a thick-film printing resistor, and a semiconductor element such as a sensor element and an amplifier cannot be kept at a high temperature in a printing and firing process. As a resistor, a metal thin film resistor is integrated on the same chip as the sensor element.

However, it is technically difficult to form a high resistance of several hundred kΩ to several MΩ with a thin film resistor, and it is also technically difficult to individually form resistors having several types of sheet resistance. There are many difficulties. Therefore, it is possible to compensate for the temperature characteristics of the sensor element without using a high resistance which is difficult to form as a thin film resistor, and there is a demand for an amplification compensation circuit of a semiconductor pressure sensor applicable to an integrated pressure sensor. I have.

The present invention has been made in view of such a problem, and can compensate for the temperature characteristics of a semiconductor pressure sensor element without requiring a high resistance which is difficult to form as a thin film resistor. An object of the present invention is to provide an amplification compensation circuit of a semiconductor pressure sensor applicable to an integrated pressure sensor.

[0018]

SUMMARY OF THE INVENTION An amplifier circuit for a semiconductor pressure sensor according to the present invention has an operational amplifier for amplifying a signal output from a semiconductor pressure sensor element. According to the temperature characteristics of the sensor element, adjust the collector current of the input transistor of the differential amplifier circuit constituting the input stage of the operational amplifier,
It is characterized by being set by changing the base-emitter voltage of this transistor.

[0019]

According to the present invention, the temperature characteristic of the semiconductor pressure sensor element is compensated by utilizing the temperature characteristic of the offset voltage of the operational amplifier for amplifying the signal output from the sensor element. That is, since the voltage output from the pressure-sensitive gauge resistance bridge circuit of the semiconductor pressure sensor element is small,
The output of the sensor element is amplified to about 100 to 300 times using an amplifier circuit. In this case, an operational amplifier in which the temperature characteristics of the offset voltage are set according to the temperature characteristics of the sensor element is used as the amplifier circuit.

Generally, an operational amplifier has a temperature characteristic called an offset voltage temperature drift (ie, a temperature characteristic of an offset voltage). This offset voltage temperature drift is mainly caused by a difference in the temperature characteristics of the base-emitter voltage V _BE of the two input transistors of the differential amplifier circuit, and the input offset voltage of the operational amplifier changes with temperature. It is a phenomenon. Since the offset voltage temperature drift is amplified by an amount corresponding to the amplification of the operational amplifier, in a general application, the smaller the offset voltage temperature drift is, the more stable the characteristic is with respect to a temperature change.

However, in the present invention, for example, the temperature characteristic of the semiconductor pressure sensor element is adjusted by adjusting the collector current of the input transistor of the differential amplifier circuit constituting the input stage of the operational amplifier according to the semiconductor pressure sensor element. An offset voltage temperature drift of the operational amplifier is generated so as to cancel. This eliminates the need for a conventionally required high resistance for zero point compensation, and enables application to an integrated pressure sensor.

[0022]

Next, an embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a circuit diagram showing an operational amplifier in an amplification compensation circuit of a semiconductor pressure sensor according to a first embodiment of the present invention. FIG. 2 is a circuit diagram showing a general operational amplifier conventionally used for amplifying the output of a semiconductor pressure sensor element.

The operational amplifier of this embodiment is different from the conventional operational amplifier in that the transistor Q ₆ for changing the ratio of the current flowing through the input transistors Q ₁ and Q ₂ of the differential amplifier circuit at the input stage of the operational amplifier is used. and in that the resistor R ₂ is provided.

In FIG. 2, transistors Q ₁ and Q ₂ are input transistors of a differential amplifier circuit at an input stage of an operational amplifier, and transistors Q _{3 to} Q ₅ constitute an active load circuit. In such a differential amplifier circuit, the base-emitter voltages V _BE1 , V _BE1 and V ₂ of the input transistors Q ₁ and Q ₂ are
_{If BE2} is the same, the two cancel each other out and no offset voltage is generated. However, when they are different, an offset voltage is generated. If the difference between the base-emitter voltages V _BE1 and V _BE2 changes depending on the temperature, the offset voltage has a temperature characteristic. Conventionally, it is considered that it is preferable that the offset voltage of the operational amplifier be as small as possible because the temperature characteristics of the output of the sensor element are compensated by an external resistor.

On the other hand, in the present embodiment, by changing the ratio of the current flowing through the input transistors Q ₁ and Q ₂ of the differential amplifier circuit of the operational amplifier in the portion constituted by the transistor Q ₆ and the resistor R _2. , Base-emitter voltages V _BE1 ′, V ₂ of the input transistors Q ₁ , Q _2
A difference is intentionally generated between _BE2 '. As a result, offset voltage temperature drift occurs in the operational amplifier. By generating the offset voltage temperature drift of the operational amplifier so as to compensate for the temperature characteristic of the output of the sensor element, the temperature characteristic of the sensor element can be compensated as a whole circuit.

The temperature compensation according to the present embodiment can be theoretically explained by the following equation.

First, the emitter current _{IE of the} transistor is expressed by the following equation (2).

[0029]

I _E = I _S exp (qV _BE / kT) where I _S ; saturation current q; electron charge k; Boltzmann constant T; absolute temperature V _BE ; base-emitter voltage

The transistor is ideal and h _FE
Is infinite, and I _E = I _C (collector current).

[0031]

Equation 3] _{V BE = (kT / q)} ln (I C / I S)

Assuming that the emitter area of the transistor is A, the saturation current I _S can be generally expressed by the following equation (4). Here, γ is a proportional constant.

[0033]

## EQU4 ## I _S = γA

The PNP transistors Q ₇ , Q in FIG.
_8, the emitter size of Q ₉ is the same, also, NPN
Assume that the transistors Q ₆ , Q ₁₀ , Q ₁₁ , and Q ₁₂ have the same emitter size, and the emitter size of the transistor Q ₁₃ is B times the emitter size of the transistor Q ₁₀ . It is also assumed that the collector currents of the active load transistors Q ₁₁ and Q ₁₂ are the same. Then, the input offset voltage V _ID of the operational amplifier becomes the input transistor Q ₁ ,
Since this is the difference between the base-emitter voltages V _BE1 ′ and V _{BE 2} ′ of Q ₂ , these relationships can be expressed by the following equation (5).

[0035]

[ _Equation 5] V _ID = V _BE1 '−V _BE2 '

When the input offset voltage V _ID is calculated using the equations (3), (4) and (5), the following equations (6) to (8) are obtained.

[0037]

V _ID = ln ｛(I ₁ + I ₂ ) / (I ₁ -I ₂ )

[0038]

I ₁ = {(kT / q) · lnB} / R ₁

[0039]

I ₂ = {(kT / q) · ln (I ₁ / I ₂ )} / R ₂

In Equations (5) to (8), since T is an absolute temperature, it is clear that the input offset voltage of the operational amplifier has a temperature dependency, and that the resistances R ₁ and R ₂ can be calculated. . That is, the values of the resistors R ₁ and R ₂ can be adjusted to appropriate values by laser trimming or the like, and the operational amplifier can be given a temperature dependency corresponding to the temperature characteristics of the output voltage of the sensor element.

In actual use, the operational amplifiers shown in FIG. 1 are used as the operational amplifiers AMP2 and AMP3 shown in FIG. 7, and each operational amplifier has a temperature characteristic of an offset voltage as an instrumentation amplifier. By doing so, it is possible to generate both positive and negative temperature characteristics with respect to temperature changes in the entire circuit. The temperature characteristic of the operational amplifier makes it possible to cancel the fluctuation of the zero point due to the temperature of the sensor element, so that the conventionally required resistor _RP becomes unnecessary.

Since the present embodiment does not require a resistor having a large resistance value, it is particularly suitable for an integrated pressure sensor in which a semiconductor pressure sensor element and an amplifier circuit are formed on the same chip.

FIG. 3 is a graph showing the variation of the output of the pressure sensor due to the temperature when the temperature is compensated according to the present embodiment by taking the applied voltage on the horizontal axis and the output voltage on the vertical axis. FIG. 4 is a graph showing the variation of the output of the pressure sensor with temperature when temperature compensation is not performed using the conventional operational amplifier shown in FIG.

As shown in FIGS. 3 and 4, -30 to 100
In the case where the temperature correction is not performed at the temperature of ° C., the fluctuation of about 20% FS (20% of full scale) due to the temperature change can be improved to about 1.5% FS in the present embodiment. .

FIG. 5 is a circuit diagram showing a differential amplifier circuit at an input section of an operational amplifier in an amplification compensation circuit of a semiconductor pressure sensor according to a second embodiment of the present invention.

In this embodiment, an operational amplifier having no active load circuit is used. That is, the emitters of the input transistors Q ₂₁ and Q ₂₂ are connected to the current source I
And collector load resistors R _C1 and R _C are connected between the collectors of the transistors Q ₂₁ and Q ₂₂ and the power supply V _CC.
C2 is interposed.

In this embodiment, the collector currents of the input transistors Q ₂₁ and Q ₂₂ are changed by appropriately adjusting the values of the collector load resistances R _C1 and R _C2 of the input transistors of the differential amplifier circuit. the base of the transistor Q _21, Q ₂₂ - changing the emitter voltage. Thus, the temperature dependence of the offset voltage according to the temperature characteristic of the output of the sensor element can be generated, and the same effect as in the first embodiment can be obtained.

[0048]

As described above, in the present invention,
Since the temperature compensation of the semiconductor pressure sensor element is performed by the operational amplifier that amplifies the output from this sensor element, the temperature compensation of the zero point of the sensor element is possible without using a high resistance that is difficult to form as a thin film resistor. It is. Therefore, the present invention is extremely useful for practical use of an integrated pressure sensor.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an operational amplifier in an amplification compensation circuit of a semiconductor pressure sensor according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional operational amplifier for amplifying the output of a semiconductor pressure sensor element.

FIG. 3 is a graph showing a change in output with temperature when temperature compensation is performed according to an embodiment of the present invention.

FIG. 4 is a graph showing changes in output with temperature when temperature compensation is not performed.

FIG. 5 is a circuit diagram showing an operational amplifier in an amplification compensation circuit of a semiconductor pressure sensor according to a second embodiment of the present invention.

FIG. 6 is a circuit diagram showing a sensitivity and zero point compensation method of a conventional semiconductor pressure sensor.

FIG. 7 is a circuit diagram showing an amplification compensation circuit of a conventional semiconductor pressure sensor.

[Explanation of symbols]

 1, 2, input terminal 3, 4, 7, 8: output terminal 5; semiconductor pressure sensor Ra, Rb, Rc, Rd; pressure-sensitive gauge resistance AMP1 to AMP3; operational amplifier

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-51733 (JP, A) JP-A-59-217375 (JP, A) JP-A-63-263773 (JP, A) JP-A-59-217773 168331 (JP, A)

Claims (1)

(57) [Claims] An operational amplifier for amplifying a signal output from a semiconductor pressure sensor element, wherein a temperature characteristic of an offset voltage of the operational amplifier is set according to a temperature characteristic of the sensor element. The amplification compensation circuit of the semiconductor pressure sensor is set by adjusting the collector current of the input transistor of the differential amplifier circuit and changing the base-emitter voltage of the transistor.