JPS6097230A - Pressure converter - Google Patents

Abstract

PURPOSE:To make it possible to compensate for sensitivity and temperature without impairing various performances, by constituting the sixth and seventh resistors by using heat sensitive diffusing resistors, which have the positive resistance temperature coefficient larger than that of the fourth and fifth resistors. CONSTITUTION:A bridge circuit 100 comprising pressure sensitive elements 1, 2, 3, and 4 is driven by driving terminals 27 and 28 at a constant voltage. In a differential amplifier circuit 300, the following basic operations are performed. Amplification of the unbalanced bridge voltage and impedance conversion are performed by a front stage amplifier circuit 301 using two operation amplifiers 30a and 30b. Differential single end conversion is accomplished by an output stage amplifier circuit 302 using an operation amplifier 30c. Of resistor element 34-37, the elements 35 and 37 are constituted by heat sensitive diffusing resistors, which have the positive temperature coefficient larger than that of the resistors 34 and 36.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pressure transducer, and more particularly to improving the temperature characteristics of a pressure transducer using a semiconductor pressure-sensitive element.

Conventionally, this type of semiconductor pressure transducer uses a pressure sensitive element formed on a semiconductor diaphragm to perform a Wheatstone bridge circuit (hereinafter simply referred to as bridge change) by driving the bridge circuit with a constant voltage or constant current source. The applied pressure ζ is detected as an unbalanced voltage of the bridge circuit, and the unbalanced voltage is further amplified by a differential amplifier circuit.
An output signal proportional to this was extracted. FIG. 1 shows a specific example of the configuration of the pressure transducer. In the figure, -Rishi is a bridge circuit composed of pressure sensitive elements 1.2.3.4;
Reference numeral 5 indicates a drive terminal for applying a constant voltage to the bridge circuit, and 6 and 7 indicate unbalanced voltage detection terminals of the bridge circuit, respectively. For example, impurity diffusion regions formed on a semiconductor diaphragm by selective diffusion, ion implantation, etc. are used as the pressure-sensitive elements 1 to 4, and the pressure-sensitive elements 1.3 and 2.4 are each subjected to the same applied pressure. On the other hand, the crystal axes in the longitudinal and transverse directions are selected and arranged so that the resistance changes in opposite directions. As a result, when the resistance value of the pressure sensitive element 2.4 increases with respect to the applied pressure, the resistance value of the pressure sensitive element 1.3 decreases, and as a result, the unbalanced voltage detection terminal 6 of the bridge circuit 100 .7, an unbalanced voltage ΔE proportional to the applied pressure is obtained. The unbalanced voltage△
E is the three operational amplifiers 8.9.10 and resistors 11.12
．． An amplifier circuit consisting of 13, 14, 15, 16, and 17 is amplified and made single-ended. In the amplifier circuit 200, a preamplifier circuit (201) consisting of resistors 11, 12, 13 and an operational amplifier 8.9 achieves impedance conversion (high input resistance - low output resistance) and at the same time reduces the unbalance of the bridge circuit 1. The voltage and voltage ΔE (differential input for the front-stage amplifier circuit) are amplified. That is,
The voltages at terminals 6 and 7 on the bridge circuit in a state where no pressure is applied are both Vcm, and the symmetrical voltage changes at terminals 6 and 7 caused by the applied pressure are respectively vz (=△E
/2) and vl (=-△E/2), and the resistance values of resistor 11.12 and 13 are respectively R,, Rs and R8,
The voltage V available at the output terminals 18 and 19 of the operational amplifiers 8 and 9. 1st place will be awarded at the withdrawal ceremony.

On the other hand, the output stage amplifier circuit (202) derived from the resistors 14 to 17 and the operational amplifier 10 converts the differential input into a single-ended output. Now resistors 14, 15, 16 and 17
Assuming that the resistance values of are R4, Rs, R6, and R7, the output voltage V obtained at the output terminal 20 of the operational amplifier 10. is given by the following equation.

where vu, Vll and V,. is the output stage amplifier circuit (
202), the differential and common mode components of the input voltage are
The relationship between the output voltages v6I and Vo2 of the front stage amplifier circuit (201) is V4z-C%2V, respectively. 1)/2=V
ll.

It is defined as vlc = (vat + VO2)/2.

Therefore, the resistor $1 in the front stage amplifier circuit (201')
If the resistance values of 2 and 13 are selected equally (& = R
s), V+□11. and via are as follows.

ViI,=vcIrL(',゛V,=-V2)
(5) Therefore, the resistance values R4, Rs of the resistors 14, 15, 16 and 17 in the output stage amplifier circuit (202),
R6 and R7 are Rs/R4=R7/R4(R
4R) = &R8), the equation (3) becomes, the common-mode voltage component VcrrL is removed, and the presoji unbalanced voltage △E (= vz Vl) is amplified, resulting in a single-ended output voltage ■. is obtained at the output terminal 20.

However, the above-mentioned pressure transducer driven by constant voltage and pressure has a drawback that the pressure sensitivity decreases as the temperature rises due to the negative temperature coefficient of the piezoresistance coefficient.

In order to compensate for temperature fluctuations in sensitivity, conventionally, the feedback circuit of the operational amplifier 10 constituting the output stage amplifier circuit (202) is configured with a diffused resistor having a positive temperature coefficient, thereby giving a positive temperature coefficient to the degree of amplification. A pressure transducer having a structure as shown in FIG. In the figure, 21 is on the same semiconductor substrate as the pressure sensitive elements 1 to 4.

The diffused resistor 22 provided in the pressure-insensitive portion is a resistor outside the semiconductor substrate, and these are connected in parallel to form a feed bank circuit (between the output terminal and the inverting input terminal) of the operational amplifier 10. In addition, in the same figure, the resistors 23 and 24 are
The DC level of the output terminal 20 is adjusted by dividing the drive voltages supplied to the drive terminals 5 and 26 and guiding the divided voltage vb obtained at the terminal 27 to the non-inverting terminal of the operational amplifier 10 via the resistor 17. It constitutes a zero point adjustment circuit. If the resistance value of the feedback circuit consisting of the diffused resistor 21 and the resistor 22 connected in parallel is R, then the output voltage of the pressure transducer is V. is given by the following equation.

In the above equation, the common mode voltage component (third term) is set to zero, and the difference M
In order to obtain an output type, voltage v0, which is proportional only to the Kh voltage component (V1*Vl+), the relationship R4R7-R,R,=O must be established uniformly. However, in the pressure transducer with the above configuration, only R8 shows a positive temperature coefficient, and R4, R6, and R7 have no temperature dependence (or have extremely small temperature coefficients compared to R), so the above relationship is The equation can only be established at a temperature of one point. As a result, the common mode gain changes with temperature, so the temperature and common mode voltage component Vi, which is independent of the applied pressure,
There was a drawback that an offset voltage depending on e was generated and this varied with temperature. Furthermore, as is clear from the fourth term of the force equation, the gain for the zero point adjustment voltage (b) has temperature dependence, so there is also the drawback that the zero balance is disrupted due to temperature changes.

As explained in detail above, in conventional pressure transducers,
Temperature compensation for sensitivity has the drawbacks of increased common-mode gain (decreased common-mode rejection ratio) and zero balance fluctuations due to temperature fluctuations.

The present invention has been made in order to eliminate the drawbacks of the conventional pressure transducers described above, and its purpose is to provide a pressure transducer with excellent performance that allows temperature compensation for sensitivity without impairing the various performances that a pressure transducer should have. Our goal is to provide the following.

According to the present invention, there is provided a Wheatstone bridge circuit including a pressure sensitive element formed of an impurity diffusion region formed on a semiconductor titanorum on at least the - side, and a non-inverting input terminal each connected to a voltage detection terminal of the bridge circuit. first and second operational amplifiers whose inverting input terminals are connected to each other via a first resistor; and a connection between the inverting input terminal and the output terminal of the first and second operational amplifiers, respectively. The second and third resistors and the inverting and non-inverting input terminals are connected to iii through the fourth and fifth resistors, respectively.
a third operational amplifier connected to the output terminals of the first and second operational amplifiers; a sixth resistor connected between the inverting input terminal and the output terminal of the third operational amplifier; In the pressure transducer comprising a seventh resistor connected between the non-inverting input terminal and the bias terminal of the operational amplifier of No. 3, at least the sixth and seventh resistors are lower than the fourth and fifth resistors. A pressure transducer is obtained, characterized in that it is constructed using a temperature-sensitive diffused resistor having a large positive temperature coefficient of resistance.

Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 3 is a block diagram showing one embodiment of a pressure transducer according to the present invention. In the figure, 1 is a bridge circuit composed of pressure-sensitive elements 1, 2, 3, and 4 as shown in Figs. The drive terminals are shown respectively, and the operational amplifiers AOA and 3OB are shown.

30c and resistor 31.32.33.34.36 and resistor 3
A differential amplifier circuit consisting of a temperature sensitive diffused resistor 35.37 having a positive temperature coefficient of resistance greater than 4.36 is shown. The differential amplifier circuit aOO in this embodiment is basically a front-stage amplifier circuit (
301) performs bridge unbalanced lightning, pressure amplification and impedance conversion, and an output stage amplifier circuit (302) using an operational amplifier 30c achieves differential-to-single-ended conversion. The feature of this embodiment is that the operational amplifier 30 of the output stage amplifier circuit (302)
In each of the resistive elements 34 to 37 connected to c, 35 and 37 are constructed using temperature-sensitive diffused resistors having a larger positive temperature coefficient than resistors 34 and 36.

As the resistors 34 and 36 in this embodiment, the resistor 31
．． In addition to 32 and 33, a metal film resistor or the like having a small temperature coefficient that can be considered as a fixed resistor in practical use can be used. Furthermore, as the temperature-sensitive diffused resistors 35 and 37, for example, diffused resistors made of impurity diffusion regions formed in pressure-insensitive parts on the same semiconductor substrate as the pressure-sensitive elements 1 to 4 can be used.

Hereinafter, the effects of this embodiment will be explained with reference to FIG. 3, but here, for convenience, we will explain the terminals 6 of the bridge circuit 100 in a state where no pressure is applied, similar to the explanation of FIGS. 1 and 2.
and 7 are both Vshin (therefore, unbalanced voltage △E
= O), and the changes in voltage at terminals 6 and 7 caused by the applied pressure are expressed as v2 and vl, respectively (△E = v2 Vl
), and it is assumed that a symmetrical pressure change of v2-ΔE/2 and vl=-ΔE/2 can be obtained. Also, resistor 31
．． The resistance value of 32, 33, 34, 36 is 11.1 in Figure 1.
Same as 2.13.14.16 < R,, R2R5, R4
, R6, and the temperature-sensitive diffused resistors 35 and 37 are R
, I+(1+kt) and R0f(1+dt). Here, Ro and R07 are the resistance values of the temperature-sensitive diffused resistors 35 and 37 at the reference temperature, σ is the resistance temperature coefficient of the temperature-sensitive diffused resistors 35 and 37, and t is the change in temperature from the reference temperature. temperature-sensitive diffused resistors 35 and 3
If each of the resistors 7 and 7 is made up of diffused resistors having the same surface impurity concentration and manufactured on the same semiconductor substrate in the same process, the sum and t for both will be the same value.

Based on the above, the front stage amplifier circuit (301
) of the operational amplifiers 30a and 30b.
The voltages Vel and Vat obtained at and 39 are given by the same formulas as in FIG.
Differential component v of the input voltage to the output amplifier circuit (302)
Us vll and in-phase component Vlc are given by equations (4) and (5), respectively.

On the other hand, the operational amplifier 3 in the output stage amplifier circuit (302)
The output lightning pressure v6 obtained at the output terminal 40 of 0c is (3)
R5 and R in the formula are each Ra in this example.
5 (1+αt) and u,t (1+αt), so the zep applied to the terminal 29
Letting the point adjustment voltage be vb-0, it is given by the following equation.

(8) Therefore, the resistor 3 in the output stage amplifier circuit (302)
Resistance value R4, Rs of 4.36 and temperature-sensitive diffused resistance 35.3
Resistance value Ra8 at reference temperature of 7, Re? The relationship between R,s/R4= R,t/Rs (R4
・R,y Ras −Rs ), (4)
, from equation (5), the above equation is. =~Reverse deafening・(1+k)・(v2−vl)R4
R+ (9), the common-mode voltage component VOW is completely removed, only the unbalanced voltage ΔE (=vt V+) of the bridge circuit 100 is amplified, and the temperature-compensated single-ended output is sent to the output terminal 40 of the pressure converter. It is taken out. That is, (9
) As is clear from the equation, in this embodiment, a positive temperature coefficient based on the positive temperature coefficients of the temperature-sensitive diffused resistors 35 and 37 can be given to the amplification degree of the differential amplifier circuit 4. It is possible to effectively compensate for the negative temperature coefficient of the pressure sensitivity due to the negative temperature coefficient of the piezoresistive coefficient. Furthermore, the output stage amplifier circuit (302) of this embodiment does not cause unbalance between the respective resistors due to temperature changes, unlike the conventional configuration shown in FIG. Therefore, the increase in the common mode gain due to temperature changes is suppressed, and it is possible to completely eliminate the extra offset voltage that occurs depending on the temperature and the common mode voltage component V (1 m), which was a drawback of the conventional configuration. For the same reason, even if voltage V is applied to the terminal 29 to adjust the zero point, the voltage V is maintained, so that temperature fluctuations in the zero balance, which are a drawback of the conventional configuration, are also suppressed.

Therefore, this embodiment achieves sensitivity temperature compensation that eliminates the increase in the common mode gain of the amplifier circuit due to temperature changes and zero balance fluctuations, which were drawbacks of the conventional configuration, and provides a high-performance pressure transducer. can get.

In this embodiment, in order to make the temperature coefficient of pressure sensitivity zero, the temperature coefficient of the amplification degree of the amplifier circuit 3 (l O,
In other words, the temperature coefficient of resistance (positive value) of the temperature-sensitive diffused resistor 35. Bye. Generally, this is achieved by appropriately controlling the impurity concentrations of the impurity diffusion regions that constitute the pressure sensitive elements 1 to 4 and the temperature sensitive diffused resistors 35 and 37, respectively.

Note that in the case of a diffused resistor consisting of a p-type impurity region formed on an n-type silicon substrate, the surface impurity concentration is 10"cm-
At the two points "and 10%-", the absolute values of the resistance temperature coefficient (positive value) and the piezoresistance coefficient temperature coefficient (negative value) become equal. Therefore, if the surface impurity concentration is selected under the above conditions, the temperature-sensitive diffused resistors 35 and 37 for sensitivity temperature compensation can be manufactured in the same process as the pressure-sensitive elements 1 to 4, which is extremely effective and easy to manufacture. Easy sensitivity temperature compensation can be achieved.

In the above embodiment, the resistors 31, 32, and 33 constituting the front stage amplifier circuit (301) of the amplifier circuit 300 are replaced by the resistors 3
4.36, we used resistors with small temperature coefficients such as metal film resistors that can be considered as fixed resistors for practical purposes, but these do not necessarily have to be resistors with small temperature coefficients and may be temperature-dependent resistors. good. That is, if the temperature coefficients between resistors 31, 32, and 33 are selected to be equal, these temperature coefficients will cancel each other out,
Since the amplification degree of the front-stage amplifier circuit (301) no longer has temperature dependence, the resistors 31, 32, and 33 can be replaced with, for example, diffused resistors formed in the same process as the temperature-sensitive diffused resistors 35, 37, etc. in the above embodiment. Exactly the same effect can be obtained. in this case,
Since the pressure sensitive elements 1 to 4, the temperature sensitive diffused resistors 35, 37, and the diffused resistors 31, 32, and 33 can all be manufactured in the same process,
Resistors 34.36 including operational amplifiers that can be easily integrated into ICs.
The components of the above embodiments except for can be mounted on-chip on the same semiconductor substrate. As a result, the number of external parts is significantly reduced, and the number of assembly and adjustment man-hours is significantly reduced.

However, in the above embodiment, the resistors 34 and 36 are external resistors with small temperature coefficients such as metal film resistors, and the resistors 35 and 37 are diffused resistors on the semiconductor substrate, thereby giving a positive temperature coefficient to the amplification degree. However, the resistor 34.36 was replaced by a temperature-sensitive diffused resistor 3
It is also possible to similarly give a positive temperature coefficient to the degree of amplification by configuring it with a diffused resistor having a relatively small temperature coefficient and formed on the same substrate as 5 and 37. This can be achieved, for example, by setting the impurity concentrations of the impurity diffusion regions constituting the resistors 34.36 and 35.37 to different values, thereby making it possible to provide an all-IC pressure transducer.

Furthermore, in the above embodiment, for convenience of explanation, the resistors 31 to 3
3.34.36 and 35.37 were each composed of a single resistor, but in the pressure transducer according to the present invention, these are composed of a plurality of resistors having various resistance values or resistance temperature coefficients. There is no problem even if the structure is configured by ■ series connection ■ parallel connection ■ series parallel connection.

As described in detail above, according to the present invention, the drawbacks of the prior art are overcome, and a high-performance pressure transducer capable of sensitivity temperature compensation is realized without impairing various performances that a pressure transducer should have.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a typical configuration of a conventional pressure transducer, Fig. 2 is a diagram showing a conventional example of a pressure transducer with sensitivity temperature compensation, and Fig. 3 is a diagram showing an example of an embodiment of the present invention. FIG. ■-Bridge circuit, 1.2.3.4...Pressure sensitive element, 5
．． 25.26.27.28... Bridge drive terminal, 2
00...Differential amplifier 111iA circuit, (201)...Pre-stage amplifier circuit, (202)...Output stage amplifier circuit, 8.9
．． 10...Operation amplifier 11.12.13.14.15
．． 16.17...Resistor 20...Output terminal, 21...
- Diffused resistor, 22... Resistor, 300... Differential amplifier circuit, (301)... Pre-stage amplifier circuit, (302)...
Output stage amplifier circuit, 30a, 30b, 30cm operational amplifier, 31.32
．． 33.34.36...Resistance, 35.37...Temperature-sensitive diffused resistor, 29...Ze p point adjustment voltage application terminal,

Claims (1)

[Claims] a Wheatstone bridge circuit including a pressure sensitive element formed on at least one side of an impurity diffusion region formed on a semiconductor diagonal; a non-inverting input terminal is led to an unbalanced voltage detection terminal of the bridge circuit, and an inverting input terminal is connected to the bridge circuit; first and second operational amplifiers connected to each other via a first resistor; and a second operational amplifier connected between the inverting input terminal and the output terminal of the first and second operational amplifiers, respectively.
and a third operational amplifier whose inverting and non-inverting input terminals are connected to the output terminals of the first and second operational amplifiers via fourth and fifth resistors, respectively; a sixth resistor connected between the inverting input terminal and the output terminal of the third operational amplifier; and a seventh resistor connected between the non-inverting input terminal and the bias terminal of the third operational amplifier. In the pressure transducer, at least the sixth and seventh
A pressure transducer characterized in that the resistor is configured using a temperature-sensitive diffused resistor having a positive temperature coefficient of resistance larger than the fourth and fifth resistors.