JPH01433A - Circuit configuration method for semiconductor pressure sensor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

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

The present invention relates to a circuit configuration method for a semiconductor pressure sensor that differentially amplifies the output voltage of a bridge circuit including a strain gauge resistor formed on a semiconductor diaphragm for pressure detection to obtain a sensor output voltage. A circuit for a semiconductor pressure sensor, in which a bias voltage component other than a pressure detection component in the voltage is negative, and the sensor detection voltage is approximately 0 until the pressure applied to the diaphragm increases to a predetermined value. Regarding the configuration method. Note that in the following figures, the same reference numerals indicate the same or corresponding parts.

[Conventional technology]

FIG. 2 is an example of a general differential amplifier circuit using one operational amplifier OPI in this type of semiconductor pressure sensor. In the same figure, VCC is a DC power supply, 5GI-3G
Reference numeral 4 denotes a semi-dedicated strain gauge formed on a silicon diaphragm, and the strain gauges SGI to SG4 are sequentially connected in a ring to form a bridge circuit. Here, the amount of resistance change of the strain gauge when pressure is applied to the diaphragm is, for example, SGI and SG3 are equal, and SG2 and SG4 are equal.
strain gauge SGI on the diaphragm so that
~The position of SG4 has been determined. Each of the two opposing connection terminals T5. of this block circuit. T
6 are respectively connected between the DC current gtVcc and the other two opposing connection terminals T2.6 of the block circuit. T.I.
A bridge output voltage Vi is output from. Operational amplifier OPI and two resistors R1 and two resistors R
2 constitutes a well-known differential amplifier circuit, and the bridge output voltage Vi is input between the inverting input terminal T- and the non-inverting input terminal T+ of the operational amplifier OPI via the respective resistors R2. ing. Further, a reference voltage Vd obtained by dividing the DC power supply Vcc by resistors R5 and R6 is inputted to the non-inverting input terminal T+ of the operational amplifier OPI via the resistor R1. It is assumed here that the resistors R5 and R6 are sufficiently smaller than the resistor R1. Normally, the bridge output voltage Vi is approximately equal to zero when no pressure is applied to the silicon diaphragm, and in this example, it is set to zero for simplicity. The voltage (sensor output voltage) Vo of the output terminal T4 of this differential amplifier OPI is approximately expressed by the following formula (
1). That is, the sensor output voltage VO is equal to the bridge output voltage Vi by R1.
This is the sum of the pressure detection component amplified by /R2 times and the reference voltage Vd as the bias voltage component. However, the reference voltage Vd is a divided voltage of the DC power supply Vcc, and is expressed by the following formula (2). R5+R6 Also, if the pressure applied to the diaphragm is p, the bridge output voltage Vi is Vi=a-p...
−−−−−・−−−−−−−−−−−−1・−−−1−
---...It is expressed as (3). However, a is a proportionality constant determined by the shape of the diaphragm, etc. Therefore, the formula (1
) is rewritten as equation (21, +31), it becomes the following equation (4). The relationship between this sensor output voltage VO and pressure p is expressed in a graph as shown in Figure 4 ■. is another circuit example of a conventional semiconductor pressure sensor. In this example, the reference voltage Vd in the sensor output potential vO of formula Tll is generated using an operational amplifier OP2 and resistors R7 to R12. The sensor output voltage Vo also shows the same tendency as the characteristic (2) in FIG.

[Problems to be solved by the invention]

The pressure sensor circuit shown in Fig. 2 can be easily configured, but when the pressure p is zero, the sensor output voltage ■0 is the reference voltage (bias voltage) Vd = (R6/ (R5 + R6)) Vcc
As shown in FIG. 4, the operating voltage range of the sensor output voltage Vo is equal to or higher than the reference voltage Vd. And it is limited to the range below the DC power supply voltage Vcc. Therefore, as shown in the characteristic shown in Figure 4 ■, the change range of the pressure p is higher than zero, and the AOVo value becomes negative at the point where the extension line of the characteristic shown in ■ intersects the axis (Y axis) of pressure p=o. Characteristics like,
In other words, the sensor output voltage VO is approximately O until the pressure p increases to a predetermined pressure po, and when the pressure increases beyond po, the sensor output voltage ■0 increases linearly. For example, it has been impossible to realize an atmospheric pressure sensor with a full range around atmospheric pressure using the same circuit pattern as in the past (that is, without changing the total number of resistors R1 to R6). Also, in the circuit shown in Figure 3, the reference voltage Vd is the output of the operational amplifier OP2, so it is limited to positive voltages, and as in Figure 2, it is impossible to achieve the characteristics shown in Figure 4 (■). there were. An object of the present invention is to provide a circuit configuration method in which the value of a resistor that constitutes a differential amplifier circuit in combination with an operational amplifier opt that outputs a pressure detection voltage within a semiconductor pressure sensor satisfies a new predetermined condition. The object of this invention is to obtain the characteristics shown in (2) in FIG. 4 without changing the pattern of the conventional circuit.

[Means to solve the problem]

In order to achieve the above-mentioned object, the method of the present invention utilizes a resistor as a strain gauge formed on a semiconductor diaphragm.
SGI-3G4, etc.) is included in at least one resistance side, and includes a bridge circuit consisting of four resistance sides sequentially connected in a ring, and of the connection points of the four resistance sides, opposing Connect two connection points (terminals T5, T6, etc.) between each DC power source (Vcc, etc.), and connect two other connection points (terminals TI, 72, etc.) that are also facing each other, or connect the voltage between the connection points. The two output terminals of a differential input/differential output type amplifier (not shown) that amplify are used as the first and second bridge output terminals, respectively, and an operational amplifier (such as OPl) and the a first resistor (R1, etc.) provided between an inverting input terminal (T-, etc.) and an output terminal (T4, etc.) of the operational amplifier; and a first resistor (R1, etc.) provided between the first bridge output terminal (T2, etc.) and the inverting a second resistor (R2, etc.) provided between the input terminal; and a third resistor provided between the second bridge output terminal (T1, etc.) and the non-inverting input terminal of the operational amplifier. (
R3, etc.) and a reference voltage (
a fourth resistor (such as R4) provided between an output terminal (such as 73) of the output terminal (such as Vd) and the non-inverting input terminal; In a semiconductor pressure sensor that detects a generated voltage (Vo, etc., hereinafter referred to as sensor output voltage), the product of the resistance values of the first and third resistors (R1, R3, etc.) and the second and fourth resistors The product of the resistance values (R2
・R4, etc.) are made different (for example, R1, R3 > R2, R4) so that the sensor output voltage is approximately zero until the pressure applied to the diaphragm increases to a predetermined value (po, etc.). "It shall be.

[For use]

In the present invention, without changing the circuit pattern of the semiconductor pressure sensor from the conventional one, the resistance values of the resistors R1-R4 are made to have a relationship of R1・R3>R2・R4, and the output voltage of the operational amplifier OPI (sensor output The components of the voltage) Vo other than the pressure detection component, that is, the fixed bias voltage component proportional to the DC power supply voltage Vcc, are made small, and even have a negative value.

【Example】

FIG. 1 shows an embodiment of a semiconductor pressure sensor circuit to which the present invention is applied, and corresponds to FIG. 2. The difference between Fig. 1 and Fig. 2 is that the resistance that is combined with the operational amplifier OPi to form the differential amplifier circuit, that is, the resistance between the bridge output terminal T1 and the non-inverting input terminal T half of the amplifier OPl, is from R2 to R3. Another difference is that the resistance between the terminal T3 for obtaining the divided voltage (conventional reference voltage) Vd of the DC power supply voltage Vcc and the non-inverting input terminal T+ has been changed from R1 to R4. Note that here, for simplicity, R5, R6 <: R4, R2, R
3<=R1, R4. It is also assumed that the output resistance of the strain gauge bridge is sufficiently higher than R2 and R3. Furthermore, as in FIG. 2, it is assumed that the bridge output voltage Vi becomes zero when no pressure is applied to the silicon diaphragm. In the present invention, as will be described later, the resistance values of the resistors R1 to R4 are selected such that the relationship R1-R3>R2*R4 holds. That is, in FIG. 1, the output voltage (sensor output voltage) Vo of the operational amplifier OPI is expressed by the following equation (5). Here, Vd is the reference voltage, that is, the connection point T between resistors R5 and R6.
3 voltage. Further, Vs is the common mode voltage of the bridge output voltage Vi with respect to the ground. Usually Vd<Vs.
It is assumed that d is determined and this example also follows. In equation (5), when R1·R3=R2·R4, the third term on the right side of equation (5) becomes zero, and equation (5) becomes equal to equation (1). Furthermore, if R1-R3>R2・R4, the third term on the right side of equation (5) becomes negative, and it is possible to add a negative voltage to the conventional differential amplifier output voltage represented by 2 (1). It is possible. Rewriting equation (5) gives the following equation (6). Here, ap=Vi (p is pressure). Here, further (R2・R4−R1・R3)Vs+R3(R1+R2)
Vd < 0------...-+7), that is, Vd R1-R3> R2, R4+R3 (R1+R2) --
−−−−−−−−−−−−−(8) By selecting R4 and VdO values for R1 so that Vs becomes
The second term on the right side of equation (6) takes a negative value, and a characteristic in which a negative bias voltage component is added to the pressure detection voltage component as shown in FIG. 4 can be obtained. However, the power supply for driving the operational amplifier OPI is the DC power supply Vcc.
Therefore, the output voltage Vo of this amplifier OPI does not actually become negative, and the characteristic shown in FIG. Next, in Fig. 1, the bridge output voltage Vi is once amplified by a differential input/differential output amplifier (not shown), and then this output voltage is amplified via resistors R2 and R3 in the same way as the voltage Vi in Fig. 1. The present invention can also be applied to the operational amplifier OPI. Further, the present invention can be similarly applied to a case where a reference voltage Vd proportional to a DC type 1fiVcc voltage is generated by a circuit including an operational amplifier OP2 as shown in FIG.

【Effect of the invention】

According to the present invention, there is provided a Brifuji circuit consisting of resistors SG1 to SG4 as strain gauges formed on a semiconductor diaphragm, and two opposing connection points ( terminal) T5. T6 are respectively connected between the DC power supplies Vce, and the other two opposing connection points (terminals) T1. T2 or the two output terminals of a differential output type amplifier (not shown) that amplifies the voltage between the connection points are used as first and second bridge output terminals, respectively, and an operational amplifier is also used. OPI, a resistor R1 installed between the inverting input terminal T- of this operational amplifier and the output terminal T4 of the operational amplifier, and a resistor R1 installed between the first bridge output terminal T2 and the inverting input terminal. a resistor R2 provided between the second bridge output terminal TI and the non-inverting input terminal of the operational amplifier; and a reference voltage V obtained by dividing the DC power supply at a predetermined voltage division ratio.
d, and a resistor R4 provided between the output terminal T3 of the operational amplifier and the non-inverting input terminal, and the pressure applied to the diaphragm is controlled by the voltage (V
o, hereinafter referred to as sensor output voltage), the product R1-R3 of the resistance values of the resistors R1 and R3 and the product R2·R4 of the resistance values of the resistors R2 and R4 are R1
・Since we decided to make R3>R2・R4,
The output voltage of operational amplifier oP1 (sensor output voltage) V can be adjusted without changing the circuit pattern of the conventional semiconductor pressure sensor.
Components other than the pressure detection component within o, that is, the fixed bias voltage component proportional to the DC power supply voltage can be made small, and even have a negative value. Therefore, the conventional characteristic shown in Figure 4 (2) can be moved in the direction of decreasing the level of the sensor output voltage VO, and the operating voltage range of the sensor output voltage (2) can be widened. By selecting the voltage Vd so that it satisfies the condition of equation (8), it is possible to lower the level of the sensor output voltage Vo until it has the characteristics shown in Figure 4 (■), for example, only near atmospheric pressure. This makes it possible to detect characteristics in which the full pressure range is higher than zero, such as a sensor that detects pressure, over a wide voltage range.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram as an embodiment of the present invention, Figs. 2 and 3 are conventional circuit diagrams corresponding to Fig. 1, and Fig. 4 is for explaining the operation of Fig. 1 or Fig. 3. FIG. Vcc: DC power supply (voltage), SGl to S64 two semiconductor strain gauges, R1 to R6: resistance, OPl: operational amplifier, Vi
Mini bridge force voltage, vd: reference voltage, VO: sensor output voltage, Tl to T6: terminal, T-: inverting input terminal, T+
: Non-inverting input terminal.

Claims (1)

[Scope of Claims] 1) A bridge circuit including a resistor as a strain gauge formed on a semiconductor diaphragm in at least one resistance side, and consisting of four resistance sides sequentially connected in a ring, Among the connection points of the four resistance sides, two opposing connection points are connected between the DC power supplies, and the other two connection points that are also opposite are connected, or a differential input that amplifies the voltage between the connection points. - The two output terminals of the differential output type amplifier are used as the first and second bridge output terminals, respectively, and further between the operational amplifier and the inverting input terminal of this operational amplifier and the output terminal of the operational amplifier. a first resistor provided, and a second resistor provided between the first bridge output terminal and the inverting input terminal.
a third resistor provided between the second bridge output terminal and the non-inverting input terminal of the operational amplifier; and an output of a reference voltage obtained by dividing the DC power supply at a predetermined voltage division ratio. a fourth terminal provided between the terminal and the non-inverting input terminal;
and a voltage (hereinafter referred to as sensor output voltage) that causes pressure applied to the diaphragm to be generated at the output terminal of the operational amplifier.
In the semiconductor pressure sensor, the product of the resistance values of the first and third resistors is made different from the product of the resistance values of the second and fourth resistors, so that the pressure applied to the diaphragm reaches a predetermined value. A method of configuring a circuit for a semiconductor pressure sensor, characterized in that the sensor output voltage remains approximately zero until the voltage increases.