JP2001091373A - Pressure sensor circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly accurate and reliable pressure sensor circuit capable of canceling out the output offset of an amplifier and obtaining correct output even if external environments such as the passage of time, humidity and the like change. SOLUTION: This pressure sensor circuit is provided with switches S1-S6 as means to reduce the output offset voltage of an amplifier 13 contained in the output voltage V1 of the amplifier 13, and a switching control part to turn on the switches S1, S3, S4 and S6 and off the switches S2 and S5 at the time when input to the amplifier 13 is inhibited in an auto zero state, and to turn on the switches S2, S3, and S5 and off the switches S1, S4, and S6 at the time when input to the amplifier 13 is permitted, and to turn off the switch S3 at the time of a transition from the time when input is permitted to the time of inverse integration. The switching control part is provided for a control part 14b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transducer circuit having a pressure sensor or an acceleration sensor mainly composed of a bridge circuit, and converting a mechanical quantity into an electric signal, and more particularly to a pressure sensor circuit. Things.

[0002]

2. Description of the Related Art FIG. 5 is a diagram showing a conventional configuration example of this type of pressure sensor circuit (see Japanese Patent Application No. 11-147362).
This pressure sensor circuit includes a pressure sensor 1 having a bridge circuit configuration, an offset correction circuit 2 for performing temperature compensation of an output offset of the pressure sensor 1, an amplifier 3 of an instrumentation amplifier type, and an output voltage of the amplifier 3 being a digital value. And a span correction circuit 5 for performing temperature compensation of the span of the pressure sensor 1 so as to perform suitable temperature compensation for the output offset and the span of the pressure sensor 1. .

Japanese Patent Laid-Open Publication No. Sho 64-10142 discloses that a constant current is applied to the input side of a bridge to detect and amplify an input voltage generated at an input terminal to generate positive and negative voltages. Amplifies the signal by utilizing or adjusting the negative voltage, M
Addition is made so that the output of the AIN amplifier becomes ZERO and ZE
A temperature compensation circuit for adjusting the RO point is described.

[0004]

However, in the pressure sensor circuit shown in FIG. 5, the offset voltage of the amplifier (the operational amplifier in the amplifier, that is, the so-called operational amplifier) increases or decreases due to changes in the external environment such as the passage of time and humidity. The output of the amplifier fluctuates, and as a result, the digital output of the pressure sensor circuit fluctuates.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and cancels out the output offset of an amplifier and provides a high-precision and high-reliability in which an accurate output can be obtained even when an external environment such as a lapse of time or humidity changes. It is an object of the present invention to provide a pressure sensor circuit.

[0006]

According to a first aspect of the present invention, there is provided a pressure sensor circuit comprising: a pressure sensor comprising a resistor having a bridge circuit configuration; and a reference signal for reducing an output offset of the pressure sensor. An offset correction circuit that generates the output signal, a differential amplification type amplifier that amplifies the detection signal of the pressure sensor while reducing the output offset with a reference signal from the offset correction circuit, and converts the output signal of the amplifier into a digital value. An A / D converter for conversion and means for reducing the output offset of the amplifier included in the output signal of the amplifier by the A / D converter are provided.

In this configuration, since the output offset of the amplifier is reduced by the A / D converter, the output offset of the amplifier is canceled, and an accurate output can be obtained even if the external environment such as the passage of time or humidity changes. A highly accurate and highly reliable pressure sensor circuit can be provided.

In the pressure sensor circuit according to the first aspect, the A / D converter has a first operational amplifier for applying a predetermined voltage to a non-inverting input terminal, and one end connected to an output terminal of the amplifier. An integration resistor, an auto-zero capacitor connected between the other end of the integration resistor and the inverting input terminal of the first operational amplifier, and a connection point between the integration resistor and the auto-zero capacitor. An integrating capacitor connected between an output terminal of the operational amplifier, a second operational amplifier having a non-inverting input terminal and an inverting input terminal connected to an output terminal and an inverting input terminal of the first operational amplifier, respectively, A current extracting unit for extracting an inverse integration current from an integrating capacitor, wherein the means includes a first switch connected between both input terminals of the amplifier, and one of the pressure sensors. A second switch provided between the input terminal of the amplifier and a non-inverting input terminal of the amplifier; and a third switch provided between the output terminal of the amplifier and the input terminal of the A / D converter. A switch, a fourth switch connected between the inverting input terminal and the output terminal of the second operational amplifier, a fifth switch interposed between the offset correction circuit and the amplifier, A sixth switch connected between a connection point of the switch and a non-inverting input terminal of the first operational amplifier; and turning on the first, third, fourth, and sixth switches when input to the amplifier is prohibited. To turn off the second and fifth switches,
When the input to the amplifier is permitted, the second, third, and fifth switches are turned on, and the first, fourth, and sixth switches are turned on.
A switching control unit that turns off a switch and turns off the third switch when shifting from the input allowable time to the reverse integration time may be provided (claim 2). According to this configuration, it is possible to provide a highly accurate and highly reliable pressure sensor circuit capable of canceling the output offset of the amplifier and obtaining an accurate output even when the external environment such as the passage of time or humidity changes.

Further, in the pressure sensor circuit according to claim 1, the A / D converter has a first operational amplifier for applying a predetermined voltage to a non-inverting input terminal, and one end connected to an output terminal of the amplifier. An integration resistor, an auto-zero capacitor connected between the other end of the integration resistor and the inverting input terminal of the first operational amplifier, and a connection point between the integration resistor and the auto-zero capacitor. An integrating capacitor connected between an output terminal of the operational amplifier, a second operational amplifier having a non-inverting input terminal and an inverting input terminal connected to an output terminal and an inverting input terminal of the first operational amplifier, respectively, A current extracting unit for extracting an inverse integration current from an integrating capacitor, wherein the means includes a first switch connected between both input terminals of the amplifier, and one of the pressure sensors. A second switch provided between the input terminal of the amplifier and a non-inverting input terminal of the amplifier; and a third switch provided between the output terminal of the amplifier and the input terminal of the A / D converter. A switch, a fourth switch connected between an inverting input terminal and an output terminal of the second operational amplifier, and, when input to the amplifier is prohibited, turning on the first, third, and fourth switches, While the switch 2 is turned off, when the input to the amplifier is allowed, the second and third switches are turned on and the first and fourth switches are turned off. A switching control unit for turning off a third switch, wherein the offset correction circuit outputs a voltage of the same level as a predetermined voltage applied to a non-inverting input terminal of the first operational amplifier when the input is prohibited. , Said input allowable time may be configured to output a voltage as the reference signal (claim 3). According to this configuration, it is possible to provide a highly accurate and highly reliable pressure sensor circuit capable of canceling the output offset of the amplifier and obtaining an accurate output even when the external environment such as the passage of time or humidity changes.

Further, in the pressure sensor circuit according to the first aspect, the pressure sensor may be configured to be adjusted so that the variation of the output offset voltage always takes a positive value. According to this configuration, the dynamic range of the amplifier can be expanded.

Further, in the pressure sensor circuit according to claim 2, the reference signal is set such that a value obtained by subtracting the predetermined voltage from a voltage as the reference signal cancels an output offset of the pressure sensor. (Claim 5). According to this configuration, the dynamic range of the amplifier can be expanded.

Further, in the pressure sensor circuit according to the second or third aspect, the back integration current may be taken out from an inverting input terminal of the first operational amplifier. According to this configuration, highly accurate A / D conversion can be performed.

[0013]

FIG. 1 is a block diagram of a pressure sensor circuit according to a first embodiment of the present invention. The first embodiment will be described below with reference to this drawing.

First, the basic configuration of the pressure sensor circuit will be described. As shown in FIG. 1, the pressure sensor circuit (apparatus) includes a pressure sensor 11, an offset correction circuit 12, an amplifier 13, and an A / D converter 14. Have been.

The pressure sensor 11 comprises resistors Rs1 to Rs4 in a bridge circuit configuration having output terminals Ts1 and Ts2 and power supply terminals Ts3 and Ts4, and outputs a detection voltage Vin at a level corresponding to a physical quantity (pressure) to both output terminals Ts1 and Ts1. The bias voltage Vbias or the bias current Ibias is applied or supplied to one power supply terminal Ts3 of the bridge circuit, and the other power supply terminal Ts4 is connected to the ground GND.

The offset correction circuit 12 includes the pressure sensor 1
Output offset voltage of 1 (hereinafter, sensor offset)
The reference voltage Vg for reduction is generated, and the level of the reference voltage Vg as an output signal can be adjusted. For example, a variable resistance voltage dividing resistor (a resistor and a resistor) that divides a predetermined voltage (VDD) into the reference voltage Vg. D) that outputs a reference voltage Vg at a level corresponding to a digital input.
/ A converter.

The amplifier 13 amplifies the detection voltage Vin of the pressure sensor 11 with a gain G while reducing the sensor offset with the reference voltage Vg from the offset correction circuit 12, and is a so-called instrumentation amplifier type. Operational amplifiers 131 to 133 constituting a differential amplifier circuit
And a reference potential (a resistor R135 in the figure) of a standard differential amplifier circuit comprising an operational amplifier 133 and resistors R134 to R137.
Voltage follower 13 for superposing the reference voltage Vg generated by the offset correction circuit 12 on the
4 is provided.

The A / D converter 14 converts the output voltage V1 of the amplifier 13 into a digital value Nout, and includes an operational amplifier (integrator) 141 to which a predetermined voltage Vr is applied to a non-inverting input terminal, an amplifier 141, and an amplifier. 13, an integrating resistor R14 having one end connected to the output terminal, an auto-zero capacitor Caz connected between the other end of the resistor R14 and the inverting input terminal of the operational amplifier 141, a resistor R14 and a capacitor Caz. And the integration capacitor Cint connected between the connection point of the operational amplifier 141 and the output terminal of the operational amplifier 141.
An operational amplifier (comparator) 142 having a non-inverting input terminal and an inverting input terminal connected to the output terminal and the inverting input terminal of the capacitor 41, respectively, and a constant connection from the connection point of the capacitors Caz and Cint to ground to discharge the capacitor Cint An A / D conversion unit 14a including a current extraction unit (current source in the figure) 143 through which the inverse integrated current Ir flows, and a control unit 14b for obtaining a digital value Nout according to the output of the A / D conversion unit 14a are provided. It is configured to be equipped.

In the pressure sensor circuit having such a basic configuration, as a feature of the first embodiment, the output offset voltage of the amplifier 13 included in the output voltage V1 of the amplifier 13 to the A / D converter 14 (hereinafter, referred to as amplifier (Offset) Means for reducing Vos are provided.

This means includes a switch S1 connected between both input terminals of the amplifier 13, and a switch S2 provided between the output terminal Ts2 of the pressure sensor 11 and the non-inverting input terminal of the amplifier 13. , A switch S3 interposed between the output terminal of the amplifier 13 and the input terminal of the A / D converter 14.
A switch S4 connected between the inverting input and output terminals of the operational amplifier 142; a switch S5 interposed between the output terminal of the offset correction circuit 12 and the input terminal of the voltage follower 134; The switch S6 connected between the input terminal of the operational amplifier 141 and the non-inverting input terminal of the operational amplifier 141, and the switches S1, S3, S3 when the input to the amplifier 13 is prohibited, that is, in a so-called auto-zero state.
4, S6 are turned on and the switches S2 and S5 are turned off.
2, S3, S5 are turned on, and switches S1, S4, S
6 and a switching control unit that turns off the switch S3 when a transition is made from the time when input is allowed to the time when reverse integration is performed. Note that this switching control unit is, for example, A
It is provided in the control unit 14b of the / D converter 14.

Next, the operation of the above means, which is a feature of the first embodiment, will be described. For example, when the input is prohibited and in the auto-zero state, the switches S1, S3, S4, and S6 are turned on, and the switches S2 and S5 are turned off.

At this time, the input to the amplifier 13 is prohibited by turning on the switch S1 and turning off the switch S2.
When the switch S5 is turned off and the switch S6 is turned on, the output voltage V1 of the amplifier 13 becomes Vos + Vr. Further, when the switch S4 is turned on, the voltages V3 and V4 of the inverting input terminal and the non-inverting input terminal of the operational amplifier 142 become the same level as the voltage Vr due to the virtual short circuit, and the voltage V2 at the connection point between the resistor R14 and the capacitor Caz is amplified. 13 and becomes the same level as the output voltage V1 and becomes stable. In this case, the charge Qaz stored in the capacitor Caz can be expressed by the following equation.

Qaz = Caz × (V1−Vr) = Caz × Vos In this bias state, that is, in a state in which the capacitor Caz has accumulated a charge corresponding to the amplifier offset, the A / D conversion section 14a at the time of auto-zero is stabilized. become.

In this state, the operation shifts to the switching control when the input to the amplifier 13 is permitted, and the switches S2, S3, S5
Is turned on, and the switches S1, S4, S6 are turned off.

At this time, the input to the amplifier 13 is permitted by turning off the switch S1 and turning on the switch S2, and the output voltage V1 of the amplifier 13 is G × Vin + Vg + Vos by turning on the switch S5 and turning off the switch S6.
become. When the switch S4 is turned off, the voltage V3 is maintained at the level of the voltage Vr, and at the same time, the terminals of the capacitors Caz on the inverting input terminal sides of the operational amplifiers 141 and 142 are disconnected from the voltage Vr.
The capacitor Caz also holds the charge amount Qaz described above. That is, even when the input to the amplifier 13 is permitted, the voltage V2 remains at Vos + Vr. Therefore, V1 is G × V
Since it becomes in + Vg + Vos, a current I1 given by the following equation flows through the resistor R14.

I1 = (V1−V2) / R14 = (G × Vin + Vg−Vr) / R14 Then, since the current I1 flows through the capacitor Cint, the voltage V4 is determined by the time for inputting the signal of the pressure sensor 11 to T1. Then, it is given by Vr−Cin × I1 × T1.

After the above state has continued for the time T1, the operation proceeds to the reverse integration and the switch S3 is turned off.
43 is in a reverse integration state in which the integration current Ir starts to flow. At this time, since the capacitor Cin discharges with the current Ir, the voltage V4 becomes Vr−I1 × T1 / Cin + Ir × T2 / Cin
become. Here, T2 is the time of the inverse integration state.

Here, if T2 is set to the time when the output level of the operational amplifier 142 switches from Low to High, since V3 = Vr, the output level of the operational amplifier 142 is such that the input of the operational amplifier 142 is Vr> V4. At this time, it becomes Low, and when Vr <V4, it becomes High. Therefore, T2 is Vr−I1 × T1 / Cin + Ir × T2 /
It is given by the following equation by Cin = Vr.

T2 = I1 × T1 / Ir Further, T1 is generated by N (constant) reference clocks (CLK), T1 = CLK × N, and during the time T2, the number of clocks having the same cycle as above is calculated. When counted, T2 = C
The following equation is established by LK × Nout. However, Nout
Is the number of counted clocks.

CLK × Nout = I1 × T1 / IrNout / N = I1 / Ir This Nout is a digital value corresponding to I1 when N and Ir are constant. That is, since the digital value Nout is determined by I1 and I1 = (G × Vin + Vg−Vr) / R14, the digital value Nout is not affected by the amplifier offset Vos. Setting Vg such that Vg-Vr cancels the sensor offset enables the sensor offset to be reduced. As a result, the output of the A / D converter 14 becomes constant even when the amplifier offset frequently changes due to a change in the external environment such as humidity, and a highly accurate and highly reliable pressure sensor circuit can be obtained.

FIG. 2 is a block diagram of a pressure sensor circuit according to a second embodiment of the present invention, and the second embodiment will be described below with reference to FIG.

The pressure sensor circuit shown in FIG. 2 includes a pressure sensor 11, an amplifier 13, and switches S1 to S4 in the same manner as in the first embodiment. An A / D converter 24 having the same configuration as that of the first embodiment is provided, and an offset correction circuit 22 different from that of the first embodiment is provided.

The A / D converter 24 includes an A / D converter 14a similar to that of the first embodiment and a controller 24b different from that of the first embodiment. The control unit 24b
When input to the amplifier 13 is prohibited and in the auto-zero state,
Turn on the switches S1, S3, S4 and switch S2
Is turned off, and when an input to the amplifier 13 is permitted, the switching control unit turns on the switches S2 and S3 and turns off the switches S1 and S4 in the same manner as the control unit 14b of the first embodiment. Be composed.

The offset correction circuit 22 generates a reference voltage for reducing the sensor offset, and is constituted by a D / A converter. Then, in the auto-zero state, the output voltage level is equal to the voltage Vr applied to the non-inverting input terminal of the operational amplifier 141, and when the input to the amplifier 13 is allowed, the output voltage level is If the offset correction circuit 22 is set to be at the same level as the offset reduction reference voltage Vg, the same effect can be obtained by the same circuit operation as in the first embodiment.

Here, the principle of correcting the sensor offset will be described. However, the output of the offset correction circuit 22 in the auto-zero state is V22, and the output of the offset correction circuit 22 when the input is allowed is V22 + ΔV22.

If no pressure is applied to the pressure sensor 11 when input is allowed, Vin becomes a sensor offset Voffset of about several mV. Therefore, V1 is G × Voffset +
Since Vos + V22 + ΔV22 and V2 is Vos + V22, the current I1 is given by the following equation.

I1 = (V1−V2) / R14 = G × Voffset + ΔV22 Since no pressure is applied to the pressure sensor 11,
If the adjustment is made so that I1 = 0, that is, ΔV22 becomes −G × Voffset, the sensor offset can be corrected.

FIG. 3 is a diagram showing a pressure sensor in a pressure sensor circuit according to a third embodiment of the present invention. The third embodiment will be described below with reference to this figure. Except for the configuration, the configuration is the same as that of the second embodiment.

The pressure sensor 31 detects the resistances Rs1 to Rs4
As shown in FIG. 3, in order to provide the same as in the embodiment and correct the variation of the sensor offset, as shown in FIG. 3, a resistor R1 interposed between the power supply terminal Ts3 and the resistor Rs1 and the power supply terminal Ts3 and the resistor Rs2 are connected to each other. , And is adjusted so that the variation in the sensor offset is always positive.

Here, the pressure sensor circuit is a pressure sensor 3
Since the configuration is the same as that of the second embodiment except that 1 is provided, it can be understood from the description of the principle of correcting the sensor offset in the second embodiment that the following expression is established.

Vin = Voffset However, at zero pressure V1 = G × Voffset + Vos + V22 + ΔV22 In this case, the amplitude dynamic range of V1 is V22 + Δ
V22 to VDD. At this time, ΔV22 becomes −
Since G × Voffset, the sensor offset Voffset
If the pressure sensor 31 is adjusted so that
2 <0, and the amplitude dynamic range of V1 can be expanded.

Next, a pressure sensor circuit according to a fourth embodiment of the present invention will be described. However, the pressure sensor circuit according to the fourth embodiment has the same configuration as that of the first embodiment.

In the case of the fourth embodiment, the following equation holds.

Vin = Voffset However, at zero pressure V1 = G × Voffset + Vos + Vg In this case, the dynamic range of the amplifier 13 is Vg to Vg.
DD, and V is corrected so as to correct the sensor offset.
By setting g = −G × Voffset, the dynamic range can be expanded.

FIG. 4 is a diagram showing a pressure sensor in a pressure sensor circuit according to a fifth embodiment of the present invention, and the fifth embodiment will be described below with reference to FIG.

The pressure sensor circuit shown in FIG. 4 includes a pressure sensor 11, an offset correction circuit 12, an amplifier 13, and switches S1 to S6 in the same manner as in the first embodiment. A / D converter 44 is provided.

The A / D converter 44 includes a control unit 14b similar to that of the first embodiment and an A / D converter 44 different from that of the first embodiment.
It is constituted by a / D conversion unit 44a. The A / D converter 44a includes an operational amplifier 14 instead of the current extractor 143.
The configuration is the same as that of the A / D conversion unit 14a of the first embodiment, except that a current extraction unit (current source in the figure) 443 that extracts the inverse integrated current from the inversion input terminal of the first embodiment is provided.

In the case of the above configuration, the potential of the inverting input terminal of the operational amplifier 141 for taking out the inverse integral current is
Since it is stable at the reference voltage Vr of 4a, it is possible to accurately take out the inverse integration current, and it is possible to perform highly accurate A / D conversion.

[0049]

As is apparent from the above description, according to the first aspect of the present invention, a pressure sensor comprising a resistor having a bridge circuit configuration and an offset for generating a reference signal for reducing an output offset of the pressure sensor are provided. A correction circuit, a differential amplification type amplifier for amplifying the detection signal of the pressure sensor while reducing the output offset with a reference signal from the offset correction circuit, and an A / A for converting the output signal of the amplifier into a digital value. Since the D / D converter and the means for reducing the output offset of the amplifier included in the output signal of the amplifier by the A / D converter are provided, the output offset of the amplifier is canceled, and the external environment such as time lapse and humidity is reduced. It is possible to provide a highly accurate and highly reliable pressure sensor circuit that can obtain an accurate output even if it changes.

According to a second aspect of the present invention, in the pressure sensor circuit according to the first aspect, the A / D converter includes a first operational amplifier for applying a predetermined voltage to a non-inverting input terminal, and the amplifier. An integration resistor having one end connected to an output terminal of the first operational amplifier; an auto-zero capacitor connected between the other end of the integration resistor and an inverting input terminal of the first operational amplifier; An integrating capacitor connected between a connection point of the capacitor and an output terminal of the first operational amplifier; and a non-inverting input terminal and an inverting input terminal connected to an output terminal and an inverting input terminal of the first operational amplifier, respectively. A second operational amplifier, and a current extracting unit for extracting a reverse integration current from the integrating capacitor, the means comprising: a first switch connected between both input terminals of the amplifier; A second switch interposed between one output terminal of the pressure sensor and the input terminal on the non-inverting side of the amplifier; and a second switch between the output terminal of the amplifier and the input terminal of the A / D converter. A third switch interposed, a fourth switch connected between an inverting input terminal and an output terminal of the second operational amplifier, and a fifth switch interposed between the offset correction circuit and the amplifier. A sixth switch connected between a connection point of the amplifier and the fifth switch and a non-inverting input terminal of the first operational amplifier; and a first, third, and fourth switches when input to the amplifier is prohibited. And the sixth switch is turned on, and the second and fifth switches are turned off. On the other hand, when the input to the amplifier is permitted, the second, third and fifth switches are turned on,
A switching control unit that turns off the first, fourth, and sixth switches, and turns off the third switch when the transition is made from the input-permitted time to the reverse integration, so that the output offset of the amplifier is canceled, It is possible to provide a highly accurate and highly reliable pressure sensor circuit that can obtain an accurate output even when an external environment such as humidity changes.

According to a third aspect of the present invention, in the pressure sensor circuit according to the first aspect, the A / D converter includes a first operational amplifier for applying a predetermined voltage to a non-inverting input terminal, and the amplifier. An integration resistor having one end connected to an output terminal of the first operational amplifier; an auto-zero capacitor connected between the other end of the integration resistor and an inverting input terminal of the first operational amplifier; An integrating capacitor connected between a connection point of the capacitor and an output terminal of the first operational amplifier; and a non-inverting input terminal and an inverting input terminal connected to an output terminal and an inverting input terminal of the first operational amplifier, respectively. A second operational amplifier, and a current extracting unit for extracting a reverse integration current from the integrating capacitor, the means comprising: a first switch connected between both input terminals of the amplifier; A second switch interposed between one output terminal of the pressure sensor and the input terminal on the non-inverting side of the amplifier; and a second switch between the output terminal of the amplifier and the input terminal of the A / D converter. A third switch interposed, a fourth switch connected between the inverting input terminal and the output terminal of the second operational amplifier, and the first, third and fourth switches when the input to the amplifier is prohibited. Turn on,
While the second switch is turned off, when the input to the amplifier is allowed, the second and third switches are turned on, the first and fourth switches are turned off, and the transition from the input allowed to the reverse integration is performed. And a switching control unit for turning off the third switch, wherein the offset correction circuit outputs a voltage of the same level as a predetermined voltage applied to the non-inverting input terminal of the first operational amplifier when the input is prohibited. On the other hand, when the input is permitted, the voltage as the reference signal is output, so that the output offset of the amplifier is canceled, and accurate output can be obtained even if the external environment such as time lapse and humidity changes. A pressure sensor circuit can be provided.

According to the fourth aspect of the present invention, in the pressure sensor circuit according to the first aspect, the pressure sensor is adjusted such that the variation of the output offset voltage is always a positive value. The dynamic range can be expanded.

According to a fifth aspect of the present invention, in the pressure sensor circuit of the second aspect, a value obtained by subtracting the predetermined voltage from the voltage as the reference signal cancels an output offset of the pressure sensor. Since the reference signal is set, the dynamic range of the amplifier can be expanded.

According to the sixth aspect of the present invention, in the pressure sensor circuit according to the second or third aspect, since the inverse integrated current is taken out from an inverting input terminal of the first operational amplifier, a highly accurate A / D is achieved. Conversion becomes possible.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a pressure sensor circuit according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a pressure sensor circuit according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a pressure sensor in a pressure sensor circuit according to a third embodiment of the present invention.

FIG. 4 is a diagram showing a pressure sensor in a pressure sensor circuit according to a fifth embodiment of the present invention.

FIG. 5 is a diagram showing a conventional configuration example of a pressure sensor circuit.

[Explanation of symbols]

 11, 31 Pressure sensor 12, 22 Offset correction circuit 13 Amplifier 14, 24, 44 A / D converter 14a, 44a A / D converter 14b, 24b Controller 141 Operational amplifier (integrator) 142 Operational amplifier (comparator) 143,443 Current extractor R14 Integrating resistor Caz Auto-zero capacitor Cint Integrating capacitor S1-S6 Switches R1, R2 Resistance

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinji Sakamoto 1048 Kazuma Kadoma, Kadoma-shi, Osaka Matsushita Electric Works F-term (reference) 2F049 AA13 CA12 2F075 AA06 AA07 EE04

Claims (6)

[Claims] A pressure sensor comprising a resistor having a bridge circuit configuration; an offset correction circuit for generating a reference signal for reducing an output offset of the pressure sensor; and a reference signal from the offset correction circuit for reducing the output offset. A differential amplification type amplifier for amplifying the detection signal of the pressure sensor, an A / D converter for converting an output signal of the amplifier into a digital value, and an output offset of the amplifier included in the output signal of the amplifier. Means for reducing by the A / D converter. 2. An A / D converter comprising: a first operational amplifier for applying a predetermined voltage to a non-inverting input terminal; an integrating resistor having one end connected to an output terminal of the amplifier; An auto-zero capacitor connected between the other end of the first operational amplifier and the inverting input terminal of the first operational amplifier, and a connection between a connection point of the integrating resistor and the auto-zero capacitor and an output terminal of the first operational amplifier. An integrating capacitor, a second operational amplifier having a non-inverting input terminal and an inverting input terminal connected to an output terminal and an inverting input terminal of the first operational amplifier, respectively, and a current for extracting a reverse integral current from the integrating capacitor. A take-out unit, the means comprising: a first switch connected between both input terminals of the amplifier; one output terminal of the pressure sensor; and a non-inverting input terminal of the amplifier. A second switch that is provided between a third switch that is provided between the input terminal of the A / D converter and the output terminal of the amplifier, the second
A fourth switch connected between the inverting input terminal and the output terminal of the operational amplifier, a fifth switch interposed between the offset correction circuit and the amplifier, a connection point between the amplifier and the fifth switch, A sixth switch connected between the non-inverting input terminal of the first operational amplifier and the first, third, fourth and sixth switches when the input to the amplifier is prohibited, When the input to the amplifier is allowed, the second, third, and fifth switches are turned on, and the first, fourth, and sixth switches are turned off. 2. The pressure sensor circuit according to claim 1, further comprising: a switching control unit that turns off the third switch when a transition is made from the time to the time of the reverse integration. 3. An A / D converter comprising: a first operational amplifier for applying a predetermined voltage to a non-inverting input terminal; an integrating resistor having one end connected to an output terminal of the amplifier; An auto-zero capacitor connected between the other end of the first operational amplifier and the inverting input terminal of the first operational amplifier, and a connection between a connection point of the integrating resistor and the auto-zero capacitor and an output terminal of the first operational amplifier. An integrating capacitor, a second operational amplifier having a non-inverting input terminal and an inverting input terminal connected to an output terminal and an inverting input terminal of the first operational amplifier, respectively, and a current for extracting a reverse integral current from the integrating capacitor. A take-out unit, the means comprising: a first switch connected between both input terminals of the amplifier; one output terminal of the pressure sensor; and a non-inverting input terminal of the amplifier. A second switch that is provided between a third switch that is provided between the input terminal of the A / D converter and the output terminal of the amplifier, the second
A fourth switch connected between the inverting input terminal and the output terminal of the operational amplifier and, when input to the amplifier is prohibited, turning on the first, third and fourth switches and turning off the second switch On the other hand, when the input to the amplifier is permitted, the second and third switches are turned on, the first and fourth switches are turned off, and when the transition from the input permitted to the time of the reverse integration is performed, the third switch is turned off. The offset correction circuit outputs a voltage of the same level as a predetermined voltage applied to a non-inverting input terminal of the first operational amplifier when the input is prohibited, and the reference when the input is allowed. The pressure sensor circuit according to claim 1, wherein the pressure sensor circuit outputs a voltage as a signal. 4. The pressure sensor circuit according to claim 1, wherein the pressure sensor is adjusted so that the variation of the output offset voltage always becomes a positive value. 5. The pressure sensor circuit according to claim 2, wherein the reference signal is set such that a value obtained by subtracting the predetermined voltage from the voltage as the reference signal cancels the output offset of the pressure sensor. 6. The pressure sensor circuit according to claim 2, wherein said inverse integrated current is taken from an inverting input terminal of said first operational amplifier.