JP2000065595A - Sensor circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a sensor circuit where no sensitivity difference is generated depending on a direction by providing a fixed capacitor that becomes a reference for comparison and comparing the fixed capacitor with a pair of variable capacitors whose capacity changes according to a physical amount, and outputting the difference. SOLUTION: A circuit 1 for detecting amount of capacity change compares a fixed capacitor C0 that becomes a reference for comparison with a pair of variable capacitors C1 and C2 whose capacity changes according to a physical amount and outputs the capacity differences ΔC1 and ΔC2. A C/V conversion circuit 2 converts the capacity differences ΔC1 and ΔC2 to voltages, and the voltage output is compared by an amplification circuit 3, and the difference is outputted. As a result, by applying, for example, to a sensor for converting the difference between double capacitance to voltage output, voltage output also equally changes when the amount of change in the capacitance is equal and sensitivity at + and - sides becomes equal, thus achieving a symmetrical circuit type sensor without generating a sensitivity difference that depends on the polarity of the direction of a detection axis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensor circuit.

[0002]

2. Description of the Related Art As a detection circuit of a capacitance type sensor,
For example, there is known a circuit as shown in FIG. 4 which uses a change in capacitance difference as a detection signal. FIG. 5 shows a specific example.

However, the capacitance C1 → the voltage V1,
When the conversion rate from the capacitance C2 to the voltage V2 is different, or when the capacitances C1 and C2 increase and decrease, the voltages V1 and V2
When the conversion rate to the data is different, the detection sensitivity of the change of the physical quantity is different depending on the change direction of the signal. That is, when the above-described circuit is used, there is a problem that a sensitivity difference occurs depending on the direction.

[0004]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a sensor circuit which does not cause a sensitivity difference depending on the direction.

[0005]

Means for Solving the Problems (Invention of Claim 1)
The sensor circuit according to the present invention is provided with a fixed capacitor serving as a reference for comparison, compares the fixed capacitor with a pair of variable capacitors whose capacity changes in accordance with a physical quantity, and outputs the difference. (Invention of Claim 2) The sensor circuit of the present invention is provided with a fixed resistor serving as a reference for comparison, compares the fixed resistor with a pair of variable resistors whose resistance changes according to a physical quantity, and determines the difference. It shall be output. According to a third aspect of the present invention, there is provided a sensor circuit including a constant time constant circuit serving as a reference for comparison, a constant time constant circuit, and a pair of time constant circuits whose time constants change according to physical quantities. And outputs the difference. (Invention of Claim 4) The sensor circuit according to the present invention relates to the invention of Claim 1 or 2, wherein a variable capacitance or a variable resistance is used as a detection unit, and a semiconductor logic circuit is used as a comparator. The output is operated by an operational amplifier. According to the sensor circuit of the present invention, a pair of time constant circuits whose time constants change in accordance with the physical quantity include a variable capacitor and a fixed resistor, and a fixed capacitor and a variable capacitor. It is composed of a resistor or a variable capacitor and a variable resistor. The variable capacitor or the variable resistor serves as a detection unit, the semiconductor logic circuit serves as a comparator, and the output from the comparator is operated and output by an operational amplifier.

The function of the sensor circuit of the present invention will be described in detail in the following embodiments of the present invention.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. (Regarding Embodiment 1) The sensor circuit of this embodiment is as follows.
As shown in FIG. 1, a fixed capacitance C0 serving as a reference for comparison is compared with a pair of variable capacitors C1 and C2 whose capacitances change according to a physical quantity, respectively, and the capacitance difference ΔC1, ΔC2 is output. Circuits 1 and 1, C / V conversion circuits 2 and 2 for converting the respective capacitance differences ΔC1 and ΔC2 into voltages, and compares the voltage outputs from the C / V conversion circuits 2 and 2 and outputs the difference. And an amplifier circuit 3.

When the above sensor circuit is formed more specifically, a circuit as shown in FIG. 2 is obtained. In FIG. 2, symbols R0, R1, R
2, R4 to R9 are fixed resistors, C1 and C2 are variable capacitances, C0 and C are fixed capacitances, U1 and U2 are EX-OR logic circuits, and U3 and U4 are operational amplifiers.

In FIG. 2, R1 = R2, C1 = C2 (when no load is applied) C1 × R1 = C2 × R2 ≠ C0 × R0 (a)₀= (1 + R6 / R7) (V_Two-V₁) ... (b) R6 / R7 = R9 / R8 The variable capacitances C1 and C2 are the force, moment, acceleration,
It changes according to physical quantities such as pressure. P due to the difference between the time constants C1 × R1 and C0 × R0₁No negatives on points
Voltage V at loading₁Occurs, while the time constants C2 × R2, C0 × R0
P due to the difference_TwoThe point is the voltage V when there is no load._TwoOccurs
You. Circuit symmetry because R1 = R2 and C1 = C2 as described above
More V₁= V_TwoAnd V₀= 0. Here, C2 changes by + ΔC due to the above physical quantity.
Then P_TwoThe voltage at the point is (V _Two+ ΔV), the output V₀
Is given by the above equation (b).₀= (1 + R6 / R7) (V_Two+ ΔV-V₁) ... (c) Conversely, C1 changes by + ΔC depending on the physical quantity, and P1
₁The voltage at the point is (V₁ + ΔV), the output V₀Is above
From equation (b), V₀= (1 + R6 / R7) (V_Two-V₁ −ΔV)... (D). Therefore, if C1 or C2 changes by + ΔC,
Force voltage V₀Of change ΔV ₀Are the same in size, ΔV₀Is the absolute value of (1 + R6 / R7)） ΔV.

For example, when this is applied to a sensor that converts a change in the difference between two capacitances into a voltage output,
If the amount of change in the capacitance is equal, the voltage output changes equally, which means that the + side and the-side sensitivity become equal. From the above description, it is clear that a symmetrical circuit type sensor that does not generate a sensitivity difference depending on the polarity in the detection axis direction can be realized. (Regarding Embodiment 2) The sensor circuit of this embodiment is as follows.
As shown in FIG. 3, a resistance change amount detection circuit for comparing a fixed resistance R0 serving as a reference for comparison with a pair of variable resistances R1 and R2 whose resistance changes according to a physical quantity and outputting the resistance differences ΔR1 and ΔR2. Circuit 1 ', 1', R / V conversion circuits 2 ', 2' for converting the respective resistance differences ΔR1, ΔR2 into voltages, and voltage outputs from the R / V conversion circuits 2 ', 2', respectively. And an amplifier circuit 3 'for outputting the difference. To form the sensor circuit more specifically, FIG.
Can be achieved by making only R1 and R2 in the circuit shown in FIG.

It is apparent that no sensitivity difference depending on the polarity in the detection axis direction occurs in this sensor circuit, as in the above embodiment. (Other Embodiments) In the first embodiment,
In place of 2, only R1, R2 and C1, C2 in the circuit shown in FIG. 2 may be made variable, and the others may be made fixed values.

Although the first and second embodiments are sensor circuits for detecting a unitary physical quantity, if necessary, a plurality of circuits shown in FIG. I can do it.

Further, the specific configuration of the sensor circuit is not limited to that shown in FIG. 2, and any circuit that performs the same function can be used freely.

[0014]

Since the present invention has the above configuration, the following effects are obtained.

As is clear from the description in the section of the embodiment of the invention, a sensor circuit in which a sensitivity difference does not occur depending on the direction can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic circuit according to a first embodiment of the present invention.

FIG. 2 is a sensor circuit diagram when the basic circuit of FIG. 1 is further embodied.

FIG. 3 is a diagram showing a basic circuit according to a second embodiment of the present invention.

FIG. 4 is a diagram of a basic circuit of a conventional sensor.

FIG. 5 is a sensor circuit diagram when the basic circuit of FIG. 4 is further embodied.

[Explanation of symbols]

 C0 Fixed capacitance C1 Variable capacitance C2 Variable capacitance R0 Fixed resistance R1 Variable resistance R2 Variable resistance U1 EX-OR logic circuit U2 EX-OR logic circuit U3 Operational amplifier U4 Operational amplifier

Claims (5)

[Claims] 1. A sensor circuit comprising: a fixed capacitor serving as a reference for comparison; comparing the fixed capacitor with a pair of variable capacitors whose capacity changes according to a physical quantity; and outputting a difference therebetween. 2. A sensor circuit, comprising: a fixed resistor serving as a reference for comparison, comparing the fixed resistor with a pair of variable resistors whose resistance changes according to a physical quantity, and outputting a difference therebetween. 3. A constant time constant circuit serving as a reference for comparison is provided. The constant time constant circuit is compared with a pair of time constant circuits whose time constants change according to physical quantities, and the difference is output. A sensor circuit characterized by the above. 4. The sensor circuit according to claim 1, wherein a variable capacitance or a variable resistance is used as a detection unit, the semiconductor logic circuit is used as a comparator, and an output from the comparator is operated and output by an operational amplifier. . 5. A pair of time constant circuits whose time constants change in accordance with a physical quantity are constituted by a variable capacitor and a fixed resistor, a fixed capacitor and a variable resistor, or a variable capacitor and a variable resistor. 4. The sensor circuit according to claim 3, wherein the resistance is used as a detection unit, the semiconductor logic circuit is used as a comparator, and an output from the comparator is operated and output by an operational amplifier.