JP2951566B2 - Signal processing circuit for acceleration sensor using change in capacitance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing circuit for a sensor which detects acceleration by using a change in capacitance.

[0002]

2. Description of the Related Art In the automobile industry and the like, the demand for small sensors capable of accurately detecting acceleration has been increasing. As one of the answers to this demand, an acceleration sensor using a change in capacitance has been proposed (Japanese Patent Laid-Open No. 4-249726). In this acceleration sensor, a capacitive element is formed by a fixed electrode formed on a fixed substrate and a displacement electrode that generates displacement by the action of acceleration, and the applied acceleration is detected based on a change in the capacitance of the capacitive element. You can do it.

[0003] A control device for an automobile or an industrial robot performs various controls based on output signals from an acceleration sensor. At this time, the output signal is a capacitance (physical quantity unit:
C) Voltage value (physical unit: V)
In the case of the shape, it is easier for the control device to handle. Conventional signal processing circuits of this type include:
There is a problem that the temperature characteristics are not good. That is, since the converted voltage value fluctuates greatly due to a change in temperature, accurate control cannot be performed in an environment where there is a temperature change. In particular, in the application field of automobiles and industrial robots,
Since severe temperature conditions such as 40 ° C. to + 85 ° C. are required, the influence is great.

As a conventional signal processing circuit for converting an output of an acceleration sensor taken out as a change in capacitance into a voltage value, for example, a circuit system shown in the circuit diagrams of FIGS. 5 and 6 (Japanese Patent Laid-Open No. 5-346357) Gazette) is known. The circuit in FIG. 5 is a circuit generally known as a voltage doubler circuit, and a capacitance element forming an acceleration sensor to be measured is indicated by C. A circuit composed of diodes 51 and 52, a capacitor 53, and a resistor 54 is connected to the capacitive element C. When a square wave of a predetermined frequency is applied to the input terminal IN, the output of the capacitive element C is applied to the output terminal OUT. An output voltage V corresponding to the capacitance value is obtained. The circuit of FIG. 6 uses an EX-OR element, and a capacitance element constituting an acceleration sensor to be measured is indicated by C. FIG.
In this circuit, a square wave signal having a predetermined frequency is supplied from the input terminal IN, and a square wave signal having a pulse width corresponding to a change in the capacitance value of the capacitor C is obtained at the output terminal OUT. FIG.
In this circuit, two first-order lag circuits are formed by the capacitive element C and the resistor 61, and the capacitor 62 and the resistor 63,
Each is connected to the X-OR element 64. The change in the capacitance value of the capacitance element C results in a change in the delay time of the square wave signal given from the input terminal IN due to the first-order delay circuit, and the time change is expressed as a change in the pulse width of the square wave signal at the output terminal OUT. Will be obtained.

[0005]

The output voltage V of the circuit shown in FIG. 5 has a drawback that the temperature characteristics of the diodes 51 and 52 are not good, and the output voltage V is greatly affected by a temperature change. Further, the EX-OR element 64 of the circuit shown in FIG. 6 has a characteristic that the transmission delay time and the threshold voltage change due to a temperature change. The change in the transmission delay time has the same effect on the two first-order lag signals, and therefore has little effect on the temperature characteristics. However, as for the change in the threshold voltage, as shown in FIG. 7, the variation is not constant and does not act equivalently for the two first-order lag signals.
There is a problem that the pulse width of the T rectangular wave signal is affected by a temperature change.

SUMMARY OF THE INVENTION An object of the present invention is to provide a signal processing circuit for an acceleration sensor using a change in capacitance, which has good temperature characteristics and eliminates the above-mentioned disadvantages of the prior art.

[0007]

Means for Solving the Problems The present inventors have intensively studied and studied to achieve the above object. As a result, a signal generation source for generating a square wave signal and a square wave inverted signal having a predetermined frequency, and two primary circuits each including the capacitor and a resistor, and a capacitor having a predetermined capacity (hereinafter referred to as a capacitor) and a resistor. A delay circuit and an adder circuit composed of an operational amplifier may be provided, and the change in the capacitance of the capacitive element may be output from the operational amplifier as a first-order delay difference between the square wave signal and the square wave inverted signal. Investigating this, they arrived at the present invention.

That is, according to the present invention, a capacitive element is formed by an electrode pair whose mutual distance changes by the action of acceleration, and the applied acceleration is changed based on a change in capacitance due to a change in the mutual distance of the capacitive elements. In a signal processing circuit used for the acceleration sensor to detect, a signal generation source for generating a square wave signal of a predetermined frequency and an inverted square wave signal,
A first delay circuit composed of the capacitive element and the resistor, a capacitor of a predetermined capacitance and a resistor, and an adder circuit composed of an operational amplifier; A signal processing circuit for an acceleration sensor using a change in capacitance, which is output from an operational amplifier as a difference between a first-order lag signal of a wave signal and an inverted square wave signal.

Further, according to the present invention, a first capacitive element is constituted by an electrode pair arranged so as to increase the mutual distance by the action of acceleration in a predetermined direction, and conversely arranged so as to reduce the mutual distance. A second capacitance element is constituted by the pair of electrodes thus set, and the applied acceleration is determined based on the difference between the change value of the capacitance of the first capacitance element and the change value of the capacitance of the second capacitance element. In a signal processing circuit used for an acceleration sensor for detecting, a signal generation source for generating a square wave signal and an inverted square wave signal of a predetermined frequency, a first-order delay circuit including the first capacitance element and a resistor, A first-order delay circuit composed of a second capacitive element and a resistor; and an adder circuit composed of an operational amplifier, wherein a change in the capacitance of the first and second capacitive elements is detected by a square wave signal. And first order delay of inverted square wave signal As a difference signal, a signal processing circuit for an acceleration sensor using a change in capacitance, characterized in that the output from the operational amplifier.

[0010]

According to the present invention, two primary delay circuits are formed by combining a capacitor and a resistor, and a capacitor and a resistor, which constitute an acceleration sensor, and a square wave signal is supplied to one of the primary delay circuits. When the inverted square wave signal is passed through the first-order lag circuit, two first-order lag signals are obtained. These two first-order lag signals are added by an adder circuit composed of an operational amplifier, and when the resistance values of the resistors of both the first-order lag circuits are made equal, the difference between the capacitances of the capacitive element and the capacitor becomes the difference. The signal can be obtained from the output of the adder circuit. The temperature characteristics of the signal processing circuit of the present invention are determined by
The temperature characteristics of the resistors, capacitors, and operational amplifiers used in the circuit, which are now very good and easy to obtain, so you get accurate readings that are less affected by temperature be able to.

Further, in the present invention, two primary delay circuits are formed by combining the first capacitive element and the resistor and the second capacitive element and the resistor which constitute the acceleration sensor, and one primary delay circuit is formed. When a square wave signal is passed through the delay circuit and an inverted square wave signal is passed through one primary delay circuit, two primary delay signals are obtained. These two first-order lag signals are added by an adder circuit composed of operational amplifiers, and when the resistance values of the resistors of both the first-order lag circuits are made equal, the capacitance of the first and second capacitance elements is reduced. The difference can be obtained from the output of the adder circuit as a difference signal. It is the temperature characteristics of the resistors, capacitors, and operational amplifiers used in the circuit that determine the temperature characteristics of the signal processing circuit of the present invention. Therefore, it is possible to obtain an accurate detection value with little influence of temperature.

[0012]

【Example】

Embodiment 1 FIG. 1 shows an example of the details of the first invention of the present application,
A description will be given based on FIG. FIG. 1 is a circuit diagram showing a signal processing circuit according to a first embodiment of the present invention, and FIG. 2 is a signal waveform at each node of the circuit shown in FIG. In FIG. 1, C is a capacitive element constituting an acceleration sensor to be measured. When a square wave signal is given from an input terminal IN1 and an inverted square wave signal is given from an input terminal IN2, an output terminal O is provided.
A signal having a waveform corresponding to a change in the capacitance value of the capacitance element C is obtained in the UT. Capacitive element C and resistor 1 and capacitor 2 and resistor 3 form two primary delay circuits, which are connected to inverting input terminals of operational amplifier 6 through resistors 4 and 5, respectively. Where resistors 4, 5 and 7
Constitutes an addition circuit using the operational amplifier 6, and the output voltage value of the addition circuit, that is, the output terminal OUT
Is given as follows. Output voltage value V
_OUT is the resistance of resistors 4, 5, and 7, respectively,
4, R5 and R7, when the voltage value of the resistor 4 and the signals passing through 5 and V ₁ and V _2, respectively, given by the following equation (1). V _OUT = − (V ₁ × R7 / R4 + V ₂ × R7 / R5) (1) The change in the capacitance value of the capacitive element C is caused by the primary delay circuit of the rectangular wave signal given from the input terminal IN. , Delay time, and the time change is obtained as a signal waveform change at the output terminal OUT.

With the above configuration, when the square wave signal is applied to the input terminal IN1 and the inverted square wave signal is applied to the input terminal IN2, as shown in FIG.
The signals Q1, Q2, V1 and V
2 is obtained. The signal V1 has a first-order signal waveform determined by a time constant defined by the product of the capacitance value of the capacitance element C and the resistance value R1 of the resistor 1 with respect to the square wave signal. Further, the signal V2 has a first-order lag signal waveform determined by a time constant defined by the product of the capacitance value of the capacitor 2 and the resistance value R3 of the resistor 3 with respect to the inverted square wave signal. These two signals are calculated in the adder circuit by the above equation (1), and the signal OUT is obtained at the output terminal OUT. Here, the magnitude of the signal OUT corresponds to the time constant in the first-order lag circuit. If the resistance value R1 of the resistor 1 is constant, the magnitude of the signal OUT is This corresponds to the capacitance value. That is, when the capacitance value of the capacitance element C increases, the signal OUT also increases, and when the capacitance value decreases, the signal OUT also decreases. Is detected as a change in the magnitude of The temperature characteristics of the signal processing circuit are determined by the resistor 1 used in the circuit,
3, 4, 5, 7, the temperature characteristic of the capacitor 2 and the operational amplifier circuit 6, because these are adapted now readily available that very good is less accurate detection of the influence of temperature Vessels can be obtained.

Embodiment 2 FIG. 3 is a circuit diagram showing a signal processing circuit according to a second embodiment of the present invention, and FIG. 4 is a signal waveform at each node of the circuit shown in FIG. In FIG. 3, a first capacitive element C1 and a second capacitive element C2 that constitute an acceleration sensor to be measured are shown. When a square wave signal is input from the input terminal IN1 and an inverted square wave signal is input from the input terminal IN2, the first capacitor C1 and the second capacitor C2 are connected to the output terminal OUT.
A signal having a waveform corresponding to the difference between the capacitance value and the capacitance value is obtained.
The first capacitive element C1 and the resistor 11 and the second capacitive element C2 and the resistor 13 form two first-order lag circuits, which pass through the resistors 14 and 15 to the inverting input terminal of the operational amplifier 16, respectively. Is connected. Here, the resistor 14,
Reference numerals 15 and 17 constitute an addition circuit using the operational amplifier 16, and the output voltage value of the addition circuit, that is,
The voltage value of the output terminal OUT is given as follows. Output voltage V _OUT1 is resistors 14, 15 and each R14, R15 and R17 the resistance value of 17, resistors 14 and 15, respectively a voltage value of the signal V ₁₁ and V ₁₂ through the
Then, it is given by the following equation (1). V _OUT1 = − (V ₁₁ × R17 / R14 + V ₁₂ × R17 / R15) (2) The change in the capacitance value of the first and second capacitance elements C1 and C2 is a square wave given from the input terminal IN1. The delay time of the signal and the inverted square wave signal supplied from the input terminal IN2 is changed by a first-order delay circuit, and the time change is obtained as a change in the signal waveform at the output terminal OUT.

With the above configuration, FIG.
As shown in FIG. 7, when the square wave signal is applied to the input terminal IN1 and the inverted square wave signal is applied to the input terminal IN2, the node Q1
1, Q12, V11 and V12
2, V11 and V12 are obtained. The signal V11 has a first-order lag signal waveform determined by a time constant defined by the product of the capacitance value of the first capacitive element C1 and the resistance value R11 of the resistor 11 with respect to the square wave signal. The signal V12 is
The inverted square wave signal has a first-order lag signal waveform determined by a time constant defined by the product of the capacitance value of the second capacitor C2 and the resistance value R13 of the resistor 13. These two signals are calculated by the above equation (2) in the addition circuit.
The signal OUT is obtained at the output terminal OUT. Here, the magnitude of the signal OUT corresponds to the time constant in the first-order delay circuit. If the resistance values of the resistors 11 and 13 are constant, the magnitude of the signal OUT is equal to the first magnitude. Capacitive element C
This corresponds to the difference between the capacitance values of the first and second capacitance elements C2. That is, if the difference between the capacitance values of the first capacitance element C1 and the second capacitance element C2 increases, the signal O
If the UT also increases and the difference between the capacitance values of the first capacitance element C1 and the second capacitance element C2 decreases, the signal OUT
This means that the change in the difference between the capacitance values of the first capacitance element C1 and the second capacitance element C2, which is also small, can be detected as a change in the magnitude of the signal OUT. The temperature characteristics of the signal processing circuit are determined by the temperature characteristics of the resistors, capacitors, and operational amplifier circuits used in the circuit. As a result, an accurate detector with little influence of temperature can be obtained.

[0016]

As described above, the signal processing circuit of the acceleration sensor according to the present invention is constituted by the capacitance element constituting the acceleration sensor, the resistor, the capacitor and the operational amplifier having excellent temperature characteristics. And acceleration can be accurately measured.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a signal processing circuit according to a first invention of the present application.

FIG. 2 is a signal waveform at each node of the circuit shown in FIG.

FIG. 3 is a circuit diagram showing a signal processing circuit according to a second invention of the present application.

FIG. 4 is a signal waveform at each node of the circuit shown in FIG. 3;

FIG. 5 is a circuit diagram illustrating an example of a signal processing circuit that converts an output of a conventional acceleration sensor into a voltage value.

FIG. 6 is a circuit diagram showing another example of a signal processing circuit for converting an output of a conventional acceleration sensor into a voltage value.

7 is a signal waveform at each node showing a situation where a change in threshold voltage affects a pulse width in the signal processing circuit of FIG. 6;

[Explanation of symbols]

C capacitive element C1 first capacitive element C2 second capacitor IN, IN1, IN2 input terminal OUT an output terminal V _OUT output voltage value _{V 1, V 2, V 11} , V 12 the voltage value R1, R3, R4, R5 , R7, R11, R13, R1
4, R15, R17 resistance values Q1, Q2, Q11, Q12, V1, V2, V11, V
12, X1, X2 nodes 1, 3, 4, 5, 7, 11, 13, 14, 15, 17,
54, 61, 63 Resistor 2, 53, 62 Capacitor 6, 16 Operational amplifier

Claims (2)

(57) [Claims] An acceleration for forming a capacitive element by a pair of electrodes whose distance changes by the action of acceleration, and detecting an applied acceleration based on a change in capacitance due to a change in the distance between the capacitive elements. In a signal processing circuit used for a sensor, a signal generation source for generating a square wave signal and an inverted square wave signal of a predetermined frequency, a first-order delay circuit including the capacitor and a resistor, a capacitor and a resistor of a predetermined capacitance And a change circuit of the capacitance of the capacitive element as a difference between a first-order lag signal of a square wave signal and a first-order lag signal of an inverted square wave signal. A signal processing circuit for an acceleration sensor using a change in capacitance, which is output from an operational amplifier. 2. A first capacitive element is constituted by an electrode pair arranged to increase the mutual distance by the action of acceleration in a predetermined direction, and conversely, an electrode pair arranged so as to decrease the mutual distance. An acceleration sensor for detecting an applied acceleration based on a difference between a change in capacitance of the first capacitor and a change in capacitance of the second capacitor. A signal generation source for generating a square wave signal and an inverted square wave signal of a predetermined frequency, a first-order lag circuit including the first capacitor and a resistor, and a second capacitor A first-order lag circuit composed of an element and a resistor; and an adder circuit composed of an operational amplifier, wherein a change in capacitance of the first and second capacitance elements is detected by a square wave signal and an inverted square wave. As the difference of the first-order lag signal of the signal A signal processing circuit for an acceleration sensor using a change in capacitance, which is output from an operational amplifier.