JP2008275428A - Proximity detection sensor and proximity detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a proximity detection sensor for performing high-accuracy detection with a circuit structure for computing and outputting a difference in pulse width. <P>SOLUTION: This proximity detection sensor is equipped with a detection electrode 2, a first detection circuit 4 converting a change in capacitance between the detection electrode 2 and ground into a detection pulse signal P<SB>1</SB>to output it, a reference capacitor 6 charged during a prescribed time period, a second detection circuit 8 converting a change in capacitance of the reference capacitor 6 into a reference pulse signal P<SB>2</SB>to output it, a trigger signal generation circuit 10 generating a trigger signal TG for charging the detection electrode 2 and the reference capacitor 6 at prescribed time intervals, and a computation circuit 12 for calculating a difference pulse signal P<SB>3</SB>from the pulse signal P<SB>1</SB>inputted from the detection circuit 4 and the pulse signal P<SB>2</SB>inputted from the detection circuit 8. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a proximity detection sensor and a proximity detection method for detecting the proximity of an object to be detected by a change in capacitance between a detection electrode and ground.

2. Description of the Related Art Conventionally, sensors that detect the proximity of an object to be detected by electrostatic capacitance are known. This type of sensor detects the proximity of an object by detecting a frequency and a duty ratio that change depending on the capacitance between a detection electrode that is a sensor unit and ground (Patent Document 1). However, such a proximity detection sensor has a problem that the detection value is easily influenced by surrounding environmental elements such as temperature, humidity, and external noise. For this reason, the sensor disclosed in Patent Document 1 is provided with a thermistor and a semiconductor temperature sensor exhibiting predetermined temperature characteristics in order to compensate for the temperature dependence of the analog circuit.
JP 2002-14174 (paragraphs 0082 to 0089, FIGS. 8 and 9)

  However, the proximity sensor as shown in Patent Document 1 is not only costly when a thermistor or a semiconductor temperature sensor is mounted, but also difficult to design to match the temperature characteristics with the analog circuit temperature characteristics. Have Further, in the above-described sensor that detects a change in the capacitance of the detection electrode, the change is output superimposed on the initial capacitance value added by the detection electrode or the analog circuit. Furthermore, since the detection output voltage value of the detection circuit is finite depending on the power supply voltage, assuming that the upper limit of the output value is up to the power supply voltage, the value corresponding to the voltage width obtained by subtracting the initial capacitance value from the power supply voltage. Can only take. In other words, since the dynamic range cannot be increased, there is a problem that high-precision detection cannot be performed.

  The present invention has been made in view of such problems, and an object thereof is to provide a proximity detection sensor and a proximity detection method capable of highly accurate detection with a circuit configuration that calculates and outputs a difference in pulse width. To do.

  According to the first aspect of the proximity detection sensor of the present invention, the detection electrode in which the capacitance between the detection object and the ground changes in accordance with the proximity of the object to be detected, and the capacitance between the detection electrode and the ground. A first detection circuit that outputs a first pulse signal having a pulse width, a reference capacitor, a second detection circuit that outputs a second pulse signal having a pulse width corresponding to the capacitance of the reference capacitor, And a calculation means for calculating and outputting a pulse width of a differential pulse obtained by subtracting the second pulse signal from the first pulse signal.

  According to the first aspect of the proximity detection sensor of the present invention, it is possible to perform highly accurate environmental characteristic compensation with a simple circuit configuration by providing the reference capacitor having the environmental characteristic equivalent to that of the detection electrode.

  The second aspect of the proximity detection sensor according to the present invention is based on a detection electrode in which the capacitance between the detection object and the ground changes as the detection object approaches, and the capacitance between the detection electrode and the ground. A first detection circuit for outputting a first pulse signal having a pulse width, a reference electrode, and a second pulse signal for outputting a second pulse signal having a pulse width corresponding to the capacitance between the reference electrode and ground. It is characterized by comprising a detection circuit and calculation means for calculating and outputting a pulse width of a differential pulse obtained by subtracting the second pulse signal from the first pulse signal.

  According to the second aspect of the proximity detection sensor according to the present invention, by arranging the detection electrode and the reference electrode in the vicinity, it is possible to eliminate external influences equally and perform highly accurate environmental characteristic compensation with a simple circuit configuration. It becomes possible.

  In the proximity detection sensor according to the second aspect, the reference electrode may be configured such that the capacitance between the reference electrode and the ground changes as the detected object approaches. With this configuration, the reference electrode can be used as the second detection electrode.

  In the proximity detection sensor according to the first and second aspects, an initial value of the second pulse signal output from the second detection circuit is an initial value of the first pulse signal output from the first detection circuit. You may comprise so that it may be a value substantially equal to a value. With this configuration, it is possible to subtract the initial capacitance of the first detection circuit and extract only the change. Even in an electric circuit that can only take a finite value with the upper limit of the power supply voltage, signal processing at a later stage can be facilitated by extracting only the change.

  The proximity detection sensor according to the first and second aspects may further include a trigger signal generation circuit that synchronizes rising edges of the first pulse signal and the second pulse signal. By synchronizing the pulse signal, the detection signal waveform and the reference signal waveform can be synchronized. Thereby, the subtraction operation at the pulse level can be easily obtained.

  The proximity detection sensor according to the first and second aspects may further include a delay circuit that delays the first pulse signal with respect to the second pulse signal. Furthermore, it may be configured to further include a low-pass filter that converts the differential pulse into a DC signal and a DC amplifier that amplifies the DC signal generated by the low-pass filter. By inserting a circuit that intentionally delays the pulse signal, it is possible to prevent the occurrence of glitches during logical subtraction. Further, by converting the difference value to a direct current, it is possible to extract only the change. Amplification and signal processing at a later stage can be performed, and a minute change can be detected.

  In the proximity detection sensor of the first and second aspects, the pulse width of the differential pulse may be compared with a threshold value, and an ON / OFF signal may be output based on the magnitude relationship. By making the difference value DC, it is possible to extract only the change. By performing amplification or the like at a later stage, ON / OFF output is possible even with a minute change in the detection signal.

  In the proximity detection sensor according to the first and second aspects, the detection electrode includes a plurality of electrodes, and further includes a selector circuit that selects a signal from the plurality of electrodes and inputs the signal to the first detection circuit. You can also

  In the first aspect of the proximity detection method according to the present invention, the first pulse width corresponding to the capacitance between the detection electrode and the ground, in which the capacitance between the detection object and the ground changes as the object to be detected approaches. A first pulse width measuring step for measuring the pulse width by inputting one pulse signal and a second pulse width measuring for measuring the pulse width by inputting a second pulse signal having a pulse width corresponding to the capacitance of the reference capacitor And a calculation step of calculating and outputting the pulse width of the differential pulse obtained by subtracting the pulse width of the second pulse signal from the pulse width of the first pulse signal.

  According to the second aspect of the proximity detection method of the present invention, the first pulse width corresponding to the capacitance between the detection electrode and the ground, in which the capacitance between the detection object and the ground changes as the object to be detected approaches. A first pulse width measuring step for inputting the first pulse signal and measuring the pulse width, and a second pulse signal having a pulse width corresponding to the capacitance between the reference electrode and the ground, and measuring the pulse width. A second pulse width measuring step; and a calculation step of calculating and outputting a pulse width of a differential pulse obtained by subtracting a pulse width of the second pulse signal from a pulse width of the first pulse signal. .

  According to the proximity detection sensor and the proximity detection method of the present invention, it is possible to perform highly accurate detection with a circuit configuration that calculates and outputs a difference in pulse width.

  Next, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing an electrical configuration of the proximity detection sensor according to the first embodiment of the present invention.

  The proximity detection sensor includes a pulse signal generation unit 1A that generates a pulse signal whose duty ratio changes according to the proximity of an object to be detected, and performs an output value corresponding to the duty ratio by performing signal processing of the generated pulse signal. A signal processing unit 3A that outputs and outputs ON / OFF is provided.

Pulse signal generator 1A includes a sense electrode 2, a first detection circuit 4 which outputs a detection pulse signal P ₁ with a pulse width corresponding to the electrostatic capacitance between the ground and the detection electrode 2, and a reference capacitor 6 a second detection circuit 8 for outputting a reference pulse signal P ₂ having a pulse width corresponding to the capacitance of the reference capacitor 6, the first detecting circuit 4 and the second detection circuit 8 outputs a trigger signal TG detection pulse A trigger signal generation circuit 10 that synchronizes rising edges of the signal P ₁ and the reference pulse signal P ₂ , a detection pulse signal P ₁ that is input from the first detection circuit 4, and a reference pulse signal P ₂ that is input from the second detection circuit 8. It is constituted by an arithmetic circuit 12 for calculating the differential pulse signals P ₃ and a.

The detection electrode 2 is installed in an area where the proximity of a detected object such as a human body can be detected. The capacitance Cx between the detection electrode 2 and the ground changes according to the proximity of the detected object. First detection circuit 4 is synchronized with the trigger signal TG inputted from the trigger signal generation circuit 10, a detection pulse signal P ₁ whose duty ratio changes depending on the electrostatic capacitance Cx between the ground and sensing electrodes 2 Configured to generate. The generated detection pulse signal P ₁ is output to the arithmetic circuit 12.

The capacitance Cref of the reference capacitor 6 does not change depending on the proximity of the detected object. The second detection circuit 8 is configured to generate a reference pulse signal P ₂ having a duty ratio corresponding to the capacitance Cref of the reference capacitor 6 in synchronization with the trigger signal TG input from the trigger signal generation circuit 10. Yes. Reference pulse signal P ₂ which generated is output to the arithmetic circuit 12.

The arithmetic circuit 12 is configured to subtract the reference pulse signal P ₂ from the input detection pulse signal P ₁ and output a differential pulse signal P ₃ (= P ₁ −P ₂ ). The differential pulse signal P ₃ is output to the signal processing unit 3A.

The signal processing unit 3A includes a CPU 13 that converts a pulse signal into a digital value and outputs the digital value to the outside, and performs ON / OFF output based on the digital value. CPU13 converts the differential pulse signal P ₃ which is inputted to a digital value corresponding to the duty ratio, and outputs a digital signal, ON / OFF output for switching the ON / OFF states of the proximity sensor based on this digital signal I do. The CPU 13 can also be configured as a logic circuit.

In this proximity sensor configured to, when the detected object approaches the sense electrode 2 and to ground electrostatic capacitance Cx through the detection object of the detection electrode 2 changes, the duty ratio of the sense pulse signal P ₁ Changes. Further, the duty ratio of the sense pulse signal P _1, the temperature, humidity, varies depending environmental change such as external noise. On the other hand, the duty ratio of the reference pulse signal P ₂ output from the second detection circuit 8 has only dependent on the surrounding environment, such as not changing, temperature and humidity by the proximity of the detected object. Arithmetic circuit 12, by subtracting the reference pulse signal P ₂ from the sense pulse signal P _1, removing the effects of temperature and ambient humidity or the like contained in the detected pulse signals P _1, varies only by the proximity of the detected object and it outputs a differential pulse signal _{P 3.}

  An example of the circuit configuration of the proximity detection sensor according to the first embodiment will be described. FIG. 2 is a diagram illustrating a circuit configuration example of the pulse signal generation unit 1A of the proximity detection sensor according to the first embodiment.

A first detection circuit 4 that generates a detection pulse signal P ₁ corresponding to the capacitance Cx between the detection electrode 2 and the ground, and a _first pulse that generates a reference pulse signal P ₂ corresponding to the capacitance of the reference capacitor 6. The two detection circuits 8 have almost the same configuration.

The first detection circuit 4 includes two comparators 14 and 16 and an RS flip-flop circuit (hereinafter referred to as “RS-FF”) in which outputs of the comparators 14 and 16 are input to a reset terminal R and a set terminal S, respectively. 18, a buffer 20 that outputs the output DIS ₁ of the RS-FF 18, and a transistor 22 that is ON / OFF controlled by the output DIS ₁ of the RS-FF 18.

The comparator 16 compares the trigger signal TG as shown in FIG. 3 output from the trigger signal generation circuit 10 with a predetermined threshold value Vth _B1 generated by the voltage dividing resistors R _A1 , R _B1 , R _C1 . The set pulse synchronized with the trigger signal TG is output. This set pulse sets the Q output of the RS-FF 18. The Q output, the transistor 22 in the OFF state as the discharge signal DIS _1. When the transistor 22 is in the off state, the speed between the detection electrode 2 and the ground is determined by a time constant based on the capacitance Cx to the ground of the detection electrode 2 and the resistor R _D1 connected between the input terminal and the power supply line. Charged. As a result, as shown in FIG. 3, the potential of the input signal Vin ₁ increases at a speed determined by the capacitance Cx. Here, when the input signal Vin ₁ exceeds the threshold value Vth _A1 determined by the voltage dividing resistors R _A1 , R _B1 , and R _C1 , the output of the comparator 14 is inverted and the output of the RS-FF 18 is inverted. As a result, the transistor 22 is turned on, and the charged charge of the detection electrode 2 is discharged through the transistor 22. Accordingly, the first detecting circuit 4 outputs a detection pulse signal P ₁ that oscillates at a duty ratio based on the electrostatic capacitance Cx between the sense electrode 2 and ground. The detection pulse signal P ₁ generated in this way is output to the arithmetic circuit 12.

Similarly, the second detection circuit 8 includes two comparators 24 and 26, an RS-FF 28 in which outputs of the comparators 24 and 26 are input to a reset terminal R and a set terminal S, respectively, and an output DIS of the RS-FF 28. ₂ is a timer circuit including a buffer 30 that outputs ₂ and a transistor 32 that is ON / OFF controlled by an output DIS ₂ of the RS-FF 28.

The comparator 26 compares the trigger signal TG output from the trigger signal generation circuit 10 with a predetermined threshold value Vth _B2 generated by the voltage dividing resistors R _A2 , R _B2 , and R _C2 , and synchronizes with the trigger signal TG. Output the set pulse. This set pulse sets the Q output of the RS-FF 18, the transistor 22 in the OFF state as the discharge signal DIS _2. Accordingly, the potential of the input signal Vin ₂ is increased at a rate determined by the resistor R _D2 connected between the capacitance Cref and the input terminal and the power supply line. Here, when the input signal Vin ₂ exceeds the threshold value Vth _A2, transistor 32 is turned ON, the charge charge reference capacitor 6 is discharged. Therefore, the detection circuit 8 outputs the reference pulse signal P ₂ which oscillates at a duty ratio based on the capacitance Cref of the reference capacitor 6. The reference pulse signal P ₂ which generated as is output to the arithmetic circuit 12.

Arithmetic circuit 12 subtracts the reference pulse signal P ₂ from the sense pulse signal P ₁ which is input, and outputs a differential pulse signal P ₃ as shown in FIG. Incidentally, the differential pulse signal P ₃ is, for example, a detection pulse signal P _1, obtained by a logical product of the inverted pulse of the reference pulse signal P _2.

Thus, if the surrounding environment characteristics of the two detection circuits 4, 8 are substantially equal, reducing the reference pulse signal P ₂ from the second detection circuit 8 having a dependency only on the surrounding environment from the sense pulse signal P ₁ Thus, the influence of temperature and humidity can be removed. Thereby, it is possible to perform highly accurate capacitance detection with a simple configuration.

  Here, the verification experiment performed in order to verify the effect of this invention using the proximity detection sensor which concerns on 1st Embodiment is demonstrated. In the proximity detection sensor according to the first embodiment, a 20 pF capacitor was connected as the detection electrode 2 and a 15 pF capacitor was connected as the reference capacitor 6. The ambient temperature of the proximity sensor configured as described above was changed from −40 ° C. to 90 ° C., and the change amount of the digital signal output from the CPU 13 was examined. FIG. 4 is a diagram showing the relationship between the ambient temperature and the amount of change in the output value when the ambient temperature is changed every 10 ° C. The amount of change was based on the digital signal value at 25 ° C. As a result, the variation in the value of the digital signal between −40 ° C. and 90 ° C. was within ± 1%. Moreover, since the digital signal value did not change according to the temperature, it was confirmed that the influence due to the temperature dependency was removed.

Incidentally, the initial value of the first output from the detection circuit 4 the detection pulse signal P ₁ having a pulse width in the non-detection state of the detection object, the reference pulse signal P ₂ of a pulse width is outputted from the second detection circuit 8 The capacitance Cref of the reference capacitor 6 can be adjusted so as to be equal to the initial value.

FIG. 5 is a graph showing the relationship between the capacitance of the detection electrode 2 and the pulse width of the detected pulse signal. The horizontal axis indicates the capacitance Cx between the detection electrode 2 and the ground. The vertical axis indicates the pulse width of the pulse signal P ₁ output from the first detection circuit 4.

When the detection object is not approaching the detection electrode 2 and the initial capacitance between the detection electrode 2 and the ground is Co, the pulse width of the detected pulse signal is P (Co). Here, if the detected object approaches, the value of the sense pulse signal P ₁ in accordance with variation ΔCx in the capacitance Cx increases the detection electrode 2. Or pulse width of the sense pulse signal _{P 1} becomes P (Co + ΔCx). When the pulse width P (Co) due to the initial capacitance of the detection electrode 2 is large and the change P (ΔCx) of the pulse width due to the capacitance change is small, the dynamic range of the amplifier circuit cannot be increased, and the amplifier circuit Even if amplification is performed, a change in pulse width cannot be detected with high accuracy.

At that time, to adjust the capacitance of the reference capacitor 6 as the reference pulse signal the pulse width of P ₂ and the initial capacitance by pulse width P of the detection electrode 2 (Co) are equal. That is, Cref is selected such that P (Cref) = P (Co). Here, since the initial capacitances also exist in the first detection circuit 4 and the second detection circuit 8, they are also estimated and the value of Cref is set.

In such a state, the differential pulse signal P ₃ obtained by taking the difference between the detection pulse signal P ₁ and the reference pulse signal P ₂ is P ₃ = P (Co + ΔCx) −P (Cref), that is, P ₃ = P (ΔCx) ( ∵P (Co) = P (Cref)).

Thus, the generated differential pulse signal P ₃ reflects only the capacitance change due to the approach of the detected object in the detection electrode 2. In this case, by increasing the dynamic range of the amplifier circuit by amplifying it, even changes in the sense pulse signal P ₁ is small, it can be reliably detected. High-precision detection can be performed with a simple circuit configuration without requiring an expensive element for measuring a minute change in signal intensity with high accuracy.

Further, in the detection electrode 2, there is a case where it is desired to detect a change in capacitance only in a predetermined section determined by the relationship with the detected object. For example, it is a case where it is desired to detect the change amount of Cx from Ca to Cb in FIG. In this case, Cref such that P (Cref) = P (Ca) may be selected as the value of the capacitance of the reference capacitor so as not to detect the capacitance change up to Ca. When the value of the capacitance of the detection electrode 2 is between from Co to Ca, the difference pulse signal P ₃ obtained by subtracting the reference pulse signal P ₂ from the sense pulse signal P ₁ is not detected. Further, the capacitance of the detection electrode 2 when larger than Ca, the difference pulse signal P ₃ obtained by subtracting the reference pulse signal P ₂ from the sense pulse signal P ₁ takes a value reflecting the change from Ca. The upper limit value Cb corresponds to, for example, the capacitance when the detected object comes into contact with the detection electrode 2.

  By comprising in this way, only the variation | change_quantity of the area with a detection electrode can be measured with high precision. In addition, noise resistance can be improved by using a capacitance change from Co to Ca as a noise margin and adding a capacitance change equivalent to external noise mixed in the detection electrode to the reference capacitor.

  Next, a proximity detection sensor according to a second embodiment of the present invention will be described. FIG. 6 is a block diagram showing an electrical configuration of the proximity detection sensor according to the second embodiment. The proximity detection sensor according to the second embodiment includes a pulse signal generation unit 1B and a signal processing unit 3B.

The pulse signal generation unit 1B is different from the pulse signal generation unit 1A in the first embodiment in that the arithmetic circuit 12 is not provided. Pulse signal generator 1B outputs the reference pulse signal P ₂ produced by the sense pulse signal P ₁ and the second detection circuit 8 generated by the first detection circuit 4 to the signal processing unit 3B.

The signal processing unit 3B is configured to include a CPU 15. Here, CPU 15 converts the detected pulse signal P ₁ and the reference pulse signal P ₂ input to digital values, according to the first embodiment in that performing the process of calculating a difference value between two digital values Different from CPU13. The CPU 15 is the same as the CPU 13 according to the first embodiment in that the difference value is output to the outside as a digital value and ON / OFF output is performed based on the digital value.

Processing in the signal processing unit 3B will be described with reference to FIG. FIG. 7 is a flowchart illustrating an example of processing for performing ON / OFF output in the CPU 15. The CPU 15, the detection pulse signal _{P 1} and the reference pulse signal _{P 2} produced by the pulse signal generator 1B is input. In step S1, CPU 15 measures the pulse width of the input detection pulse signal _{P 1,} and generates a sense digital signal _{D 1.} In step S2, measured similarly input pulse width of the reference pulse signal P _2, to generate a reference digital value D _2. In step S3, CPU 15 will reduce the reference digital value _{D 2} from the sense digital values _{D 1,} generates difference digital value _{D 3} which is the width of the difference pulse, and outputs it as a digital value. In step S4, it is compared with the threshold CPU15 is predetermined and the difference digital value D ₃ produced. In this embodiment mode, the ON output proceeds to step S5 if the difference digital value D ₃ is greater than the set threshold, if the below as to perform the OFF output proceeds to step S6 Yes. While the proximity sensor is operating, the CPU 15 repeats this process.

Thus, in the signal processing unit 3B, by the detection pulse signal P ₁ and the reference pulse signal P ₂ is treated with a CPU 15, there is no need to provide an arithmetic circuit to the pulse signal generating unit, the configuration of the pulse signal generator Can be made simpler. Further, the sign of the difference digital value can be identified, and the threshold value can be set flexibly including the upper and lower limits.

Note that an output signal from the CPU may be used instead of the trigger signal TG generated in the trigger signal generation circuit 10. In CPU 15, in addition to measuring the pulse width of the sense pulse signal P ₁ and the reference pulse signal P _2, measures the sense pulse signal P ₁ and the reference pulse signal P ₂ with the AD converter or the like so as to output as a digital value configuration It is also possible to do.

  Next, a proximity detection sensor according to a third embodiment of the present invention will be described. FIG. 8 is a block diagram illustrating an electrical configuration of the proximity detection sensor according to the third embodiment. The proximity detection sensor according to the third embodiment includes a pulse signal generation unit 1C and a signal processing unit 3C.

In this embodiment, the signal processing unit 3C is converted into a preceding stage of the CPU13 includes a low-pass filter (LPF) 40 and a DC amplifier 42, a differential pulse signal P ₃ generated once into an analog value. The trigger signal generation circuit 10 in FIG. 1 includes an oscillation circuit 35 and a frequency division circuit 34 that divides the output of the oscillation circuit 35 to generate a trigger signal TG. The oscillation circuit 35 is capable of internal oscillation, and may be one having a crystal or ceramic resonator connected to the outside. Arithmetic circuit 12 in FIG. 1, the logic inverter 38 for inverting the reference pulse signal P ₂ output from the second detection circuit 8, the output of the detection pulse signal P ₁ and the inverter 38 is outputted from the first detection circuit 4 The AND circuit 36 is configured to be stacked.

Differential pulse signal _{P 3} outputted from the AND circuit 36 is converted into a DC voltage by the LPF 40, is input to CPU13 are amplified by the DC amplifier 42. The CPU 13 performs digital value output and ON / OFF output based on this signal.

Thus, in order to direct the differential pulse signals P _3, it is possible to reduce the voltage initial value, it is higher than direct current pulses including the initial capacitance of the amplification degree of the subsequent DC amplifier 42 And high-precision detection with a large dynamic range becomes possible. Further, the signal processing unit 3C, it is possible difference by a pulse signal smoothing the P _3, to remove the glitch resulting from a time difference between the rise of the detection pulse signal P ₁ and the reference pulse signal P ₂ with the LPF 40.

  A proximity detection sensor according to a fourth embodiment of the present invention will be described. FIG. 9 is a block diagram showing an electrical configuration of the proximity detection sensor according to the fourth embodiment of the present invention.

  The proximity detection sensor according to the fourth embodiment includes a pulse signal generation unit 1D and a signal processing unit 3A.

The pulse signal generator 1D is provided with a delay circuit 44 for removing glitches. The delay circuit 44 slightly delays the detection pulse signal P ₁ output from the first detection circuit 4 with respect to the reference pulse signal P ₂ output from the second detection circuit 8.

Thereby, it is possible to remove a glitch resulting from a time difference between the rise of the detection pulse signal P ₁ and the reference pulse signal P _2.

As another means for removing the glitch, a flip-flop circuit is provided, and a sampling clock is input to the flip-flop circuit to form a synchronous sampling circuit to sample the pulse signals P ₁ and P ₂ . You may do it. Alternatively, the outputs from the first detection circuit 4 and the second detection circuit 8 can be synchronized and output.

  A proximity detection sensor according to a fifth embodiment of the present invention will be described. FIG. 10 is a block diagram showing an electrical configuration of the proximity detection sensor according to the fifth embodiment of the present invention.

The fifth embodiment includes a pulse signal generation unit 1C and a signal processing unit 3D. The pulse signal generation unit 1C has the same configuration as that of the third embodiment. The signal processing unit 3D includes a pulse width measuring circuit 46 to the pulse width of the difference pulse signal P ₃ which is inputted from the pulse signal generator 1C into a digital value and outputs the threshold setting circuit for generating a threshold 48 and a comparison circuit 50 for inputting a digital value and a threshold value, comparing the magnitude relation, and performing ON / OFF output based on the magnitude relation.

Differential pulse signal P ₃ generated by the pulse signal generator 1C is converted into a digital value corresponding to the pulse width by the pulse width measuring circuit 46. This digital value is output to the outside and also output to the comparison circuit 50. The comparison circuit 50 inputs this digital value to one side, and inputs the threshold value set by the threshold value setting circuit 48 to the other side, and performs ON / OFF output according to the magnitude relationship.

  A proximity detection sensor according to a sixth embodiment of the present invention will be described. FIG. 11 is a block diagram showing an electrical configuration of the proximity detection sensor according to the sixth embodiment.

  The sixth embodiment includes a pulse number generation unit 1C and a signal processing unit 3E. The pulse signal generation unit 1C has the same configuration as that of the third embodiment.

The signal processing unit. 3E, a differential pulse signal P ₃ generated by the pulse signal generator 1C and LPF40 to direct current, amplifies the signal output from the LPF40 in amplification degree set by the Gain setting section 54 DC amplifier 42, the threshold value setting circuit 52, and the magnitude relationship between the signal amplified by the DC amplifier 42 and the threshold value generated by the threshold value setting circuit 52, and ON / OFF output according to the magnitude relationship. And a hysteresis setting circuit 58 for setting the hysteresis characteristics of the hysteresis comparator 56.

Differential pulse signal P ₃ generated by the pulse signal generator 1C, after being DC by LPF 40, is amplified by the gain set by the Gain setting unit 54 in a DC amplifier 42. The amplified DC signal is output to the outside as an analog value, compared with a threshold value by a hysteresis comparator 56, and converted to an ON / OFF output according to the magnitude relationship. In this embodiment, since the hysteresis comparator 56 is used, the noise resistance characteristics are further improved.

Here, a verification experiment performed to verify the effect of the present invention using the proximity detection sensor according to the sixth embodiment will be described. In the proximity detection sensor according to the sixth embodiment, the pulse signal generation unit 1C and the signal processing unit 3E are configured by electronic circuits. A 5 pF capacitor was connected as the detection electrode 2, and a 3 pF capacitor was connected as the reference capacitor 6. The ambient temperature of the proximity sensor configured as described above was changed to −40 ° C., 25 ° C., and 85 ° C., and the amount of change in the analog signal output from the DC amplifier 42 was examined. In this temperature characteristic measurement, the difference between the case where the second detection circuit 8 is stopped and the signal of only the first detection circuit 4 is passed, and the case where the second detection circuit 8 is operated and the signal of the first detection circuit 4 is operated. This was done in two ways: when the value was calculated. In the experiment, capacitors having the same environmental characteristics such as temperature characteristics were used. Table 1 is a table showing the relationship between the ambient temperature and the amount of change in the output value when the ambient temperature is changed. The amount of change was based on an analog signal value at 25 ° C.

  As a result, the analog output value of the proximity detection sensor according to the present embodiment at −40 ° C. and 85 ° C. is approximately half the amount of change compared to the analog output value based on the signal of only the first detection circuit 4. Improvement was confirmed. Moreover, the variation of the analog signal value is within ± 1%, and it was confirmed that the influence on the proximity detection sensor due to the temperature was removed.

  A proximity detection sensor according to a seventh embodiment of the present invention will be described. FIG. 12 is a block diagram showing an electrical configuration of the proximity detection sensor according to the seventh embodiment.

  The seventh embodiment includes a pulse number generation unit 1E and a signal processing unit 3E. The signal processing unit 3E has the same configuration as that of the sixth embodiment.

  In the pulse signal generation unit 1E, the detection electrode 61 is connected to the first detection circuit 4 via the selector circuit 60. The selector circuit 60 is connected to a CPU 62 that outputs a ch select signal. The CPU 62 is connected to an LED 64 whose lighting is controlled by the CPU 62 based on the ON / OFF output.

  The pulse signal generator 1E further includes an operational amplifier 65. The operational amplifier 65 constitutes a buffer with a gain of 1, and prevents charging / discharging between the sensing electrode 61 and the surrounding guard electrode, shield line, and the like by keeping them at the same potential. The operational amplifier 65 is selectively operated by an ON / OFF signal.

In the present embodiment, the CPU 62 outputs a ch select signal to the selector circuit 60. The selector circuit 60 sequentially scans a plurality of electrodes included in the detection electrode 61 based on the ch select signal. Signals from a plurality of electrodes of the detection electrode 61 are respectively inputted to the first detection circuit 4 in turn, it is outputted as a detection pulse signal P _1. The detection pulse signal P ₁ and the reference pulse signal P ₂ differential pulse signal P ₃ generated based on the output from the second sense circuit 8 is DC conversion by LPF40 and DC amplifier 42 of the signal processor 3E, an analog value Is output as The analog value output is compared with a threshold value in the hysteresis comparator 56. For an electrode of a channel having the detection electrode 61 scanned by the selector circuit 60, ON / OFF output is performed when an analog value output based on the signal exceeds a threshold value. In the present embodiment, the ON output is performed when the analog output is higher than the threshold value.

  This ON / OFF output is input to the CPU 62. The CPU 62 lights the LED 64 with an output corresponding to the channel that is turned on. Thereby, display according to detection of each channel of the detection electrode can be performed.

  The ON / OFF output is input to the operational amplifier 65. The operational amplifier 65 outputs a guard to the guard electrode around the detection electrode 61 by an ON / OFF signal.

  In the seventh embodiment of the present invention, a verification experiment conducted for verifying the effect of the present invention will be described.

  FIG. 13 is a plan view showing the detection electrode 61 used in the verification experiment. FIG. 13A shows the front surface portion of the detection electrode 61, and FIG. 13B shows the back surface portion of the detection electrode 61. The detection electrode 61 has 16 ring-shaped electrode portions 66 arranged in 4 rows and 4 columns on the surface portion. The interval between the electrodes of the electrode portion 66 is 2.5 mm. The electrode portion 66 is connected to the back surface portion of the detection electrode through a through hole 68, and is wired to the connection terminal 72 by a wiring 70. The electrodes of the 16 channels of the detection electrode 61 are connected to the selector circuit 60, respectively. A guard electrode 74 is disposed around the electrode portion 66. The guard output of the operational amplifier is input to the guard electrode 74.

  In this verification experiment, the detection resistors used for the first detection circuit 4 and the second detection circuit 8 are both 75 kΩ. A 56 pF capacitor was used as the reference capacitor 6. Further, the gain of the DC amplifier 42 by the gain setting unit 54 is doubled, and the threshold value in the threshold setting circuit 52 is 2.5V.

In this verification experiment, the analog value output of one electrode in a state in which the detection electrode 61 is touched with a finger and another electrode in a state in which the detection electrode 61 is not touched with a finger was measured. Further, when the second detection circuit 8 is stopped and the signal of only the first detection circuit 4 is allowed to pass, the second detection circuit 8 is operated, and the difference value from the signal of the first detection circuit 4 is calculated. The above measurements were performed in two ways. Table 2 is a table showing the relationship between the output voltage of the LPF and the DC amplifier between the electrode in contact with the finger and the electrode not in contact.

  The analog value output of the DC amplifier 42 based on the signal of only the first detection circuit 4 is that both the electrode touched by the finger and the electrode not touched exceed the threshold value of 2.5 V, and both output ON. Is done. For this reason, it does not operate as a proximity detection sensor in this state.

Operates the second sense circuit 8, when the subtraction of the reference pulse signal P ₂ based on the output of the reference capacitor 6 was carried out, the analog value output of the DC amplifier 42 indicates different values. Here, when the ch16 electrode of the detection electrode 61 is touched with a finger, the output voltage exceeds the threshold value of 2.5 V, and an ON output is made. On the other hand, when the ch12 electrode of the detection electrode 61 is not touched with a finger, the output voltage does not exceed the threshold value, and an OFF output is made. In this state, when a finger touches a predetermined electrode, it is possible to light a predetermined LED with an ON output based on the output voltage. Therefore, it operates as a proximity detection sensor that detects the proximity of the detected object.

  In the proximity detection sensor operated only by the first detection circuit 4 of the verification experiment, if the threshold value is set to a value of 4.4 V or more and the Gain in the Gain setting unit is set to 1 time, the discrimination of the finger contact is Is possible. However, the upper limit of measurement of the circuit in the signal processing unit is 5 V of the power supply voltage, and using a value close to this makes it difficult to secure a design margin. Since it is difficult to increase the amplification degree in the signal processing unit, detection with a lower sensitivity becomes impossible.

  On the other hand, in the proximity detection sensor in which the second detection circuit 8 is operated, the analog value output is about two-thirds of the power supply voltage that is the measurement upper limit value. For this reason, even detection with low sensitivity can be detected by increasing the subtraction value or increasing the amplification degree.

  In this verification experiment, the guard electrode 74 is used. If detection is performed without the guard electrode 74, the electrode portions 66 may affect each other. For this reason, the electrode 70 and the wiring 70 from each electrode to the first detection circuit 8 are shielded by using the guard electrode 74. GND can also be used for this guard electrode, and it is not necessary to use it when the electrode part 66 is arranged apart.

  In the proximity detection sensor according to the present embodiment, it is possible to detect a minute change in capacitance by performing a subtraction operation even within a finite power supply voltage.

  In all the above embodiments, the reference electrode 76 can be used instead of the reference capacitor 6. In this case, for example, as shown in FIG. 14, a reference electrode 76 can be arranged on the back side of the detection electrode 2 via a shield 78. With such a configuration, the detection electrode 2 changes the detection value with the proximity of the detected object, but the reference electrode 76 can output the reference value without being affected by the proximity of the detected object. Further, a shield 78 may be further provided on the back side of the reference electrode 76 in order to remove the influence of noise on the reference electrode 76 generated from the back side of the reference electrode 76.

  A proximity detection sensor according to an eighth embodiment of the present invention will be described. FIG. 15 is a block diagram showing an electrical configuration of the proximity detection sensor according to the eighth embodiment of the present invention.

  The eighth embodiment includes a pulse signal generation unit 1F and a signal processing unit 3F. The pulse signal generator 1F is the third embodiment in that a detection electrode 76 that changes the capacitance by the approach of the detected object is used as a reference electrode instead of the reference capacitor 6 in the third embodiment. This is different from the pulse signal generation unit 1C according to the above. Also, the point that the capacitor 80 is connected to the first detection circuit 4 is different from the pulse signal generation unit 1C according to the third embodiment. The signal processing unit 3F has the same configuration as the analog value output portion in the signal processing unit 1E according to the sixth embodiment.

In the pulse signal generator 1F, the detection electrode 2 is connected to the first detection circuit 4, the first detection circuit 4 outputs a detection pulse signal P _1. Here, even when the detection object is not in proximity to the detection electrode 2 and the detection electrode 76, the initial capacitance is increased at the input terminal of the first detection circuit 4 so that the output shows the intermediate value of the full range. A capacitor 80 is connected.

In the pulse signal generation unit 1F, the detection electrode 76 is connected to the second detection circuit. Similar to the first detection circuit 4, the second detection circuit 8 converts the capacitance change between the detection electrode 76 and the ground into a reference pulse signal P ₂ and outputs it. Here, the initial capacitance of the detection electrode 76 is substantially equal to the initial capacitance of the first detection circuit 4, and the capacitance between the detection electrode 76 and the ground changes due to the approach of the detected object. The pulse width of the reference pulse signal P ₂ with the change in the electrostatic capacitance also changes.

  According to the proximity detection sensor according to the eighth embodiment, the capacitance of the detection electrode 2 changes due to the detection object approaching the detection electrode 2, and the voltage value output as an analog value is in the middle of the full range. Increase from value. Further, when the object to be detected approaches the detection electrode 76, the capacitance of the detection electrode 76 changes, and the output voltage value decreases from the intermediate value of the full range. In the first to seventh embodiments described above, the reference value output from the reference capacitor 6 is used for temperature correction to reduce the detected value. However, as shown in the present embodiment, the reference capacitor 6 is connected to the electrode 76. It is also possible to use as the second detection electrode by replacing with. In this case, the ambient environment change is canceled because it is in-phase noise.

  Here, a verification experiment performed in order to verify the effect of the proximity detection sensor according to the eighth embodiment will be described. A 50 mm square copper foil was used as the detection electrode 2 and the detection electrode 76 in the pulse signal generation unit, and the two detection electrodes were arranged with an interval of 20 mm. In addition, an acrylic plate having a thickness of 1 mm was disposed on each detection electrode. Then, a 20 pF capacitor was connected to the input terminal of the first detection circuit. The output voltages of the state where the finger is not in contact with the detection electrodes of the proximity detection sensor configured as described above and the state where the finger is in contact were measured.

Table 3 below shows a comparison between the output voltage in a state where nothing is in contact with both electrodes and the output voltage in a state where the finger is in contact with the detection electrode in this verification experiment.

  As a result, it was confirmed that the change in the output in contact with the detection electrode 2 and the detection electrode 76 can be sufficiently measured. In addition, the change in output when the electrodes are in contact with each other substantially coincides with the difference value of the change in output when the electrodes are in contact with each other. Therefore, when both detection electrodes are contacted at the same time, the proximity detection sensor can notify the non-detection state. Further, such a proximity detection sensor can be configured without using a capacitor that increases the initial capacitance.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to these, A various change, addition, etc. are possible in the range which does not deviate from the meaning of invention.

  For example, the trigger signal generation circuit 10 is configured using an oscillation circuit capable of internal oscillation, but may be configured to input a sample synchronization signal from the outside.

It is a block diagram which shows the electrical structure of the proximity detection sensor which concerns on 1st Embodiment. It is a circuit diagram which shows the partial circuit structure of the proximity detection sensor which concerns on 1st Embodiment. It is a timing chart in the circuit structural example of the proximity detection sensor which concerns on 1st Embodiment. It is a figure which shows the relationship between ambient temperature and a variation | change_quantity. It is a graph which shows the electrostatic capacitance of the detection electrode of the proximity detection sensor which concerns on 1st Embodiment, and the pulse width of the detected pulse signal. It is a block diagram which shows the electric constitution of the proximity detection sensor which concerns on 2nd Embodiment. 5 is a flowchart illustrating an example of processing for performing ON / OFF output in a CPU. It is a block diagram which shows the electric constitution of the proximity detection sensor which concerns on 3rd Embodiment. It is a block diagram which shows the electric constitution of the proximity detection sensor which concerns on 4th Embodiment. It is a block diagram which shows the electric constitution of the proximity detection sensor which concerns on 5th Embodiment. It is a block diagram which shows the electric constitution of the proximity detection sensor which concerns on 6th Embodiment. It is a block diagram which shows the electric constitution of the proximity detection sensor which concerns on 7th Embodiment. It is a top view which shows the structural example of a detection electrode. It is the schematic which shows the example of arrangement | positioning of a detection electrode and a reference electrode. It is a block diagram which shows the electric constitution of the proximity detection sensor which concerns on 8th Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 2,61 ... Detection electrode, 4 ... 1st detection circuit, 6 ... Reference capacitor, 8 ... 2nd detection circuit, 10 ... Trigger signal transmission circuit, 12 ... Arithmetic circuit 14, 16, 24, 26 ... Comparator 18, 28 ... RS flip-flop circuit, 20, 30 ... buffer, 22, 32 ... transistor.

Claims (11)

A sensing electrode whose capacitance with the ground changes with the proximity of the object to be detected;
A first detection circuit that outputs a first pulse signal having a pulse width corresponding to a capacitance between the detection electrode and the ground;
A reference capacitor;
A second detection circuit that outputs a second pulse signal having a pulse width corresponding to the capacitance of the reference capacitor;
A proximity detection sensor comprising: a calculation means for calculating and outputting a pulse width of a differential pulse obtained by subtracting the second pulse signal from the first pulse signal. A sensing electrode whose capacitance with the ground changes with the proximity of the object to be detected;
A first detection circuit that outputs a first pulse signal having a pulse width corresponding to a capacitance between the detection electrode and the ground;
A reference electrode;
A second detection circuit that outputs a second pulse signal having a pulse width corresponding to the capacitance between the reference electrode and the ground;
A proximity detection sensor comprising: a calculation means for calculating and outputting a pulse width of a differential pulse obtained by subtracting the second pulse signal from the first pulse signal.   The proximity detection sensor according to claim 2, wherein a capacitance between the reference electrode and the ground changes as the object to be detected approaches.   The initial value of the second pulse signal output from the second detection circuit is substantially equal to the initial value of the first pulse signal output from the first detection circuit. Item 5. The proximity detection sensor according to any one of Items 1 to 3.   The proximity detection sensor according to claim 1, further comprising a trigger signal generation circuit that synchronizes rising edges of the first pulse signal and the second pulse signal.   The proximity detection sensor according to claim 1, further comprising a delay circuit that delays the first pulse signal with respect to the second pulse signal.   The low-pass filter that converts the differential pulse into a direct-current signal and the direct-current amplifier that amplifies the direct-current signal generated by the low-pass filter are further provided. Proximity detection sensor.   The pulse width of the differential pulse is compared with a threshold value, and an ON / OFF signal is output based on the magnitude relationship thereof. Proximity detection sensor.   9. The detection electrode according to claim 1, further comprising a selector circuit configured to select a signal from the plurality of electrodes and input the signal to the first detection circuit. The proximity detection sensor according to the item. A first pulse signal having a pulse width corresponding to the capacitance between the detection electrode and the ground, in which the capacitance between the ground and the object to be detected changes, is measured. A pulse width measurement step;
A second pulse width measuring step of inputting a second pulse signal having a pulse width corresponding to the capacitance of the reference capacitor and measuring the pulse width;
A proximity detection method comprising: a calculation step of calculating and outputting a pulse width of a differential pulse obtained by subtracting a pulse width of the second pulse signal from a pulse width of the first pulse signal. A first pulse signal having a pulse width corresponding to the capacitance between the detection electrode and the ground, in which the capacitance between the ground and the object to be detected changes, is measured. A pulse width measurement step;
A second pulse width measurement step of inputting a second pulse signal having a pulse width corresponding to the capacitance between the reference electrode and the ground and measuring the pulse width;
A proximity detection method comprising: a calculation step of calculating and outputting a pulse width of a differential pulse obtained by subtracting a pulse width of the second pulse signal from a pulse width of the first pulse signal.

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