JP2015219703A - Electrostatic detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrostatic detection device capable of enlarging a capacitance change to be detected.SOLUTION: The electrostatic detection device comprises: a detection unit (Cx)100 in which a capacitance value changes when an object approaches or comes into contact therewith; a converter 20 converting a charge amount of the detection unit (Cx)100 into a voltage change of a modulation capacitor 110 by charging and discharging of the detection unit (Cx)100 and charging and discharging of the modulation capacitor 110; a comparison unit 30 comparing a reference voltage Vwith a voltage value of the modulation capacitor 110, and outputting a detection signal V; and a processing unit 40 calculating an output signal Vcorresponding to the capacitance value of the detection unit 100 based on the detection signal of the comparison unit 30. The reference voltage Vis variable, and is switched to different voltages at a predetermined timing when the detection unit (Cx)100 is charged and discharged.

Description

  The present invention relates to an electrostatic detection device, and more particularly, to an electrostatic detection device that expands and detects a capacitance change.

  Conventionally, there has been proposed an electrostatic detection device that measures a change in capacitance by charging a modulation capacitor with electric charge stored in an electrostatic touch electrode and observing a change in voltage at that time. A comparator is connected to the modulation capacitor, and a pulse is output when the capacitor voltage exceeds a threshold value, and a change in capacitance is measured from the number of pulses (for example, Patent Document 1).

  Specifically, a plurality of detection electrodes arranged on a support substrate and a voltage waveform corresponding to the capacitance of a detection target such as a detection electrode connected to each of the plurality of detection electrodes A CV conversion means comprising a series connection of a resistor and a capacitor, and a general-purpose microcomputer in which an input / output port is connected to each of the detection electrodes, and the capacitance of each of the detection electrodes or The position of the approaching object is calculated from the value corresponding to the change.

  According to this electrostatic detection device, it is said that electrostatic capacitance can be detected with high resolution with a relatively simple configuration with a low member cost.

JP 2010-152876 A

  However, in such a configuration, there is a problem that as the sensitivity is increased, the offset increases and the detection range of the capacitance change becomes narrow.

  Accordingly, an object of the present invention is to provide an electrostatic detection device that can detect a change in capacitance in an enlarged manner.

[1] In order to achieve the above object, the amount of electric charge of the detection unit is determined by the detection unit whose capacitance value changes due to the proximity or contact of an object, charging and discharging of the detection unit, and discharging and charging of the modulation capacitor. A converter for changing the voltage of the modulation capacitor; a comparison unit for comparing a reference voltage with a voltage value of the modulation capacitor and outputting a detection signal; and an electrostatic of the detection unit based on the detection signal of the comparison unit And a processing unit that calculates an output signal corresponding to a capacitance value, wherein the reference voltage is set to a different voltage when the detection unit is charged and discharged. To do.

[2] The electrostatic detection device according to [1], wherein the reference voltage is set to be smaller during discharging than during charging of the detection unit.

[3] The detection unit may be charged and discharged, the modulation capacitor may be discharged and charged, the comparison unit may perform comparison processing, and the output signal may be calculated by the processing unit. The electrostatic detection device according to [1] or [2] may be used.

  According to the electrostatic detection device of the present invention, it is possible to provide an electrostatic detection device that can detect a change in electrostatic capacitance in an enlarged manner.

FIG. 1 is an overall block configuration diagram of the electrostatic detection device of the present invention, and shows a state where a detection unit (Cx) is charged and a modulation capacitor (C _MOD ) is discharged. FIG. 2 is an overall block diagram of the electrostatic detection device of the present invention, and shows a state where the detection unit (Cx) is discharged and the modulation capacitor (C _MOD ) is charged. 3A to 3E are (a) a waveform diagram of V _MOD , (b) a waveform diagram of PWM, (c) a waveform diagram of V _REF , (d) a waveform diagram of V _DFF , and (e), respectively. ) _VAND waveform diagram. FIG. 4 shows (a) V _MOD waveform diagram, (b) PWM waveform diagram, and (c) V _REF when reference voltage V _REF that is the threshold voltage of comparator 170 is constant (2.8 V). (D) Waveform diagram of V _DFF . FIG. 5 is a graph showing the sensitivity to the parasitic capacitance _CX , and shows ΔV _REF as a parameter. FIG. 6 is a graph showing an offset with respect to the parasitic capacitance C _X , and shows ΔV _REF as a parameter. FIG. 7 is a graph showing the relationship between the capacitance value _CF and the detection value due to finger contact.

(Embodiment of the present invention)
FIG. 1 is an overall block configuration diagram of the electrostatic detection device of the present invention, and shows a state where a detection unit is charged and a modulation capacitor is discharged. FIG. 2 is a diagram illustrating a state where the detection unit is discharged and the modulation capacitor is charged.

(Configuration of electrostatic detection device)
The electrostatic detection device 1 according to the embodiment of the present invention includes a detection unit (Cx) 100 whose capacitance value changes due to the proximity or contact of an object, charging and discharging of the detection unit (Cx) 100, and a modulation capacitor 110. The converter 20 changes the charge amount of the detection unit (Cx) 100 to the voltage change of the modulation capacitor 110 by discharging and charging the reference voltage V _REF and the voltage value of the modulation capacitor 110, and outputs the detection signal V _COM And a processing unit 40 that calculates an output signal _VOUT corresponding to the capacitance value of the detection unit 100 based on the detection signal of the comparison unit 30. The reference voltage V _REF is variable and is switched to a different voltage at a predetermined timing when the detection unit (Cx) 100 is charged and discharged.

(Detection unit)
The detection unit (Cx) 100 is a stray capacitance such as an electrode as a sensor whose capacitance value changes due to the proximity or contact of an object, for example. Further, it may be a capacitance such as a capacitor formed by two terminals. Below, it demonstrates as a floating capacitance of the electrode as a touch sensor.

(Conversion unit)
The conversion unit 20 has a function of changing the charge amount of the detection unit (Cx) 100 to a voltage change of the modulation capacitor 110 by charging and discharging the detection unit (Cx) 100 and discharging and charging the modulation capacitor 110. The converter 20, the switch portion (SW1) 120 for switching the charge or discharge of electric charge, the modulation capacitor _(C MOD) switch unit for switching the charge or discharge of 110 (SW2) 130, a discharge resistor _(R B) 140, the discharge resistor (R _B ) 140 includes a switch unit (SW3) 150 that switches between charging and discharging, a sequencer (PRS) 160 that drives the switch unit (SW1) 120 and the switch unit (SW2) 130 at a predetermined timing, and the like. .

(Comparison part)
The comparator 30 compares the modulation capacitor voltage V _MOD of the modulation capacitor (C _MOD ) 110 with a reference voltage V _REF that is a threshold voltage of the comparator, and outputs a Hi or Lo level signal (detection signal V _COM ). (Com) 170 or the like.

(Processing part)
The processing unit 40 calculates the output signal V _OUT corresponding to the capacitance value of the detection unit 100 based on the detection signal V _COM of the comparator 170. D flip-flop circuit 180, PWM circuit 190 that generates pulses of a predetermined cycle, AND circuit 200 that outputs Hi or Lo by the logical product of the outputs of PWM circuit 190 and D flip-flop circuit 180, counter unit 210, control It is composed of the part 220 and the like. The control unit 220 receives the output signal _VOUT from the counter unit 210, calculates the capacitance value of the detection unit (Cx) 100, calculates a value corresponding to the capacitance value, and calculates the capacitance value. A process for calculating the change and a process for making the reference voltage V _REF of the comparator 170 variable based on the pulse output from the PWM circuit 190 are performed.

(Connection configuration of electrostatic detection device)
One end of the detection unit (Cx) 100 is connected to a switch unit (SW1) 120 and a switch unit (SW2) 130, and the other end is connected to a constant voltage power source, which is a ground (GND) in this embodiment. The other end of the switch unit (SW1) 120 is connected to a constant voltage power supply V _DD . The other end of the switch unit (SW2) 130 is connected to one end of a modulation capacitor (C _MOD ) 110 and a discharge resistor (R _B ) 140 and is input to the comparator 170. The other end of the modulation capacitor (C _MOD ) 110 is connected to the ground (GND). The other end of the discharge resistor (R _B ) 140 is connected to the ground (GND) via the switch unit (SW 3) 150.

The pulse generator (OSC) 230 is connected to the sequencer (PRS) 160, and generates and outputs a pulse (clock φ) having a predetermined frequency f _S. The sequencer (PRS) 160 is connected to the switch unit (SW1) 120 and the switch unit (SW2) 130, and based on the pulse generated by the pulse generation unit (OSC) 230, the switch unit (SW1) 120 and switch The part (SW2) 130 is opened and closed.

As described above, one end of the switch unit (SW2) 130, the modulation capacitor (C _MOD ) 110, and the discharge resistor (R _B ) 140 is connected to the input end of the comparator 170, and the modulation capacitor voltage V _MOD is input. . The threshold input terminal of the comparator 170 is connected to the control unit (CPU) 220, and the value of the reference voltage _VREF is variable based on the signal timing of the PWM circuit 190. The output terminal of the comparator 170 is connected to a D flip-flop circuit ( _DFF circuit) 180.

Pulse generator (OSC) 230, via a divider _240, is connected to the CLK terminal of the _{D FF} circuit 180, it is also connected to the PWM circuit 190. The output terminal of the _DFF circuit 180 is connected to the input terminal of the AND circuit 200 and is connected to the switch unit (SW3) 150, and the switch unit (SW3) 150 is opened and closed based on the output timing of the _DFF circuit 180. Do.

The output side of the PWM circuit 190 is connected to one of the input terminals of the AND circuit 200. The output side of the PWM circuit 190 is also connected to a control unit (CPU) 220, and a signal from the PWM circuit 190 is used as a switching signal for the reference voltage _VREF .

  In the counter unit (Counter) 210, the output unit of the 1/2 frequency divider 240 is connected to the CLK terminal, and the output terminal of the AND circuit 200 is connected to the input terminal. The output unit is connected to a control unit (CPU) 220.

(Charging / discharging operation of detector (Cx))
The sequencer (PRS) 160 alternately opens and closes the switch unit (SW1) 120 and the switch unit (SW2) 130 every clock. Here, FIG. 1 is a diagram illustrating a state where the detection unit (Cx) 100 is charged and the modulation capacitor C _MOD 110 is discharged. The switch unit (SW1) 120 and the switch unit (SW2) 130 are alternately opened and closed at a timing at which they are not closed simultaneously.

In FIG. 1, the switch unit (SW1) 120 is closed, the switch unit (SW2) 130 is opened, and the detection unit (Cx) 100 is charged from the constant voltage power supply V _DD . Further, the switch unit (SW3) 150 is closed, and the modulation capacitor C _MOD 110 is discharged via the discharge resistor (R _B ) 140.

At the next clock pulse, as shown in FIG. 2, the switch unit (SW1) 120 is opened, the switch unit (SW2) 130 is closed, and the detection unit (Cx) 100 is discharged to the modulation capacitor C _MOD 110. The At this time, the switch unit (SW3) 150 is in an open state and is not discharged to the discharge resistor (R _B ) 140.

As described above, since charging and discharging are performed every clock pulse, the modulation capacitor voltage V _MOD is continuously charged and discharged by a small voltage increase as shown in the waveform diagram of V _MOD in FIG. However, the algorithm operation of the electrostatic detection device according to the present embodiment is not affected.

3A to 3E are (a) a waveform diagram of V _MOD , (b) a waveform diagram of PWM, (c) a waveform diagram of V _REF , (d) a waveform diagram of V _DFF , and (e), respectively. ) _VAND waveform diagram.

(Operation when electrostatic detection device is not touched)
Based on the pulse (clock φ) of the pulse generation unit (OSC) 230, the PWM circuit 190 generates a PWM signal having a predetermined cycle and duty ratio (FIG. 3B).

The controller 220 sets the reference voltage V _REF that is different between the period when the PWM signal is Hi (on) and the period when the PWM signal is Lo (off), and uses the reference voltage V _REF as the threshold voltage of the comparator 170 (FIG. 3C). ). The reference voltage V _REF during the period when the PWM signal is Lo is set smaller by ΔV _REF than during the period when the PWM signal is Lo. For example, PWM signal and 2.7V reference voltage _{V REF} period Lo, the 2.8V reference voltage _{V REF} period Hi.

Period of PWM signal is Hi, the modulation capacitor voltage _{V MOD} is a small voltage increase around the reference voltage _{V REF,} is maintained at a substantially constant value while repeating the decrease (the reference voltage _{V REF)} (FIG. 3 (a)) .

When the PWM signal is switched from Hi to Lo, the control unit 220 decreases the reference voltage V _REF that is the threshold voltage of the comparator 170 by ΔV _REF . As a result, the modulation capacitor voltage V _MOD becomes equal to or lower than the threshold value, and the voltage drops (FIG. 3A).

When the PWM signal is switched from Lo to Hi, the modulation capacitor voltage V _MOD increases as the threshold value increases. However, the D flip-flop circuit 180 is used until a certain time T1 when the modulation capacitor voltage V _MOD reaches V _REF elapses. No pulse is output (FIG. 3 (d)).

A pulse is output during a period when the PWM signal is Hi and the output V _DFF of the D flip-flop circuit 180 is Hi. This pulse output is accumulated in a counter unit (Counter) 210 that performs pulse counting of the output V _AND of the AND circuit 200 in synchronization with the clock output from the frequency divider 240, and corresponds to the capacitance value of the detection unit 100. The output signal is _VOUT (FIG. 3 (e)).

Therefore, by reducing the reference voltage V _REF that is the threshold voltage of the comparator 170 by ΔV _REF at the time of discharging, the output pulse V _AND corresponding to the capacitance value of the detection unit 100 in which the PWM signal is counted in the Hi period is reduced. Become. As a result, the offset value decreases. This offset value is a capacitance detection value at the time of non-touch.

(Operation when touching the electrostatic detection device)
When the finger to the detector (Cx) 100 touches only the capacitance value capacitance value C _F by finger contact is increased. Thus, when touched, the capacitance value becomes Cx + _{C F.}

As can be seen from the waveform at the time of touch shown in FIG. 3A, the time required for the modulation capacitor voltage V _MOD to return to the original V _REF (voltage recovery by charging) is the capacitance value C due to finger contact. Depends on _F increase. For increasing the number of pulses for an increment of the electrostatic capacitance value C _F by the finger contact is large, the sensitivity is increased as a result of enlarged volume change due to human body contact is obtained.

Here, the detection sensitivity d of the electrostatic detection device is:
d = R _B · f _S (V _DD / V _REF −1) × (Cx + C _F )
It can be expressed as.
_CF is a capacitance value due to contact of an object (finger).

(Comparative example)
FIG. 4 shows (a) V _MOD waveform diagram, (b) PWM waveform diagram, and (c) V _REF when reference voltage V _REF that is the threshold voltage of comparator 170 is constant (2.8 V). (D) Waveform diagram of V _DFF .

As shown in FIG. 4C, when the reference voltage V _REF is constant (2.8 V) regardless of whether or not a finger touches the detection unit (Cx) 100, as shown in FIG. The modulation capacitor voltage V _MOD is maintained at a substantially constant value (reference voltage V _REF ) while repeating small voltage increases and decreases around the reference voltage V _REF (threshold voltage).

On the other hand, in the embodiment of the present invention, the reference voltage V _REF is switched in accordance with the charging and discharging of the modulation capacitor C _MOD . In general, the capacitance value C _F with a finger contacting electrodes, the parasitic capacitance of the wiring portion smaller than the (several tens pF), is difficult to measure the capacitance change. Therefore, in the embodiment of the present invention, the ratio of the change in the output pulse to the capacitance variation is limited by limiting the period in which the reference voltage of the modulation capacitor (C _MOD ) is V _REF only when the modulation capacitor (C _MOD ) is charged. Has increased.

FIG. 5 is a graph showing the sensitivity to the parasitic capacitance Cx, and shows ΔV _REF as a parameter. The simulation is performed by making the reference voltage V _REF of the comparator 170 shown in the configuration of FIG. 1 variable and using the decrease ΔV _REF of the reference voltage as a parameter. As a result, when the reference voltage V _REF is set to be small in the discharge period such as ΔV _REF = 0.5V and 1.0V, the sensitivity is about 1.5 times that of ΔV _REF = 0 regardless of the parasitic capacitance Cx. Became.

FIG. 6 is a graph showing an offset with respect to the parasitic capacitance Cx, and shows ΔV _REF as a parameter. The simulation is performed by making the reference voltage V _REF of the comparator 170 shown in the configuration of FIG. 1 variable and using the decrease ΔV _REF of the reference voltage as a parameter. As a result, when the reference voltage V _REF is set to be small in the discharge period such as ΔV _REF = 0.5V and 1.0V, the offset of the detected value can be reduced to a maximum of 1/5. In the present embodiment, since the number of resolution bits of the detection value is 10, the resolution is 512.

FIG. 7 is a graph showing the relationship between the capacitance value _CF and the detection value due to finger contact. From the above equation of sensitivity d, the larger R _B · f _S is, the higher the sensitivity is, but the offset is increased, so the detection range of _CF is narrowed (graph L1). In the present embodiment, as in L2, the offset can be reduced even with high sensitivity, so that the detection range r of _CF can be increased.

(Effect of embodiment)
In the embodiment of the present invention, the reference voltage V _REF is switched in accordance with the charging and discharging of the modulation capacitor (C _MOD ). The capacitance change due to the touch operation on the detection unit (Cx) is about 0.2 pF, which is smaller than the parasitic capacitance (several tens of pF) of the electrodes and wiring portions, and it is difficult to measure the capacitance change. Therefore, by limiting the period during which the reference voltage of the modulation capacitor (C _MOD ) is V _REF only when the modulation capacitor (C _MOD ) is charged, the ratio of the output pulse change to the capacitance variation can be increased. As a result, it is possible to provide an electrostatic detection device capable of improving detection accuracy and expanding and detecting a change in capacitance.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to this embodiment, and various modifications and applications can be made without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Electrostatic detection apparatus 20 ... Conversion part 30 ... Comparison part 40 ... Processing part 100 ... Detection part (Cx)
110: Modulation capacitor (C _MOD )
120 ... switch part (SW1)
130 ... Switch part (SW2)
140 ... discharge resistor _(R B)
150 ... Switch part (SW3)
160 ... Sequencer (PRS)
170: Comparator (Com)
180 ... _DFF circuit 190 ... PWM circuit 200 ... AND circuit 210 ... Counter
220 ... Control unit (CPU)
230 ... Pulse generator (OSC)
240: Divider _VREF : Reference voltage
V _MOD ... modulation capacitor voltage V _COM ... detection signal V _AND ... output pulse V _OUT ... output signal

Claims (3)

A detection unit whose capacitance value changes due to the proximity or contact of an object;
A conversion unit that changes the amount of charge of the detection unit into a voltage change of the modulation capacitor by charging and discharging the detection unit and discharging and charging the modulation capacitor;
A comparison unit that compares a reference voltage with the voltage value of the modulation capacitor and outputs a detection signal;
A processing unit that calculates an output signal corresponding to the capacitance value of the detection unit based on the detection signal of the comparison unit;
The electrostatic detection device, wherein the reference voltage is set to a different voltage when charging and discharging the detection unit.   The electrostatic detection device according to claim 1, wherein the reference voltage is set smaller during discharging than when charging the detection unit.   The charging and discharging of the detection unit, the discharging and charging of the modulation capacitor, the comparison processing in the comparison unit, and the output signal calculation in the processing unit are performed in synchronization. The electrostatic detection device according to 1.

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