JPH03289715A - Capacity change detector and touch panel using same - Google Patents

Abstract

PURPOSE:To stabilize operations and to improve noise resistivity by absorbing the charge of a first input terminal in an operational amplifier to the side of loaded capacity when loading the capacity to a detecting electrode, and detecting the logical level of an output from the operational amplifier is changed. CONSTITUTION:Since the charge charged to the capacity set by a reference capacity set circuit 4 is injected to the first input terminal of an operational amplifier 7a by the operation of a first analog IC switch 5 when the capacity provided for a detection object is not loaded to a detection electrode 1, the output of the operational amplifier 7a is maintained at the first logical level. when the capacity of the detection object is loaded to the detection electrode 1, the output of the operational amplifier 7a is maintained at the first logical level. On the other hand, since the charge of the first input terminal in the operational amplifier 7a is absorbed to the added capacity when the capacity of the detection object is added to the detection electrode 1, the output of the operational amplifier 7a is changed to the second logical level. Thus, control, stability and noise resistivity can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a detection device that detects when a detection target comes close to or comes into contact with a detection electrode.

[Conventional technology]

FIG. 8, FIG. 9, and FIG. 1O are block diagrams showing a proximity switch and a touch sensor, respectively, which are conventional examples of this type of detection device.

The capacitance between the electrode 41 of the proximity switch shown in FIG. 8 and ground varies depending on the amount of liquid injected into the container 40. The oscillator 42 is, for example, a Colpitts type, and the capacitance loaded on the electrode 41 is incorporated into the oscillation conditions. Therefore, when the liquid level in the container 40 reaches a predetermined level (for example, the position where the electrode 41 is located), the oscillator 42
can be set to start or stop oscillation. The detector 43 detects the output of the oscillator 42 and converts it into direct current. The comparator 44 compares the reference voltage from the reference voltage circuit 45 and the output voltage of the detector 43, and when the output voltage of the detector 43 is higher, outputs a high level (hereinafter referred to as H level). When the level is low, a low level (hereinafter referred to as L level) is output to notify the arrival of the liquid level.

The touch sensor shown in FIG. 9 is the same as that shown in FIG. 8 with a protection circuit 46 added between the electrode 41 and the oscillator 42. This is to prevent damage to subsequent circuits.

The touch sensor shown in Figure 1O is powered by a commercial AC power source (5
Contact of the human body with the electrode is detected by detecting the alternating current voltage induced in the human body (0 Hz or 60 Hz).

When the human body is not touching the electrode 51, the bias circuit 5
3, P-type FET 54 is reverse biased and N-type FET 5 is reverse biased.
5 is biased in the forward direction, and the potential applied to the capacitor 58 is the ground potential. At this time, Schmitt circuit 6
The output of 0 is H level.

When a human body touches the electrode 1, the electrostatic discharge from the human body is bypassed to the power supply or ground by the protection circuit 52, while the induced voltage of the human body is transferred to the P-type FET 54 and the N-type FE.
Drive the gate of T55 within the power supply voltage range. If the value of the resistor 56 is selected to be two orders of magnitude smaller than the value of the resistor 55, charging of the capacitor 58 will be more dominant, and the potential will settle to a potential close to the power supply voltage. However, as it is,
Since there is some pulsating current due to the power supply frequency, the low-pass filter 59 reduces this influence. At this time, the final stage Schmitt circuit 60 outputs the L level.

Other conventional examples include a type that detects the resistance value of a human fingertip on a liquid crystal display, and a type that runs infrared rays horizontally and vertically close to the display surface to detect the position indicated by the finger by blocking light from the fingertip. There is a type.

[Problems to be Solved by the Invention] The conventional detection devices described above each have the following drawbacks.

1) In the case of the proximity switches and touch sensors shown in Figures 8 and 9, ground capacitance is incorporated into the oscillation conditions of the oscillation circuit, so in order to accurately detect changes in ground capacitance, the power supply voltage must be Stabilization of components O Element sensitivity of components O Adjustment and its stability O Noise resistance, etc. must be fully considered, and in particular, adjustments and stability, and noise resistance can cause problems even after being incorporated into an actual device. is the mainstream. Further, if the proximity switch is disposed of on a manufacturing line, it is necessary to reset the adjustment every time the detection target changes.

2) In the case of the touch sensor shown in FIG. 6, since the voltage induced in the human body from a commercial AC power source is used, a) it cannot operate in a place where the induced voltage is low (battery operation outdoors).

b) Even with AC power supply operation, operation becomes impossible depending on the polarity.

c) AC power has a slow response speed because it is 50/60 Hz.

Things like this occur.

3) In the case of a liquid crystal display, since it is necessary to detect the touch of a finger on the display surface or the shading of the finger, a) the life of the display is deteriorated due to the load of the finger applied perpendicularly to the display surface.

b) A space of at least 5 mm must be secured on the liquid crystal display surface for emitting and receiving infrared light, which is disadvantageous for miniaturization. Power consumption can no longer be ignored.

[Means for Solving the Problems] The capacitance change detection device of the present invention has a coupling capacitor whose one end is connected to a conductive detection electrode, an a contact, a b contact, and a common contact, and the b contact is connected to a power source. a first analog IC switch to which is connected, a second analog IC having an a contact, a b contact, and a common contact, the b contact is connected to ground, and the common contact is connected to the other end of the coupling capacitor. A switch; 1. A switch drive circuit that switches the connection to the common contact of the second analog IC switch in synchronization with the A contact side or the B contact side, and temporarily puts both the common contacts in a floating state during switching; 1. an operational amplifier connected to the a contact of the second analog IC switch, whose second input terminal is supplied with double voltage of the power supply, whose output terminal is connected to the first input terminal through an integrating capacitor, and which outputs a detection output; When compared with the contact capacitance and the stray capacitance, which are the capacitances seen from the common contact of the second analog IC switch when the detection target is in substantial contact with the detection electrode and when the detection target is not in substantial contact with the detection electrode, the contact capacitance is smaller than the contact capacitance; a reference capacitance setting circuit that loads a reference capacitance larger than the stray capacitance to the common contact of the first analog IC switch, preferably the substantial contact is proximity of a detection electrode to be detected, and more preferably, Provide an electrostatic protection circuit between the detection electrode and one end of the coupling capacitor to bypass high-voltage static electricity to the power supply or ground side, or connect one end to the output end of the operational amplifier and the other end to the a contact of the first analog IC switch. , the first . . . connected to the common contact of the second analog IC switch, respectively. It has a second resistance.

Further, the touch panel of the present invention includes a plurality of the capacitance change detection devices, two detection electrodes are used as counter electrodes, and the plurality of counter electrodes are arranged in a matrix on the display panel. Each detection electrode is driven in a time-divisional manner, and when it is detected that there is an increase in the capacitance of any of the counter electrodes, it is detected that the counter electrode has been touched.

[For production]

When the detection electrode is not loaded with the capacitance of the object to be detected, the charge charged to the capacitance set by the reference capacitance setting circuit is injected into the first input terminal of the operational amplifier by the operation of the first analog IC switch. Therefore, the output of the operational amplifier is maintained at the first logic level, and when the detection electrode is loaded with the capacitance to be detected, the charge at the first input terminal of the operational amplifier is absorbed by the loaded capacitor, so the output of the operational amplifier is Change to a second logic level.

[Example] Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the capacitance change detection device of the present invention, and FIG. 2 is a waveform diagram showing the output state of FIG. 1.

The detection electrode 1 is conductive, and when a detection object, for example a human body, comes into contact with it, the human body's capacitance C(l (minimum about 20 pF) is loaded. When high voltage static electricity is applied, this high voltage static electricity is input through the resistor 2a and bypassed to the power supply side or the ground side through the diode 2b or diode 2C.

The coupling capacitor 3 has a capacitance C6, and if the ground capacitance seen from the detection electrode is the capacitance C6, the combined capacitance C0 seen from the node N is selected as Cc)Co, so it is expressed by equation (1). .

The stray capacitance Cs (~several pF) is obtained.

Analog IC switches 5a and 5b have contacts a and 5b, respectively.
b and a common contact C, both contacts a are connected to the inverting input terminal of the operational amplifier 7a, and the contacts are connected to the power supply V.
It is connected to DD and ground, and the common terminal C is connected to the reference capacitance setting circuit 4 and node N, respectively. moreover,
The reference capacitance setting circuit 4 is adjusted in advance to load a predetermined reference capacitance CREF to the common terminal of the analog IC switch 5a in accordance with the capacitance of the detection target to be detected by the detection electrode (C3<CREF<C6 ). The integrating circuit 7 is
It consists of an operational amplifier 7a, a capacitor 7b and a resistor 7d connected between the output terminal and the inverting input terminal of the operational amplifier 7a. A resistor 7C connects the output end of the operational amplifier 7a and the node N for stable operation. The bias circuit 8 is connected to the power supply V
When half of the voltage detection electrodes 1 of DD are electrostatically coupled to the detection target (without I/), the above C0 is applied from the node N to the detection electrode 1. The output circuit 9 includes a resistor 9a and a transistor 9b, and amplifies and outputs the output of the operational amplifier 7a.

Next, the operation of the embodiment shown in FIG. 1 will be explained with reference to FIG. 2.

The non-inverting input terminal of the operational amplifier 7a is biased, and since the operational amplifier 7a operates so that a virtual grounding condition is established at both input terminals, the inverting input terminal also becomes -VDD.

When the detection electrode 1 is open to the detection target, the difference Qd between the charge charged in the reference capacitor CREF and the charge charged in the stray capacitance C8 seen from the common terminal C of the analog switch 5b, that is, the node N. Since the reference capacitance CREF is set sufficiently larger than the stray capacitance C8, the difference Q6 is positive, and the charge based on this difference Qd acts to raise the potential at the inverting input terminal, and the operational amplifier 7a The output becomes the ground level, and the charge difference Qd is drawn to the ground via the capacitor 7b (inverse integration interval ■ and negative saturation interval ■).Conversely, the conductive detection electrode 1 Electrical ground capacity C6
(conductive detection electrode 1 is connected to the detection target)
There is no need for the two to be in physical contact) Difference Q
, is expressed by equation (3).

Since Ca > CREF, the difference Q is negative,
Since it acts to lower the potential of the inverted input wave, the output of the operational amplifier 7a rises to the power supply voltage side, and the capacitor 7
A charge is injected into the inverting input terminal of the operational amplifier 7a via the input terminal b, and the operation is performed to neutralize the difference Qd (integration interval (2) and positive saturation interval (2)). Note that the resistors 7c and 7d function as DC feedback resistors in the integrating circuit, and stabilize the on/off state of the switch.

Next, a case in which this embodiment is applied to a medical device equipped with a laser generator will be described in more detail.

There are devices used for medical treatment that irradiate the human body with laser light in a concentrated manner, but if the laser light is accidentally irradiated on important parts of the human body, it is extremely dangerous because the irradiated area will be destroyed. Therefore, in order to make it possible to irradiate laser light only when the laser irradiation port of the laser generator comes into contact with the human body, the device of this embodiment is attached, and its detection electrode is placed at the tip of the laser generator, and the laser beam is attached to the human body. If the device is operated so that it can irradiate only when there is contact, the purpose can be effectively achieved. When we used the following constants as actual constants, we obtained very good results.

Resistor 2a...100Ω Coupling capacitor 3...1μF Reference capacitance CREF...22pF (non-adjustable) Capacitor 7b...4700pF Resistor 7C...3.3MΩ Resistor 7d... ...00 (open) Oscillation frequency of non-overlapping two-phase oscillator...60KHz Resistor 9a...2.2Ω Next, when this example is applied to a proximity switch, This was done using the following constants. Reference capacitance CRE of reference capacitance setting circuit 4
F can be adjusted using a circuit as shown in FIG.

Resistance 2a...IKΩ Coupling capacitor 3...1μF The reference capacitance setting circuit 4 is as shown in FIG.

Capacitor 7b...O,0ILLF Resistor 7c...3.3MΩ Resistor 7d...510Ω Oscillation frequency of non-overlapping two-phase oscillator 6...3.3MHz Resistor 9a... ....2, 2.Ω Although two application examples have been shown above, it is clear that these constants are not limited to the above ones. For example, the oscillation frequency of 60 KHz can be varied within a wide range.

FIG. 4 is a block diagram showing one embodiment of the touch panel of the present invention, and FIGS. 5 and 6 are a time chart and a flow chart showing the operation of the embodiment of FIG. 4, respectively.

In this embodiment, two sets of the main parts shown in FIG. 1 are applied to a touch panel (also referred to as a touch screen).

The operation unit IA forms a 4×4 grid-like wiring network using transparent wiring materials on the screen of a CRT or liquid crystal display. At each of the 16 intersections, the vertical and horizontal transparent wiring materials expose conductive parts electrically independently from each other on the panel surface within an area that can be easily touched with a fingertip.
Consider the behavior when a human fingertip touches any one intersection above.

First, if there is an electrostatic discharge from a human fingertip, the input protection circuit 2A connected to the selected vertical and horizontal directions,
Depending on the polarity of electrostatic discharge, either of 2B, 2H, and 2B is bypassed to the power supply or circuit GND to protect the subsequent circuit.

The CPU clock from the microcomputer 10 is normally several MHz, but it is divided by the frequency divider 11 into several tens of kHz as the source oscillation of the non-overlapping two-phase oscillator 6, and further generates the scan signal (T1 to T9) for the input section. As a driving clock for the timing generator 12, several K
The frequency is divided into Hz.

The non-overlapping two-phase oscillator 6 includes analog switches 5a and 5c that drive the reference capacitance circuit 4 and ground capacitance (
The analog switches 5b and 5d that drive the human fingertips are made conductive in the direction shown in FIG. 4 when φ+=H, and φi=
When H, conduction is made in the opposite direction to the direction shown in FIG. When either φ1 or φ2 is L, the analog switches 5a to 5d are in an intermediate state.

On the other hand, since the timing generator 12 operates at the timing shown in FIG. 2, the analog switches 13a to 13
j are driven at timings T1 to T9, and assuming that each is conductive when the signal is H, 16 intersections on the operation unit 1 will be scanned in 20 m5. For example, if a human fingertip touches the intersection of the line connected to the input protection circuit 2C and the line connected to the input protection circuit 2F (indicated by an asterisk in Figure 1),
In the interval indicated by * on the timing chart, operational amplifier 7
a and 7d start integration at the same time, and the integration capacitor 7
If b and 7e are selected to be constants such that the integration is completed in several hundred microseconds, for example, 100 pF, the output E of the NAND gate 9 becomes the L level 1 mS after the fall of T9. Analog switches 13i and 13j
is conductive when timing T9 is at H level, and 1.2
The integration circuit is reset every 5m5. Therefore NA
The output E of the ND gate 9 does not remain at L level continuously for more than 1.25 m5.

The falling edge of timing T is the microcomputer 1
Drives the 0 interrupt pin and starts the 1mS timer. When the 1mS timer counts up, the microcomputer 10 outputs 4-bit binary data A and B.
, C, and D are read from the timing generator 12.

If the output E of the NAND gate 9 is at L level at this time, it can be determined that the corresponding intersection is touched by a human fingertip.

In addition, if a human does not touch the operation unit 1, 20
While scanning 16 intersections with m5, no integration is performed and no touch is detected.

Next, the response when a plurality of intersections on the operating section 1A are touched in this embodiment will be described with reference to FIGS. 6 and 7.

When the timing signal T9 falls, a 1 mS timer starts. When the timer counts up, the signal A,
Read the logic levels of B, C, and D (step S1)
, A+2B+4G+8D as i (step S2).

Step S3) to determine whether the output E is at L level or not.
If it is L level, it is determined whether the flag is 1 or not (step S4); if it is not 1, i is set as DATA (step S5). The flag is set to 1 (step 56) 0. Next, it is determined whether i is 15 or not (step S5). S7), if 1=15, it is determined whether the flag is 1 or not (step S8); if 1, predetermined processing is performed (step S8), and the flag is set to 0.
(step S9), and the process ends. If the output E is not at the L level in step S3 and if the flag is 1 in step S4, the process moves to step S7. 1 in step S7
If not = 15, the process ends. If the flag is not 1 in step S8, the process moves to step S9.

In this embodiment, the reference capacitance circuit is a varicap whose junction capacitance can be controlled by a DC reverse bias voltage.
However, as in this embodiment, when it is difficult to determine the amount of stray capacitance due to wiring length, etc., the reference capacitance can be easily set.

[Effects of the Invention] As explained above, in the present invention, when a capacitance is loaded on the detection electrode, the charge at the first input terminal of the operational amplifier is absorbed by the loaded capacitor, and the logic level of the output of the operational amplifier is changed. By detecting the change 1-, the following effects can be obtained.

1) The elements that make up the device become unrelated to the oscillation conditions,
The operation is stable and resistant to noise.

2) Since all the constituent elements are suitable for IC implementation, it is possible to downsize to a single chip.

3) Furthermore, a thin touch panel with low R power consumption can be made possible.

[Brief explanation of drawings]

1 is a block diagram showing a first embodiment of the capacitance change detection device of the present invention, FIG. 2 is a waveform diagram showing the output state of FIG. 1, and FIG. 3 is an example of the reference capacitance setting circuit 4. A circuit diagram, FIG. 4 is a block diagram showing an embodiment of the touch panel of the present invention, FIG. 5 is a time chart showing the operation of the embodiment of FIG. 4, and FIGS. 6 and 7 are a block diagram showing the embodiment of the touch panel of the present invention. FIGS. 8, 9vA, and 10 are block diagrams showing conventional examples. 1.--Detection electrode, 2.--Electrostatic protection circuit, 3.
...Coupling capacitor, 4...Reference capacitance setting circuit, 1 5...Analog RC switch, 6...Non-overlapping two-phase oscillator, 7...Integrator circuit, 8...Bias circuit, 9.19 -...Output circuit, 0...Microcomputer, 11-°° frequency divider, 2
...timing generator.

Claims (1)

[Claims] 1. A first analog IC switch having a coupling capacitor with one end connected to a conductive detection electrode, an a contact, a b contact, and a common contact, the b contact being connected to a power source. and a second analog IC switch having an a contact, a b contact, and a common contact, the b contact being connected to ground, and the common contact being connected to the other end of the coupling capacitor, and the first and second analog IC switches. A switch drive circuit that synchronizes the connection with the common contact of the IC switch to the a contact side or the b contact side and temporarily puts the common contact in a floating state during the switching, analog IC switch a
An operational amplifier is connected to the contact point, the second input terminal is supplied with 1/2 voltage of the power supply, and the output terminal is connected to the first input terminal through an integrating capacitor to output a detection output, and the detection target is connected to the detection electrode. Compared with the contact capacitance and stray capacitance, which are the capacitances seen from the common contact of the second analog IC switch when there is substantial contact and when there is no substantial contact, the reference capacitance is smaller than the contact capacitance and larger than the stray capacitance. and a reference capacitance setting circuit that loads the common contact of the first analog IC switch. 2. The capacitance change detection device according to claim 1, wherein the substantial contact is proximity to the detection electrode of the detection target. 3. The capacitance change detection device according to claim 1, further comprising an electrostatic protection circuit provided between the detection electrode and one end of the coupling capacitor to bypass high-voltage static electricity to a power supply or ground side. 4. First and second resistors having one end connected to the output end of the operational amplifier and the other end connected to the a contact of the first analog IC switch and the common contact of the second analog IC switch, respectively. The capacitance change detection device according to claim 3. 5. A plurality of capacitance change detection devices according to any one of claims 1 to 4 are provided, and two detection electrodes are used as counter electrodes,
A plurality of counter electrodes are arranged in a matrix on a display panel, and each capacitance change detection device including each detection electrode arranged in a matrix is driven in a time-sharing manner, and it is determined that there is an increase in the capacitance of one of the counter electrodes. A touch panel that detects that the counter electrode has been touched when detecting.