JPS6229810B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Technical Field of the Invention The present invention relates to a coordinate detection device, and particularly to a coordinate detection device that specifies a specific intersection among a large number of electrode intersections in which electrodes are arranged in a matrix, and determines whether or not a specific intersection is specified. The present invention relates to a coordinate detection device that causes a change in capacitance in an electrode, detects the capacitance change, and detects the position of a designated point.

(b) Background of the technology A device that detects a specified position using changes in capacitance requires only an electrode to be used as the contact point for the human body or pen, etc., and does not require a mechanical device such as a well-known key switch. Since no contact points are required, it is easy to make the detection panel transparent. Therefore, in recent years, it has attracted attention as an information input means in combination with a display device or the like. That is, a transparent position detection panel is installed in front of the display surface of the display device, and desired information is input by pointing a contact portion on the panel corresponding to the information display position.

(c) Prior Art and Problems Various coordinate detection devices having such detection panels have been proposed, and Figure 1 is a schematic diagram of the main parts of one example of a coordinate detection device that utilizes the resonance phenomenon of a resonant circuit. be. The detection panel PN is, for example, a thin glass plate on which touch electrodes X ₁ to X ₄ and Y ₁ to Y ₄ are provided. Then, each intersection of these touch electrodes is used as a contact portion. It is also shown surrounded by a dotted line.
TCD is a touch detection section, and the touch detection section TCD detects a change in capacitance caused by a touch operation on each of the touch electrodes. The touch detection unit TCD has the following configuration. That is,
A resonant circuit is formed by connecting a capacitor C and a coil _L2 in parallel, and a resistive element R is connected to the resonant circuit, for example.
is connected. One input side of the comparator CM is connected to the connection point between the resistance element R and the resonant circuit, and the output side of the comparator CM is further connected to a control circuit (not shown). In addition, an oscillator is connected to the resistive element R of the touch detection section TCD having such a configuration.
OSC is connected. This oscillator OSC supplies a search signal of a frequency resonant to the resonant circuit to the resonant circuit via the resistive element R. Also, MPX is a touch electrode switching switch composed of an analog multiplexer, for example, and the switching switch MPX
Accordingly, the touch electrodes X ₁ to X ₄ and Y ₁ to Y ₄ are sequentially selected one by one and connected to the resonant circuit of the touch detection unit TCD via the coil L ₁ . Now, in such a configuration, if it is assumed that the operator gives an instruction by touching the contact part at the intersection of touch electrodes X ₁ and Y ₁ , then the touch electrode
The values of X ₁ and Y ₁ are different from the capacitance before the tentacle. The output of the touch detection unit TCD becomes "0" when there is a change in capacitance in the touch electrodes that are sequentially and selectively connected to the detection unit. In this example, the output of the touch detection section becomes "0" at the timing when the touch electrodes X ₁ and Y ₁ are switched and connected to the touch detection section TCD, and at the timing when the other touch electrodes are switched and connected to the touch detection section TCD. In this case, the output of the touch detection section becomes "1". As a result, the indicated position of the contact portion is detected.

By the way, in the detection panel PN, the touch electrodes X ₁ to X ₄ on the X side and the touch electrodes Y ₁ to _{Y 4} on the Y side are arranged adjacent to each other and intersecting with each other. Adjacent capacitances exist between the electrodes, and opposing capacitances exist at each intersection between the X-side electrode and the Y-side electrode. The existence of these unnecessary adjacent capacitances and opposing capacitances poses a problem in that a contact portion corresponding to a touch electrode that is not originally designated is detected as if it were designated. Therefore, in order to prevent false detection due to the presence of such adjacent capacitances and opposing capacitances, each touch electrode X ₁ to X ₄ and Y ₁ to _{Y 4}
A method has been proposed in which switches are connected between the search touch electrode and the ground, and the switches selectively clamp all the touch electrodes except one sequentially selected search touch electrode to the ground level. In this method of selectively clamping all touch electrodes other than the selected search touch electrode to the ground level, the distance between each successively selected search touch electrode and the other touch electrodes clamped to the ground level is There are specific electrode capacitances, and these electrode capacitances are connected in parallel to the resonant circuit of the touch detection unit TCD. The specific electrode capacitance of each touch electrode is different, for example, when the number of touch electrodes on the X side and the number of touch electrodes on the Y side are different, or when the length of the touch electrodes on the X side and the Y side are different. etc., the variation becomes even greater. Therefore, when the touch detection electrodes X ₁ to X ₄ and Y ₁ to Y ₄ are sequentially selected and connected to the resonance circuit of the touch detection unit TCD, the resonance frequency of the resonance circuit differs depending on the touch electrodes. When the frequency of the search signal supplied from the oscillator OSC to the resonant circuit is constant,
Depending on the touch electrode, the detection sensitivity may be significantly reduced.
There is a problem that stable position detection becomes difficult.
Therefore, it is conceivable to correct the electrode capacitances specific to each touch electrode X ₁ to X ₄ and Y ₁ to _{Y 4} to be the same. For this purpose, a duplex switch circuit SW and a read-only memory (hereinafter referred to as RM) are provided. R
The same signal as the address signal supplied to the changeover switch MPX is supplied to M, and a specified switch of the correction switch circuit SW is opened or closed in response to the input address signal. That is, the capacitance specific to each electrode is measured, and the correction capacitors C ₁ , C ₂ , C ₄ , C ₈ , and C ₁₆ are selectively connected so that each electrode capacitance has the same value. Capacity C ₁₁ is a changeover switch
This is the ground capacitance of MPX, and the capacitance _C12 is the ground capacitance of the correction switch circuit SW. Also, capacitor
C ₁₃ is for temperature compensation, and the correction capacitors C ₁ , C ₂ , C ₄ , C ₈ , capacitor C forming the C ₁₆ parallel resonant circuit, etc. have a positive temperature coefficient against temperature changes. In contrast, capacitor C ₁₃ has a negative temperature coefficient, which reduces the overall capacitance change with respect to temperature changes.

In such a coordinate detection device, if there is no instruction at any contact point, the resonant circuit is an oscillator.
Curve Q ₁ in Figure 2 for frequency c from OSC
It resonates as shown by (resonant state), and as a result, the touch detection unit TCD outputs V ₂ [V].
If one of the contact parts is pointed by a part of the human body, such as a finger, the resonance point of the resonant circuit moves as shown by curve Q ₂ in Figure 2 (non-resonant state), and as a result, the output The voltage Vout becomes V1 [V].
In this way, the presence or absence of a contact instruction is detected by changes in the output voltage, so the voltage during non-contact
If the ratio of voltage V ₁ at the time of contact to V ₂ is large, detection sensitivity will be improved, and as a result, false detection can be prevented.

However, the capacity added at the time of contact is 20
[PF] is small, while the capacity in non-contact mode is 15 to 20 times that value. Especially the correction capacitor,
When a temperature compensation capacitor is added, the capacitance during non-contact becomes significantly larger than the human body capacitance. Therefore, even if a small human body capacitance is added to a large non-contact capacitance, the amount of movement of the resonance point will be small, and the ratio of voltages V ₂ and V ₂ , that is, the detection sensitivity, will inevitably decrease. Ta.

In addition, the increase in capacitance during non-contact is due to the oscillator.
The frequency from the OSC must also be set to a low frequency. This is because the angular velocity ω=1/√,
This is because frequency is inversely proportional to capacitance. oscillator
As a result of having to set the frequency from the OSC low, the disadvantages described below arise. In other words, when we consider that the changeover switch MPX is scanning one electrode, the resonant circuit, comparator CM,
The number of cycles that must be applied to the resonant circuit while scanning one electrode is determined by the responsiveness of various circuits connected to subsequent stages.
Therefore, since the frequency of the oscillator is low, the time for scanning one electrode increases accordingly, resulting in a decrease in the detection speed, that is, a decrease in the permissible manual speed.

(d) Purpose of the Invention In view of the above drawbacks, the present invention aims to improve the detection sensitivity and detection speed by increasing the ratio of the human body capacity to the non-contact capacity. The purpose of this invention is to provide a compact coordinate detection device.

(e) Structure of the Invention For this purpose, the present invention provides a detection panel having a plurality of electrodes, a touch detection section that detects changes in capacitance in the electrodes based on instructions to the electrodes, and a touch detection section that selectively connects each electrode to the touch detection section in sequence. A coordinate detecting device including a connecting switch means is characterized in that the output signal of the switch means is non-inverting amplified, and a capacitive element is connected between the output terminal thereof and the input terminal of the touch detecting section.

(f) Embodiments of the invention Examples of the coordinate detection device according to the present invention will be described below with reference to the drawings.

In Fig. 3, MPX is a changeover switch, SW is a correction switch circuit, CCL is a capacitance cancel circuit, TCD is a touch detection section, and CM is a comparator. Components that are the same as those in Fig. 1 are given the same reference numerals. There is. The capacitance cancel circuit CCL consists of a non-inverting operational amplifier AMP, a capacitor _C0 , and resistors _R1 and _R2 . The output of the changeover switch MPX, that is, the input of the touch detection unit TCD, is connected to the positive terminal (+) of the amplifier AMP, and the input of the touch detection unit TCD is connected to the output terminal of the amplifier AMP via a capacitor _C0 . . On the other hand, the amplifier
The output terminal of the AMP is grounded via resistors R ₁ and R ₂ , and the intermediate point between the resistors R ₁ and R ₂ is connected to the negative terminal (−) of the amplifier AMP. Therefore, if the values of resistors R ₁ and R ₂ are now the same, the amplification factor of the operational amplifier AMP will be doubled.

FIG. 4 shows the detailed circuit in FIG. 3. Here, focusing on the impedance Z ₀ seen from the input terminal of the touch detection unit TCD, Z ₀ = V ₁ / (I ₁ − I ₂ ), while the impedance Z ₁ before adding the capacitance cancel circuit CCL is Z ₁ = V ₁ /I ₁ . Therefore, the capacitance cancel circuit CCL
By adding , the impedance seen from the input terminal of the touch detection unit TCD becomes Z ₀ >Z ₁ and appears to have increased. As a result, Z=1/
Since it is expressed as ωC, an increase in impedance results in a decrease in capacitance.

On the other hand, if the value of the capacitor _C0 constituting the capacitance cancel circuit CCL is _C0 , by adding this cancel circuit CCL, the touch detection section
The total capacitance CT seen from the input end of the TCD is CT = (Ct - C ₀ ). However, Ct is the total capacitance of the ground capacitance C ₁₁ of the changeover switch MPX, the correction switch circuit C ₁₂ , and the temperature compensation capacitor C ₁₃ . That is, I ₁ =V ₁ ωCt, I ₂ =(2V ₁ −V ₁ )ωC ₀ , so I ₁ −I ₂ becomes I ₁ −I ₂ =V ₁ ω(Ct−C ₀ ). As a result, the impedance Z ₀ becomes Z ₀ = V ₁ / (I ₁ − I ₂ ) = V ₁・ω・(Ct − C ₀ ), and if the total capacitance is CT, then Z ₀ = 1/ωCT=1/ ω・(Ct−C ₀ ) That is, by adding the capacitance cancel circuit CCL, the total capacitance CT seen from the input terminal of the touch detection unit TCD becomes (Ct−C ₀ ).

Note that the operational amplifier satisfies CT=(Ct−C ₀ )
This is when the amplification factor of AMP is set to double, and even if the capacitance of the capacitor C ₀ is the same, the apparent total capacitance CT can be changed by changing the amplification factor. However, if the value and amplification factor of the capacitor C ₀ are set so that CT has a negative value, it becomes an equivalent negative resistance and oscillation occurs. Therefore, for example, if the amplification factor is set to 2, the capacitor
The value of C ₀ is subject to the condition that C ₀ < Ct, and preferably
It is best to set a value close to the Ct value.

In addition, in the above embodiment, the correction switch circuit SW
Alternatively, although an example in which a temperature compensation capacitor is provided has been described, the present invention is not necessarily limited to a coordinate detection device to which these circuits and elements are added.

(g) Effects of the Invention As explained in detail above, according to the present invention, the total capacitance seen from the input terminal side of the touch detection section can be reduced in appearance, so the output of the touch detection section during non-contact and It is possible to improve the ratio to the output at the time of contact, thereby increasing the detection sensitivity. Furthermore, since the apparent capacitance is reduced, the resonant frequency of the resonant circuit can be set high, so the electrode scanning time can be shortened and the allowable input speed can also be set high.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional coordinate detection device, Fig. 2 is a resonance characteristic diagram, Figs. 3 and 4 are related to the present invention, Fig. 3 is a block diagram showing details of the coordinate detection device, Fig. 4 shows the equivalent circuit of FIG. In the figure, PN is the detection panel, X ₁ to X ₄ , Y ₁ to _{Y 4} are the touch detection parts, CCL is the capacitance cancel circuit, and AMP
indicates a non-inverting operational amplifier.

Claims (1)

[Claims] 1 Coordinate detection comprising a detection panel having a plurality of electrodes, a touch detection section that detects changes in capacitance in the electrodes based on instructions to the electrodes, and switch means that sequentially selectively connects each electrode to the touch detection section. A coordinate detecting device characterized in that the output signal of the switch means is amplified in a non-inverting manner, and a capacitive element is connected between the output terminal thereof and the input terminal of the touch detecting section.