JP2001125744A - Coordinate input device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a coordinate deviation caused by the influence of noises concerning a coordinate input device, for which a touch panel is used. SOLUTION: Noise signals are extracted from analog data, which contain noises, a signal, for which these noise data are inverted, is added to the original analog data, which contain noises, so that only a noise component can be canceled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coordinate input device using a touch panel, which has a noiseless coordinate detection method.

[0002]

2. Description of the Related Art A touch panel has a structure in which two resistive films made of transparent sheets are overlapped with each other at right angles to a Y axis and an X axis. The coordinate input device has a structure in which the touch panel is stacked on the display device, and is easily affected by disturbances radiated from a clock or a circuit of the display device. Since these noises are superimposed on the analog data via the touch panel, the values converted into digital by the AD converter also include the noises, and display a position (coordinate deviation) different from the actually input coordinate position. Will be.

[0003]

Conventionally, when noise is superimposed on an analog signal output from a touch panel, a band-pass filter using a hardware, a noise cut-off using a shield, and an average of coordinates using software are used to remove the noise. Processing such as chemical conversion. Noise removal by a band-pass filter functions strongly for noise related to a specific frequency, but has no effect on noise outside the band and lacks reliability. Furthermore, the capacitor used in the filter also has a large effect on performance, such as erroneous detection of pen-down due to residual charge and waveform rounding longer than the conversion time as the sampling speed increases. There was a limit and the filter effect was also limited.

[0004] In a filter by software processing, it is possible to suppress variations to some extent, but it is impossible to completely remove noise components. Further, as the filtering process becomes more sophisticated, the process becomes heavier and the effect on performance cannot be ignored. The present invention makes it possible to realize a function of preventing a coordinate shift due to the influence of noise in hardware in a coordinate input device using a touch panel without affecting performance.

[0005]

A coordinate input device using a touch panel detects an input section in which a pressure-sensitive touch panel using a resistive film is laminated on a display section, a switch for applying a voltage to the touch panel, and an input state of a pen. Pen input detection unit, a filter unit that extracts noise components from analog data, an inversion unit that performs logical inversion of noise components, an addition unit that adds the original analog data and a logically inverted noise signal, and converts analog data to digital A / D conversion unit, and a CPU that controls the entire system.

The CPU fetches the digital data output from the A / D converter at a certain interval in the order of the Y coordinate and the X coordinate, calculates the coordinate value, and outputs it to the display unit. Where A / D
If noise is superimposed on the voltage input to the converter,
Since noise is also included in the converted digital data, data different from the actual input coordinates is converted and displayed on the display unit (FIG. 2). In order to solve this problem, from the analog signal before input to the AD converter,
The superimposed noise (AC) component is extracted, and the noise component is logically inverted and added to an analog signal containing the original noise to cancel only the noise. This effectively works for irregular noise superimposed on an analog signal in addition to noise generated from the display.

[0007] This noise also affects the pen input detection unit that detects touch panel presses, and may erroneously detect touch panel presses. Misdetection of pen input due to noise can be solved by reducing the input impedance of the pen input section. However, if this input impedance becomes a value that cannot be ignored compared to the resistance of the touch panel, it may affect the sampling of this circuit. Becomes large, which may cause a coordinate shift.

In the present invention, the pen input detecting section is electrically connected to the touch panel in a state of waiting for pen input, and the pen input detecting section is electrically disconnected from the touch panel during sampling of coordinates to prevent the influence. With the above method, it is possible to realize a coordinate input device free from the influence of noise without affecting the performance.

[0009]

An embodiment of the present invention will be described with reference to FIG. In the touch panel 100, in a state of waiting for pen input, the switch 200 is ON and a DC voltage is applied. The pen input detection unit 600 is connected to one end of the touch panel, and when the touch panel 100 is pressed, a voltage is applied to the pen input detection unit from the signal line TPY. This signal turns on the pen input detection unit 600 and interrupts TP to the CPU 1100.
Generates an IRQ and detects pen input. CPU1100
Starts sampling coordinates periodically when pen input is detected. First, the switch 1200 is turned off to electrically disconnect the pen input detection unit 600 from the touch panel. This is to prevent voltage division by the detection resistor Rg of the pen input detection unit 600 and the touch panel. If the resistance value of the detection resistor Rg is very large, the pen input detection unit may malfunction due to noise induced on the touch panel. For this reason, the detection resistance Rg of the pen input detection unit is reduced and tuned so as to be lowered to a detectable voltage, but if the circuit of the pen input detection unit is not separated, the detection resistance value will Since it cannot be ignored, a position different from the input position is displayed (coordinate deviation).
In this circuit, the problem is solved by setting the detection resistor to a resistance value that does not affect the noise and that can detect the pen input, and disconnects from the circuit when the pen input is detected.

Next, in order to detect the coordinates of the Y coordinate, the switches 200 and 400 are turned on and a voltage is applied in the Y-axis direction for a certain period of time. During this time, the voltage divided at the pressed position is sampled as an analog signal from the signal line TPY. Next, the switch 200 and the switch 400 are turned off, and the switch 300 and the switch 500 are turned on for a certain period of time to perform X-axis sampling from the signal line TPX.

Next, the superimposed noise component is removed from the sampled analog data (FIG. 2). First, the filter unit 700 extracts a noise signal from analog data. The filter here is a mechanism that treats noise as an AC signal and extracts only the AC component without attenuating the signal level. Next, the phase of the extracted noise signal is inverted by 180 degrees in the logic inversion section 800. The noise signal obtained by inverting the phase by 180 degrees is added to the original analog data containing noise in the adding unit 900 (FIG. 3). Therefore, an inverted signal of the same level as the noise is added to the noise component included in the analog signal, and only the noise can be canceled. As described above, since the noiseless analog signal is converted into digital data by the A / D converter 1000, no coordinate shift occurs.

Finally, the data converted into digital data by the A / D converter 1000 is taken into the CPU 1100 and output to a display so that the input position can be displayed. Y
Switch 1200 is turned on when A / D conversion of axis / X axis is completed
Then, the pen input detection unit 600 is electrically connected to the touch panel to detect the current input state (during input or input end), and determine whether to continue sampling. If there is no pen input, the processing is terminated here and the apparatus waits for pen input (only switch 200 is ON). If pen input is detected, sampling is performed continuously and the switch is switched alternately by the combination of "switch 200-switch 400" and "switch 300-switch 500".
Apply voltage to each of the 100 Y-axis and X-axis, signal line TPY
The voltage corresponding to the coordinates pressed from TPX is sampled sequentially.

[0013]

According to the present invention, in a coordinate input device using a touch panel, a superposed noise is canceled by adding a signal obtained by inverting a noise component and an analog signal containing noise to prevent a coordinate shift. Things. The present invention reduces the load of software to reduce noise superimposed by hardware, and further functions independently of a control system such as a CPU, thereby preventing a coordinate shift without affecting performance. .

[Brief description of the drawings]

FIG. 1 is a coordinate input circuit using a touch panel according to an embodiment of the present invention.

FIG. 2A is an original waveform. FIG. 2B is a waveform of an analog signal on which noise is superimposed.

FIG. 3 is a diagram showing a mechanism of the present invention.

[Explanation of symbols]

 100 Touch panel 200 to 500 Touch panel applied voltage control switch 600 Pen input detection switch 700 Filter unit 800 Logical inversion unit 900 Addition unit 1000 A / D conversion unit 1100 CPU 1200 Pen input detection unit disconnection switch TPIRQ Pen input detection interrupt signal TPY Touch panel Y axis Direction signal output TPX Touch panel X axis direction signal output TPU, TPD, TPR, TPL Touch panel applied voltage control signal Rg Pen input detection resistor

Claims (4)

[Claims] 1. Y made of two transparent sheets of resistive film
In a coordinate input device that uses a touch panel with a structure in which the X-axis and X-axis sheets are superimposed on a display such as a liquid crystal, the noise component included in the analog signal that detects the pressed position is extracted, and this noise is logically inverted. A coordinate input device having a function of adding the signal to a signal containing noise. 2. The coordinate input device according to claim 1, wherein
A filter unit having a function of extracting a noise component included in the analog signal as an AC signal, a logic inversion unit having a function of logically inverting the extracted noise component, and a function of adding an analog signal containing noise and logically inverted noise A coordinate input device comprising an adder having: 3. The coordinate input device according to claim 2, wherein
A coordinate input device having a function of preventing an erroneous detection of a pen input due to the influence of noise by adjusting an input impedance of a pen input detection unit that detects a touch panel press. 4. The coordinate input device according to claim 3, wherein
A coordinate input device having a function of electrically disconnecting a pen input detection unit from a touch panel during coordinate sampling.