JPH10124259A - Touch panel input device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a display from deviating owing to the contact resistance of a touch panel by providing a voltage holding means which does not vary in voltage abruptly with the contact resistance. SOLUTION: When input is detected, an interrupt is initiated with an input detection signal TPPDDX and an AD converter 22 starts AD conversion. As for a Y axis, a voltage divided by the touch panel 1 is taken out of a terminal TPL and an AD converter 22 converts it into a digital voltage. At this time, a switch TM1 is turned ON to charge a capacitor C1 with the voltage divided by the touch panel. As for an X axis, a divided voltage is similarly taken out of a terminal TPD and converted by the AD converter 22 into a digital voltage. At this time, a switch TM2 is turned ON to charge a capacitor C2 with the divided voltage. Consequently, even if the contact resistance increases abruptly as an input position moves, a stable state is held with the electric charges accumulated in the capacitor without any variation in the input of the AD conversion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an input device using a touch panel for an electronic organizer or an electronic information device. The present invention relates to a touch panel interface circuit.

[0002]

2. Description of the Related Art FIG. 1 is a block diagram of a conventional touch panel interface circuit. Control is performed by an interface control circuit including a touch panel 1, a touch panel control unit 2, a pen input detection unit 3, an interface power supply unit 4, and an AD conversion unit 5. Here, the touch panel control unit 2 includes switching elements 10, 11, 12, and 13, and the output terminals TPL, TPR, and TP corresponding to the resistance of the touch panel 1.
U and TPD are connected.

[0006] The pen input detecting section 3 is connected to one end of the touch panel 1 and interrupts the interface control circuit 6 when a voltage (pen pressure) exceeding a certain level is input. With this operation, the interface control circuit 6 starts the operation of the interface power supply unit 4 and supplies power to the touch panel control unit 2 and the AD conversion unit 5. Then, the voltage from the touch panel 1 is read by an AD converter in the AD converter 5 and converted into a digital value.

[0004]

In the conventional input device, as shown in FIG. 2, a voltage E applied to a resistor R of the touch panel 1 is divided by a uniform and continuous voltage gradient. The detected voltage is detected and AD
The signal is converted into a digital signal by the converter 22. At this time, a contact resistance of the contact portion occurs at the input position of the touch panel 1, and the voltage is divided by the input impedance of the circuit. Next, FIG. 4 shows a change in voltage at the point A in FIG. When the contact resistance changes, the discontinuous voltage value is subjected to A / D conversion, which causes a problem that the voltage is displayed at a position shifted from the actual input (FIG. 3).
This leads to problems such as blurred characters and broken typefaces when inputting by handwriting.

[0005]

According to the present invention, there is provided means for holding a voltage which does not fluctuate to a sudden change in voltage due to a change in contact resistance. In addition, a means is provided to prevent abnormal data from being captured by discharging the touch panel and speeding up the response of the pen input detection unit except during data capture (AD conversion).

According to the present invention, in the input device using the touch panel, since the voltage holding means is provided, a display shift (coordinate jump) due to the contact resistance of the touch panel can be prevented. In particular, it is possible to reproduce smooth lines in a high-resolution display without losing the font.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 5 shows a pen input interface circuit using a touch panel according to an embodiment of the present invention.

First, the configuration of the circuit will be described. The vertical axis and the horizontal axis of the touch panel 1 are defined as a Y axis and an X axis, respectively.
The touch panel 1 has a resistance 1 on the Y axis of the touch panel 1.
4 and output terminals TPL and TPR for detecting the X-axis resistance 15 of the touch panel 1. The switching element 10 having a power supply VCC and an input terminal for the touch panel control signal SWU is connected to the output terminal TPU. Similarly, a switching element 11 having a power supply VCC and an input terminal for a touch panel control signal SWR is connected to the output terminal TPR.

Next, the output terminal TPL is a switching element 12 having an input terminal for the touch panel control signal SWL;
The switching element 30 connected to the power supply VCC via the resistor 31 is connected to an input terminal for switching. Here, an input detection signal is extracted from between the resistor 31 and the switching element 30. Further, the terminal TPL is a switch T
The capacitor C1 is connected via M1 and the resistor R1 is connected via switch TM3. Here, the touch panel control signal SWL is input to the switch TM1. Switch TM
3, the NOR of the touch panel control signals SWL and SWRX is input via the NOR circuit 32. Where SWR
X is an inverted version of the SWR signal.

A switching element 13 is connected to the terminal TPD, and a touch panel control signal SWD for switching the switching element 13 is also connected. A capacitor C2 is connected to the terminal TPD via a switch TM2, and a touch panel control signal SW is connected to the switch TM2.
D has been entered.

Finally, the output terminals TPL and TPD are connected to the selection means 33 and output AD conversion data ADCO through the AD converter 22. Next, the operation of the circuit will be described. When an input is detected, an interrupt is generated by the input detection signal TPPDDX, and the AD converter 22 starts AD conversion. For the Y axis, the voltage divided by the touch panel 1 is taken out from the terminal TPL and converted into digital by the AD converter 22. At this time, the switch TM1 is turned on to connect the capacitor C1 in parallel. Capacitor C1 is
It is charged with the divided voltage of the touch panel. A on the Y axis
During the D conversion, the capacitor C1 is kept connected, and the switch TM1 is turned off and the capacitor C1 is disconnected when the Y-axis conversion is completed.

Similarly, for the X axis, the divided voltage is obtained by taking out the divided voltage from the terminal TPD and converting it into a digital signal by the AD converter 22. At this time, switch TM2
Turn on, connect the capacitor C2 in parallel, and charge the capacitor C2 with the divided voltage. When the conversion of the X axis is completed, the switch TM2 is turned off. Due to the capacitors C1 and C2, even when there is a sudden increase in the contact resistance due to the movement of the input position, the input of the AD conversion can be kept stable without fluctuation due to the charge accumulated in the capacitor.

When the Y-axis / X-axis AD conversion is completed, the switch TM3 is turned on, and the resistor R1 is connected to the signal line of the input detection unit. This increases the input detection speed by discharging the charge of the touch panel. When the speed of the AD conversion is high, the detection of the end of the pen input is delayed due to the charge of the touch panel. During this time, the charge on the touch panel is A / D converted and abnormal data is captured. Discharge of the touch panel to increase the detection speed can prevent abnormal data from being captured, that is, display shift.

The operation timings of the switches TM1, TM2 and TM3 are as shown in FIG. When the switch TM1 is turned on, the Y-axis voltage is AD-converted.
1 and then switch TM2 to ON instead X
The voltage of the axis is AD-converted. Next, switch TM2 is turned off.
Then, the AD conversion is completed. Finally, switch TM3 is turned on.
Set to N.

[Brief description of the drawings]

FIG. 1 is a block diagram of a conventional touch panel interface circuit.

FIG. 2 is a diagram showing a contact resistance of a touch panel.

FIG. 3 is a diagram showing a display shift due to an actual input and a contact resistance.

FIG. 4 is a diagram showing a voltage change due to contact resistance.

FIG. 5 is a circuit diagram of a touch panel interface according to an embodiment of the present invention.

FIG. 6 is an operation timing chart of the circuit of the present invention.

[Explanation of symbols]

TPPDDX input detection signal TPL, TPR, TPU, TPD output terminal SWU, SWD, SWR, SWL Touch panel control signal ADCO AD conversion data TM1, TM2, TM3 Switch

Claims (6)

[Claims] 1. An input device using a touch panel, comprising: means for converting input coordinates into a voltage; and means for preventing the voltage from changing due to contact resistance of the touch panel. 2. An input device using a touch panel, wherein the input device has means for discharging the electric charge of the touch panel. 3. An input device using a touch panel, wherein: a power supply connected to one end of an output terminal for a resistance of at least one coordinate axis of the touch panel; a switch connected to the other end of the output terminal; And a switching element connected to the other end of the output terminal. 4. An input device using the touch panel 1, wherein the switching element 10 connected to one output terminal TPU of the resistor 14 on one coordinate axis of the touch panel 1 and the other output terminal TPD of the resistor 14 A switching element 13 connected thereto, a switch TM2 connected to the output terminal TPD, a capacitor C2 connected to the switch TM2, and a switching connected to one output terminal TPR of the resistance 15 of the other coordinate axis of the touch panel 1. Element 11
A switching element 12 connected to the other output terminal TPL of the resistor 15, a switch TM1 connected to the output terminal TPL, a capacitor C1 connected to the switch TM1, the switching element 10 and the switching element 11
An input device having a power supply VCC connected to the input terminal. 5. An input device using a touch panel, comprising: a power supply connected to one end of an output terminal corresponding to a resistance of at least one coordinate axis of the touch panel; a switch TM3 connected to an output terminal TPL; Input device having a configured resistor R1. 6. An input device using a touch panel, comprising: means for charging a capacitor connected to an output terminal of another coordinate when detecting one coordinate of the touch panel.