JPS62165229A - Coordinates input device - Google Patents

Abstract

PURPOSE:To improve the detection precision by providing a control circuit which selects automatically an additional capacity which sets the oscillation period of a relaxation oscillator due to additional capacitors to a value approximating 1/n of an induced noise period. CONSTITUTION:A measured output 19 due to a period measuring circuit 13 is inputted to an operating and selective control circuit 12. A capacity selecting signal which selects a prescribed capacity from external additional capacities, namely, plural additional capacities C1-C6 by which an oscillation reference point of relaxation oscillation at a period approximating the harmonic component period, which is the period, a 1/2 period, a 1/3 period - of a horizontal synchronizing signal 20 driving a CRT 9, is set to a relaxation oscillator 10 to which a CR constant is set preliminarily is outputted from the control circuit 12 to drive a switch circuit 17. Thus, the influence of induced noise is evaded automatically even in case of an input device provided with CRT display device different in horizontal synchronizing signal. Thus, input coordinates detection of touch operation is stabilized and the detection precision is improved.

Description

[Detailed Description of the Invention] [(Already needed)] In a coordinate input device that detects a touch position by a finger touch operation, the accuracy of detecting the coordinate position where a touch input is made is reduced due to induced noise from a dual display device (CRT). It is intended to improve the

[Industrial application field]

The present invention relates to a coordinate input device equipped with a CR relaxation oscillator and the like for detecting the capacitance of an input cover panel applied to an input/output terminal.

A so-called capacitive coordinate input device is attracting attention as an information retrieval terminal that allows desired information to be retrieved sequentially by touching a specific input item with a finger from a plurality of selection menus displayed on a CRT screen.

However, it is known that the detection accuracy and reliability of touch operation input decreases due to induced noise from the Cr1T drive system circuit. A control circuit is presented that allows the drive period of the relaxation oscillator to be an appropriate cycle.

[Conventional technology]

FIG. 2 is a simplified block circuit diagram of a coordinate detection panel and input detection of the panel. The structure of the sheep will be explained according to the diagram.

In the block circuit diagram, 25 is a transparent conductive film (for example,
26 and 27 are analog switches placed on both ends of the input cover panel 25 on the X coordinate side, and analog switches 28 and 29 are placed on both ends of the same panel 25 on the Y coordinate side. The analog switch and 30 are ×(!!!IY side coordinate switching switches.

If there is a touch on the input cover panel 25 at point X in Figure 1, an equivalent human body capacitance of 1 cb (about cb 100 FF) will be added to the panel, and the capacitance cb when the touch point is viewed from the left and right panel ends, respectively. The equivalent capacity is expressed as follows.

Left side = R+-x -Cb/ (Rx+R,-,) Right side = Rx ・Cb/ (Rx + R1-x) However, RX
+Rsx is the equivalent resistance of the ITO film uniformly deposited on the panel substrate.

The above is a basic formula for capacitance measurement that detects the X coordinate of the panel where a touch operation has been performed, and the first formula has a linear relationship with the touch coordinate point.

The capacitance measurement formula with a linear relationship is the same when detecting the Y coordinate of an input point where a touch operation has been performed.

Next, the input detection of the panel, that is, the coordinate detection circuit using the equivalent capacitance will be explained.

In the simplified block circuit diagram, 31 is a CR relaxation oscillator that inputs the equivalent capacitance via the X-side and Y-side coordinate changeover switch 30, 32 is a buffer amplifier, and 33 is the oscillation period of the oscillator 31 that is measured by a time reference pulse 35. , and 34 is a control calculation circuit.

The charge/discharge cycle of the CR relaxation oscillator 31 has an oscillation cycle due to the basic capacitance of the panel itself when there is no touch input.

However, when a touch operation is performed, the period of relaxation oscillation changes depending on the combined capacitance of the basic capacitance and the equivalent capacitance formed on both sides of the touch point.

The period of the oscillation is digitally counted via a one-period counter 33, and then inputted to an arithmetic circuit 34, where it is arithmetic-processed as a digital variation ratio to determine the coordinate position of the panel input point.

However, there is a problem in that stabilization of the oscillation frequency of the relaxation oscillator 31 in the coordinate input device is likely to be inhibited by induced noise (display noise) on the display device side.

FIG. 3 shows an example of the oscillation waveform 36 of al, which is a basic waveform of one period T, but this is a diagram pointing out the problem that induced noise 37 causes the waveform to have a shorter period as shown by the dotted line in the figure. In order to improve the improvement, an additional capacitor 1 related to region selection of one oscillation frequency dispersion is added at the input end of the CR oscillator 31 shown in FIG.
There have been proposals such as adding and inserting c (this proposal was previously applied for as a patent, for example, for a "coordinate detection device").

[Problems that the invention attempts to solve]

The main factor that hinders the stabilization of the device for detecting coordinates is induced noise received from the CRT display device. For this purpose, we measure the periodic pulses included in the inductive noise source, process the results, select an additional capacitor that will prevent the noise period from synchronizing with the oscillation period, and insert this into the CR relaxation oscillator. It is something to do.

[Means for solving problems]

FIG. 1 is a circuit block diagram illustrating an embodiment of the present invention for automatically selecting and controlling additional capacitors.

In the coordinate input device 9, according to the present invention, the induced noise 14 is measured by the period measuring circuit 13 for the CRT display device 9 to which the device is attached, and the relaxation oscillator by the additional capacitance ffl 11 is calculated based on the measured counter data. 10
The coordinate input device is equipped with a selection control circuit for an additional capacitor 11 and an arithmetic circuit 12 for setting the oscillation period of the noise to be around 1/n (where n is an integer) of the induced noise period.

[Effect]

In the present invention, since the frequency of the CR relaxation oscillator is disturbed by the fundamental frequency of the 1st inductive noise and the nth harmonic noise, an additional capacitor is provided to set the relaxation oscillation frequency between these noise frequencies. The present invention aims to improve the detection accuracy by focusing on the fact that the input coordinates of touch submissions can be detected stably by selective control.

〔Example〕

Hereinafter, the present invention will be explained with reference to FIG. 1, which is a block diagram of an embodiment of the circuit for selectively controlling the additional capacitance of the present invention. In the embodiment diagram, the input panel 25 for touch operation is not particularly shown, but
The CR relaxation oscillator 10 detects touch point coordinates (XY coordinate points) using the same capacitance measurement principle as explained in the circuit block diagram of FIG.

In addition, in Figure 9, 35 is the oscillation period counter (
This is the same pulse signal as the reference pulse 35 for time measurement inputted into the circuit (see FIG. 2).

A plurality of additional capacitors 11 shown in the example C6 are coupled to the input side of the CR relaxation oscillator 10, so that the oscillation frequency range in which the oscillator 10 is predetermined can be easily selected.

In the embodiment diagram, a period measuring circuit 13 of the present invention is shown.

Inductive noise 14 from the CRT display device 9 is taken in through a coupling capacitor 18 and its period is measured by a period measurement counter 15 . The noise input section of the 1-period measuring circuit 13 is as shown in the figure.
It is necessary to perform waveform shaping to facilitate period measurement.

The measurement output 19 from the period measurement circuit 13 is input to the arithmetic and selection control circuit 12, where the period of the horizontal synchronization signal 20 (H synchronization signal) for driving the CRT 9 is determined for the relaxation oscillator whose CR constant is set in advance. , or an external additional capacitor such that an oscillation reference point for relaxation oscillation is set in the vicinity of a harmonic component period of 1/2 period, 173 periods, . . . of the synchronization signal.

That is, a capacitance selection signal for selecting a predetermined capacitance from a plurality of additional capacitances C+=Cs is output from the control circuit 11 circuit 12 to drive the switch circuit 17.

In this way, even in the case of an input device that includes a CRT display device with a different horizontal synchronization signal, the influence of induced noise can be automatically avoided and panel coordinates can be detected stably by touch operation.

〔Effect of the invention〕

As is clear from the above description, according to the coordinate input device of the present invention, an additional capacitor is selected such that the induced noise period and the oscillation period do not match, and the selected capacitor is added to the CR relaxation oscillator. Since the insertion process is performed automatically, there is a remarkable effect that the input coordinate detection of the touch operation is stabilized and the detection accuracy is improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an additional capacitance selection control circuit for a CR relaxation oscillator according to the present invention. FIG. 2 is a simplified block circuit diagram of a conventional coordinate detection (input) panel. Figure 3 (al is a relaxation oscillation waveform diagram (period!tII). The same figure (bl is a schematic circuit diagram of a CR relaxation oscillator in which an additional capacitor C is inserted. In the figure, 9 is a display device, 10 is a CR relaxation oscillator) Oscillator. 11 is an additional capacitor, 13 is a period measuring circuit. 12 and 34 are control calculation circuits. 14 is an inductive noise, 15 is a period counter. And 25 is an input panel for coordinate detection. I mouth

Claims (2)

[Claims] (1) A CR for impedance measurement that places a resistive film on the panel (25), measures the capacitance of the touch point on the panel (25) from both ends of the resistive film, and detects the coordinates of the touch input point from the ratio of these capacitances. In a device comprising a relaxation oscillator (10), induced noise (
The additional capacitance (1) is measured by the period measuring circuit (13) of
A control circuit (12) that automatically selects an additional capacitor (11) that causes the oscillation period of the relaxation oscillator (10) according to 1) to be set near 1/n (n is an integer) of the period of the induced noise (14). A coordinate input device comprising: (2) The induced noise (14) is a horizontal synchronizing signal, and the fundamental period of the CR relaxation oscillator (10) is set to approximately 1/2 of the period of the signal. Coordinate input device as described in section.