JPS6237725A - Coordinate detector - Google Patents

Abstract

PURPOSE:To detect the coordinates with reduced effect of noises by setting the oscillation frequency of a CR oscillator for detection of coordinates in relation to the induction noises produced from a coordinate display device after providing an additional capacity. CONSTITUTION:When a touch finger is given to a touch panel 12 of a resistance film containing a transparent electrode of ITO, the change of impedance due to the capacity ratio set up to the touch position is detected by a CR oscillator 16 of a capacity measuring part 15. Then, the oscillation output of a frequency corresponding to the coordinate position is produced. The oscillation frequency of the oscillator 16 is set at the medium level between the n-degree and (n+1)-degree higher harmonic waves of the induction noise given from a display device by an additional capacity 23 when no connection of impedance is given to the resistance film. Thus, the oscillation frequency of the oscillator 16 corresponding to the coordinate value is kept within the frequencies between the n-degree and (n+1)-degree higher harmonic waves excluding these waves. This attains the detection of coordinates with reduced effect of noises.

Description

[Detailed Description of the Invention] [Summary] A method for setting the oscillation frequency of a capacitance detection oscillator of a non-pad type touch panel, and a method for selecting a frequency range free of display device noise (display noise), and defining a variable range. The present invention provides a coordinate detection device with good noise characteristics.

[Industrial application field]

The present invention relates to a capacitive coordinate detection device, and more specifically, to a coordinate detection device that improves coordinate detection accuracy by appropriately comparing capacitance measurement conditions.

[Conventional technology]

Capacitance measurement methods range from traditional methods using a current-voltage measurement system to methods that measure the CR time constant or CR relaxation oscillation period. When considering the combination with a digital system, the voltage /
The latter method, which can be converted into time, is simpler and cheaper than the current method.

On the other hand, if the capacitor contains noise (e.g. human body capacitance, hum noise, etc.), the relaxation oscillation method switches between charging and discharging by comparing the voltage of the capacitor with another reference potential, so fluctuations in the oscillation cycle due to noise may occur. There is a problem that the accuracy cannot be improved because of the large value.

One way to remove noise is to use a filter, but this is difficult in the case of a relaxation oscillator because the fundamental period has already been lost.

Fig. 3 is a diagram for explaining the problem of the relaxation oscillator, and the oscillation period shown by the solid line a is charged to the reference potential vrH when viewed from the left.
When it reaches t, it discharges and drops to the reference potential VyηL, and then repeats charging and discharging. However, if the noise shown by the line enters, the oscillation period a repeats the operation shown by the solid line, and the dotted line C when there is no noise occurs. There is a problem that the oscillation period deviates from the one shown in .

[Problem that the invention seeks to solve]

In the above-mentioned method, a method is used to measure the capacitance by using a CR relaxation oscillator and determining the capacitance from the oscillation period of the CR relaxation oscillator. However, this method has a problem in that the oscillation period changes due to the influence of induced noise from the display, which tends to reduce accuracy.

The present invention was created in view of these points, and an object of the present invention is to provide a coordinate detection device that is less affected by noise.

[Means for Solving the Problems] FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a diagram showing the principle of the present invention.

According to the present invention, there is provided a coordinate input cover panel in which a resistive film is arranged on a substrate, a buffer circuit with high input impedance and low output impedance that keeps both ends of the resistive film at the same potential, and an input/output n1 of the buffer circuit and both ends of the resistive film. and an impedance detection circuit connected to the input end of the buffer circuit, which measures the impedance seen from one end of the resistive film in a time-sharing manner, and determines the impedance connection on the resistive film based on the relative ratio of the impedance. It is a coordinate detection device that knows the position, and in particular, in a coordinate detection circuit that uses a CR relaxation oscillator as an impedance measurement method and converts impedance into an oscillation period, the oscillation frequency when there is no impedance connection on the resistive film is measured using the device. The detection circuit oscillation period is set between the nth harmonic and the (n+1)th harmonic of the induced noise emitted from the display device to be worn, and further changes due to the impedance connection on the resistive film.
+1) Select the indicated impedance or CR oscillator constant so that it falls within the harmonic range.

[Effect]

In the present invention, fluctuations (errors) in the oscillation frequency due to noise are
Noting that the noise is large in the region close to the fundamental frequency and its harmonic components, and becomes smaller as it moves away from these frequencies, the oscillation frequency of the CR oscillator for capacitance measurement is set between these noise frequencies to improve the coordinate detection accuracy. This is intended to improve the quality of life.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a configuration diagram of an embodiment of the present invention, and in the same figure,
11 is a coordinate detection device developed by the applicant, which is an IT
Touch panels 12 with O transparent electrodes, 10 each
The touch panel 12 consists of 141 analog switch arrays, and includes analog switches 13a and 13b arranged on the left and right, top and bottom as seen in the figure, and an analog switch 13c for the coordinate detection device 11, and the coordinate detection device 11 includes a buffer amplifier. The capacitance measuring section 15 is connected to the capacitance measuring section 15 via a CR oscillator 16, a resistor 17 (R),
It includes a clock 18 that generates a 6 MHz clock signal, an AND gate 19, and a counter 20, and the counter 20 is a micro processing unit (MPt) for calculation.
l) 21, and an output 22 is output from the MPU 21. 23 is an additional capacitance of, for example, 73 pF according to the present invention.

A feature of the present invention lies in the selection of the CR oscillation frequency. This can be easily set by changing either the CR oscillation frequency C or R or the level comparison voltage. The CR oscillator 16 used in this embodiment is NE-555 manufactured by Mygnetics, and its oscillation period is T=1.4 RC. C is the panel capacity (
Since the input/output capacitance (mainly analog switch input/output capacitance) is approximately 400 pF, the amount of change in capacitance is 150 pF above the human body capacitance.
Then, 400 pF (when not touched) ~ 550 pF
P (at the time of touch). As shown in Figure 2, the fundamental frequency of the noise is 15.75 K, the horizontal synchronizing signal of the CRT.
Hz and the noise window (region with less noise)
63 KHz to 78.75 KHz was selected. In FIG. 2, the horizontal axis shows the oscillation period in Hz, and the vertical axis shows the capacitance measurement error in %.

In order to keep the change in oscillation frequency due to capacitance change during finger touch within this range, f max = 77 KHz (Tmin =
15.511s) f min = 65 KHz
(Tmin = 13/-Is) is selected as the frequency setting range. In order to keep the frequency change within this range, 15.5/13=(550pF+ΔG>/(
400pF+ΔC), theoretically additional capacitance ΔC=73
pF is added, and the value R of the resistor 17 at this time is R=20
was set to Ω.

As a result, the oscillation frequency was kept within the range of the noise window, and the influence of noise could be minimized. In reality, the values of the additional capacitance 23 and the resistor 17 for each coordinate detection device are set to the above-mentioned values of 73 pF and 20 KΩ, respectively, based on the above-mentioned theoretical values, and the product is marketed as a product with the least amount of noise. It is something.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to minimize the influence of noise in a coordinate detection device, and high accuracy of the coordinate detection device is realized.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a diagram illustrating the principle of the present invention, and FIG. 3 is a diagram illustrating problems with a relaxation oscillator. In FIG. 1, 11 is a coordinate detection device, 12 is a touch panel, 13a, 13b, 13c are analog switches, and 14
is a buffer amplifier, 15 is a capacitance measuring section, 16 is a CR generator, 17 is a resistor (R), 18 is a clock, 19 is an AND gate, 20 is a counter, and 21 is an MPU. 22 is an output, and 23 is an additional capacitor. 1 example of brutal brutality (ffi Figure 1)

Claims (2)

[Claims] (1) Place a resistive film on the panel, measure the capacitance from both ends of the resistive film to the finger touch position on the panel, and use the impedance measurement to detect the coordinates of the finger touch position from the ratio of these capacitances. Device (1) using an oscillator (16)
In 1), the oscillation frequency when there is no impedance connection on the resistive film is set between the nth harmonic and the (n+1)th harmonic of the induced noise generated from the display device to which the device (11) is attached. A coordinate detection device characterized in that an additional capacitor (23) and a resistor (17) are provided for the purpose of detecting coordinates. (2) Additional capacitor (23), resistor (17) and C
The coordinate detection device according to claim 1, characterized in that an R oscillator (16) is provided.