JPS6232489B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a coordinate input device comprising an oscillator and an LC resonant circuit.

[Background of the invention]

Touch entry devices, which have a transparent touch-type coordinate detection panel installed in front of the display surface of a display device, and input desired information by pointing the contact point on the panel that corresponds to the information display position, have been attracting attention in recent years. are collecting. When performing instructions using a touch entry device, there may be differences between people,
Alternatively, due to differences in the external environment, the touch capacity may vary, causing problems such as malfunctions.

[Conventional technology and problems]

FIG. 1 is a block diagram of a touch detection circuit constructed from a conventional LC resonant circuit.

A, B, and C are the measurement points of the output waveform at each location, A is the point on the negative input terminal of the comparator, B is the point on the input terminal of comparator 1, and C is the point on the input terminal of comparator 1. It is a point on the output terminal.

The oscillator 3 outputs a sine wave with a constant frequency. When each switch of the input panel 5 is not turned on, the sine wave of this frequency matches the resonant frequency of the parallel resonant circuit of the capacitor 6 and the coil 7, so it resonates without attenuation.

FIG. 2 shows this waveform as the output waveform at point A. V _OFF is the peak value of this waveform.

Next, when one of the switches on the input panel 5 is touched with a finger, the resonant circuit becomes a composite resonant circuit consisting of the capacitor 6, the coil 7, the coil 8, and the touch capacitor 4, and when the switch is not touched, The resonant frequency of the capacitor 6 and the coil 7, that is, the resonant frequency different from the output frequency from the oscillator 3.

FIG. 3a shows this waveform as an output waveform at point A, and the output level is decreasing while exhibiting transient characteristics. Also, set Vth to comparator 1
If the potential input to the positive input side of the
The waveform at the output becomes a high-level pulse waveform when the voltage is higher than Vth, as shown in FIG. 3b. Therefore, as shown in FIG. 3c, the output of the smoothing circuit 2 at point C becomes a low level when it is below Vth, and it is determined that this low level output of the smoothing circuit 22 is touched. However, when this detection device is used, for example when the touch capacitance 4 is small, as shown in Fig. 4 a.
As shown in the figure, the peak value of the waveform at point A does not fall below Vth. Therefore, the output of the comparator 1 at point B also shows a pulse waveform as shown in FIG. As shown, it has the disadvantage that it is always at a high level and does not go low, making it impossible to judge touch.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned drawbacks, and its object is to provide a coordinate input device that can perform reliable touch detection.

[Structure of the invention]

The purpose of this is to send instructions to the detection electrode in an input device consisting of a touch detection section that uses a detection circuit consisting of an oscillator and a resonant circuit to detect electrical changes based on instruction operations to the touch detection electrode. This is achieved by providing a coordinate input device characterized in that touch detection is performed by sequentially searching for changes in the detection circuit output based on an operation at timings synchronized with the oscillation frequency of the oscillator.

[Embodiments of the invention]

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

FIG. 5 is a circuit diagram of a touch input device according to the present invention.

In the figure, each switch 10 to 13 provided on the input panel 9 is connected to each input terminal of a multiplexer 14, and the output terminal of the multiplexer 14 is connected to a coil 15. The other end of the coil 15 is connected to one end of a parallel circuit of a capacitor 16 and a coil 17 and one end of a resistor 18 . Also capacitor 1
The other end of the parallel circuit of 6 and coil 17 is grounded, and the other end of resistor 18 is connected to oscillator 19 and timing pulse generation circuit 20. The output of the timing pulse generation circuit 20 is input to the strobe of the comparator 21, and at the same time the output is input to the touch determination section 22.
Enter.

On the other hand, the other end of the oscillator 19 is grounded, and the other input terminal of the comparator 21 has a threshold voltage.
A power supply 23 is connected for Vth by a comparator 21, and the negative side of the power supply 23 is grounded.

Further, A is a point on the input terminal of the comparator 21, B is a point on the output terminal of the comparator 21, C is a point on the output terminal of the touch determination section 22, and D is a point on the output terminal of the timing pulse generation circuit 20. It is a point on the output terminal.

The operation of the touch input device configured as described above will be explained using FIGS. 6 to 8.

When the switches 10 to 13 on the input panel 9 are not touched, the oscillator 19 outputs a sine wave of a constant frequency. This output matches the resonant frequency of the parallel circuit of capacitor 16 and coil 17 via resistor 18. Therefore, the frequencies of FIG. 6a, which is a diagram showing the output waveform of the oscillator 19, and FIG. 6b, which is a diagram showing the output waveform at point A, are the same. Furthermore, the peak value is as high as V _OFF . Here, the timing pulse generator 20 is set so that the high level of the timing pulse coincides with the vicinity of the peak of the detection circuit in the non-touch state, and this output is input to the comparator 21 and the touch determination section 22. This input signal causes the output of the comparator 21 to generate pulses at all timings, and the touch determination unit 2
In case 2, since both the timing pulse and the output pulse of the comparator 21 are held at a high level, they are always kept at a low level, and it is determined that the touch is not touched.

Next, when one of each of the switches 10 to 13 on the input panel 9 is touched, the capacitor 1 is
6. It becomes a composite resonant circuit of the coil 17, the touch capacitance, and the coil 15, and the peak point is attenuated, and
During the period exhibiting transient characteristics, the oscillator 19 temporarily
The resonant frequency will be different from the output frequency from the

FIG. 6c is an output waveform diagram at point A showing this, and unlike FIG. 6a, which is an output waveform diagram of the oscillator 19, both the peak point and the frequency are shifted. FIG. 7a is a diagram showing this in detail, showing the waveform when the touch is not made and the waveform when the touch is made.

Here, as shown in FIG. 7b, if we look at the output level at timings synchronized with the frequency of the oscillator 19 as T ₁ , T ₂ , T ₃ . . . , when the waveform is touched,
The level is lower than that peak. For example, at point E at timing _T9 , the level is much lower than the peak point.

FIG. 8 is a waveform diagram when the threshold value Vth is set lower than the peak value at the time of touch. Furthermore, as mentioned above, since the timing pulse generator 20 is set so that the high level of the timing pulse coincides with the vicinity of the peak of the detection circuit output in the non-touch state,
The level comparison operation of the comparator 21 uses the timing pulse as a strobe, and operates only during the high level period of the timing pulse.

Therefore, the timing pulse from the timing pulse generator 20 has the waveform shown in FIG. 8b, which deviates from the peak time of the waveform shown in FIG. 8a, which is the output waveform at point A. Therefore, the level of the detection circuit output during the high level period of the timing pulse is not near the peak, but is much smaller than the peak value at point F.
becomes.

Therefore, during the period when the timing pulse is at a high level, it is less than the threshold value Vth, and therefore, as shown in FIG.
As shown, no pulse waveform is generated at the output point B of the comparator 21. For this reason, the touch determination unit 22 determines that a touch has been made, as shown in FIG. 8d, since the timing pulse from the timing pulse generator 20 is at high level while the comparator output is at low level. In this way, the output at point C is changed from low level to high level.

Therefore, in the present invention, the output level is searched in synchronization with the timing pulse generated from the timing pulse generator 20 by utilizing the temporary shift in the resonance frequency when the switches 10 to 13 on the input panel 9 are touched. Detection sensitivity can be improved.

In addition, in the above-mentioned operation, the multiplexer 14
is configured to scan each of the switches 10 to 13, and the response to a touch is when the multiplexer 14 selects the touched switch. Note that if there is only one touch switch, the multiplexer 14 is not necessary.

〔Effect of the invention〕

As described above in detail, the present invention has the effect of improving detection sensitivity and being able to reliably detect a touch even with a small touch capacitance.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional touch detection circuit;
The figure is an output waveform diagram at point A, Figure 3a is an output waveform diagram at point A, Figure 3b is an output waveform diagram at point B, and Figure 3a is an output waveform diagram at point B.
Figure c is an output waveform diagram at point C, Figure 4 a is an output waveform diagram at point A when touched, and Figure 4 b is an output waveform diagram at point B when touched.
Figure 4c is an output waveform diagram at point C when touched, Figure 5 is a configuration diagram of the touch detection circuit according to the present invention, Figure 6a is an oscillator output waveform diagram,
Figure 6b is an output waveform diagram at point A when the touch input device of the present invention is not touched, Figure 6c is an output waveform diagram at point A when the touch input device is touched, and Figure 7a is when it is touched. Figure 7b is a waveform diagram showing the relationship between Figure 7a and timing time, and Figure 8a is the output waveform diagram at point A when touched and when not touched. Figure 8b is an output waveform diagram at point D of the touch input device of the present invention, Figure 8c is an output waveform diagram at point B of the touch input device, and Figure 8d is a diagram of the output waveform at point B of the touch input device. It is an output waveform diagram at point C. 9...Input panel, 10, 11, 12, 13...
...Switch, 14...Multiplexer, 15,1
7... Coil, 16... Capacitor, 18... Resistor, 19... Oscillator, 20... Timing pulse generation circuit, 21... Comparator, 22... Touch determination unit, 23... Power supply.

Claims (1)

[Claims] 1 In an input device consisting of a touch detection section that detects an electrical change based on an instruction operation to the touch detection electrode with a detection circuit composed of an oscillator and a resonant circuit, an electrical change based on an instruction operation to the touch detection electrode is detected. A coordinate input device characterized in that touch detection is performed by sequentially searching for changes in the detection circuit output at timings synchronized with the oscillation frequency of the oscillator.