JP2013069079A - Capacitive touch panel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a capacitive touch panel having high accuracy in detecting an input operation position.SOLUTION: A potential between a uniformly conductive layer laminated on an input operation surface and a reference node is vibrated at a natural frequency f. A signal detection circuit detects a natural oscillation signal with the natural frequency f appearing in each detection electrode relatively to the reference node. Then, signal voltages are compared with each other to detect an input operation position. The signal voltage of the natural oscillation signal with the natural frequency f is not detected in an input standby state, so that the signal voltage appearing in each detection electrode due to the approach of an input operation body can be detected with high accuracy.

Description

  The present invention relates to a capacitive touch panel that detects an input operation position of an input operation that causes an input operation body to approach a conductive layer on an insulating panel via an insulating protective layer, and more specifically, a resistance value per unit length. The present invention relates to a surface-type capacitive touch panel in which a plurality of detection electrodes are connected around a uniform conductive layer, and a signal voltage appearing on each detection electrode is compared to detect an input operation position.

  A conductive layer covered with an insulating protective layer such as synthetic resin or glass is formed on the input operation surface on an insulating substrate as a pointing device that inputs position coordinates indicating the input operation position to higher-level models such as electronic devices and mobile phones. There is also known a capacitive touch panel that detects an input operation position of an input operation body such as a finger approaching a conductive layer through an electrostatic capacitance of an insulating protective layer. In this capacitive touch panel, an insulating substrate, a conductive layer and an insulating protective layer laminated on the surface thereof can be formed of a transparent material, so that they are arranged on a display such as a liquid crystal display device and displayed on the display. While looking at the icon, input and cursor movement operations can be performed, and the display can be protected from mechanical external force by a hard insulating substrate.

  In the capacitive touch panel, a plurality of detection electrode patterns are further arranged along the detection direction on the insulating substrate, and an input operation is performed from the detection electrode pattern arrangement position where the input operation body approaches and the capacitance increases. Compare the signal level of the projection type that detects the position and the detection electrode that forms the uniform conductive layer evenly on the surface of the input operation surface and connects the natural oscillation signal flowing through the input operation body to the four corners of the uniform conductive layer. And surface type for detecting the input operation position (Patent Document 1).

  In the projection type, when the input operation surface is enlarged, the number of detection electrode patterns is increased accordingly, and the detection time for scanning all to detect the input operation position is extended, so the input operation surface is enlarged. The surface type capacitive touch panel is used. Hereinafter, the surface-type capacitive touch panel 100 described in Patent Document 1 will be described with reference to FIG.

  In this conventional surface capacitive touch panel 100, a uniform transparent conductive layer 102 having a constant resistance value per unit length is formed on the input operation surface of the surface of the insulating substrate 101. Detection electrodes 103 a and 103 d are connected to the four corners around the transparent conductive layer 102, and the entire surface is covered with an insulating protective layer 104. Each of the detection electrodes 103a and 103d includes a current detection circuit 105 that detects the signal currents Ia and ~ Id flowing through the detection electrodes 103a and 103d, and a predetermined reference node (for example, a ground pattern wired in the touch panel 100). An AC power source 107 that applies an alternating voltage of a predetermined frequency to the detection electrodes 103a and 103d with respect to the potential of 106 is connected.

  Therefore, the potentials of the detection electrodes 103 a to 103 d and the transparent conductive layer 102 vary with the potential of the AC voltage output from the AC power source 107. As shown in the figure, when an input operation is performed with the finger 110 as an input operation body approaching the input operation surface, the finger 110 is slightly moved from the input operation position of the transparent conductive layer 102 via the capacitance of the insulating protective layer 104. Current I flows. This minute current I is the sum of the signal currents Ia and .about.Id flowing through the detection electrodes 103a and 103d, and the circuit constants of the current detection circuit 105 and the AC power source 106 connected to the detection electrodes 103a and 103d are the same. In this case, the signal currents Ia and ˜Id are shunted by the resistance values Ra and ˜Rd of the transparent conductive layer 102 that are proportional to the distances between the detection electrodes 103a and 103d and the input operation positions.

The input operation position (x, y) in the XY direction shown in the figure is, for example, with k1 and k2 as constants.
x = k1 + k2 · (Ib + Ic) / (Ia + Ib + Ic + Id) (1)
y = k1 + k2 · (Ia + Ib) / (Ia + Ib + Ic + Id) (2) is obtained from the equation (2). Therefore, the signal currents Ia and ˜Id are detected using the current detection circuit 105, and the equations (1) and (2) are obtained. Is used to detect the input operation position (x, y).

JP 2010-262626 A

  However, in the conventional capacitive touch panel 100 exemplified in Patent Document 1, the current I that flows through the input operation body 110 close to the input operation surface is an operator or operator 108 with a very high impedance and the reference node 106. Since the signal currents Ia and Id flowing through the detection electrodes 103a and 103d are further shunted, the current detection circuit 105 accurately determines the value. It was difficult to detect.

  Even when the input operation is not performed, the transparent conductive layer 102 fluctuates with the potential of the AC voltage output from the AC power source 106, so that radiated electromagnetic waves are radiated from the surface, and the radiated current is reduced. By flowing, the current detection circuit 105 always detects a certain amount of standby currents Ia ′ and ˜Id ′. Therefore, the signal currents Ia and ˜Id need to be obtained from the difference between the current value actually detected by the current detection circuit 105 and the standby currents Ia ′ and ˜Id ′. Or the input operation position detection accuracy is reduced.

  Further, since an AC voltage is applied to the transparent conductive layer 102 via the detection electrodes 103a and 103d, the signal voltage appearing superimposed on the detection electrodes 103a and 103d when the input operation body approaches is detected. The current detection circuit 105 detects the signal currents Ia and ˜Id. However, it is difficult to detect the current value itself, and the signal currents Ia and ~ Id are unsuitable for arithmetic processing using the formulas (1) and (2) by a microcomputer or the like. Eventually, the signal currents Ia and ˜Id were passed through the internal resistors, and the signal currents Ia and ˜Id had to be converted into voltages at both ends of the internal resistors.

  The present invention has been made in consideration of such conventional problems, and an object of the present invention is to provide a capacitive touch panel with high detection accuracy of the input operation itself and the input operation position.

  It is another object of the present invention to provide a capacitive touch panel that can detect an input operation position with a simple configuration that does not use a current detection circuit.

  In order to achieve the above object, the capacitive touch panel according to claim 1 has a uniform conductive layer having a constant resistance value per unit length and an insulating protective layer covering the uniform conductive layer on the input operation surface. An insulating substrate, a plurality of detection electrodes connected to the uniform conductive layer at positions around the uniform conductive layer, and a natural oscillation signal having a natural frequency f are output, and the potential of the uniform conductive layer is set at the natural frequency f. A signal output circuit that vibrates and a signal detection circuit that detects a signal voltage of a specific oscillation signal that appears at each detection electrode from the voltage of each detection electrode with respect to a reference node, and an input operation that causes the input operation body to approach the input operation surface The capacitive touch panel detects the input operation position from the signal voltage of the natural oscillation signal detected for each detection electrode and the connection position of each detection electrode to the uniform conductive layer, one of which is grounded or fixed. A low-voltage reference power supply line and a high-voltage reference power supply line, a DC power supply that outputs a DC voltage between the low-voltage reference power supply line and the high-voltage reference power supply line, a low-voltage vibration power supply line, and a high-voltage A vibration power supply circuit in which a vibration power supply line is wired, a first inductor connected between the low-voltage reference power supply line and the low-voltage vibration power supply line and having a high impedance with respect to a natural oscillation signal having a natural frequency f, a high-voltage reference power supply line, A second inductor connected between the vibration power supply lines and having a high impedance with respect to the natural oscillation signal of the natural frequency f, and all the detection electrodes and reference nodes are connected to the low-voltage vibration power supply line or the high-voltage vibration power supply line. In addition to connecting, the signal output circuit and signal detection circuit are connected to the vibration power supply circuit, driven by the output of the DC power supply via the first inductor and the second inductor, and output from the signal output circuit Is output to the low-voltage reference power supply line and the high-voltage reference power supply line of the reference power supply circuit through the capacitor, and the potential of the uniform conductive layer connected to each detection electrode and the reference node of the signal detection circuit is set to the natural frequency f. It is characterized by vibrating.

  Since the reference power supply circuit and the vibration power supply circuit are connected via the first inductor and the second inductor that have high impedance to the natural oscillation signal having the natural frequency f, when the natural oscillation signal is output to the reference power supply circuit, the reference power supply circuit The voltage between the circuit and the vibration power supply circuit relatively varies at the natural frequency f of the natural oscillation signal. Since one of the low-voltage reference power supply line and the high-voltage reference power supply line of the reference power supply circuit is grounded or at a constant potential, the potential of the reference power supply circuit is stable and the potential of the vibration power supply circuit varies at the natural frequency f. Therefore, in a standby state where the input operation body does not approach, all the detection electrodes connected to the low-voltage vibration power supply line or the high-voltage vibration power supply line and the reference node vibrate at the natural frequency f with the same potential or constant voltage, and the signal detection circuit The natural oscillation signal having the natural frequency f does not appear in the voltage of each detection electrode to be detected. On the other hand, when the input operating body at the ground or constant potential approaches the uniform conductive layer that vibrates at the natural frequency f, the input operating body vibrates at the natural frequency f relative to the potential of the reference node. A natural oscillation signal having a natural frequency f appears in FIG. Since the natural oscillation signal is attenuated according to the distance between the input operation position and each detection electrode, the input operation of the input operation is determined from the signal voltage of the natural oscillation signal having the natural frequency f appearing on each detection electrode and the arrangement position of each detection electrode. The position is detected.

The capacitive touch panel according to claim 2, wherein the combined inductance of the first inductor and the second inductor between the reference power supply circuit and the vibration power supply circuit is L / 2, the signal output circuit and the low-voltage side power supply line of the reference power supply circuit, and the signal When the combined capacitance of the capacitors interposed between the output circuit and the high-voltage power supply line of the reference power supply circuit is 2C, the natural frequency f of the natural oscillation signal is
f = 1 / [2π (LC) ^1/2 ]
It is characterized by.

The first inductor and the second inductor between the reference power supply circuit and the vibration power supply circuit, and the capacitor between the signal output circuit and the reference power supply circuit are connected in series, and the natural frequency f is 1 / [2π (LC) ^1/2 ]. When the natural oscillation signal flows, the voltage Vo of the vibration power supply circuit that resonates in series and vibrates with respect to the voltage Vi of the natural oscillation signal is theoretically infinite. Accordingly, the potential of the uniform conductive layer connected to the vibration power supply circuit can be expanded and vibrated, and even if the current value of the characteristic oscillation signal generated on the input operation body side is relatively small, the characteristic signal appearing on the detection electrode is displayed. The signal voltage of the oscillation signal can be expanded to a level where detection is easy.

  According to another aspect of the present invention, the signal output circuit is composed of a microprocessor connected to the vibration power supply circuit and driven by the output of the DC power supply, and the frequency fck of the clock for operating the microprocessor is divided or multiplied. It circulates and outputs the natural oscillation signal of the natural frequency f.

  Since the frequency fck of the clock for operating the microprocessor is divided or multiplied to generate a natural oscillation signal of the natural frequency f, it can also serve as a signal output circuit by adding a simple frequency divider or frequency multiplier to the microprocessor. Can output a natural oscillation signal.

  Further, the natural frequency f and amplitude of the natural oscillation signal can be adjusted by the microprocessor.

  According to the first aspect of the present invention, the uniform conductive layer on the input operation surface side is vibrated at the natural frequency f, and the input operation body relatively generates the natural oscillation signal of the natural frequency f. It is not necessary to prepare a signal output circuit that outputs a natural oscillation signal having a natural frequency f on the body side.

  In the standby state of the input operation, the potential between each detection electrode and the reference node of the signal detection circuit is maintained at a constant voltage, so that the input operation body approaches the uniform conductive layer and the signal of the natural oscillation signal that appears on each detection electrode The voltage can be detected from the voltage oscillating at the natural frequency f by the signal detection circuit. Therefore, it is not necessary to convert a signal current flowing through the detection electrode into a signal voltage using a current detection circuit having a complicated configuration.

  In addition, since the natural oscillation signal of the natural frequency f does not appear in the voltage of each detection electrode detected by the signal detection circuit in a state where the input operation body does not approach the input operation surface, the input operation body approaches each detection. The signal voltage of the natural oscillation signal having the natural frequency f appearing in the electrode voltage can be detected with high accuracy.

  In addition, the reference power supply circuit to which the DC power supply is connected and the vibration power supply circuit to which the detection electrode is connected are separated without using expensive insulating parts such as an insulated DC-DC converter, and the voltage fluctuation of the vibration power supply circuit is independently performed. Can be made.

  According to the invention of claim 2, even if the natural oscillation signal flows through the insulating protective layer with the operator and the current value of the natural oscillation signal that appears in the input operation body is relatively small, the natural frequency f is adjusted. The signal voltage of the natural oscillation signal appearing on the detection electrode can be adjusted to a voltage that can be accurately detected.

  According to the invention of claim 3, the natural oscillation signal having the natural frequency f can be generated from the clock for operating the microprocessor, and there is no need to provide a signal output circuit separately from the microprocessor.

  In addition, the natural frequency f and amplitude of the natural oscillation signal adjusted according to the use environment and the circuit constants of the inductor and capacitor can be easily obtained from the microprocessor.

1 is a block diagram showing a capacitive touch panel 1 according to an embodiment of the present invention. 3 is an equivalent circuit diagram of a power supply circuit of the capacitive touch panel 1. FIG. 1 is a longitudinal sectional view of a capacitive touch panel 1. FIG. 1 is a plan view of a capacitive touch panel 1. FIG. FIG. 6 is an equivalent circuit diagram of a conventional capacitive touch panel 100.

  Hereinafter, a capacitive touch panel (hereinafter referred to as a touch panel) 1 according to an embodiment of the present invention will be described with reference to FIGS. 1 to 4. As shown in FIG. 1, the touch panel 1 includes main circuit components constituting the touch panel 1 divided into two types of a non-vibration side circuit board 2 and a vibration side circuit board 3.

  The non-vibration circuit board 2 is provided with a reference power supply circuit 4 including a low-voltage reference power supply line GND and a high-voltage reference power supply line VCC that are set to the ground potential, and a DC voltage Vcc between the low-voltage reference power supply line GND and the high-voltage reference power supply line VCC. Is connected to a DC power source 5. Thereby, each circuit component such as the interface circuit 6 mounted on the non-vibration circuit board 2 is connected to the reference power supply circuit 4 and driven by the output voltage Vcc of the DC power supply 5.

  Further, the vibration side circuit board 3 is provided with a vibration power circuit 7 including a low voltage vibration power line SGND and a high voltage vibration power line SVCC. The low-voltage vibration power supply line SGND is connected to the low-voltage reference power supply line GND, and the high-voltage vibration power supply line SVCC is connected to the high-voltage reference power supply line VCC via the coils 8 and 9, respectively. The inductances of the coil 8 and the coil 9 are both set to values having high impedance with respect to a natural oscillation signal SG having a natural frequency f described later. Here, the coils 8 and 9 having the same inductance L are used. As a result, as shown in FIG. 1, when the natural oscillation signal SG having the natural frequency f is synchronized and output to the low voltage reference power supply line GND and the high voltage reference power supply line VCC of the reference power supply circuit 4, the low voltage reference of the reference power supply circuit 4 is output. Since the power supply line GND is grounded and at a stable potential, the potentials of the low-voltage vibration power supply line SGND and the high-voltage vibration power supply line SVCC of the vibration power supply circuit 7 fluctuate synchronously with the natural frequency f. The DC output voltage Vcc is the same as that of the reference power supply circuit 4.

  On the vibration side circuit board 3 to which the vibration power supply circuit 7 is wired, four types of detection electrodes E1E2, E3, and E4 shown in FIG. 1 are connected to either the low-voltage vibration power supply line SGND or the high-voltage vibration power supply line SVCC of the vibration power supply circuit 7. Here, it is connected to the high-voltage vibration power supply line SVCC.

  The four types of detection electrodes E1E2, E3, and E4 are respectively connected to the four corners of the uniform conductive layer 21 formed on the entire surface serving as the input operation surface of the rectangular insulating substrate 11, as shown in FIGS. The uniform conductive layer 21 is set to the potential of the high-voltage vibration power supply line SVCC. The rectangular insulating substrate 11 may be a part of the vibration side circuit board 3 described above, but is provided separately from the vibration side circuit board 3 here. The uniform conductive layer 21 is formed on the surface of the insulating substrate 11 as a thin film having a thickness of 10 to uniform, and the resistance value per unit length along the surface of the insulating substrate 11 is constant. The entire surface of the uniform conductive layer 21 is covered with an insulating protective layer 22 so that the uniform conductive layer 21 is not deformed or damaged and its resistance value does not change.

  The touch panel 1 configured as described above is arranged on a display device such as a liquid crystal display element so that the display of the display device can be visually observed through the touch panel 1, the insulating substrate 11, the detection electrode E, the uniform conductive layer 21, and the insulation. The protective layer 22 is made of a transparent material.

  The vibration side circuit board 3 further includes circuit elements of an analog multiplexer 12, a signal detection circuit 13, an A / D converter 14, an MPU (microprocessor unit) 10 that also serves as a signal output circuit, and an oscillation circuit 15. Both are connected to the low-voltage vibration power supply line SGND and the high-voltage vibration power supply line SVCC of the vibration power supply circuit 7 and operate by receiving the output voltage Vcc from the DC power supply 5. The reference node for comparing the voltage of each detection electrode E in the signal detection circuit 13 is also connected to either the low-voltage vibration power line SGND or the high-voltage vibration power line SVCC of the vibration power circuit 7, here the high-voltage vibration power line SVCC. doing.

  Each detection electrode E1, E2, E3, E4 is connected to four types of inputs of the analog multiplexer 12, and the analog multiplexer 12 is controlled by switching from the MPU 10 so that each detection electrode E1, E2, E3, E4 is switched and connected to the signal detection circuit 13 through an amplifier circuit (not shown).

  The signal detection circuit 13 is a band-pass filter that cuts low-frequency components such as DC signals and high-frequency noise such as common mode noise by passing a signal in a frequency band centered on the natural frequency f of the natural oscillation signal SG. And an integrating circuit using an operational amplifier for detecting a signal voltage with respect to a reference node of the natural oscillation signal SG output from the band pass filter.

  The output of the band-pass filter is pulled up by a pull-up resistor and clamped by a diode whose forward direction is the direction of the low-voltage oscillation power supply line SGND, and is connected to the inverting input terminal of the operational amplifier constituting the integrating circuit. As a result, the natural oscillation signal SG output from the bandpass filter is clamped at the lowest point (lowest potential) of the AC signal waveform to the potential obtained by adding the forward voltage of the diode to the reference node, and is applied to the inverting input terminal of the operational amplifier. Entered. On the other hand, the reference potential of the non-inverting input terminal of the operational amplifier is also matched with the clamped potential of the inverting input terminal by adding a voltage obtained by adding a DC voltage corresponding to the forward voltage of the diode to the potential of the reference node. As a result, the output voltage of the operational amplifier rises with the elapsed time in proportion to the amplitude (signal voltage) of the natural oscillation signal SG. It can be detected as a signal voltage obtained by expanding the amplitude of the signal SG.

  The signal voltage of the natural oscillation signal SG detected by the signal detection circuit 13 is sampled at a frequency at least twice the natural frequency f by the A / D converter 14 in order to execute arithmetic processing in the MPU 10, and the quantized data Is output to the MPU 10.

  Since the quantized data output from the A / D converter 14 represents the signal voltage of the natural oscillation signal SG that appears at the detection electrode E selectively connected by the analog multiplexer 12 at that time, the MPU 10 displays it in one scanning cycle. The sum of signal voltages appearing at the detection electrodes E1, E2, E3, and E4 output from the A / D converter 14 is compared with a predetermined threshold value. As the finger 20 approaches the input operation surface and the natural oscillation signal SG appears on the detection electrode E, the input operation is determined.

In addition, after the input operation is determined, the individual signal voltages appearing on the detection electrodes E1, E2, E3, and E4 input in one scanning cycle are compared, and the input operation surface on which the finger 20 approaches is compared by a method described later. The upper input operation position (x, y) is detected. Input operation data including the input operation position (x, y) detected by the MPU 10 is output to the interface circuit 6 mounted on the non-vibration circuit board 2 via the signal line 16 in which the direct current is insulated. To the host device that uses the input operation data by USB communication, I ² C communication, or the like.

  The oscillation circuit 15 outputs a clock CK having a fixed frequency fck to the analog multiplexer 12, the signal detection circuit 13, the A / D converter 14, and the MPU 10, and synchronizes the series of operations described above by these circuits.

  The MPU 10 also functions as a signal output circuit that outputs the natural frequency f of the natural oscillation signal SG to the low-voltage reference power supply line GND and the high-voltage reference power supply line VCC of the reference power supply circuit 4. The natural oscillation signal SG having an amplitude (voltage Vp-p between peaks Vp-p) of 5 V is output. The natural frequency f of the natural oscillation signal SG is obtained by dividing or multiplying the frequency fck of the clock CK input from the oscillation circuit 15, and the amplitude (signal voltage) is the low-voltage vibration power supply line SGND and the high-voltage vibration power supply line SVCC. The voltage Vcc between them can be arbitrarily adjusted by increasing or decreasing the voltage Vcc.

  The output of the MPU 10 that outputs the natural oscillation signal SG is bifurcated and connected to the low-voltage reference power supply line GND and the high-voltage reference power supply line VCC of the reference power supply circuit 4 through capacitors 17 and 18, respectively. Since the capacitor 17 and the capacitor 18 are interposed for the purpose of blocking the DC voltage of the power supply line, the respective capacitances are arbitrary, but here, the capacitors 17 and 18 having the same capacitance C are used.

  When the natural oscillation signal SG having the natural frequency f flows in the reference power supply circuit 4 and the vibration power supply circuit 7, the low voltage reference power supply line GND and the high voltage reference power supply line VCC and the low voltage vibration power supply line SGND and the high voltage vibration power supply line SVCC are close to each other. If the power supply lines are short-circuited in the band of the natural frequency f, the reference power supply circuit 4 and the vibration power supply circuit 7 of FIG. 1 are shown in the equivalent circuit diagram of FIG.

As shown in FIG. 2, since capacitors 17 and 18 having a capacitance C are connected in parallel between the output of the MPU 10 and the reference power supply circuit 4, the combined capacitance is 2C, and the reference power supply circuit 4 And the combined inductance of the coils 8 and 9 connected in parallel between the vibration power supply circuit 7 is L / 2. These capacitors and inductors are connected in series in a closed circuit through which the natural oscillation signal SG having the natural frequency f flows. The amplitude (level) of the natural oscillation signal SG is Vi, the reference power supply circuit 4 at both ends of the coils 8 and 9 and the vibration power supply. If the voltage between the circuits 7 is Vo, and the angular velocity represented by 2πf is ω (rad / sec),
Vo = [ω ² LC / (ω ² LC-1)] Vi expressed by the equation (3).
Here, the circuit shown in FIG. 2 resonates in series at ω ² LC = 1, and the frequency f _{0 at} that time is
f ₀ = 1 / [2π (LC) ^1/2 ] (4).

That is, if the resonance frequency f ₀ obtained from the relationship of the equation (4) is the natural frequency f of the natural oscillation signal SG, the vibration power supply circuit 7 is theoretically obtained from the equation (3) with respect to the signal voltage of the natural oscillation signal SG. And the potential of the detection electrode E connected to the vibration power supply circuit 7 and the uniform conductive layer 21 can be vibrated infinitely. As a result, even if the capacitance between the uniform conductive layer 21 and the finger 20 through the insulating protective layer 22 is very small and the impedance between the input operator and the vibration power supply circuit 7 is extremely high, the detection electrode E and the finger Since the signal voltage appearing between 20 can theoretically be arbitrarily increased to infinity, the signal voltage of the natural oscillation signal SG appearing at the detection electrode E can be raised to a level detectable by the signal detection circuit 14.

  For example, in the touch panel 1 shown in FIG. 1, assuming that the inductances of the coils 8 and 9 are 220 μH and the capacitances of the capacitors 17 and 18 are 330 pF, the amplitude (Vp−p) of the natural oscillation signal SG is 5 V and the natural frequency f is 187 kHz. Is output from the MPU 10, and it was actually measured that the vibration power supply circuit 7 and the detection electrode E connected to the vibration power supply circuit 7 vibrate with an amplitude (Vp-p) of 20V that is four times.

The actual touch panel 1 does not resonate at the frequency f ₀ obtained from the equation (4) due to the influence of the inductance, stray capacitance, etc. of the reference power supply circuit 4 and the vibration power supply circuit 7, and the reference power supply circuit 4 and the vibration power supply circuit 7 Due to the energy loss or the like when the natural oscillation signal SG flows in the oscillation power supply circuit 7, the potential vibrates with the amplitude expanded to a finite magnification with respect to the level of the natural oscillation signal SG. On the other hand, it is impossible to flow a specific oscillation signal SG of a large current through the operator's finger 20, or remove the natural frequency f of the natural oscillation signal SG from the resonance frequency f _0, the inherent oscillation signal SG outputted from the MPU10 The amplitude is adjusted, and the upper limit of the signal voltage appearing at the detection electrode E is set within the signal voltage range in which the input operation position (x, y) can be reliably detected.

  An operation for detecting the input operation position of the finger 20 by the touch panel 1 configured as described above will be described below. In the standby state where no input operation is performed, the detection electrode E connected to the uniform conductive layer 21 vibrates at the natural frequency f, but the signal detection circuit 14 also vibrates at the natural frequency f due to an equipotential difference. There is no signal passing through the band-pass filter of the signal detection circuit 14. Since both the pair of inputs of the operational amplifier constituting the integrating circuit are equipotentials obtained by adding the forward voltage Vf of the diode to the reference node connected to the low-voltage oscillation power supply line SGND, the output voltage of the operational amplifier is a predetermined period later. And the signal voltage of the natural oscillation signal SG is not detected. Therefore, the sum of the signal voltages output from the signal detection circuit 14 in one scanning cycle is also less than the predetermined threshold value, and it is determined that no input operation is performed.

  When the finger 20 approaches the uniform conductive layer 21 on the input operation surface by the input operation, all the detection electrodes E are connected to the high-voltage vibration power supply line SVCC, so that the potential of the uniform conductive layer 21 vibrates at the natural frequency f. On the other hand, since the potential of the finger 20 of the operator whose part such as the foot is grounded is a constant potential, as shown in FIG. 3, from the position (input operation position) of the uniform conductive layer 21 where the finger 20 approaches. A natural oscillation signal SG having a natural frequency f is output to the finger 20 through the insulating protective layer 22. If this is seen from each element of the signal circuit side circuit board 3 that vibrates at the natural frequency f, the natural oscillation signal of the natural frequency f output from the finger 20 is input to the input operation position (x, y) of the uniform conductive layer 21. In the signal detection circuit 13 that appears as input and is driven by the vibration power supply circuit 7, the natural oscillation signal SG of the natural frequency f that appears at each detection electrode E is detected. Accordingly, when the sum of the signal voltages output from the signal detection circuit 14 in one scanning cycle is equal to or greater than a predetermined threshold value, it is determined that an input operation has been performed, and then the input operation position (x, y) is determined. To detect.

  The signal voltage of the natural oscillation signal SG appearing on each detection electrode E depends on the distance from each detection electrode E1, E2, E3, E4 to the input operation position (x, y). That is, the signal voltage of the natural oscillation signal SG appearing at each detection electrode E is the sum of the internal resistance r0 between each detection electrode E and the reference node and the resistance value r between each detection electrode E and the input operation position (x, y). The resistance values r1, r2, r3, r4 of the uniform conductive layer 21 from the detection electrodes E1, E2, E3, E4 to the input operation position (x, y) shown in FIG. Since it is almost proportional, the input operation position from each of the detection electrodes E1, E2, E3, E4 at the four corners of the input operation surface from the signal voltage of each detection electrode E1, E2, E3, E4 input to the MPU 10 in one scanning period. The distance L to (x, y) is calculated, and the input operation position (x, y) on the input operation surface where the finger 20 approaches is detected.

  In the above-described embodiment, the four detection electrodes E1, E2, E3, and E4 are arranged at the four corners of the input operation surface. However, the number and arrangement position are not limited to the above-described example, and for example, input on a straight line In the case of detecting the operation position, a pair of detection electrodes E may be arranged along the linear direction.

  The signal output circuit that also serves as the PMU 10 may be mounted separately from the MPU 10 on the vibration side circuit board 3 as long as it is connected to and driven by the vibration power supply circuit 7.

  Further, the input operation body 20 has been described with the finger 20 on which the operator performs an input operation. However, the input operation body 20 may be an operation body different from the operator, such as a dedicated input pen held by the operator.

  Further, although the low-voltage reference power line GND is grounded and the reference power supply circuit 4 is set to a constant potential, the means for setting the constant potential is not limited to this method, and the low-voltage reference power line GND and the high-voltage reference power line VCC are input operators. As long as the finger 20 and the input operating body are kept at a constant potential, the method is arbitrary.

  The present invention is suitable for a capacitive touch panel that detects an input operation position of an input operation body in a non-contact manner through an insulating protective layer.

1 Capacitive touch panel 4 Reference power supply circuit 5 DC power supply (DC power supply)
7 Vibration Power Supply Circuit 8 First Inductor 9 Second Inductor 10 Signal Output Circuit (MPU)
11 Insulating substrate 13 Signal detection circuit 17 Capacitor 18 Capacitor 20 Input operation body (finger)
21 Uniform conductive layer 22 Insulation protective layer E Detection electrode GND Low voltage reference power line VCC High voltage reference power line SGND Low voltage vibration power line SVCC High voltage vibration power line

Claims (3)

An insulating substrate in which a uniform conductive layer having a constant resistance value per unit length and an insulating protective layer covering the uniform conductive layer are laminated on the input operation surface;
A plurality of detection electrodes connected to the uniform conductive layer at positions apart from each other around the uniform conductive layer;
A signal output circuit that outputs a natural oscillation signal having a natural frequency f and vibrates the potential of the uniform conductive layer at the natural frequency f;
A signal detection circuit for detecting the signal voltage of the natural oscillation signal appearing on each detection electrode from the voltage of each detection electrode relative to the reference node;
Capacitance for detecting the input operation position of the input operation for bringing the input operation body close to the input operation surface from the signal voltage of the natural oscillation signal detected for each detection electrode and the connection position of each detection electrode to the uniform conductive layer Type touch panel,
A low-voltage reference power line with one side grounded or at a constant potential and a reference power supply circuit wired with a high-voltage reference power line;
A DC power supply that outputs a DC voltage between the low-voltage reference power supply line and the high-voltage reference power supply line of the reference power supply circuit;
A vibration power supply circuit in which a low-voltage vibration power supply line and a high-voltage vibration power supply line are wired;
A first inductor connected between the low-voltage reference power line and the low-voltage vibration power line, and having a high impedance with respect to the natural oscillation signal having the natural frequency f;
A second inductor connected between the high-voltage reference power line and the high-voltage vibration power line and having a high impedance with respect to the natural oscillation signal of the natural frequency f;
All the detection electrodes and the reference node are connected to the low-voltage vibration power supply line or the high-voltage vibration power supply line, and the signal output circuit and the signal detection circuit are connected to the vibration power supply circuit, and the DC power source is connected via the first inductor and the second inductor. Drive with
The characteristic oscillation signal output from the signal output circuit is output to the low-voltage reference power line and the high-voltage reference power line of the reference power supply circuit through the capacitor, and the uniform conductive layer connected to each detection electrode and the reference node of the signal detection circuit A capacitive touch panel that vibrates an electric potential at a natural frequency f. The combined inductance of the first inductor and the second inductor between the reference power supply circuit and the vibration power supply circuit is L / 2, between the signal output circuit and the low voltage side power supply line of the reference power supply circuit, and between the signal output circuit and the high voltage side power supply line of the reference power supply circuit When the combined capacitance of the capacitors interposed between them is 2C, the natural frequency f of the natural oscillation signal is
f = 1 / [2π (LC) ^1/2 ]
The capacitive touch panel according to claim 1, wherein: The signal output circuit is composed of a microprocessor connected to the vibration power supply circuit and driven by the output of the DC power supply,
3. The capacitive touch panel according to claim 1, wherein the frequency fck of a clock for operating the microprocessor is divided or multiplied to output a natural oscillation signal having a natural frequency f.

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