TWI507951B - Capacitive touch panel - Google Patents

Description

Capacitive touch panel

The present invention relates to a capacitive touch panel that detects an input operation of a detecting electrode disposed on an insulating panel in a non-contact manner in accordance with an increase in a floating capacitance of a detecting electrode.

A pointing device that inputs an icon (icon) displayed on a display of an electronic device, etc., when an input operation body approaches a input operation surface such as a finger, a capacitance in the vicinity thereof changes, according to static electricity The capacitance change, even on the back side of the display, is known to be non-contact to detect the input operation of the capacitive touch panel.

In the conventional capacitive touch panel, a plurality of X electrodes and Y electrodes are insulated from each other on the input operation surface, and are formed in a matrix shape so as to intersect with each other. Since the electrostatic capacitance between the X electrode and the Y electrode changes, an input operation of the arrangement position of the X electrode and the Y electrode after the change in electrostatic capacitance is detected (Patent Document 1).

In the capacitive touch panel described in Patent Document 1, a predetermined pulse voltage is sequentially applied to a plurality of Y electrodes and scanned to detect voltages of the respective X electrodes that intersect the Y electrode to which the pulse voltage is applied. . When an input device such as a finger is brought close to the insulating panel, the capacitance between the X electrode and the Y electrode that intersects at the position where the input operating body approaches is changed, and the X electrode whose voltage changes due to the change in the electrostatic capacitance is changed. And the arrangement position of the Y electrode to which the pulse voltage is applied at this time, to detect the operation position of the input operating body to the insulating panel.

However, if the input operation surface of the insulating panel is large, as the input area increases, the number of X electrodes and Y electrodes that detect changes in electrostatic capacitance increases, and the scanning period for scanning the intersection position of each electrode It will become longer, and there will be problems in that the input operation position cannot be detected in a short time. Further, in addition to the means for applying a pulse voltage, in order to scan a plurality of X electrodes and Y electrodes wired in a matrix, it is necessary to use a multiplexer corresponding to an appropriate number, and the circuit configuration is complicated and large. problem.

Therefore, with a simpler circuit configuration for detecting a change in the electrostatic capacitance (floating capacitance) of the detecting electrode, the unknown at the input operating position is detected based on the time constant of the electrostatic capacitance and the known resistance value. The method of electrostatic capacitance is known. The detection method is a CR time constant circuit in which a capacitor C belonging to an electrostatic capacitance of an unknown capacitance is connected in series or in parallel to the detection resistor R, and applying a predetermined voltage Vdd to one side of the detection resistor R or grounding one side depends on The potential of the capacitor C which rises or falls with the time constant rc determined by the capacitance c of the capacitor C and the resistance value r of the detection resistor R is compared with a predetermined critical potential, and the static electricity is judged by the charging time or the discharge time reaching the critical potential. The size of the capacitor. According to this detection method, the floating capacitance of the detecting electrode disposed on the insulating panel (the electrostatic capacitance between the detecting electrode and the ground) increases as the input operating body such as a finger approaches, and the charging and discharging time becomes longer. The charge/discharge time count until the potential of the detection electrode becomes a predetermined critical potential is compared with the charge/discharge time when the input operation is not performed, and the presence or absence of the input operation close to the detection electrode can be detected.

However, the floating capacitance c when the finger is brought close to the detecting electrode is slightly increased by a few pF from about 10 pF. Therefore, the detection method using the CR time constant circuit is to connect the 10 MΩ detecting resistors in series in order to detect, for example, an electrostatic capacitance of 1 pF. The time constant is also changed by only 10 μsec, and it is extremely difficult to directly detect the input operation to the detecting electrode based on the comparison of the charging time or the discharging time until reaching the critical potential. In order to solve this problem, a method of increasing the resistance value of the detecting resistor is considered. However, a high impedance close to the insulating state is formed, and a detection current is passed through the microcomputer or the like to which the detection voltage is applied, and detection is impossible. Therefore, a charge conversion type electrostatic capacitance detecting method in which a capacitor having a larger capacitance is prepared and the charge of the floating capacitor is repeatedly transferred to the capacitor and the charging time of the capacitor is compared has been proposed (Patent Document 2).

Hereinafter, a method of detecting a capacitance of a charge conversion method will be described using FIG. 5 and FIG. The capacitor C1 shown in Fig. 5 is a capacitor for detecting a small capacitance c1 of a change in capacitance, for example, a capacitor having a minute floating capacitance generated between an operator's finger and a pattern. One side of the capacitor C1 is grounded by the operator, and while the other side SW1 is in the ON operation, it is charged by the charging voltage Vdd. Further, in parallel with the capacitor C1, a capacitor C2 whose capacitance relative to the capacitor C1 is a sufficiently large capacitor c2 is connected through the SW2.

In the detection circuit configured as described above, in the first step, SW1 is turned ON, SW2 is turned OFF, capacitor C1 is charged by charging voltage Vdd, and after charging, SW1 and SW2 are turned on in the second step. Both are formed as OFF. In the second step, the voltage V1 of the capacitor C1 is Vdd. Next, in the third step, SW1 is turned OFF, SW2 is turned ON, a part of the charged electric charge of the capacitor C1 is transferred to the capacitor C2, and then, in the fourth step, SW1 and SW2 are both turned OFF again. . In the fourth step, the voltage V1 of the capacitor C1 and the voltage V2 of the capacitor C2 are equal.

The voltage V2 of the capacitor C2 at the time of the Nth step to the fourth step is expressed by V2 = Vdd × (1 - c2 / (c1 + c2) ^N ), and the charging voltage Vdd and the capacitance c2 of the capacitor C2 are already Therefore, the capacitance C1 of the capacitor C1 to be detected can be obtained by determining the number N of times when the voltage V2 of the capacitor C2 reaches the critical potential Vref set to 1/2 of the charging voltage Vdd shown in FIG. .

As shown in Fig. 6, as the electrostatic capacitance c1 increases, the number N of repetitions reaching Vref becomes shorter. Therefore, if only the input operation body is close to the detection electrode, that is, a sufficient capacitance type touch panel is used, the number of repetitions will be repeated. The threshold value Nref is set to, for example, 1100 in the figure. When the number of repetitions shorter than the threshold value Nref reaches Vref, a finger having an input operation is approached to generate a floating capacitance of 10 pF or more to detect the detection electrode. Enter the action.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] JP-A-2005-337773 (Instruction Item 0017 to Item 0031, Figure 1)

[Patent Document 2] JP-A-2009-70004 (Instruction Item 0014 to Item 0020, Fig. 2)

In the conventional capacitive touch panel described in Patent Document 1, since it is necessary to apply a pulse voltage to all of the detecting electrodes, the floating capacitance of all the detecting electrodes can be charged and discharged at the same time, and the detection can be performed in a shorter time. It is preferable to detect the CR time constant circuit in which the capacitance is changed. However, since the change in the floating capacitance due to the input operation is small, it is difficult to detect the situation from the difference in charge and discharge time until the critical potential is reached. The detection is performed by expanding the charge conversion method described in Patent Document 2.

However, this charge conversion method is necessary to control the operation of SW1 and SW2 1000 times or more in order to detect a change in electrostatic capacitance once. As a result, the input operation close to the detection electrode cannot be detected by a change in the floating capacitance in a short time.

The present invention has been made in view of the conventional problems as described above, and aims to provide a change in the floating capacitance of a plurality of detecting electrodes at the same time, and further, even if the variation of the floating capacitance is small, it is possible to reach the critical potential. The charge and discharge time is used to detect the capacitive touch panel of the input operation of the detecting electrode.

Further, it is an object of the invention to provide a capacitive touch panel which can select a voltage control method with higher detection accuracy in accordance with a threshold potential which is compared with a charging voltage Vdd or a potential Vc of a detecting electrode.

In order to achieve the above object, the capacitive touch panel of claim 1 is characterized in that: the detecting electrode is disposed on the insulating panel, and the floating capacitance increases as the input operating body is approached; the resistive element is attached to the detecting electrode A CR time constant circuit is formed between the values of the floating capacitors; the charge and discharge switch connects the common terminal on one side of the resistive element to the switching terminal located at a predetermined charging potential or ground potential from the reference, and the CR time constant is The time constant of the circuit charges or discharges the floating capacitor, increases the potential of the detecting electrode from the ground potential to the charging potential, or decreases the charging potential to the ground potential; and the timing means measures the floating capacitor by the reference. Or an electric discharge, and an elapsed time from a potential of the detecting electrode at the charging potential or the ground potential to a predetermined critical potential set between the charging potential and the ground potential, and an elapsed time which increases as the floating capacitance increases To detect an input operation of the position of the detecting electrode, the electrostatic capacitance side The touch panel is characterized in that: the charge-discharge relationship is controlled by switching the PWM pulse signal of the fixed-frequency rectangular wave pulse signal with a predetermined modulation value to be pulse-width modulated, according to the binary value of the PWM modulation signal. The signal value, the common terminal on one side of the resistive element is closely separated from the aforementioned switching terminal.

The PWM modulation signal changes the duty ratio of the binary signal value for switching the charge and discharge switch according to the modulation value. One side of the resistance element is between the charging potential or the ground potential and the open potential. The time interval determined by the modulation value is compared to alternate switching. One side of the resistive element is located at a charging potential or a ground potential, and the potential of the detecting electrode at the ground potential or the charging potential rises or falls according to a time constant determined by the resistance value of the resistor and the floating capacitance, but is located at During the period of the open potential, the potential of the detecting electrode does not change, and its rise or fall stops. Therefore, the slope at which the potential of the detecting electrode changes when the floating capacitor is charged and discharged is lowered, and the elapsed time from the reference time to the potential of the detecting electrode reaching the critical potential can be lengthened according to the modulation value, so that even the input operation is caused. The floating capacitance is a small increase and can also be detected based on the increased elapsed time.

In the capacitive touch panel of claim 2, the charge/discharge relationship is applied to the first switching terminal at the charging potential, the second switching terminal at the ground potential, and the third switching switch that is open by the PWM modulation signal. Any one of the terminals switches the connection of the common terminal, and switches the connection of the common terminal to the first switching terminal and the third switching terminal according to the binary signal value of the PWM modulation signal. The floating capacitance of the detecting electrode is charged, and/or the switching capacitance between the second switching terminal and the third switching terminal is switched to discharge the floating capacitance of the detecting electrode.

When the charging control of the floating capacitor is performed, the connection of the common terminal is switched between the first switching terminal and the third switching terminal, and during the discharging control, the connection of the common terminal is between the second switching terminal and the third switching terminal. In the case of a switching connection, a common charge and discharge switch can extend the elapsed time from the reference time to the potential of the detecting electrode to the critical potential in accordance with the modulation value.

In the capacitive touch panel of claim 3, the resistive element and the charge-discharge relationship are provided for each of the plurality of detecting electrodes disposed on each of the insulating panels, and the measured time is measured for each detecting electrode. Time, the input operation position is detected by the position of the detection electrode whose elapsed time is increased.

For most of the detecting electrodes, a CR time constant circuit is used to detect the change of the floating capacitance of each detecting electrode, so that the floating capacitances of most of the detecting electrodes are simultaneously charged or discharged, and the input operation to any detecting electrodes can be detected in a short time. .

According to the invention of claim 1, the CR time constant circuit is used, and even if the increase in the floating capacitance of the detecting electrode due to the input operation is small, the input operation to the detecting electrode can be detected.

According to the invention of claim 2, even in the case where the floating capacitor is charged to detect the change thereof and the discharge is detected to detect the change, a common charge and discharge switch can be used, from the reference time to the detecting electrode. The elapsed time until the potential reaches the critical potential is extended by the modulation value, and the floating capacitance of the minute change can be surely detected.

In addition, during the period in which the floating capacitor is charged and the period in which the discharge is performed, the slope of the detected potential changes due to the elapsed time from the reference. Therefore, the slope of the potential of the detecting electrode is set near the critical potential by the critical potential. Smaller, it is possible to select a charge control or discharge control of a floating capacitor that has undergone a more extended time to exhibit a change in floating capacitance.

According to the invention of claim 3, in the period in which the floating capacitor is subjected to charge and discharge control, the change in the floating capacitance of the plurality of detecting electrodes disposed on the insulating panel is detected, and the input operating position can be detected in a short period of time.

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 . The touch panel 1 is provided with a plurality of detecting electrodes 3 ₁ , 3 ₂ , 3 ₃ , and 3 ₄ on the insulating panel (not shown) so as to be insulated from each other by, for example, several mm. The floating capacitance Cs of each of the detecting electrodes 3 is represented by a sum of capacitances formed between the conductive patterns formed around the shielded casing and the ground, but the other capacitances are substantially constant. In contrast, the fingers of the operator are equal. The input operator increases as it approaches. Therefore, the floating capacitances Cs ₁ , Cs ₂ , Cs ₃ , and Cs _{4 of the} respective detecting electrodes 3 are compared, and the input operating body of the input operation is compared with the other detecting electrodes 3 whose floating capacitance Cs is the largest compared with the other. An input operation close to the arrangement position of the detecting electrode 3 is detected.

Here, for convenience of explanation, the touch panel 1 compares the floating capacitances Cs ₁ , Cs ₂ , Cs ₃ , and Cs _{4 of the} four detecting electrodes 3 ₁ , 3 ₂ , 3 ₃ , and 3 ₄ to detect the input operator. Description. In order to compare the floating capacitances Cs ₁ , Cs ₂ , Cs ₃ , and Cs _{4 of} the respective detecting electrodes 3, as shown in FIG. 1 , the floating capacitance Cs is connected to each of the detecting electrodes 3 as a time width of the binary signal c. The capacitor-time conversion circuit 2 that performs the output.

Each of the capacitance-time conversion circuits 2 includes a first switching terminal 4 ₁ that forms a potential of the reference charging voltage Vdd for the common terminal 4c, a second switching terminal 4 ₂ that is formed to have the ground potential GND, and an open 3 switching/discharging switch 4 for switching between terminals 4 ₃ ; detecting resistors R1 and R2 between the common terminal 4c of the charging and discharging switch 4 and the detecting electrode 3; and connecting the non-inverting input to the detecting resistors R1 and R2 At the point, the comparator 5, which is formed as a critical potential _VSH , is inverted. The detecting resistor R2 is a resistor of the detecting electrode 3, and a capacitor having a floating capacitance Cs of the detecting electrode 3 and a detecting resistor R1, R2 connected in series form a CR time constant circuit.

The threshold potential V _SH is a potential that is arbitrarily set between the reference charging voltage Vdd and the ground potential GND, and is set to a potential of 70% of Vdd, whereby the common terminal 4c of the charge and discharge switch 4 is grounded by the ground potential GND. When the switching terminal 4 _{2 is} switched to the first switching terminal 4 ₁ side of the reference charging voltage Vdd, the floating capacitance Cs of the floating resistance Cs is detected by the resistance values r of the detecting resistors R1 and R2 (in the description, the floating capacitance Cs is used) The capacitance of the capacitor is referred to as a time constant csr determined by the floating capacitor cs) to charge the floating capacitor Cs. When the potential of the detecting electrode 3 rising from the ground potential GND exceeds the critical potential _VSH , the output c of the comparator 5 is inverted. .

As shown in FIG. 4, it is assumed that when the microcomputer 5 is in the charging control period Tc, the charge/discharge switch 4 is normally switched by the switching control signal a' of the "H" level, and at the reference time t0 is at the ground potential GND. When the potential Vc of the detecting electrode is set to t by the elapsed time t0 when the reference voltage Tdd is applied and the natural logarithm is ε,

Vc=Vdd(1-ε ^-t/csr )...(1)

It is shown that it rises as shown by b' in the figure, and when the transition period of t = 5csr is passed, the charging voltage Vdd is substantially reached (hereinafter, in the present specification, this is referred to as the reached charging voltage Vdd for convenience of explanation).

Here, in the charging control period Tc, the rising speed of the floating potential Cs at the potential Vc of the detecting electrode 3 when the reference charging voltage Vdd is charged is obtained by multiplying the resistance value r of the detecting resistors R1 and R2 by the floating capacitor cs. The time constant is determined, but mainly depends on the floating capacitance cs. The larger the floating capacitance cs is, the more gentle the voltage rises, and the longer the elapsed time from the reference time t0 to the output c of the comparator 5 is reversed. However, in general, the floating capacitance cs of the detecting electrode 3 is about 10 pF, and the amount of change in the floating capacitance cs which changes due to the proximity of the input operating body such as a finger is about 1 to 3 pF, so the change is made to the output c. The difference in elapsed time until the rotation of the detection resistors R1 and R2 is increased to 10 MΩ, which is a small time of 10 to 30 μsec, which is not easy to discriminate.

Therefore, in the present embodiment, in the charging control period Tc, the common terminal 4c of the charge and discharge switch 4 is at the first switching terminal 4 ₁ and the third switching terminal by the switching control signal a output from the microcomputer 5. Switch between 4 and ₃ to make a connection. The switching control signal a is a PWM modulation circuit 20 described later in the microcomputer 5, and the square wave pulse signal of a fixed frequency is PWM-modulated with a predetermined modulation value, and is formed into a duty ratio D corresponding to the modulation value. The PWM modulation signal is constructed. Here, the 2.5 MHz rectangular wave pulse signal is PWM-modulated, and the microcomputer 5 outputs a PWM modulation signal a having a duty ratio of 0.16 μsec and a duty ratio of 0.4 at a period of 0.4 μsec.

The charge/discharge switch 4 connects the common terminal 4c to the first switching terminal 4 ₁ located at the reference charging voltage Vdd while the switching control signal (PWM modulation signal) a is at the "H" level, and is at the "L" level. The period is connected to the open third switching terminal 4 ₃ . As a result, the potential Vc of the detecting electrode in the charging control period Tc is such that the waveform b of FIG. 4 is amplified, and the switching control signal a is at the "H" level, and rises according to the above formula (1). During the period of the L" level, the potential is maintained and the situation is repeated. In other words, when the switching control signal a is at the "L" level, since the potential Vc of the detecting electrode does not rise, the slope of the rising is reduced by the ratio corresponding to the duty ratio D, as shown by the waveform b in the figure. Rise gently.

By the waveform b of the potential Vc of the detection electrode 3 which is relatively gentle compared with b', the change of the floating capacitance cs of about 1 to 3 pF by the input operation is from the reference time t0 to the critical potential V. The difference in elapsed time from _SH is expanded to 2.5 times 25 to 75 μsec, and the input operation can be sufficiently detected by the difference even if the resolution of the means for measuring the elapsed time described later is low.

In the present embodiment, the resistance values r of the detection resistors R1 and R2 of the capacitance-time conversion circuit 2, the circuit constants of the comparator 5 and the like, and the potential of the critical potential _VSH are for the respective detection electrodes 3 ₁ , 3 ₂ , and 3 _{3 .} 3 and ₄ are the same. Further, each of the charge and discharge switches 4 is simultaneously controlled by the microcomputer 5 shown in FIG. 2 by the same switching control signal a, so that the reference switch t0 is synchronized with the first switching terminal 4 ₁ and third switching terminal ₄₃ for switching between connection.

The change in the floating capacitance cs of the detecting electrode 3 by the input operation can be detected in the same manner in the discharge control period Td after tg at the time of switching. The charge/discharge switch 4 is switched and controlled by the switching control signal a or a'. The potential Vc of the detecting electrode at the charging voltage Vdd at the time of switching is performed by the common terminal 4c of the charge and discharge switch 4 and the ground potential GND. second switching terminal ₄₂ is connected, and that the time constant csr discharge stray capacitance Cs. The potential Vc of the detecting electrode is set to t' when the elapsed time tg when switching is formed as the charging voltage Vdd is

Vc=Vddxε ^-t'/csr (2)

It is shown that when the transition period of t'=5csr is passed, the potential Vc of the detecting electrode reaches substantially the ground potential (hereinafter, in the present specification, it is referred to as having reached the ground potential for convenience of explanation).

In order to detect small changes in the stray capacitance cs occur in controlling the discharge period Td, the microcomputer 5 by the output switching control signal a, the charge-discharge switch common terminal 4c of the second switching terminal ₄₂ and the third in switching between the switching terminals ₄₃ are connected. Here, the switching control signal a is the same as the switching control signal a described in the charging control period Tc, and the switching control signal a is at the "H" level, and the common terminal 4c and the second terminal at the ground potential GND are switching terminal ₄₂ is connected, for the period "L" level, the connection was open to the third switching terminal _43. As a result, the potential Vc of the detecting electrode in the discharge control period Td is a period in which the switching control signal a is at the "H" level, and falls in accordance with the above formula (2), and the period of the "L" level is maintained, and the potential is maintained. This situation. Therefore, the slope of the drop of the potential Vc of the detecting electrode is also gentled by the ratio corresponding to the duty ratio D, which is caused by a small change in the floating capacitance cs due to the input operation, from the switching time tg to the reaching of the critical potential V. The difference in elapsed time from _SH is expanded to 2.5 times the reciprocal of the duty ratio D, and even in the discharge control period Td, the input operation can be sufficiently detected by the difference.

Here, if the potential Vc is compared to the detection electrode potential V _SH is close to the critical charge voltage Vdd, when the charging control by the former, since in the vicinity of the critical potential V _SH is close to the transition period, so the relative elapsed time, less increase in potential Vc of the detection electrodes, when the discharge control by the latter, in the vicinity of the critical potential V _SH, down detection electrode potential Vc is large. Therefore, if the potential V _SH critical potential Vc of the detection electrode for the lower resolution of the comparison circuit comparing, the latter system is appropriate discharge control, if the resolution of the measurement through a lower measurement circuit when the time t, Then the charging control of the former is appropriate.

On the other hand, when the critical potential V _SH compared with the potential Vc of the detecting electrode is close to the ground potential GND, the rise of the potential Vc of the detecting electrode is large near the critical potential V _SH by the charge control of the former. According to the discharge control of the latter, since the vicinity of the critical potential _VSH is close to the transition period, the drop in the potential Vc of the detecting electrode is small. Therefore, when the resolution of the comparison circuit comparing the threshold potential _VSH with the potential Vc of the detecting electrode is low, it is preferable that the charging control of the former is performed, and if the resolution of the measuring circuit for measuring the elapsed time t is low, Therefore, the discharge control of the latter is preferable, and the appropriate control can be selected without changing the circuit configuration depending on the level of the critical potential _VSH or the resolution of the detection circuit.

As shown in Fig. 2, the outputs c1, c2, c3, and c4 of the comparator 5 of each of the capacitance-time conversion circuits 2 are input as parallel data of 4 bits in parallel to the PIPO belonging to 4 bits (parallel input parallel output) Shape) The first register (T) of the scratchpad. The metadata of the parallel data corresponds to the value of the binary signal of each of the outputs c1, c2, c3, and c4. When the output is "H", it is memorized as "1", and when it is "L", it is memorized as "0." "." Further, the parallel output of the first register (T) 6 is similarly connected to the parallel input of the second register (T-1) 7 belonging to the 4-bit PIPO register. The first register (T) 6 and the second register (T-1) 7 are connected to the microcomputer 5, and the shift clock terminal (SFT) is connected to the reset output terminal (RESET). When the clock terminal (SFT) is input to shift the clock, the input and output of the stored 4-bit register value is performed, and if the reset signal is input by the reset output terminal (RESET), the reset is reset. The stored 4-bit scratchpad value. That is, the first register (T) 6 memorizes the binary data of the outputs c1, c2, c3, and c4 stored as the 4-bit register value when the shift clock is input. Next, the shift register is input, and similarly, the second register (T-1) 7 memorizes the 4-bit register value output by the first register (T) 6 to Next, the shift clock is input. Further, when the first register (T) 6 receives a trigger signal from the register value comparison circuit 8 to be described later, the register value stored at this time is stored in the RAM 10.

Each time the new 4-bit register value of c1, c2, c3, and c4 is stored in the first register (T) 6, the register is stored in the register value comparison circuit 8. The value is compared with the register value stored in the second register (T-1) 7, and when any of the bit data of at least 4 bits is different, the trigger value is output by the register value comparison circuit 8. The first register (T) 6 and the counter 11 to be described later. Further, in the present embodiment, in order to detect the t0 of the input operation, the count value to be described later is stored in the RAM 10 in association with the register value, and the trigger value is outputted from the register value comparison circuit 8. The register value stored in the second register (T-1) 7 is stored in the register value of the first register (T) 6 immediately before the latest shift clock is input. Therefore, the trigger signal is outputted when at least one of the outputs c1, c2, c3, and c4 changes in addition to the reference time t0.

The microcomputer 5 is built-in: a clock signal is input from the clock oscillation circuit 9, and the frequency of the 20 MHz clock signal is divided by 8 to form a frequency dividing circuit 21 having a frequency of 2.5 MHz, and the frequency dividing circuit 21 is to be used by the frequency dividing circuit 21. The 2.5 MHz square wave pulse signal to be output is pulse width modulated by the predetermined modulation value, and the 2.5 MHz clock signal output by the frequency dividing circuit 21 is used as the shift clock. The operation of the registers 6, 7 is controlled, and the PWM modulation signal outputted by the PWM modulation circuit 20 is used as the switching control signal a to switch the charge and discharge switches 4 of the respective capacitance-time conversion circuits 2. control.

In the present embodiment, as described above, the PWM modulation signal is modulated into a pulse signal having a duty ratio of 0.4, and each of the charge and discharge switches 4 is simultaneously switched and controlled. Further, since the frequency of the shift clock is the input time and the time difference until the binary data of the output c is inverted as described above is about 25 to 75 μsec, the frequency is at least 1 MHz or more in order to surely detect the time difference. (Period 1 μsec or less), here, a frequency of 2.5 MHz having a period of 0.4 μsec is formed.

Further, the microcomputer 5 specifies the combination of the count value and the register value which are stored in the RAM 10 in association with the detection period Tp of each FIG. 4 to specify the detection electrode 3 to which the input operation body is approaching, and performs detection on the detection. Detection processing of an input operation of detecting the arrangement position of the electrode 3.

The counter 11 counts up the count value at a frequency higher than the frequency of the clock pulse and at a frequency obtained from the clock signal output from the clock oscillation circuit 9. The count value of the counter 11 is reset by the reset signal outputted by the microcomputer 5. When the trigger signal is input from the register value comparison circuit 8, as shown in Fig. 2, the count value at this time is output. To RAM10.

As shown in FIG. 2, the RAM 10 as the temporary memory device causes the count value of the counter 11 at this time to be stored in the first register every time the trigger signal is output from the register value comparison circuit 8. The register value of T)6 is correlated and stored until the register value in which all the bit data becomes "1" is input, and each combination associated with the count value is memorized. The data of the respective combinations stored in the RAM 10 is cleared by the control from the microcomputer 5 every detection period Tp before the reference time t0.

The operation of detecting the input operation of the touch panel 1 configured as described above will be described below. The microcomputer 5 is configured to detect an operation mode of the input operation. As shown in FIG. 4, the detection period Tp obtained by adding the rest time Tr to the charging time Tc and the discharging time Td for charging and discharging the floating capacitance Cs of each detecting electrode 3 is as shown in FIG. , to repeatedly test the input operation. Here, it is explained that the input operator to the detecting electrode 3 is detected at the charging time Tc at which the floating capacitor Cs is charged and controlled. The charging time Tc charging and discharging switching system 4 at _41, and was open to the third switching terminals of the reference switch ₄₃ is located between the reference charging voltage Vdd of the first switched terminal until the time tg to the switching time t0, switch The time tg is set in a period after the potential of all the detecting electrodes 3 exceeds the critical potential _VSH and reaches the reference charging voltage Vdd. The maximum value of the floating capacitor Cs is about 10 pF, and the time constant composed of the series-connected detecting resistors R1 and R2 of 10 MΩ is 100 μsec, the switching control signal a having a duty ratio of 0.4, and the detecting electrode 3 of the floating capacitor Cs being charged. The elapsed time until the potential reaches the reference charging voltage Vdd is 2.5 msec, and the charging time Tc until the switching time tg is 3 msec.

Further, in the discharge time Td, since the input operation is not detected, as shown in Fig. 4, the switching control signal a after tg at the time of switching is "L" level, and the common terminal 4c of the charge and discharge switch 4 is located and located. ground potential GND second switching terminal ₄₂ is connected through all the switching tg detection electrode potential after the discharge time Td 3 becomes the ground potential GND. In the discharge time Td, since the floating capacitor Cs is often discharged, the elapsed time from the switching time tg to the ground potential GND is 0.5 msec, and the discharge time Td is set to be shorter than the charging time Tc by 1 msec. In order to further increase the detection frequency of the input operation, the time when the discharge time Td has passed is the reference time t0. Although the rest time Tr is not necessarily set in the detection period Tp, in the present embodiment, the rest time Tr of 0.5 msec is set. The detection period Tp was set to 4 msec. The microcomputer 5 performs detection processing for calculating the input operation position from the data stored in the RAM 10 from the discharge time Td to the rest time Tr.

As described above, according to the present embodiment, since the floating capacitance Cs of the plurality of capacitance-time conversion circuits 2 is simultaneously charged and discharged, the charging time Tc and the discharge time Td are not increased depending on the number of the capacitance-time conversion circuits 2, even if By setting the rest time Tr, the input operation can also be detected with a short detection period Tp. Therefore, even if the microcomputer 5 detects the operation mode of the input operation, it is possible to use the input device of the portable device such as a remote power transmitter or a mobile phone that cannot obtain power from the outside, without replacing the battery. Use for a long time.

The microcomputer 5 outputs a reset signal from the reset output terminal (RESET) at the reference t0, and stores the register value of the first register (T) 6 and the second register (T-1) 7 with the counter 11 The count value is reset and the data that is memorized in RAM 10 is cleared. However, when the detection period Tp elapses, the register values of the first register (T) 6 and the second register (T-1) 7 become "0", so it is not necessary to reset. .

Further, the microcomputer 5 outputs a switching control signal a for switching the charge/discharge switch 4 of each of the capacitance-time conversion circuits 2 between the reference charging voltage Vdd and the open potential at the same reference time t0, and the floating capacitance Cs of the detecting electrode 3 Charging is performed at a time ratio of 0.4. The charge/discharge switch 4 is switched to the ground potential GND at which the potential of the detecting electrode 3 of the ground potential GND is _{equal to} or lower than the critical potential V _SH until the reference time t0. Therefore, the outputs c1, c2, and c3 of the comparators 5 at the reference time t0 are C4 is "L", and the parallel data of "0000" of the 4-bit of the first register (T) 6 is memorized.

The register value comparison circuit 8 outputs a trigger signal to the counter 11 and the first register (T) 6 at the reference time t0. As shown in FIG. 2, the RAM 10 indicates the count value C(t0) of the reference time t0. And at the reference time t0, the register value "0000" stored in the first register (T) 6 is stored in association with each other.

When a finger is assumed that the input operation of the input operations thereof disposed close to a position detection electrode _32, since the operation member away from the input, the input operation is not affected by body caused by the stray capacitance detecting electrode ₄ of Cs 3 ₄ minimum, Therefore, as shown in FIG. 3, with the detection resistor R1, the resistance value R2 of the time constant of the potential was increased stepwise detection electrode ₃₄ beyond the critical potential V _SH at the earliest time t1. As a result, the output c4 of the comparator 5 is inverted from "L" to "H", and the parallel data "0001" in which the lowest bit is "1" is stored in the first register (T) 6. Since the register value comparison circuit 8 is different from the register value "0000" stored in the second register (T-1) 7, the counter 11 and the first register (T) The output trigger signal 6 is stored in the RAM 10 in association with the count value C(t1) indicating the time t1 and the register value "0001" re-stored in the first register (T) 6.

Next, the detection electrodes are arranged on both sides _32, and is relatively close to the detection electrode ₃₂ of the input operation member, the detection electrodes arranged substantially equidistant detection electrode ₃₁ and the stray capacitance Cs ₃ 3 to _1, Cs ₃ lines More than the floating capacitor Cs ₄ , the potentials of the detecting electrodes 3 ₁ and 3 ₃ exceed the critical potential V _SH at time t2 , and the outputs c1 and c3 of the comparator 5 are inverted from "L" to "H" in the first register ( T) 6 memory has parallel data "1011". In the register value comparison circuit 8, since the first bit and the third bit of the register value are different from the register value "0001" stored in the second register (T-1) 7, The counter 11 and the first register (T) 6 output a trigger signal, and the RAM 10 and the count value C(t2) indicating the time t2 are associated with each other and are temporarily stored in the first register (T) 6 for temporary storage. The value of the device is "1011".

Closest to the input position detection electrode ₃₂ is floating capacitance Cs ₂ is compared with the other lines becomes maximum, therefore, as shown in FIG. 3, the detection system ₃₂ of the electrode potential at the end of time t ₃ exceeds the threshold potential V _SH The output c3 of the comparator 5 is inverted from "L" to "H". As a result, the first register 1 (T) 6 at the time t ₃ memory based parallel data "1111", the register value is due to the comparison circuit 8 and the register value is memorized in the second register (T- 1) The register value "1011" of 7 is different, so the trigger signal is output to the counter 11 and the first register (T) 6, and as shown in Fig. 2, the count value C(t3) at time t3 is indicated, The register value "1111" stored in the first register (T) 6 is stored in the RAM 10 in association with each other.

The microcomputer 5 switches the charge/discharge switch 4 to the ground potential GND at the switching time tg after the charging time Tc has elapsed from the reference time t0, and discharges the electric charge accumulated in each floating capacitor Cs during the discharge time Td. The potential of the detecting electrode 3 is set to the ground potential GND.

At the time of switching tg, since the potential of all the detecting electrodes 3 exceeds the critical potential _VSH , the register value "1111" stored in the first register (T) 6 is not changed until the switching time tg, and the microcomputer is not changed. In the case of switching 5, the combination of the count value C(t) stored in the RAM 10 and the register value is read. The count value C(t) indicates the elapsed time from the reference time t0 after the start of charging, and the register value indicates the bit in which the bit data is changed in comparison with the register value of the combination before the moment. In addition, the bit of each register value corresponds to the floating capacitance Cs of each detecting electrode 3, and depending on the size of the floating capacitor Cs, the elapsed time from the reference time t0 becomes longer, so the microcomputer 5 can be stored in the RAM 10 according to the memory. The data of each combination is used to compare the magnitude of the floating capacitance Cs of the detecting electrode 3. Here, as shown in FIG. 2, since the 4-bit bit data is changed in the order of the 4th bit (LSB), the 1st bit (MSB), the 3rd bit, and the 2nd bit, the detection is performed. The floating capacitance Cs is increased in the order of Cs ₄ , Cs _{1 ,} Cs ₃ , and Cs ₂ . Accordingly, the microcomputer 5 may be determined based input operation stray capacitance Cs ₂ body close to the maximum position detection electrode ₃₂ is arranged to detect the position detection electrodes ₃₂ arranged in operation to input operation position.

The microcomputer 5 inputs an input operation position detected as described above to an external control circuit that controls the cursor movement control or the operation of the electronic device on the display screen to perform predetermined processing corresponding to the input operation position.

The microcomputer 5 performs the above-described detection processing of the input operation position and the input operation during the discharge time Td and the rest time Tr after the discharge time T1, and after the detection input operation, the data stored in the RAM 10 is cleared before the next reference time t0. .

The detection of the input operation position may also compare the magnitude of the floating capacitance Cs of the plurality of detection electrodes 3, and the position between the arrangement positions of the plurality of detection electrodes 3 obtained by proportionally distributing the plurality of floating capacitances Cs as the input operation position. .

In the above embodiment, the capacitance of the plurality of capacitors is compared as the floating capacitance of the complex detection electrode, and the capacitive touch panel for detecting the input operation of the detection electrode having the largest floating capacitance is described. If the capacitance of the capacitor can be converted into a time that can be measured by the counter value of the counter, it is not limited to the floating capacitor, and can be applied to a capacitance discriminating device that compares the capacitances of other types of capacitors.

Further, circuit elements such as the register value comparison circuit 8, the first register (T) 6, and the second register (T-1) 7 may be built in the microcomputer 5.

Moreover, charge-discharge switch 4 lines to form a first switching terminal to the reference charge potential voltage Vdd of _41, is formed to the second switching terminal _42, and was open to the third switch terminal connected to ground potential GND ₄₃ like 3 species intercropping switching switch terminal to be described, but in which only one of charge and discharge control to detect the input operation may be omitted, in which one of the first switching terminal ₄₁ and the second switching terminal ₄₂ is. Further, if possible charging control, the common terminal of the first switching terminal ₄₁ approaches to and separates, or the discharging control, the common terminal and the second switching terminal ₄₂ closer to a separated manner, and a predetermined operation control ratio Therefore, it is not necessary to provide the third switching terminal 4 _{3 that} is open.

[Industrial Applicability]

The present invention is applied to a capacitive touch panel that detects an input operation in a non-contact manner based on an electrostatic capacitance that changes slightly due to an input operation.

1‧‧‧Separate capacitive touch panel

2‧‧‧Capacitance-time conversion circuit

3, 3 ₁ , 3 ₂ , 3 ₃ , 3 ₄ ‧ ‧ detection electrodes

4‧‧‧Charge and discharge switch

4c‧‧‧Shared terminal

4 ₁ ‧‧‧1st switching terminal

4 ₂ ‧‧‧2nd switch terminal

4 ₃ ‧‧‧3rd switch terminal

5‧‧‧Microcomputer

6‧‧‧1st register (T)

7‧‧‧2nd register (T-1)

8‧‧‧ register value comparison circuit

9‧‧‧clock oscillation circuit

10‧‧‧RAM

11‧‧‧ counter

20‧‧‧PWM modulation circuit

21‧‧‧dividing circuit

Cs, Cs ₁ , Cs ₂ , Cs ₃ , Cs ₄ ‧ ‧ floating capacitance

R1, R2‧‧‧ sense resistor

Vc‧‧‧Detection electrode potential

Vdd‧‧‧reference charging voltage

V _SH ‧‧‧critical potential

Fig. 1 is a circuit diagram showing a plurality of detecting electrodes 3 and a capacitance-time converting circuit 2 of a capacitive touch panel 1 according to an embodiment of the present invention.

FIG. 2 is a block diagram of an input position detecting circuit that detects an input operation of the capacitive touch panel 1.

Fig. 3 is a waveform diagram for explaining a method of detecting the detection electrode 3 to which the input operation body is approaching.

Fig. 4 is a waveform diagram showing the waveforms of a, b, and c in Fig. 1 compared with the waveforms a' and b' of the conventional method.

Fig. 5 is a block diagram showing a conventional method of detecting a capacitance of a charge conversion method.

Fig. 6 is a waveform diagram showing the relationship between the number of times of charging N and the voltage V2 of the capacitor C2 by the electrostatic capacitance detecting method shown in Fig. 6.

Tp. . . Detection cycle

Tc. . . Charging time

Td. . . Discharge time

Tr. . . Rest time

T0. . . Benchmark

Tg. . . When switching

V _SH . . . Critical potential

a, a’. . . Control signal

b, b’. . . Waveform

c. . . Output

Claims (3)

An electrostatic capacitive touch panel is provided with: a detecting electrode disposed on an insulating panel, and a floating capacitance is increased as approaching an input operating body; and a resistive element is formed between a floating capacitor and a detecting capacitor a CR time constant circuit; a charge and discharge switch that connects a common terminal on one side of the resistive element to a switching terminal located at a predetermined charging potential or a ground potential from a reference, and floats the floating capacitor with a time constant of the CR time constant circuit Charging or discharging, increasing the potential of the detecting electrode from the ground potential to the charging potential, or decreasing the charging potential to the ground potential; and timing means charging or discharging the floating capacitor from the reference, and charging at the foregoing The potential of the detecting electrode of the potential or the ground potential reaches an elapsed time set to a predetermined critical potential between the charging potential and the ground potential, and the arrangement of the detecting electrodes is detected by an elapsed time that increases as the floating capacitance increases. The input operation of the position, the capacitive touch panel is characterized by: charging The discharge on-off relationship is controlled by switching the PWM pulse signal of the fixed-frequency rectangular wave pulse signal with a predetermined modulation value, and according to the binary signal value of the PWM modulation signal, one side of the resistance element The common terminal is separated from the aforementioned switching terminal. The capacitive touch panel of claim 1, wherein the charge/discharge relationship is performed by a PWM modulation signal, a first switching terminal located at the charging potential, a second switching terminal at a ground potential, and Any one of the open third switching terminals performs switching control of the connection of the common terminal, and connects the common terminal according to the binary signal value of the PWM modulation signal between the first switching terminal and the third switching terminal The switching connection is performed to charge the floating capacitance of the detecting electrode, and/or the switching connection between the second switching terminal and the third switching terminal is performed to discharge the floating capacitance of the detecting electrode. The capacitive touch panel of claim 1 or 2, wherein the resistive element and the charge-discharge relationship are provided for each of the plurality of detecting electrodes disposed on each of the insulating panels, for each detecting electrode The elapsed time measured by the timing means is compared, and the input operation position is detected by the arrangement position of the detection electrodes whose elapsed time has elapsed.