KR20090055532A - Capacitance measuring circuit for touch sensor - Google Patents

Abstract

A capacitance measuring circuit for a touch sensor is provided to measure capacitance and variation of an electrode by measuring time required for charging/ discharging of capacitance. A reference voltage generation unit(10) generates a first reference voltage and a second reference voltage. A mux unit(60) selects one electrode from a plurality of electrodes(70), and a comparison unit(20) compares a voltage from the electrode and with a voltage generated from a reference voltage unit. A charge / discharge circuit part(50) charges the electrode from a first reference voltage electrode to a second reference voltage. A timer(40) measures charge and discharge time of the charge / discharge circuit part.

Description

Capacitance measuring circuit for touch sensor

The present invention relates to a capacitance measuring circuit of a touch sensor, and more particularly, a touch capable of measuring a capacitance of a corresponding electrode in a faster time by performing a time measurement by applying a predetermined constant current to both charge and discharge. It relates to a capacitance measuring circuit of the sensor.

The capacitance of the PAD is determined by the contact of a capacitor or an equivalent material or human body with an electrical element connected to the electrode PAD. In this case, the human body may not only directly contact a finger or a specific part of the body with the electrode PAD, but even if the human body does not have direct contact with the electrode PAD, it may be located between the electrode PAD and the human body by simply approaching the PAD. It can be seen that a fine capacitance component is formed in.

In addition, the capacitance changes according to the change of the distance between the adjacent body part and the electrode, which is measured as a result that the capacitance increases as the distance between the electrode and the body increases, and the capacitance decreases as the distance increases.

As such, the distance between the electrode and the human body can be determined to a certain level by measuring the change in capacitance generated by the change of the distance between the electrode and the body part, and the value of a specific critical capacitance is set using the result of the determination. After that, if the capacitance component measured from the electrode is larger than the threshold value, it is determined that the switch is in contact, otherwise it is determined that the switch is non-contact.

The threshold value is a general method of determining the threshold value by adding or subtracting the initial measured value when the touch sensor is not contacted at the time of touch-on, and experimentally calculating the value changed by the surrounding environment. .

In this way, a semiconductor product is a touch sensor IC. Currently, touch sensor ICs are used in many electronic products (mobile phones, TVs, washing machines, air conditioners, microwave ovens, etc.) instead of mechanical switches used in various electronic products.

However, in the touch sensor IC, since the capacitance formed between the electrode and the human body is only a few pF to several tens of pF, a method for calculating this is conventionally used as an electrical switch (SW) as shown in FIGS. 1 and 2. After discharging the electrode PAD to ground GND, it is necessary to charge the capacitor (Cpad) component of the capacitance generated by the electrode and the human body from the constant current source connected to VDD to the reference voltage (Vref). The time was measured by a timer using a high speed clock (count clock) and the value of the capacitance was measured by the value of the timer.

At this time, the comparator compares the reference voltage (Vref) and the voltage (Vpad) of the electrode changed by the charging of the capacitance component (Cpad) formed in the electrode, and the resultant OUT signal is High In the section, it is used as a signal to control the switch used to discharge the electrode. In the section, which is low, the high-speed clock is used as the control signal of the timer to measure the time during the tchar section.

This conventional technique has a very small current to complete the discharge in a relatively short time, such as the interval of tdis during discharge due to the limitation of the high-speed clock used for measuring the capacitance, and to obtain a sufficient timer value during charging Use a current source to supply. At this time, the value of the current supplied from the current source generally uses a few hundred pA ~ several microA of the current. As shown in FIG. 2, the reason why the charging voltage characteristic appears to increase linearly in the tchar period is because charging is performed using a current source that is a constant current source.

In this case, the capacitance obtained between the human finger and the electrode is generally only a few pF to several tens of pF. As the value of the current to be charged decreases, more charging time is required and more timer value can be measured. On the other hand, if the current used for charging is too small, the influence on the external noise signal and the parasitic current inside the touch sensor semiconductor increase, so that the amount of change in the time required for charging increases due to the noise component or Because of the tendency to decrease, many problems arise in measuring the time it takes to charge the capacitance efficiently.

3 and 4 relates to a capacitance measuring circuit of a touch sensor using another conventional technology. As shown, after charging the electrode PAD to VDD completely using the electrical switch SW, the capacitor (Cpad) component of the capacitance generated by the electrode and the human body through the resistor connected to the ground (GND) is referenced to a reference voltage. The time required for discharging up to (Vref) was measured by a timer using a fast clock (count clock), and the value of the capacitance was measured by the value of the timer.

Ctl, a signal used to charge or discharge the capacitance component of the electrode, is a control signal for turning on / off an electrical switch. When ctl is high, the switch is turned on to rapidly charge the capacitance component of the electrode within a relatively fast time, and in the off period, the amount of charge charged in the capacitor of the electrode is discharged to ground by the resistor R.

At this time, COMP (comparator) compares the reference voltage (Vref) and the voltage (Vpad) changed by the discharge of the electrode, and the result of the logical product (AND) of the resultant OUT signal and the ctlb signal of the ctl reverse phase signal (AND) The output cnten signal is measured by the timer to measure the value of capacitance.

This conventional technology also, due to the limitation of the high-speed clock used for measuring capacitance, completes charging in a relatively short time such as the tcharg section during fast charging, and at the time of discharge, the R value to obtain a sufficient timer value. Connect resistors that are significantly larger than MEGA OHM. In this case, in general, when the charge charged in the Cpad is discharged through the resistor R, the discharge current uses a microcurrent of several hundred pA to several uA.

As shown in FIG. 4, the reason why the discharge voltage characteristic decreases in the form of an exponential function in the sections tdis1 and tdis2 is because the discharge path is made through the resistor R, and thus has a slope of the discharge characteristic of the RC circuit, which is a general electric circuit. .

However, in the conventional technology as described above, since the capacitance obtained between a human finger and an electrode is only a few pF to several tens of pF, as the value of the discharge current is reduced, more charging time is required, resulting in more timer values. On the other hand, if the current used for charging is too small, the influence of external noise signal and parasitic current inside the touch sensor semiconductor increases, so the amount of change in charging time is noisy. Because of the tendency to increase or decrease by the components, many problems arise in measuring the time taken to efficiently charge the capacitance.

When the conventional technology as described above is implemented as a semiconductor IC, since the current used for charging or discharging used to measure the desired capacitance is only a few hundred pA to several uA as described above, a silicon wafer ( Signal-to-noise on the effects of disturbance components on the operating environment such as leakage current, temperature, external moisture, and electromagnetic wave (propagation) due to parasitic resistances parasitic on semiconductor devices implemented on silicon wafers There have been many difficulties due to the inability to increase the ratio.

In addition, as shown in FIGS. 2 and 4, even when the discharge or charge of the component of the capacitance of one electrode PAD is completed to obtain a stable capacitance timer value, as in tdis [FIG. 2] and tcharg [FIG. 4]. In order to reduce the influence of the change amount on the external environment, after waiting for a certain time, charging or discharging using a fine current had to be performed to obtain a desired timer value.

Also, in case the timer value of the charging and discharging is not sufficiently obtained, since the capacity of the electrode is calculated from the measured timer values after repeating a plurality of tcycles, a lot of time is spent for each electrode. For example, if you need a touch sensor that has a large number of PADs and measures the capacitance of each PAD sequentially, you cannot obtain the response characteristics for each pin you want. In this case, use multiple touch sensor ICs. There was a disadvantage.

The present invention for solving the above problems is a few hundred pA ~ several uA for measuring the charge or discharge time of the capacitance (capacitance) formed on the electrode is too small value of the capacitance formed between the body and the electrode in the touch sensor Minimize the influence on the external environment caused by the use of current only and the leakage characteristics of the silicon-based semiconductor itself, and maximize the signal-to-noise ratio to measure capacitance more reliably The purpose is to provide an electrical circuit capable of doing so.

In addition, since a predetermined constant current is applied to both charging and discharging, time measurement is performed to provide a structure capable of measuring the capacitance of the corresponding electrode within a shorter time.

In addition, the constant current required for charging and discharging is sequentially supplied at the time of charging and discharging through a current source using a current mirror, even if the current value of the current source becomes larger than the conventional method. Within a certain time, only the number of cycles increases, but the same effect can be obtained for measuring capacitance. The ratio of signal to noise is greatly improved, so that the influence of leakage current on the external environment and semiconductor silicon wafer is minimized. Its purpose is to.

The present invention for achieving the above object, the mux unit for selecting one of the reference voltage generating unit for generating the first reference voltage and the second reference voltage, the electrode voltage input from the electrode voltage input through a plurality of electrodes And a voltage comparison unit comparing the voltage generated by the reference voltage generator with the electrode voltage input from the electrode, charging the input electrode voltage from the first reference voltage to the second reference voltage or from the second reference voltage to the first reference voltage. A charging / discharging circuit unit for discharging the battery, a timer unit for receiving an external control signal and measuring the charging and discharging time made by the charging / discharging circuit unit and the time required for the entire charging and discharging, respectively, and outputting an output signal according thereto; And a control unit which receives the output signal and the external control signal of the comparator and controls the charge / discharge circuit unit and the timer unit. The charging / discharging circuit unit continuously performs charging / discharging for a predetermined period N times, but when the capacitance is input from the electrode, a time difference is generated in the predetermined period so that the timer measures the accumulated time difference for N periods. It is characterized by determining whether the capacitance input.

In addition, when the capacitance is measured through the electrode, the resulting time difference is characterized in that the number of charge / discharge is established by the equation dtN = dt0 × N.

Where dt = time difference of one cycle according to capacitance measurement, N = number of charge / discharge cycles

In addition, as the number of charge / discharge cycles increases, the time required for charge / discharge increases proportionally if the capacitance is measured through the electrode.

In addition, the total charge / discharge time is characterized in that applied to the reference value for measuring the capacitance.

In addition, the reference value is characterized in that the charging time and the discharge time is also incidentally output and applied together.

In addition, in the capacitance measurement circuit of the touch sensor, a reference voltage generator for generating a first reference voltage and a second reference voltage, and charges from the first reference voltage to the second reference voltage or from the second reference voltage to the first reference voltage. Charge / discharge is continuously performed for N times to generate a reference waveform of a predetermined period by the charge / discharge circuit unit discharging to a voltage, and the respective charging time and discharge time for the reference waveform generated by the charge / discharge circuit unit are And a reference waveform time including the total charge / discharge time, and a measurement waveform generated by the input of the capacitance when capacitance is input from a reference waveform of a predetermined period generated by the charge / discharge circuit unit. Capacitance input is determined by measuring the measured waveform time of and comparing the reference waveform time with the measured waveform time for N cycles and checking the accumulated time difference. Characterized in that to set.

In addition, when the capacitance is measured through the electrode, the resulting time difference is characterized in that the number of charge / discharge is established by the equation dtN = dt0 × N.

Where dt = time difference of one cycle according to capacitance measurement, N = number of charge / discharge cycles

In addition, as the number of charge / discharge cycles increases, the time required for charge / discharge increases proportionally if the capacitance is measured through the electrode.

The present invention constructed and operated as described above repeats the process of simultaneously calculating the time required for charging and discharging by using a much larger amount of current than the charging and discharging current, and thus a certain number of cycles regardless of the amount of charging and discharging current. When the time is read as a timer value, the change in capacitance is measured to minimize the influence on the internal and external environment of the touch sensor, and more accurate capacitance measurement is possible even when using the same clock as in the prior art. There is an advantage that can be done with.

Hereinafter, an embodiment of a capacitance measuring circuit of a touch sensor according to the present invention will be described in detail with reference to the accompanying drawings.

5 is a schematic diagram of a capacitance measuring circuit of a touch sensor according to the present invention.

The capacitance measuring circuit of the touch sensor according to the present invention includes a reference voltage generator 10 for generating a first reference voltage and a second reference voltage, and a plurality of electrodes 70 (PADs) touched by the user. A mux unit 60 for selecting one electrode to be input, a comparator 20 for comparing the voltage generated by the reference voltage generator 10 and the voltage input from the electrode, and the electrode as a first reference Charge / discharge circuit unit 50 charging from the voltage to the second reference voltage or discharging from the second reference voltage to the first reference voltage, the charge and discharge time by the charge / discharge circuit unit is measured and the output signal accordingly And a controller for controlling the charge / discharge circuit unit 50 and a timer by receiving the output signal 40 and the output signal of the comparator 20 and an external control signal.

6 is a detailed view of a touch sensor capacitance measurement circuit according to the present invention.

The reference voltage generator 10 is configured by connecting three resistors, which are the first to third resistors 11, 12, and 13, in series, and generates a first reference voltage Vref_dn and a second reference voltage Vref_up. do. One end of the first resistor 11 is connected to the power supply voltage VDD, and then the second resistor 12 and the third resistor 13 are connected in series, and the other end of the third resistor is connected to the ground. . The second reference voltage is generated at the connection of the first resistor 11 and the second resistor 12, and the first reference voltage is generated by connecting the second resistor 12 and the third resistor 13.

The reference voltage generator 10 is not limited to the above-described configuration, and may be supplied from the outside or may obtain the first reference voltage and the second reference voltage from components other than the resistor.

 The first reference voltage and the second reference voltage generated are compared with the voltage Vpad input from the electrode 70 to output respective output signals odn and oup. Here, the reference voltage may be changed by changing the resistance value of the reference voltage generator 10.

Comparing the electrode voltage Vpad to the first reference voltage and the second reference voltage is performed by the comparator 20. The comparator 20 includes a first comparator 21 (COM1) and a second comparator (22; COMP2), and the negative terminal of the first comparator is connected to a second reference voltage, The negative terminal is connected to the first reference voltage. Also, the positive terminal of each comparator is connected to the electrode voltage Vpad. The function of the comparison unit 20 is as follows.

 Comparator  Condition  Output value  One  COMP 1  Vref_up> Vpad  Oup = Low  2  Vref_up <Vpad  Oup = High  3  COMP 2  Vref_dn> Vpad  Odn = Low  4  Vref_dn <Vpad  Odn = High

The controller 30 receives the output signals odn and oup and the external control signal ctl1 output from the comparator 20 and controls the charge / discharge circuit unit 50 and the timer 40.

The timer 40 receives an external control signal CTL3, the controller 30, and a clock to determine the time for charging and discharging through the charge / discharge circuit unit 50 from the capacitance present in the electrode 70. Measure and output the signal accordingly.

7 is a detailed view of a charge / discharge circuit unit according to the present invention.

As shown in the drawing, the charge / discharge circuit unit 50 is composed of a current source 51 for supplying a constant current and a switch unit 52 for selecting charge and discharge, respectively. The resistance R of the current source 51 is the resistance R that determines the amount of current of the bias of the NMOS TR (n0), and is defined between the drain and the source GND of the NMOS TR (n0) by the R value. The amount of current flowing is determined. The NMOS TR (n1) and the PMOS TR (p0) are for mirroring the current of the NMOS TR (n0).

The NMOS TR (n2) and the PMOS TR (p1) are for charging or discharging the capacitance of the electrode voltage Vpad and supplying a current equal to the current of the NMOS TR (n0) determined from the resistor R1. Perform the function.

In more detail, the current source 51 is described in detail. One end of the resistor R1 is connected to the power supply voltage VCC and the other end thereof is connected to the drain terminal of the NMOS TR (n0). The source terminal of the NMOS TR (N0) is connected to the ground terminal, and the gate terminal is commonly connected to the gate terminal of the NMOS TR (n1). Further, the drain terminal and the gate terminal of the NMOS TR (n0) are commonly connected to the gate terminal of the NMOS TR (n2), the source terminal of the NMOS TR (n2) is connected to the ground terminal, and the drain terminal of the switch unit (described later) 52).

The drain terminal of the NMOS TR (n1) is connected to the drain terminal of the PMOS TR (p0) and the source terminal is connected to the ground terminal. The source terminal of the PMOS TR (p0) is connected with the power supply voltage VCC, the gate terminal is commonly connected with the gate terminal of the PMOS TR (p1), and the source terminal of the PMOS TR (p1) is connected with the power supply voltage VCC. The drain terminal is connected to the switch unit 51 described later. In addition, the drain terminal and the gate terminal of the PMOS TR (p0) are commonly connected.

On the other hand, by changing the value of the resistance (R1) of the current source 51 to control the charge / discharge voltage value to change the time constant for the value of the capacitance changed by the area of the electrode provided on the PCB of the application I can adjust it.

FIG. 8 is a detailed view of the switch unit 52 of the charge / discharge circuit unit, and selects charge and discharge, respectively, as described above, and includes an analog switch or a 2 to 1 analog switch and an inverter. The switch unit 52 includes a first switch 52a for selecting charging and a second switch 52b for selecting discharge.

The output signal oup of the first comparator COMP1 is connected to the input terminal of the first inverter int1, and the output signal odn of the second comparator COMP2 is connected to the input terminal of the second inverter int2. Connected.

In the case of the first switch 52a, the output terminal of the first inverter int1 is connected to the gate terminal of the PMOS TR (p2). The source terminal of the PMOS TR (p2) is connected to the drain terminal of the NMOS TR (n3), the drain terminal is connected to the source terminal of the NMOS TR (n3), and the input terminal of the first inverter int1 is NMOS TR (n3). Is connected to the gate terminal of.

In addition, the source terminal of the PMOS TR (p2) and the drain terminal of the NMOS TR (n3) are connected to the drain terminal of the PMOS TR (p2) of the current source 51.

In the case of the second switch 52b, the output terminal of the second inverter int2 is connected to the gate terminal of the PMOS TR (p3). The source terminal of the PMOS TR (p3) is connected to the drain terminal of the NMOS TR (n3), the drain terminal is connected to the source terminal of the NMOS TR (n3), and the input terminal of the first inverter int2 is NMOS TR (n3). Is connected to the gate terminal of.

Meanwhile, the source terminal of the NMOS TR (n3) connected to the PMOS TR (p2) drain terminal is connected to the drain terminal of the NMOS TR (n3) connected to the source terminal of the PMOS TR (p3). This is connected to the electrode voltage (Vpad).

As shown in FIG. 9, the voltage waveform of the Vpad is changed from the waveform of C0 to the waveform of C1 only when the capacitance increases due to the contact of the human body to the existing capacitance at the same electrode, and when calculating one cycle In comparison, the time owned for charging and discharging becomes dt0, and the time difference occurs between dt1 in two times and dt2 in three times, and the magnitude of the difference is proportional to the number of times of charging / discharging. Is established.

dt2 = dt1 + dt0

dt1 = dt0 * 2

That is, dtN = dt0 * N, N = number of executions of charge and discharge cycle

Therefore, as the number of charge / discharge cycles increases, the time required for charging / discharging the increased capacitance relative to the existing capacitance increases proportionally.

Therefore, if a very fast clock is needed because the conventional method measures only once with a high-speed timer in the case of charging or discharging each time in a charge / discharge cycle, the present invention can measure the difference in accumulated time for N cycles. Therefore, as the time increases, it is possible to measure with a slower clock than when measuring every time, and when using the same high speed clock as in the conventional method, more accurate time measurement can be made. Therefore, the capacitance formed on the electrode 70 can be measured more precisely.

In addition, when the capacity of the charge and discharge current used in the present invention is increased, the time required for each charge and discharge is reduced, and the number of charge / discharge cycles during the specific time t4_c0 and t4_c1 is increased. The value of timer due to the difference between the capacitances C0 and C1 at the end of the charge / discharge cycle near t4_c0 and t4_c1 time is not different from the value before increasing the current capacity. have.

Therefore, despite the increase in charge or discharge current, the relative difference in charge / discharge time due to the capacitance of C0 and C1 remains relatively constant when measuring the difference by increasing the cycle number in proportion to the time of the shortened cycle. It can be seen that.

12 is a flowchart illustrating the operation of the capacitance measuring circuit according to the present invention. Referring to FIG. 11 together, the operation sequence will be described in detail. In order to measure the charge time and the discharge time for calculating the capacitance present in the electrode 70, the first Vpad is in an open state (high impedance) (S10). .

Thereafter, when the external control signal CTL1 is input (S20), the control unit 100 discharges the battery as shown in (S30) of FIG. 11 so that cdn becomes 1 and the voltage of Vpad is set to be less than the voltage of Vref_dn (S30). .

Here, the voltage of Vpad is compared with Vref_dn, which is the first reference voltage (S40), and the discharge is performed until the voltage becomes lower than the first reference voltage. After the discharge is completed, charging is performed again to Vref_dn (S50). Here, the Vpad voltage is compared with the first reference voltage (S60), and when the Vpad voltage is small, charging is performed until the voltage is higher.

When the charging of the Vpad voltage coincides with the first reference voltage Vref_dn, the timer 40 is operated from this time to measure the charging time (S70). While charging is performed, it is checked whether the battery is charged above the second reference voltage Vref_up or higher (S80). If the battery is charged above the battery, the charging completion and charging time timers are terminated (S90).

When the charging is completed up to the second reference voltage Vref_up, the timer is operated by measuring the discharge time while performing the discharge next to measure the discharge time (S100). When the discharge is completed, the discharge is completed until the first reference voltage is compared with the first reference voltage and the Vpad voltage (S110). When the discharge is completed below the first reference voltage, the discharge completion and the discharge time measurement are stopped (S120).

Accordingly, the charge / discharge is performed N times (S130), and the charge timer value (tc1, tc2, tc3, .... tcn) of the respective charge times and the discharge time are measured by measuring the respective charge and discharge times. The timer value td1, td2, td3, .... tdn and the total timer value ta used for charging and discharging are output (S140).

In general, the time ta for charging and discharging the electrode PAD for N times is used as the most important reference value for determining the capacitance of the electrode, but there are realistic trends depending on the charging time and the discharge time due to the external environment. In this regard, the charge timer values and the discharge timer values are also incidentally output in order to determine whether the human body is in contact with the human body, and serves to help determine whether the external human body is in contact with the logical part of the touch sensor circuit.

The present invention constructed and operated as described above is more stable and accurate because it can use a much larger current for charging and discharging the electrode, compared to the leakage current and internal noise present in the semiconductor. The time required to charge and discharge the capacitance of the can be measured, and thus there is an advantage that can measure the value and the amount of change of the capacitance of the electrode.

While the invention has been described and illustrated in connection with a preferred embodiment for illustrating the principles of the invention, the invention is not limited to the construction and operation as shown and described as such.

Rather, those skilled in the art will appreciate that many modifications and variations of the present invention are possible without departing from the spirit and scope of the appended claims. Accordingly, all such suitable changes and modifications and equivalents should be considered to be within the scope of the present invention.

1 to 4 is a configuration diagram and a graph of a touch sensor according to the prior art,

5 is a schematic diagram of a capacitance measuring circuit of a touch sensor according to the present invention;

6 is a detailed view of a capacitance measuring circuit of a touch sensor according to the present invention;

7 is a detailed view of a charge / discharge circuit unit according to the present invention;

8 is a detailed view of a switch unit of a charge / discharge circuit unit according to the present invention;

9 to 11 are graphs showing charge and discharge cycles of the capacitance measuring circuit according to the present invention;

12 is an operation flowchart of a measuring circuit according to the present invention;

<Description of symbols for major symbols in the drawings>

10: reference voltage generator

20: comparator

30: control unit

40: timer

50: charge / discharge circuit

60: musbu

70 electrode

Claims (8)

A reference voltage generator configured to generate a first reference voltage and a second reference voltage; A mux unit for selecting one electrode voltage input from among electrode voltages input through the plurality of electrodes; A voltage comparator comparing the voltage generated by the reference voltage generator with an electrode voltage input from the electrode; A charge / discharge circuit unit configured to charge the input electrode voltage from the first reference voltage to the second reference voltage or discharge the input electrode voltage from the second reference voltage to the first reference voltage; A timer unit which receives an external control signal and measures charge and discharge time and total time required for charging and discharging by the charge / discharge circuit unit, respectively, and outputs an output signal according thereto; And And a control unit which receives the output signal and the external control signal of the comparator and controls the charge / discharge circuit unit and the timer unit. The charging / discharging circuit unit continuously performs charging / discharging of a predetermined period N times, but when a capacitance is input from the electrode, a time difference is generated in the predetermined period so that the timer measures the accumulated time difference for N periods. Capacitance measurement circuit of the touch sensor, characterized in that for determining the capacitance input. The method of claim 1, When the capacitance is measured through the electrode, the resulting time difference is the number of charge / discharge cycles, DtN = dt0 × N Capacitance measurement circuit of the touch sensor, characterized in that established by. Where dt = time difference of one cycle according to capacitance measurement, N = number of charge / discharge cycles The method of claim 1, The capacitance measuring circuit of the touch sensor, characterized in that the time required for charging / discharging increases proportionally if the number of charge / discharge is measured through the electrode. The method according to any one of claims 1 to 3, Capacitance measurement circuit of the touch sensor, characterized in that the total charge / discharge time is applied to a reference value for capacitance measurement. The method of claim 5, wherein the reference value, Capacitance measurement circuit of the touch sensor, characterized in that the charging time and the discharge time is also output incidentally. In the capacitance measuring circuit of the touch sensor, A constant period by a reference voltage generator which generates a first reference voltage and a second reference voltage, and a charge / discharge circuit part that charges from the first reference voltage to the second reference voltage or discharges it from the second reference voltage to the first reference voltage. Charge / discharge continuously for N reference waveform generation of A reference waveform time including each charge time and discharge time, and the total charge / discharge time for the reference waveform generated by the charge / discharge circuit unit is measured; When a capacitance is input from an electrode in a reference waveform of a predetermined period generated by the charge / discharge circuit unit, the measurement waveform time of the measurement waveform generated by the input of the capacitance is measured. The capacitance measuring circuit of the touch sensor, characterized in that for determining the capacitance input by checking the accumulated time difference by comparing the reference waveform time and the measurement waveform time for N cycles. The method of claim 6, When the capacitance is measured through the electrode, the resulting time difference is the number of charge / discharge cycles, DtN = dt0 × N Capacitance measurement circuit of the touch sensor, characterized in that established by. Where dt = time difference of one cycle according to capacitance measurement, N = number of charge / discharge cycles The method of claim 6, The capacitance measuring circuit of the touch sensor, characterized in that the time required for charging / discharging increases proportionally if the number of charge / discharge is measured through the electrode.

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