KR20080041799A - Touch sensor - Google Patents

Abstract

A touch sensor is provided to prevent wrong operation due to capacitance change caused by noise by removing the noise with a filter unit and delaying a contact signal at a predetermined time with a delay unit. A touch sensor includes a signal generation unit(120), a counter unit(130), a previous count unit(140), a subtraction process unit(150), and a comparison process unit(170). The signal generation unit converts change of sensed electrostatic capacity into an electric signal(S1) to output the electric signal. The counter unit outputs a size of a current frequency(Cn) of the electric signal by measuring the electric signal generated from the signal generation unit for a predetermined time. The just previous count unit outputs a size of a just previous frequency(Cn-1) counted just before counting the size of the frequency outputted from the counter unit prior to a predetermined interval. The subtraction process unit subtracts the size of the current frequency and the size of the just previous frequency. The comparison process unit compares a subtracted count signal outputted from the subtraction process unit with a predetermined reference count signal.

Description

Touch Sensor {TOUCH SENSOR}

1 is a block diagram of a touch sensor according to an embodiment of the present invention;

2 is a waveform diagram of each part of the touch sensor according to an embodiment of the present invention;

3 is a signal processing state diagram of a touch sensor according to the present invention;

4 is a waveform diagram when the delay time is reduced according to an embodiment of the present invention;

5 is a waveform diagram of each part when the change in the initial capacitance of the capacitor according to an embodiment of the present invention is small;

6 is a configuration diagram of a touch sensor according to another embodiment of the present invention;

7 is a block diagram of a touch sensor according to another embodiment of the present invention.

* Description of the main parts of the drawings *

110: sensor unit 120: signal generator

130: counter unit 140: counter storage unit

150: subtraction processing unit 161: reference control unit

160: reference counter unit 170: comparison processing unit

180: filter unit 181: delay unit

190: output driver

The present invention relates to a touch switch circuit, and more particularly, to a capacitive touch sensor that determines whether or not a contact is measured by measuring an increased capacitance due to contact with an external object.

Conventional sensor device is composed of a sensor unit, waveform conversion unit, control unit, signal storage unit, comparison unit and output unit. The sensor unit includes a touch pad that senses a change in capacitance, and the waveform converting unit includes a signal converter that generates a sawtooth wave by using the change in capacitance, and a Schmitt trigger that converts the sawtooth wave into a square wave. The control unit is composed of a timer for measuring a signal at a predetermined time, and an automatic controller for automatically adjusting a reference value for the measured signal. The signal storage unit includes a reference register for storing a reference value and a sense register for storing a signal when a human hand touches it. The comparator is composed of a subtractor which receives two signals at the same time and calculates a difference between the two values, and a determiner that determines whether to detect the signal according to the result value of the subtractor. The output unit is composed of an output driver for generating a TTL signal by means of a signal obtained from the determiner.

In the conventional sensor device, the sensor unit senses a capacitance generated by the surrounding environment when the first person does not touch it, and the capacitance is converted into a sawtooth wave by a signal converter of the waveform conversion unit. The sawtooth wave is converted into a digital signal population wave by Schmitt trigger. The signal is stored in a reference register among the signal storage units of the reference value, and the capacitance stored in the reference register is used as the reference value of the switch. At this time, the reference value used is automatically re-measured by the signal generated at a certain time interval from the timer attached to the sensor part, and the value measured according to the changing surrounding environment and conditions is reset to the reference value by the automatic setter. do.

Thereafter, when a human hand touches the touch pad or another environmental change occurs, the sensor detects the changed capacitance value and the detected capacitance is converted into a sawtooth wave by the signal converter of the waveform converter. The sawtooth wave is converted into a square wave which is a digital signal by the Schmitt trigger, and then stored in the sense register, which is the signal storage of the sensing value, and the value stored in the sense register and the value stored in the reference register are passed through the subtractor in the comparator. Compute the difference from the reference value stored in the reference register and compare it. If the signal value of the sense register is large, the output driver generates a TTL signal and outputs it. If the signal value of the sense register is larger than the signal value of the reference register for a certain time, the automatic setter Set the value of to the new reference value.

However, the related art works when the capacitance increases as the object contacts the touch pad, but when the capacitance decreases, smooth operation cannot be expected.

In addition, since the magnitude of the reference capacitance signal stored in the reference register is determined, there is a problem that it is difficult to detect a minute change value having a very small capacitance difference according to before and after contact of the touch pad.

In particular, in the case of using a capacitor with a small capacity of the capacitor to detect small changes, the output signal is distorted due to noise, and the touch pad function is degraded in sensitive contact.

The present invention includes a counter storage unit capable of storing a signal measured by the counter unit, and by using a difference value between the signal measured by the counter unit and the signal stored in the counter storage unit, the input capacitance changes over time or changes in the surrounding environment. It is an object of the present invention to provide a touch sensor that automatically corrects the increase and decrease of capacitance due to stable operation.

The touch sensor of the present invention includes a signal generator for converting the detected change in capacitance into an electrical signal and outputs; A counter unit for measuring the electric signal generated by the signal generator for a predetermined time and outputting a magnitude of a current frequency of the electric signal; A previous counting unit for outputting the magnitude of the immediately preceding frequency which counted the magnitude of the frequency output from the counter before a predetermined interval; A subtraction processing unit for subtracting the magnitude of the current frequency and the magnitude of the immediately preceding frequency; And a comparison processing unit for comparing the subtraction count signal output from the subtraction processing unit with a predetermined reference count signal.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms or words used in the specification and claims should not be construed as having a conventional or dictionary meaning, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention.

Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiment of the present invention and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

1 is a configuration diagram of a touch sensor according to an exemplary embodiment of the present invention, and FIG. 2 is a sub waveform diagram.

Hereinafter, a description of the operation of the touch sensor will be described with a signal diagram output from the configuration of the touch sensor of FIG. 2.

The sensor unit 110 is composed of a touch pad (not shown) and a capacitor 111, the capacitor 111 is used to change the capacitance change frequency according to whether or not the object is in contact with the touch pad (not shown) It is connected to a signal generator 120 for generating an electrical signal S1 such as a pulse.

The signal generator according to the present invention may use an RC oscillator provided with a controller 121, the period of the electrical signal (S1) output from the signal generator 120 is inversely proportional to the magnitude of the capacitance as shown in Equation 1 below. do.

[Equation 1]

f = 1 / (2πRC)

The counter 130 is connected to the timer 131 and measures the frequency of the electrical signal S1 for the predetermined time Ti × n of the electrical signal S1 output from the signal generator 120 to measure the magnitude of the current frequency. (Cn) is output, and the immediately before counting unit 140 outputs the magnitude (Cn-1) of the immediately preceding frequency which counted the frequency magnitude output from the counter 130 before a predetermined interval.

The subtraction processing unit 150 outputs a subtraction count signal dC which is an absolute value obtained by subtracting the magnitude Cn of the current frequency and the magnitude Cn-1 of the previous frequency, and the comparison processing unit 170 outputs the subtraction count signal dC. ) And the reference count signal Cr output from the reference count providing unit 160 are compared.

If the subtraction count signal dC is greater than the reference count signal Cr, the comparison processing unit 170 determines that the external object is in contact with the sensor unit 110 or the external object is separated from the sensor unit 110, and the output driver ( The contact signal S5 is output through the 190.

The filter unit 180 removes noise included in the contact signal S5, and the delay unit 181 connected to the filter unit 180 delays the contact signal S5 output by the comparison processor 170 by a predetermined time. It is possible to prevent malfunction due to a change in capacitance due to noise that may occur momentarily between the sensor unit 110 and the contact object.

3 shows a signal processing diagram of a touch sensor according to the present invention.

1. A state

When the output is "L" and the delay time Td is "0", when the subtraction count signal dC is greater than the reference count signal Cr, the process returns to the step of comparing again, and the subtraction count signal dC is If it is less than or equal to the reference count signal Cr and the subtraction count signal dC is a down edge, the output is increased to "L" while increasing the delay time Td by one (B state).

2. B state

While the output is in the "L" state and the delay time Td is "1", while the delay time Td is less than "3", the subtraction count signal dC is greater than or equal to the reference count signal Cr and subtracted. When the count signal dC transitions to the up edge, it transitions to the A state, and the delay time Td is greater than or equal to "3" while the subtraction count signal dC is greater than or equal to the reference count signal Cr. The output then transitions to "H" (C state).

3. C state

When the output is " H " state and the delay time Td is " 0 ", when the subtraction count signal dC is smaller than the reference count signal Cr, the process returns to the comparison step, and the subtraction count signal dC ) Is greater than or equal to the reference count signal Cr and the subtraction count signal dC is an up edge, the output is increased by one while the delay time Td is increased by one (D state).

4. D status

While the output is in the "H" state and the delay time Td is "1", while the delay time Td is less than "3", the subtraction count signal dC is less than or equal to the reference count signal Cr and subtracted. When the count signal dC transitions to the down edge, it transitions to the C state, and the delay time Td is greater than or equal to "3" while the subtraction count signal dC is greater than or equal to the reference count signal Cr. The output then transitions to " L " (A state).

4 is an output waveform diagram of each configuration of a touch sensor according to an exemplary embodiment of the present invention.

When the logic state of the subtraction count signal dC is changed before the predetermined delay time Td = 3, it can be seen that the logic state of the contact signal S5 that is determined and output as a noise signal is not changed.

5 is a waveform diagram of each part when the capacitance of the capacitor according to the exemplary embodiment of the present invention is changed.

The initial capacitance 51 is the capacitance of the capacitor constituting the sensor unit before the object contacts the sensor unit. The initial capacitance 51 is almost similar to the magnitude of a signal generated by the actual contact of the object with the sensor unit, and the output drive outputs a contact signal. May cause However, when a series of two signals including the initial capacitance of this type is subtracted by the subtraction processing unit, the subtraction count signal dC becomes the reference count signal Cr or less, and the touch sensor is judged to have no contact. It shows that the sensor can be prevented from malfunctioning.

6 is a block diagram of a touch sensor according to another embodiment of the present invention.

The touch sensor according to another exemplary embodiment of the present invention has the same configuration as that of the touch sensor of FIG. 1, but the reference count providing unit 660 uses the previous subtraction count signal dCn-1 output from the subtraction processor. There is a difference. That is, the sensitivity of the touch sensor may be adjusted by using the magnitude of the previous subtraction count signal dCn-1 as the input of the reference count providing unit 660. Specifically, a new reference count signal is generated even when the subtraction count signal dCn is smaller than the reference count signal Cr by multiplying the previous subtraction count signal dCn-1 by the detection rate k and using the reference count signal Cr. By outputting (Cr = k * dCn-1), the contact signal may be output by continuously comparing with the subtraction count signal dCn.

Detection rate (k) according to an embodiment of the present invention can be determined experimentally to a value less than 1, preferably about 0.20 to 0.30. For example, when the subtraction count signal dC falls from -100 to +100 to -40 to +40 while the reference count signal Cr is set to -50 to +50, the previous subtraction count signal dCn-1 ) Is output as the reference count signal (Cr) by -10 ~ +10 multiplied by the detection rate (k = 0.25).

When the subtraction count signal dC increases from -40 to +40 to -70 to +70, -17.5 to +17.5 is obtained by multiplying the previous subtraction count signal dCn-1 by the detection rate (k = 0.25). Output the reference count signal Cr. Therefore, when the reference count signal Cr is corrected by using the detection rate k, it is applicable to the case where the strength of the subtraction count signal dC increases or decreases.

7 is a block diagram of a touch sensor according to another embodiment of the present invention.

A touch sensor according to another embodiment of the present invention has the same configuration as that of the touch sensor of FIG. 1, but a plurality of reference counters 760-1 that can simultaneously output a reference count signal Cr having different values. And 760-2, 760-3, and 760-4, it is different that the capacitance change of the capacitor can be detected. For example, the comparison processor 170 may simultaneously compare and output the subtraction count signal dC output from the subtraction processor 150 and a plurality of reference count signals Cr having different values. Here, although not shown, it will be apparent to those skilled in the art that the comparison processing unit 170 is provided with the number of reference count signals Cr so as to compare with the subtraction count signal dC.

Accordingly, the output driver 190 may output a 2-bit signal of 00, 01, 10, and 11 when the degree of contact is four levels. In addition, when the degree of contact is set to 9 levels, the 3-bit signals 00, 01, 02, 10, 11, 12, 20, 21, 22 may be output. As a result, the touch sensor can be used in an environment in which a larger range of contact force is generated.

Although the present invention has been shown and described with reference to the preferred embodiments as described above, it is not limited to the above embodiments and those skilled in the art without departing from the spirit of the present invention. Various changes and modifications will be possible.

The touch sensor of the present invention has the effect that it can operate accurately even if the initial capacitance of the capacitor changes or fine increase or decrease. In addition, the present invention can provide a touch sensor resistant to noise.

Claims (7)

A signal generator for converting the detected change in capacitance into an electrical signal and outputting the converted signal; A counter unit for measuring the electric signal generated by the signal generator for a predetermined time and outputting a magnitude of a current frequency of the electric signal; A previous counting unit for outputting the magnitude of the immediately preceding frequency which counted the magnitude of the frequency output from the counter before a predetermined interval; A subtraction processing unit for subtracting the magnitude of the current frequency and the magnitude of the immediately preceding frequency; And A comparison processing unit for comparing the subtraction count signal outputted from the subtraction processing unit with a predetermined reference count signal; Touch sensor comprising a. The method of claim 1, A delay unit for delaying and outputting the comparison processing signal for the predetermined time when the logic state of the comparison processing signal output from the comparison processing unit is maintained for a predetermined time Touch sensor further comprising. The method of claim 2, And the reference count signal has a fixed value. The method of claim 2, And the reference count signal is multiplied by a predetermined detection rate by a previous subtraction count signal which is a signal immediately before the subtraction count signal. The method of claim 4, wherein The predetermined detection rate is a touch sensor, characterized in that 0.2 to 0.3. The method of claim 2, The reference count signal is a touch sensor, characterized in that a plurality of reference count signal having a different value. The method of claim 1, The electrical signal is a touch sensor.

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