KR101486295B1 - Capacitive sensor with low frequency noise removal function - Google Patents

Abstract

The present invention relates to an electrostatic sensor having a low-frequency noise canceling function, and more particularly, to an electrostatic sensor having a low-frequency noise canceling function, including: a charge amount sensing unit including a capacitor whose capacitance changes due to a touch or noise and whose charge amount changes due to a change in capacitance; A charge amplification unit for amplifying and outputting a fundamental noise applied from the outside when the TX signal is on and amplifying a change amount of the charge input from the charge amount sensing unit when the TX signal is off; A sampling unit for sampling a fundamental noise received from the charge amplification unit to output a first signal, sampling a change amount of the charge, and outputting a second signal; A noise component removing unit for calculating and outputting a third signal which is a difference between a first signal and a second signal received from the sampling unit; And an analog-to-digital converter converting the third signal received from the noise component removing unit into a digital signal and outputting the digital signal.
According to the present invention, an algorithm for eliminating low-frequency noise is processed in the front end of the ADC to sufficiently cope with external noise and to minimize sensitivity loss.
In addition, there is an effect that sensitivity can be improved by removing noise common to a reference signal and a signal with respect to an input noise signal, followed by a differential method.
In addition, the algorithm for eliminating low-frequency noise is processed at the analog end of the ADC so that problems such as reduction in operating speed, increase in current, and increase in area due to processing at the rear end of the ADC can be solved.

Description

[0001] CAPACITIVE SENSOR WITH LOW FREQUENCY NOISE REMOVAL FUNCTION [0002]

The present invention relates to an electrostatic sensor having a low frequency noise canceling function, and more particularly to an electrostatic sensor having a low frequency noise canceling function capable of minimizing loss of sensitivity by removing low frequency noise inputted to a mutual capacitance electrostatic sensor Sensor.

The principle of the electrostatic sensor is a structure that senses a change in the amount of charge input to the sensor. The change of the charge amount can be changed in various ways, and a typical device for applying the change is a device for inducing a change of the charge amount by the touch.

FIG. 1 is a circuit diagram of a conventional mutual capacitance type electrostatic sensor, and FIG. 2 is a driving waveform diagram of the conventional mutual capacitance type electrostatic sensor of FIG. 1 and 2, c1 is a capacitor whose value is physically fixed, and c2 is a capacitor whose value changes by a change in the amount of charge. and c3 is a capacitor necessary for changing a change in the amount of charge that varies depending on the voltage TX applied to c1 and c2 to a change amount of the voltage. 1, a difference in the amount of change is generated as shown by dV in FIG. 2 due to the amount of change in c2. The difference in the amount of change is represented by a digital value dV_code And output.

FIG. 3 is a circuit diagram showing a path through which noise is introduced in the conventional mutual capacitance type electrostatic sensor of FIG. 1, and FIG. 4 is a driving waveform diagram of a conventional mutual capacitance type electrostatic sensor when noise is introduced. Referring to FIG. 3 and FIG. 4, the period of time when the noise is introduced typically flows in the change of c2 which causes a change in the amount of charge. Generally, the input noise is generated because vss1, which is the ground of the system, and vss2, which is the ground of the external system, which causes the change of the charge amount, are not equal to each other. The frequency of the noise is relatively low frequency noise of several tens Hz to several hundreds of Khz .

The external noise vn is amplified by c3. The vout output by the noise has the frequency of the external system noise and oscillates with a very large amplitude. As a result, the amount of change dV is greatly reduced as compared with that in FIG. 2, resulting in a problem that the margin of the output sensitivity becomes very small.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems of the prior art, and it is an object of the present invention to provide an electrostatic discharge type electrostatic discharge The present invention has an object of providing a sensor.

Also, it is desirable to provide an electrostatic sensor having a low-frequency noise canceling function capable of enhancing sensitivity by eliminating a common noise component by applying a common noise to a reference signal and a signal with respect to an inputted noise signal, It is an object of the invention.

According to an aspect of the present invention, there is provided an electrostatic sensor having a low frequency noise canceling function, including: a charge amount sensing unit including a capacitor whose capacitance changes due to a touch or noise and whose charge amount changes due to a change in capacitance; A charge amplification unit for amplifying and outputting a fundamental noise applied from the outside when the TX signal is on and amplifying a change amount of the charge input from the charge amount sensing unit when the TX signal is off; A sampling unit for sampling a fundamental noise received from the charge amplification unit to output a first signal, sampling a change amount of the charge, and outputting a second signal; A noise component removing unit for calculating and outputting a third signal which is a difference between a first signal and a second signal received from the sampling unit; And an analog-digital converter for converting the third signal received from the noise component removing unit into a digital signal and outputting the digital signal.

Also, the charge amplifying unit may include: an amplifier for amplifying and outputting a variation amount of the charge inputted from the external noise and the basic noise applied from the outside; A feedback capacitor connected between the inverting input terminal and the output terminal of the amplifier; And a switch connecting both ends of the feedback capacitor. When the TX signal is on, when the switch is turned off, a fundamental noise applied from the outside by the amplifying action of the amplifier and the feedback capacitor is And amplifying and outputting a change amount of the charge input from the charge amount sensing unit by the amplifying action of the amplifier and the feedback capacitor when the TX signal is turned off when the switch is off, have.

The charge quantity sensing unit may include a first capacitor having a fixed charge value and a second capacitor having a capacitance varying due to a touch or noise and varying in charge amount due to a change in the capacitance, The first capacitor and the second capacitor can be initialized in a state in which the TX signal is on and the switch is on.

Also, the charge amplifying unit may include: an amplifier for amplifying and outputting a variation amount of the charge inputted from the external noise and the basic noise applied from the outside; A first variable capacitor connected between an inverting input terminal and an output terminal of the amplifier; A first switch connecting both ends of the first variable capacitor; A second variable capacitor connected to one end of the first switch; And a second switch for connecting the other end of the first switch and the second variable capacitor. When the TX signal is on, when the first switch and the second switch are turned off, And amplifying and outputting a fundamental noise applied from the outside by the amplifying action of the first variable capacitor, and when the first switch is off, the TX signal is turned off and the second switch is turned on ), The amount of change of the charge input from the charge amount sensing unit can be amplified and output by the amplifying action of the amplifier, the first variable capacitor, and the second variable capacitor.

The charge quantity sensing unit may include a first capacitor having a fixed charge value and a second capacitor having a capacitance varying due to a touch or noise and varying in charge amount due to a change in the capacitance, Wherein the first capacitor and the second capacitor are electrically connected to each other while the TX signal is on and the first switch is on and the second switch is off, The second capacitor can be initialized.

The sampling unit includes: a noise sampling unit for sampling a fundamental noise received from the charge amplification unit according to a first control signal and outputting a first signal; And a signal sampling unit for sampling a change amount of the charge received from the charge amplification unit according to a second control signal and outputting a second signal, wherein the noise sampling unit comprises: The signal sampler samples the basic noise by the signal and the signal sampling unit samples the variation of the charge by the second control signal in the off state of the TX signal to output the second signal .

In addition, the analog-to-digital converter may convert the third signal into a digital signal in accordance with the third control signal while the TX signal is off.

According to the electrostatic sensor having a low-frequency noise canceling function according to the present invention, an algorithm for eliminating low-frequency noise is processed in the front end of the ADC to sufficiently cope with external noise and to minimize sensitivity loss.

In addition, there is an effect that sensitivity can be improved by removing noise common to a reference signal and a signal with respect to an input noise signal, followed by a differential method.

In addition, the algorithm for eliminating low-frequency noise is processed at the analog end of the ADC so that problems such as reduction in operating speed, increase in current, and increase in area due to processing at the rear end of the ADC can be solved.

1 is a circuit diagram of a conventional mutual capacitance type electrostatic sensor.
2 is a drive waveform diagram of the conventional mutual capacitance type electrostatic sensor of FIG.
3 is a circuit diagram showing a path through which noise flows in the conventional mutual capacitance type electrostatic sensor of FIG.
4 is a driving waveform diagram of a conventional mutual capacitance type electrostatic sensor when noise is introduced.
5 is a block diagram of an electrostatic sensor having a low-frequency noise canceling function according to the present invention.
6 is a circuit diagram of an electrostatic sensor having a low frequency noise canceling function according to a first embodiment of the present invention.
7 is a driving waveform diagram of an electrostatic sensor having a low frequency noise canceling function according to the first embodiment of the present invention.
8 is a circuit diagram of an electrostatic sensor having a low-frequency noise canceling function according to a second embodiment of the present invention.
9 is a driving waveform diagram of an electrostatic sensor having a low frequency noise canceling function according to a second embodiment of the present invention.

Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings.

In the present invention, since the TX signal and various signals have phases, the present invention is also applicable to the case where the phases of the signals are opposite to each other, and it is obvious that they belong to the scope of the present invention.

5 is a block diagram of an electrostatic sensor having a low frequency noise canceling function according to the present invention.

5, an electrostatic sensor 100 having a low frequency noise canceling function includes a charge amount sensing unit 10, a charge amplifying unit 20, a sampling unit 30, a noise component removing unit 40, (ADC) 50, as shown in FIG. A drive control unit (not shown) for generating and controlling various control signals for controlling the operation of the sampling unit 30 and the analog-to-digital conversion unit 50, the voltage TX applied to the capacitors included in the charge amount sensing unit 10, Time).

The charge quantity can be varied by various methods. Typically, the amount of charge can be changed by a touch, but the present invention can be applied to all devices in which the amount of charges other than the touch can change.

The charge quantity sensing unit 10 includes a capacitor whose capacitance changes due to a touch or noise, and whose amount of charge changes due to such a change in capacitance. Preferably, it can be realized by a mutual capacitance method.

The charge amplification unit 20 amplifies and outputs the fundamental noise vn applied from the outside when the TX signal is turned on in the drive control unit and outputs the amplified basic noise vn Amplifies and outputs the change amount of the charge.

The sampling unit 30 samples the fundamental noise vn received from the charge amplification unit 20, outputs a first signal, samples a change amount of the charge, and outputs a second signal.

Specifically, when a signal for controlling the driving of the sampling unit 30 is inputted by the drive control unit in the ON state of the TX signal, the basic noise vn is sampled and the first signal is output. The first signal is a reference. After the first signal is outputted, the TX control signal is turned off by the drive control unit, and when the signal for controlling the driving of the sampling unit 30 is inputted, the variation of the charge is sampled and the second signal is outputted . The second signal is a signal.

The noise component removing unit 40 calculates and outputs a third signal which is a difference between the first signal and the second signal received from the sampling unit 30. [ Specifically, the third signal is a component obtained by subtracting the first signal from the second signal.

The analog-to-digital converter (ADC) 50 converts the third signal received from the noise component removing unit 40 into a digital signal and outputs the digital signal.

[First Embodiment]

FIG. 6 is a circuit diagram of an electrostatic sensor having a low-frequency noise canceling function according to a first embodiment of the present invention, FIG. 7 is a driving waveform diagram of an electrostatic sensor having a low- to be.

6 and 7, the charge amplification unit 20 includes an amplifier 21 for amplifying and outputting a fundamental noise vn applied from the outside and a change amount of the charge input from the charge amount sensing unit 10, A feedback capacitor c3 connected between the inverting input terminal and the output terminal of the feedback capacitor c1 and a switch sw connecting both ends of the feedback capacitor c3.

When the switch SW is turned off while the TX signal is turned on by the drive control unit, the amplifier 21 and the feedback capacitor c3 amplify the fundamental noise vn applied from the outside by the amplifying action of the feedback capacitor c3. And when the TX signal is turned off by the drive control unit in the state that the switch SW is off, the charge amount detection unit 10 is activated by the amplifying action of the amplifier 21 and the feedback capacitor c3, And outputs the amplified amount of change.

The charge quantity sensing unit 10 includes a first capacitor c1 whose charge value is fixed and a second capacitor c2 whose capacitance is changed by a touch or noise and whose charge amount is changed by the change of the capacitance , The change of the amount of charge is sensed by the interaction of the first capacitor c1 and the second capacitor c2 and the change of the charge amount is detected by the drive control unit in the state where the TX signal is on and the switch sw is on, Thereby initializing the one-capacitor c1, the second capacitor c2 and the capacitor c4. The charge amount sensing unit 10 is grounded by the capacitor c4. At this time, the fundamental noise vn applied from the outside by the feedback operation of the amplifier 21 is absorbed by the amplifier 21, so that the noise vn is not observed. Then, in a state in which the TX signal is on, the switch sw is turned off to amplify and output the fundamental noise vn externally applied by the amplifying action of the amplifier 21 and the feedback capacitor c3, the amplifier 21 and the feedback capacitor c3 amplify the amount of change of the charge input from the charge amount sensing unit 10 by the amplifying action of the amplifier 21 and the feedback capacitor c3 when the TX signal is turned off with the switch sw off, .

The sampling unit 30 includes a noise sampling unit 31 for sampling a fundamental noise received from the charge amplification unit 20 according to a first control signal smp_ref and outputting a first signal vsnh_ref, and a signal sampling unit 32 for sampling a variation amount of the charge received from the charge amplification unit 20 according to the smp_sig signal and outputting a second signal (vsnh_sig).

The noise sampling unit 31 samples the fundamental noise by the first control signal smp_ref of the drive control unit in the TX signal on state by the drive control unit and outputs the first signal (vsnh_ref) (32) samples the amount of change in charge by the second control signal (smp_sig) while the TX signal is off by the drive control unit and outputs the second signal (vsnh_sig).

The noise component removing unit 40 calculates a third signal V_diff obtained by subtracting the first signal (vsnh_ref) received from the noise sampling unit 31 from the second signal (vsnh_sig) received by the signal sampling unit 32 Output.

The ADC 50 converts the third signal V_diff into a digital signal ADC_OUT according to the third control signal adc_ena in the state that the TX signal is off by the drive control unit, do.

7, the operation of the TX signal, the operation of the switch, the sampling unit 30 and various signals output from the noise component removing unit 40 of the electrostatic sensor described in the first embodiment, the sampling unit 30, Various control signals for controlling the analog-to-digital converter (ADC) 50, and a drive waveform of dV_code having improved output sensitivity compared with the conventional technique dV_code in FIG. 4 can be seen.

[Second Embodiment]

FIG. 8 is a circuit diagram of an electrostatic sensor having a low-frequency noise canceling function according to a second embodiment of the present invention, FIG. 9 is a driving waveform diagram of an electrostatic sensor having a low-frequency noise canceling function according to the second embodiment of the present invention to be.

8 and 9, an electrostatic sensor 100 having a low-frequency noise canceling function according to a second embodiment of the present invention includes a charge quantity sensing unit 10, a sampling unit 30, a noise component removing unit 40 ) And the analog-to-digital converter (ADC) 50 are the same as those in the first embodiment.

Specifically, the difference is the charge amplification part 20, and therefore, the description will be focused on this point.

The charge amplification unit 20 includes an amplifier 21 for amplifying and outputting a basic noise vn and an amount of change of charges input from the charge amount sensing unit 10 from the outside and an inverting input terminal and an output terminal of the amplifier 21, A first switch sw1 connecting both ends of the first variable capacitor c5, a second variable capacitor c6 connected to one end of the first switch sw1, and a second variable capacitor c5 connected to one end of the first switch sw1. 1 switch (sw1) and a second switch (sw2) connecting the other end of the switch (sw1) and the second variable capacitor (c6).

When the first switch sw1 and the second switch sw2 are turned off while the TX signal is turned on by the drive control unit, the amplifying operation of the amplifier 21 and the first variable capacitor c5 Amplifies and outputs the basic noise vn applied from the outside and turns off the TX signal by the drive control section while the first switch sw1 is off and turns on the second switch sw2 ) Amplifies the amount of change of the charge input from the charge amount sensing unit 10 by the amplifying action of the amplifier 21, the first variable capacitor c5 and the second variable capacitor c6.

The charge quantity sensing unit 10 includes a first capacitor c1 having a fixed charge value and a second capacitor c2 having a capacitance change due to a touch or noise and having a charge amount changed due to a change in the capacitance The first switch sw1 is turned on and the TX switch is turned on by the drive control unit to sense a change in the amount of charge due to the interaction between the first capacitor c1 and the second capacitor c2, And initializes the first capacitor (c1) and the second capacitor (c2) while the second switch (sw2) is off. The charge amount sensing unit 10 is grounded by the capacitor c4. At this time, the fundamental noise vn applied from the outside by the feedback operation of the amplifier 21 is absorbed by the amplifier 21, so that the noise vn is not observed. Then, when the TX signal is on, the first switch sw1 and the second switch sw2 are turned off, and the amplifying operation of the amplifier 21 and the first variable capacitor c5 is performed, Amplifies and outputs the noise vn and turns off the TX signal and turns on the second switch sw2 when the first switch sw1 is off, And amplifies and outputs the amount of change of the charge input from the charge amount sensing unit 10 by the amplifying action of the first variable capacitor c5 and the second variable capacitor c6.

Details of the other components are the same as those of the first embodiment, and thus will not be described.

9, the operation of the TX signal and the switch of the electrostatic-type sensor described in the second embodiment and the driving of various control signals for controlling the sampling unit 30 and the analog-to-digital converter (ADC) You can see the waveform.

According to the present invention, an algorithm for eliminating low-frequency noise is processed in the front end of the ADC to sufficiently cope with external noise and to minimize sensitivity loss.

In addition, there is an effect that sensitivity can be improved by removing noise common to a reference signal and a signal with respect to an input noise signal, followed by a differential method.

In addition, the algorithm for eliminating low-frequency noise is processed at the analog end of the ADC so that problems such as reduction in operating speed, increase in current, and increase in area due to processing at the rear end of the ADC can be solved.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents. Obviously, such modifications are intended to be within the scope of the claims.

10: charge amount sensing unit 20: charge amplification unit
21: amplifier 30: sampling unit
31: Noise sampling unit 32: Signal sampling unit
40: noise component removing unit 50: analog-to-digital converter (ADC)

Claims (7)

A charge amount sensing unit including a capacitor whose capacitance changes due to a touch or noise and whose charge amount changes due to such a change in capacitance;
A charge amplification unit for amplifying and outputting a fundamental noise applied from the outside when the TX signal is on and amplifying a change amount of the charge input from the charge amount sensing unit when the TX signal is off;
A sampling unit for sampling a fundamental noise received from the charge amplification unit to output a first signal, sampling a change amount of the charge, and outputting a second signal;
A noise component removing unit for calculating and outputting a third signal which is a difference between a first signal and a second signal received from the sampling unit; And
And an analog-to-digital converter converting the third signal received from the noise component removing unit into a digital signal and outputting the digital signal. The method according to claim 1,
Wherein the charge amplification unit comprises:
An amplifier for amplifying and outputting a basic noise applied from the outside and a variation amount of the charge input from the charge amount sensing unit;
A feedback capacitor connected between the inverting input terminal and the output terminal of the amplifier; And
And a switch connecting both ends of the feedback capacitor,
When the TX signal is on, amplifying and outputting a fundamental noise applied from the outside by the amplifying action of the amplifier and the feedback capacitor when the switch is turned off, and when the switch is off, Wherein when the TX signal is turned off, a change amount of the charge input from the charge amount sensing unit is amplified by the amplifying action of the amplifier and the feedback capacitor, and then the amplified charge amount is outputted. 3. The method of claim 2,
Wherein the charge quantity sensing unit includes a first capacitor whose charge value is fixed and a second capacitor whose capacitance is changed by a touch or noise and whose charge amount is changed by a change of the capacitance, Sensing the change in charge quantity by the interaction of the capacitors,
Wherein the first capacitor and the second capacitor are initialized when the TX signal is on and the switch is on. The method according to claim 1,
Wherein the charge amplification unit comprises:
An amplifier for amplifying and outputting a basic noise applied from the outside and a variation amount of the charge input from the charge amount sensing unit;
A first variable capacitor connected between an inverting input terminal and an output terminal of the amplifier;
A first switch connecting both ends of the first variable capacitor;
A second variable capacitor connected to one end of the first switch; And
And a second switch connecting the other end of the first switch and the second variable capacitor,
Amplifying and outputting a fundamental noise applied from the outside by amplifying the amplifier and the first variable capacitor when the first switch and the second switch are turned off while the TX signal is on, When the TX signal is turned off while the first switch is turned off and the second switch is turned on, the amplification of the amplifier, the first variable capacitor, and the second variable capacitor, Amplifies the amount of change of the charge input from the charge pump, and outputs the amplified charge. 5. The method of claim 4,
Wherein the charge quantity sensing unit includes a first capacitor whose charge value is fixed and a second capacitor whose capacitance is changed by a touch or noise and whose charge amount is changed by a change of the capacitance, Sensing the change in charge quantity by the interaction of the capacitors,
Wherein the first and second capacitors are initialized when the TX signal is on, the first switch is on, and the second switch is off. Electrostatic sensors equipped. The method according to claim 2 or 4,
Wherein the sampling unit comprises:
A noise sampling unit for sampling a fundamental noise received from the charge amplification unit according to a first control signal and outputting a first signal; And
And a signal sampling unit for sampling a change amount of the charge received from the charge amplification unit according to a second control signal and outputting a second signal,
Wherein the noise sampling unit samples the fundamental noise by the first control signal and outputs a first signal when the TX signal is on,
Wherein the signal sampling unit samples a change amount of the charge by the second control signal and outputs a second signal when the TX signal is off. The method according to claim 1,
Wherein the analog-to-digital converter converts the third signal into a digital signal and outputs the digital signal according to a third control signal when the TX signal is off.

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