TW201519054A - Capacitive touch sensor and switching method between self capacitance and mutual capacitance therefor - Google Patents

Abstract

A capacitive touch sensor comprises a touch interface, a sensing unit, a driving and sensing unit and a control unit for providing self-capacitance and mutual-capacitance sensing. The control unit has an analog mux. The switching of the mux integrates the driving unit and the sensing to simplify the circuitry for reducing the circuit (or chip) area. In the mutual-capacitive mode, the sensing signal is integrated to provide the sensing result. In the self-capacitive mode, charging/discharging the parasitic capacitance(s) to a balance voltage level in a predetermined frequency and converting the balance voltage level to the sensing result.

Description

Capacitive touch sensor and switching method of self-capacity and mutual capacitance

The invention relates to a touch sensor, and in particular to a capacitive touch sensor and a self-capacitance and mutual capacitance switching method thereof.

Capacitive touch sensors are used as input tools for human-machine interfaces. In general, projected capacitive touch sensors have self capacitance and mutual capacitance. The so-called self-containment means that both the driver and the sensing end are the same point; and the mutual capacitance refers to the two points where the driving end and the sensing end are separated. The self-capacity and the mutual capacity have their own advantages and disadvantages, and the self-contained ghost points ( Ghost point), mutual compatibility is not, so mutual compatibility can achieve true multi-touch.

Taiwan Patent Publication No. TW 201133319 discloses a touch sensing system, an electronic touch device and a touch sensing method, the circuit blocks of which are shown in FIGS. 1A and 1B. The electronic touch device 100 includes a touch interface 110 , at least one sensing unit 120 (including 120 a , 120 b ), a switching unit 130 , a processing unit 140 , and a driving unit 160 . The driving unit 160 is coupled to the switching unit 130 and the processing unit 140 and is adapted to transmit a driving signal.

In the mutual capacitance mode of FIG. 1B, the switching unit 130 is firstly switched to the driving unit 160, the driving unit 160 drives the signal to the driving line 114, and the sensing unit 120 sequentially receives the receiving line 112 (receive line). And finally the processing unit 140 converts the received analog signal into a digital signal until the last one The signal of the receiving line is processed. Next, switch to the next drive line. Therefore, if the drive line has m traces and the receive line has n lines, scanning a frame must correspond to m*n scan paths.

To perform the self-contained mode, as shown in the self-capacity mode of FIG. 1A, the switching unit 130 is switched and connected to the sensing unit 120, and the overall scanning mechanism is sequentially scanning the X-axis and the Y-axis, and the driving contact is sensed by self-capacitance ( Pin) shares the same contact with the sensing contact. When scanning one line, the driving signal drives the line, and the processing unit 140 senses the analog signal of the line and converts it into a digital signal. If there are m lines on the X axis and n lines on the Y axis, scanning one frame requires m+n scan paths.

The mutual-capacity scanning takes a long time, but the mutual capacitance has no ghost point problem; in contrast, the self-contained scanning time is shorter, but the self-contained problem has a ghost point. It can be seen that the main feature of the conventional method is that the driving unit 160 for mutual capacitance sensing and the self-capacitating sensing unit 120 need to construct a set of circuits, and also need to switch the switch 130 for switching the driving unit 160. With the sensing unit 120, such a mechanism wastes wafer area and increases wafer cost.

The embodiment of the invention provides a capacitive touch sensor and a self-capacitance and mutual capacitance switching method thereof, which can provide sensing of self-capacity and mutual capacitance.

The embodiment of the invention provides a capacitive touch sensor, which comprises a touch interface, a sensing unit, a driving/sensing unit and a control unit. The touch interface has a plurality of first lines and a plurality of second lines. The sensing unit is configured to couple the contact interface. The drive/sense unit generates a drive signal. The control unit controls the sensing unit and the driving/sensing unit, and the control unit switches the capacitive touch sensor to the mutual capacitance sensing mode or the self-capacitive sensing mode. The control unit has an analog multiplexer, and the output end of the analog multiplexer is coupled to the sensing unit, the first input end of the analog multiplexer is coupled to the first line, and the second input end of the analog multiplexer is coupled to the second line . When the capacitive touch sensor is in the mutual capacitance sensing mode, the driving/sensing unit provides a driving signal to the second line, and the sensing unit is coupled to the first line through the analog multiplexer to enable the sensing unit to sense The first sensing signal of the first line. When the capacitive touch sensor is in the self-capacitance sensing mode, the sensing unit is coupled to the first line or the second line according to the switching of the analog multiplexer, and senses the first sensing signal of the first line or The second sensing signal of the second line.

The embodiment of the invention provides a self-capacitance and mutual capacitance switching method, which is used for a capacitive touch sensor, and the capacitive touch sensor comprises a touch interface, a sensing unit, a driving/sensing unit and a control unit, The control unit has an analog multiplexer, and the method includes the following steps. First, it is determined that the capacitive touch sensor operates in a mutual capacitance sensing mode or a self-capacitive sensing mode, wherein the analog multiplexer couples the sensing unit to the touch according to the mutual capacitance sensing mode or the self-capacitive sensing mode. The first line or the second line of the interface. Then, when the capacitive touch sensor is in the mutual capacitance sensing mode, a bias voltage is supplied to the first line through the analog multiplexer, and the first sensing signal of the first line is integrated, and the first The integrated result of the sensing signal is converted into a sensing result signal. Then, when the capacitive touch sensor is in the self-capacity detection mode, the second line is coupled to the ground, the first line is coupled to the sensing unit through the analog multiplexer, and the sensing unit is connected to the first line at a specific frequency. The formed parasitic capacitance is charged and discharged so that the potential of the first line approaches the equilibrium potential, and then the balanced potential is converted into the sensing result signal.

In summary, the embodiments of the present invention provide a capacitive touch sensor and a self-capacitance and mutual capacitance switching method thereof, which are driven by switching of an analog multiplexer according to sensing conditions of self-capacity and mutual capacitance. The unit is integrated with the sensing unit to simplify the structure of the circuit to save the area of the circuit (or wafer).

The detailed description of the present invention and the accompanying drawings are to be understood by the claims The scope is subject to any restrictions.

100‧‧‧Electronic touch device

110‧‧‧Touch interface

120, 120a, 120b‧‧‧ sensing unit

130‧‧‧Switch unit

140‧‧‧Processing unit

160‧‧‧ drive unit

114‧‧‧Drive line

112‧‧‧Sensing line

2‧‧‧Capacitive touch sensor

210‧‧‧ Touch interface

220, 41‧‧‧ Sensing unit

230‧‧‧Control unit

240‧‧‧Processing unit

250‧‧‧Drive/Sensor Unit

212, RCV‧‧‧ first line

214, DRV‧‧‧ second line

42‧‧‧ analog multiplexer

VP‧‧‧ drive signal

TS1‧‧‧first sensing signal

TS2‧‧‧ second sensing signal

TS3‧‧‧Sensor signal

CPD, CPR, CM‧‧‧ parasitic capacitance

OP1‧‧‧ Comparator

412‧‧‧Bias circuit

411‧‧‧current mirror

413‧‧‧Reset circuit

CLD, CS‧‧‧ capacitor

S1, S2, S3, S4, S5, S6, S7‧‧ switch

P1, P2, P3, P4, N1, P5, P6, P7‧‧‧ transistors

Vo, M1‧‧‧ output

M2‧‧‧ first input

M3‧‧‧ second input

T1‧‧‧ first output

T2‧‧‧ second output

OP2‧‧‧Operational Amplifier

SENS‧‧‧ endpoint

V _SENS ‧‧‧Sensor signal

Vref‧‧‧ reference signal

Cmp‧‧‧ comparison signal

pRECT, pISRC, pGATE, pDISCHRG, nSENS, pINIT‧‧‧ control signals

nSENS‧‧‧balance signal

ISRC1, ISRC2‧‧‧ current source

GND‧‧‧ Grounding

VDD‧‧‧ voltage

S101, S103, S105‧‧‧ step procedure

1A is a circuit block diagram of a conventional electronic touch device.

FIG. 1B is a circuit block diagram of a conventional electronic touch device.

2 is a circuit block of a capacitive touch sensor according to an embodiment of the invention. Figure.

3 is a circuit layout diagram of a touch interface provided by an embodiment of the present invention.

4 is an equivalent circuit diagram of the touch interface of FIG. 3.

5A is a circuit diagram of a circuit for a sensing unit and a driving/sensing unit provided by an example of the present invention.

Figure 5B is a waveform diagram of the circuit of Figure 5A.

FIG. 6 is a circuit diagram of a sensing unit in a mutual capacitance sensing mode according to an embodiment of the present invention.

FIG. 7 is a timing diagram of the sensing unit of FIG. 6.

FIG. 8 is a circuit diagram of a sensing unit in a self-capacitance sensing mode according to an embodiment of the present invention.

9 is a waveform diagram of the sensing unit of FIG. 8.

FIG. 10 is a circuit diagram of a sensing unit in a self-capacitance sensing mode according to an embodiment of the invention.

FIG. 11 is a flowchart of a method for switching between self-capacity and mutual capacitance according to an embodiment of the present invention.

The self-capacitance scan time is proportional to the sum of the number of traces of the X-axis and the Y-axis (X+Y), and the scan time of the mutual capacitance is proportional to the product of the number of lines of the X-axis and the Y-axis (X*Y). Therefore, the self-contained scanning time is shorter and more power-saving. Therefore, in order to integrate the advantages of self-contained and mutual capacity, the present invention provides a capacitive touch sensor and a self-capacitance and mutual capacitance switching method thereof, which has the advantages of saving circuit (or wafer) area. The self-capacity and mutual capacitance switching circuit and method thereof proposed by the present invention are exempt from the switching unit 130 of FIG. 1A (and FIG. 1B), and the driving unit 160 and the sensing unit 120 of FIG. 1A (and FIG. 1B) are integrated. .

[Embodiment of Capacitive Touch Sensor]

The circuit block of the capacitive touch sensor of the present invention is shown in FIG. 2, and the capacitive touch The control sensor 2 includes a touch interface 210, a sensing unit 220, a driving/sensing unit 250, a processing unit 240, and a control unit 230. The touch interface 210 has a plurality of first lines 212 (represented by receiving lines in FIG. 2) and a plurality of second lines 214 (represented by driving lines in FIG. 2), and the sensing is performed according to self-capacity and mutual capacitance. A line 212 and a second line 214 may be a driving line or a receiving line. The present invention does not limit the first line 212 and the second line 214 to be a driving line or a receiving line.

According to the architecture of FIG. 2 , the control unit 230 controls the sensing unit 220 and the driving/sensing unit 250 , and the control unit 230 switches the capacitive touch sensor 2 into a mutual capacitive sensing mode or a self-capacitive sensing mode. The control unit 230 has an analog multiplexer (not shown in FIG. 2 , referring to the analog multiplexer 42 of FIG. 6 ). The output M1 of the analog multiplexer 42 is coupled to the sensing unit 220 and the analog multiplexer. The first input terminal M2 of the 42 is coupled to the first line 212 (the first line RCV of FIG. 4), and the second input terminal M3 of the analog multiplexer 42 is coupled to the second line 214 (the second line DRV of FIG. 4). When the capacitive touch sensor 2 is in the mutual capacitance sensing mode, the driving/sensing unit 250 provides the driving signal VP to the second line 214, and the sensing unit 220 is coupled to the first line 212 through the analog multiplexer to The sensing unit 220 is caused to sense the first sensing signal TS1 of the first line 212. When the capacitive touch sensor 2 is in the self-capacitance sensing mode, the sensing unit 220 is coupled to the first line 212 or the second line 214 according to the switching of the analog multiplexer, and senses the first line 212. A sensing signal TS1 or a second sensing signal TS2 of the second line 214.

In detail, the driving/sensing unit 250 can be switched by the control unit 230 into a driving mode or a sensing mode, the driving mode corresponding to the mutual capacitance sensing mode, the sensing mode corresponding to the self-capacitance sensing mode. The processing unit 240 is coupled to the sensing unit 220, the driving/sensing unit 250, and the control unit 230, and converts the analog first sensing signal TS1 and the second sensing signal TS2 into digital signals. In other words, the processing unit 240 receives the analog signal from the sensing unit 220 or the driving/sensing unit 250 and converts it into a digital signal. The control unit 230 is configured to control the sensing unit 220, the driving/sensing unit 250, and the processing unit 240.

The drive/sense unit 250 generates a drive signal VP. When the mutual capacitance sensing mode is to be performed, the driving/sensing unit 250 is switched to the driving mode by the control unit 230, and the driving/sensing unit 250 provides a driving signal to the second line 214 (drive line) of the touch interface 210. The first sensing signal TS1 from the first line 212 of the touch interface 210 is sequentially received by the sensing unit 220, and then the received analog signal is converted into a digital signal by the processing unit 240 until the last first line 212. The signal (receive line) is processed. Then, switching to the next second line 214 (drive line), the first sensing signal TS1 is sequentially sensed again. Therefore, if the second line 214 (drive line) has m traces and the receive line has n lines, scanning a frame requires m*n scan paths.

To perform the self-capacitance sensing mode, the overall scanning mechanism scans the X-axis and the Y-axis sequentially. Since the self-capacitance senses that the driving contact (pin) and the sensing contact share the same contact, each time a line is scanned, The drive signal is driven to the line while the processing unit 240 receives the analog signal of the line sensed by the sensing unit 220 and converts it into a digital signal. If the X-axis has m lines and the Y-axis has n lines, scanning a frame requires m+n scanning paths.

Referring to FIG. 3 and FIG. 4 simultaneously, it is assumed that the line layout of the two interleaved second lines DRV (X-axis) and the first line RCV (Y-axis) is as shown in FIG. 3, and the parasitic capacitance of the second line DRV to the ground is CPD, and the parasitic capacitance of the first line RCV to ground is CPR, and the parasitic capacitance between the second line DRV and the first line RCV is CM, and the equivalent circuit is as shown in FIG. It should be noted that, in FIG. 3, the second line DRV and the first line RCV are represented by nodes, the second line DRV is the first line 212 in FIG. 2, and the first line RCV is the second line 214 in FIG. . In this embodiment, in the mutual capacitance sensing mode, the second line DRV is a driving line, and the first line RCV is a sensing line. In the self-capacitance sensing mode, the second line DRV (or the first line RCV) is both a drive line and a sense line.

Referring to FIG. 2, FIG. 5A and FIG. 6, FIG. 5A is a circuit used in the sensing unit 220 and the driving/sensing unit 250. FIG. 6 is a sensing provided by an embodiment of the present invention. The circuit diagram of the unit in the mutual capacitance sensing mode. The circuit architecture of the sensing unit 220 in FIG. 2 is further described below. The sensing unit 220 is implemented with the sensing unit 41 of FIG. The sensing unit 41 includes a comparator OP1 (in this embodiment, an operational amplifier), a bias circuit 412, a current mirror 411, a first capacitor CLD, a second capacitor CS, a reset circuit 413, and a first transistor P1. The second transistor P2, the third transistor P3, the fourth transistor P4, the second switch S2, the third switch S3, the current source ISRC1, and the fourth switch S4. Analog signal multiplexer 42, control signals pRECT, pISRC, pGATE, pDISCHRG, third transistor P3, fourth transistor P4, and control signal nSENS of transistor N1 for all switches (S1, S2, S3, S4, S5) The pINIT is controlled by the control unit 230.

The first input terminal (-) of the comparator OP1 receives the reference signal Vref, and the second input terminal (+) of the comparator receives the first sensing signal TS1 or the second sensing signal TS2 according to the switching of the analog multiplexer 42. The output of comparator OP1 produces a comparison signal Cmp. The bias circuit 412 is coupled to the second input terminal (+) of the comparator OP1, and the bias circuit 412 provides a bias voltage. In the embodiment, the bias voltage is Vref, but the invention is not limited thereto. The bias voltage can be adjusted according to the actual design. The bias circuit 412 includes a first switch S1 and a unit gain buffer (consisting of the operational amplifier OP2). The current mirror 411 has a first output terminal T1 and a second output terminal T2. In the present embodiment, the current mirror 411 is composed of transistors P5, P6, and P7 and a current source ISRC2. The first end of the first capacitor CLD is coupled to the second input end (+) of the comparator OP1 and the first output end T1 of the current mirror 411, and the second end of the second capacitor CLD is coupled to the ground GND. The first end of the second capacitor CS is coupled to the second output terminal T2 of the current mirror 411, the second end of the second capacitor CS is coupled to the ground GND, and the first end of the second capacitor CS (ie, the output terminal Vo) provides sensing Result signal TS3. The reset circuit 413 is coupled to the first end of the second capacitor CS (ie, the output terminal Vo) for resetting the potential of the second terminal (Vo) of the second capacitor CS. In the present embodiment, the reset circuit 413 is implemented by a transistor N1. The first transistor P1 is coupled between the first output terminal T1 of the current mirror 411 and the first terminal of the first capacitor CLD, and is controlled by the comparison signal Cmp. The second transistor P2 is coupled to the electricity The second output terminal T2 of the flow mirror 411 and the first end (Vo) of the second capacitor CS are controlled by the comparison signal Cmp. The third transistor P3 is coupled between the first transistor P1 and the first end of the first capacitor CLD and is controlled by a balance signal nSENS. The fourth transistor P4 is coupled between the second transistor P2 and the first end (Vo) of the second capacitor CS, and is controlled by the balance signal nSENS. The second switch S2 is coupled between the output terminal M1 of the analog multiplexer 42 and the second input terminal (+) of the comparator OP1. The current source ISRC1 is coupled to the second input terminal (+) of the comparator OP1 via the third switch S3. The fourth switch S4 is coupled between the output terminal M1 of the analog multiplexer 42 and the ground GND.

In the present embodiment, the first transistor P1, the second transistor P2, the third transistor P3, and the fourth transistor P4 are P-type transistors (PMOS). The above transistor is used to control the operation of the sensing unit 41, and the above transistor may be replaced by an N-type transistor (NMOS). In order to achieve the same function or operation, those skilled in the art can easily replace the P-type transistor with the N-type transistor to complete a circuit similar to that of FIG. 5A, and will not be described again.

Comparator OP1, current mirror 411, first capacitor CLD, second capacitor CS, reset circuit 413, first transistor P1, second transistor P2, third transistor P3, fourth transistor P4 in FIG. This is depicted in Figure 5A to further illustrate its mode of operation. The mode of operation of the circuit of Figure 5A is described below. The basic form of the circuit of Figure 5A is a peak detector with reference signal Vref as the reference potential. SENS signal on the endpoint to sense signals V _SENS, Example V sense signal _SENS in the present embodiment a first sensing signal TS1. When the sense signal at the terminal SENS _SENS V lower than the potential Vref, the sensing circuit to react, the waveform shown in FIG. 5B. In the present embodiment, the operational amplifier (OP1) acts as a potential comparator, aligning the reference signal Vref with the sense signal V _SENS . When the sensing signal V _{SENS is} higher than the reference signal Vref, the comparison signal Cmp outputted by the operational amplifier (OP1) is high, and turns off the P-type transistors (PMOS) P1 and P2 (ie, the first The transistor and the second transistor) do not change the potential of the output terminal Vo. The output terminal Vo is cleared by the control signal pINIT so that each detection can be accumulated by the ground potential (GND). That is, the control signal pINIT is a reset signal to reset the potential of the second capacitor CS to the ground potential (GND). When the sensing signal V _{SENS is} lower than the reference signal Vref, the comparison signal Cmp output by the operational amplifier (OP1) is low (low), and turns on the P-type transistors P1 and P2 (ie, the first transistor and The second transistor) simultaneously pulls up the potential of the sensing signal V _SENS and the output terminal Vo until the sensing signal V _SENS is equal to the reference signal Vref, that is, V _SENS =Vref. In this way, the signal conversion is completed once. The signal conversion can be done several times to accumulate enough charge on the output Vo (generating the sensing result signal TS3). It is worth noting that the control signal pINIT resets the potential of the output terminal Vo only at the beginning of the signal detection. The accumulation of multiple signal transitions can help eliminate background noise.

Please refer to FIG. 6 and FIG. 7 at the same time. As shown in FIG. 6, when the circuit is set to the mutual capacitance sensing mode, the analog multiplexer 42 connects the first line RCV of the touch interface 210 to the sensing circuit 41, and the switch S5 is closed, and the driving signal is turned on. (voltage pulse) VP is input to the second line DRV of the touch interface 210, the third switch S3 and the fourth switch S4 are opened, and the operational amplifier OP2 provides the first line RCV and the end point SENS in the form of a unity gain buffer. Bias point. When the second line DRV transitions, the output of the unity gain buffer 412 is turned off, and the first switch S1 is opened by the control signal pRECT. At the rising edge of the second line DRV, the second switch S2 is to be closed to integrate the signal to the capacitor CLD. The timing diagram is shown in Figure 7.

It is worth mentioning that in the mutual capacitance sensing mode, since the parasitic capacitance CM becomes smaller when the finger touches the touch interface 210, the sensing signal is not touched when the finger is not in contact at the rising edge of the second line DRV. The potential of V _SENS is relatively high. In contrast, when the finger is in contact, the potential of the sensing signal V _SENS is relatively low. Therefore, the presence of the finger can be distinguished.

In other words, when the capacitive touch sensor 2 is in the mutual capacitance sensing mode, the capacitive touch sensor 2 first operates in a biasing phase and then operates in a sensing phase. In the bias phase, the first switch S1 is closed to bias the bias circuit 412 to the second input (+) of the comparator OP1, and the bias circuit 412 is passed through the analog multiplexer 42 Supply biased to the first line RCV. Then, in the sensing phase, the first switch S1 is opened, the second switch S2 is closed to integrate the first sensing signal TS1 to the first capacitor CLD, and the third transistor P3 and the fourth transistor are P4 is turned on, and the integration result of the first sensing signal TS1 is converted into the sensing result signal TS3 by the current mirror 411.

Referring to FIG. 8 and FIG. 9 simultaneously, in the embodiment, when the capacitive touch sensor 2 is in the self-capacitance sensing mode, the sensing unit 41 pairs the first line RCV or the second line with a specific frequency f. The parasitic capacitance formed by the DRV is charged and discharged, so that the potential of the first line RCV or the second line DRV approaches an equilibrium potential, and the balanced potential is converted into a sensing result signal TS3 through a current mirror. For detailed circuit operation, please refer to the following instructions.

Referring to FIG. 8, when the circuit is set to the self-capacit mode and the second line DRV is sensed, the sensing line RCV is grounded through the switch S6 (controlled by the control unit 230), causing the parasitic capacitance CPD to be in parallel with the parasitic capacitance CM, and the analogy is The device 42 connects the second line DRV of the touch interface 210 to the sensing circuit 41, the first switches S1 and S5 are open, and the third switch S3 is closed. The opening and closing of the second switch S2 and the fourth switch S4 are controlled by a specific frequency. When the second switch S2 is turned off, the fourth switch S4 is turned on, and the current source ISRC1 is charged to the parasitic capacitance CPD and the parasitic capacitance CM. When the second switch S2 is turned on, the fourth switch S4 is turned off, so that the charge that has been charged to the parasitic capacitance CPD and the parasitic capacitance CM is discharged via the fourth switch S4. This is a capacitor-to-resistance conversion circuit (C to R circuit) whose equivalent resistance is as follows:

Where f is the frequency. Current source ISRC1 provides current I _DAC . When the control signal pISRC closes or enables the third switch S3, the sensing signal V _SENS is balanced as follows:

The timing chart is shown in Fig. 9. The sense signal V _SENS represented by the above equation is the equilibrium potential. After the equilibrium potential is reached, the control signals pGATE and pISRC turn off the second switch S2 and the third switch S3, respectively, and the control signal nSENS turns on the P-type transistors P6 and P7. As can be seen from the above description, the second sensing signal TS2 can be obtained according to the above-described circuit operation mode. It is worth mentioning that the sensing unit 41 can be the sensing unit 220 or the driving/sensing unit 250 of FIG. 2, and the driving/sensing unit 250 has the same circuit as the sensing unit 220 (the sensing unit 41 In the circuit), the driving/sensing unit 250 can directly sense the second sensing signal TS2 of the second line DRV.

It is worth mentioning that in the self-capacitance sensing mode, the parasitic capacitance is increased when the finger touches the touch interface 210, and the potential of the sensing signal V _SENS is relatively high when the finger is not in contact. In contrast, when the finger is in contact, the potential of the sensing signal V _SENS is relatively low. Therefore, the presence of the finger can be distinguished.

In other words, when the capacitive touch sensor 2 is in the self-capacitance sensing mode, in order to sense the second line DRV, the capacitive touch sensor 2 first operates in a balancing phase and then operates in a sensing phase. . In the balancing phase, the first switch S1 is open, the first line RCV is coupled to the ground GND, the third switch S3 is closed, and the second switch S2 and the fourth switch S4 are alternately switched at a specific frequency f to cause current The source ISRC1 charges and discharges the parasitic capacitance (parasitic capacitance CPD in parallel with the parasitic capacitance CM) formed by the second line DRV at a specific frequency f such that the potential of the second input terminal (+) of the comparator OP1 approaches the equilibrium potential. Then, in the sensing phase, the second switch S2, the third switch S3 and the fourth switch S4 are opened, and the balancing signal nSENS turns the third transistor P3 and the fourth transistor P4 on, and utilizes the current. The mirror 411 converts the balanced potential of the second input terminal (+) of the comparator OP1 into the sensing result signal TS3.

As shown in FIG. 10, when the circuit is set to the self-capacitance sensing mode and the first line RCV is sensed, the second line DRV is grounded through the switch S7 (controlled by the control unit), causing the parasitic capacitance CPR to be in parallel with the parasitic capacitance CM. . The analog multiplexer 42 connects the first line RCV of the touch interface 210 to the sensing unit 41. Charge and discharge the parasitic capacitance formed by the first line 212 at a specific frequency, so that the potential of the first line 212 approaches a balanced power And shifting the balanced potential through the current mirror 411 into a sensing result signal. The remaining operation modes will be similar to when the self-capacitance sensing mode senses the second line DRV, as described below.

When the capacitive touch sensor 2 is in the self-capacitance sensing mode, in order to sense the first line RCV, the capacitive touch sensor 2 first operates in a balancing phase and then operates in a sensing phase. In the balancing phase, the first switch S1 is open, the second line S2 is coupled to the ground GND, the third switch S3 is closed, and the second switch S2 and the fourth switch S4 are alternately switched at a specific frequency f to cause current The source ISRC1 charges and discharges the parasitic capacitance (parasitic capacitance CPR in parallel with the parasitic capacitance CM) formed by the first line RCV at a specific frequency f such that the potential of the second input terminal (+) of the comparator OP1 approaches the equilibrium potential. Then, in the sensing phase, the second switch S2 and the third switch S3 are opened, the balance signal nSENS turns the third transistor P3 and the fourth transistor P4 on, and the comparator is used by the current mirror 411. The balanced potential of the second input terminal (+) of OP1 is converted into the sensing result signal TS3.

[Embodiment of self-capacity and mutual capacitance switching method]

Referring to FIG. 2, FIG. 6, and FIG. 11, FIG. 11 is a flowchart of a method for switching between self-capacity and mutual capacitance according to an embodiment of the present invention. The method for switching the self-capacitance and mutual capacitance of the present embodiment is used in the capacitive touch sensor 2 of FIG. 2 . The capacitive touch sensor 2 includes a touch interface 210 , a sensing unit 220 , and a driving/sensing The unit 250, the control unit 230 and the processing unit 240. Control unit 230 has an analog multiplexer 42 as shown in FIG. The method includes the following steps. First, in step S101, it is determined that the capacitive touch sensor 2 operates in a mutual capacitance sensing mode or a self-capacitive sensing mode, wherein the analog multiplexer 42 is configured according to the mutual capacitance sensing mode or the self-capacitive sensing mode. The sensing unit 41 is coupled to the first line RCV or the second line DRV of the touch interface 210 (ie, the first line 212 and the second line 214 of FIG. 2 ).

Then, in step S103, when the capacitive touch sensor 2 is in the mutual capacitance sensing mode, a bias voltage (provided by the bias circuit 412) is supplied to the first line RCV through the analog multiplexer 42. And integrating the first sensing TS1 signal of the first line RCV, The integration result of the first sensing signal TS1 is converted into the sensing result signal TS3. In general, when the capacitive touch sensor 2 is in the mutual capacitance sensing mode, the driving/sensing unit 250 can provide the pulse signal VP to the second line DRV of the touch interface 210.

Then, in step S105, when the capacitive touch sensor 2 is in the self-contained detection mode, the second line DRV is coupled to the ground GND, and the first line RCV is coupled to the sensing unit 41 through the analog multiplexer 42 (ie, The sensing unit 220), and the sensing unit 41 charges and discharges the parasitic capacitance (the parasitic capacitance CPR is connected in parallel with the parasitic capacitance CM) formed by the first line RCV at a specific frequency f, so that the potential of the first line RCV approaches the equilibrium potential, The equilibrium potential is then converted into a sensing result signal TS3.

After the end of step S105, in order to sense the second line DRV, a step similar to step S105 may be performed to interchange only the roles of the first line RCV and the second line DRV. As described below, when the capacitive touch sensor 2 is in the self-contained detection mode, in order to sense the second line DRV, the first line RCV is coupled to the ground GND, and the second line DRV is coupled through the analog multiplexer 42. The measuring unit 41, and the sensing unit 41 charges and discharges the parasitic capacitance (the parasitic capacitance CPD and the parasitic capacitance CM) formed by the second line DRV at a specific frequency f to bring the potential of the second line DRV close to the equilibrium potential, and then The equilibrium potential is converted into a sensing result signal TS3.

In detail, the manner in which the sensing result signal TS3 is generated can be realized by the current mirror 411 of FIG. When the capacitive touch sensor 2 is in the mutual capacitance sensing mode, the integration result of the first sensing signal TS1 is converted into the sensing result signal TS3 by using the current mirror 411. When the capacitive touch sensor 2 is in the self-contained detection mode, the balance potential is converted into the sensing result signal TS3 by the current mirror 411.

[Possible effects of the examples]

In summary, the capacitive touch sensor provided by the embodiment of the present invention and the self-capacity and mutual capacitance switching method thereof are switched by the analog multiplexer according to the sensing conditions of the self-capacity and the mutual capacitance. The drive unit is integrated with the sensing unit to simplify the structure of the circuit to save the area of the circuit (or wafer). In the self-capacitance sensing mode, the parasitic capacitance formed by the first line or the second line of the touch interface is charged and discharged at a specific frequency, The potential of the first line or the second line is brought close to the equilibrium potential, and the balanced potential is converted into a sensing result signal through the current mirror.

The above description is only an embodiment of the present invention, and is not intended to limit the scope of the invention.

2‧‧‧Capacitive touch sensor

210‧‧‧ Touch interface

220‧‧‧Sensor unit

230‧‧‧Control unit

240‧‧‧Processing unit

250‧‧‧Drive/Sensor Unit

212‧‧‧First line

214‧‧‧second line

TS1‧‧‧first sensing signal

TS2‧‧‧ second sensing signal

Claims (14)

A capacitive touch sensor includes: a touch interface having a plurality of first lines and a plurality of second lines; a sensing unit coupled to the touch interface; and a driving/sensing unit, Generating a driving signal; and a control unit that controls the sensing unit and the driving/sense unit, the control unit switches the capacitive touch sensor to a mutual capacitance sensing mode or a self-capacitive sensing mode The control unit has an analog multiplexer, and the output end of the analog multiplexer is coupled to the sensing unit, and the first input end of the analog multiplexer is coupled to the first line, the analog multiplexer The second input end is coupled to the second line; wherein, when the capacitive touch sensor is in the mutual capacitance sensing mode, the driving/sensing unit provides the driving signal to the second line, The sensing unit is coupled to the first line through the analog multiplexer, so that the sensing unit senses one of the first sensing signals of the first line; wherein, when the capacitive touch sensor is In the capacitive sensing mode, the sensing unit is coupled according to the switching of the analog multiplexer The first line or the second line, and senses the sensing signal from the first line of the first or second line of the second one of the sensing signal. The capacitive touch sensor of claim 1, wherein the sensing unit is configured to the first line or the first frequency at a specific frequency when the capacitive touch sensor is in the self-capacitance sensing mode The parasitic capacitance formed by the two lines is charged and discharged, so that the potential of the first line or the second line approaches an equilibrium potential, and the balanced potential is converted into a sensing result signal through a current mirror. The capacitive touch sensor of claim 1, further comprising: a processing unit coupled to the sensing unit, the driving/sensing unit and the control unit, the processing unit being controlled by the control unit And analogizing the first sensing signal and the second sensing signal into a digital signal. The capacitive touch sensor of claim 1, wherein the sensing unit comprises: a comparator, the first input of the comparator receives a reference signal, and the second input of the comparator receives the first sensing signal or the second sensing signal according to the switching of the analog multiplexer The output of one of the comparators generates a comparison signal; a biasing circuit is coupled to the second input end of the comparator, the bias circuit provides a bias voltage, and the bias circuit has a first a current mirror having a first output and a second output; a first capacitor, the first end of the first capacitor coupled to the second input of the comparator and the current mirror An output end, the second end of the second capacitor is coupled to a ground; a second capacitor, the first end of the second capacitor is coupled to the second output end of the current mirror, and the second end of the second capacitor The first end of the second capacitor is coupled to the ground, the first end of the second capacitor is coupled to the first end of the second capacitor for resetting the potential of the second end of the second capacitor; a first transistor coupled to the first output end of the current mirror and the first capacitor Between the terminals, controlled by the comparison signal; a second transistor coupled between the second output end of the current mirror and the first end of the second capacitor, controlled by the comparison signal; a third transistor coupled between the first transistor and the first end of the first capacitor and controlled by a balanced signal; a fourth transistor coupled to the second transistor and the second capacitor The first end is controlled by the balance signal; a second switch is coupled between the output end of the analog multiplexer and the second input end of the comparator; a current source is transmitted through the The third switch is coupled to the second input of the comparator; and a fourth switch coupled between the output of the analog multiplexer and the ground. The capacitive touch sensor of claim 4, wherein the first transistor, the second transistor, the third transistor, and the fourth transistor are P-type transistors (PMOS). The capacitive touch sensor of claim 4, wherein the reset circuit is controlled by a reset signal to reset the potential of the second capacitor to a ground potential. The capacitive touch sensor of claim 4, wherein the bias circuit comprises a unity gain buffer. The capacitive touch sensor of claim 4, wherein when the capacitive touch sensor is in the mutual capacitance sensing mode, the capacitive touch sensor operates first in a bias phase Operating in a sensing phase, wherein the first switch is closed to cause the bias circuit to provide the bias to the second input of the comparator, and the bias circuit Providing the bias voltage to the first line through the analog multiplexer, and then in the sensing phase, the first switch is opened, and the second switch is closed to integrate the first sensing signal to The first capacitor, and the third transistor and the fourth transistor are turned on, and the integrated result of the first sensing signal is converted into the sensing result signal by using the current mirror. The capacitive touch sensor of claim 4, wherein when the capacitive touch sensor is in the self-capacitance sensing mode, the capacitive touch sensor operates in a balancing phase and then operates In a sensing phase, in the balancing phase, the first switch is open, the second line is coupled to the ground, the third switch is closed, and the second switch and the fourth switch are The specific frequency is alternately switched, so that the current source charges and discharges the parasitic capacitance formed by the first line at the specific frequency, so that the potential of the second input end of the comparator approaches an equilibrium potential, and then in the sensing phase. The second switch is opened to the third switch, the balance signal turns the third transistor and the fourth transistor on, and the second input of the comparator is used by the current mirror The equilibrium potential of the terminal is converted to the sensing result signal. The capacitive touch sensor of claim 4, wherein when the capacitive touch sensor is in the self-capacitance sensing mode, the capacitive touch sensor operates first The balancing phase is further operated in a sensing phase, wherein in the balancing phase, the first switch is open, the first line is coupled to the ground, the third switch is closed, the second switch and the second The four switches are alternately switched at a specific frequency, so that the current source charges and discharges the parasitic capacitance formed by the second line at the specific frequency, so that the potential of the second input terminal of the comparator approaches an equilibrium potential, and then During the sensing phase, the second switch, the third switch and the fourth switch are opened, the balancing signal turns the third transistor and the fourth transistor on, and uses the current mirror The balanced potential of the second input of the comparator is converted to the sensing result signal. A capacitive touch sensor includes a touch interface, a sensing unit, a driving/sensing unit, and a control unit. The control unit has an analog multiplexer, and the method includes: determining that the capacitive touch sensor operates in a mutual capacitance sensing mode or a self-capacitive sensing mode, wherein the analog multiplexer is based on the mutual capacitance The sensing unit or the self-capacitance sensing mode is coupled to the first line or the second line of the touch interface; when the capacitive touch sensor is in the mutual capacitance sensing mode a bias voltage is supplied to the first line through the analog multiplexer, and the first sensing signal of one of the first lines is integrated, and the integration result of the first sensing signal is converted into a sensing a result signal; when the capacitive touch sensor is in the self-capacitance detection mode, the second line is coupled to a ground, the first line is coupled to the sensing unit through the analog multiplexer, and the sensing The unit charges and discharges the parasitic capacitance formed by the first line at a specific frequency, so that The potential of the first line approaches an equilibrium potential, which is then converted to the sensed signal. The method for switching the self-capacity and the mutual capacitance according to the claim 11 further includes: when the capacitive touch sensor is in the self-capacitance detection mode, the first line is coupled to a ground, and the second line is transmitted through The analog multiplexer is coupled to the sensing unit, and the sensing unit charges and discharges the parasitic capacitance formed by the second line at the specific frequency to The potential of the second line is brought close to the equilibrium potential, and then the balanced potential is converted into the sensing result signal. According to the method of switching the self-capacity and the mutual capacitance of the claim 11, wherein the driving/sensing unit provides a pulse signal to the touch interface when the capacitive touch sensor is in the mutual capacitance sensing mode The second line. According to the method for switching the self-capacity and the mutual capacitance according to Item 11 of the claim, wherein when the capacitive touch sensor is in the mutual capacitance sensing mode, the integration result of the first sensing signal is converted by using a current mirror For the sensing result signal, when the capacitive touch sensor is in the self-capacity detecting mode, the current potential is converted into the sensing result signal by using the current mirror.