CN101825976A - Ghost detection method of capacitive touch panel - Google Patents

Abstract

A ghost detection method for a capacitive touch pad is provided, wherein a ghost phenomenon occurs at a first position and a second position on the capacitive touch pad, the detection method comprises driving X-direction traces and Y-direction traces at the first position and the second position in a staggered manner by in-phase or out-phase synchronous signals to obtain capacitance values at the first position and the second position, and preferably, the capacitance values are matched with cross calibration to accurately distinguish the actual position of a finger.

Description

Ghost detection method for capacitive touch panel

technical field

The invention relates to a capacitive touch panel, in particular to a ghost detection method of the capacitive touch panel.

Background technique

Among many touch technologies, Axis Intersect (AI) array projected capacitance (Projected Capacitance) sensing technology has become the most popular due to its high optical clarity, durability and low cost. It is a welcome technology, but its scanning method may produce ghost-points (Ghost-Point) when two or more fingers are used for multi-finger touch, so it is impossible to distinguish the correct position of each finger.

Figure 1 is a schematic diagram of the ghost phenomenon. When the position of the user's two fingers on the capacitive touch panel is upper left and lower right (A, D) or lower left and upper right (C, B), the traces Y1 and Y2 Both traces X1 and X2 cause capacitance changes, so the waveforms of capacitance changes in the X direction and Y direction detected by the control circuit are the same, so the control circuit cannot determine the real finger contact position.

In the two-finger input state, there are two possible coordinates when the ghost phenomenon occurs, as shown in FIG. 2 . When the ghost phenomenon occurs, the capacitance value in the X direction changes at the traces _x1 and _x2 , while the capacitance value in the Y direction increases at the traces _y1 and _y2 , excluding those with the same X or Y coordinates After the permutation and combination of , there are two groups of possible finger coordinates (x ₁ y ₁ , x ₂ y ₂ ) and (x ₁ y ₂ , x ₂ y ₁ ), one of which is the actual coordinate and the other is the ghost coordinate. When more fingers are input, the number of ghost coordinates will increase rapidly. For example, as shown in Figure 3, when three fingers are input, the possible finger coordinates are (x ₁ y ₁ , x ₂ y ₂ , x ₃ y ₃ ), (x ₁ y ₁ , x ₂ y ₃ , x ₃ y ₂ ), (x ₁ y ₂ , x ₂ y ₁ , x ₃ y ₃ ), (x ₁ y ₂ , x ₂ y ₃ , x ₃ y ₁ ) , (x ₁ y ₃ , x ₂ y ₂ , x ₃ y ₁ ), (x ₁ y ₃ , x ₂ y ₁ , x ₃ y ₂ ) six groups, five of which are ghost coordinates.

Multi-touch application (Multi-touch) is bound to be one of the development trends of touch technology in the future. Therefore, it is hoped to provide a ghost detection method to improve the ghost point problem in the known AI-type array projected capacitive sensing technology.

Contents of the invention

One of the objectives of the present invention is to provide a method for detecting ghost positions.

According to the present invention, a ghost image detection method occurs in the first position and the second position on the capacitive touch panel, and the first position and the second position have the same first position When coordinates in one direction:

(A) driving the first direction trace at the first position with a first signal, and driving the second direction trace at the first position with a second signal synchronized with the first signal;

(B) obtaining the first or second direction trace capacitance value of the first position;

(C) driving a first directional trace at the second location with the first signal, and driving a second directional trace at the first location with the second signal;

(D) obtaining the first or second direction trace capacitance value of the second position; and

(E) Judging the actual contact position according to the capacitance value of the first or second direction trace at the first position and the first or second direction trace capacitance at the second position.

Alternatively, the first and second signals are synchronous in-phase or synchronous out-of-phase signals.

Preferably, cross-calibration is performed on the traces on the capacitive touch panel, so that each trace obtains the same basic capacitance value.

Description of drawings

FIG. 1 is a schematic diagram of a ghost phenomenon;

FIG. 2 is a schematic diagram of a ghost phenomenon caused by two-finger touch;

FIG. 3 is a schematic diagram of a ghost phenomenon caused by three-finger touch;

4 and 5 are schematic diagrams of an embodiment of the present invention;

6 and 7 are schematic diagrams of another embodiment of the present invention;

Fig. 8 is a schematic diagram of capacitance on two-phase intersecting traces;

9 and 10 are schematic diagrams of an embodiment of detecting the capacitance value between two traces;

Fig. 11 is a flow chart of applying an embodiment of the present invention;

Fig. 12 is a schematic diagram of the in-phase interleaving drive proposed by the present invention;

Fig. 13 is a schematic diagram of the difference in ADC reading value caused by in-phase interleaved driving;

Fig. 14 is a schematic diagram of cross-calibration proposed by the present invention;

Fig. 15 is a schematic diagram of ghost images caused by fingers of different thicknesses;

16 is a schematic diagram of an embodiment of a capacitive touch panel applying the present invention; and

FIG. 17 is a flow chart of an embodiment of detecting the ghost phenomenon in FIG. 15 .

Reference number

12 fingers

14 fingers

16 tested positions

200 start

201X direction trace detection

202 Y direction trace detection

203 ghosting happened?

204 end

205 Generate ghost candidate list

206 Take a point from the ghost candidate list

207 said point is the last point of the ghost image candidate list?

208 output answer list

209 ghost analysis sensing

210 The points mentioned are ghost points

211 Remove the point from the ghost candidate list

212 Add the point to the answer list

213 Remove candidate points with the same X or Y coordinates as the point from the ghost candidate list

30 capacitive touchpad

32 sensors

34 analog multiplexers

36 modulators

38 demodulator

40 voltage processing circuit

501 General Adjustment

502 cross calibration

503 touchpad scan

504 The number of fingers in the first and second directions is greater than 2?

505 judged as a single-finger application

506 Find out the Y-direction traces Y1 and Y2 where capacitance changes occur

507 Find the trace Xmax with the maximum value in the X direction

508 drives trace Y1 with signal Mux2, and detects trace X_max with signal Mux1

509 Obtain and store the ADC value ADC_Y1 of trace Y1

510 drives trace Y2 with signal Mux2 and detects trace X_max with signal Mux1

511 obtains and stores the ADC value ADC_Y2 of trace Y2

512 ADC_Y1>ADC_Y2?

513 The actual position of the finger is at (Xmax, Y1) and (Xmin, Y2)

514 The actual position of the finger is at (Xmax, Y2) and (Xmin, Y1)

515 judged as multi-finger application

Detailed ways

Fig. 4 is a schematic diagram of the first embodiment of the present invention, the coordinates of the finger 12 are represented by x _m y _k , and the coordinates of the finger 14 are represented by x _n y ₁ , the finger 12 and the finger 14 cause capacitance changes on the capacitive touch panel Values at positions x _m y ₁ , x _m y _k , x _n y ₁ and x _n y _k all have peak values, resulting in ghost images, and the control circuit cannot tell whether the finger 12 is located at x _m y ₁ or x _m y _k . It is also impossible to judge whether the finger 14 is located at x _n y ₁ or x _n y _k . At this time, two groups of ghost image candidate coordinates (x _m y ₁ , x _n y _k ) and (x _m y _k , x _n y ₁ ) appear, Positions x _m y ₁ , x _m y _k , x _n y ₁ and x _n y _k are ghost candidate positions. The present invention proposes a ghost detection method. When a ghost phenomenon occurs, each position where a peak value appears, that is, the X and Y direction traces on each ghost candidate position is simultaneously charged and the capacitance value is detected. When the tested position 16 (x _m y _k ) is detected, the switches S1 and S3 are turned off, and the controller (not shown in the figure) charges the traces x _m and y _k at the same time to obtain the traces x _m and y _k capacitance value. The capacitance value Cx on the track x _m is Cx _m +Cx _m y ₁ +dCx _m +Cx _m y _k , dCx _m represents the capacitance change of the track x _m due to the proximity of the finger 12, and Cx _m represents the contact between the other ground traces and The total capacitance value between ground and trace x _m , Cx _m y ₁ represents the capacitance value between trace x _m and trace y ₁ , Cx _m y _k represents the capacitance value between trace x _m and trace y _k , where the measured value of Cx _m y _k is zero because trace x _m and trace y _k are equipotential. Since the measured position 16 is the position actually touched by the finger 12, the total capacitance value Cx measured from the trace x _m is equal to the actual position capacitance value Cr _x =Cx _m +Cx _m y ₁ +dCx _m . The trace capacitance value Cy in the Y direction measured from the trace y _k is also due to the actual contact position of the finger 12 at x _m y _k , and the measured capacitance value is the actual position capacitance value Cr _y =Cy _k +Cx _n y _k +dCy _k .

Fig. 5 shows a schematic diagram when the actual contact position of the finger 12 is x _m y ₁ and the measured position 16 is a ghost position, the controller also charges the trace x _m and trace y _k at the same time, and the trace x _m and y _k is equipotential, so the measured value of Cx _m y _k is zero, but finger 12 at x _m y ₁ causes a capacitance change dCx m y ₁ between trace y ₁ and trace x _m , dCx _{m y 1} is negative value, the total capacitance Cx on the trace x _m at this time is equal to the ghost position capacitance value Cg _x =Cx _m +Cx _m y ₁ +dCx _m y ₁ +dCx _m . The Y-direction capacitance value Cy measured from the trace y _k is because the 14-bit finger is at x _n y _k , causing a negative capacitance change dCx _n y _k between the traces x _n and y _k , so the measured capacitance value Cy It is the ghost position capacitance value Cg _y =Cy _k +Cx _n y ₁ +dCx _n y _k +dCy _k .

Comparing the X-direction capacitance and Y-direction capacitance obtained in Figure 4 and Figure 5, since dCx _m y ₁ is a negative value, the X-direction capacitance Cr _x measured at the actual position = Cx _m + Cx _m y ₁ +dCx _m is greater than the capacitance value in the X direction measured at the ghost position Cg _x ＝Cx _m +Cx _m y ₁ +dCx _m y ₁ +dCx _m , similarly, because dCx _n y _k is a negative value, the Y measured at the actual position The directional capacitance Cr _y =Cy _k +Cx _{ny k} +dCy _k is also greater than the Y-directional capacitance Cg _y =Cy _k +Cx _{ny k} +dCx _{ny k} +dCy _k measured at the ghost position. In short, after the simultaneous charging of the XY traces is completed and the capacitance values in the X and Y directions are obtained, the capacitance values obtained at the two points are compared to determine which is the actual contact position.

Fig. 6 and Fig. 7 are another embodiment of the ghost detection method of the present invention, connect the trace of X direction and the trace of Y direction of the tested position, to directly obtain the capacitance value of the trace of X direction of the measured position and Y The sum of the direction trace capacitance values. As shown in Figure 6, when the measured position 16 is the actual position of the finger 12, the measured capacitance value Cx _y is the actual position capacitance value Crx _y = Cx _m + Cyk + Cx _m y ₁ + Cx _n y _k + dCx _m +dCy _k , referring to Figure 7, when the measured position 16 is not the actual position of the finger, the measured capacitance value Cx _y is the ghost position capacitance value Cgx _y =Cx _m +Cy _k +Cx _m y ₁ +Cx _n y _k +dCx _m +dCy _k +dCx _m y ₁ +dCx _n y _k , where dCx _m y ₁ and dCx _n y _k are negative values. Although there are four ghost candidate positions for the ghost phenomenon caused by two-finger touch, after the first actual position is determined, the ghost candidate position having the same X or Y coordinates as the actual position cannot be the second candidate position. Two actual positions, so when detecting the ghost phenomenon caused by the two-finger touch, only need to compare two ghost candidate positions with the same X or Y coordinates to obtain the coordinates of the actual position.

When using the detection method to deal with the ghosting phenomenon caused by three-finger touch, there are nine ghosting candidate positions in total. Referring to FIG. First test two points (x ₁ , y ₁ ) and (x ₁ , y ₂ ) with the same X coordinate as an example, if the capacitance values obtained from the test are equal, it means (x ₁ , y ₁ ) and (x ₁ , y ₂ ) are ghost positions, and the remaining (x ₁ , y ₃ ) with the same X coordinates as the two points is the actual position; if the measured capacitance values are not equal, the point with the larger capacitance value is Actual position, so only one detection is required to determine the first actual position. After the first actual position is determined, for example, (x ₁ , y ₃ ) is determined to be the actual position, other ghost candidate positions (x 1 , y 3 ) having the same X or Y coordinates as (x1, _y3 ) can be known. y ₁ ), (x ₁ , y ₂ ), (x ₂ , y ₃ ) and (x ₃ , y ₃ ) must all be ghost positions, so these ghost positions can be directly excluded, and then the ghost Candidate positions (x ₂ , y ₂ ) and (x ₂ , y ₁ ) are used for ghost detection, and after the second actual position is determined, ghost candidate positions with the same X or Y coordinates as the second actual position are deleted , the last actual position can be obtained. In other words, even in the ghost phenomenon caused by three fingers, the detection method proposed by the present invention only needs to perform two comparisons to determine the actual finger coordinates. In other embodiments, each ghost candidate point can also be detected one by one to obtain the trace capacitance value of each ghost candidate point, and then the firmware makes a judgment based on the trace capacitance values, so as to improve reliability.

Figure 8 is a schematic diagram of capacitance on two-phase intersecting traces, where Cx _m represents the capacitance value of trace x _m to ground, Cy _n represents the capacitance value of trace y _n to ground, and Cx _m y _n represents trace x _m and the coupling capacitance value between the traces y _n , when the finger touches the junction of the traces x _m and y _n , the capacitance value Cx _m y _n will drop, and the present invention proposes a method for directly detecting the traces x _m and the traces y The capacitance value Cx _m y _n between _n is used to distinguish the ghost position and the actual contact position. First, the traces x _m and y _n are charged at the same time, and the capacitance value on the trace x _m is detected. At this time, the traces x _m and y _n are equipotential, the measured value of Cx _m y _n is zero, and the measured capacitance The value is the capacitance Cx _m of the trace x _m to _{the ground, and then the trace x m is charged} and the trace _{y n is} grounded. The capacitance value is Cx _m +Cx _{my n} , and the coupling capacitance value Cx _{my n} between the traces x _m and y _n can be obtained by subtracting the two.

9 and 10 are schematic diagrams of an embodiment of detecting the capacitance between two traces. FIG. 9 shows the situation when the tested position 16 is the actual position of the finger 12. FIG. 10 shows the situation when the tested position 16 is a ghost position. situation at the time. As shown in Figure 9, when the measured position 16 is the actual position of the finger 12, at first the traces x _m and y _k are charged simultaneously in phase1, and the capacitance value Cx=Cx _m obtained by detecting the trace x _m at this time; then, Charge the trace x _m in phase 2 and ground the trace y _k to obtain the capacitance value Cx=Cx _m +Cx _m y _k +dCx _m y _k on the trace x _m ; combine the capacitance value obtained in phase 2 with The capacitance difference ΔCx obtained by subtracting the capacitance values obtained in phase 1 is the actual position capacitance difference ΔCr _x =Cx _m y _k +dCx _m y _k . When the tested position 16 is a ghost position, as shown in FIG. 10 , the detected position 16 is detected, and the obtained capacitance difference ΔCx is the ghost position capacitance difference ΔCg _x =Cx _m y _k , wherein, dCx _m y _k is less than zero, so the determination of the actual finger position can be achieved by comparing the capacitance difference ΔCx. The various embodiments proposed by the present invention implement the calculation with firmware, and in other embodiments, errors caused by fingers and traces can be added to the calculation.

Fig. 11 is a flow chart of an embodiment of the touch panel control method of the present invention. After starting 200, the X-direction trace detection 201 is performed first, and then the Y-direction trace detection 202 is performed to determine whether there is a ghost image 203. If No, output the detection result and end 204. In step 203, if it is found that there is a ghost image, then enter the ghost image processing program, first generate a ghost image candidate list 205, add all ghost image candidate points in the described ghost image candidate list, then in step 206 from the described ghost image candidate list Take a ghost candidate point from the ghost candidate list, and judge whether the point is the last point in the ghost candidate list 207 , if yes, output the answer list 208 , if not, perform ghost analysis and sensing 209 . The steps of ghost image analysis and sensing 209 are as mentioned above, obtain the capacitance value of the X-direction trace of the measured point, the capacitance value of the Y-direction trace, the capacitance value after the sum of the two or the distance between the X-direction and Y-direction of the measured point. The capacitance value is compared with the capacitance values obtained from other candidate points to determine whether the measured point is a ghost point 210, if so, remove the measured point 211 from the ghost candidate list, and Go back to step 206, continue to detect and judge other candidate points, if not, it means that the measured point is the actual position, then add the measured point to the answer list 212, and remove it from the ghost candidate list The point and the candidate point 231 having the same X or Y coordinates as the point return to step 206 to continue detecting other candidate points in the ghost candidate list, and finally output the answer list 208 and end 204 . In this embodiment, the position of each ghost candidate point is represented by XY coordinates, so the final output answer list already includes the XY coordinates of the answer points, which can provide accurate contact point positioning capability.

The present invention also proposes an in-phase interleaved (In-Phase Crisscross) driving method, so that the basic capacitance value on the interleaved point (measured point) becomes smaller, so that the high and low changes in the capacitance value of the measured point are more obvious , which is beneficial to the actual circuit control, as shown in Figure 12, when the capacitance value on (XN, YN) is to be detected to perform the interleaved driving judgment, the control circuit drives the trace XN with the signal Mux1, and at the same time uses the signal Mux1 The in-phase signal Mux 2 drives the trace YN and senses the trace XN to obtain the capacitance value on it. Figure 13 is a schematic diagram of the difference in ADC reading values caused by in-phase interleaved driving. The signal Mux1 is used to drive the trace X1, and the in-phase signal Mux2 is used to drive the traces Y1 and Y2 respectively. The measured point A is the actual contact position of the finger, so in the same phase When traces X1 and Y2 are driven alternately, the ADC (Analog-to-Digital Converter, analog-to-digital conversion) reading value obtained by detecting trace X1 is high, which is judged to be logic High (1), and the measured point C is a ghost position, so When the traces X1 and Y1 are driven alternately in phase, the ADC reading value obtained by detecting the trace X1 is low, which is judged as logic Low (0).

Since the capacitance value difference between the actual position and the ghost position detected by the interleaving drive is small, the present invention proposes a calibration (Calibration) method, which adds a single-axis cross-calibration (Intersectional Calibration) step, to further improve the accuracy of detection, Figure 14 is its schematic diagram. Use the signal Mux2 to drive one of the traces YM of the Y-axis, and use the signal Mux1 to drive and scan all the X-axis direction traces, obtain the ADC value of each trace, and provide it to the modulator (Modulator) for subsequent adjustments The parameter is used to correct the modulation value and DAC value on the trace, so that the ADC (Analog-to-Digital Converter) reading value of each trace is at the same level.

Since the present invention judges the actual position of one finger first, and then derives the position of the other finger, in order to reduce the error rate caused by the large difference in finger thickness, referring to Fig. The finger of (X_max) is used as the first finger for judgment.

16 is a schematic diagram of an embodiment of a capacitive touch panel applying the present invention. There are multiple sensors 32 on the capacitive touch panel 30, and the longitudinal sensors 32 are connected by wires to form a trace (trace) X1, X2...XM, the horizontal inductors 32 also form traces Y1, Y2...YM respectively, and the current signal generated by the modulator 36 selects the trace to be connected to through the analog multiplexer 34 line, modulated into signals mux1 and mux2, since this embodiment adds the cross-calibration step in the original calibration process, after the known 1st modulation parameters and 1st DAC parameters are generated, the cross-calibration The 2nd modulation parameter and the 2nd DAC parameter provided in the step are also provided to the modulator 36 to assist in adjusting the ADC reading value of each trace, and due to the use of in-phase interleaved driving, the demodulator 38 of this embodiment needs to provide an additional The reference signal Mux_Vref demodulates the signal mux1 to generate the signals ppeak and npeak to the voltage processing circuit 40, and the voltage processing circuit 40 converts the voltage difference between the signals ppeak and npeak to obtain the capacitance change information on the capacitive touch panel 10 . It is a known technology for the modulator to adjust the basic capacitance value of the trace by the modulation parameter and the DAC parameter, and those skilled in the technical field of the present invention should know it.

In other embodiments, synchronous but out-of-phase signals can also be used as Mux1 and Mux2 to perform the interleaved driving and interleaved calibration to distinguish the ghost position from the actual position.

FIG. 17 is a flowchart of an embodiment of detecting the ghost phenomenon in FIG. 15 . In FIG. 15 , the finger at point A is thicker than that at point D, so the capacitance at point A is larger than that at point D. Firstly, the 1st modulation parameter and 1st DAC parameter of each trace on the capacitive touch panel are obtained by known general calibration 501, and then the 2nd modulation parameter and 2nd DAC parameter are obtained by cross calibration 502 and provided to the modulator , after each trace on the capacitive touch panel has the same ADC reading value, scan 503 the touch panel to determine whether the number of fingers on the X and Y axes is greater than 2504, if not, determine that it is a single finger at this time Apply 505, return to step 503; if not, enter the interleave driver. In the interleaved driving program, first find the traces Y1 and Y2 506 in the Y direction where the capacitance changes, and then find the trace Xmax(X1) 507 with the maximum value in the X direction, and then drive the trace with the signal Mux2 in step 508 Y1, and use the signal Mux1 to detect the trace Xmax, obtain and store the ADC value ADC_Y1 of the trace Y1 in step 509, then, in step 510, use the signal Mux2 to drive the trace Y2 and use the signal Mux1 to detect the trace X_max, obtain and store The ADC value ADC_Y2511 of trace Y2, judge whether ADC_Y1 is greater than ADC_Y2512; if yes, judge that the finger position is at (Xmax, Y1), (Xmin, Y2) 513; if not, judge that the finger position is at (Xmax, Y2), (Xmin, Y1 ) 514, after judging the position of the fingers, it is judged that it is a multi-finger application 515, and returning to step 503 to continue scanning the touchpad.

The above description of the preferred embodiments of the present invention is for the purpose of illustration, and is not intended to limit the present invention to the disclosed form. It is possible to modify or change based on the above teachings or imitate from the embodiments of the present invention. Yes, the embodiments are selected and described for explaining the principles of the present invention and allowing those skilled in the art to use the present invention in practical applications with various embodiments, and the technical ideas of the present invention are intended to be determined by the claims and their equivalents .

Claims (5)

1. the ghost detecting method of a capacitive touch control plate, it is characterized in that, the ghost phenomenon appears in the primary importance on the described capacitive touch control plate and the second place, and the described primary importance and the described second place have identical first direction coordinate, and described detection method comprises the following steps:

(A) drive the first direction trace of described primary importance with first signal, and drive the second direction trace of described primary importance with secondary signal with described first signal Synchronization;

(B) obtain first or second direction trace capacitances value of described primary importance;

(C) drive the first direction trace of the described second place with described first signal, and drive the second direction trace of described primary importance with described secondary signal;

(D) obtain first or second direction trace capacitances value of the described second place; And

(E) according to first or second direction trace capacitances value of first or the second direction trace capacitances value and the described second place of described primary importance, judge the actual contact position.

2. ghost detecting method as claimed in claim 1 is characterized in that, described secondary signal and described first signal Synchronization and homophase.

3. ghost detecting method as claimed in claim 1 is characterized in that, described secondary signal and described first signal Synchronization but out-phase.

4. ghost detecting method as claimed in claim 1 is characterized in that, step (E) comprising:

First or second direction trace capacitances value of first or the second direction trace capacitances value and the described second place of more described primary importance;

If first or second direction trace capacitances value of described primary importance judge that greater than first or second direction trace capacitances value of the described second place described primary importance is the actual contact position; And

If the first direction trace capacitances value of described primary importance judges that less than the first direction trace capacitances value of the described second place the described second place is the actual contact position.

5. ghost detecting method as claimed in claim 1 is characterized in that described method more comprises the following steps:

Drive arbitrary second direction trace on the described capacitive touch control plate with described secondary signal;

Drive and scan first direction traces all on the described capacitive touch control plate with described first signal; And

Obtain the capacitance of each described first direction trace, for the basic capacitance of each trace on the described capacitive touch control plate of adjustment.

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