Self-sensing touch panel

Abstract

A differential self-capacitance measurement method is used to enhance the signal-to-noise ratio of the sensing lines in a touch panel display, thereby improving the accuracy of the touch sensor. The differential self-capacitance measurement is implemented for the touch panel using charge sharing between adjacent sensing lines of the touch panel matrix. The differential self-capacitance can be calculated by S1 ‑C S2 |‑|C S2 ‑C S1 |To compare the time-sequential differential self-capacitance measurements to each other for sensing changes caused by intervening events. By scanning the entire touch panel matrix, events can be tracked across the touch panel.

Description

[0001] Divisional Application Instructions

[0002] This application is a divisional application of a Chinese patent application with a filing date of June 16, 2017, application number 201710458725.9, and name “SELF-SENSING TOUCH PANEL”. Technical Field

[0003] The present disclosure relates to touch screen technology, and in particular to improving touch screen sensitivity.

[0004] Related technical notes

[0005] Touch screens serve as user interfaces for many types of electronic devices currently in use, including, for example, smart phones, tablet computers, kiosks, vehicle control panels, etc. A touch screen includes a touch-sensitive panel overlaid on a display. The display provides visual output to a user of the electronic device. The display also presents text and graphics indicating selections (e.g., web links, play buttons, etc.) that can be activated by contact with the overlaid touch-sensitive panel. The display utilizes various display technologies, such as, for example, liquid crystal (LCD), plasma, organic light emitting diode (OLED), etc.

[0006] A touch-sensitive panel (or "touch panel") typically includes a matrix of drive lines and sense lines that are arranged transversely to each other and in a plane separated from each other by a small distance. Sensor electrodes are placed at the junctions where the drive lines intersect the sense lines. These sensor electrodes can sense touches through a capacitive mechanism. When a finger makes contact with the touch-sensitive panel at the electrode location, the capacitance of the finger increases the capacitance of the electrode relative to ground. Therefore, the detection of this "self-capacitance" increase indicates a touch event. However, in some cases, touch events may be missed, or non-events may be misjudged as touch events. For example, some touch panels may not be able to detect multiple touch events at the same time. In addition, the self-capacitance detection method may not be able to detect a finger hovering above the touch panel. Drops of water falling on the touch panel may be misjudged as touch events. To improve accuracy in this case, it is desirable to increase the signal-to-noise ratio of the self-capacitive touch panel. Summary of the invention

[0007] A method of differential capacitance measurement is used to enhance the signal-to-noise ratio of sensing lines in a touch panel, thereby improving the accuracy of touch sensors that use absolute capacitance measurements. Differential capacitance measurements are normalized electrical signal values ​​that provide greater sensitivity to noise fluctuations. Because the differential measurement value is much smaller than the absolute measurement value, the increase in sensitivity occurs.

[0008] Differential capacitance measurement is implemented for a touch panel by using a charge sharing method to compare the capacitance values ​​on adjacent sense lines of a touch panel matrix. In the first step, the charge sharing method requires discharging a first sense line S1 while charging an adjacent second sense line S2. In the second step, the two sense lines are coupled so that they are at a common voltage while sharing the charge previously stored in sense line S2. A differential capacitance measurement (C) is then performed by comparing the common voltage of the two sense lines with a reference voltage. S2 -C S1 ). Then, the sequence can be reversed as is usually done when using chopping techniques. The first sense line is charged while the second sense line is discharged. After coupling the two sense lines, C can be generated by comparing the common voltage of the two sense lines with a reference voltage. S1 -C S2 , to make another differential capacitance measurement. Then, by calculating the difference |C S1 -C S2 |-|C S2 -C S1 |To compare sequential differential capacitance measurements to each other for sensing changes caused by intervening events. By scanning the entire matrix, events can be tracked across the touch panel. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1A is a circuit diagram of a self-capacitance sensing touch panel according to an embodiment as described herein.

[0010] Figure 1B is a simplified circuit diagram of a self-capacitance sensing touch panel during a touch sensing event according to embodiments as described herein.

[0011] Figure 2 is a circuit diagram illustrating junction capacitance of a touch screen according to an embodiment as described herein.

[0012] Figure 3 is a flow chart illustrating a series of steps in a method of operating a self-capacitance sensor according to an embodiment as described herein.

[0013] Figure 4A is a circuit diagram of a charge sharing circuit with a certain magnification according to an embodiment as described herein.

[0014] Figure 4B is Figure 4A 2 is a timing diagram of the charges on the sense lines S1 and S2 during operation of the charge sharing circuit shown in FIG.

[0015] Figure 5A-5B The operations that occur when a charge sharing differential self mode for scanning odd numbered sense lines are shown according to embodiments as described herein.

[0016] Figure 5C-5D The operations that occur when a charge sharing differential self mode for scanning even-numbered sense lines are shown according to embodiments as described herein.

[0017] Fig. 6A is a differential capacitance curve for a charge sharing self mode according to embodiments as described herein.

[0018] Figure 6B It is a conventional normalized signal value capacitance curve plot.

[0019] Figure 7-11 is a circuit schematic diagram of a touch panel for implementing a charge sharing differential self-mode according to various embodiments as described herein. DETAILED DESCRIPTION

[0020] In the following description, certain specific details are set forth to provide a comprehensive understanding of the various aspects of the disclosed subject matter. However, the disclosed subject matter can be implemented without these specific details. In some instances, the known structures and methods of the embodiments of the disclosed subject matter have not yet been described in detail to avoid blurring the description of other aspects of the present disclosure.

[0021] Unless the context requires otherwise, throughout the specification and the appended claims, the word "comprise" and its various variations (such as, "comprises" and "comprising") are to be interpreted in an open, inclusive sense, that is, as "including, but not limited to."

[0022] References throughout this specification to "one embodiment" or "an embodiment" mean that a particular feature, structure, or characteristic described in conjunction with the embodiment is included in at least one embodiment. Thus, the phrases "in one embodiment" or "in an embodiment" appearing in various places throughout this specification are not necessarily all referring to the same aspect. Furthermore, the particular features, structures, or characteristics may be combined in any appropriate manner in one or more aspects of the present disclosure.

[0023] In the drawings, identical reference numerals identify similar elements or operations unless the context specifically dictates otherwise. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale.

[0024] Specific embodiments are described herein with reference to touch screens that have been produced; however, the disclosure and references to certain materials, dimensions, and details and sequences of processing steps are exemplary and should not be limited to those shown.

[0025] In the accompanying drawings, the same reference numerals indicate similar features or elements. The sizes and relative positions of features in the accompanying drawings are not necessarily drawn to scale.

[0026] Turning now to the accompanying drawings, Figure 1A According to an embodiment, a self-capacitance sensor 80 is shown. As part of a touch panel, the self-capacitance sensor 80 is configured to detect a touch event, such as a finger contacting the touch panel. The self-capacitance sensor 80 includes an AC power source 82 and a single touch panel electrode 84. The sensing line capacitor C s represents the capacitance of the touch panel electrode 84. The self-capacitance sensor 80 monitors C s Touch events are detected relative to the value of ground 86. Figure 1A No touch event occurred.

[0027] Figure 1B A touch event 90 is shown in which a human finger 91 is introduced, hovering a distance d above the touch panel electrode 84. The human finger 91 is aligned with an axis 94, which is oriented at an angle Φ relative to the plane of the touch panel. The presence of the human finger 91 increases the capacitance of the touch panel electrode 84 relative to ground 86. Capacitor C H represents the change in capacitance of the touch panel electrode 84 introduced by the human finger 91. Therefore, in addition to sensing the finger in contact with the touch panel, the self-capacitance sensor 80 is also able to sense the finger hovering. In addition, the self-capacitance sensor 80 can distinguish between the human finger 91 and the water droplets that have fallen on the touch panel, because the water droplets on the touch panel change the capacitance of the touch panel electrode 84, but the change is not related to C H Other types of touch panel sensors, such as mutual capacitance sensors that measure the capacitance between a pair of electrodes, can detect contact with a touch panel. However, mutual capacitance sensors cannot detect hovering fingers or provide "water repellency" functionality.

[0028] Figure 2 The embodiment described in the present disclosure shows a portion of a self-capacitive touch panel 96. The self-capacitive touch panel 96 is made of glass, wherein the drive line T x and sensing line S x A matrix of is formed as thin conductive lines embedded in the touch panel 96. Two examples of sensing lines S1 and S2 (vertically oriented) and one example of a driving line T are shown. x (horizontally oriented). In a full self-capacitive touch panel 96, there will be dozens or hundreds of such lines S x and T x . Sensing line S x Crossing the drive line T at node 98 x, thus forming a parallel plate capacitor, in which the glass touch panel acts as a dielectric material separating the conductors. The touch controller drives the line T x Apply a drive signal and from the sensing line S x Therefore, each sensing line S x There is a panel capacitance C between the corresponding adjacent driving line Tx px , where x = 1, 2, etc. In addition, when a touch event occurs, a self-capacitance C is generated between each sensing line and the ground. sx When there is no touch event, the self capacitance is equal to zero. Panel capacitance C px and self capacitance C sx is modeled as a flat plate capacitor. C can be monitored by scanning and comparing adjacent sense lines. px and C sx The value of .

[0029] A hovering finger causes small capacitance fluctuations. To increase sensitivity to such small changes, a differential capacitance measurement |C S1 -C S2 |. In general, it is easier to detect small changes using differential measurements than absolute measurements. This is because fluctuations are larger relative to differential measurements. Therefore, differential capacitance measurements will be more sensitive to touch events than absolute capacitance measurements. More sensitive measurements also improve noise performance by increasing the signal-to-noise ratio. That is, the ratio of the differential signal to noise measurement will be greater than the ratio of the absolute signal to noise measurement.

[0030] Figure 3 The steps of operating the self-capacitive touch panel 96 in method 100 are shown according to an embodiment incorporating a charge sharing technique for performing a scan sequence. Figure 4A As shown, the method 100 may be performed by the self-mode charge sharing circuit 130 and is described as follows. Figure 4B As shown, the method 100 is further illustrated by a timing diagram 160, according to which the self-mode charge sharing circuit 130 is operated. The self-mode charge sharing circuit 130 can be used to cyclically charge, and by doing so, the power requirements are reduced while increasing the sensitivity of the touch panel. Charge sharing is a well-known technology and has been used in many electrical design fields, including low-power digital CMOS circuits, LCD display drivers, and touch sensor panels, such as disclosed in U.S. Patent No. 8,432,364. It is shown herein that charge sharing can be used to facilitate sensing the differential self-capacitance of a touch screen associated with a touch event.

[0031] Figure 4A The self-mode charge sharing circuit 130 shown includes a capacitor C coupled to a parallel capacitor C via switches 154 and 156. S1 and CS2 The output buffer 132 of FIG. 154 is a charge sharing switch. Figure 4A The charge sharing switch 154 is used to share charge between the two sensing lines S1 and S2. The switch 154 switches C S1 and C S2 The switches 154, 156 then couple the sense lines S1 and S2 to the output buffer 132. As is known in the art, the switches 154, 156 may be, for example, standard CMOS transistor gating circuits, or transmission gate switches made from paired CMOS transistor gating circuits.

[0032] In an embodiment, the output buffer 132 is an operational amplifier (op amp) buffer. The output buffer 132 is used to provide a voltage V at the two input terminals. C最小 The voltage difference between the voltage at node 92 and the voltage at node 92 is a differential amplifier with a gain factor applied. Reference capacitor 144 is connected in the feedback loop of output buffer 132. Reference capacitor 144 is an internal reference capacitor that can be bypassed by closing switch 146. Transistor 122 switches C S1 Coupled to power supply V DD In order to C S1 Charge. V DD This can be a standard supply voltage in the range of about 3.3V-12V. Transistor 152 bypasses C S2 Or connect node 92 directly to ground for C S2 Discharge. Figure 4B As shown in the timing diagram, the self-mode charge sharing circuit 130 monitors the self capacitances associated with the sense lines S1 and S2, respectively.

[0033] like Figure 4B As shown, in step 102 of method 100, at initial time t0, transistors 122 and 152 are turned on, so that capacitor C S1 is set to a voltage V DD And charge to q 输入 =C S1 *V DD At the same time, capacitor C S2 is discharged and is at 0V.

[0034] In step 104, charge sharing is engaged. Transistors 122, 122C, 152, and 152C are turned off, and switch 154 is closed, thereby shorting sense lines S1 and S2 together at node 92. During initial time interval 162, capacitor C S1 Start to discharge, and at the same time, the capacitor C S2Before the end of time interval 162, the voltages of S1 and S2 are approximately the same, for example, V DD / 2.

[0035] In step 106, switch 146 is opened and switch 156 is closed. As is typical in switched capacitor circuits, during the amplification period coinciding with time interval 164, C S1 and C S2 A portion of the shared charge is transferred to capacitor 144 .

[0036] In step 108, at the end of time interval 164, the transferred charge q is extracted 输出 +To determine the differential capacitance |C S1 -C S2 |. For example, using V C最小 =V DD / 2 and q 输出 + = V DD / 2(C S1 -C S2 ), then the equation V 输出 -V DD / 2=V DD / 2(C S2 -C S1 ) can be used to calculate the differential capacitance |C S1 -C S2 |. The calculations may be performed by a microprocessor and associated memory that is part of the touch screen controller.

[0037] At step 110, as is common in chopping circuits, the process can be reversed to improve flicker noise rejection. During time interval 166, switch 146 is opened to reset the previous value of the output signal, and transistors 122C, 152C are turned on, causing S1 to be discharged to 0V and S2 to be precharged to V DD During time interval 168, transistors 122C, 152C are turned off and the two sensing lines S1 and S2 are shorted together, thereby causing C S2 Discharge, while C S1 During the amplification and charge sharing time interval 170, the two capacitors C S1 and C S2 During time interval 170, switches 146 and 154 are closed, allowing charge q to be transferred through output buffer 132. 输出 -. Then you can pass it through the V C最小 =V DD / 2 when the amplified charge q is extracted 输出 - and using the equation q 输出 + = VDD / 2(C S2 -C S1 ) to calculate the differential capacitance |C at the end of time interval 170 S2 -C S1 |. During the last time interval 172, the charge sharing switch 154 is turned off and the capacitor C S2 Discharge, at the same time, C S1 Restore to the power supply voltage V DD .

[0038] The differential capacitance measurement made at the end of the charge transfer interval 16, 170 can be made by sampling using an analog-to-digital converter. By monitoring the differential capacitance value over time and across the touch panel, a touch event can be detected by the disturbance it creates in the differential capacitance value.

[0039] At 112, method 100 may be repeated to monitor an adjacent pair of sense lines and move across the touch panel in a serial manner.Alternatively, method 100 may be performed by replicating the self-mode charge sharing circuit 130 in parallel to monitor multiple pairs of sense lines simultaneously.

[0040] As an example, Figures 5A-5D Various charge sharing scan sequences involving up to five lines of line sense lines S1-S5, or channels, are shown. For example, there may be 32 channels or any number of channels. Each charge sharing instance indicated by a solid line bow-tie switch 154 represents an execution of the above method 100. A dashed line bow-tie switch indicates an open switch. The number of sense lines scanned depends on the size of the touch screen.

[0041] Figure 5A In the first scan shown, charge sharing is applied to sense lines S1 and S2 to determine the differential capacitance |C S2 -C S1 |, and is applied to the sensing lines S3 and S4 for determining the differential capacitance |C S3 -C S4 |. Figure 5B In the second scan shown, charge sharing is applied to sense lines S2 and S3 to determine the differential capacitance |C S2 -C S3 |, and is applied to the sensing lines S4 and S5 for determining the differential capacitance |C S4 -C S5 |. Figure 5C In the third scan shown, charge sharing is applied to the sense lines S1 and S2 to determine the differential capacitance |C S1 -C S2 |, and is applied to the sensing lines S3 and S4 for determining the differential capacitance |C S3 -CS4 |. Figure 5D In the fourth scan shown, charge sharing is applied to sense lines S2 and S3 to determine the differential capacitance |C S2 -C S3 |.

[0042] Fig. 6A and 6B The differential capacitance is compared to the absolute capacitance determined during a touch event. A touch event occurs at the origin (0) and can be measured outward to approximately two radial units from the touch point. Figure 6B The example shown in FIG. 1 shows an absolute capacitance 174 having a value greater than Fig. 6A The corresponding normalized differential capacitance measurement results shown in 173 are approximately 1000 times.

[0043] Figure 7-11 shows the variation of the self-mode charge sharing circuit 130, where the panel capacitance C P1 and C P2 is taken into account. Therefore, Figure 7-11 Including parallel to C S1 The panel capacitor C P1 , parallel to C S2 The panel capacitor C P2 , and additional components such as the error elimination stage CX. The error elimination stage CX is used to eliminate the capacitor C P1 , C P2 The charge on the self-capacitance will not affect the charge measurement q associated with the self-capacitance during a touch event. 输出 + and q 输出 -. The error cancellation stage CX is a switched capacitor circuit consisting of capacitors and a driver that removes the charge on the S2 line, thereby compensating for the error caused by the differential capacitance |C P1 -C p2 |The error introduced.

[0044] Figure 7 According to an embodiment of the present disclosure, a low power self-mode circuit 175 is shown. When the touch panel is in a "wake-up" mode after an idle period, the low power self-mode circuit 175 can replace the self-mode charge sharing circuit 130. In use, the power supply V for the low power self-mode circuit 175 is DD is set to 3.3V, then the V C最小 The input is 3.3V / 2=1.65V. Due to charge sharing, the voltage used in the self-mode circuit described herein is lower, and therefore error cancellation occurs quickly and efficiently. The use of low power self-mode circuit 175 also generates less noise than conventional touch panel circuits that detect capacitance rather than differential capacitance.

[0045] Figure 8 According to an embodiment, a low-power self-mode circuit 180 is shown. The low-power self-mode circuit 180 is also intended for use, for example, when the touch panel is in a "wake-up" mode after an idle period. The low-power self-mode circuit 180 is a complementary reverse circuit corresponding to the low-power self-mode circuit 175, wherein the power supply V DD The transistor 122 is coupled to the sensing line S2, and the transistor 121 is coupled to the sensing line S1. As explained above, the low power self-mode circuit 180 can be used in conjunction with the chopping technique. In use, the power supply V for the low power self-mode circuit 180 is DD is set to 3.3V, then the V C最小 Input is V DD / 2=1.65V.

[0046] Fig. 9 A self-mode circuit 200 is shown in accordance with an embodiment of the present disclosure. The self-mode circuit 200 is intended for use during normal operation of a touch panel and provides cancellation of differential panel capacitance for faster scanning. The self-mode circuit 200 is similar to the self-mode circuit 175 except that a switch 202 has been added to the output of the output buffer 132, the switch 146 has been removed from the feedback loop of the output buffer 132, and the switch 192 has been added between the inputs of the output buffer 132. As is common in switched capacitor circuits, such components allow discrimination between the output and input common modes of the operational amplifier 132. In use, the power supply V for the self-mode circuit 200 is DD is set to 5.0V, then the V C最小 Input is V DD / 2=2.5 V. In addition, the switch 202 is coupled to a 1.65 V power supply.

[0047] Fig.10 A self-mode circuit 210 is shown according to an embodiment of the present disclosure. The self-mode circuit 210 is intended for use during normal operation of a touch panel and provides for differential C p Self-mode circuit 210 is similar to self-mode circuit 200, except that error cancellation stage CX is removed and tunable voltage divider 212 is used to generate reference voltage V 基准 In use, the power supply V for the self-mode circuit 210 is DD is set to 5.0V, then the V 基准 Input is V DD / 2=2.5V. Replace the error elimination stage CX, V 基准 is coupled to a voltage divider 212, which includes a voltage divider coupled to an intermediate power supply V ddThe resistor R and the variable resistor R1. For example, V DD Can be set to 3.3V.

[0048] Fig.11 A self-mode circuit 220 is shown according to an embodiment of the present disclosure. The self-mode circuit 220 is intended for use during normal operation of the touch panel. Fig.11 The self-mode circuit 200 shown is similar to the self-mode circuit 210, except that the transistor 152 is connected to a negative voltage instead of ground. In use, the power supply V for the self-mode circuit 220 is DD is set to 5.0V, then V C最小 The node is effectively ground. In addition, switch 202 is coupled to a 1.65V supply.

[0049] All U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications, and non-patent publications mentioned in this specification and / or listed in the Application Data Sheet are incorporated herein by reference in their entirety.

[0050] It will be appreciated that, although a number of specific embodiments of the present disclosure are described herein for illustrative purposes, various modifications may be made without departing from the spirit and scope of the present disclosure. The various embodiments described above may be combined to provide further embodiments. Aspects of the embodiments may be modified if necessary to employ the concepts of various patents, applications, and publications to provide more embodiments.

[0051] These and other changes can be made to the embodiments in light of the description detailed above. In summary, in the following claims, the terms used should not be interpreted as limiting the claims to the specific embodiments disclosed in the specification and claims, but should be interpreted to include all possible embodiments, along with the full range of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the present disclosure.

Claims

1. A circuit comprising: An output buffer having a first input terminal, a second input terminal and an output terminal; a first sense line capacitor coupled to a power supply node via a first switch, the first switch being configured to be turned on during a first time period to charge the first sense line capacitor; a second sensing line capacitor coupled to a ground node via a second switch, the second switch being configured to be turned on during the first time period to discharge the second sensing line capacitor; a first charge sharing switch, which is in line between the first sensing line capacitor and the second sensing line capacitor and is configured to be turned on during a second time period after the first time period to enable the first sensing line capacitor and the second sensing line capacitor to perform charge sharing; a second charge sharing switch coupled between the first sensing line capacitor and the first input terminal of the output buffer and configured to be turned on during a third time period after the second time period to couple the first sensing line capacitor to the output buffer, the output buffer being configured to receive a reference voltage at the second input terminal, compare a common voltage sensed at the first sensing line capacitor with the reference voltage, and output a voltage representing a difference between the common voltage and the reference voltage to determine a position on the touch panel where a finger is adjacent to the touch panel; as well as An adjustable voltage divider is coupled to the second input terminal and is configured to output the reference voltage to the second input terminal.

2. The circuit according to claim 1, wherein The output buffer includes an operational amplifier having two input terminals.

3. The circuit of claim 2, wherein the output buffer further comprises a reference capacitor in a feedback loop of the operational amplifier.

4. The circuit according to claim 3 further comprising a first panel capacitor coupled in parallel with the first sensing line capacitor; and A second panel capacitor is coupled in parallel with the second sensing line capacitor. 5 . The circuit according to claim 2 , wherein the output buffer is further equipped with an input switch which selectively couples two input terminals of the operational amplifier.

6. The circuit according to claim 3, further comprising: A bypass switch is configured to selectively remove the reference capacitor from the feedback loop.

7. The circuit according to claim 3, wherein: Two input terminals of the operational amplifier are coupled to each other, and the output buffer further includes an output switch located in the feedback loop.

8. The circuit according to claim 3, wherein: One of the terminals of the operational amplifier is a ground terminal.

9. The circuit according to claim 1, wherein: The touch panel is a component of a mobile electronic device.

10. A circuit comprising: An output buffer having a first input terminal, a second input terminal and an output terminal; a first sense line capacitor coupled to a power supply node via a first switch, the first switch being configured to be turned on during a first time period to charge the first sense line capacitor; a second sensing line capacitor coupled to a ground node via a second switch, the second switch being configured to be turned on during the first time period to discharge the second sensing line capacitor; a first charge sharing switch, in line between the first sensing line capacitor and the second sensing line capacitor, and configured to be turned on during a second time period after the first time period to enable the first sensing line capacitor and the second sensing line capacitor to perform charge sharing; a second charge sharing switch coupled between the first sensing line capacitor and the first input terminal of the output buffer and configured to be turned on during a third time period after the second time period to couple the first sensing line capacitor to the output buffer, the output buffer being configured to receive a reference voltage at the second input terminal, compare a common voltage sensed at the first sensing line capacitor with the reference voltage, and output a voltage representing a difference between the common voltage and the reference voltage to determine a position on the touch panel where a finger is adjacent to the touch panel; as well as An input switch is coupled between the first input terminal and the second input terminal and is configured to switch between a conducting state in which the first input terminal and the second input terminal are coupled to each other and a non-conducting state in which the first input terminal and the second input terminal are decoupled from each other.

11. The circuit according to claim 10, wherein: The output buffer includes an operational amplifier and a reference capacitor located in a feedback loop of the operational amplifier.

12. The circuit according to claim 11, wherein One of the terminals of the operational amplifier is a ground terminal.

13. The circuit according to claim 10, further comprising a first panel capacitor coupled in parallel with the first sensing line capacitor; and A second panel capacitor is coupled in parallel with the second sensing line capacitor.

14. The circuit according to claim 10, wherein: The touch panel is a component of a mobile electronic device.

15. A method comprising: discharging a first sensing line capacitor of the touch panel; charging a second sensing line capacitor of the touch panel; coupling the first sensing line capacitor and the second sensing line capacitor to each other for charge sharing; Determine the differential self capacitance; Output reference voltage through adjustable voltage divider; comparing a common voltage of the first sensing line capacitor and the second sensing line capacitor with the reference voltage; Repeating the steps of discharging, charging, coupling, determining, outputting, and comparing for a plurality of first sensing line capacitors and second sensing line capacitors of the touch panel; as well as The location of a finger adjacent to the touch panel is determined based on changes in the differential self-capacitance measurements.

16. The method according to claim 15, comprising: discharging the first sensing line capacitor; charging the second sensing line capacitor; coupling the first sensing line capacitor and the second sensing line capacitor to each other for charge sharing; determining a differential capacitance measurement to compare the capacitance of the first sense line capacitor and the second sense line capacitor; as well as An output signal of the sensing line capacitor is amplified.

17. The method according to claim 15, comprising: Signals of the first sensing line capacitor and the second sensing line capacitor are amplified using an operational amplifier.

18. The method according to claim 15, wherein: The discharging is accomplished by connecting the second sense line capacitor to ground.

19. The method of claim 15, wherein charging the sense line capacitor comprises coupling the sense line capacitor to a power supply in the range of 3.3V-12V.

20. A circuit for a touch panel, the circuit comprising: Power node; Ground node; an output buffer having a first input terminal, a second input terminal and an output terminal; a first sense line capacitor coupled to the power supply node via a first switch, the first switch being configured to be turned on during a first time period to charge the first sense line capacitor; a second sensing line capacitor coupled to the ground node via a second switch, the second switch being configured to be turned on during the first time period to discharge the second sensing line capacitor; a first charge sharing switch, which is in line between the first sensing line capacitor and the second sensing line capacitor and is configured to be turned on during a second time period after the first time period to enable the first sensing line capacitor and the second sensing line capacitor to perform charge sharing; as well as A second charge sharing switch is coupled between the first sensing line capacitor and the first input terminal of the output buffer and is configured to be turned on during a third time period after the second time period to couple the first sensing line capacitor to the output buffer, the output buffer being configured to receive a reference voltage at the second input terminal, compare a common voltage sensed at the first sensing line capacitor with the reference voltage, and output a voltage representing a difference between the common voltage and the reference voltage to determine a position on the touch panel where a finger is adjacent to the touch panel.

21. The circuit of claim 20, wherein: The output buffer includes an operational amplifier having two input terminals.

22. The circuit of claim 21, wherein: The output buffer also includes a reference capacitor in a feedback loop of the operational amplifier.

23. The circuit of claim 22, further comprising a first panel capacitor coupled in parallel with the first sensing line capacitor; and A second panel capacitor is coupled in parallel with the second sensing line capacitor.

24. The circuit of claim 23, further comprising a panel capacitance cancellation device coupled between the sense line capacitor and the second charge sharing switch.

25. The circuit of claim 24, wherein the output buffer is further equipped with an input switch that selectively couples two input terminals of the operational amplifier.

26. The circuit of claim 25, further comprising: A bypass switch is configured to selectively remove the reference capacitor from the feedback loop.

27. The circuit of claim 24, wherein: Two input terminals of the operational amplifier are coupled to each other, and the output buffer further includes an output switch located in the feedback loop.

28. The circuit of claim 25, wherein: One of the terminals of the operational amplifier is a ground terminal.

29. The circuit of claim 24, wherein: The touch panel is a component of a mobile electronic device.

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