Capacitive touch system and sensing method for a capacitive touch system

The present invention is related to a capacitive touch system and a sensing method for a capacitive touch system.

In conventional applications, all the large scale capacitive touch panels use a surface capacitance sensing technique to scan thereto for determining a touch information, which uses a set of detecting currents, each directed to an endpoint of the large scale touch panel to produce detected values, and therefore, even multiple fingers simultaneously touch the large scale touch panel, this sensing technique still retrieves only one set of detected currents in response to this multi-finger touch. For this reason, the surface capacitance sensing technique can identify only one set of absolute coordinates. In a two dimensional matrix for instance, only one set of parameters (X,Y) will be determined, and thereby it can't implement a multi-finger touch detection.

An all points addressable (APA) projected capacitance sensing technique is capable of implementing a multi-finger touch detection, but not applicable to large scale touch panels because, to implement this sensing technique, it is necessary to charge and discharge each point sensor on the large scale touch panel. Taking a matrix-type touch panel for example, when the X and Y traces increase, the pixel number of an APA projected capacitance touch panel dramatically increases and thereby significantly degrades the frame rate of the touch panel due to the very long time period for scanning the large scale touch panel in a frame.

An axis intersect (AI) projected capacitance sensing technique is also capable of implementing a multi-finger touch detection, but not applicable to large scale touch panels, too. FIG. 1 is a schematic diagram of a conventional AI projected capacitance sensing technique applied to a small scale touch panel 10 , in which an AI projected capacitance touch IC 12 is used to scan the small scale touch panel 10 . Assuming that the AI projected capacitance touch IC 12 can support up to twenty-two traces, a good frame rate can be attained for a small scale touch panel 10 having ten X traces TRX 1 -TRX 10 and ten Y traces TRY 1 -TRY 10 . However, if a this type touch IC 12 is applied to a large scale touch panel 14 having forty X traces TRX 1 -TRX 40 and forty Y traces TRY 1 -TRY 40 , as shown in FIG. 2 , the total number of traces that the touch IC 12 needs to scan dramatically increases. Moreover, the frame rate of the overall touch panel application is dependent to a very large extent on the time it takes the touch IC 12 to charge and discharge capacitors each time. In other words, the frame rate is determined mainly by the time in a frame that the touch IC 12 charges and discharges the capacitors. Hence, if an AI projected capacitance touch IC capable of scanning a greater number of traces is applied to a large scale touch panel 14 , a major drawback would be a significantly decreased frame rate in the overall application, which leads to compromised performance at the application end.

An object of the present invention is to provide a capacitive touch system.

Another object of the present invention is to provide a sensing method for a capacitive touch system.

According to the present invention, a capacitive touch system includes a touch panel and two touch integrated circuits connected to the touch panel to scan thereto. The touch panel has a boundary trace. The two touch integrated circuits both are connected to the boundary trace, but do not charge/discharge thereto simultaneously. When one of the two touch integrated circuits charges/discharges the boundary trace, the boundary trace is floating or has a high impedance to the other touch integrated circuit. By this way, the boundary problem caused by using more than two touch integrated circuits to scan a touch panel is eliminated. In addition, the difference between two sensed values retrieved by two touch integrated circuits for a same trace can be used at a backend circuit to eliminate the difference between the sensed values retrieved by the two touch integrated circuits. Moreover, two sensed values retrieved by two touch integrated circuits for a same trace can be filtered to produce a value used as the sensed value of the trace, thereby reducing the influence of noise.

These and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a conventional AI projected capacitance sensing technique applied to a small scale touch panel;

FIG. 2 is a schematic diagram of a conventional AI projected capacitance sensing technique applied to a large scale touch panel;

FIG. 3 is a schematic diagram of a capacitive touch system using at least two AI projected capacitance touch ICs to scan a touch panel;

FIG. 4 is a schematic diagram of an enlarged portion of the capacitive touch system of FIG. 3 ;

FIG. 5 is a schematic diagram showing a first embodiment according to the present invention;

FIG. 6 is a schematic diagram showing a second embodiment according to the present invention; and

FIG. 7 is a schematic diagram showing a third embodiment according to the present invention.

As shown in FIG. 3 , a capacitive touch system 20 uses at least two AI projected capacitance touch ICs 24 and 26 to scan a touch panel 22 . The touch panel 22 has a plurality of first traces TRX 1 -TRX 10 connected to the touch IC 24 , and a plurality of second traces TRX 11 -TRX 20 connected to the touch IC 26 , of which the first one TRX 11 of the second traces TRX 11 -TRX 20 is next to the last one TRX 10 of the first traces TRX 1 -TRX 10 . FIG. 4 is a schematic diagram of an enlarged portion of the capacitive touch system 20 , which shows the boundary trace TRX 10 and its neighboring traces. In the capacitive touch system 20 , the touch IC 24 is responsible for scanning the traces TRX 1 -TRX 10 , and the touch IC 26 is responsible for scanning the traces TRX 11 -TRX 20 . By using the touch ICs 24 and 26 to simultaneously scan the touch panel 22 , a multi-finger touch detection and a good frame rate can be achieved, even the touch panel 22 is a large scale touch panel. Conventionally, a capacitive touch IC for a small scale touch panel generally uses two traces to determine a sensed value for a trace, by which the trace to be sensed and the neighboring one next to this trace (with their capacitors) are simultaneously charged thereto and discharged therefrom to obtain two analog-to-digital conversion (ADC) values therefrom, and then a better ADC value is produced by calculating with these two ADC values as the sensed value of the trace to be sensed.

If the above sensing method is applied to a capacitive touch system using at least two capacitive touch ICs to scan the traces in a same direction, as that shown in 4 , there will be a boundary issue. When the touch IC 24 scans the traces TRX 1 -TRX 10 , the sensed values of the traces TRX 1 -TRX 9 could be determined by the conventional sensing method. For example, to determine a sensed value for the trace TRX 7 , both the traces TRX 7 and TRX 8 are charged thereto and discharged therefrom at a same time to obtain the ADC values of the traces TRX 7 and TRX 8 , and then these two ADC values are used to determine the sensed value of the trace TRX 7 . Similarly, the ADC values of the traces TRX 8 and TRX 9 are used to determine a sensed value for the trace TRX 8 , and the ADC values of the traces TRX 9 and TRX 10 are used to determine a sensed value for the trace TRX 9 . For the boundary trace TRX 10 , however, the next trace TRX 11 is connected to another touch IC 26 , instead of the touch IC 24 , and thus the touch IC 24 cannot determine a sensed value for the trace TRX 10 as done by the conventional sensing method. Since the trace TRX 11 is not connected to the touch IC 24 , the sensed value of the trace TRX 10 is determined by the ADC value of the trace TRX 10 itself alone. As a result, the sensed value of the trace TRX 10 may be incorrect or smaller than it should be.

According to the present invention, a trace overlapping layout is proposed to solve the above boundary problem caused by using at least two capacitive touch ICs to scan the traces in a same direction of a touch panel. FIG. 5 is a schematic diagram showing a first embodiment according to the present invention, in which the touch IC 24 is connected to the traces TRX 1 -TRX 10 as it was in a conventional capacitive touch system. However, in addition to the traces TRX 11 -TRX 20 , the boundary trace TRX 10 is also connected to the touch IC 26 . In other words, the trace TRX 10 overlaps in its connection with the touch ICs 24 and 26 . With this arrangement, the trace TRX 10 could be charged/discharged by either the touch IC 24 or the touch IC 26 . In the process of charging/discharging two neighboring traces at a same time, the touch IC 24 does not charge/discharge the boundary trace TRX 10 while scanning the traces TRX 1 -TRX 8 . Therefore, if the trace TRX 10 is set to be floating or have a high impedance to the touch IC 24 during the touch IC 24 scanning the traces TRX 1 -TRX 8 , the touch IC 26 can charge/discharge the trace TRX 10 without affecting the touch IC 24 during the touch IC 24 scanning the traces TRX 1 -TRX 8 . Similarly, the touch IC 24 can charge/discharge the trace TRX 10 without affecting the touch IC 26 if the trace TRX 10 is floating or has a high impedance to the touch control IC 26 . In other words, the touch ICs 24 and 26 do not charge/discharge the boundary trace TRX 10 at a same time. When one of the touch ICs 24 and 26 charges/discharges the boundary trace TRX 10 , the boundary trace TRX 10 is floating or has a high impedance to the other of the touch ICs 24 and 26 . Furthermore, assuming that the touch ICs 24 and 26 start scanning their responsible traces simultaneously, when the touch IC 24 charges/discharges the traces TRX 1 and TRX 2 to retrieve a sensed value for the trace TRX 1 , the touch IC 26 can charge/discharge the traces TRX 10 and TRX 11 to retrieve a sensed value for the trace TRX 10 , thereby eliminating the boundary problem. At this time, the trace TRX 10 is floating or has a high impedance to the touch IC 24 , so that the touch IC 26 is allowed to charge/discharge the trace TRX 10 without affecting the touch IC 24 . When the touch IC 24 charges/discharges the traces TRX 9 and TRX 10 to obtain a sensed value for the trace TRX 9 , the touch IC 26 does not charge/discharge the trace TRX 10 . At this time, the trace TRX 10 is floating or has a high impedance to the touch IC 26 , thereby allowing the touch IC 24 to charge/discharge the trace TRX 10 without affecting the touch IC 26 .

FIG. 6 is a schematic diagram showing a second embodiment according to the present invention, in which more boundary traces TRX 8 , TRX 9 and TRX 10 are connected to both of the touch ICs 24 and 26 . As mentioned above, the touch ICs 24 and 26 do not charge/discharge a same one of the trace TRX 8 , TRX 9 or TRX 10 simultaneously. For example, when the touch IC 24 charges/discharges the trace TRX 8 , the trace TRX 8 is floating or has a high impedance to the touch IC 26 . Similarly, when the touch IC 26 charges/discharges the trace TRX 8 , the trace TRX 8 is floating or has a high impedance to the touch IC 24 . In this embodiment, if there are two traces to be selected to be charged/discharged each time, both the touch ICs 24 and 26 will obtain sensed values of the traces TRX 8 and TRX 9 . Hence, the sensed values obtained by the touch ICs 24 and 26 for a same trace can be filtered, for example by being averaged, to reduce the difference between the touch ICs 24 and 26 after preliminary calibration, and obtain the difference between the sensed values, thereby producing a better sensed value.

If there are two traces are selected to be charged/discharged each time, the trace overlapping layout of the present invention can be extended to such extent that, when the touch IC 24 charges/discharges traces TRX[N] and TRX[N+1], the touch IC 26 charges/discharges traces TRX[N+2] and TRX[N+3], whereas all the pins that are not used in charging/discharging are set to be floating or have a high impedance. FIG. 7 is a schematic diagram showing a third embodiment according to the present invention issue. When the touch IC 24 selects the traces TRX 1 and TRX 2 to retrieve a sensed value for the trace TRX 1 , the touch IC 26 selects the next two traces TRX 3 and TRX 4 to retrieve a sensed value for the trace TRX 3 . Similarly, when the touch IC 24 selects the traces TRX 2 and TRX 3 to retrieve a sensed value for the trace TRX 2 , the touch IC 26 selects the traces TRX 4 and TRX 5 to retrieve a sensed value for the trace TRX 4 . The process goes on analogously, in which the touch ICs 24 and 26 do not charge/discharge a same trace simultaneously.

While the present invention has been described in conjunction with preferred embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and scope thereof as set forth in the appended claims.