Method for controlling operations of input device having resistor matrix

A method for controlling an input device is provided. The input device has a resistor matrix having M first traces, N second traces and M×N resistors. Each second trace is coupled to a reference resistor and M−1 variable resistors. M and N are integers greater than 1. A first voltage level of each second trace is measured when a first voltage is applied to a first end of the reference resistor and a second voltage is applied to first ends of the M−1 variable resistors via the M first traces. Variations of the first voltage level of each second trace are measured, such that it could be determined whether any touch point of the input device exists according to the variations of the first voltage level of each second trace.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to a method for controlling operations of an input device, and more particularly to a method for controlling operations of an input device having a resistor matrix.

2. Description of the Prior Art

Please refer toFIG. 1, which is a schematic diagram of an input device100according to the prior art. The input device100has a power control circuit110and a switch matrix120. The power control circuit110sequentially supplies voltages V1, V2, V3and V4to the switch matrix120. The switch matrix120has a plurality of first traces121, a plurality of second traces122and a plurality of switches P11to P44. A first end of each of the switches P11to P44is coupled to one of the first traces121, and a second end of each of the switches P11to P44is coupled to one of the second traces122. Each of the second traces122is coupled to one of output terminals O1to O4of the input device100.

When a user touches the input device100, a switch located at the touch point is turned on. For example, when the user touches an area around the switch P11, the switch P11is turned on. Since the switch P11is turned on, when the power control circuit110supplies the voltage V1to the switch matrix120, a current flows from the power control circuit110through the switch P11to the output terminal O1. Therefore, the location of the touch point of the input device100could be determined according to detected currents outputted from the output terminals O1to O4and the timing of sequentially applying the voltages V1, V2, V3and V4to the first traces121.

However, when two or more touch points of the input device100are triggered at the same time, the input device100may miscalculate the locations of the touch points . For example, when the user touches an area around the switches P21, P12and P22, the switches P21, P12and P22are turned on accordingly. Since the switches P21, P12and P22are turned on, when the power control circuit110supplies the voltage V1to the switch matrix120, a current I flows from the power control circuit110through the switch P21, P22and P12sequentially to the output terminal O1. Accordingly, the input device100miscalculates that the touch point is located on the position of the switch P11.

SUMMARY OF THE INVENTION

A method for controlling operations of an input device is disclosed. The input device comprises a resistor matrix having M first traces, N second traces and M×N resistors. First ends of resistors of a same column are connected to one of the M first traces, second ends of resistors of a same row are connected to one of the N second traces, and each second trace are coupled to a reference resistor and M−1 variable resistors. M and N are integers greater than 1. The method comprises measuring a first voltage level of the each second trace when a first voltage is applied to a first end of the reference resistor and a second voltage is applied to first ends of the M−1 variable resistors via the M first traces; measuring variations of the first voltage level of the each second trace; and determining at least one touch point of the input device according to the variations of the first voltage level of the each second trace.

DETAILED DESCRIPTION

Please refer toFIG. 2, which is a schematic diagram of an input device200according to an embodiment of the present invention. The input device200has a resistor matrix210, a power control circuit220and a measurement circuit230. The resistor matrix210has M first traces2111to2114, N second traces2121to2124, and M×N resistors R11to R44. In the embodiment, both of M and N are equal to 4. However, the present invention is not limited thereto. M and N could be any integer greater than 1.

Regarding the resistors R11to R44, the first ends of resistors of a same column are connected to one of the M first traces2111to2114. For example, the first ends of resistors R11, R21, R31and R41of a first column of the resistor matrix210are connected to the first trace2111; the first ends of resistors R12, R22, R32and R42of a second column of the resistor matrix210are connected to the first trace2112; the first ends of resistors R13, R23, R33and R43of a third column of the resistor matrix210are connected to the first trace2113; and the first ends of resistors R14, R24, R34and R44of a fourth column of the resistor matrix210are connected to the first trace2114.

Moreover, regarding the resistors R11to R44, the second ends of resistors of a same row are connected to one of the N second traces2121to2124. For example, the second ends of resistors R11, R12, R13and R14of a first row of the resistor matrix210are connected to the second trace2121; the second ends of resistors R21, R22, R23and R24of a second row of the resistor matrix210are connected to the second trace2122; the second ends of resistors R31, R32, R33and R34of a third row of the resistor matrix210are connected to the second trace2123; and the second ends of resistors R41, R42, R43and R44of a fourth row of the resistor matrix210are connected to the second trace2124.

Additionally, each of the second traces2121to2124is coupled to a reference resistor and M−1 variable resistors. For example, in the embodiment, the resistors R11, R21, R31and R41are reference resistors and have constant resistances, and the resistors R12to R14, R22to R24, R32to R34and R42to R44are variable resistors. The second trace2121is coupled to the reference resistor R11and the variable resistors R12to R14. The second trace2122is coupled to the reference resistor R21and the variable resistors R22to R24. The second trace2123is coupled to the reference resistor R31and the variable resistors R32to R34. The second trace2124is coupled to the reference resistor R41and the variable resistors R42to R44.

In an embodiment of the present invention, for the sake of accuracy of measurement, a ratio of resistance of the reference resistors to resistance of each of the variable resistors under activation force in each row of the resistor matrix210may fall in a range of 0.2 to 5. The strength of the activation force is greater than or equal to a predetermined threshold (e.g. 20 grams). When the activation force is applied to one of the variable resistors, a touch point around the variable resistor, which is applied with the activation force, is determined to being triggered. In this document, the resistance of the variable resistor under the activation force is termed “activation force resistance”. In other words, the ratio of the resistance of the reference resistors R11to the activation force resistance of each of the variable resistors R12to R14in the first row of the resistor matrix210falls in the range of 0.2 to 5. The ratio of the resistance of the reference resistors R21to the activation force resistance of each of the variable resistors R22to R24in the second row of the resistor matrix210falls in the range of 0.2 to 5. The ratio of the resistance of the reference resistors R31to the activation force resistance of each of the variable resistors R32to R34in the third row of the resistor matrix210falls in the range of 0.2 to 5, and the ratio of the resistance of the reference resistors R41to the activation force resistance of each of the variable resistors R42to R44in the fourth row of the resistor matrix210falls in the range of 0.2 to 5.

The power control circuit220is coupled to the first traces2111to2114and is configured to supply voltage signals S1to S4to the first traces2111to2114. Please refer toFIGS. 2 and 3.FIG. 3is a timing diagram of the voltage signals S1to S4. The voltage signals S1to S4are respectively transmitted to the first traces2111,2112,2113and2114by the power control circuit220. During a period T1, a voltage level of the voltage signal S1is equal to a first voltage V1, and voltage levels of the remaining voltage signals S2to S4are equal to a second voltage V2. In the embodiment, the first voltage V1is greater than the second voltage V2, and the second voltage V2could be a positive voltage, a ground voltage (i.e. 0 volt) or a negative voltage. In another embodiment, the first voltage V1could be less than the second voltage V2, and the first voltage V1could be a positive voltage, the ground voltage (i.e. 0 volt) or a negative voltage. Similarly, during a period T2, the voltage level of the voltage signal S2is equal to the first voltage V1, and the voltage levels of the remaining voltage signals S1, S3and S4are equal to the second voltage V2. During a period T3, the voltage level of the voltage signal S3is equal to the first voltage V1, and the voltage levels of the remaining voltage signals S1, S2and S4are equal to the second voltage V2. During a period T4, the voltage level of the voltage signal S4is equal to the first voltage V1, and the voltage levels of the remaining voltage signals S1to S3are equal to the second voltage V2. In other words, the power control circuit220applies the first voltage V1to the first traces2111to2114in a predetermined sequence. In the embodiment, the predetermined sequence is2111→2112→2113→2114. However, the present invention is not limited thereto. For example, the predetermined sequence also could be2112→2111→2114→2113, or other sequences. When the first voltage V1is applied to one of the first traces2111to2114, the voltage control circuit220applies the second voltage V2to the remaining first traces which are not applied with the first voltage V1.

The measurement circuit230is coupled to the second trances2121to2124and is configured to measure variations of voltage levels Va, Vb, Vc and Vd of the second traces2121to2124when the power control circuit220applies the first voltage V1and the second voltage V2to the first traces2111to2114. Moreover, the measurement circuit230outputs a control signal Sc according to the measured voltage levels Va, Vb, Vc and Vd of the second traces2121to2124. In an embodiment of the present invention, the measurement circuit230comprises a plurality of analog to digital converters (ADCs)2321to2324. Each of the ADCs2321to2324is coupled to one of the second traces2121to2124and is configured to convert the voltage level Va, Vb, Vc or Vd into a digital value Da, Db, Dc or Dd. In an embodiment of the present invention, the measurement circuit230could generate and output the control signal Sc according to the digital values Da to Dd.

Please refer toFIGS. 2 and 4.FIG. 4is an equivalent circuit diagram of resistors R11, R12, R13and R14of the first row of the resistor matrix210during the period T1. During the period T1, the voltage level of the voltage signal S1is the first voltage V1, and the voltage levels of the remaining voltage signals S2to S4are the second voltage V2. Since the first ends of the resistors R12, R13and R14are applied with the second voltage V2, and the second ends of the resistors R12, R13and R14are coupled to the second trace2121, the resistors R12, R13and R14are connected in parallel and connected to the resistor R11in series during the period T1. Therefore, the equivalent resistance of the resistors R11, R12, R13and R14during the period T1could be represented as follows:

If the voltage level Va during the period T1is represented as Va1, the voltage level Va1could be represented as follows according to the principle of voltage division:

Please refer toFIGS. 2 and 5.FIG. 5is an equivalent circuit diagram of the resistors R11, R12, R13and R14of the first row of the resistor matrix210during the period T2. During the period T2, the voltage level of the voltage signal S2is the first voltage V1, and the voltage levels of the remaining voltage signals S1, S3and S4are the second voltage V2. Since the first ends of the resistors R11, R13and R14are applied with the second voltage V2, and the second ends of the resistors R11, R13and R14are coupled to the second trace2121, the resistors R11, R13and R14are connected in parallel and connected to the resistor R12in series during the period T2. Therefore, the equivalent resistance of the resistors R11, R12, R13and R14during the period T2could be represented as follows:

If the voltage level Va during the period T2is represented as Va2, the voltage level Va2could be represented as follows according to the principle of voltage division:

According to the equations (1) and (2), if the second voltage V2is 0 volt, then:

Moreover, since the ADC2321converts the voltage level Va1into a digital value Da1and converts the voltage level Va2into a digital value Da2, the equation (3) could be also represented as follows:

Based on the equation (3) or (4), a ratio of the voltage level Va1to the voltage level Va2is equal to a ratio of the resistance of the resistor R12to the resistance of the resistor R11. Similarly, if the voltage level Va during the period T3and T4is represented as Va3and Va4respectively, and the second voltage V2is 0 volt, then:

Therefore, the measurement circuit230may obtain the ratios among the resistors R11, R12, R13and R14according to the voltage levels Va1, Va2, Va3and Va4of the second trace2121respectively measured within the periods T1, T2, T3and T4. Similarly, the voltage levels of each of the second traces2122to2124measured within the periods T1, T2, T3and T4could be obtained by the measurement circuit230in a similar way.

Moreover, based on the equation (4), the resistance of the variable resistor R12could be represented as follows since the resistor R11has a constant resistance:

Similarly, the resistances of the variable resistors R13and R14could be represented as follows:

Where Da3is a digital value outputted from the ADC2321when the voltage level of the second trace2121is measured as Va3within the period T3, and Da4is a digital value outputted from the ADC2321when the voltage level of the second trace2121is measured as Va4within the period T4. Since the resistances of the variable resistors R12, R13and R14of the first row of the resistor matrix210could be obtained as described above, it could be understood that the resistance of each of other variable resistors R22to R24, R32to R34and R42to R44coupled to other rows of the resistor matrix210could be determined in a similar way.

Accordingly, the resistance of any variable resistor is equal to

ADC⁢⁢1×RREFADC⁢⁢2,
where RREFis resistance of a reference resistor (e.g. R11) located in a same row with the variable resistor, ADC1is a voltage level (e.g. Va1) of the second end of the variable resistor measured within the period T1, and ADC2is a voltage level (e.g. Va2) of the second end of the variable resistor when the first end of the variable resistor is applied with the first voltage V1.

As mentioned previously, the resistors R11, R21, R31and R41are reference resistors and have constant resistances. In an embodiment of the present invention, the resistances of the resistors R11, R21, R31and R41are the same. In an embodiment of the present invention, the resistances of the resistors R11, R21, R31and R41may different from each other. The resistors R12to R14, R22to R24, R32to R34and R42to R44are variable resistors. When the input device200is touched or depressed with an external force, the resistances of the resistors R12to R14, R22to R24, R32to R34and R42to R44may be changed, such that the voltage levels of the second traces2121to2124measured within the periods T1, T2, T3and T4are changed accordingly. Therefore, if any touch point of the input device200exists, the coordinates of the touch point could be determined according to the voltage levels of each of the second traces2121to2124measured within the periods T1, T2, T3and T4.

In an embodiment of the present invention, the measurement circuit230comprises a lookup table (LUT)233. The measurement circuit230selects the resistances of the variable resistors R12to R14, R22to R24, R32to R34and R42to R44from the lookup table233according to the voltage levels of the second traces2121to2124measured within the periods T1, T2, T3and T4. For example, the resistance of the variable resistor R12is selected from the lookup table233according to the voltage levels Va1and Va2measured within the periods T1and T2; the resistance of the variable resistor R13is selected from the lookup table233according to the voltage levels Va1and Va3measured within the periods T1and T3; and the resistance of the variable resistor R14is selected from the lookup table233according to the voltage levels Va1and Va4measured within the periods T1and T4.

Please refer toFIG. 6, which is a flow chart of a method of controlling operations of the input device200according to an embodiment of the present invention. The method comprises the following steps:

Step S610: Measure a first voltage level (e.g. Va1) of each second trace when the first voltage V1is applied to the first end of the reference resistor (e.g. R11) of each row and the second voltage V2is applied to the first ends of the M−1 variable resistors (e.g. R12, R13and R14) of each row via the M first traces;

Step S620: Obtain M−1 second measured voltage levels (e.g. Va2, Va3and Va4) of each second trace by applying the first voltage V1to the first ends of the M−1 variable resistors of each row in a predetermined sequence (e.g. R12→R13→R14); and

Step S630: Determine at least one touch point of the input device200according to the first voltage level and the M−1 second measured voltage levels of each second trace.

It should be noted that, in step S620, when the first voltage V1is applied the first end of one (e.g. R12) of the M−1 variable resistors of each row of the resistor matrix210, the second voltage V2is applied to first ends of the reference resistor (e.g. R11) and remaining M−2 variable resistors (e.g. R13and R14) of the row. Moreover, steps S610, S620and S630may be repeated to determine another touch point of the input device200at a different time.

In an embodiment of the present invention, the measurement circuit230may obtain and output information of strength of a force applied to the touch point, and the information of the strength of the force may be included in the control signal Sc. Please refer toFIGS. 2 and 7.FIG. 7is a relationship diagram of the conductance of a variable resistor and the force applied to the variable resistor. The conductance of the variable resistor is equal to a reciprocal of the measured resistance of the variable resistor. In the embodiment, the variable resistors R12to R14, R22to R24, R32to R34and R42to R44have the same relationship between the conductance of the variable resistors and strength of the force applied thereon, and a curve710may represent the relationship between the conductance of each of variable resistors R12to R14, R22to R24, R32to R34and R42to R44and the force applied thereon. As shown inFIG. 7, the conductance of the variable resistor and the strength of the force substantially have a linear relationship. Therefore, the strength of the force could be determined by using an interpolation algorithm. For example, it is assumed that the coordinates (P1, C1) and (P3, C3) of two points A and C of the curve710have been known. Then, the coordinates (P2, C2) of another point B of the curve710could be determined according to the coordinates (P1, C1) and (P3, C3) of the points A and C. That is, P2={[(C2−C1)×(P3−P1)/(C3−C1)]+P1}. Since the conductance of the variable resistor is equal to the reciprocal of the measured resistance of the variable resistor, the strength P2could be determined if the values of conductance C1, C2and C3and the strength P1and P2have been known.

In an embodiment of the present invention, it could be assumed that a force is applied to the variable resistor R12, and the strength of the force is S12. Since the resistance of the variable resistor R12is equal to

Va⁢⁢1Va⁢⁢2×R11,
the conductance of the variable resistor R12is equal to the reciprocal

(i.e.⁢1/R12⁢⁢or⁢⁢Va⁢⁢2Va⁢⁢1×R11)
of the variable resistor R12, and the conductance of the variable resistor R12and the strength S12of the force substantially have a linear relationship, the strength S12of the force could be obtained according to a function of

Va⁢⁢2Va⁢⁢1×R11.
The function of

Va⁢⁢2Va⁢⁢1×R11,
for example, could be represented as follows:

Where the parameters a and b are constants.

Va⁢⁢2Va⁢⁢1×R11
is equal to

Da⁢⁢2Da⁢⁢1×R11,
the strength S12of the force also could be represented as follows:

Accordingly, the strength of the force applied to any variable resistor (or touch point) of the input device200could be obtained according to a function of

(ADC⁢⁢2ADC⁢⁢1×RREF),
where RREFis resistance of a reference resistor (e.g. R11) located in a same row with the variable resistor, ADC1is a voltage level (e.g. Va1) of the second end of the variable resistor measured within the period T1, and ADC2is a voltage level (e.g. Va2) of the second end of the variable resistor when the first end of the variable resistor is applied with the first voltage V1.

In an embodiment of the present invention, the variable resistors R12to R14, R22to R24, R32to R34and R42to R44have the same relationship between the conductance of the variable resistors and strength of the force applied thereon, and the measurement circuit230further comprises a lookup table (LUT)236. The measurement circuit230selects the strength of forces applied on the variable resistors R12to R14, R22to R24, R32to R34and R42to R44from the lookup table236according to the voltage levels of the second traces2121to2124measured within the periods T1, T2, T3and T4. For example, strength of a force applied on the variable resistors R12is selected from the lookup table236according to the voltage levels Va1and Va2measured within the periods T1and T2; strength of a force applied on the variable resistors R13is selected from the lookup table236according to the voltage levels Va1and Va3measured within the periods T1and T3; and strength of a force applied on the variable resistors R14is selected from the lookup table236according to the voltage levels Va1and Va4measured within the periods T1and T4. Therefore, the resistance of each variable resistor not only can be calculated according to the formula of

ADC⁢⁢1×RREFADC⁢⁢2,
but also can be obtained from the lookup table236according to the voltage levels of the second traces2121to2124measured within the periods T1, T2, T3and T4.

In an embodiment of the present invention, the variable resistors R12to R14, R22to R24, R32to R34and R42to R44have the same relationship between the conductance of the variable resistors and strength of the force applied thereon, and the measurement circuit230selects the strength of the force applied to the touch point from the lookup table236according to the resistance of the variable resistor at the touch point. For example, the strength of a force applied to the variable resistor R12is selected from the lookup table236according to the resistance of the variable resistor R12; the strength of a force applied to the variable resistor R13is selected from the lookup table236according to the resistance of the variable resistor R13; and the strength of a force applied to the variable resistor R14is selected from the lookup table236according to the resistance of the variable resistor R14.

In an embodiment of the present invention, the variable resistors R12to R14, R22to R24, R32to R34and R42to R44have the same relationship between the conductance of the variable resistors and strength of the force applied thereon, and the conductance of each variable resistor and the strength of the force have a nonlinear relationship. However, by using the lookup table236, the strength of forces applied on the variable resistors R12to R14, R22to R24, R32to R34and R42to R44could be determined accurately.

In an embodiment of the present invention, only when the strength of the force applied to the touch point is greater than or equal to a predetermined threshold (e.g. 20 grams), the touch point is determined to being triggered. In other words, if the strength of the force applied to the touch point is less than the predetermined threshold, the touch point is determined to be un-triggered. Accordingly, if the strength of the force applied to the touch point is not great enough, the touch point would be regarded as an invalid touch point. In an embodiment, the measurement circuit230may further comprise another lookup table235for recording the predetermined threshold.

Please refer toFIGS. 2 and 8.FIG. 8is a relationship diagram of the conductance of three different variable resistors and the forces applied to the three variable resistors. In the embodiment, the variable resistors R12to R14, R22to R24, R32to R34and R42to R44have different relationships between the conductance of the variable resistors and strength of forces applied thereon, and curves810,820and830may represent the relationships between the conductance of three of the variable resistors R12to R14, R22to R24, R32to R34and R42to R44and the forces applied thereon. As shown inFIG. 8, the conductance of the variable resistors and the strength of the forces substantially have linear relationships. Therefore, the strength of each force could also be determined by using an interpolation algorithm. Moreover, in the embodiment, only when the strength of the force applied to the touch point is greater than or equal to the predetermined threshold (e.g. 20 grams), the touch point is determined to being triggered. Since the variable resistors R12to R14, R22to R24, R32to R34and R42to R44have different relationships between the conductance of the variable resistors and strength of forces applied thereon, the values of the conductance CA, CBand CCcorresponded to the predetermined threshold are different from each other.

In an embodiment of the present invention, the variable resistors R12to R14, R22to R24, R32to R34and R42to R44have different relationships between the conductance of the variable resistors and strength of forces applied thereon, and the measurement circuit230further comprises a plurality of lookup tables (LUT)234_12to234_44. Each of the lookup tables234_12to234_44corresponds to one of the variable resistors R12to R14, R22to R24, R32to R34and R42to R44. The measurement circuit230selects the strength of the force from a corresponding lookup table according to the voltage levels of a corresponding second trace measured within corresponding periods. For example, the strength of a force applied to the variable resistor R12is selected from the lookup table234_12according to the voltage levels Va1and Va2of the second trace2121measured within the periods T1and T2; the strength of a force applied to the variable resistor R13is selected from the lookup table234_13according to the voltage levels Va1and Va3of the second trace2121measured within the periods T1and T3; and the strength of a force applied to the variable resistor R14is selected from the lookup table234_14according to the voltage levels Va1and Va4of the second trace2121measured within the periods T1and T4.

In an embodiment of the present invention, when a touch point of the input device200is determined, a first coordinate (i.e. location of corresponding row of resistor matrix210) and a second coordinate (i.e. location of corresponding column of the resistor matrix210) of the touch point would be determined by the measurement circuit230, and the measurement circuit230selects a lookup table from the plurality of lookup tables234_12to234_44according to the first coordinate and the second coordinate of the touch point. Then, the measurement circuit230selects the strength of a force applied to a variable resistor located in the touch point from the selected lookup table.

In an embodiment of the present invention, the variable resistors R12to R14, R22to R24, R32to R34and R42to R44have different relationships between the conductance of the variable resistors and strength of forces applied thereon. When the corresponding lookup table is selected according to the first coordinate and the second coordinate of the touch point, the measurement circuit230selects the strength of the force from the selected lookup table according to the resistance of the variable resistor at the touch point. For example, the strength of a force applied to the variable resistor R12is selected from the lookup table234_12according to the resistance of the variable resistor R12; the strength of a force applied to the variable resistor R13is selected from the lookup table234_13according to the resistance of the variable resistor R13; and the strength of a force applied to the variable resistor R14is selected from the lookup table234_14according to the resistance of the variable resistor R14.

In an embodiment of the present invention, the variable resistors R12to R14, R22to R24, R32to R34and R42to R44have different relationships between the conductance of the variable resistors and strength of forces applied thereon, and the conductance of each variable resistor and the strength of the force applied thereon have a nonlinear relationship. However, by using the lookup tables234_12to234_44, the strength of forces applied on the variable resistors R12to R14, R22to R24, R32to R34and R42to R44could be determined accurately.

In an embodiment of the present invention, the measurement circuit230outputs the control signal Sc according to the strength of the force applied to the touch point. Please refer toFIGS. 2 and 9.FIG. 9is another relationship diagram of the conductance of three different variable resistors and the forces applied to the three variable resistors. In the embodiment, if the strength of the force is greater than or equal to a first predetermined value (e.g. 20 grams), the control signal Sc is a first control signal. If the strength of the force is less than the first predetermined value (e.g. 20 grams) and not less than a second predetermined value (e.g. 10 grams), the control signal Sc is a second control signal, where the second predetermined value is less than the first predetermined value, and the first control signal is different from the second control signal. Accordingly, if the input device200is used to control an electric apparatus (e.g. a computer, a mobile phone, etc.), the operations of electric apparatus may be different based on different control signals received from the input device200. In an embodiment, the measurement circuit230may select the first predetermined value and the second predetermined value from the lookup table235.

Please refer toFIG. 10.FIG. 10is a flow chart of a method of controlling operations of the input device inFIG. 2according to another embodiment of the present invention. In the embodiment, the method comprises the following steps:

Step S1010: Measure a first voltage level (e.g. Va1) of each second trace when the first voltage V1is applied to the first end of the reference resistor (e.g. R11) of each row and the second voltage V2is applied to the first ends of the M−1 variable resistors (e.g. R12, R13and R14) of each row via the M first traces;

Step S1020: Measure variations of the first voltage level (e.g. Va1) of each second trace (i.e. the second traces2121to2124);

Step S1030: Determine whether at least one touch point is triggered according to the variations of the first voltage level (e.g. Va1) of the each second trace; if the result is positive, step S1040will be executed; otherwise, steps S1010to S1030will be repeated;

Step S1040: Obtain M−1 second measured voltage levels (e.g. Va2, Va3and Va4) of each second trace by applying the first voltage V1to the first ends of the M−1 variable resistors of each row in a predetermined sequence (e.g. R12→R13→R14); and

Step S1050: Determine a first coordinate (i.e. location of corresponding row of resistor matrix210) and a second coordinate (i.e. location of corresponding column of the resistor matrix210) of the at least one touch point according to the first voltage level and the M−1 second measured voltage levels.

It should be noted that, in step S1040, when the first voltage V1is applied the first end of one (e.g. R12) of the M−1 variable resistors of each row of the resistor matrix210, the second voltage V2is applied to first ends of the reference resistor (e.g. R11) and remaining M−2 variable resistors (e.g. R13and R14) of the row. Moreover, since steps S1040and S1050will not be executed until at least one touch point is determined to being triggered in step S1030, the first voltage V1is constantly applied to the first ends of the reference resistors R11, R12, R13and R14and the second voltage V2is constantly applied to first ends of the variable resistors R12to R14, R22to R24, R32to R34and R42to R44until at least one touch point is determined to being triggered.

Refer toFIG. 2again. The second traces2121to2124may be coupled to a general-purpose input/output (GPIO) circuit240of the measurement circuit230, and the GPIO circuit240may detect the variations of the voltage levels Va, Vb, Vc and Vd of the second traces2121to2124while steps S1010and S1030are executed. When any of the first voltage levels Va, Vb, Vc and Vd satisfies predetermined criteria, the GPIO circuit240outputs a wake-up signal Sw, and the input device200determines that at least one touch point is determined to being triggered, such that the steps S1040and S1050are executed. The predetermined criteria, for example, could be that any of the voltage levels Va, Vb, Vc and Vd detected by the GPIO circuit240is greater than or less than a predetermined level (e.g. 1.5 volts). In the embodiment, when the voltage level of the wake-up signal Sw is equal to a first level VH, it means that at least one touch point is determined to being triggered. However, when the voltage level of the wake-up signal Sw is equal to a second level VL, it means that no triggered touch point is determined.

Please refer toFIG. 11with reference ofFIGS. 2 and 10.FIG. 11is a timing diagram of voltage signals of the input device inFIG. 2which operates according to the method ofFIG. 10. At time of TA, the voltage level of the wake-up signal Sw is pulled up from the second level VL to the first level VH. In response to the raising of the wake-up signal Sw, step S1040is executed, such that the voltage level of the voltage signal S1is pulled down from the first voltage V1to the second voltage V2, and that the voltage levels of the voltage signals S2, S3and S4are sequentially pulled up from the second voltage V2to the first voltage V1. Accordingly, during the duration between TAand TB, M−1 second measured voltage levels (e.g. Va2, Va3and Va4) of each second trace are obtained (step S1040). Moreover, after the time of TB, since the voltage level of the wake-up signal Sw is equal to the second level VL, the first voltage V1is constantly applied to the first ends of the reference resistors R11, R12, R13and R14and the second voltage V2is constantly applied to first ends of the variable resistors R12to R14, R22to R24, R32to R34and R42to R44until another touch point is determined to being triggered.

Please refer toFIG. 12.FIG. 12is a flow chart of a method of controlling operations of the input device inFIG. 2according to an embodiment of the present invention. As compared to the method illustrated inFIG. 10, the method of the present embodiment further comprises step S1060. If no triggered touch point is determined in step S1030, step S1060will be executed. Therefore, step S1010will be executed when step S1030is completed after a predetermined period. Accordingly, steps S1010, S1020and S1030are repeated at regular intervals. Moreover, during the predetermined period, the first voltage V1is not applied to the resistor matrix210. As a result, the power consumption of the input device200could be reduced. In an embodiment of the present invention, the predetermined period could be 0.5 second. However, the present invention is not limited thereto.

Please refer toFIG. 13with reference ofFIGS. 2 and 12.FIG. 13is a timing diagram of voltage signals of the input device inFIG. 2which operates according to the method ofFIG. 12. Similarly, at time of TA, the voltage level of the wake-up signal Sw is pulled up from the second level VL to the first level VH. In response to the raising of the wake-up signal Sw, step S1040is executed, such that the voltage level of the voltage signal S1is pulled down from the first voltage V1to the second voltage V2, and that the voltage levels of the voltage signals S2, S3and S4are sequentially pulled up from the second voltage V2to the first voltage. Accordingly, during the duration between TAand TB, M−1 second measured voltage levels (e.g. Va2, Va3and Va4) of each second trace are obtained (step SS1040). Moreover, after the time of TB, since the voltage level of the wake-up signal Sw is equal to the second level VL, steps S1010to S1030are repeated at regular intervals. It assumed that the foresaid predetermined period is Tp. As shown inFIG. 13, the voltage levels of the voltage signals S1to S4within each predetermined period Tp are equal to the second voltage V2. It means that the first voltage V1is not applied to the resistor matrix210within each predetermined period Tp. As a result, the power consumption of the input device200could be reduced.

Moreover, it assumed that the voltage signal S1has a voltage level of V1within a duration TS1, the voltage signal S2has a voltage level of V1within a duration TS2, the voltage signal S3has a voltage level of V1within a duration TS3, and the voltage signal S4has a voltage level of V1within a duration TS4. The predetermined period Tp may be greater than the duration TS1, and the duration TS1may be greater than each of the durations TS2, TS3and TS4. However, the present invention is not limited thereto. For example, the duration TS1may less than or equal to each of the durations TS2, TS3and TS4.

In an embodiment of the present invention, the ADCs2321to2324inFIG. 2could be replaced by a multiplexer1410and an ADC1420inFIG. 14. Please refer toFIGS. 3 and 14. The multiplexer1410has a plurality of input terminals coupled to the second traces2121to2124. The multiplexer1410selects one of the voltage levels Va, Vb, Vc and Vd as an output voltage level Vo thereof, and the ADC1420converts the output voltage level Vo into the digital values Da, Db, Dc and Dd sequentially. For example, each of the periods T1to T4maybe divided into four sub-periods. During a first sub-period of the four sub-periods within each period T1, T1, T1or T4, the multiplexer1410selects the voltage level Va as the output voltage level Vo, and the ADC1420converts the output voltage level Vo into the digital values Da. During a second sub-period of the four sub-periods within each period T1, T1, T1or T4, the multiplexer1410selects the voltage level Vb as the output voltage level Vo, and the ADC1420converts the output voltage level Vo into the digital values Db. During a third sub-period of the four sub-periods within each period T1, T1, T1or T4, the multiplexer1410selects the voltage level Vc as the output voltage level Vo, and the ADC1420converts the output voltage level Vo into the digital values Dc. During a fourth sub-period of the four sub-periods within each period T1, T1, T1or T4, the multiplexer1410selects the voltage level Vd as the output voltage level Vo, and the ADC1420converts the output voltage level Vo into the digital values Dd. Accordingly, the number of the analog to digital converters (ADCs) of the measurement circuit230of the input device200could be reduced.

Additionally, since the resistance of each of the variable resistors R12to R14, R22to R24, R32to R34and R42to R44could be calculated independently, the input device200will not miscalculate the location of any touch point even when two or more touch points are triggered at the same time.

In summary, the present invention provides a method for controlling operations of an input device. The input device has a resistor matrix, which comprises a plurality of variable resistors. The variable resistors are pressure-sensitive, such that the resistances thereof would be changed due to any external force applied thereon. The strength of the external force can be calculated according to voltage levels measured within corresponded periods. Moreover, since the variable resistors may have the same or different relationships between the conductance of the variable resistors and strength of forces applied thereon, a lookup table or a plurality of lookup tables may be used to determine the resistances of the variable resistors and/or the strength of the external force. Additionally, any touch point of the input device could be determined to being trigged if the strength of the force applied thereon is greater than or equal to a predetermined threshold. Further, it is unnecessary to constantly apply the first voltage and the second voltage to the resistor matrix of the input device, such that the power consumption of the input device could be reduced.