CAPACITIVE TOUCH PANEL AND CAPACITANCE SENSING APPARATUS AND METHOD FOR THE SAME
First Claim
1. A capacitance sensing apparatus used for a capacitive touch panel and electrically connected to one electrode of the capacitive touch panel through a connection node to measure a capacitance on the electrode, the capacitance sensing apparatus comprising:
- a first discharging current source electrically connected the connection node to provide a first discharging current;
a second discharging current source electrically connected the connection node to provide a second discharging current, where the first discharging current is larger than the second discharging current;
a differential comparator comprising a first input end electrically connected to the connection node and a second input end;
a reference voltage source electrically connected to the second input end, wherein the reference voltage source receives a predetermined reference voltage and a DC common voltage of an liquid crystal display to generate a modified reference voltage, wherein the DC common voltage is also electrically connected to the capacitive touch panel;
wherein the differential comparator generates a pulse width modulation signal by comparing the modified reference voltage and an input voltage, which is present at the connection node and resulted from a touch on the capacitive touch panel;
wherein the pulse width modulation signal indicates the capacitance on the electrode.
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Accused Products
Abstract
A capacitive touch panel and capacitance sensing apparatus and method for the same are disclosed. The capacitive touch panel includes a plurality of electrodes, a multiplexer and a capacitance sensing apparatus. The multiplexer selectively connects one of the electrodes to the capacitance sensing apparatus. The capacitance sensing apparatus includes a reference voltage source and a differential comparator, where the reference voltage source generates a modified reference voltage according to noise on stray capacitance of the capacitive touch panel. In a discharging process, the comparator compares an input voltage at the selected electrode and the modified reference voltage. The capacitance change in the electrode can be precisely detected because the noise is eliminated by differential comparison.
23 Citations
20 Claims
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1. A capacitance sensing apparatus used for a capacitive touch panel and electrically connected to one electrode of the capacitive touch panel through a connection node to measure a capacitance on the electrode, the capacitance sensing apparatus comprising:
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a first discharging current source electrically connected the connection node to provide a first discharging current; a second discharging current source electrically connected the connection node to provide a second discharging current, where the first discharging current is larger than the second discharging current; a differential comparator comprising a first input end electrically connected to the connection node and a second input end; a reference voltage source electrically connected to the second input end, wherein the reference voltage source receives a predetermined reference voltage and a DC common voltage of an liquid crystal display to generate a modified reference voltage, wherein the DC common voltage is also electrically connected to the capacitive touch panel; wherein the differential comparator generates a pulse width modulation signal by comparing the modified reference voltage and an input voltage, which is present at the connection node and resulted from a touch on the capacitive touch panel; wherein the pulse width modulation signal indicates the capacitance on the electrode. - View Dependent Claims (2, 3, 4, 5)
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6. A method for measuring capacitance for a capacitive touch panel, the method measuring a capacitance on an electrode of the capacitive touch panel and comprising:
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a. charging the electrode through a connection node and then discharging the electrode with a first discharging current; b. discharging the electrode with a second discharging current, where the first discharging current is larger than the second discharging current; c. providing a modified reference voltage being a superimposition of a predetermined reference voltage and a DC common voltage of an liquid crystal display, wherein the DC common voltage is electrically connected to the capacitive touch panel; d. during the discharging of the second discharging current, judging the value of the capacitance by comparing the modified reference voltage and an input voltage present at the connection node. - View Dependent Claims (7, 8, 9, 10)
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11. A capacitive touch panel comprising:
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a plurality of first electrodes in longitudinal direction and having a first number M; a plurality of second electrodes in transversal direction and having a second number N; a capacitance sensing apparatus electrically connected a selected electrode at a connection node, wherein the selected electrode is selected from the first electrodes and the second electrodes, the capacitance sensing apparatus comprising; a first discharging current source electrically connected the connection node to provide a first discharging current; a second discharging current source electrically connected the connection node to provide a second discharging current, where the first discharging current is larger than the second discharging current; a differential comparator comprising a first input end electrically connected to the connection node and a second input end; a reference voltage source electrically connected to the second input end, wherein the reference voltage source receives a predetermined reference voltage and a DC common voltage of an liquid crystal display to generate a modified reference voltage, wherein the DC common voltage is also electrically connected to the capacitive touch panel; wherein the differential comparator generates a pulse width modulation signal by comparing the modified reference voltage and an input voltage, which is present at the connection node and resulted from a touch on the capacitive touch panel; wherein the pulse width modulation signal indicates the capacitance on the electrode. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification