Capacitance measurement system and method
First Claim
1. An apparatus comprising:
- a capacitive touch screen panel; and
a touch screen panel controller having a precharge phase, a measurement conversion phase, wherein the touch screen panel controller includes;
a capacitor bank that includes a plurality of weighted capacitors that are coupled in parallel with one another to a node;
a first switching circuit that is coupled to the capacitive touch screen panel, wherein the first switching circuit is configured to precharge at least a portion of the capacitive touch screen panel during the precharge mode, and wherein the first switching circuit is configured to couple the portion of the touch screen panel to the capacitor bank during the measurement phase;
a comparator that is coupled to the node;
successive approximation register (SAR) logic that is coupled to the comparator; and
a second switching circuit that is coupled to the first switching circuit and the capacitor bank, wherein the second switching circuit is controlled by the SAR logic during the conversion phase, and wherein at least a portion of the second switching circuit is activated during the precharge phase.
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Abstract
A capacitance measurement system precharges first terminals (21-0 . . . 21-k . . . 21-n) of a plurality of capacitors (25-0 . . . 25-k . . . 25), respectively, of a CDAC (capacitor digital-to-analog converter) (23) included in a SAR (successive approximation register) converter (17) to a first voltage (VDD) and pre-charges a first terminal (3-j) of a capacitor (CSENj) to a second voltage (GND). The first terminals are coupled to the first terminal of the capacitor to redistribute charges therebetween so as to generate a first voltage on the first terminals and the first terminal of the capacitor, the first voltage being representative of a capacitance of the first capacitor (CSENj). A SAR converter converts the first voltage to a digital representation (DATA) of the capacitor. The capacitance can be a touch screen capacitance.
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Citations
12 Claims
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1. An apparatus comprising:
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a capacitive touch screen panel; and a touch screen panel controller having a precharge phase, a measurement conversion phase, wherein the touch screen panel controller includes; a capacitor bank that includes a plurality of weighted capacitors that are coupled in parallel with one another to a node; a first switching circuit that is coupled to the capacitive touch screen panel, wherein the first switching circuit is configured to precharge at least a portion of the capacitive touch screen panel during the precharge mode, and wherein the first switching circuit is configured to couple the portion of the touch screen panel to the capacitor bank during the measurement phase; a comparator that is coupled to the node; successive approximation register (SAR) logic that is coupled to the comparator; and a second switching circuit that is coupled to the first switching circuit and the capacitor bank, wherein the second switching circuit is controlled by the SAR logic during the conversion phase, and wherein at least a portion of the second switching circuit is activated during the precharge phase. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. An apparatus comprising:
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a capacitive touch screen panel having; a plurality of row electrodes; and a plurality of column electrodes, wherein the plurality of row electrodes and the plurality of column electrodes are arranged to form an array of sensing capacitors; and a touch screen panel controller having a precharge phase, a measurement phase, and a conversion phase, wherein the touch screen panel controller includes; a first switch that is coupled to each row electrode and that is configured to receive a first voltage, wherein the first switch is configured to be closed during the precharge phase; a second switch that is coupled to each row electrode and that is configured to receive a second voltage, wherein the second switch is configured to be closed during the measurement phase; a first set of switches, wherein each switch from the second set of switches is coupled to at least one column electrode, and wherein each switch from the second set of switches is configured to be closed during the precharge phase; a second set of switches, wherein each switch from the second set of switches is coupled to the touch screen panel, wherein each switch from the second set of switches is configured to be closed during the measurement phase; a plurality of capacitors, wherein each capacitor coupled to at least one of the switches from the second set of switches; a third set of switches, wherein each switch from the third set of switches is configured to receive the first voltage, and wherein each switch from the third set of switches is coupled to at least one of the capacitors, and wherein each switch from the third set of switches is configured to be closed during the precharge phase; and a fourth set of switches, wherein each switch from the fourth set of switches is coupled to at least one of the capacitors; a comparator that is coupled to each of the capacitors; and SAR logic that is coupled to the comparator and that is configured to control each switch from the third and fourth sets of switches during the conversion phase. - View Dependent Claims (9, 10, 11, 12)
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Specification