Multiple channel capacitive voltage divider scanning method and apparatus
First Claim
1. A method for determining change in capacitance of at least one capacitive sensor of a plurality of capacitive sensors, said method comprising the steps of:
- charging by first switches the plurality of capacitive sensors to a first voltage;
charging by second switches a sample and hold capacitor to a second voltage;
subsequently, individually coupling by a multiplexer the sample and hold capacitor in a sequence only to each one of the plurality of capacitive sensors, wherein electron charge from each of the individually coupled ones of the plurality of capacitive sensors is transferred to the sample and hold capacitor;
measuring by a controller a resulting voltage on the sample and hold capacitor after all of the plurality of capacitive sensors have been individually coupled to the sample and hold capacitor; and
comparing by the controller the measured resulting voltage to a previously measured resulting voltage, wherein if the measured resulting voltage is different than the previously measured resulting voltage then at least one capacitive sensor of the plurality of capacitive sensors has changed capacitance value.
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Abstract
Relative capacitance of a plurality of capacitive sensors may be monitored by using only one ADC conversion. A plurality of capacitive sensors individually charges a sample and hold capacitor. After all of the plurality of capacitive sensors have charged the sample and hold capacitor, a digital conversion of the resulting analog on the sample and hold capacitor is made and stored in a memory. This stored digital collective voltage is compared to a previously stored one and if different then a proximity/touch event may have occurred. Therefore, an entire panel of capacitive sensors may be quickly monitored for a change in the “group” capacitance thereof, or portions of the capacitive sensors may be monitored for a change in the “subgroup” capacitance thereof. By knowing which subgroup of capacitive sensors has changed its collective capacitive value, a more focused and selective capacitive sensor measurement can be made that uses less power.
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Citations
18 Claims
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1. A method for determining change in capacitance of at least one capacitive sensor of a plurality of capacitive sensors, said method comprising the steps of:
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charging by first switches the plurality of capacitive sensors to a first voltage; charging by second switches a sample and hold capacitor to a second voltage; subsequently, individually coupling by a multiplexer the sample and hold capacitor in a sequence only to each one of the plurality of capacitive sensors, wherein electron charge from each of the individually coupled ones of the plurality of capacitive sensors is transferred to the sample and hold capacitor; measuring by a controller a resulting voltage on the sample and hold capacitor after all of the plurality of capacitive sensors have been individually coupled to the sample and hold capacitor; and comparing by the controller the measured resulting voltage to a previously measured resulting voltage, wherein if the measured resulting voltage is different than the previously measured resulting voltage then at least one capacitive sensor of the plurality of capacitive sensors has changed capacitance value. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. An apparatus for determining change in capacitance of at least one capacitive sensor of a plurality of capacitive sensors, comprising:
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a plurality of capacitive sensors; a sample and hold capacitor; a multiplexer having a plurality of inputs and an output; a plurality of capacitive sensor switches coupled to the plurality of capacitive sensors, and adapted to selectively couple each of the plurality of capacitive sensors to a first voltage, a second voltage or a respective input of the multiplexer; a sample and hold switch coupled between the output of the multiplexer and the sampler and hold capacitor; an analog-to-digital converter (ADC) having an analog input coupled to the sample and hold capacitor; and a digital processor coupled to an output of the ADC and adapted to control the plurality of capacitive sensor switches, multiplexer, and sample and hold switch, wherein the apparatus is configured; to charge by the plurality of capacitive sensor switches the plurality of capacitive sensors to a first voltage; to charge by the sample and hold switch a sample and hold capacitor to a second voltage; subsequently, to individually couple by the multiplexer the sample and hold capacitor in a sequence only to each one of the plurality of capacitive sensors, wherein electron charge from each of the individually coupled ones of the plurality of capacitive sensors is transferred to the sample and hold capacitor; to measure by the digital processor a resulting voltage on the sample and hold capacitor after all of the plurality of capacitive sensors have been individually coupled to the sample and hold capacitor; and to compare by the digital processor the measured resulting voltage to a previously measured resulting voltage, wherein if the measured resulting voltage is different than the previously measured resulting voltage then at least one capacitive sensor of the plurality of capacitive sensors has changed capacitance value. - View Dependent Claims (11, 12, 13, 14)
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15. A system comprising:
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a plurality of capacitive sensors coupled with a microcontroller; wherein the microcontroller comprises; a capacitive sensor scan controller; a sample and hold capacitor; a multiplexer having a plurality of inputs and an output; a plurality of capacitive sensor switches coupled to the plurality of capacitive sensors, and adapted to selectively couple each of the plurality of capacitive sensors to a first voltage, a second voltage or a respective input of the multiplexer; a sample and hold switch coupled between the output of the multiplexer and the sampler and hold capacitor; an analog-to-digital converter (ADC) having an analog input coupled to the sample and hold capacitor; and a digital processor coupled with the capacitive sensor scan controller, wherein, while the digital processor is in a low power sleep mode, the capacitive sensor scan controller is configured; to control the plurality of capacitive sensor switches to charge the plurality of capacitive sensors to a first voltage; to control the sample and hold switch to charge a sample and hold capacitor to a second voltage; subsequently, to control the multiplexer to individually couple the sample and hold capacitor only to each one of the plurality of capacitive sensors, wherein electron charge from each of the individually coupled ones of the plurality of capacitive sensors is transferred to the sample and hold capacitor; to measure through the ADC a resulting voltage on the sample and hold capacitor after all of the plurality of capacitive sensors have been individually coupled to the sample and hold capacitor; and to compare the measured resulting voltage to a previously measured resulting voltage, wherein if the measured resulting voltage is different than the previously measured resulting voltage then at least one capacitive sensor of the plurality of capacitive sensors has changed capacitance value. - View Dependent Claims (16, 17, 18)
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Specification