Automated capacitive touch scan
First Claim
1. An apparatus for measuring changes in the capacitances of a plurality of capacitive touch sensors, said apparatus comprising:
- a multiplexer having an output and a plurality of inputs adapted for coupling to a plurality of capacitive touch sensors, wherein each of the plurality of inputs is coupled to a respective one of the plurality of capacitive touch sensors;
an analog-to-digital converter (ADC) having an analog input coupled to the output of the multiplexer;
a discharge switch coupled between the output of the multiplexer and a supply common;
a constant current source having a current value and an output;
a charge switch coupled between the output of the multiplexer and the output of the constant current source;
a threshold register having a threshold value stored therein;
a digital comparator having a first input coupled to the threshold register and a second input coupled to an output of the ADC, wherein the threshold value stored in the threshold register is compared with a digital voltage value from the output of the ADC;
a sequence controller coupled to and controlling the multiplexer, the ADC, the discharge switch, the charge switch, and an output from the digital comparator, wherein the sequence controllerselects one input at a time from the plurality of inputs of the multiplexer,closes the discharge switch so that the respective one of the plurality of capacitive touch sensors coupled to the selected one of the plurality of inputs has substantially all voltage charge removed therefrom,opens the discharge switch and closes the charge switch for a time period, wherein during the time period the respective one of the plurality of capacitive touch sensors is coupled to the constant current source, whereby the respective one of the plurality of capacitive touch sensors is charged to a voltage value determined by the time period and the current value of the constant current source,triggers the ADC to sample and convert the voltage value to a digital representation thereof at the end of the time period,generates a touch detected signal when the digital representation of the voltage value is less than the threshold value stored in the threshold register, andindicates which one of the plurality of capacitive touch sensors is associated with the measured voltage value, otherwise no touch detection signal is generated.
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Accused Products
Abstract
A scan module of an electronic device scans a capacitive keypad for detection of the actuation of any capacitive touch sensor. This scan module remains in operation even when major power consuming circuits of the electronic device are in a sleep mode, and will not wake up the major power consuming circuits until an action requiring the circuits is needed, thereby, reducing overall power consumption of the electronic device while still maintaining scanning of the capacitive keypad. Upon detection of a valid key press of a capacitive touch sensor, an interrupt to the electronic device brings it out of a sleep mode and into an operating mode for further processing and appropriate action commensurate with the actuation of the specific capacitive touch sensor.
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Citations
23 Claims
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1. An apparatus for measuring changes in the capacitances of a plurality of capacitive touch sensors, said apparatus comprising:
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a multiplexer having an output and a plurality of inputs adapted for coupling to a plurality of capacitive touch sensors, wherein each of the plurality of inputs is coupled to a respective one of the plurality of capacitive touch sensors; an analog-to-digital converter (ADC) having an analog input coupled to the output of the multiplexer; a discharge switch coupled between the output of the multiplexer and a supply common; a constant current source having a current value and an output; a charge switch coupled between the output of the multiplexer and the output of the constant current source; a threshold register having a threshold value stored therein; a digital comparator having a first input coupled to the threshold register and a second input coupled to an output of the ADC, wherein the threshold value stored in the threshold register is compared with a digital voltage value from the output of the ADC; a sequence controller coupled to and controlling the multiplexer, the ADC, the discharge switch, the charge switch, and an output from the digital comparator, wherein the sequence controller selects one input at a time from the plurality of inputs of the multiplexer, closes the discharge switch so that the respective one of the plurality of capacitive touch sensors coupled to the selected one of the plurality of inputs has substantially all voltage charge removed therefrom, opens the discharge switch and closes the charge switch for a time period, wherein during the time period the respective one of the plurality of capacitive touch sensors is coupled to the constant current source, whereby the respective one of the plurality of capacitive touch sensors is charged to a voltage value determined by the time period and the current value of the constant current source, triggers the ADC to sample and convert the voltage value to a digital representation thereof at the end of the time period, generates a touch detected signal when the digital representation of the voltage value is less than the threshold value stored in the threshold register, and indicates which one of the plurality of capacitive touch sensors is associated with the measured voltage value, otherwise no touch detection signal is generated. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. An integrated circuit digital device having logic circuits capable of being placed into a low power sleep mode or an operating mode, the digital device also having capacitance measurement circuits that operate independently of whether the logic circuits are in the sleep mode or the operating mode, wherein the capacitance measurement circuits measure changes in capacitances of a plurality of capacitive touch sensors, said apparatus comprising:
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a digital processor having logic circuits capable of being in a low power sleep mode or an operating mode; a multiplexer having an output and a plurality of inputs adapted for coupling to a plurality of capacitive touch sensors, wherein each of the plurality of inputs is coupled to a respective one of the plurality of capacitive touch sensors; an analog-to-digital converter (ADC) having an analog input coupled to the output of the multiplexer; a discharge switch coupled between the output of the multiplexer and a supply common; a constant current source having a current value and an output; a charge switch coupled between the output of the multiplexer and the output of the constant current source; a threshold register having a threshold value stored therein; a digital comparator having a first input coupled to the threshold register and a second input coupled to an output of the ADC, wherein the threshold value stored in the threshold register is compared with a digital voltage value from the output of the ADC; a sequence controller coupled to and controlling the multiplexer, the ADC, the discharge switch, the charge switch, and an output from the digital comparator, wherein the sequence controller selects one input at a time from the plurality of inputs of the multiplexer, closes the discharge switch so that the respective one of the plurality of capacitive touch sensors coupled to the selected one of the plurality of inputs has substantially all voltage charge removed therefrom, opens the discharge switch and closes the charge switch for a time period, wherein during the time period the respective one of the plurality of capacitive touch sensors is coupled to the constant current source, whereby the respective one of the plurality of capacitive touch sensors is charged to a voltage value determined by the time period and the current value of the constant current source, triggers the ADC to sample and convert the voltage value to a digital representation thereof at the end of the time period, generates a touch detected interrupt when the digital representation of the voltage value is less than the threshold value stored in the threshold register, and indicates which one of the plurality of capacitive touch sensors is associated with the measured voltage value, otherwise no touch detection interrupt is generated, wherein the touch detected interrupt causes the logic circuits of the digital processor to go from the low power sleep mode to the operating mode. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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Specification