Low power capacitive touch detector
First Claim
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1. A capacitive touch detection system of a microcontroller, the capacitive touch detection system comprising:
- a counter module configured to detect an input signal, count a number of first occurrences that the input signal has a first value during a first time period and a number of second occurrences that the input signal has a second, different value during a second time period successive to the first time period, and generate a raw count signal having a raw count value based on the number of first occurrences and the number of second occurrences;
a filtering system coupled to the counter module, the filtering system configured to remove noise from the raw count signal and to generate a processed count signal having a processed count value; and
a first state detector coupled to the filtering system, the first state detector configured to perform a first comparison of the processed count value against a first threshold value and generate a first output signal based on the first comparison.
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Abstract
A low power capacitive detector is disclosed. The detector includes a mechanism to measure and detect touch on capacitive sensors. The detector uses signal processing to suppress noise and increase sensitivity. The detector does not require dedicated analog circuitry, making it easy to adopt in a microcontroller system. The detector can be scaled to a larger number of capacitive sensors without noticeable increase in silicon cost.
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Citations
20 Claims
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1. A capacitive touch detection system of a microcontroller, the capacitive touch detection system comprising:
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a counter module configured to detect an input signal, count a number of first occurrences that the input signal has a first value during a first time period and a number of second occurrences that the input signal has a second, different value during a second time period successive to the first time period, and generate a raw count signal having a raw count value based on the number of first occurrences and the number of second occurrences; a filtering system coupled to the counter module, the filtering system configured to remove noise from the raw count signal and to generate a processed count signal having a processed count value; and a first state detector coupled to the filtering system, the first state detector configured to perform a first comparison of the processed count value against a first threshold value and generate a first output signal based on the first comparison. - View Dependent Claims (2, 3, 4, 5, 7, 8, 9, 10)
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6. A capacitive touch detection system of a microcontroller, the capacitive touch detection system comprising:
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a counter module configured to detect an input signal, count a number of occurrences that the input signal has a certain value during a time period, and generate a raw count signal having a raw count value based on the number of occurrences; a filtering system coupled to the counter module, the filtering system configured to remove noise from the raw count signal and to generate a processed count signal having a processed count value; and a first state detector coupled to the filtering system, the first state detector configured to perform a first comparison of the processed count value against a first threshold value and generate a first output signal based on the first comparison, wherein the filtering system comprises; a median-3 filter configured to generate a median filter output signal based on three consecutive raw count values; a memory unit configured to store the three consecutive raw count values; a first moving average filter coupled to the median-3 filter, the first moving average filter configured to filter the median filter output signal and produce the processed count signal; and a second moving average filter, slower than the first moving average filter, coupled to the median-3 filter, the second moving average filter configured to filter the median filter output signal and generate an idle signal having an idle value; wherein the system is configured to reduce the raw count value by the idle value.
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11. A method for detecting a capacitive touch input, the method comprising:
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counting a number of first occurrences that an input signal has a first value during a first time period; counting a number of second occurrences that an input signal has a second, different value during a second time period successive to the first time period; generating a raw count signal having a raw count value proportional to the number of first occurrences and the number of second occurrences; filtering the raw count signal to remove noise and to generate a processed count signal having a processed count value; and comparing the processed count value against a first threshold value to generate a first output signal. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification