Continuous time anti-alias filter for capacitive touch sensing
First Claim
Patent Images
1. A method for sensing an input device, comprising:
- receiving a signal with a capacitive sensor electrode;
forwarding the signal to a low-impedance input of a current conveyor configured to provide a virtual ground at the low-impedance input;
outputting a current to an anti-aliasing filter;
filtering the current with the anti-aliasing filter to produce an anti-aliased signal, the anti-aliasing filter having an output and comprising a continuous time analog infinite impulse response filter; and
integrating the anti-aliased signal with a charge integrator having an input, wherein the output of the anti-aliasing filter is directly connected to the input of the charge integrator.
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Abstract
Embodiments described herein include an input device with a plurality of capacitive sensor electrodes configured to receive a signal. The input device also includes a processing system coupled to the plurality of capacitive sensor electrodes. The processing system includes an analog front end (AFE). The AFE includes an anti-aliasing filter comprising a continuous time analog infinite impulse response (IIR) filter configured to filter out interference from the received signal at frequencies higher than a signal frequency of the processing system to produce an anti-aliased signal. The AFE also includes a charge integrator configured to integrate the anti-aliased signal.
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Citations
17 Claims
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1. A method for sensing an input device, comprising:
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receiving a signal with a capacitive sensor electrode; forwarding the signal to a low-impedance input of a current conveyor configured to provide a virtual ground at the low-impedance input; outputting a current to an anti-aliasing filter; filtering the current with the anti-aliasing filter to produce an anti-aliased signal, the anti-aliasing filter having an output and comprising a continuous time analog infinite impulse response filter; and integrating the anti-aliased signal with a charge integrator having an input, wherein the output of the anti-aliasing filter is directly connected to the input of the charge integrator. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. An input device, comprising:
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a plurality of capacitive sensor electrodes configured to receive a signal; and a processing system coupled to the plurality of capacitive sensor electrodes, the processing system comprising an analog front end, the analog front end comprising; a current conveyor having a low-impedance input configured to receive the signal forwarded by at least one of the plurality of capacitive sensor electrodes, to provide a virtual ground at the low-impedance input, and to output a current; an anti-aliasing filter having an input and an output, the input of the anti-aliasing filter configured to receive the current from the output of the current conveyor, the anti-aliasing filter comprising a continuous time analog infinite impulse response filter configured to filter out interference from the current at frequencies higher than a signal frequency of the processing system to produce an anti-aliased signal; and a charge integrator having an input and configured to integrate the anti-aliased signal and, wherein the output of the anti-aliasing filter is directly connected to the input of the charge integrator. - View Dependent Claims (9, 10, 11, 12)
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13. A processing system for filtering a received signal from a capacitive touch sensor device, the processing system comprising:
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a current conveyor having a low-impedance input configured to receive the received signal forwarded by the capacitive touch sensor device, to provide a virtual ground at the low-impedance input, and to output a current; an anti-aliasing filter having an input and an output, the input of the anti-aliasing filter configured to receive the current from the output of the current conveyor, and comprising a continuous time infinite impulse response filter configured to filter out interference from the current at frequencies higher than a signal frequency of the processing system to produce an anti-aliased signal; and a charge integrator having an input and configured to integrate the anti-aliased signal, wherein the output of the anti-aliasing filter is directly connected to the input of the charge integrator. - View Dependent Claims (14, 15, 16, 17)
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Specification