Calibrating a continuous-time receiver for capacitive sensing
First Claim
1. An input device, comprising:
- a plurality of sensor electrodes in a sensing region of the input device; and
a processing system coupled to the plurality of sensor electrodes, the processing system configured to;
generate a first measurement of a capacitive sensing signal acquired using a first sensor electrode of the plurality of sensor electrodes during a first time period, wherein the capacitive sensing signal comprises effects of a first modulated signal driven onto at least one of the plurality of sensor electrodes;
generate a second measurement of the capacitive sensing signal acquired using the first sensor electrode during a second time period, wherein a phase difference between the first and second measurements is ninety degrees; and
determine a phase offset between the capacitive sensing signal and the first modulated signal based on the first and second measurements; and
phase shift a sampling signal used to generate a third measurement of the capacitive sensing signal acquired using the first sensor electrode by the phase offset,wherein phase shifting the sampling signal by the phase offset aligns the third measurement with a peak amplitude of the capacitive sensing signal, andwherein the capacitive sensing signal has the same shape as the first modulated signal but with different corresponding amplitudes and phase delays.
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Abstract
Embodiments herein describe input devices that include receivers for sampling capacitive sensing signals. In one embodiment, the receivers perform continuous demodulation where the sampling of the capacitive sensing signal is not synchronized with the modulated signal applied to the sensor. To calibrate, the receiver generates first and second measurements of the capacitive sensing signal when driving a modulated signal onto one or more sensor electrodes during two respective time periods. However, the phase of at least one signal is controlled during the time periods so that the first and second measurements have a phase difference of ninety degrees. Using the first and second measurements, the receiver can determine a phase offset between the capacitive sensing signal and the modulated signal which can be used to alter future measurements so that at least some of these measurements are captured when the capacitive sensing signal is at a peak amplitude.
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Citations
17 Claims
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1. An input device, comprising:
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a plurality of sensor electrodes in a sensing region of the input device; and a processing system coupled to the plurality of sensor electrodes, the processing system configured to; generate a first measurement of a capacitive sensing signal acquired using a first sensor electrode of the plurality of sensor electrodes during a first time period, wherein the capacitive sensing signal comprises effects of a first modulated signal driven onto at least one of the plurality of sensor electrodes; generate a second measurement of the capacitive sensing signal acquired using the first sensor electrode during a second time period, wherein a phase difference between the first and second measurements is ninety degrees; and determine a phase offset between the capacitive sensing signal and the first modulated signal based on the first and second measurements; and phase shift a sampling signal used to generate a third measurement of the capacitive sensing signal acquired using the first sensor electrode by the phase offset, wherein phase shifting the sampling signal by the phase offset aligns the third measurement with a peak amplitude of the capacitive sensing signal, and wherein the capacitive sensing signal has the same shape as the first modulated signal but with different corresponding amplitudes and phase delays. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A processing system, comprising:
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sensor circuitry configured to drive a first modulated signal onto at least one of a plurality of sensor electrodes for capacitive sensing; a receiver configured to; generate a first measurement of a capacitive sensing signal acquired using a first sensor electrode of the plurality of sensor electrodes during a first time period, wherein the capacitive sensing signal comprises effects of the first modulated signal being driven onto the at least one sensor electrode; generate a second measurement of the capacitive sensing signal acquired using the first sensor electrode during a second time period, wherein a phase difference between the first and second measurements is ninety degrees; and determine a phase offset between the capacitive sensing signal and the first modulated signal based on the first and second measurements; and phase shift a sampling signal used to generate a third measurement of the capacitive sensing signal acquired using the first sensor electrode by the phase offset, wherein phase shifting the sampling signal by the phase offset aligns the third measurement with a peak amplitude of the capacitive sensing signal, and wherein the capacitive sensing signal has the same shape as the first modulated signal but with different corresponding amplitudes and phase delays. - View Dependent Claims (8, 9, 10, 11, 12, 13)
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14. A method for performing capacitive sensing, the method comprising:
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generating a first measurement of a capacitive sensing signal acquired using a first sensor electrode of a plurality of sensor electrodes during a first time period, wherein the capacitive sensing signal comprises effects of a first modulated signal driven onto at least one of the plurality of sensor electrodes; generating a second measurement of the capacitive sensing signal acquired using the first sensor electrode during a second time period, wherein a phase difference between the first and second measurements is ninety degrees; determining a phase offset between the capacitive sensing signal and the first modulated signal based on the first and second measurements; and phase shifting a sampling signal used to generate a third measurement of the capacitive sensing signal acquired using the first sensor electrode by the phase offset, wherein phase shifting the sampling signal by the phase offset aligns the third measurement with a peak amplitude of the capacitive sensing signal, and wherein the capacitive sensing signal has the same shape as the first modulated signal but with different corresponding amplitudes and phase delays. - View Dependent Claims (15, 16, 17)
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Specification