Absolute Capacitive Sensing for Multi-Object Detection
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Solution Overview
Problem
Existing input devices, such as touchpads and touch screens, face reliability issues in detecting multiple input objects at a distance due to the limitations of transcapacitance sensing, which becomes less reliable as the distance between objects and sensing regions increases.
Innovation Solution
The implementation of a processing system that employs absolute capacitive sensing by driving sensor electrodes with capacitive sensing signals and reference signals to acquire changes in capacitance, allowing for the determination of a capacitive image based on these changes, thereby enhancing the detection of multiple input objects at proximity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If transcapacitance sensing is used to detect input objects, then multiple input objects can be resolved at a given time, but the reliability of detection deteriorates as the distance between input objects and sensing regions increases
Solution Approach 1:
The patent changes the sensing parameter from transcapacitance (mutual capacitance between sensor electrodes) to absolute capacitance (capacitance between sensor electrode and input object). This parameter change enables reliable detection at greater distances because absolute capacitance sensing measures the capacitance to ground through the input object, which maintains signal strength over longer distances compared to transcapacitance that requires direct coupling between sensor electrodes and objects.
2Productivity
If transcapacitance sensing is used, then a capacitive image can be generated from multiple sensing regions, but the results become less reliable for proximity or hover sensing at increased distances
Solution Approach 1:
The patent makes the sensor electrodes universal by enabling them to perform both multi-touch detection and proximity/hover sensing with high reliability using absolute capacitance sensing. The same sensor electrode array that generates capacitive images for multi-touch can now also reliably detect proximity and hover inputs at greater distances, eliminating the need for separate sensing mechanisms.
3Measurement precision
If sensor electrodes are driven with capacitive sensing signals, then changes in capacitance can be acquired, but the system complexity increases when implementing absolute capacitive sensing
Solution Approach 1:
The patent uses a reference signal that copies the characteristics of the capacitive sensing signal but is applied to different sensor electrodes (first set vs. second set). This copying approach allows the system to measure absolute capacitance by comparing signals from electrodes driven with identical reference waveforms, simplifying the measurement process while maintaining high precision.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach improves the reliability of detecting multiple input objects by using absolute capacitance sensing, which is more effective at greater distances than transcapacitance sensing, enabling unambiguous multi-touch sensing and hover detection.
Implementation Method 1
drive sensor electrodes with a capacitive sensing signal to acquire first changes of capacitance between each of the sensor electrodes and at least one input object
Implementation Method 2
drive at least one sensor electrode in a first set of the sensor electrodes with a reference signal and at least one sensor electrode in a second set of the sensor electrodes with a capacitive sensing signal to acquire second changes of capacitance
Data Source
AI summary
In an example, a processing system includes a sensor module having sensor circuitry. The sensor module is configured to drive sensor electrodes with a capacitive sensing signal to acquire first changes of capacitance between each of the sensor electrodes and at least one input object; and drive at least one sensor electrode in a first set of the sensor electrodes with a reference signal and at least one sensor electrode in a second set of the sensor electrodes with a capacitive sensing signal to acquire second changes of capacitance between the at least one sensor electrode in the second set and the at least one input object. The processing system further includes a capacitive measurer module configured to determine a capacitive image based at least in part on the first and second changes of capacitance.