Modulated Power Supply for Capacitive Sensing Parasitic Reduction
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Solution Overview
Problem
Capacitive touch sensing devices face challenges in detecting input objects due to parasitic capacitance from nearby conductive components, which reduces the ability to accurately sense the presence and location of input objects, especially in 'in-cell' display embodiments where sensing electrodes are close to conductive elements.
Innovation Solution
A modulated power supply is used to drive sensor electrodes with modulated signals, reducing parasitic capacitance by maintaining sensor electrodes at a constant voltage with respect to a modulated ground signal, thereby minimizing voltage differential with other components and enhancing the detection of input objects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sensor electrodes are driven with modulated signals to reduce parasitic capacitance, then measurement precision is improved, but device complexity increases due to the need for modulated power supply and coordinated timing control
Solution Approach 1:
The modulated power supply serves dual functions: it provides power to the display device and simultaneously modulates the sensor electrodes to reduce parasitic capacitance. This multi-functionality eliminates the need for separate dedicated modulation circuitry, resolving the technical contradiction by improving measurement precision without proportionally increasing device complexity.
Solution Approach 2:
The patent combines the power supply function with the modulation function into a single integrated system. The modulated power supply unit generates signals that simultaneously perform display driving and sensor electrode modulation, merging multiple functions into one component to avoid the complexity overhead of separate systems.
2Area of stationary object
If sensor electrodes are positioned close to conductive elements for compact design, then device area is reduced, but parasitic capacitance increases reducing detection accuracy
Solution Approach 1:
The patent changes the electrical parameters of the system by introducing modulated signals to the sensor electrodes. This parameter change (modulation frequency and amplitude) transforms the capacitive coupling characteristics, allowing the sensor electrodes to maintain close proximity to conductive elements for compact design while the modulation technique compensates for and reduces the detrimental effects of parasitic capacitance on detection accuracy.
3Productivity
If touch sensing and display updating are performed simultaneously to improve productivity, then operational efficiency is improved, but signal interference increases due to voltage variations
Solution Approach 1:
The patent employs periodic modulation of the power supply signals at specific frequencies. By using periodic action with carefully selected frequencies, the system can simultaneously perform touch sensing and display updating because the modulation creates distinct temporal patterns that allow the sensing circuitry to differentiate touch signals from display refresh signals, maintaining signal stability while improving operational efficiency.
Solution Approach 2:
The system uses feedback mechanisms where the modulated sensor signals are processed to detect touch events, and this information feeds back to control the display updating process. The feedback loop allows the system to adjust timing and signal levels dynamically, ensuring that simultaneous touch sensing and display updating occur without harmful interference, thus maintaining reliability while achieving high productivity.
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
The use of a modulated power supply effectively reduces parasitic capacitance, improving the accuracy of input object detection and allowing simultaneous touch sensing and display updating in capacitive sensing devices.
Implementation Method 1
parasitic capacitance between the sensor electrodes and conductive objects other than an input object
Data Source
AI summary
Embodiments described herein include an input device for capacitive sensing. The input device includes a plurality of sensor electrodes, a modulated power supply, a plurality of analog front end channels, and a sensor module. The modulated power supply is configured to generate a modulated reference signal. The plurality of analog front end channels are coupled to the plurality of sensor electrodes and to the modulated power supply and are configured to flow charge in response to an input object in a sensing area associated with the plurality of sensor electrodes. The sensor module comprises transmitter circuitry that is coupled to the plurality of sensor electrodes and to the plurality of analog front end channels. The sensor module is configured to drive the plurality of sensor electrodes with a modulated sensor electrode signal that is based on the modulated reference signal, via the plurality of analog front end channels.