Capacitive Sensor Driving With OFDM Phase Modulation
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Solution Overview
Problem
Capacitive sensor devices in electronic systems face issues with touch-to-display noise due to interference between sensing signals and display signals, leading to potential overloading and interference.
Innovation Solution
A phase modulation scheme using orthogonal frequency division multiplexing (OFDM-PM) is employed to control the instantaneous phase of transmitter channels, constraining the peak power to minimize peak-to-average-power ratio (PAPR), thereby reducing interference and allowing for a smaller analog front end.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sensing signals with high power are used to drive sensor electrodes, then sensing precision is improved, but touch-to-display interference increases
Solution Approach 1:
The patent applies parameter changes by modulating the phase of sensing signals dynamically. The instantaneous phase adjustment allows the system to maintain high average power for good sensing precision while controlling peak power to reduce interference with display signals. This phase modulation transforms the signal characteristics without changing the fundamental sensing mechanism.
Solution Approach 2:
The patent employs periodic phase adjustment of sensing signals to minimize peak-to-average-power ratio. By periodically modulating the phase of multiple sensing signals, the system achieves constructive interference for sensing purposes while destructive interference reduces peak power that causes touch-to-display noise. This periodic action creates a controlled pattern that separates sensing function from interference generation.
2Power
If peak power of sensing signals is increased, then sensing signal strength is improved, but peak-to-average-power ratio increases causing interference
Solution Approach 1:
The patent changes the phase parameter of sensing signals dynamically to control power characteristics. By adjusting instantaneous phase rather than amplitude, the system maintains consistent signal strength for sensing while avoiding high peak power conditions. This parameter transformation allows decoupling of signal strength from peak power generation.
Solution Approach 2:
The patent converts the potentially harmful high peak power into a beneficial controlled phenomenon. By using phase modulation, the system creates intentional constructive and destructive interference patterns where the destructive interference specifically targets peak power reduction, transforming what would be harmful power spikes into useful signal control for minimizing interference.
3Measurement precision
If multiple sensor electrodes are driven simultaneously with high power, then measurement coverage is improved, but total power consumption increases
Solution Approach 1:
The patent applies periodic phase modulation across multiple sensor electrodes to control power distribution. By coordinating the phase adjustment timing across multiple channels, the system achieves simultaneous measurement coverage while ensuring that peak powers of individual channels do not sum to excessive total power. The periodic nature allows energy-efficient operation through controlled signal coordination.
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 solution effectively minimizes touch-to-display interference and reduces dynamic range requirements, enabling a more efficient capacitive sensing system with reduced noise and smaller component sizes.
Implementation Method 1
adjust, while driving the sensor electrodes of the plurality of sensor electrodes with the sensing signals, instantaneous phase(s) of one or more of the sensing signals
Data Source
AI summary
A system includes a plurality of sensor electrodes and a processing system. The processing system is configured to: drive sensor electrodes of the plurality of sensor electrodes with sensing signals corresponding to a plurality of frequencies; adjust, while driving the sensor electrodes of the plurality of sensor electrodes with the sensing signals, instantaneous phase(s) of one or more of the sensing signals; and obtain, via at least one sensor electrode of the plurality of sensor electrodes, resulting signals corresponding to the sensing signals, wherein the resulting signals are indicative of one or more of presence, position, motion, or features of one or more input objects.