Asymmetric Excitation Voltages for Touch Sensor Noise Cancellation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Touch sensors face challenges in enhancing signal-to-noise ratio (SNR) due to external low-frequency noise, which affects the accuracy of detecting object presence and position within a touch-sensitive area.
Innovation Solution
Generating and measuring asymmetric excitation signals with a first and second voltage magnitude, where the second voltage is greater than the first, to cancel out noise during charging and discharging cycles, thereby improving the SNR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional excitation signals are used for touch sensing, then the touch sensor can detect object presence and position, but external low-frequency noise reduces the signal-to-noise ratio and detection accuracy
Solution Approach 1:
The patent applies asymmetry by using asymmetric excitation signals where the charging phase uses a different voltage magnitude than the discharging phase. This asymmetric approach allows the system to differentiate between the desired touch signal and symmetric external noise, thereby improving measurement precision while maintaining robustness against noise interference.
Solution Approach 2:
The patent implements periodic action through alternating charging and discharging cycles of the capacitive node. By periodically switching between charging (with first voltage magnitude) and discharging (with second voltage magnitude), the system creates a modulated signal that can be distinguished from continuous low-frequency noise, enhancing detection accuracy.
2Measurement precision
If asymmetric excitation signals with different voltage magnitudes are used, then external low-frequency noise is canceled out and signal-to-noise ratio is improved, but the device complexity increases
Solution Approach 1:
The patent changes the voltage magnitude parameter between charging and discharging phases to create asymmetric excitation signals. By varying this electrical parameter rather than changing the physical structure or adding complex filtering hardware, the system achieves noise cancellation while keeping the device complexity manageable.
Solution Approach 2:
The patent uses a simplified approach by generating excitation signals through controlled voltage switching rather than complex signal generation circuits. The charging and discharging phases are essentially copies of each other in structure but differ in voltage magnitude, reducing the complexity of the excitation signal generation mechanism.
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 effectively cancels out external low-frequency noise, enhancing the signal-to-noise ratio and improving the accuracy of detecting object presence and position within the touch-sensitive area.
Implementation Method 1
measuring a charge response of the capacitive node in response to the applied excitation voltages
Data Source
AI summary
A method including applying a first excitation voltage to an electrode of a touch sensor which charges a capacitive node associated with the electrode from a first voltage level to a second voltage level that is greater than the first voltage level. A first measurement measures a charge to change from the first voltage level to the second voltage level. A second excitation voltage is applied to the electrode which charges the capacitive node from the second voltage level to a third voltage level that is greater than the second voltage level. The capacitive node is discharged from the third voltage level to a fourth voltage level that is less than the second voltage level. A second measurement measures a charge to change from the third voltage level to the fourth voltage level. A measured charge signal is generated based on the first measurement and the second measurement.