Touch Sensor Signal Processing for Noise Reduction
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Solution Overview
Problem
Touch sensors face interference from external sources, such as fluorescent lights and spurious signals, which can distort output and reduce the accuracy of coordinate calculations due to low signal-to-noise ratios.
Innovation Solution
A touch sensor system that includes a touch panel with driving and sensing lines, a driver for providing a driving signal, and a digital signal processor that uses oversampling and downsampling to enhance the signal-to-noise ratio by generating a driving signal with signal sections and a sink section, and includes an amplifier, comparator, and delta-sigma analog-digital converter to convert and filter signals effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional capacitance sensing is used without oversampling and filtering, then the device structure remains simple, but the signal-to-noise ratio deteriorates due to external interference
Solution Approach 1:
The patent applies oversampling before downsampling to improve the signal-to-noise ratio. By sampling at a higher rate than the Nyquist rate and then downsampling with appropriate filtering, the system achieves better noise rejection. The driving signal includes a sink section inserted before the sensing operation to ensure the driving line voltage is at a stable intermediate level, preparing the system in advance for accurate measurement.
Solution Approach 2:
The patent introduces an intermediate voltage level (second voltage level) between the high voltage level (first voltage level) and low voltage level (third voltage level) in the driving signal. This intermediate level serves as a stable reference point during the sink section, allowing the sensing operation to occur when the driving line is at a predictable voltage, thereby improving measurement accuracy without requiring complex shielding or filtering hardware.
2Measurement precision
If external interference is present without synchronization, then the device structure remains simple, but coordinate calculation accuracy deteriorates
Solution Approach 1:
The patent employs periodic driving signals with distinct voltage levels (first, second, and third voltage levels) applied to the driving line. The sensing operation is synchronized to occur during specific phases of this periodic signal, particularly when the driving line is at the intermediate second voltage level during the sink section. This periodic structure with synchronization enables the system to distinguish true touch signals from random external interference, improving coordinate calculation accuracy.
Solution Approach 2:
The patent uses the sensed signal from the sensing line to determine when to perform the downsampling operation. The digital signal processor monitors the sensing output and synchronizes the downsampling timing with the driving signal phases. This feedback mechanism ensures that measurements are taken at optimal moments when the driving line voltage is stable, thereby improving measurement precision without requiring complex hardware synchronization circuits.
3Reliability
If oversampling and downsampling are implemented, then the signal-to-noise ratio is improved, but the processing time increases
Solution Approach 1:
The patent applies oversampling at a moderate rate (e.g., 2x or 4x the Nyquist rate) rather than extreme oversampling. This partial oversampling provides sufficient noise rejection for touch sensing applications while avoiding the excessive processing time that would result from much higher sampling rates. The subsequent downsampling reduces the sample rate to a practical level for coordinate calculation, balancing noise rejection with processing efficiency.
Solution Approach 2:
The patent performs the downsampling and filtering operations in advance of the coordinate calculation process. By preparing the downsampled signal with improved signal-to-noise ratio before the firmware performs coordinate extraction, the system reduces the computational burden during the critical coordinate calculation phase. The sink section of the driving signal also prepares the driving line in advance by setting it to an intermediate voltage level, ensuring stable conditions for the sensing operation.
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 system improves the signal-to-noise ratio, reducing interference and enhancing the accuracy of touch location information by synchronizing the driving signal with the sampling clock and filtering noise, thus providing stable and precise coordinate calculations.
Implementation Method 1
a node capacitor formed between a driving line and a sensing line adjacent to one another
Data Source
AI summary
A touch sensor includes a touch panel including driving lines, sensing lines, and a node capacitor formed between a driving line and a sensing line adjacent to one another, a driver for providing a driving signal to each of the driving lines, a sensor for converting a digital signal received from the sensing lines using an oversampling scheme to an oversampled digital signal; and a digital signal processor for downsampling the oversampled digital signal and filtering the downsampled digital signal, wherein, the digital signal processor generates the driving signal in response to a driving clock signal, and the driving signal includes a signal section for driving of the driving lines and a sink section for synchronizing the driving signal and the downsampled digital signal.