Touch Sensor Code Modulation for Noise-Resistant Position Detection
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Solution Overview
Problem
Existing position sensors, such as touchpads, face challenges in effectively detecting position-based attributes of objects in the presence of noise from sources like display screens, power sources, and radio frequency interference, which affects their performance and accuracy.
Innovation Solution
The implementation of spread spectrum techniques, specifically code division multiplexing (CDM), is used to create distinct modulation signals applied to sensing electrodes, increasing the effective power of signals and reducing noise interference by spreading the signal across a wider spectrum, thereby maintaining a minimum signal-to-noise ratio and improving noise immunity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional sampling and filtering techniques are used to reduce noise, then noise reduction is achieved to some extent, but the signal-to-noise ratio remains insufficient and noise interference persists
Solution Approach 1:
The patent applies spread spectrum techniques that dynamically spread the signal across a wide frequency band rather than using fixed frequency sampling. This dynamic approach allows the signal to evade narrowband noise interference and enables more effective noise rejection through correlation processing, directly resolving the contradiction between noise immunity and signal-to-noise ratio.
Solution Approach 2:
The invention changes the frequency domain parameters by spreading the signal spectrum across a wide bandwidth. This parameter transformation converts a concentrated signal vulnerable to noise into a distributed signal that can be more effectively separated from noise through correlation detection, thereby improving both noise immunity and signal-to-noise ratio simultaneously.
2Object-affected harmful factors
If shielding and noise-reduction techniques are implemented, then external noise interference is reduced, but device complexity increases
Solution Approach 1:
The patent replaces physical shielding mechanisms with signal processing-based noise rejection. Instead of using complex electromagnetic shielding structures, the invention uses spread spectrum modulation and correlation detection to achieve noise immunity, significantly reducing device complexity while maintaining or improving noise rejection performance.
Solution Approach 2:
The invention introduces pseudo-random code sequences as intermediaries between the signal source and detection process. These codes spread the signal in the frequency domain and enable correlation-based detection that inherently rejects noise, providing an elegant solution that avoids complex physical shielding while achieving superior noise immunity.
3Measurement precision
If multiple sampling points are used to improve detection accuracy, then measurement precision improves, but processing time and complexity increase
Solution Approach 1:
The patent combines multiple frequency components into a single spread spectrum signal that carries all position information simultaneously. Instead of sequentially sampling at multiple time points, the invention encodes position information across multiple frequency components that can be decoded in parallel through correlation processing, maintaining high measurement precision while reducing processing time.
Solution Approach 2:
The invention uses periodic pseudo-random code sequences to modulate the signal, creating a structured pattern that enables efficient correlation-based detection. This periodic structure allows the system to process multiple sampling points simultaneously through correlation operations, achieving high measurement precision without the time penalty of sequential processing.
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 enhances the signal-to-noise ratio and improves the noise immunity of position sensors, leading to more accurate and reliable detection of position-based attributes, even in noisy environments, and allows for more efficient sensor designs with improved performance.
Implementation Method 1
The stimulus creates a capacitive, inductive or other electrical effect upon a carrier signal applied to the sensing region that can be detected and correlated to the position or proximity of the stimulus
Implementation Method 2
The stimulus creates a capacitive, inductive or other electrical effect upon a carrier signal applied to the sensing region
Data Source
AI summary
Methods, systems and devices are described for detecting a position-based attribute of a finger, stylus or other object with a touchpad or other sensor having a touch-sensitive region that includes a plurality of electrodes. Modulation signals for one or more electrodes are produced as a function of any number of distinct digital codes. The modulation signals are applied to an associated at least one of the plurality of electrodes to obtain a resultant signal that is electrically affected by the position of the object. The resultant signal is demodulated using the plurality of distinct digital codes to discriminate electrical effects produced by the object. The position-based attribute of the object is then determined with respect to the plurality of electrodes from the electrical effects.