Touch Sensor Code Division Multiplexing Noise Mitigation
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Solution Overview
Problem
Current touch sensor systems using time division multiplexing (TDM) schemes limit sensing time for each drive-sense pair and fail to adequately address noise signals, resulting in low signal-to-noise ratios (SNR) due to environmental interference.
Innovation Solution
Incorporating code division multiplexing (CDM) with code hopping algorithms, which allows for longer sensing time and improved SNR by assigning unique codes to drive lines, distributing noise power across multiple frequencies, and using predictive noise cancellation to optimize signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If time division multiplexing (TDM) schemes are used on drive lines, then scanning of drive line and sense line pairs can be performed separately, but sensing time for each drive-sense pair is limited and signal-to-noise ratio decreases
Solution Approach 1:
The patent replaces the mechanical time-sequenced scanning approach of TDM with a code-based signal processing system. Drive signals are encoded with unique codes and transmitted simultaneously across multiple drive lines, eliminating the need for sequential time-based scanning while improving signal detection through code correlation processing.
Solution Approach 2:
The system dynamically assigns different codes to different drive lines and allows flexible reconfiguration of code assignments. The code hopping algorithm dynamically changes codes over time to optimize performance and mitigate noise, providing adaptability that static TDM schemes lack.
2Device complexity
If TDM schemes are used to scan drive-sense pairs separately at differing times, then multiplexing is achieved, but noise signals from environmental interference are not adequately addressed
Solution Approach 1:
The patent converts the harmful effect of noise by using code division multiplexing where noise signals, being random and uncorrelated with the assigned codes, can be effectively filtered out through code correlation processing. The unique codes assigned to each drive line allow the system to distinguish between legitimate signals and noise interference.
Solution Approach 2:
Unique codes serve as intermediaries between drive signals and sense lines. These codes modulate the drive signals and enable the receiver to distinguish between multiple simultaneous signals through correlation processing, effectively mediating the interaction between multiple drive lines and sense lines without interference.
3Measurement precision
If sensing time is increased for each drive-sense pair, then signal quality improves, but scanning speed and overall system productivity decrease
Solution Approach 1:
The patent merges multiple drive line operations into a single time window by transmitting coded signals simultaneously across multiple drive lines. This consolidation allows the system to maintain high scanning productivity while providing sufficient sensing time for each drive-sense pair through parallel code-based signal processing.
Data Source
AI summary
In one embodiment, a system includes a touch sensor and a computer-readable storage media coupled to the touch sensor and embodying logic that is configured when executed to receive a first plurality of sense signals from sense electrodes of the touch sensor and determine, based on characteristics of the first plurality of sense signals, a plurality of codes. The logic may then assign the plurality of codes to each of the drive electrodes of the touch sensor and determine, based on the assignment of the first plurality of codes to the drive electrodes, encoded drive signals which may be applied to the drive electrodes. The logic may then receive, based on the encoded drive signals, a second plurality of sense signals from the sense electrodes and determine, based on the assignment of the first plurality of codes to drive electrodes, a first touch on the touch sensor.