Differential Transmission for Crosstalk Reduction in Capacitive Touch Sensors
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Solution Overview
Problem
Existing user input systems, particularly capacitive touch sensors, face challenges in accurately distinguishing between multiple touch events and minimizing crosstalk, leading to interference and false readings due to shared signal pathways and electromagnetic noise.
Innovation Solution
The implementation of a differential transmission system in projective capacitive touch sensors using orthogonal signaling schemes, such as frequency-division multiplexing (FDM) or code-division multiplexing (CDM), where each row and column transmit unique orthogonal signals, allowing for precise identification of touch events and minimizing crosstalk by requiring signal matching between rows and columns for valid touch detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional capacitive touch sensors use shared signal pathways for row and column conductors, then device complexity is reduced, but crosstalk and electromagnetic interference increase leading to false readings
Solution Approach 1:
The patent divides the signal transmission system into separate row and column conductor sets, where rows transmit drive signals and columns receive them, eliminating shared pathways. This segmentation prevents crosstalk between different signal pathways while maintaining the basic matrix structure of the touch sensor.
Solution Approach 2:
The patent introduces orthogonal signaling as an intermediary mechanism between row and column conductors. By using frequency-division multiplexing (FDM) or code-division multiplexing (CDM), the system creates distinct signal identifiers that allow the touch controller to differentiate between valid touch events and crosstalk interference, resolving the reliability issue without adding physical structural complexity.
2Productivity
If multiple touch events are detected using traditional signaling methods, then productivity is improved, but crosstalk between touches increases causing false readings
Solution Approach 1:
The patent changes the signal parameters by introducing orthogonal modulation (FDM or CDM) to the row and column conductors. This transforms the signal space so that multiple touches can be distinguished by their unique orthogonal code or frequency signatures, enabling multi-touch detection without crosstalk interference between simultaneous touches.
3Measurement precision
If orthogonal signaling with separate row and column transmitters is implemented, then measurement precision of touch events is improved, but device complexity increases
Solution Approach 1:
The patent makes the row and column conductors multi-functional by having them serve both as signal transmitters and receivers. The same physical conductors that transmit drive signals also receive response signals, eliminating the need for separate transmitter and receiver components and reducing overall device complexity while maintaining measurement precision.
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 enables low-latency, high-accuracy detection of multiple touch events with reduced interference, improving the reliability and precision of user input systems by ensuring that only valid signal couplings are registered as touch events, even in the presence of electromagnetic noise.
Implementation Method 1
capacitive touch sensor
Implementation Method 2
signal coupling between rows and columns
Data Source
AI summary
Differential transmission is provided in a capacitive sensor for reducing cross-talk between rows and columns. A capacitive touch sensitive device as disclosed herein includes row conductors and column conductors, a first row signal generator for transmitting a first row signal on a first row conductor, a second row signal generator for transmitting a second row signal on a second row conductor, and a touch processor for identifying a touch event on the touch interface by processing signals present on at least one of the column conductors. The first and second row signals together form a differential row group of signals that cancel each other out or at least substantially mitigate each other so as to reduce cross-talk interference in the sensor.