Multi-Frequency CDM Touch Sensing for T2D Interference Reduction
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Solution Overview
Problem
Touch-to-display interference (T2D) is a significant issue in thin touchscreen devices, particularly in OLEDs, due to the close proximity of touch sensing and display circuitry, leading to display artifacts and detection issues with small input objects or low ground mass conditions.
Innovation Solution
Implementing multi-frequency zero-row-sum code-division-multiplexing (CDM) touch sensing using multiple CDM driving matrices at different frequencies, which cancel out touch driving signals at the display circuitry and utilize signal level recovery to enhance detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If touch sensing is performed using conventional single-frequency driving, then the sensing process is simpler, but touch-to-display interference (T2D) occurs causing display artifacts and detection issues
Solution Approach 1:
The touch sensing process is segmented into multiple frequency components. Instead of using a single driving frequency, the system divides the sensing operation into multiple frequency bands (e.g., first frequency for first subset of transmitter electrodes, second frequency for second subset), allowing interference cancellation through frequency-based separation and processing
Solution Approach 2:
The system changes the driving frequency parameter dynamically. Different subsets of transmitter electrodes are driven at different frequencies (first frequency, second frequency, etc.), and the receiver electrodes process signals at these respective frequencies. This parameter variation enables differentiation between touch signals and display interference
2Object-affected harmful factors
If multiple frequencies are used for touch sensing, then T2D interference is minimized, but the sensing process becomes more complex
Solution Approach 1:
The system employs periodic driving patterns at multiple frequencies. Transmitter electrodes are driven in periodic sequences with different frequencies assigned to different subsets, and receiver electrodes perform periodic sampling at corresponding frequencies. This periodic structure simplifies the processing complexity by enabling regular, predictable signal patterns that are easier to decode
Solution Approach 2:
Frequency acts as an intermediary parameter that separates touch sensing from display interference. By introducing frequency as a distinguishing characteristic, the system can process multiple signals simultaneously without direct interference, as each frequency band carries independent information that can be decoded separately
3Speed
If conventional touch sensing is used, then the detection process is faster, but detection of small input objects and low ground mass conditions suffers with false negatives
Solution Approach 1:
The system replaces conventional single-frequency sensing mechanics with multi-frequency signal processing. Instead of relying on a single driving frequency that may be susceptible to interference and noise, the system uses multiple frequencies with CDM encoding, enabling more robust detection through signal combination and interference cancellation, thereby improving detection accuracy for small objects
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
Minimizes T2D interference, allows faster sensing, and improves detection of small input objects and low ground mass conditions, reducing false negatives and image artifacts.
Implementation Method 1
a touch sensor device determines the presence, location and/or motion of one or more input objects
Data Source
AI summary
An input device includes a plurality of sensor electrodes and a processing system. The plurality of sensor electrodes includes transmitter electrodes and receiver electrodes. The processing system configured to: drive the transmitter electrodes using multiple frequencies and multiple zero-row-sum code-division-multiplexing (CDM) drive matrices, wherein respective subsets of the transmitter electrodes are driven with sensing signals at respective frequencies of the multiple frequencies, and wherein each of the zero-row-sum CDM drive matrices corresponds to a respective frequency of the multiple frequencies; obtain resulting signals via the receiver electrodes based on the transmitter electrodes being driven with the zero-row-sum CDM drive matrix; decode the resulting signals, wherein decoding the resulting signals includes performing a signal level recovery process; and determine presence, location and/or motion of one or more input objects based on the decoded resulting signals.