Touchscreen Controller Charger Noise Reduction via Frequency Shaping
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Solution Overview
Problem
Touchscreen controllers face difficulties in differentiating user touch occurrences from aliased noise, particularly when battery chargers couple high-frequency noise into the system, making it challenging to effectively use touchscreens during charging.
Innovation Solution
The touchscreen controller employs digital processing circuitry to detect aliased noise and adjusts the analog-to-digital converter sampling frequency and panel scan frequency to mitigate aliasing, using noise tracking and shaping techniques to remove high-frequency noise from the low pass filter pass band, thereby enhancing the ability to identify user touch occurrences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the touchscreen controller uses a fixed sampling frequency and panel scan frequency, then the system operates stably, but charger noise is aliased into the low pass filter pass band making it difficult to differentiate from user touch occurrences
Solution Approach 1:
The patent implements dynamic adjustment of the sampling frequency and/or panel scan frequency based on detected noise conditions. The controller monitors for charger noise aliasing and automatically reconfigures the scanning operation frequencies to move aliased noise outside the low pass filter pass band, transforming the system from static to adaptive and resolving the contradiction between stable operation and noise immunity.
Solution Approach 2:
The patent changes the operational parameters (sampling frequency and panel scan frequency) in response to detected noise conditions. By adjusting these parameters dynamically, the system moves the aliased charger noise frequency outside the pass band of the low pass filter, thereby eliminating the interference while maintaining reliable touch detection.
2Measurement precision
If the controller uses a low pass filter to separate touch signals from charger noise, then DC and low frequency touch signals can be detected, but aliased high frequency noise folds into the pass band and cannot be differentiated from valid touch signals
Solution Approach 1:
The patent performs preliminary detection of noise aliasing conditions before they corrupt touch signal detection. By monitoring the aliased noise frequency and proactively adjusting the sampling and scan frequencies, the system prevents noise from folding into the pass band, thereby maintaining the integrity of touch signal detection without requiring complex post-processing differentiation.
Solution Approach 2:
The patent implements a feedback mechanism where the controller continuously monitors for charger noise aliasing and automatically reconfigures the scanning operation in response. This closed-loop feedback system detects when aliased noise enters the pass band and adjusts frequencies to eliminate the interference, preserving the ability to differentiate valid touch signals from noise.
3Object-affected harmful factors
If the sampling frequency is increased to reduce aliasing, then high frequency noise can be better filtered, but the panel scan operation becomes more complex and may introduce additional noise folding
Solution Approach 1:
The patent implements a self-service mechanism where the controller automatically detects noise aliasing conditions and autonomously reconfigures the scanning operation frequencies. This eliminates the need for manual intervention or complex external configuration, as the system self-adjusts to optimal frequencies that prevent noise folding while maintaining simplified operation for the user.
Data Source
AI summary
Touch screen controllers and methods are presented for removing charger noise and other high frequency noise from touch screens in the presence of aliasing in which a digital low pass filter rejects the high frequency noise, a noise tracker determines whether noise is being aliased into the low pass filter pass band, and a noise shaper artificially induces or modifies aliasing in the system by adjusting an analog-to-digital converter sampling frequency and/or a panel scan frequency to try to move the aliased noise outside the low pass filter pass band.