Touch AFE Polarity Inversion for Noise Immunity
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Solution Overview
Problem
Capacitive touch screens, particularly those with hover touch recognition, face performance degradation due to external noise, leading to erroneous readings and signal-to-noise ratio issues, especially when capacitive profiles become negative due to environmental interference.
Innovation Solution
A touch analog front-end (AFE) system that includes a transmitter to charge and a receiver to sense the touch panel, featuring a charge-to-voltage converter, filter, integrator, and polarity detection circuit. The system filters noise, accumulates capacitive profiles, and reverses polarity when negative, ensuring accurate signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitive touch screens use high sensitivity for hover touch recognition, then hover touch recognition capability is improved, but performance is degraded by external noise
Solution Approach 1:
The patent implements a feedback mechanism where the capacitive profile is continuously monitored, and when noise is detected (capacitive profile below threshold), the system automatically activates noise cancellation by applying an opposing voltage signal. This closed-loop feedback ensures that high sensitivity for hover detection is maintained while external noise is actively compensated for in real-time.
Solution Approach 2:
The patent converts the harmful effect of external noise into a beneficial signal by detecting the noise-induced capacitive profile deviation and generating an opposing voltage signal that cancels the noise. The noise signal itself becomes the basis for creating the cancellation signal, transforming the harmful interference into a useful reference for noise reduction.
2Measurement precision
If the system accumulates capacitive profiles to improve signal-to-noise ratio, then measurement accuracy is improved, but negative capacitive profiles due to noise cause erroneous readings
Solution Approach 1:
The patent applies polarity inversion to the capacitive profile when noise is detected. By inverting the sign of the capacitive profile value when it falls below the threshold, the system ensures that accumulated values remain positive and meaningful, preventing erroneous readings while maintaining the ability to detect genuine touch signals through accumulation.
Solution Approach 2:
The patent performs preliminary noise detection and polarity correction before the capacitive profile accumulation is finalized. By checking the capacitive profile threshold and applying polarity inversion in advance, the system prevents negative values from contaminating the accumulated signal, ensuring measurement reliability from the outset.
3Measurement precision
If the system processes capacitive signals with high gain amplification, then sensitivity is improved, but noise is also amplified leading to signal degradation
Solution Approach 1:
The patent converts the amplified noise signal into a useful reference by detecting when the capacitive profile becomes negative (noise condition) and using this information to generate a cancellation signal. The amplified noise, rather than degrading the measurement, provides the basis for creating an opposing signal that eliminates the noise effect.
Solution Approach 2:
The system implements feedback by continuously monitoring the capacitive profile after amplification and automatically activating noise cancellation when noise is detected. This feedback loop allows high gain amplification to maintain sensitivity while the feedback mechanism compensates for any noise that gets amplified, preserving signal quality.
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
The solution effectively minimizes the impact of external noise, maintaining signal integrity and enhancing the accuracy of touch and hover touch recognition by converting negative capacitive profiles to positive, thus stabilizing the output and improving the overall performance of capacitive touch screens.
Implementation Method 1
a charge-to-voltage (C2V) converter configured to convert an amount of change of capacitance received from the touch panel into a voltage signal
Implementation Method 2
a filter configured to filter a noise from the voltage signal, resulting in a filtered voltage signal
Implementation Method 3
an integrator configured to accumulate the filtered voltage signal and generate a capacitive profile using the accumulated voltage signal
Data Source
AI summary
A touch analog front-end (AFE) and a touch sensor controller (TSC) are provided. The touch AFE includes a transmitter configured to charge a touch panel and a receiver configured to sense the touch panel. The receiver includes a charge-to-voltage (C2V) converter configured to convert an amount of change of capacitance received from the touch panel into a voltage signal, a filter configured to filter a noise from the voltage signal, resulting in a filtered voltage signal, an integrator configured to accumulate the filtered voltage signal, and a polarity detection circuit configured to monitor the filtered voltage signal and to control the integrator to invert a polarity of the filtered voltage signal when it is negative.