Touch Screen Control Circuit Noise Filtering via Differential Sensing
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Solution Overview
Problem
Capacitive touch screens suffer from low Signal to Noise Ratio (SNR) due to various noises, including random and periodic noises, which can lead to errors in touch recognition.
Innovation Solution
A control circuit that performs differential sensing on two adjacent sensing lines of a touch screen panel, filters noises using a moving average method, and integrates voltages stored from previous cycles to block noise incorporation during signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If differential sensing is performed on two adjacent sensing lines, then display noise is filtered, but device complexity increases
Solution Approach 1:
The control circuit divides the sensing lines into pairs of adjacent lines (first sensing line and second sensing line) and processes them separately through dedicated differential sensing circuits. This segmentation allows independent noise filtering for each pair while maintaining overall system manageability.
Solution Approach 2:
The control circuit merges the processing of adjacent sensing lines by performing differential sensing on pairs of lines simultaneously. The differential sensing circuit combines signals from two adjacent lines to cancel common-mode display noise, achieving noise filtering through signal combination.
2Measurement precision
If periodic noise filtering is performed using moving average method, then periodic noise is removed, but processing time increases
Solution Approach 1:
The control circuit performs differential sensing and noise filtering operations before the main touch detection processing. By preparing filtered signals in advance through preliminary differential processing, the main detection algorithm receives pre-processed data, reducing overall processing time.
Solution Approach 2:
The control circuit applies periodic sampling and moving average filtering at regular intervals during the touch detection process. This periodic action allows the system to maintain continuous monitoring while processing noise filtering in manageable time segments, balancing accuracy and speed.
3Measurement precision
If charger noise is filtered by blocking integration during noise detection, then charger noise is removed, but touch detection accuracy may be affected
Solution Approach 1:
The control circuit implements a feedback mechanism that continuously monitors the sensing signals for charger noise characteristics. When charger noise is detected, the system adjusts the integration blocking strategy based on the noise level and pattern, ensuring that noise filtering does not inadvertently block valid touch signals.
Solution Approach 2:
The control circuit dynamically changes integration parameters based on detected noise conditions. When charger noise is present, the integration time constant and blocking duration are adjusted to match the noise characteristics, allowing effective noise rejection while preserving touch detection sensitivity through adaptive parameter tuning.
Data Source
AI summary
Disclosed are a control circuit and a noise removing method for a touch screen. The present invention includes technology for performing differential sensing on the outputs of two adjacent sensing lines of a touch screen panel and integrating a differential sensing signal to filter noises. The control circuit and noise filtering according to the present invention may remove the display noise, tri-wave lamp noise having a predetermined frequency, 60 Hz noise and charger noise caused by battery charging that might affect the two adjacent sensing lines.