Touch Sensor Noise Reduction via Display Scan Timing
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Solution Overview
Problem
Capacitive touch sensors in touch-sensitive display systems face noise interference from nearby display scanning circuitry, particularly due to high switching voltages in electrophoretic displays and 'punch through' effects in LCD designs, leading to unreliable touch detection and increased power consumption when filtering is used to mitigate noise.
Innovation Solution
Configuring the display controller circuit and touch sensor controller circuit to perform touch sensor acquisition cycles during periods of reduced noise in the display scanning duty cycle, such as by operating at reduced switching voltages, avoiding simultaneous scanning and acquisition, or using phase mismatches to minimize noise coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If additional shielding layers are added to reduce noise, then noise reduction is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent implements periodic action by timing the touch sensor acquisition cycles to occur during specific periods in the display scanning duty cycle when noise is reduced. The controller is configured to perform sensor acquisition during low-noise intervals, effectively using temporal separation to avoid noise interference without adding physical shielding layers.
Solution Approach 2:
The patent extracts the touch acquisition operation from the noisy period of the display scanning cycle. By separating the acquisition timing from the high-noise scanning periods and performing it during quieter intervals, the system removes the harmful interaction between scanning noise and touch sensing without requiring additional shielding materials.
2Object-affected harmful factors
If filtering is used to reduce noise, then noise reduction is improved, but response time increases and power consumption increases
Solution Approach 1:
Instead of using continuous filtering that processes all data regardless of noise conditions, the patent employs periodic action by only performing touch acquisition during specific low-noise periods. This eliminates the need for continuous filtering operations, thereby reducing processing time and power consumption while maintaining noise reduction effectiveness.
Solution Approach 2:
The system performs preliminary action by identifying and selecting optimal acquisition periods before actual touch sensing occurs. By pre-determining when noise levels are acceptable for accurate measurement, the system avoids unnecessary filtering operations during high-noise periods, thus reducing overall processing time and energy consumption.
3Object-affected harmful factors
If filtering is used to reduce noise, then noise reduction is improved, but power consumption increases
Solution Approach 1:
The patent applies periodic action by limiting touch acquisition operations to specific time windows when noise is reduced. This temporal selection strategy eliminates the need for continuous filtering operations that would consume power throughout the entire scanning cycle, thereby reducing overall power consumption while maintaining effective noise reduction during critical measurement periods.
Solution Approach 2:
The system uses partial action by performing touch acquisition only during the portion of the scanning cycle when noise levels are acceptable, rather than continuously monitoring and filtering throughout the entire cycle. This partial operation approach reduces power consumption by activating sensing and processing only when necessary for accurate measurement.
Data Source
AI summary
In touch sensitive display devices, the display scanning circuitry responsible for driving images of the panel screen can cause noise on the electrodes of nearby touch sensors. The display controller circuit and/or the touch sensor controller circuit of the exemplary touchscreen display devices may be configured to reduce such noise during the touch sensor acquisition cycle by implementing one or more of several techniques in which a portion of each of the sensor acquisition cycles occurs within a period of reduced noise from a cycle of the scanning of the display.