Switched Power Supply Synchronization for Touch and Display Noise
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Solution Overview
Problem
Noise generated by switched power supplies in electronic devices interferes with both display updating and touch sensing, making it difficult to maintain image quality and accurately detect user interactions, as existing solutions like high power supply rejection ratios add cost and bulk without fully mitigating noise issues.
Innovation Solution
Synchronizing the switching frequency of the power supply with display and touch timing events, using communication paths between power management, display, and touch controllers to adjust the power supply switching frequency to align with specific events, thereby canceling out noise effects during both display updates and touch sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If high power supply rejection ratios are used to mitigate noise, then noise interference is reduced, but device cost and bulk increase
Solution Approach 1:
The patent changes the timing parameter of the power supply switching frequency to align with display refresh rates and touch sampling rates. By adjusting the switching frequency parameter to be synchronous with these operational rates, noise is generated at predictable intervals that can be filtered out during signal processing, eliminating the need for expensive high rejection ratio power supplies while maintaining performance
Solution Approach 2:
The system implements feedback by monitoring the timing of display refresh operations and touch sampling operations, then uses this information to dynamically adjust the power supply switching frequency. This closed-loop approach ensures that noise generation is coordinated with the system's operational rhythm, allowing the noise to be anticipated and compensated for in the signal processing pipeline
2Loss of energy
If switched power supply frequency is increased to improve power efficiency, then energy loss decreases, but noise interference with touch sensing increases
Solution Approach 1:
The patent employs periodic action by synchronizing the power supply switching frequency with the periodic nature of display refresh and touch sampling operations. The switching frequency is set to match these periodic operations, creating a rhythm where noise occurs at regular, predictable intervals that coincide with natural dead times in the operational cycle, allowing energy efficiency to be maintained while noise interference is minimized through temporal coordination
Data Source
AI summary
Embodiments described herein synchronize a switching frequency of switched power supplies with timing events associated with updating a display screen or performing touch sensing. For example, a touch event may be the time needed for a touch controller to scan a plurality of sensing electrodes. Because noise is introduced each time switched power supplies switch between different stages, the touch controller may instruct a power management controller to switch between the stages (i.e., adjust the switching frequency) at the same time during each touch event. Even though the switched power supplies are permitted to introduce noise into the touch system, the noise happens at the same time during each touch event. Accordingly, the effect of the noise is the same for each touch event and is cancelled out. A similar process may be used for synchronizing the switching frequency to display events.