Variable Refresh Rate Display DC Bias Remediation

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Solution Overview

Problem

Variable refresh rate displays face challenges in maintaining a balanced average voltage across pixels, leading to charge accumulation and visual artifacts like flicker due to unbalanced polarity patterns, which conventional displays cannot efficiently address.

Innovation Solution

A method is introduced to dynamically analyze frame sequences for DC imbalance in variable refresh rate displays, intelligently inserting repeat frames between input frames from a GPU to an LCD monitor, and applying remediation counter-measures to maintain a balanced charge accumulation, ensuring the average voltage remains close to zero.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If variable refresh rate is implemented to synchronize with GPU rendering, then visual artifacts like stutter and tearing are reduced, but charge accumulation occurs in pixels due to unbalanced polarity patterns

Engineering Contradiction:

Improvevisual artifactsVSAvoidcharge accumulation

Core Design Contradiction:

Object-affected harmful factorsVSObject-generated harmful factors

Solution Approach 1:

The patent applies periodic action by implementing a polarity inversion scheme where the polarity of voltage applied to pixels is systematically alternated between positive and negative for different frames. This periodic polarity switching prevents charge accumulation by ensuring that charge buildup in one direction is counterbalanced by opposite polarity frames, thereby eliminating the harmful effect of DC bias while maintaining variable refresh rate operation.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent changes the parameter of voltage polarity by dynamically adjusting the polarity state of pixel driving voltages based on frame timing and accumulation detection. The system monitors the duration of positive and negative polarity frames and adjusts the polarity assignment to ensure balanced charge accumulation, effectively using parameter changes to resolve the contradiction between variable refresh rate benefits and charge buildup prevention.

Inventive Principle:

Principle #35Parameter changes

2Object-affected harmful factors

If polarity is changed for each frame to prevent charge accumulation, then flicker is reduced, but average voltage balance becomes difficult to maintain in variable refresh rate scenarios

Engineering Contradiction:

ImproveflickerVSAvoidvoltage balancing mechanism

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent implements feedback by continuously monitoring the actual frame timing and calculating the accumulated charge in pixels based on the duration of positive and negative polarity frames. The system uses this feedback information to dynamically adjust the polarity assignment for subsequent frames, ensuring that the average voltage remains balanced. This closed-loop feedback mechanism simplifies the overall system by using intelligent software control rather than complex hardware circuitry to maintain voltage balance.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent applies self-service by enabling the display system to automatically detect and correct its own polarity imbalance issues. The embedded controller monitors frame timing, calculates charge accumulation, and autonomously adjusts polarity patterns without requiring external intervention or complex additional hardware, allowing the system to self-regulate and maintain optimal operation.

Inventive Principle:

Principle #25Self-service

3Device complexity

If conventional LCD panels are used without specialized DC balancing circuitry, then device complexity is reduced, but charge accumulation and visual artifacts occur in variable refresh rate mode

Engineering Contradiction:

ImprovecircuitryVSAvoidvisual artifacts

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

The patent replaces the mechanical/electrical DC balancing circuitry traditionally found in LCD panels with a software-based control mechanism. Instead of using specialized hardware circuits to detect and correct charge accumulation, the invention uses the GPU's frame timing information and software algorithms to calculate and adjust polarity patterns, thereby eliminating the need for complex additional hardware while still preventing visual artifacts.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS9711099B2Techniques for avoiding and remedying DC bias buildup on a flat panel variable refresh rate display

Publication Date: 2017.07.18 NVIDIA CORP

AI summary

A method for driving a display panel having a variable refresh rate is disclosed. The method comprises receiving a current input frame from an image source. Next, it comprises determining a number of re-scanned frames to insert between the current input frame and a subsequent input frame, wherein the re-scanned frames repeat the input frame, and wherein the number of re-scanned frames depends on the minimum refresh interval (MRI) of the display panel. Further, it comprises calculating respective intervals at which to insert the re-scanned frames between the current input frame and the subsequent input frame. Subsequently, it comprises determining if a charge accumulation in pixels of the display panel has crossed over a predetermined threshold value. Finally, responsive to a determination that the charge accumulation has crossed over a predetermined threshold value, it comprises performing a counter-measure to remediate the charge accumulation.