Pixel Circuit Anode Reset for Flicker-Free Display
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Solution Overview
Problem
Organic light emitting display devices experience variations in luminance when frame frequency changes, leading to potential flicker and reduced image quality due to changes in the holding time of data voltage and current flow through light emitting elements.
Innovation Solution
A pixel circuit design that includes a driving element, a light emitting element, switch elements, and a capacitor, where an anode reset is performed at a constant frequency to stabilize the anode voltage, preventing luminance variations without the need for an additional anode reset voltage line.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the frame frequency of the input image is changed, then the holding time of data voltage in pixels is changed, but the luminance of pixels is reduced and flicker is visually recognized
Solution Approach 1:
The patent implements a dual-reset mechanism where the anode electrode of the light emitting element is reset periodically at a constant frequency regardless of frame frequency changes. This periodic reset action maintains stable anode voltage and prevents luminance reduction and flicker that would otherwise occur when holding time changes due to frame frequency variations
2Speed
If the frame frequency of the input image is changed, then the holding time of data voltage is changed, but image quality is degraded due to luminance variations
Solution Approach 1:
The patent employs periodic reset actions at constant frequency to maintain stable anode voltage conditions regardless of frame frequency changes, thereby preserving image quality and preventing luminance variations
Solution Approach 2:
The patent implements a feedback mechanism where the anode reset pulse is generated based on the relationship between frame frequency and holding time. When the holding time exceeds a predetermined threshold, the anode reset pulse is applied to restore the anode voltage, creating a closed-loop control system that maintains luminance stability
3Stability of the object's composition
If an anode reset voltage line is added to stabilize anode voltage, then luminance variations are suppressed, but device complexity increases
Solution Approach 1:
The patent merges the anode reset function with existing circuit elements by utilizing the fourth switch element and capacitor that are already present in the pixel circuit for other functions. This integration approach enables anode voltage stabilization without adding separate dedicated reset voltage lines, thereby suppressing luminance variations while avoiding increased device complexity
Solution Approach 2:
The patent makes existing circuit components multi-functional: the fourth switch element and capacitor serve both as part of the data writing circuitry and as the anode reset mechanism. This universal usage of components achieves voltage stabilization without increasing the number of dedicated reset voltage lines
Data Source
AI summary
A pixel circuit includes: a driving element including a first electrode connected to a first node to which a pixel driving voltage is applied, a gate electrode connected to a second node, and a second electrode connected to a third node; a light emitting element including an anode electrode connected to the third node, and a cathode electrode connected to a power line; a first switch element to supply a data voltage of pixel data to the second node; a second switch element to supply an initialization voltage to the second node; a third switch element to supply a reference voltage to the third node; a fourth switch element configured to connect the third node to a power line to reset a voltage of the anode electrode of the light emitting element to the pixel reference voltage; and a capacitor between the second and third node.