Pixel Circuit OBS Initialization for LTPS Display FFR Stability
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Solution Overview
Problem
Inorganic light-emitting display devices using P-channel LTPS TFTs experience significant luminance reduction when transitioning from black to white grayscale due to hysteresis characteristics, leading to poor first frame response (FFR) performance and flicker issues.
Innovation Solution
Implementing a pixel circuit with a driving element and switch elements that utilize on-bias stress (OBS) driving in the initialization stage using a pixel driving voltage or data voltage without additional configurations like a separate voltage source or control TFT, including a capacitor and multiple switch elements to stabilize the driving element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If P-channel LTPS TFTs are used for driving element and switch elements, then the display device can achieve fast response speed and high luminous efficiency, but luminance is greatly reduced when data voltage changes from black grayscale to white grayscale due to hysteresis characteristics
Solution Approach 1:
The patent applies preliminary action by performing on-bias stress (OBS) driving during the initialization stage before the actual display frame. This OBS driving pre-stresses the P-channel LTPS TFTs to compensate for hysteresis effects, ensuring that when the data voltage transitions from black to white grayscale, the TFTs are already in an optimized state that prevents luminance reduction. The initialization circuit applies specific voltages to the gate and source/drain terminals of the TFTs to create this preliminary condition.
2Loss of time
If additional configurations such as separate voltage source and control TFT are added to improve FFR performance, then stabilization time can be reduced, but device complexity increases
Solution Approach 1:
The patent applies universality by designing the initialization circuit to perform multiple functions using the existing pixel circuit components. The same switch elements and voltage lines used during normal operation are repurposed during the initialization stage to apply OBS driving. This eliminates the need for separate dedicated initialization components, achieving fast stabilization (reduced loss of time) without increasing device complexity. The circuit structures serve both initialization and display functions.
3Use of energy by stationary object
If on-bias stress driving is implemented without additional configurations, then power consumption is reduced and ease of manufacture is improved, but achieving effective stabilization becomes more difficult
Solution Approach 1:
The patent applies parameter changes by carefully controlling voltage levels and timing parameters during the OBS driving initialization process. Specific voltage magnitudes and durations are optimized to achieve effective TFT stabilization without requiring additional power-consuming components. By adjusting these parameters, the patent maintains high reliability of stabilization while keeping power consumption low and the circuit easy to manufacture with standard P-channel LTPS TFTs.
Data Source
AI summary
A pixel circuit of a display device presented herein includes a driving element including a first electrode connected to a first node, a gate electrode connected to a second node, and a second electrode connected to a third node; a first switch element connecting the second node to the third node; a second switch element applying a data voltage to the first node; a third switch element connecting a pixel driving voltage line to the first node; a fourth switch element connecting the third node to a fourth node; a fifth switch element applying a first initialization voltage to the second node; a sixth switch element applying a second initialization voltage to the fourth node; a capacitor connected to the pixel driving voltage line and the second node; and a light-emitting element connected to the fourth node and a low potential power voltage line.