LED Transistor Threshold Voltage Hysteresis Compensation
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Solution Overview
Problem
Electronic display panels experience flicker and image blur due to threshold voltage transients caused by hysteresis in transistors, particularly at low refresh rates and during transitions between gray scale levels, leading to visible artifacts like dim first frames and blur during page scrolling.
Innovation Solution
Applying voltage stress to transistors during a refresh period to boost the threshold voltage to a target level, independent of previous gray scale levels, ensuring proper settling for emission, thereby reducing hysteresis-based artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage stress is applied to transistors during refresh period to boost threshold voltage, then hysteresis-based artifacts are reduced, but additional control complexity is introduced
Solution Approach 1:
The patent applies voltage stress to transistors during a first portion of the refresh period before emission to proactively boost the threshold voltage to a target level. This preliminary action ensures the threshold voltage is properly elevated before the emission phase, preventing hysteresis-based artifacts such as flicker and image blur without requiring complex real-time adjustments during emission.
Solution Approach 2:
The patent implements periodic voltage stress application during the refresh period at fixed timing intervals. By applying the stress voltage in a periodic manner synchronized with the display refresh cycle, the system maintains consistent threshold voltage levels across frames while using simple, repeatable control logic rather than complex adaptive algorithms.
2Loss of time
If threshold voltage is boosted during refresh period, then settling time is reduced, but energy consumption increases
Solution Approach 1:
The patent divides the refresh period into distinct portions: a first portion for applying voltage stress to boost threshold voltage, and a second portion for emission. By segmenting the refresh period in this manner, the voltage stress is applied only during the necessary initialization phase rather than continuously, reducing overall energy consumption while ensuring adequate settling time before emission.
Solution Approach 2:
The patent applies voltage stress exceeding what would be naturally present to rapidly boost the threshold voltage to the target level during the first portion of the refresh period. This excessive action ensures the threshold voltage reaches the desired level quickly with sufficient margin, minimizing the required settling time while the stress is applied only partially (during a limited portion of the refresh period) to control energy consumption.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces the likelihood of flicker and blur by ensuring consistent luminance and image quality across frames, regardless of previous gray scale levels, by dynamically or statically adjusting the duration of voltage stress to achieve the target threshold voltage level.
Implementation Method 1
threshold voltage transients may exist at the transistors due to hysteresis. Such fluctuations of the threshold voltage may cause flicker and/or image blur.
Data Source
AI summary
Electronic devices, storage medium containing instructions, and methods pertain to determining a target boosted threshold voltage level based at least in part on a target emission threshold voltage level. Using the determined target boosted threshold voltage level, a light emitting diode (LED)-controlling transistor is submitted to voltage stress to boost a threshold voltage of the transistor to the target boosted threshold voltage level during a first portion of a refresh period between first and second emission periods. During a second portion of the refresh period, the voltage stress is de-asserted to settle the threshold voltage to a target emission threshold voltage level for the second emission period. After the voltage is settled, the LED-controlling transistor is driven based at least in part on the target emission threshold voltage level.