OLED Driving Transistor Threshold Voltage Compensation Circuit
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional OLEDs using amorphous silicon TFTs face image quality degradation due to shifting threshold voltages over time, affecting current driven to the light emitting element and resulting in varying luminance, especially when DC control voltage is applied.
Innovation Solution
A display device with a light emitting element, a driving transistor, and a capacitor that stores a control voltage derived from the data voltage and threshold voltage of the driving transistor, utilizing a complex switching unit configuration to stabilize the voltage and maintain consistent current supply to the light emitting element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If amorphous silicon TFT is used for driving transistor, then ease of manufacture and applicability to large displays is improved, but threshold voltage stability deteriorates over time under DC control voltage
Solution Approach 1:
The patent employs a dual-mode driving scheme that dynamically switches between DC control voltage mode (for power saving) and AC control voltage mode (for threshold voltage stability). The driving transistor operates in different electrical states depending on the emission phase, transforming a static threshold voltage problem into a dynamically managed condition that maintains stability while preserving manufacturing simplicity.
Solution Approach 2:
The patent implements periodic alternation between DC and AC control voltage application to the driving transistor. During non-emission periods, DC voltage is applied for power saving; during emission periods, AC voltage is applied to prevent threshold voltage shifts. This periodic action resolves the contradiction by exploiting time-domain separation to achieve both ease of manufacture and threshold voltage stability.
2Use of energy by moving object
If DC control voltage is applied to driving transistor for power saving, then energy consumption is reduced, but threshold voltage shifts causing luminance variation occur
Solution Approach 1:
The patent applies periodic alternation between DC and AC control voltages to the driving transistor. During non-emission periods (power saving mode), DC control voltage is applied to reduce power consumption. During emission periods (display mode), AC control voltage is applied to maintain threshold voltage stability and prevent luminance variation. This temporal separation resolves the contradiction between power saving and luminance stability.
Solution Approach 2:
The patent applies AC control voltage during emission periods as a preliminary protective action before DC voltage is applied during non-emission periods. By maintaining the transistor in an AC-driven state during emission, the threshold voltage is stabilized in advance, preventing shifts that would occur if DC voltage were continuously applied, thereby ensuring luminance stability while enabling power saving.
3Device complexity
If light emitting element is connected to source of driving TFT, then simple circuit configuration is achieved, but threshold voltage shift of light emitting element affects source voltage and varies driven current
Solution Approach 1:
The patent introduces a capacitor as an intermediary element between the light emitting element and the driving transistor source terminal. This capacitor couples the source terminal to the light emitting element while providing a stable reference potential, isolating the source voltage from threshold voltage shifts of the light emitting element. This intermediary component maintains the simple circuit configuration while improving current driving stability.
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 compensates for threshold voltage shifts, ensuring consistent image quality by isolating the control terminal and capacitor from external signals and using a reference voltage to stabilize the output current, reducing variations and maintaining image quality over time.
Implementation Method 1
a capacitor that stores a control voltage being a function of the data voltage and the threshold voltage of the driving transistor
Data Source
AI summary
Each pixel includes: a light emitting element; a capacitor; a driving transistor that has a control terminal, an input terminal, and an output terminal and supplies a driving current to the light emitting element to emit light; a first switching unit that diode-connects the driving transistor and supplies a data voltage to the driving transistor in response to a scanning signal; and a second switching unit that supplies a driving voltage to the driving transistor and connects the light emitting element and the capacitor to the driving transistor in response to an emission signal, wherein the capacitor is connected to the driving transistor through the first switching unit, stores a control voltage being a function of the data voltage and the threshold voltage of the driving transistor, and is connected to the driving transistor through the second switching unit to supply the control voltage to the driving transistor.