LTPS Pixel Circuit with Oxide Transistor for VRR Luminance Stability
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Solution Overview
Problem
Display devices driven in variable refresh rate mode experience luminance differences and quality degradation due to IR drop and hysteresis in pixel circuits, leading to image distortion and flicker.
Innovation Solution
A pixel circuit design that includes a light emitting device, a driving transistor, a storage capacitor, and transistors controlled by scan signals, with an oxide semiconductor thin film transistor and low temperature poly-silicon transistors to minimize current leakage and apply on-bias stress voltage to reduce hysteresis, ensuring uniform luminance control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If variable refresh rate mode is used to reduce power consumption, then power consumption is reduced, but luminance difference and image quality degradation occur due to IR drop and hysteresis
Solution Approach 1:
The patent applies preliminary action by performing on-bias stress treatment on the driving transistor before the light emission period. This preliminary treatment stabilizes the threshold voltage and reduces hysteresis effects, ensuring uniform luminance output even when operating in variable refresh rate mode with different driving frequencies.
Solution Approach 2:
The patent utilizes parameter changes by dynamically adjusting the on-bias stress voltage applied to the driving transistor based on the refresh rate. By changing the voltage parameter in response to different operating conditions, the circuit maintains consistent luminance characteristics across variable refresh rates while keeping power consumption low.
2Use of energy by moving object
If conventional pixel circuits are used in variable refresh rate mode, then power consumption is reduced, but hysteresis occurs in the driving transistor causing luminance instability
Solution Approach 1:
The patent applies preliminary action by performing on-bias stress treatment on the driving transistor before the light emission period. This preliminary treatment stabilizes the threshold voltage and reduces hysteresis effects, ensuring uniform luminance output even when operating in variable refresh rate mode with different driving frequencies.
Solution Approach 2:
The patent implements feedback by using the storage capacitor to maintain the gate-source voltage of the driving transistor throughout the light emission period. This feedback mechanism compensates for threshold voltage shifts and hysteresis effects, ensuring stable luminance output despite variations in refresh rate and power consumption levels.
3Ease of manufacture
If standard transistors are used without oxide semiconductor, then manufacturing is simpler, but current leakage occurs reducing pixel circuit performance
Solution Approach 1:
The patent applies local quality by using oxide semiconductor thin film transistors specifically for the switching transistors (first and second transistors) where low leakage is critical, while other transistors in the circuit can use standard manufacturing processes. This localized application of advanced material technology minimizes current leakage in critical paths without requiring complete redesign of the entire manufacturing process.
Data Source
AI summary
Embodiments of the present disclosure relate to a pixel circuit comprising: a light emitting device which emits light with a luminance corresponding to an amount of driving current applied thereto; a driving transistor which controls the amount of the driving current applied to the light emitting device; a storage capacitor which is connected to the driving transistor; a first transistor which is turned on according to a first scan signal and transmits a data voltage to the storage capacitor; and a second transistor which is turned on according to a second scan signal and diode-connects the driving transistor, wherein the driving transistor and the first transistor are low temperature poly-silicon (LTPS) thin film transistors, and wherein the second transistor is an oxide semiconductor thin film transistor.