Oxide-Semiconductor Driving Transistor Pixel Circuits for Flicker Reduction
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Solution Overview
Problem
Light emitting display apparatuses experience flickering due to changes in threshold voltages and hysteresis characteristics of driving transistors, leading to variations in luminance during refresh and anode reset periods, and abnormal driving of light emitting devices.
Innovation Solution
The use of an oxide semiconductor for the driving transistor in the pixel driving circuit to control current supply to the light emitting device, with a switching transistor activated only during the refresh period and a driving transistor formed of an oxide semiconductor to stabilize luminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If data voltages are supplied to data lines only during refresh period to improve power consumption, then power consumption is reduced, but threshold voltages of driving transistors change causing luminance variation and flicker
Solution Approach 1:
The pixel circuit performs preliminary actions during the refresh period including charging the storage capacitor with data voltage, initializing the light emitting device anode, and compensating for threshold voltage. These preliminary actions prepare the circuit for stable operation during the anode reset period when no data voltage is supplied, preventing luminance variation and flicker while maintaining low power consumption
Solution Approach 2:
The patent changes the operational parameters of the pixel circuit by dividing the operating cycle into refresh period and anode reset period with different voltage supply conditions. During refresh period, data voltage is supplied to charge capacitors and initialize devices; during anode reset period, no data voltage is supplied but the circuit maintains stable luminance through previously established parameter configurations
2Ease of operation
If light emitting control signals are used during anode reset period to control light emissions, then light emission control is achieved, but images displayed in refresh period and anode reset period vary causing flicker
Solution Approach 1:
The patent segments the operating cycle into two distinct periods: refresh period for data voltage supply and circuit initialization, and anode reset period for light emission control without data voltage. This segmentation allows independent optimization of each period's function while maintaining overall image consistency and eliminating flicker
Solution Approach 2:
The storage capacitor and initializing transistor act as intermediaries that maintain the relationship between data voltage and light emitting device anode voltage. The storage capacitor holds the data voltage value, and the initializing transistor controls the voltage relationship, ensuring consistent luminance across different operating periods even when data voltage is not supplied
3Use of energy by moving object
If voltage compensation for anode characteristics change is not supplied during anode reset period, then power consumption is reduced, but light emitting device is abnormally driven causing luminance variation
Solution Approach 1:
The pixel circuit performs preliminary compensation actions during the refresh period by charging the storage capacitor with data voltage and establishing the voltage relationship between the light emitting device anode and cathode. This preliminary compensation ensures the light emitting device is properly biased before the anode reset period begins, enabling abnormal-free operation without additional power consumption during the anode reset period
Data Source
AI summary
A light emitting display apparatus includes a light emitting display panel including a pixel driving circuit and a light emitting device, and a gate driver to supply gate signals to the pixel driving circuit. The pixel driving circuit includes a first light emitting transistor connected to the light emitting device, a driving transistor connected to the first light emitting transistor, a first switching transistor connected to a gate electrode of the driving transistor and a first terminal of the driving transistor, and a second switching transistor connected to a first node between the driving transistor and the first light emitting transistor. With the light emitting display apparatus in use, one second is divided into at least one refresh period and at least one anode reset period. The second switching transistor is turned on only during the at least one refresh period. The first switching transistor includes an oxide semiconductor.