Precharge Circuit for Emissive Display Subfield Driving
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Solution Overview
Problem
Polysilicon TFTs in organic electroluminescence displays exhibit significant variations in electric properties, leading to display uniformity issues and reduced lifetime due to burn-in caused by decreased ON current over time.
Innovation Solution
A display device with a digital driving method using a data driver that supplies binary ON or OFF currents, aided by an auxiliary circuit with enhanced current supplying capability, which includes a transistor and capacitor to store gate voltage, ensuring consistent current delivery to the diode emissive element, even as the driving voltage increases with element deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a polysilicon TFT is used as a switch to drive the organic EL element with digital driving, then display uniformity is improved by suppressing variation in properties, but the ON current decreases over time due to deterioration of the organic EL element, causing burn-in and shortened lifetime
Solution Approach 1:
The patent applies preliminary action by writing data to the pixel circuit before the select line is turned off. Specifically, the data signal is written to the pixel during the period when the select line is active (ON), ensuring that the pixel receives the correct data before the switching transistor turns off. This timing arrangement prevents burn-in by ensuring proper current control throughout the display's operational lifetime, while maintaining display uniformity through digital driving.
2Illumination intensity
If a voltage is applied to the gate terminal of the TFT supplying driving current to the organic EL element to control luminance, then the intensity of emitted light can be adjusted, but the intensity of light becomes very sensitive to variations in TFT properties, deteriorating display uniformity
Solution Approach 1:
The patent changes the control parameter from voltage-based to current-based control. Instead of controlling luminance by adjusting the gate voltage of the TFT, the system uses a current source that directly supplies a predetermined current to the pixel circuit based on the data signal. This current control approach makes the luminance less sensitive to TFT property variations, thereby improving display uniformity while maintaining precise luminance control capability.
3Speed
If a driving voltage is raised in a short time to turn on the organic EL element, then response speed is improved, but the ON current decreases due to deterioration of the organic EL element, leading to burn-in
Solution Approach 1:
The patent applies preliminary action by completing the data writing process before the select line turns off. The data signal is fully written to the pixel circuit during the active period of the select line, ensuring that the pixel is properly configured before the switching transistor turns off. This timing arrangement maintains fast response speed while preventing burn-in by ensuring proper current control throughout the display's operational lifetime.
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
This approach prevents burn-in and prolongs the display's usable lifetime by maintaining digital driving with a fixed current, regardless of polysilicon TFT degradation, and allows for efficient data writing with a large current in a short time.
Implementation Method 1
an auxiliary circuit with enhanced current supplying capability, which includes a transistor and capacitor to store gate voltage
Implementation Method 2
an active matrix display array including pixel circuits arranged in a matrix of columns and rows, each pixel circuit having a current-driven diode emissive element
Data Source
AI summary
A display device, includes an active matrix display array including pixel circuits arranged in a matrix of columns and rows, each pixel circuit having a current-driven diode emissive element, and a plurality of thin film transistors for controlling the diode emissive element; a data line provided corresponding to each column of the matrix for supplying a data signal to a pixel circuit in the corresponding column; a data driver for controlling supply of the data signal to the data line; a select line provided corresponding to each row of the matrix for supplying a select signal to the pixel circuit in the corresponding row; and a gate driver for supplying the select signal to the select line; wherein the data signal is a digital signal indicating “1” or “0” as to whether or not to supply ON or drive current to the diode emissive element.