EL Cell Driving Circuit with Backward Bias
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Solution Overview
Problem
The life of electro-luminescence (EL) display panels is shortened due to direct current (DC) flow, particularly in forward direction currents during light-emitting periods and non-light-emitting periods with floating anodes in digital driving methods.
Innovation Solution
An EL display panel and driving method that apply a backward bias to the EL cell during non-light-emitting periods, using a combination of PMOS and NMOS transistors to manage current flow and bias, preventing DC-induced life shortening by allowing forward current during light-emitting periods and backward bias during non-light-emitting periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a forward current is applied to the EL cell during light-emitting periods in digital driving method, then the EL cell can emit light according to video data signal, but the life of the EL cell is shortened due to DC flow in forward direction
Solution Approach 1:
The patent applies periodic alternating current (AC) driving instead of direct current (DC) by switching between forward current during light-emitting periods and backward bias during non-light-emitting periods. This periodic action prevents DC-induced degradation while maintaining light emission control through sub-frame based digital driving methods.
Solution Approach 2:
The patent introduces backward bias during non-light-emitting periods, which is the opposite direction of the forward current used during light-emitting periods. This inversion prevents accumulation of DC stress on the EL cell, thereby extending its operational life while maintaining display functionality.
2Illumination intensity
If the anode is left floating during non-light-emitting periods to control light emission, then the EL cell can be turned off, but DC flow still occurs causing life shortening
Solution Approach 1:
Instead of leaving the anode floating during non-light-emitting periods, the patent applies periodic backward bias to actively manage current flow. This ensures that no DC accumulates during off-periods while maintaining precise control over light emission through the alternating forward-backward current cycle.
Solution Approach 2:
The patent converts the potentially harmful floating anode state during non-light-emitting periods into a beneficial backward bias state. This backward bias not only prevents DC-induced degradation but also actively contributes to extending EL cell life while maintaining display control functionality.
3Illumination intensity
If analog driving method is used to control current amount, then brightness can be controlled by voltage or current level, but the same DC-induced life shortening problem occurs
Solution Approach 1:
The patent transitions from analog driving with continuous DC current to digital driving with periodic AC current. By using sub-frames and alternating forward-backward bias, the patent maintains brightness control capability while eliminating DC-induced degradation that plagues analog driving methods.
Solution Approach 2:
The patent changes the fundamental parameter from continuous analog voltage/current control to discrete digital timing control with alternating current polarity. This parameter change from DC to AC operation enables brightness control through light-emitting period ratios while preventing DC stress accumulation.
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 prolongs the life of EL cells by managing current flow and applying a backward bias during non-light-emitting periods, thereby preventing DC-induced degradation.
Implementation Method 1
The EL display panel of such display devices is a self-luminous device capable of light-emitting a phosphorous material by a re-combination of electrons with holes
Data Source
AI summary
An electro-luminescence display panel and a driving method thereof for preventing a life shortening of the EL caused by a direct current are disclosed. In the electro-luminescence display panel implementing a gray level by a combination of light-emitting periods of sub-frames corresponding to each bit of video data, each of pixels includes an electro-luminescence (EL) cell, and a cell driver for allowing a forward current to be flown into the EL cell in accordance with a supplied data signal in a light-emitting period of the sub-frame while allowing a backward bias to be applied to the EL cell in a non-light-emitting period of the sub-frame.