OLED Pixel Circuit for Uniform Luminance via Dual Current Charging
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Solution Overview
Problem
Conventional organic light emitting display devices face challenges in displaying images of uniform luminance due to variations in electron mobility and non-uniformity between threshold voltages of transistors, especially when data signals are supplied as electric currents, which take a long time to charge the data lines.
Innovation Solution
The solution involves a pixel structure with first and second drivers, and selectors that manage a reference current and a pixel current during different periods of a horizontal period, allowing for rapid charging of data lines and uniform image display, regardless of transistor variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If data signal is supplied as electric current to achieve uniform luminance, then image uniformity is improved, but charging time of data line increases
Solution Approach 1:
The patent applies preliminary action by charging the data line with a reference current before the actual pixel current. The reference current charging phase prepares the data line by establishing a baseline charge level, which reduces the subsequent charging time when the pixel current needs to be delivered. This two-stage approach (reference current charging followed by pixel current charging) resolves the contradiction by pre-conditioning the system to enable faster response when actual data needs to be transmitted.
Solution Approach 2:
The patent segments the data signal transmission into two distinct phases: a reference current phase and a pixel current phase. The reference current serves as a separate preparatory signal that charges the data line capacitance, while the pixel current carries the actual image data. This segmentation allows the system to optimize each phase independently - the reference current can be larger to quickly charge the line, while the pixel current maintains uniformity benefits without suffering from the same charging time penalty.
2Use of energy by moving object
If small electric current is used as data signal to maintain low power consumption, then power efficiency is improved, but charging speed of data line decreases
Solution Approach 1:
The reference current charging phase acts as a preliminary action that uses a larger current to quickly establish the baseline charge on the data line. This preliminary charging with higher current overcomes the speed limitation that would otherwise result from using only small currents. After this initial fast charging phase, the system can maintain low power consumption during the actual pixel current phase while still benefiting from the reduced charging time established by the preliminary action.
3Speed
If reference current is added to pixel current to charge data line rapidly, then charging speed is improved, but current management complexity increases
Solution Approach 1:
The patent segments current management into distinct time phases with clearly defined functions. The reference current operates during a specific time window to charge the data line, followed by the pixel current phase for data transmission. This temporal segmentation simplifies the control logic compared to attempting to manage multiple currents simultaneously, as each current source has a dedicated operational window and function.
Solution Approach 2:
The patent implements periodic action by alternating between reference current charging phases and pixel current data transmission phases in a regular time sequence. This periodic structure creates a predictable rhythm to the current management, making the system easier to control and synchronize. The regular alternation between these two current modes simplifies the timing and control logic compared to continuous multi-current management.
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 enables the display of images with uniform luminance by efficiently managing currents and voltages, ensuring rapid charging and consistent image quality across the display device.
Implementation Method 1
Organic light emitting display devices are a type of flat panel display device that make use of organic light emitting diodes that emit light by re-combination of electrons and holes
Data Source
AI summary
A pixel including an organic light emitting diode, an organic light emitting display device including the pixel, and a method for driving the organic light emitting display device. The pixel includes first and second drivers and first and second selectors. A horizontal period for driving the pixel includes first and second periods. The first driver charges a first voltage corresponding to a reference current flowing into a data line during the first period. The second driver charges a second voltage corresponding to a sum of the reference current and a pixel current during the second period. The first selector is turned-on during the horizontal period for connecting the data line to the first and second drivers. The second selector controls the flow of current to the organic light emitting diode and is turned-off during the horizontal period but is otherwise turned-on.