Display Apparatus Driving Circuit for Time-Division Gradation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional driving circuit methods for current driving type display elements, such as organic EL, face challenges in achieving high luminance and long duration due to current non-uniformity, threshold voltage variations, and time-consuming current setting processes, which hinder the attainment of time-division gradation displays.
Innovation Solution
The proposed solution involves a driving circuit with a first transistor for controlling current, a second transistor in series with the display element for supplying or stopping current, and a current setting circuit that sets the output current of the first transistor during the OFF period of the second transistor, allowing for time-division gradation driving and reducing the number of transistors required. Additionally, a third transistor is introduced to set the output current irrespective of the second transistor's state, ensuring sufficient time for current setting and maintaining constant current flow through the first transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional voltage program method is used to compensate threshold voltage variation, then current uniformity is improved, but writing time becomes excessively long (60 microseconds or longer)
Solution Approach 1:
The patent segments the pixel circuit into multiple functional transistors: a first transistor for current control, a second transistor for time-division gradation driving, and a third transistor for maintaining constant current. This segmentation allows the current setting operation to be performed during the OFF period of the second transistor, separating the current control function from the display function and enabling faster writing times while maintaining current uniformity.
Solution Approach 2:
The patent implements preliminary action by setting the output current of the first transistor during the OFF period of the second transistor before the display operation begins. The current setting circuit completes the current control operation in advance, so that when the second transistor turns ON for display, the first transistor is already configured with the correct current, eliminating the need for slow analog voltage programming during the display period.
2Duration of action of moving object
If active matrix driving is used to achieve high luminance and long duration, then display performance is improved, but current non-uniformity and threshold voltage non-uniformity problems arise
Solution Approach 1:
The patent employs feedback mechanisms through the current setting circuit that compensates for threshold voltage variations in the first transistor. By measuring and adjusting the current based on the actual threshold voltage conditions, the system maintains uniform current flow across all pixels despite manufacturing variations, enabling active matrix driving to achieve both long duration and high current uniformity.
Solution Approach 2:
The patent changes the operating parameters by introducing a third transistor that maintains a constant current flow through the first transistor regardless of the second transistor's state. This parameter change ensures that the current through the organic EL element remains stable and uniform across all pixels, solving the current non-uniformity problem while maintaining long display duration.
3Adaptability or versatility
If time-division gradation driving is implemented, then display gradation is improved, but current setting time becomes insufficient
Solution Approach 1:
The patent implements periodic action by utilizing the OFF period of the second transistor within each frame cycle to perform current setting operations. The current setting circuit operates periodically during the non-display period, allowing sufficient time for current calibration while maintaining the time-division gradation display capability during the ON period. This periodic operation enables both gradation display and current setting without time conflict.
4Device complexity
If the number of transistors is reduced to simplify the pixel circuit, then device complexity is decreased, but current control capability may be compromised
Solution Approach 1:
The patent applies multi-functionality by designing the pixel circuit where the first transistor serves dual purposes: it controls the current for display operation and also serves as the subject of current setting during the OFF period. The current setting circuit uses the same first transistor to both display and calibrate current, eliminating the need for separate dedicated transistors for each function while maintaining reliable current control capability.
Data Source
AI summary
When the transistor Q3 is OFF, a predetermined potential is supplied to a potential wire Ui such that a switching transistor Q2 becomes ON. This changes a gate potential of a driving transistor Q1 from an ON potential to a threshold potential. Thereafter, the transistor Q2 is turned OFF, with the result that the potential of the potential wire Ui is changed (in cases where the transistor Q1 is a p-type transistor, the potential is decreased). With this, the transistor Q1 allows a current to constantly flows therethrough, irrespective of the threshold potential. This shortens time for setting an output current of the driving TFT for driving a current driving type display element.