Pixel Circuit Data Storage Capacitor Voltage Compensation
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Solution Overview
Problem
Existing display devices with current drive type light emitting elements, such as OLEDs, face issues with pixel current variation due to potential variations in power supply voltage, leading to inconsistent brightness and difficulty in accurately writing signal voltages across driving transistors.
Innovation Solution
A display device with a matrix arrangement of pixels, incorporating a driving transistor with a source electrode connected to a second power supply, a data storage capacitor, and switches that control the connection between the capacitor and a reference power supply, allowing the potential of the capacitor's second electrode to be changed between selection and non-selection periods to compensate for power supply voltage variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the resistance of the power supply line is lowered to reduce voltage variation, then power supply voltage stability is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
A reference potential line is introduced as an intermediary element to provide a stable reference potential to the data storage capacitor. This reference potential line acts as a mediator that decouples the capacitor from direct dependence on the power supply line voltage, thereby maintaining stability without requiring the power supply line itself to have extremely low resistance.
2Use of energy by moving object
If current flow in the driving transistor is turned off during pixel selection period to reduce power consumption, then energy efficiency is improved, but signal writing accuracy deteriorates
Solution Approach 1:
The data storage capacitor is pre-charged to the appropriate voltage level during the pixel selection period when the driving transistor is still conducting. This preliminary charging action ensures that the capacitor holds the correct data voltage before the transistor is turned off for the display period, thus maintaining both power efficiency and writing accuracy.
3Reliability
If the resistance of the power supply line is lowered, then voltage variation is reduced, but manufacturing cost and process complexity increase
Solution Approach 1:
The reference potential line serves as a manufacturable intermediary structure that can be implemented using standard thin-film transistor process techniques. Rather than requiring extreme precision in power supply line resistance, the reference potential line provides a practical and manufacturable solution to voltage variation problems.
4Device complexity
If the data storage capacitor potential is kept fixed, then circuit simplicity is maintained, but power supply voltage drop effects cannot be compensated
Solution Approach 1:
The potential of the data storage capacitor is made dynamic by connecting it to the reference potential line through a switching transistor. During the selection period, the capacitor can be charged to the data voltage, and during the display period, it maintains its charge while the reference potential provides a stable baseline. This dynamic configuration allows compensation for power supply variations without excessive complexity.
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
A display device in which a plurality of pixels are arranged in a matrix form, corresponding to intersections of a plurality of data lines and a plurality of scan lines, wherein each pixel includes a light emitting element having a first electrode connected to a first power supply and which emits light according to a current that flows; a driving transistor having a source electrode connected to a second power supply and which supplies a drain current to a second electrode of the light emitting element; a data storage capacitor having a first electrode connected to a gate electrode of the driving transistor; and a first switch which is switched ON during a pixel selection period so that data of a data line is written to the data storage capacitor, and wherein a potential of a second electrode of the data storage capacitor is changed.