OLED Pixel Circuit Voltage Drop Compensation
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Solution Overview
Problem
Organic light emitting displays face issues with displaying images with desired brightness due to voltage drops in the first power source, as insufficient voltages are stored in storage capacitors.
Innovation Solution
A pixel design incorporating specific transistors and a reference power source with the same voltage as the first power source, along with optimized control signals for scan, control, and emission control lines, ensures that desired brightness is maintained regardless of voltage drops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a first power source is used to supply currents to pixels, then power supply is achieved, but voltage drop occurs causing insufficient voltage storage in capacitors
Solution Approach 1:
A reference power source is introduced as an intermediary element with the same voltage as the first power source. This reference power source connects to the second node through a third transistor and provides a stable voltage reference that compensates for voltage drops in the first power source, ensuring reliable voltage storage in the capacitor regardless of power source fluctuations
Solution Approach 2:
The circuit changes the voltage parameter at the second node by switching between the first power source (through fourth transistor) and the reference power source (through third transistor). By controlling the switching timing and using the reference power source during critical charging phases, the circuit maintains stable voltage parameters for capacitor charging despite variations in the first power source
2Illumination intensity
If voltage is stored in storage capacitors, then image brightness is improved, but voltage drop in power source reduces storage capacity
Solution Approach 1:
The reference power source acts as a mediator that ensures sufficient voltage is available for capacitor charging. By providing a stable voltage reference at the second node, it enables the capacitor to store adequate voltage for desired image brightness even when the first power source experiences voltage drops
Solution Approach 2:
The circuit performs preliminary voltage stabilization by using the reference power source to establish a stable voltage level at the second node before the capacitor charging process. This preliminary action ensures that the capacitor charges to the required voltage level for proper image brightness display
Data Source
AI summary
A pixel according to an embodiment includes: an organic light emitting diode (OLED); a first transistor coupled between a data line and a first node and configured to be turned on when a scan signal is supplied to a scan line; a third transistor coupled between a reference power source and a second node and configured to be concurrently turned on and off with the first transistor; a storage capacitor coupled between the first node and the second node; a second transistor coupled between a first power source and the OLED and having a gate electrode coupled to the first node; a fourth transistor coupled between the first power source and the second node and having a gate electrode coupled to a control line; and a fifth transistor coupled between the second transistor and the OLED and having a gate electrode coupled to an emission control line.