Pixel Circuit Switch Module Prevents AMOLED Startup Flicker
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Solution Overview
Problem
Existing AMOLED display panels face issues with screen flicker due to abnormal drive current output during startup and abnormal displaying caused by the self-protection function of the power supply signal chip, triggered by difficulties in the low level signal terminal receiving a positive potential and negative potential.
Innovation Solution
A pixel circuit is introduced with a switch module that is initially in an off state during the first frame to prevent abnormal drive current from flowing, and switches to an on state from the second frame to output a normal drive current, ensuring the light emitting device receives a normal drive current, and a control module that outputs the normal drive current to the light emitting device during the light emitting stage, preventing high level signals from reaching the low level signal terminal until a low level signal is received.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the power supply signal VDD is loaded onto the pixel circuit as ground level signal (0V) before startup, then the gate voltage of the drive transistor M3 becomes 0V-Vth, but during the light emitting stage the voltage difference Vgd becomes larger causing abnormal drive current and screen flicker
Solution Approach 1:
The patent applies preliminary action by introducing a startup control signal that prevents the drive transistor from operating during the first frame after power-on. The switch transistor M7 is controlled to be turned off during startup, blocking the abnormal drive current before it can affect the OLED, thereby eliminating screen flicker without requiring hardware modifications.
2Reliability
If the low level signal terminal VSS is at positive potential when transistors M3 and M6 are turned on, then the power supply signal chip output terminal cannot receive the signal, triggering self-protection function and causing abnormal displaying
Solution Approach 1:
The patent applies preliminary action by using the startup control signal to preemptively control the switch transistor M7 to be turned off before the low level signal terminal VSS encounters positive potential. This prevents the potential conflict from occurring in the first place, avoiding activation of the self-protection function and ensuring normal display operation.
Solution Approach 2:
The switch transistor M7 acts as an intermediary between the drive transistor M3 and the OLED. By controlling M7 to be turned off during startup, it isolates the OLED from abnormal drive currents and prevents the potential conflict at the VSS terminal, thereby protecting the power supply chip without requiring modifications to the power supply signal chip itself.
3Reliability
If a switch module is added to control drive current flow during startup, then screen flicker and abnormal displaying are prevented, but the device complexity increases
Solution Approach 1:
The switch transistor M7 is designed to perform multiple functions: it controls the drive current during startup to prevent screen flicker, protects the power supply chip from potential conflicts, and maintains normal display operation during subsequent frames. By integrating these multiple functions into a single transistor controlled by the startup control signal, the patent minimizes the increase in device complexity while achieving comprehensive protection.
Data Source
AI summary
The present disclosure discloses a pixel circuit, an organic electroluminescent display panel and a display apparatus. By adding one switch module in the pixel circuit, the abnormal drive current output by the driving module may be prevented from flowing to the light emitting device during a first frame of display picture as startup, and thus the problem of screen flicker can be overcome in the screen of the first frame when the display panel is started up.