Pixel Driving Circuit Compensation for AM-OLED Gray Level Nonuniformity
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Solution Overview
Problem
The nonuniformity of threshold voltage in transistors and power supply IR drop in traditional Active Matrix Organic Light Emitting Diode (AM-OLED) displays leads to significant gray level nonuniformity and brightness inconsistencies, which existing technologies have not effectively compensated.
Innovation Solution
A pixel driving circuit with a voltage storage element that converts data and initial voltages into a compensation voltage, controlling the current supplied to the light-emitting unit, thereby compensating for threshold voltage nonuniformity and IR drop effects, using a combination of switches and capacitors to manage voltage and power distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the traditional 2T1C pixel driving circuit is used, then the circuit structure is simple, but the gray level nonuniformity reaches up to 30%-40% due to threshold voltage nonuniformity and IR drop
Solution Approach 1:
The pixel circuit is divided into multiple functional modules: a first capacitor for storing data voltage, a second capacitor for storing compensation voltage, and a switching network with multiple transistors. This segmentation allows independent optimization of each module to achieve both simplicity and high precision gray level control.
Solution Approach 2:
The circuit performs preliminary compensation by storing the data voltage in the first capacitor before the light-emitting phase, and uses the switching network to pre-adjust the voltage levels to compensate for expected threshold voltage variations and IR drop effects, ensuring uniform gray levels throughout the display.
2Ease of manufacture
If LTPS technology with ELA is adopted, then the transistor can be manufactured, but the threshold voltage nonuniformity increases causing 30%-40% gray level nonuniformity
Solution Approach 1:
The circuit implements feedback compensation by using the switching network to sense and compensate for threshold voltage variations in real-time during operation. The compensation mechanism adjusts the voltage levels based on the actual transistor characteristics, eliminating the need for extremely tight manufacturing tolerances.
Solution Approach 2:
The circuit changes the operating parameters by using multiple voltage storage capacitors and a complex switching network to dynamically adjust voltage levels, compensating for threshold voltage nonuniformity without requiring changes to the transistor manufacturing process itself.
3Area of stationary object
If the pixel power line is made long to cover the display area, then the display coverage is improved, but the IR drop increases causing more than 70% brightness nonuniformity
Solution Approach 1:
The circuit performs preliminary compensation by storing the data voltage in the first capacitor before the light-emitting phase, and uses the switching network to pre-adjust the voltage levels to compensate for expected IR drop effects, ensuring uniform gray levels throughout the display.
Solution Approach 2:
The voltage storage capacitors and switching network act as intermediaries between the power supply and the light-emitting element, isolating the light-emitting element from the effects of IR drop in the power lines and ensuring uniform brightness across the display.
Data Source
AI summary
A pixel driving circuit includes a light-emitting working unit, a driving unit, a data signal input, a initial voltage input, a driving power input and a plurality of control level inputs. The driving unit includes a voltage storage element and a driving element. The driving element includes a first electrode, a second electrode and a control terminal. One end of the voltage storage element is connected to the control terminal of the driving element. The first electrode of the driving element forms a first input port of the input port of the driving unit. The pixel circuit is capable of improving the display effect and improving the display life of AM-OLED.