OLED Pixel Circuit Threshold Voltage Compensation
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Solution Overview
Problem
In organic light-emitting diode (OLED) display devices, the deterioration of switching transistors leads to non-uniform threshold voltages across pixels, resulting in inconsistent gray scale levels when displaying the same image data, due to variations in the characteristics of both driving and switching transistors over time.
Innovation Solution
A display device with a pixel circuit design that includes multiple switching transistors and a storage capacitor, allowing for the detection and compensation of threshold voltage deterioration by using a voltage sensing method through the data line, ensuring uniformity in gray scale representation across pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional pixel circuit without threshold voltage detection is used, then the device complexity is low, but the display uniformity and gray scale consistency deteriorate due to transistor threshold voltage variations
Solution Approach 1:
The patent implements threshold voltage detection and compensation in advance during a sensing period before the actual display period. The sensing transistor detects the threshold voltage of the driving transistor, and the compensation capacitor stores the detected voltage for subsequent use during light emission, ensuring uniform gray scale display without adding complexity to the main display operation
Solution Approach 2:
The patent introduces a sensing transistor as an intermediary element that mediates between the driving transistor and the data line. This sensing transistor enables threshold voltage detection by forming a temporary conduction path during the sensing period, allowing the system to measure and compensate for threshold variations without directly modifying the driving transistor's main function
2Measurement precision
If multiple switching transistors are added for threshold voltage detection, then the measurement precision of threshold voltage improves, but the device complexity increases
Solution Approach 1:
The patent designs the sensing transistor to perform multiple functions: it acts as a normal switching transistor during the display period to control data signal transmission, and simultaneously serves as a detection transistor during the sensing period to measure the threshold voltage of the driving transistor. This multi-functionality enables precise threshold voltage measurement without adding dedicated detection components that would increase circuit complexity
Solution Approach 2:
The patent employs periodic switching between sensing mode and display mode. During the sensing period, the sensing transistor is configured to detect threshold voltage by forming a conduction path through the driving transistor. During the display period, the same transistor returns to its normal switching function. This periodic alternation enables continuous threshold voltage monitoring without permanently increasing circuit complexity
Data Source
AI summary
A display device includes a display panel, a data driving circuit, a gate driving circuit, and a timing controller, each pixel of the display panel includes a light-emitting diode, a driving transistor, second to sixth switching transistors, and a storage capacitor, and at a sensing step at which the light-emitting diode does not emit light, a conduction path that is connected through the sixth switching transistor, the driving transistor, the second switching transistor, and the third switching transistor is formed, and an electrical signal reflecting a threshold voltage of one of the second to fourth switching transistors is transferred to a data line through the conduction path.