Threshold Voltage Compensation in Electroluminescent Displays
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Active matrix electroluminescent display devices using polysilicon thin film transistors face issues due to varying threshold voltages across the substrate, leading to artefacts in the displayed image, and existing solutions complicate pixel circuitry and require additional components for threshold voltage compensation.
Innovation Solution
Incorporating a shorting transistor between the gate and drain of the drive transistor, allowing for external measurement of the threshold voltage using the data line, which simplifies the pixel circuit and reduces complexity by using existing control lines for threshold measurement, enabling operation in two modes: threshold voltage measurement and normal drive mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional pixel circuitry is used without threshold voltage compensation, then device complexity is low, but threshold voltage variations cause image artefacts and display quality deteriorates
Solution Approach 1:
The patent combines the threshold voltage measurement function with the existing data line by allowing the data line to float and store the gate voltage during measurement mode. This merges the measurement function into an existing component rather than adding separate measurement circuitry, thereby improving display quality without significantly increasing pixel circuit complexity
Solution Approach 2:
The data line is designed to serve multiple functions: it acts as both the normal data input line during drive mode and as the measurement path for threshold voltage during measurement mode. The line is switched between these modes using control signals, enabling one component to perform multiple roles and avoiding additional dedicated measurement circuitry
2Measurement precision
If additional components are added for threshold voltage compensation, then measurement precision improves, but pixel circuit complexity increases
Solution Approach 1:
The patent merges the threshold voltage measurement function with the existing data line by allowing the data line to float and store the gate voltage during measurement mode. This combines measurement capabilities into existing circuitry rather than adding separate measurement components, achieving measurement precision without proportionally increasing circuit complexity
Solution Approach 2:
The pixel circuit uses its own existing components (data line, address transistor, drive transistor) to perform the threshold voltage measurement function. The data line itself serves as the measurement path when allowed to float, and the existing transistors are utilized in measurement mode, making the circuit self-sufficient for measurement without requiring external measurement equipment or additional dedicated measurement components within the pixel
3Reliability
If more circuit elements are included in each pixel, then threshold voltage compensation capability improves, but manufacturing ease deteriorates
Solution Approach 1:
The patent combines the threshold voltage measurement function with the existing data line and control transistors. By allowing the data line to float and store voltage during measurement mode, the system achieves threshold voltage compensation capability without adding discrete measurement components that would complicate the manufacturing process
Solution Approach 2:
The data line and control transistors are designed to serve dual purposes: normal pixel addressing and control during drive mode, and threshold voltage measurement during measurement mode. This multi-functionality reduces the total component count per pixel, simplifying the manufacturing process while maintaining compensation capability
4Area of moving object
If pixel circuit elements are reduced, then pixel aperture and resolution improve, but threshold voltage measurement capability may be compromised
Solution Approach 1:
The patent merges the measurement function into the existing data line and control transistors by utilizing their inherent electrical characteristics during measurement mode. This approach requires no additional physical space for dedicated measurement components, preserving pixel aperture area while maintaining threshold voltage measurement capability through clever use of existing circuit behavior
Solution Approach 2:
The existing data line and transistors are designed to perform both normal pixel control functions and threshold voltage measurement functions. By switching between operational modes using control signals, the same physical components serve multiple purposes, eliminating the need for separate measurement circuitry that would consume valuable pixel area and potentially reduce resolution
Data Source
AI summary
An active matrix electroluminescent display device has a shorting transistor (30) connected between the gate and drain of the drive transistor (22). Means (42) is provided for measuring a voltage on the data line (6). The shorting transistor (30) can be used to discharge the voltage on the gate of the drive transistor (22) until it switches off. By storing the resultant voltage on the data line (6) through an address transistor (16), the data line is used as one of the control/measurement lines for the threshold measurement.