Active Matrix Display Cell Voltage Compensation Circuit
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current display technologies, such as OLED and iLED, face issues with non-uniform brightness due to threshold voltage variations in TFTs, leading to inefficiencies in power consumption and display performance, particularly in high-performance displays with high frame rates.
Innovation Solution
Implementing a cell design that compensates for threshold voltage variations by using an additional Vth compensation circuit and adjusting TFT dimensions, allowing for simultaneous frame programming and threshold voltage compensation, and incorporating multiple light emitting devices for redundancy and mode switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If threshold voltage compensation is implemented using conventional methods, then brightness uniformity is improved, but programming time increases and frame rate decreases
Solution Approach 1:
The patent combines threshold voltage compensation and frame programming into a single simultaneous operation phase. The compensation circuit extracts threshold voltage information while the display data is being programmed to the cells, eliminating the need for separate compensation phases and thereby reducing programming time while maintaining brightness uniformity.
Solution Approach 2:
The compensation circuit performs threshold voltage extraction and compensation in advance during the programming phase, preparing the cell voltages before the actual display refresh. This preliminary compensation ensures that subsequent display operations proceed without additional time penalties, enabling high frame rates.
2Reliability
If multiple light emitting devices are placed per cell, then reliability is improved through redundancy, but device complexity increases
Solution Approach 1:
The patent divides each display cell into multiple independent light emitting device segments (e.g., first and second light emitting devices). Each device can be independently controlled through separate control lines, allowing individual defective devices to be disabled while others remain operational, thereby improving reliability without requiring complete cell replacement.
Solution Approach 2:
The patent implements mode switching capability that changes the operational parameters of the cell by selecting different light emitting devices based on their health status. The control circuit can dynamically switch between devices, change their brightness levels, or activate repair modes, adding functionality without fundamental structural changes to the cell architecture.
3Use of energy by moving object
If constant supply voltage is used to drive light emitting devices, then power consumption is reduced, but brightness uniformity deteriorates due to TFT threshold voltage variations
Solution Approach 1:
The patent implements a feedback mechanism where the compensation circuit continuously monitors and extracts threshold voltage variations in the TFTs. This information is fed back to adjust the cell voltages dynamically, compensating for TFT variations while maintaining constant supply voltage to the light emitting devices, thereby preserving both low power consumption and brightness uniformity.
Solution Approach 2:
The patent dynamically changes the cell voltage parameters based on extracted threshold voltage information. By adjusting the cell voltages in response to TFT variations, the system maintains uniform brightness output while keeping the supply voltage to light emitting devices constant, thus preserving energy efficiency.
Data Source
AI summary
An active matrix display wherein each cell comprises: two thin-film transistors (TFTs) connected in series, the first TFT having its drain connected to a high supply line and the second TFT having its source connected to a low supply line. Gates of the first and second TFTs are selectively connected to respective first and second data driver signals under the control of a scan line signal. A storage capacitance is connected to a node joining the first and second TFT. A driving TFT has a gate connected to the joining node and is connected to drive a light emitting device with a bias current. In one embodiment, the first and second TFTs are sized relative to one another and the first and second data driver signal voltages are related proportionally, so that the data driver signals and the bias current are related to one another by a function substantially independent of a threshold voltage of the driving TFT.