Active Matrix Display Loopback Control for Uniformity
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Solution Overview
Problem
Active matrix displays face challenges in achieving uniform light output due to transistor material property variations, leading to differences in current flow and light intensity across pixels, despite the same programmed voltage level, which existing designs attempt to address with complex structures and increased transistor counts, resulting in reduced yield and aperture ratio.
Innovation Solution
The implementation of a data driver circuit with a loopback control circuit that senses and adjusts the voltage of the data line based on the current drawn by each pixel, ensuring that the pixel current matches an external reference current, thereby maintaining uniformity without increasing pixel complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If various pixel designs with increased number of transistor and control lines are used to address transistor material property variations, then output uniformity is improved, but device complexity increases and manufacturing yield decreases
Solution Approach 1:
The patent implements a feedback mechanism where the current through the OLED is sensed and used to adjust the gate voltage of the regulating transistor. A sense transistor copies the OLED current, and this sensed current feeds back to modulate the data voltage, creating a closed-loop system that automatically compensates for transistor parameter variations and achieves uniform output without increasing pixel complexity
Solution Approach 2:
The patent introduces a sense transistor as an intermediary element that copies the OLED current without directly affecting the pixel circuit complexity. This intermediary transistor acts as a mediator between the OLED and the feedback mechanism, enabling current sensing and uniformity correction while maintaining a simple 2-TFT pixel structure
2Manufacturing precision
If various pixel designs with increased number of transistor and control lines are used to address transistor material property variations, then output uniformity is improved, but manufacturing yield decreases
Solution Approach 1:
The feedback mechanism continuously monitors and corrects for transistor parameter variations during operation, compensating for manufacturing tolerances and material property mismatches. This real-time correction improves output uniformity across pixels with varying transistor characteristics, thereby improving manufacturing yield without requiring more complex pixel designs
3Speed
If the same programmed voltage level is applied to different pixels, then programming speed is maintained, but light output uniformity deteriorates due to transistor material property variations
Solution Approach 1:
The feedback mechanism operates during the programming phase, continuously adjusting the gate voltage based on the sensed OLED current. This allows the system to maintain uniform light output while programming pixels at the same voltage level, as the feedback compensation occurs simultaneously with the programming process rather than requiring separate calibration steps
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in improved output uniformity, higher aperture ratio, lower OLED operating voltages, reduced power consumption, and lower production costs, while minimizing the impact of transistor material mismatches and allowing for rapid programming.
Implementation Method 1
Each pixel includes an electronic circuit that controls a light emitting diode
Implementation Method 2
The amount of current determines an amount of diode emitted light
Data Source
AI summary
An active matrix display includes at least one data driver circuit comprising a column data line and a parallel column current line; a plurality of pixels connected in series to both the column data line and the parallel column current line comprising at least one pixel that is responsive to the column data line to drive a selected pixel current to the at least one pixel; and a loopback control circuit at the head of the column and external to the plurality of pixels that senses a voltage difference between an input column current in the current line and a voltage of a load drawing on the current line and that adjusts a data programming voltage according to the difference.