Shared Transistor Current Driver for OLED Uniformity
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Solution Overview
Problem
Active matrix organic EL display devices face challenges in achieving uniform current flow and high image quality due to variations in TFT characteristics, leading to uneven luminance and reduced pixel size, which affects display resolution and reliability.
Innovation Solution
A current control driver is designed to allow a larger write current by sharing transistors between pixels, using a configuration with multiple scanning lines to average the drain-gate voltage and reduce the impact of wiring and driver capacitance, ensuring accurate current delivery to each pixel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional pixel circuit configuration with individual TFTs per pixel is used, then each pixel can be independently controlled, but TFT characteristic variations cause uneven current flow and luminance non-uniformity
Solution Approach 1:
The patent merges multiple pixel circuits by sharing the conversion transistor T1 across multiple pixels. Instead of having dedicated conversion transistors for each pixel, a single conversion transistor T1 serves multiple pixels, and its drain-gate voltage is averaged through capacitive coupling to reduce the impact of TFT characteristic variations on current uniformity.
Solution Approach 2:
The conversion transistor T1 performs a multi-function by serving multiple pixels simultaneously. It converts the data line current to voltage for multiple pixels, reducing the number of required transistors and minimizing the impact of manufacturing variations through the averaging effect.
2Measurement precision
If more transistors are allocated per pixel for precise current control, then current accuracy improves, but pixel area decreases and display resolution is affected
Solution Approach 1:
The patent combines the functions of multiple transistors into fewer shared transistors. The conversion transistor T1 and holding capacitor C1 are shared among multiple pixels, reducing the total transistor count per pixel while maintaining current control accuracy through the averaging mechanism.
Solution Approach 2:
The conversion transistor T1 and holding capacitor C1 serve multiple pixels simultaneously, performing current-to-voltage conversion and voltage holding functions for several pixels. This multi-functionality reduces the area required per pixel while preserving control precision.
3Measurement precision
If individual conversion transistors are used for each pixel, then current-to-voltage conversion is precise, but the number of transistors increases and pixel area decreases
Solution Approach 1:
The patent merges the current-to-voltage conversion function across multiple pixels by using a single shared conversion transistor T1. The drain-gate voltage of T1 is averaged through capacitive coupling, maintaining conversion accuracy while reducing the total number of transistors in the display device.
Solution Approach 2:
The conversion transistor T1 performs current-to-voltage conversion for multiple pixels simultaneously, serving as a universal conversion element. This reduces device complexity by eliminating the need for individual conversion transistors in each pixel circuit.
4Measurement precision
If larger write current is applied to overcome wiring and driver capacitance effects, then current delivery accuracy improves, but TFT variations cause uneven current distribution
Solution Approach 1:
The patent applies preliminary averaging of the drain-gate voltage of the conversion transistor T1 through capacitive coupling before the current is delivered to the pixels. This preliminary action reduces the impact of TFT variations on current distribution uniformity while allowing larger write currents to overcome wiring and driver capacitance effects.
Data Source
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AI summary
In a current control driver that drives an active matrix device, a write current can be set larger and unevenness in currents can be reduced between elements receiving the currents. In the current control driver having an element circuit (Pn-1, Pn, Pn+1) for each of the elements (Gn-1, Gn, Gn+1) comprising a converting unit (T1) for converting an applied current into a voltage, a retaining unit (Cs) for retaining the voltage converted by the converting unit (T1), and a driving unit (T2) that converts the voltage retained by the retaining unit (Cs) into an output current and supplies the output current, the converting unit (T1) is shared between two or more of the element circuits and a switch (T5) located between the shared converting units connects two or more of the converting units (T1) to one of the elements during a current supply period for the element.