AMOLED Pixel Circuit Threshold Voltage Drift Compensation
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Solution Overview
Problem
In AMOLED displays, the threshold voltage drifts when displaying a black image, leading to reduced display contrast due to the OLED device turning on and emitting light, even when a black image is intended.
Innovation Solution
A pixel circuit design that includes a potential reset unit to reset the threshold voltage and a potential maintenance unit to maintain the voltage difference, preventing the threshold voltage from drifting, comprising a light emitting unit, a drive unit, a switch unit, a voltage maintenance unit, and a potential reset unit, with additional components like compensation, storage, and maintenance capacitors to control and stabilize the voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a 3T1C pixel unit circuit is used with IJP OLED device, then the turn-on voltage is reduced and manufacturing is simplified, but the threshold voltage drifts during black image display causing poor display contrast
Solution Approach 1:
The pixel circuit is divided into multiple functional units: drive unit (T1), voltage maintenance unit (Cst), potential reset unit (T2), potential maintenance unit (C1), and compensation unit (T3). Each unit performs a specific function to collectively solve the threshold voltage drift problem while maintaining the simplicity of IJP manufacturing process.
Solution Approach 2:
The potential reset unit T2 and compensation unit T3 perform preliminary actions before the main display operation. T2 resets the threshold voltage of T1 before black image display, and T3 compensates for voltage variations, preventing threshold drift before it affects display contrast.
2Device complexity
If the threshold voltage is allowed to drift naturally, then the circuit operation is simple, but the OLED device turns on during black image display reducing contrast
Solution Approach 1:
The compensation unit T3 implements a feedback mechanism by monitoring the source voltage of drive transistor T1 and adjusting the compensation voltage accordingly. This feedback loop ensures that threshold voltage drift is continuously compensated, maintaining display contrast without excessive circuit complexity.
Solution Approach 2:
The voltage maintenance capacitor Cst and potential maintenance capacitor C1 enable the circuit to self-maintain critical voltages. These capacitors store and maintain voltages automatically during operation, reducing the need for continuous external control while preventing threshold drift.
3Reliability
If additional voltage maintenance and potential maintenance units are added, then the threshold voltage stability is improved, but the device complexity increases
Solution Approach 1:
The voltage maintenance unit Cst and potential maintenance unit C1 are merged into the same pixel circuit structure, sharing common nodes and transistors where possible. This integration approach maintains voltage stability while minimizing the increase in overall circuit complexity by consolidating functions rather than adding completely separate circuits.
Data Source
AI summary
A pixel circuit is provided. The pixel circuit includes a light emitting unit, a drive unit, a switch unit connected to a first control terminal of the drive unit, a voltage maintenance unit, a potential reset unit connected to a second control terminal of the drive unit, and a potential maintenance unit.