OLED Pixel Circuit Threshold Voltage Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Organic LED displays face issues with uneven brightness due to threshold voltage variations in driving transistors, which are exacerbated by increasing resolution and shorter scan times, necessitating a solution for compensation within limited scan time.
Innovation Solution
A pixel circuit comprising specific transistors and capacitors, along with a driving method that adjusts control signals to compensate for threshold voltage variations, ensuring even brightness and improved display quality in high-resolution environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the resolution of the display is increased, then the display quality is improved, but the scan time of the scan driver decreases and the number of scan signal lines increases
Solution Approach 1:
The pixel circuit is divided into multiple functional modules: a compensation module (including first and second transistors, first and second capacitors) that operates during a compensation period to compensate for threshold voltage, and a display module (including third and fourth transistors, third capacitor, and light emitting element) that operates during a display period. This temporal segmentation allows compensation operations to be completed before the display period, enabling high-resolution displays to be scanned within limited time while maintaining uniform brightness.
2Device complexity
If the threshold voltage variation of transistors is not compensated, then the circuit is simple, but the brightness of organic LEDs becomes uneven
Solution Approach 1:
The compensation module performs threshold voltage compensation in advance during a compensation period before the display period begins. The first transistor and first capacitor measure the threshold voltage of the second transistor, and the second transistor and second capacitor store the compensation value. This preliminary action ensures that when the display period starts, the threshold voltage variation has already been compensated, achieving uniform brightness without adding excessive complexity to the overall circuit operation.
Solution Approach 2:
The compensation module acts as an intermediary between the data signal input and the light emitting element. It includes a first transistor and first capacitor that measure the threshold voltage of the driving transistor, and a second transistor and second capacitor that store the compensation value. This intermediary module isolates the threshold voltage variation effect from the display output, enabling uniform brightness while keeping the main display circuit relatively simple.
3Reliability
If the scan time is extended to complete compensation operations, then the threshold voltage variation is compensated, but the scan speed decreases and productivity is reduced
Solution Approach 1:
The pixel circuit operates in periodic cycles consisting of a compensation period followed by a display period. During the compensation period, the compensation module actively measures and stores the threshold voltage compensation value. During the display period, the stored compensation value is used to drive the light emitting element uniformly. This periodic action allows complete compensation operations to be performed within each frame cycle without extending the overall scan time, maintaining high scan speed and productivity.
Data Source
AI summary
A pixel circuit of a light emitting diode display includes a light emitting diode, six transistors and two capacitors. The effect of the variation of the threshold voltage of the transistor in the pixel circuit on the display quality can be improved through supplying specific the first to fourth control signals and the first to third reference voltages to the pixel circuit. A light emitting diode display using the aforementioned pixel circuit and a driving method of the aforementioned pixel circuit are also provided.