Active Matrix OLED Drive Circuit Segmentation for Luminance Uniformity
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Solution Overview
Problem
Active-matrix organic EL display units face challenges in reducing the scale of the drive circuit, leading to high production costs and potential degradation in uniformity due to variations in threshold voltage and mobility of drive transistors, which necessitate complex and large-scale power line drive circuits.
Innovation Solution
The display unit incorporates a pixel circuit with specific transistor configurations and a drive circuit that includes a signal line drive circuit, a scan line drive circuit, and a control line drive circuit, where the control pulse is sequentially output for each unit to perform threshold voltage correction in the first half of a frame period, and the signal voltage is written in the second half, reducing the scale of the drive circuit by bundling control lines into units.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a control transistor is provided for each pixel to control the source voltage of the drive transistor, then the emission luminance uniformity is improved, but the scale of the drive circuit becomes large, leading to high production cost
Solution Approach 1:
The patent segments the control function by providing control transistors only at the intersection of control lines and scan lines, rather than at every pixel. This segmentation reduces the total number of control transistors while maintaining the ability to adjust source voltages for luminance uniformity correction.
Solution Approach 2:
The control transistor at each intersection serves multiple pixels by controlling the source voltage through the scan line to multiple drive transistors. This multi-functional approach allows a single control transistor to affect multiple pixels, reducing the overall circuit scale.
2Ease of operation
If pulse power controlling emission and extinction of the organic EL element is applied to the power line, then the emission luminance can be controlled, but the power line drive circuit has an extremely large scale, and accordingly the display panel has a large bezel
Solution Approach 1:
The patent extracts the power line drive circuit functionality and relocates it to the control transistor and control line. By using the control transistor to regulate source voltage from the power line, the complex power line drive circuit is eliminated, reducing the required bezel area for circuit placement.
Solution Approach 2:
The control transistor acts as an intermediary between the power line and the drive transistor. It receives power from the power line and provides controlled source voltage to the drive transistor, eliminating the need for a large-scale power line drive circuit.
3Manufacturing precision
If threshold voltage Vth or mobility of drive transistor varies across pixels, then the emission luminance fluctuates, but correction operation to reduce fluctuation increases the complexity of the drive circuit
Solution Approach 1:
The patent applies preliminary action by using the control transistor to adjust the source voltage of the drive transistor before the drive transistor operates. This preliminary voltage adjustment compensates for threshold voltage and mobility variations, enabling simple correction operations to achieve uniform emission luminance.
Data Source
AI summary
A display unit includes a display panel and a drive circuit, the display panel including pixels, each pixel including a light emitting element and a pixel circuit, wherein the pixel circuit includes a first transistor being configured to sample a voltage of a signal line, a second transistor being configured to control a current applied to the light emitting element, a third transistor being connected to the source of the second transistor, and a holding capacitor configured to hold the voltage sampled by the first transistor, the drive circuit being configured to, when pixel rows are grouped into units, sequentially perform correction of adjusting a gate-to-source voltage of the second transistor to be close to a threshold voltage of the second transistor for each of the units, being configured to sequentially output a fixed voltage to a source of the second transistor before performing the correction.