OLED Pixel Driving Circuit for Threshold and Mobility Compensation
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Solution Overview
Problem
In organic electroluminescent (OLED) displays, variations in transistor mobility and threshold voltage lead to image unevenness, complicating driving methods and increasing power consumption, while current compensation techniques are insufficient and often require separate circuits for pixel and signal line drivers, increasing costs and potential for contact failures.
Innovation Solution
A driving method for semiconductor devices using a transistor with a switch and capacitor to hold and discharge voltages, allowing for efficient current supply to OLED elements, enabling compensation of mobility and threshold voltage variations within a single substrate and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate circuits are used for pixel and signal line drivers to compensate for transistor variations, then compensation accuracy is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent combines the pixel driver circuit and signal line driver circuit into a single integrated circuit structure. The transistor variation compensation function is merged with the signal driving function, eliminating the need for separate compensation circuits while maintaining compensation accuracy through unified control mechanisms.
Solution Approach 2:
The driver circuit is designed to perform multiple functions simultaneously: it drives the OLED pixels, compensates for transistor variations, and controls signal timing all within a single circuit architecture. This multi-functional design reduces overall device complexity while maintaining the precision benefits of dedicated compensation circuits.
2Loss of time
If mobility compensation is performed during image signal input period, then compensation time is reduced, but compensation accuracy deteriorates due to waveform distortion
Solution Approach 1:
The circuit performs preliminary compensation actions by pre-charging capacitors and pre-positioning voltages before the actual image signal is fully input. This allows mobility compensation to begin in advance, reducing the time needed during the critical image input period while avoiding waveform distortion issues.
Solution Approach 2:
The driver circuit implements periodic charging and discharging cycles of capacitors that are synchronized with the image signal input. These periodic actions create distinct time phases where compensation can occur without interfering with the image signal waveform, allowing both speed and accuracy requirements to be met.
3Productivity
If one gate selection period is used for both image signal input and mobility compensation, then productivity is improved, but manufacturing precision deteriorates due to insufficient process time
Solution Approach 1:
The patent introduces an additional temporal dimension by implementing multiple sub-phases within the gate selection period. Instead of performing all operations sequentially in a single dimension of time, the circuit uses overlapping voltage charging phases, compensation phases, and signal input phases that occur in different temporal layers, effectively increasing the available process time without reducing productivity.
Solution Approach 2:
The gate selection period is segmented into multiple distinct operational phases: a first period for capacitor charging, a second period for voltage holding and compensation, and a third period for image signal input. This segmentation allows each process to be optimized independently with sufficient time allocation, maintaining both high productivity and precise compensation.
Data Source
AI summary
To provide a method for driving a semiconductor device, by which influence of variation in threshold voltage and mobility of transistors can be reduced. The semiconductor device includes an n-channel transistor, a switch for controlling electrical connection between a gate and a first terminal of the transistor, a capacitor electrically connected between the gate and a second terminal of the transistor, and a display element. The method has a first period for holding the sum of a voltage corresponding to the threshold voltage of the transistor and an image signal voltage in the capacitor; a second period for turning on the switch so that electric charge held in the capacitor in accordance with the sum of the image signal voltage and the threshold voltage is discharged through the transistor; and a third period for supplying a current to the display element through the transistor after the second period.