OLED Pixel Circuit Driving Method for Gray Scale Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional OLED pixel circuits face challenges in accurately controlling gray scale due to noise, leakage current, and characteristic deviations, especially at low gray scale levels, leading to errors and increased complexity in circuit design.
Innovation Solution
A pixel circuit driving method that combines pulse amplitude modulation (PAM) and pulse width modulation (PWM) signals, applying PAM signals with multiple levels to a transistor and using PWM signals with fewer sub-frames to control the operation of a light-emitting element, reducing the number of components and simplifying the circuit configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PAM driving method is used to control OLED current by adjusting voltage strength, then gray scale control is achieved, but the voltage difference becomes vulnerable to noise, characteristic deviation, and leakage current especially at low gray scale levels
Solution Approach 1:
The patent divides the frame period into multiple sub-frames with different emission times, where each sub-frame corresponds to a specific gray scale level. By segmenting the driving waveform into distinct time intervals (e.g., first sub-frame with longer emission time for low gray scale, second sub-frame with shorter emission time for high gray scale), the system achieves precise gray scale control without relying on vulnerable voltage differences, thereby improving both measurement precision and reliability
Solution Approach 2:
The patent changes the emission time parameter of the driving waveform across different sub-frames to control gray scale levels. Instead of adjusting voltage strength (PAM), the system varies the duration of the emission period (e.g., first emission time for low gray scale, second emission time for high gray scale), making the control mechanism more robust against noise and characteristic deviation while maintaining precision
2Measurement precision
If conventional PWM driving circuit with multiple transistors and capacitors is used, then gray scale expression is achieved, but the circuit complexity increases and compensation for light-emitting element deviation becomes difficult
Solution Approach 1:
The patent extracts and eliminates unnecessary circuit components from the conventional PWM driving circuit. By using a simplified driving waveform generation approach that relies on time-multiplexed sub-frames rather than multiple transistors and capacitors, the system maintains gray scale expression accuracy while significantly reducing circuit complexity and removing the need for complex compensation circuits
Solution Approach 2:
The patent makes the driving transistor serve multiple functions: it acts as both a switch for PWM control and a current source for driving the light-emitting element. This multi-functionality eliminates the need for separate compensation circuits and additional transistors, reducing overall circuit complexity while maintaining the ability to express multiple gray scale levels through different emission time patterns
3Measurement precision
If 8-bit sub-frames are used to express 256 gray scale levels, then comprehensive gray scale coverage is achieved, but the number of sub-frames increases and implementation becomes difficult
Solution Approach 1:
The patent uses a reduced number of sub-frames (e.g., 6 sub-frames) with varying emission times to express gray scale levels, rather than using all 8-bit sub-frames. By applying partial action (using fewer sub-frames than the maximum possible), the system achieves sufficient gray scale coverage for practical applications while significantly reducing implementation complexity and making the system more manageable
Data Source
AI summary
A pixel circuit driving method of controlling an operation of a light-emitting element provided in a pixel of a display panel may comprise: applying pulse amplitude modulation (PAM) signals having a plurality of levels to a first terminal of a first transistor having a second terminal connected to a control terminal of a second transistor configured to drive the light-emitting element with a current according to a gray scale required for the light-emitting element; and applying a PAM signal of any one level selected from the PAM signals to the control terminal of the second transistor during each sub-frame time corresponding to a turn-on time of the first transistor controlled by a pulse width modulation (PWM) signal having a plurality of sub-frames in a single frame according to the gray scale.