OLED Pixel Circuit Penetration Current Blocking
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Solution Overview
Problem
Active-matrix organic light-emitting diode (OLED) displays face issues with power efficiency due to penetration currents flowing during non-luminous periods, leading to increased power consumption and reduced luminance uniformity across pixels due to variations in transistor mobility and threshold voltage.
Innovation Solution
The display apparatus incorporates a pixel circuit with a sampling transistor, a driving transistor, a switching transistor, and a holding capacitor, where the switching transistor is used to connect the output current terminal to a fixed potential during non-luminous periods, and the sampling transistor applies an OFF voltage to the driving transistor to prevent penetration currents, allowing for mobility and threshold voltage corrections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the switching transistor is used to connect the output current terminal to a fixed potential during non-luminous periods, then penetration currents are blocked and power consumption is reduced, but device complexity increases due to additional switching components
Solution Approach 1:
The pixel circuit is segmented into distinct functional blocks: a driving transistor for current control, a switching transistor for penetration current blocking, and a holding capacitor for voltage storage. This segmentation allows each component to perform its specific function efficiently, with the switching transistor isolated to only block penetration currents during non-luminous periods without interfering with the driving transistor's operation.
Solution Approach 2:
The switching transistor is activated in advance during non-luminous periods to connect the output current terminal to a fixed potential before penetration currents can flow. This preliminary action prevents the harmful current flow from occurring in the first place, thereby reducing power consumption without requiring complex real-time detection systems.
2Manufacturing precision
If the sampling transistor applies OFF voltage to the driving transistor to prevent penetration currents, then luminance uniformity is maintained, but manufacturing precision requirements increase due to additional voltage control mechanisms
Solution Approach 1:
The sampling transistor implements a feedback mechanism by monitoring the driving transistor's state and applying OFF voltage when penetration currents are detected. This feedback loop ensures that the driving transistor is properly controlled to maintain uniform luminance across all pixels, compensating for variations in transistor characteristics without requiring extremely tight manufacturing tolerances.
Solution Approach 2:
The system dynamically changes the voltage parameter applied to the driving transistor by the sampling transistor. During normal operation, the driving transistor receives its standard control voltage, but when penetration currents occur, the sampling transistor applies an OFF voltage to shut it down. This parameter change allows the system to adapt to manufacturing variations and maintain luminance uniformity.
3Measurement precision
If mobility and threshold voltage corrections are implemented, then current control accuracy is improved, but device complexity increases due to additional correction circuits
Solution Approach 1:
The mobility correction and threshold voltage correction functions are merged into the existing pixel circuit structure. The holding capacitor serves dual purposes: storing the display voltage and facilitating correction operations. The sampling transistor performs both sampling and correction functions, eliminating the need for separate correction circuits and reducing overall device complexity while maintaining current control accuracy.
Solution Approach 2:
The sampling transistor is designed with multi-functionality, serving as both a sampling element during normal display operation and as a correction element during non-luminous periods. It can apply different voltages (display voltage or OFF voltage) based on operational requirements, thereby implementing both mobility and threshold voltage corrections without requiring dedicated correction transistors or circuits.
Data Source
AI summary
A display apparatus includes: a pixel array section including a row of scanning lines, a column of signal lines, and pixels in a matrix, each of the pixels disposed at an intersection of both of the lines; and a drive section. The drive section performs line progressive scanning on the pixels. The pixel includes a light emitting device, a sampling transistor, a driving transistor, a switching transistor, and a holding capacitor. The sampling transistor samples a video signal in the holding capacitor, the driving transistor changes the device to a luminous state, the switching transistor becomes ON in advance of the sampling of the video signal to change the light emitting device to a non-luminous state, and the sampling transistor takes in the OFF voltage from the signal line to the driving transistor, thereby preventing a penetration current from flowing from the power source toward the fixed potential.