Pixel Circuit Anode Voltage Dropping for Deep Black OLED
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Solution Overview
Problem
Organic light emitting display apparatuses face issues with luminance non-uniformity and inability to achieve deep black due to variations in electrical characteristics and degradation of driving transistors, leading to residual images and increased power consumption.
Innovation Solution
A display apparatus with a pixel circuit that includes a driving transistor, data supply transistor, light emitting control transistors, and capacitors, where the voltage of the anode electrode is dropped to the threshold voltage or lower when the data voltage reaches a minimum value, preventing light emission by synchronizing with the falling time of the scan signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the data voltage is reduced to minimum value to prevent light emission, then power consumption is reduced, but the voltage of anode electrode remains larger than threshold voltage causing slight light emission and inability to achieve deep black
Solution Approach 1:
The patent applies preliminary action by dropping the anode electrode voltage to threshold voltage or lower in synchronization with the falling time of scan signal before the light emitting device would otherwise emit light. This preemptive voltage reduction prevents light emission during minimum data voltage periods, achieving deep black without compromising data voltage margin for subsequent operations.
2Illumination intensity
If the gate-source voltage of driving transistor is reduced to realize deep black, then light emission is prevented, but data voltage margin is reduced
Solution Approach 1:
The patent applies local quality by selectively dropping the voltage of the anode electrode (second node) to threshold voltage or lower only during specific timing conditions when data voltage has minimum value, while maintaining normal voltage levels during other periods. This localized voltage control achieves deep black precisely when needed without affecting data voltage margin during normal operation.
Solution Approach 2:
The voltage dropping operation is performed in synchronization with the falling time of scan signal, which is a preliminary action before the light emitting device would emit light. This timing ensures deep black is achieved without compromising the data voltage margin required for subsequent data writing and display operations.
3Adaptability or versatility
If the voltage of anode electrode is maintained at normal level, then data voltage margin is secured, but light emission occurs even at minimum data voltage preventing deep black
Solution Approach 1:
The patent implements periodic action by rhythmically dropping and restoring the anode electrode voltage in synchronization with the scan signal cycles. During minimum data voltage periods, the voltage is dropped to prevent light emission, while during normal periods it is restored to maintain data voltage margin. This periodic voltage modulation resolves the contradiction between preventing light emission and maintaining voltage margin.
Data Source
AI summary
A display apparatus includes a plurality of pixels configured to display an image, wherein the plurality of pixels is configured to be driven through a plurality of signals according to an initialization period, a programming period, a sampling period, and an emission period. The signals include a first scan signal having a high level in the initialization period and the sampling period, and having a low level in the programming period and the emission period; a second scan signal having a high level in the programming period and the sampling period, and having a low level in the initialization period and the emission period; and a voltage of a first electrode being dropped in synchronization with a falling time of the first scan signal of the initialization period.