OLED Pixel Circuit with Voltage Correction for Image Retention
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Solution Overview
Problem
Organic light-emitting diode (OLED) display devices suffer from image retention, also known as ghosting, due to variations in the threshold voltage and charge mobility of driving transistors, leading to inconsistent light emission and hysteresis effects.
Innovation Solution
A pixel circuit is designed with a driving transistor, storage capacitor, and a capacitor with a resistor to correct the voltage applied to the driving transistor, adjusting the data signal to minimize the transient response characteristic and reduce image retention by optimizing the capacitance ratio and time constant.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a driving transistor is used to control light emission in OLED pixels, then the display achieves low power consumption and high contrast ratio, but variations in threshold voltage and charge mobility cause image retention and ghosting
Solution Approach 1:
The pixel circuit performs preliminary correction of the data signal voltage before it is applied to the driving transistor. The correction circuit adjusts the voltage based on the hysteresis characteristic of the driving transistor, compensating for threshold voltage variations before they cause image retention. This preliminary action prevents the ghosting effect from occurring in the first place.
Solution Approach 2:
The circuit incorporates feedback mechanisms where the corrected voltage is stored in a storage capacitor and used to control the driving transistor. The correction amount is determined based on the relationship between the data signal voltage and the hysteresis characteristic, creating a feedback loop that compensates for transistor variations and reduces image retention.
2Speed
If the gate-source voltage of the driving transistor changes rapidly, then the response speed of the pixel circuit is improved, but the hysteresis effect causes different drain current flows and transient response, leading to ghosting
Solution Approach 1:
The correction circuit applies a preliminary counteracting voltage adjustment to compensate for the hysteresis effect before the gate-source voltage changes cause harmful drain current variations. By correcting the data signal voltage in advance based on the hysteresis characteristic, the circuit prevents the transient response that leads to ghosting while maintaining rapid voltage changes for fast response.
Solution Approach 2:
The circuit changes the voltage parameter of the data signal through correction based on the hysteresis characteristic. By adjusting the voltage to account for the non-linear drain current response, the circuit maintains fast response speed while eliminating the parameter variations that cause ghosting images.
3Reliability
If a correction circuit is added to compensate for threshold voltage variations, then image retention is reduced, but the device complexity increases
Solution Approach 1:
The correction circuit is integrated into the existing pixel circuit structure, merging the correction function with the driving transistor control. By combining multiple functions (data signal transmission, voltage correction, and driving control) into a unified circuit architecture, the patent reduces overall complexity while maintaining effective compensation for threshold voltage variations and hysteresis effects.
Solution Approach 2:
The pixel circuit is designed with multi-functional components that serve multiple purposes. The storage capacitor both stores the corrected voltage for driving the transistor and acts as part of the correction mechanism. The first switching transistor both transmits the data signal and enables the correction function, reducing the need for separate dedicated components and simplifying the overall circuit.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces image retention to near zero, improving the display's image quality by controlling the driving current and minimizing the intensity of ghosting, thereby enhancing the overall performance of OLED display devices.
Implementation Method 1
a storage capacitor configured to receive the signal from the first switching transistor and store a voltage to be applied to the gate of the driving transistor
Implementation Method 2
This is caused by hysteresis effect of the driving transistors. The hysteresis effect causes a phenomenon in a field-effect transistor that the drain current flows differently between the case where the gate-source voltage changes from a high voltage to a low voltage and the case where the gate-source voltage changes from the low voltage to the high voltage.
Data Source
AI summary
A pixel circuit for controlling driving current for a light-emitting element is disclosed. The pixel circuit includes a driving transistor configured to supply driving current to the light-emitting element, a first switching transistor configured to transmit a data signal corresponding to the driving current, a storage capacitor configured to receive the signal from the first switching transistor and store a voltage to be applied to a gate of the driving transistor, a second switching transistor configured to correct the voltage to be stored to the storage capacitor, and a first capacitor including an electrode connected with a drain of the driving transistor and an electrode to be supplied with a predetermined potential.