Electro-optic Device Driving Method Threshold Compensation
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Solution Overview
Problem
In electro-optic devices, such as organic electroluminescence (EL) displays, variations in threshold voltage of driving transistors lead to uneven gradation in display images due to differences in transistor characteristics, causing issues with current control and light emission.
Innovation Solution
A driving method that initializes the gate voltage of a driving transistor by using first and second transistors connected in series between the drain and gate, with a capacity element to hold the voltage, compensating for the threshold voltage and controlling the light-emitting operation by adjusting the transistors' states to reduce kickback influence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a current light-emitting element is used to emit light based on supplied current intensity, then light emission control is achieved, but display uniformity deteriorates due to threshold voltage variations in driving transistors
Solution Approach 1:
The patent divides the single transistor control function into multiple transistors (first transistor connected to drain, second transistor connected to gate) that work together in a coordinated sequence. This segmentation allows independent control of different voltage phases, enabling threshold voltage compensation while maintaining light emission control, thus resolving the contradiction between illumination control and display uniformity.
Solution Approach 2:
The patent applies preliminary action by performing threshold voltage compensation before the light-emitting operation. The first transistor is turned on during a data write operation to compensate for threshold voltage variations, and the compensated voltage is stored in a capacitance element before the actual light emission occurs. This preliminary compensation ensures uniformity is established before illumination, resolving the contradiction.
2Ease of operation
If a driving transistor is used to control gradation by supplying voltage signals to the gate, then light emission control is achieved, but threshold voltage changes cause gradation unevenness
Solution Approach 1:
The patent implements feedback by using the first transistor to sense and compensate for threshold voltage variations in the driving transistor. The compensation mechanism monitors the actual threshold voltage through the transistor's electrical characteristics and adjusts the gate voltage accordingly, creating a feedback loop that maintains gradation uniformity despite threshold voltage changes, thus resolving the contradiction between ease of operation and gradation uniformity.
3Productivity
If transistors are turned on and off during data write operation, then data signaling is achieved, but kickback voltage variations occur
Solution Approach 1:
The patent applies preliminary anti-action by turning off the second transistor (connected to the gate) before turning off the first transistor (connected to the drain). This sequential switching order prevents kickback voltage from coupling into the gate node, as the gate is already isolated when the drain switching occurs. This preliminary protective action eliminates the harmful kickback effect while maintaining fast data write speeds, resolving the contradiction between productivity and harmful voltage variations.
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
This method improves display uniformity by reducing variations in the driving voltage of the driving transistor, minimizing the impact of kickback and ensuring consistent light emission across the display.
Implementation Method 1
a voltage is provided to a capacity element connected to the gate of the driving transistor to hold a voltage of the compensated data signal as a gate voltage
Data Source
AI summary
A driving method of an electro-optic device includes initializing a gate voltage of a driving transistor; and performing a data write operation where a threshold voltage of the driving transistor is compensated by turning on a first transistor and a second transistor connected in series between a drain and a gate of the driving transistor and a voltage is provided to a capacity element connected to the gate of the driving transistor to hold a voltage of the compensated data signal as a gate voltage. The first transistor is at a drain side of the driving transistor and the second transistor is between the first transistor and a gate side of the driving transistor. When the data write operation ends, the second transistor is first turned off and, subsequently, the first transistor is turned off. The second transistor is again turned on after the first transistor is turned off.