Active-Matrix Light-Emitting Device Scanning Line Drive Capability
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Solution Overview
Problem
Active-matrix-type light-emitting devices experience a decrease in contrast during black display due to unnecessary current flow, known as 'black float,' caused by a large instantaneous leak current, which results in increased black levels and reduced image quality.
Innovation Solution
The solution involves setting a lower current drive capability for the second scanning line in the pixel circuit, achieved by adjusting the size and channel conductance of transistors in the output buffers and optionally using a resistor, to reduce the coupling current that flows through the parasitic capacitance of the emission control transistor, thereby suppressing the increase in black level without complicating the circuit configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the current drive capability of the second scanning line is reduced to suppress coupling current, then black float is reduced and contrast is improved, but the switching speed and response time of the emission control transistor may be degraded
Solution Approach 1:
The patent applies parameter changes by adjusting the channel conductance of the transistor in the output buffer to a specific range (0.5 to 2.0 times the channel conductance of transistors in other output buffers). This optimized parameter range allows the transistor to provide sufficient drive capability for fast switching while simultaneously limiting the coupling current to prevent black float, thus resolving the contradiction between switching speed and contrast
Solution Approach 2:
The patent implements dynamic control by making the channel conductance of the second scanning line's output buffer transistor adjustable or variable during operation. This allows the system to optimize the balance between switching speed and coupling current suppression based on operational requirements, enabling fast switching when needed while maintaining low contrast degradation during normal operation
2Object-affected harmful factors
If the channel conductance of transistors in the output buffer is adjusted to reduce coupling current, then black level increase is suppressed, but the drive capability for other scanning lines may be affected
Solution Approach 1:
The patent applies local quality by differentiating the transistor channel conductance for the second scanning line from that of other scanning lines. Specifically, the transistor in the second scanning line's output buffer has a channel conductance within 0.5 to 2.0 times that of other output buffer transistors, creating a localized modification that targets coupling current suppression without impacting the drive capability of other scanning lines
Solution Approach 2:
The patent segments the output buffer circuitry by creating distinct transistor configurations for different scanning lines. The second scanning line's output buffer uses transistors with specifically adjusted channel conductance, separating the function of this scanning line from others and allowing independent optimization of coupling current suppression without affecting overall system performance
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 approach effectively reduces the instantaneous coupling current, preventing a significant increase in black level and maintaining image quality by ensuring that the contrast is not compromised, even in highly integrated light-emitting devices.
Implementation Method 1
a large instantaneous leak current, which results in an increase in a black level... a changed component of an electric potential of the second scanning line leaks to a light-emitting element through a parasitic capacitance between a gate and a source of an emission control transistor
Data Source
AI summary
An active-matrix-type light-emitting device includes: a pixel circuit including a light-emitting element, a driving transistor that drives the light-emitting element, a holding capacitor whose one end is connected to the driving transistor and which stores electric charges corresponding to written data, at least a control transistor that controls an operation associated with writing of data into the holding capacitor, and an emission control transistor; a first scanning line for controlling ON/OFF of the control transistor and a second scanning line for controlling ON/OFF of the emission control transistor; a data line through which the written data is transmitted to the pixel circuit; and a scanning line driving circuit which drives the first and second scanning lines and in which a current drive capability associated with the second scanning line is set to be lower than a current drive capability associated with the first scanning line.