Semiconductor Device Precharge Circuit for OLED Signal Writing Speed
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Solution Overview
Problem
The parasitic capacitance in wiring for semiconductor devices using organic light emitting diodes (OLEDs) leads to slow signal writing speeds due to large time constants, especially when signal currents are small, and existing solutions are complex and inefficient.
Innovation Solution
A semiconductor device with a circuit that supplies an optimal voltage precharge to pixels, utilizing a video voltage signal line, voltage control switches, current source circuits, and current control switches to control gate-source and drain-source voltages, improving signal writing speed by reducing transistor characteristic variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a current-driven type light emitting element is used in an active matrix display device, then luminance can be controlled by current, but signal writing speed becomes slow due to large parasitic capacitance in wiring
Solution Approach 1:
The patent applies preliminary action by pre-charging the signal line to an optimal voltage level before writing the signal current. The voltage control switch charges the parasitic capacitance of the signal line in advance, so when the current control switch closes to write the signal current, the charging time constant is significantly reduced, thereby improving signal writing speed while maintaining luminance control capability
2Loss of energy
If signal current is reduced to improve display accuracy, then power consumption decreases, but signal writing speed becomes even slower due to larger time constant
Solution Approach 1:
The patent resolves this contradiction by pre-charging the signal line voltage before current writing. The voltage control switch operates in advance to charge the parasitic capacitance to an optimal level, which reduces the charging time constant. This allows small signal currents (low power consumption) to be written quickly, simultaneously achieving low power consumption and high signal writing speed
3Stability of the object's composition
If existing circuit configurations are used to prevent current variation due to TFT characteristics, then luminance variation is suppressed, but circuit complexity increases
Solution Approach 1:
The patent applies parameter changes by controlling the voltage level (pre-charging to optimal voltage) rather than using complex circuit configurations. By changing the voltage parameter of the signal line before current writing, the patent achieves current stability and suppresses luminance variation due to TFT characteristics, while maintaining simple circuit structure with fewer components
Data Source
AI summary
A semiconductor device which can supply an accurate current without being affected by the variation of transistors for supplying currents to EL pixels even when the signal current is small is provided. A video signal voltage is inputted to each signal line dot-sequentially. This operation corresponds to a precharge operation to a video signal current which is inputted subsequently. After the input of the video signal voltage, a video signal current is inputted to each signal line. Accordingly, an effect of variation of a transistor in each pixel can be reduced. In addition, since a video signal voltage is inputted prior to the input of a video signal current, signal writing speed can be increased even when the signal current is small. Further, as a video signal voltage is inputted dot-sequentially, simple configuration can be realized.