Pixel Circuit Digital-to-Analog Conversion for Display Uniformity
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Solution Overview
Problem
The challenge is to create a cost-effective driver for organic electroluminescent (EL) displays using low-temperature polysilicon TFTs, which have significant variations in threshold voltage and mobility, making it difficult to achieve uniform analog potential and requiring external correction circuits.
Innovation Solution
Incorporating a digital-to-analog (DA) conversion function within the pixel circuit, allowing the driver to be constructed solely with TFTs and eliminating the need for external driver ICs, by using a 6-bit DAC built-in pixel circuit with specific transistor and capacitance configurations that correct for threshold and mobility variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If low-temperature polysilicon TFT is used to drive organic EL elements, then production cost is reduced and device size can be increased, but threshold voltage and mobility characteristics become significantly variable requiring correction circuits
Solution Approach 1:
The pixel circuit performs self-correction of threshold voltage variations through automatic adjustment mechanisms. The circuit autonomously compensates for Vth variations without requiring external correction circuits, allowing low-temperature polysilicon TFT to be used while maintaining display uniformity.
Solution Approach 2:
The pixel circuit incorporates feedback mechanisms that monitor and adjust for threshold voltage variations in real-time. This feedback system enables the circuit to compensate for manufacturing variations in low-temperature polysilicon TFT characteristics.
2Ease of manufacture
If low-temperature polysilicon TFT is used in driver circuits, then external driver ICs can be eliminated for cost reduction, but uniform analog potential cannot be achieved due to characteristic variations
Solution Approach 1:
The pixel circuit performs self-correction of threshold voltage variations through automatic adjustment mechanisms. The circuit autonomously compensates for Vth variations without requiring external correction circuits, allowing low-temperature polysilicon TFT to be used while maintaining display uniformity.
Solution Approach 2:
The correction function is extracted from external driver ICs and integrated directly into the pixel circuit. This eliminates the need for external correction circuits while maintaining the ability to compensate for threshold voltage variations.
3Manufacturing precision
If correction circuits are introduced within pixels to correct Vth variations, then display uniformity is improved, but pixel circuit complexity increases
Solution Approach 1:
The correction circuit functions are merged with the basic pixel circuit components. By combining the correction functionality with existing transistors and capacitors in the pixel, the overall circuit complexity is minimized while achieving display uniformity.
Solution Approach 2:
Existing pixel circuit components are designed to serve multiple functions - both basic pixel operation and threshold voltage correction. This multi-functionality reduces the need for additional dedicated correction components.
Data Source
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AI summary
[Problem to be solved] Obtain a constitution for a data driver which does not easily affected by transistor characteristics. [Solution] A plurality of coupling capacitances 7 is connected to data enable lines which is equipped to at least two set potentials. A plurality of bit transistors 6 which is turned on and off in accordance with the display data of a plurality of bits controls the relation of connection between a plurality of coupling capacitances and data enable lines to control the total capacitance of the said plurality of coupling capacitances. Display element operates in accordance with the voltage accumulated to the total capacitance of the said coupling capacitance according to the difference between the two set potentials equipped to the data enable line. By the operations above, a display is controlled by multi-bit display data per each pixel.