Precharge Circuit Stabilizes Luminosity Gradation in Display Devices
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Solution Overview
Problem
In light emitting device type displays, particularly those using organic electroluminescent devices, achieving stable luminosity gradation over time is challenging due to variations in device characteristics, such as channel resistance, which affect the light emitting drive current, leading to inadequate display image quality and inefficient gradation control as the number of pixels increases.
Innovation Solution
A display device employing a current application method with a precharge circuit to set the parasitic capacitance on data lines to a predetermined charged state, allowing for accurate gradation current supply and maintaining a non-light emitting state until the stored charge is used for light emission, thereby stabilizing the luminosity gradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of pixels is increased to improve display resolution, then display image quality is improved, but variations in device characteristics such as channel resistance increase leading to unstable luminosity gradation
Solution Approach 1:
The patent applies a precharge circuit to charge the parasitic capacitance on data lines to a predetermined voltage level before supplying gradation current to display pixels. This preliminary charging action ensures that when current is supplied, the voltage drop across parasitic capacitance does not cause insufficient write-in states, thereby maintaining stable luminosity gradation even as the number of pixels increases.
2Measurement precision
If the current application method is used to improve gradation control accuracy, then luminosity gradation precision is improved, but parasitic capacitance on data lines causes insufficient write-in states leading to display defects
Solution Approach 1:
The precharge circuit charges the parasitic capacitance on data lines to a predetermined voltage level before gradation current is supplied to display pixels. This preliminary charging ensures that the voltage drop across parasitic capacitance during current supply does not cause the voltage to fall below the threshold needed for proper pixel activation, thereby preventing insufficient write-in states while maintaining accurate gradation control.
3Productivity
If the scanning period is reduced to improve display refresh rate, then productivity is improved, but the time available for charging parasitic capacitance is reduced causing write-in deficiencies
Solution Approach 1:
The precharge circuit charges the parasitic capacitance on data lines to a predetermined voltage level before the scanning period begins. By performing this charging action in advance, the patent ensures that during the actual scanning and current supply phase, the parasitic capacitance does not cause voltage drops that would lead to write-in deficiencies, thereby maintaining write-in accuracy even with reduced scanning periods for higher refresh rates.
Data Source
AI summary
A display device which displays image information based on display data comprising a display panel having a plurality of signal lines and scanning lines with a plurality of display pixels containing current control type light emitting devices; a scan driver circuit applies a scanning signal to each of the scanning lines and sets the display pixels connected to the scanning lines in a selective state; a signal driver circuit generates gradation current based on the display data luminosity gradation component and supplies to the display pixels set in the selective state; a precharge circuit applies a precharge voltage to each signal line and sets a capacity component attached to each of the scanning lines in a predetermined charged state; and an operation control circuit controls setting of the light emitting devices in a non-light emitting state when the capacity component is set in a predetermined charged state.