OLED Data Driver Precharge DAC for Faster Gray Scale Charging
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Solution Overview
Problem
Conventional organic light emitting displays experience low driving speed due to the time required for voltage division using resistors, which can result in insufficient charging of pixels within the required horizontal period, leading to reduced image brightness and precision in gray scale levels.
Innovation Solution
The implementation of a data driver circuit that includes a second DAC with a ninth switch to initially charge pixels with a reference voltage directly, bypassing voltage dividing resistors, and the use of a capacitor to rapidly generate intermediate gray scale voltages, enhancing charging speed and precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage division using resistors is used to generate gray scale voltages, then the voltage can be divided into multiple levels, but the driving speed is reduced due to the time required for voltage division
Solution Approach 1:
The patent applies preliminary action by pre-charging the pixel electrodes to an initial voltage level (e.g., ELVDD or ELVSS) before the actual gray scale voltage is applied. This pre-charging step prepares the pixel in advance, so that when the final gray scale voltage is applied through the switch, the voltage transition occurs more rapidly. The pixel is already at a known voltage state, reducing the time needed for voltage division and charging, thus resolving the contradiction between gray scale precision and driving speed.
2Manufacturing precision
If voltage division using resistors is used, then intermediate gray scale voltages can be generated, but the charging time of pixels becomes insufficient within the horizontal period
Solution Approach 1:
The patent pre-charges the pixel electrodes to an initial voltage level before applying the final gray scale voltage. This preliminary charging action ensures that the pixel is ready to receive the precise gray scale voltage quickly, reducing the charging time within the horizontal period while maintaining gray scale precision.
Solution Approach 2:
The patent segments the voltage application process into two distinct phases: (1) pre-charging phase where the pixel is charged to an initial voltage level through a dedicated pre-charge switch, and (2) gray scale voltage application phase where the precise gray scale voltage is applied through the DAC switch. This segmentation allows each phase to be optimized independently, ensuring both precision and timing requirements are met.
3Measurement precision
If conventional DAC circuit with voltage dividing resistors is used, then gray scale voltages can be generated, but the image brightness is reduced due to insufficient pixel charging
Solution Approach 1:
The patent pre-charges the pixel electrodes to an initial voltage level before applying the gray scale voltage. This preliminary action ensures that the pixel reaches its final voltage level faster, allowing sufficient charging within the horizontal period, which maintains image brightness while preserving gray scale precision.
Solution Approach 2:
The patent changes the voltage parameter of the pixel by applying a pre-charge voltage (ELVDD or ELVSS) before the gray scale voltage. This parameter change approach ensures that the pixel is already at a high voltage level, reducing the voltage difference that needs to be charged, thereby maintaining image brightness while achieving precise gray scale control.
Data Source
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AI summary
A data driver, including a first digital-to-analog converter configured to select two reference voltages of a plurality of reference voltages depending on upper bits of data, and a second digital-to-analog converter configured to divide the two reference voltages into a plurality of voltages and supply any one voltage of the two reference voltages and the divided voltages to an output terminal as a data signal depending on lower bits of the data, wherein the second digital-to-analog converter is configured to supply an intermediate gray scale voltage to the output terminal prior to supplying the data signal, the intermediate gray scale voltage having a voltage between the two reference voltages.