Source Driver Overdrive Voltage Compensation for LCD Brightness
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Solution Overview
Problem
Conventional overdrive methods for liquid crystal display (LCD) panels are ineffective for high gray level codes due to limitations in maximum gray level data, resulting in reduced image quality and unsatisfactory brightness variation.
Innovation Solution
A novel overdrive method that drives the source line with a normal high voltage or a lower voltage in a first cycle, followed by the same high voltage in a second cycle, and an overdrive voltage greater than the normal high voltage in subsequent cycles, performed in the gamma voltage domain to overcome the limitations of the gray level domain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional overdrive methods modify the gray level code to a value further from the previous gray level code, then the source line is driven to a higher voltage level, but the overdrive performance is unsatisfactory when the original gray level code approximates its maximum value due to the limitation of maximum gray level data
Solution Approach 1:
The patent transitions from operating solely in the gray level domain to incorporating a voltage domain approach. By introducing an overdrive voltage that exceeds the normal maximum voltage corresponding to the maximum gray level code, the system adds a new dimension (voltage headroom) to overcome the limitation of maximum gray level data. This allows effective overdrive compensation even when the original gray level code is already at or near its maximum value.
2Productivity
If the gray level code changes from the minimum code L0 to the maximum code L255, then the overdrive operation requires a higher code, but the overdrive processing device can only output the code L255 in maximum, hence the overdrive compensation for high gray level codes may not be effective
Solution Approach 1:
The patent segments the voltage generation process into two distinct parts: a normal voltage generation section that handles standard gray level codes (L0 to L255), and an overdrive voltage generation section that generates an overdrive voltage exceeding the normal maximum voltage. This segmentation allows each section to be optimized independently, with the overdrive section providing the necessary voltage headroom without complicating the normal operation.
3Ease of manufacture
If amorphous silicon thin-film transistor (TFT) LCD panels are used, then the mobility is lower, but the insufficient charging problem becomes more serious
Solution Approach 1:
The patent applies preliminary action by using an overdrive voltage in the initial stage of charging to rapidly charge the liquid crystal capacitor. The overdrive voltage, being higher than the normal maximum voltage, provides a stronger electric field that accelerates the charging process. After the initial overdrive phase, the system transitions to the normal voltage for maintaining the charge, thus achieving both fast charging and stable operation.
Data Source
AI summary
The present invention discloses a driving method for a source driver, for driving a source line of a display panel. The driving method includes the steps of: driving the source line with a first voltage or a second voltage smaller than the first voltage in a first driving cycle; driving the source line with the first voltage in a second driving cycle next to the first driving cycle when the source line is driven with the first voltage in the first driving cycle; and driving the source line with an overdrive voltage in the second driving cycle when the source line is driven with the second voltage in the first driving cycle. The first voltage is a normal high voltage of the display panel, and the overdrive voltage is greater than the normal high voltage.