Display Driver Duty Ratio Adjustment for Electrode Capacitance
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Solution Overview
Problem
In liquid crystal panel driving, the increase in capacitive load due to larger segment electrodes results in reduced effective voltage, leading to display failures and inconsistent transmittance, as existing techniques fail to account for differences in capacitive load, causing issues with tone display and liquid crystal control across varying electrode areas.
Innovation Solution
A display driver with separate drive terminals and circuits for segment electrodes of different sizes, adjusting duty ratios to maintain consistent effective voltage across electrodes, allowing for the same transmittance and contrast across icons and liquid crystal shutters with varying areas, using a single power supply voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If PWM drive signals with the same duty ratio are applied to segment electrodes of different areas, then the drive circuit is simple, but the effective voltage decreases for larger electrodes causing display failure
Solution Approach 1:
The patent applies different duty ratios to segment electrodes based on their individual area characteristics. The drive circuit identifies the area of each segment electrode and adjusts the duty ratio accordingly, allowing larger electrodes to receive higher duty ratios and thus maintain sufficient effective voltage, while smaller electrodes receive lower duty ratios. This local differentiation resolves the contradiction by tailoring the drive signal to each electrode's specific needs rather than applying a uniform approach.
2Area of stationary object
If the area of segment electrodes is increased, then the display coverage is improved, but the capacitive load increases causing effective voltage to decrease
Solution Approach 1:
The patent changes the duty ratio parameter of the PWM drive signal based on the area of the segment electrode. For larger segment electrodes with higher capacitive load, the duty ratio is increased to compensate for the voltage drop caused by the larger capacitance. This parameter adjustment ensures that the effective voltage remains within the required range regardless of the segment electrode area, allowing both small and large electrodes to achieve reliable display performance.
3Ease of operation
If a single duty ratio is used for all segment electrodes, then the drive signal is simple, but transmittance varies across different electrode areas
Solution Approach 1:
The patent implements local quality control by setting different duty ratios for segment electrodes based on their area. This ensures that each electrode receives a drive signal optimized for its specific characteristics, resulting in uniform transmittance across the display. The drive circuit automatically determines the area of each segment electrode and applies the appropriate duty ratio, achieving both ease of operation through automated control and precision in transmittance uniformity.
Data Source
AI summary
A display driver (100) includes terminals (TSEG1 and TSEG2) and a drive circuit (130). The terminal (TSEG1) can be connected to a segment electrode (ESEG1). The terminal (TSEG2) can be connected to a segment electrode (ESEG2) whose area is larger than the area of the segment electrode (ESEG1). The drive circuit (130) outputs a PWM segment drive signal (SSEG1) to the terminal (ESEG1), and outputs a PWM segment drive signal (SSEG2) to the terminal (TSEG2). When the same effective voltage is applied to the segment electrode (ESEG1) and the segment electrode (ESEG2), the duty ratio of the segment drive signal (SSEG1) is smaller than the duty ratio of the segment drive signal (ESEG2).