Linear DAC in LCD Column Driver for Gamma Correction
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Solution Overview
Problem
Existing LCD driver circuits face challenges in handling large data volumes, maintaining brightness uniformity, and compensating for temperature-induced gamma gradients while keeping manufacturing costs and reliability high, particularly due to the size and complexity of decoder and communication bus components.
Innovation Solution
Implementing a linear digital-analog-conversion (DAC) circuit in the column driver with a gamma function in the timing controller, using look-up tables to generate voltages and correct for temperature dependencies, allowing higher bit rates without significant chip size increase and enabling consistent color temperature across different voltage levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a non-linear DAC circuit is used in the column driver to handle gamma curves, then the LCD can compensate for temperature-induced gamma gradients, but the chip size and device complexity increase significantly
Solution Approach 1:
The patent divides the gamma curve compensation function into two separate components: a lookup table in the timing controller that stores pre-calculated gamma values, and a simple linear DAC in the column driver. This segmentation moves the complex gamma curve generation away from the column driver chip, reducing its size while maintaining temperature compensation capability through the timing controller's lookup table.
Solution Approach 2:
The patent extracts the gamma curve implementation from the column driver and places it in the timing controller. By taking out the complex gamma curve generation logic from the column driver chip, the column driver can use a simple linear DAC, significantly reducing chip size and complexity while maintaining the ability to compensate for temperature-induced gamma gradients.
2Illumination intensity
If the gamma curve is implemented in the column driver, then brightness uniformity can be maintained, but the decoder and communication bus size increase
Solution Approach 1:
The patent segments the brightness control function by implementing the gamma curve in the timing controller's lookup table rather than in the column driver's decoder. This allows the column driver to receive pre-processed voltage values that already account for gamma correction, maintaining brightness uniformity while reducing the decoder and communication bus area in the column driver chip.
3Device complexity
If a linear DAC is used in the column driver with gamma function in timing controller, then chip size is reduced, but data transfer requirements increase
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing gamma-corrected voltage values in a lookup table in the timing controller before data transfer to the column driver. This allows the column driver to receive ready-to-use voltage values that already incorporate gamma correction, reducing the need for complex real-time calculations and enabling simpler linear DAC circuitry while maintaining high data transfer rates.
Data Source
AI summary
A method and circuit for providing analog voltages to an LCD panel based on digital voltages. A gamma curve defining a relationship between the applied voltage and a luminescence of the liquid crystals is implemented in a timing controller through a look-up table, an algorithm, and the like. The digital grey level voltages provided by the timing controller are converted to analog voltages by a linear digital-analog-converter (DAC) in each column driver. Implementation of the gamma curve in the timing controller and use of linear DAC allows accommodation of higher bit rate without significant die area increase. Furthermore, look-up table style implementation of the gamma curve allows for easy modification of the curve for temperature, color temperature, different color schemes, and the like.