Source Driver Bias Control for Ground Bounce in High-Bit Displays
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Solution Overview
Problem
High-resolution display panels with increased bits for gray level representation lead to higher peak currents during short operation times, causing ground bouncing that affects adjacent circuits, modules, and interfaces.
Innovation Solution
A display driving device that includes a level shifter configured to receive image data and a bias control signal, generating decoded data and controlling the output bias current, and a digital-analog converter (DAC) that selects gamma voltages based on the decoded data, with a bias circuit to limit output bias currents of level shifters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of bits representing gray levels is increased, then the gray expression capability is improved, but the peak current level increases causing ground bouncing
Solution Approach 1:
The source driver is divided into multiple amplifier areas (first amplifier area, second amplifier area, etc.), each independently driving a portion of the pixel array. This segmentation distributes the peak current across multiple independent channels, preventing ground bouncing while maintaining high gray level resolution through the combined output of all amplifier areas.
Solution Approach 2:
Each amplifier area is configured with specific level shifters and DACs tailored to its local requirements. The level shifters in different amplifier areas can operate with different bias currents optimized for their specific loading conditions, allowing high gray expression where needed while limiting peak current in other areas to prevent ground bouncing.
2Productivity
If multiple level shifters operate together for a short time, then the high-resolution display is enabled, but the peak current level increases
Solution Approach 1:
The display panel is divided into multiple independently driven regions (amplifier areas), each with its own level shifters and DACs. This allows the system to achieve high-resolution display across the entire panel while limiting the number of level shifters that simultaneously draw peak current in any single amplifier area, thus controlling overall peak current levels.
Solution Approach 2:
The bias control signal dynamically adjusts the bias current of level shifters based on operating conditions. During periods when multiple level shifters operate simultaneously, the bias current is reduced to limit peak current, while maintaining sufficient current levels to ensure proper signal levels and high-resolution display quality.
3Reliability
If the output bias current of level shifters is increased, then the signal quality is improved, but ground bouncing occurs affecting adjacent circuits
Solution Approach 1:
The harmful effect of ground bouncing is extracted and isolated by providing each amplifier area with its own independent power supply lines and ground connections. This separates the high current paths of different amplifier areas, preventing ground voltage fluctuations in one area from affecting adjacent circuits and interfaces, while still allowing sufficient bias current for high signal quality within each isolated area.
Data Source
AI summary
An example display driving device includes a level shifter and a digital-analog converter (DAC). The level shifter is configured to receive image data and a bias control signal, to generate decoded image data including a plurality of bits by level shifting the image data, and to control an output bias current of the decoded image data based on the bias control signal. The DAC is configured to receive the decoded image data and a plurality of gamma voltages, to select one gamma voltage of the plurality of gamma voltages based on the decoded image data, and to output the selected gamma voltage.