Source Driver DAC with Parallel Transistors for Gamma Voltage
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In liquid crystal display (LCD) source driver chips, the increasing number of transistors in transmission paths leads to higher on-resistance and longer transmission times, causing delays in outputting Gamma voltages, particularly for voltages close to the middle voltage, resulting in abnormal displays, especially in high-image-updating-rate applications.
Innovation Solution
The digital to analog converter in the source driver chip employs a configuration where the transmission path corresponding to the Gamma voltage closest to the middle voltage has lower on-resistance than others, achieved by using transistors with lower threshold voltages and greater mobility, or by connecting transistors of different types in parallel to form transmission gates, reducing the effective on-resistance and time constant.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of transistors in transmission paths is increased to support more Gamma voltage levels, then the resolution and accuracy of voltage selection is improved, but the on-resistance increases and transmission time increases causing delays
Solution Approach 1:
The transmission paths are segmented into multiple stages with different transistor configurations. Critical paths (those closest to middle voltage) use parallel transistor connections to reduce resistance, while less critical paths use standard series connections, dividing the problem into manageable segments with optimized characteristics for each.
Solution Approach 2:
Different transistor configurations are applied to different transmission paths based on their specific requirements. Paths transmitting voltages closest to middle voltage (which are most critical) use parallel transistor connections with lower on-resistance, while other paths use standard configurations, creating local quality variations optimized for each path's function.
2Loss of energy
If transistors with higher threshold voltages are used to reduce leakage current, then power consumption is reduced, but the on-resistance increases and transmission speed decreases
Solution Approach 1:
The patent changes the electrical parameters of transistors in critical transmission paths by connecting them in parallel, which effectively reduces the on-resistance and increases the drive current capability. This parameter change allows faster charging/discharging of capacitive loads, improving transmission speed without significantly increasing leakage in the off state.
3Loss of time
If the transmission path configuration is optimized for speeds, then the transmission time is reduced, but the circuit complexity and manufacturing difficulty increase
Solution Approach 1:
The circuit uses dynamic control signals to selectively activate different transmission paths based on the required Gamma voltage level. The control logic dynamically selects the appropriate path, allowing the system to adapt to different operating conditions without requiring all paths to be optimized simultaneously, thus managing complexity while maintaining speed performance.
Data Source
AI summary
A digital to analog converter for a source driver chip of a liquid crystal display device is disclosed. The digital to analog converter comprises an output terminal for outputting an output voltage, a plurality of receiving terminals for receiving a plurality of Gamma voltages, and a plurality of transmission paths comprising a plurality of first-type transistors coupled between the plurality of receiving terminals and the output terminal, respectively, for outputting one of the plurality of Gamma voltages as the output voltage according to a digital select signal; wherein a first transmission path corresponding to a first receiving terminal receiving a first Gamma voltage closest to a middle voltage among the plurality of Gamma voltages has lower on-resistance than other transmission paths among the plurality of transmission paths when a same source-to-gate voltage is applied.