Output Driver Bias Trimming for LCD Slew Rate Uniformity
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Solution Overview
Problem
The variation in slew rate among multiple driver ICs for liquid crystal display panels leads to brightness differences and deteriorated display quality, while increasing bias current to enhance slew rate results in increased power consumption and heat generation.
Innovation Solution
A driver circuit with a bias setting circuit, memory, and adjustment circuit that adjusts the slew rate of the output amplifier using a trimming code to maintain it within a target range, either during shipping inspection or in normal operation, without uniformly increasing bias current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the bias current of the output amplifier is increased to increase the slew rate, then the slew rate is improved, but power consumption increases and heat generation occurs
Solution Approach 1:
The patent applies local quality by adjusting the bias current individually for each driver IC rather than uniformly increasing it across all driver ICs. Each driver IC's output amplifier receives a customized bias current level based on its specific slew rate characteristics, allowing precise control of power consumption and heat generation at each local position while achieving the required slew rate performance.
2Speed
If the bias current is uniformly increased across all driver ICs to increase slew rate, then the slew rate is improved, but it becomes difficult to drive liquid crystal display panels with many driver ICs due to power consumption and heat generation
Solution Approach 1:
The patent implements local quality by enabling independent bias current adjustment for each driver IC through a resistance adjustment circuit. This allows each driver IC to be optimized individually, making it possible to drive large liquid crystal display panels with many driver ICs by preventing excessive power consumption and heat generation that would occur with uniform bias current increase across all driver ICs.
3Speed
If the slew rate varies among multiple driver ICs, then individual driver IC performance may be adequate, but brightness differences occur among blocks of the liquid crystal display panel and display quality deteriorates
Solution Approach 1:
The patent applies parameter changes by adjusting the bias current parameter of each driver IC's output amplifier to achieve consistent slew rate characteristics. By changing the bias current parameter individually for each driver IC based on measured slew rate variations, the system achieves uniform brightness across all blocks of the liquid crystal display panel, eliminating display quality deterioration caused by slew rate mismatches.
Data Source
AI summary
In a driver circuit, a bias voltage generation circuit generates and outputs a bias voltage for determining a bias current of an output amplifier. A memory stores a trimming code with which a slew rate of an output voltage outputted by the output amplifier is adjusted to fall within a target range set in advance. In an adjustment mode for adjusting the slew rate, a slew rate adjustment circuit adjusts the slew rate of the output amplifier based on a trimming code inputted from a shipping inspection device. Then, in a normal operation mode, the slew rate adjustment circuit changes a resistance value based on the trimming code stored in the memory to change a bias level of the bias voltage generation circuit and adjust the slew rate of the output amplifier.