Display Driver Amplifier Gain Calibration for High-Gradation Uniformity
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Solution Overview
Problem
Existing display drivers face challenges in maintaining consistent gain across amplifier circuits due to process variations, leading to variations in data voltages and reduced image quality, especially at high gradations.
Innovation Solution
The display driver incorporates an adjustment resistance circuit that adjusts the first and second adjustment resistance values between the input and inverting input nodes of the operational amplifier, allowing for precise control of the gain of each amplifier circuit, thereby reducing gain variations and improving image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a voltage follower circuit is used as the amplifier circuit, then the bias point of the differential pair can be stabilized, but the gain fluctuates when the bias point changes and high gain cannot be achieved over the entire fluctuation range
Solution Approach 1:
The patent changes the circuit configuration from a voltage follower to a resistor type inverting amplifier circuit, fundamentally altering the operational parameters to achieve stable gain. By using fixed resistors for feedback and input, the gain becomes determined by resistance ratios rather than transistor bias points, eliminating the gain fluctuation problem while maintaining reliability
2Reliability
If a resistor type inverting amplifier circuit is used to reduce bias point fluctuation, then bias stability improves, but gain varies among amplifier circuits due to process variation in resistors
Solution Approach 1:
The patent introduces a feedback mechanism where the output of each amplifier circuit is fed back to its own input through a feedback resistor. This negative feedback reduces the impact of resistor variations by automatically adjusting the operating point, thereby stabilizing the gain across multiple amplifier circuits despite process variations
Solution Approach 2:
The patent modifies the resistor configuration by introducing feedback resistors and adjusting the resistance ratios to account for process variations. By carefully selecting feedback resistor values and implementing resistance matching techniques, the gain consistency across amplifier circuits is improved while maintaining the stability provided by the inverting amplifier topology
3Speed
If the gain of the operational amplifier is increased to drive data voltage at high speed, then the driving speed improves, but the bias point fluctuates more and gain consistency deteriorates
Solution Approach 1:
The patent changes the amplifier topology to a resistor type inverting amplifier configuration, which provides gain determined by external resistors rather than internal transistor parameters. This allows high gain to be achieved through resistance ratios while the feedback mechanism maintains bias point stability, enabling fast data voltage transitions without sacrificing gain consistency
Data Source
AI summary
A display driver includes a D/A converter circuit for outputting a gradation voltage, and an amplifier circuit that is input with a gradation voltage at an input node. The amplifier circuit includes an operational amplifier, resistance provided between the input node and a node, resistance provided between a node and an output node of the operational amplifier, and an adjustment resistance circuit. The adjustment resistance circuit adjusts a first adjustment resistance value, that is a resistance value between a node and an inverting input node of the operational amplifier, and a second adjustment resistance value, that is a resistance value between the node and the inverting input node.