Driver Circuit for Display Grayscale Voltage Control
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Solution Overview
Problem
In liquid crystal display devices, the amplifier circuit of the drain driver struggles to output a complete GND potential, leading to increased brightness during black display and reduced contrast due to the small voltage difference between the drain and source of MOS transistors, which affects the grayscale voltage supply.
Innovation Solution
A driver circuit with a DA converting circuit, amplifying circuit, and switch circuit that outputs a predetermined GND voltage when the minimum-level grayscale is required, ensuring the pixel and counter electrode voltages are identical, thereby maintaining a potential difference of 0 V during black display.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the amplifier circuit uses a MOS transistor to supply grayscale voltage from VDD to GND, then the circuit can generate multi-level grayscale voltages, but the output voltage cannot reach complete GND potential (0 V) causing brightness increase during black display
Solution Approach 1:
The patent divides the voltage supply function into two separate circuits: a first amplifier circuit that generates grayscale voltages from VDD, and a second amplifier circuit that separately supplies GND potential. This segmentation allows each circuit to specialize in its function, with the second circuit ensuring complete GND potential delivery without being constrained by the MOS transistor voltage drop issue of the first circuit.
Solution Approach 2:
The patent introduces a switch circuit as an intermediary component that selectively connects either the first amplifier circuit or the second amplifier circuit to the image line based on the required voltage level. This intermediary mechanism enables the system to use the second amplifier circuit's GND output when minimum-level grayscale is required, ensuring complete potential delivery while maintaining the versatility of multi-level grayscale generation.
2Manufacturing precision
If the MOS transistor output voltage approaches GND level, then the grayscale voltage can reach minimum level, but the voltage difference between drain and source becomes small causing current to stop flowing
Solution Approach 1:
The patent separates the voltage generation function (first amplifier circuit) from the GND potential delivery function (second amplifier circuit). The first circuit can precisely generate minimum-level grayscale voltages using standard MOS transistor operation, while the second circuit independently ensures reliable current flow to the image line by using a different transistor configuration that maintains sufficient voltage difference even at minimum grayscale levels.
Solution Approach 2:
The switch circuit acts as an intermediary that routes the appropriate circuit output to the image line based on operating conditions. When minimum-level grayscale is required, the switch connects the second amplifier circuit's GND output to the image line, ensuring reliable current flow without depending on the voltage difference limitations of the first amplifier circuit's MOS transistor.
3Device complexity
If a single amplifier circuit supplies both grayscale voltage and GND potential, then the circuit structure is simple, but the contrast performance deteriorates due to inability to output complete GND potential
Solution Approach 1:
The patent divides the single amplifier circuit into two separate amplifier circuits: a first amplifier circuit for generating grayscale voltages from VDD, and a second amplifier circuit for supplying GND potential. This segmentation increases circuit complexity but enables independent optimization of each function, with the second circuit specifically designed to deliver complete GND potential for optimal contrast performance during black display.
Solution Approach 2:
The switch circuit serves as an intermediary that manages the connection between the two amplifier circuits and the image line. It selectively routes the output of either the first or second amplifier circuit based on the required voltage level, enabling the system to achieve high contrast performance by using the second amplifier circuit's complete GND potential output while maintaining manageable overall system complexity through controlled switching.
Data Source
AI summary
A driver circuit including a DA converting circuit that converts video data input from the outside to a grayscale voltage; an amplifying circuit that amplifies the grayscale voltage; and a switch circuit that selects the grayscale voltage output from the amplifying circuit and a predetermined voltage as a voltage that is output to the image line. When video data indicating a minimum grayscale, the switch circuit outputs the predetermined voltage to the image line, and when video data indicating a grayscale other than the minimum grayscale is input, the switch circuit outputs the grayscale voltage output from the amplifying circuit to the image line. The predetermined voltage allows a voltage of the pixel electrode and a voltage of the counter electrode after passage of the writing of the image voltage to be coincident with each other.