LCD Gray Level Control via Constant Current Time Division
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Solution Overview
Problem
Conventional liquid crystal display (LCD) devices face limitations in realizing a variety of gray levels due to a small range of input gamma voltages, which restricts the ability to achieve 1024 gray levels or more.
Innovation Solution
An apparatus and method that supply a constant current to pixels instead of voltage, with the charging duration divided by the number of gray levels, using a positive and negative constant current source, a switch, and a pulse generator to control the charging process, allowing for precise control of pixel voltage through varying charging durations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a voltage-based method with a small range of input gamma voltages (5 mV) is used, then the device complexity is reduced, but the number of gray levels that can be realized is limited
Solution Approach 1:
The patent changes the fundamental parameter from voltage-based control to current-based control. By using a constant current source instead of a voltage source and controlling the charging duration (time) rather than voltage magnitude, the system can achieve a much larger number of gray levels (1024 or more) without proportionally increasing device complexity. This parameter transformation allows fine-grained control of pixel brightness through time division multiplexing.
Solution Approach 2:
The patent employs periodic scanning of pixel rows with time-divided current injection. The constant current is applied to different pixel rows at different time intervals within each frame period, with the charging duration for each row being time-divided according to the gray level value. This periodic action with time-division multiplexing enables high-resolution gray level control across the entire display panel.
2Manufacturing precision
If a voltage-based method is used, then the ease of operation is maintained, but the manufacturing precision for achieving various gray levels deteriorates
Solution Approach 1:
The patent replaces the voltage-based control mechanism with a current-based control mechanism combined with time-duration control. Instead of varying voltage magnitude to control gray levels, the system uses a constant current whose application duration is precisely controlled based on the desired gray level. This substitution provides superior manufacturing precision because time can be controlled with higher accuracy than small voltage differences, enabling consistent reproduction of 1024 or more gray levels.
3Quantity of substance
If the charging time for all input gray levels is equal to the scan duration of one horizontal line, then the ease of operation is maintained, but the variety of gray levels that can be realized is limited
Solution Approach 1:
The patent segments the horizontal scan duration into multiple time slots, with each time slot allocated to a specific gray level range. By dividing the total charging time proportionally according to the number of gray levels, the system can accommodate 1024 or more gray levels within the same horizontal scan period. This time segmentation allows fine-grained temporal resolution while maintaining the overall scanning rhythm.
Solution Approach 2:
The patent introduces dynamic time allocation where the charging duration for each pixel row is dynamically adjusted based on the gray level value and the current row's position in the scanning sequence. This dynamic timing control enables the system to vary charging times across different gray levels and different rows, achieving high precision gray level control without extending the total frame period, thus preventing loss of time efficiency.
Data Source
AI summary
Disclosed is an apparatus and a method, in which gray levels are realized in such a manner that a pixel is supplied with a constant current instead of a voltage and charging duration (required for inputting data until a gate is turned on/off) is time-divided by the number of gray levels to be realized. The apparatus includes a current supplier for supplying a current filling a pixel, a buffer for latching display data, an adder for adding currently-input display data and display data latched the buffer, a pulse generator for receiving data outputted from the adder and delivering a switch-on pulse having a pulse width corresponding to the outputted data to the current supplier, and a controller for controlling the current supplier, the adder, and the pulse generator.