Passive Matrix LCD Driving Method Reducing Column Voltage Transitions
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Solution Overview
Problem
Passive matrix LCDs face challenges with high power consumption and optical performance, particularly in portable devices, due to intensive data processing and frequent transitions in column driving signals, which affect overall power consumption and can lead to flickering issues.
Innovation Solution
The solution involves a display device with a liquid crystal material between substrates, using a combination of frame rate control and pulse width modulation, along with phase mixing, to minimize column voltage transitions and data processing, by concentrating grey scale code changes in specific phases and optimizing phase mixing tables to reduce the number of transitions and calculations per row selection time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If frame rate control and pulse width modulation are used to generate grey scales, then optical performance is improved, but the number of column voltage transitions increases causing higher power consumption
Solution Approach 1:
The patent applies periodic action by using frame rate control where grey scales are generated through periodic switching of pixel states across multiple frames. The display alternates between different grey scale representations in a cyclic manner, exploiting the persistence of vision to create the perception of stable grey scales while actually using periodic on/off switching. This reduces the need for multiple distinct voltage levels and minimizes column voltage transitions.
Solution Approach 2:
The patent changes the parameter approach from using multiple voltage levels to generate grey scales to using temporal modulation of a single or limited set of voltage levels. By varying the duration and timing of pixel activation across frames rather than changing voltage magnitudes, the system achieves grey scale differentiation without increasing column voltage transitions.
2Measurement precision
If intensive data processing is performed to calculate column voltages for each frame, then grey scale accuracy is improved, but processing time and power consumption increase
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing grey scale patterns in lookup tables before display operation. Instead of performing intensive calculations in real-time for each frame, the system prepares grey scale representations in advance and simply retrieves the appropriate pre-computed patterns during display, significantly reducing processing time while maintaining grey scale accuracy.
Solution Approach 2:
The patent uses copying by storing pre-computed grey scale patterns in memory tables that can be repeatedly referenced. Rather than recalculating grey scale representations each frame, the system copies identical or slightly varied patterns from the lookup tables, eliminating redundant calculations and reducing processing burden while preserving precision.
3Reliability
If the column voltage signal transitions frequently to accommodate dynamic images, then image quality is improved, but power consumption increases due to driver activity
Solution Approach 1:
The patent uses periodic action to create the illusion of dynamic images through temporal modulation. By periodically switching pixels on and off at different durations within a frame cycle, the system achieves grey scale and motion representation without requiring frequent column voltage transitions. The periodic nature of the switching allows image dynamics to be conveyed through timing variations rather than voltage level changes.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces power consumption by minimizing transitions and data processing, while maintaining good optical performance, and allows for efficient grey scale generation with fewer RAM readouts and reduced chip area requirements, effectively addressing the challenges of high power consumption and flickering.
Implementation Method 1
A layer with liquid crystals is provided between said substrates. The intersections of these electrodes form pixels. These electrodes are supplied with voltages that orient the liquid crystal molecules of the driven pixels in an appropriate direction so that the driven pixel appears in a different brightness.
Data Source
AI summary
Method of driving a liquid crystal display by supplying selectable column voltages Gj(t) from a predetermined number of column voltages levels, selection signals to groups of mutually orthogonal p rows (p≧1) for the duration of a row selection time p×nfrc during a supcrframe nfrc to generate grey scales. The column voltage is calculated depending on the grey scales of the p pixels in a column and on the mutually orthogonal selection signals Fi for the corresponding group of rows. The row selection time is subdivided in npwm sub selection time. The grey scales are coded in grey scale tables having nfrc phases with npwm. The superframes grey scales are generated using phase mixing. The change in the column voltage level defines a transition. The column voltage has always less transitions per row selection time than the number npwm of sub selection time of the row selection time.