Column Voltage Waveform Mirroring for LCD Power Reduction
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Solution Overview
Problem
Passive matrix LCDs in portable devices face increasing power consumption issues due to high column voltage transitions and intensive data processing, particularly when using Pulse Width Modulation (PWM) with driving schemes like Alt & Pleshko and Multiple Row Addressing (MRA), which negatively impact overall power efficiency.
Innovation Solution
The implementation of adaptive column voltage mirroring, where the column voltage waveform for a subsequent row selection time is mirrored based on the voltage at the end of the current time, reducing the number of transitions and thus lowering power consumption, can be applied to various driving schemes including Alt & Pleshko and MRA when combined with PWM.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If Pulse Width Modulation (PWM) with Alt & Pleshko or Multiple Row Addressing (MRA) driving schemes is used to display grey scales, then the display quality is improved, but the number of column voltage transitions increases and power consumption increases
Solution Approach 1:
The patent applies inversion by mirroring the column voltage waveform of the current row selection time around a mirror axis to generate the waveform for the subsequent row selection time. This reverse approach reduces transitions by exploiting the symmetry between consecutive frames, achieving up to 50% transition reduction while maintaining display quality.
Solution Approach 2:
The patent performs preliminary action by pre-calculating and storing the mirror axis position based on the column voltage at the end of the current row selection time before generating the subsequent waveform. This advance preparation enables efficient waveform generation and reduces real-time computational burden.
2Measurement precision
If column voltage waveform is frequently changed to achieve grey scales, then the display precision is improved, but the number of transitions increases and power consumption increases
Solution Approach 1:
The patent uses inversion by mirroring the column voltage waveform to reduce transitions between consecutive row selection times. This approach maintains grey scale precision while minimizing unnecessary voltage changes, thereby reducing power consumption associated with frequent transitions.
Solution Approach 2:
The patent changes the parameter of column voltage waveform generation from direct calculation to mirror-based generation. By changing how the waveform is produced rather than changing the waveform itself, the patent maintains display precision while reducing transition frequency and power consumption.
3Illumination intensity
If intensive data processing is performed to calculate column voltages for each row sub selection time slot, then the display quality is improved, but the device complexity increases
Solution Approach 1:
The patent performs preliminary action by pre-determining the mirror axis position based on the column voltage at the end of the current row selection time. This advance calculation simplifies the generation of subsequent waveforms, reducing real-time processing complexity while maintaining display quality.
Solution Approach 2:
The patent uses copying by mirroring the current column voltage waveform to generate the subsequent waveform. Instead of performing intensive calculations for each new waveform, the system copies and transforms the existing waveform around a mirror axis, significantly reducing computational complexity.
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 can save up to 50% of column transitions, significantly reducing the power consumption of the driver without increasing the number of transitions, thereby enhancing the energy efficiency of the display device.
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
The invention concern a display device comprising a liquid crystal material between a first substrate provided with row electrodes (7) and a second substrate provided with column electrodes (6), in which overlapping parts of the row and column electrodes define pixels (8), driving means (5) for driving the column electrodes (6) in conformity with an image to be displayed, and driving means (4) for driving the row electrodes (7), wherein the row electrodes (7) select at least one row during a row selection time and column voltages (Gj(t)) are supplied to the column electrodes (6), wherein the column voltage waveform depends on the grey scale to be displayed by the driven pixel in a certain column and depends on a used selection signal (Fi) for the selected row, wherein a column voltage (Gj(t)) is switchable between at least two different column voltage levels during a row selection time. To provide a display device having low power consumption and in particular to minimize the number of transitions of the column driving signal the column voltage waveform for a following row selection time is mirrored on a mirror axis, if the column voltage at the end of the current row selection time is the same as the column voltage at the end of the following row selection time.