Variable Frame Frequency LCD with Adjustable Storage Capacitance
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Solution Overview
Problem
Conventional liquid-crystal displays (LCDs) face challenges in reducing power consumption, especially in mobile devices, as they require high frame frequencies for video display and low frequencies for static images, making it difficult to achieve the necessary Ion/Ioff ratio for efficient operation.
Innovation Solution
An active matrix LCD system with adjustable storage capacitance in each pixel's charging circuit, allowing the capacitance to be maintained at different levels for varying frame frequencies, enabling operation at both low and high frame rates while minimizing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the frame frequency is reduced to lower power consumption, then energy consumption decreases, but the leakage current through each pixel and associated TFT must be suppressed to maintain image quality
Solution Approach 1:
The patent applies preliminary action by pre-charging the storage capacitance to a voltage higher than the liquid crystal threshold voltage before the refresh cycle begins. This pre-charging ensures that even when the frame frequency is reduced and the pixel must hold the charge for a longer period, the stored voltage remains sufficient to maintain the liquid crystal orientation and prevent image degradation, thereby addressing the image retention challenge at lower frame frequencies
Solution Approach 2:
The patent implements parameter changes by dynamically adjusting the storage capacitance voltage to different levels based on the operating conditions. Specifically, the storage capacitance is charged to a first voltage level when operating at a first frame frequency, and to a second, higher voltage level when operating at a second, lower frame frequency. This parameter adjustment compensates for the increased leakage effects at lower refresh rates while maintaining power efficiency
2Use of energy by moving object
If the frame frequency is reduced for static images, then power consumption decreases, but the capacitance must be maintained at appropriate levels to prevent image degradation
Solution Approach 1:
The patent applies dynamics by making the storage capacitance voltage level adjustable and adaptive rather than fixed. The system dynamically switches between different voltage levels (first voltage level for higher frame frequencies, second higher voltage level for lower frame frequencies) based on the operating mode. This dynamic adjustment allows the display to optimize between power consumption and image quality maintenance depending on whether static images or video is being displayed
Solution Approach 2:
The patent implements parameter changes by modifying the storage capacitance voltage parameter according to the frame frequency being used. When the display operates at a reduced frame frequency for static images, the storage capacitance is charged to a higher voltage level to compensate for the longer hold time and prevent image degradation, while still consuming less power overall due to the lower refresh rate
3Reliability
If the Ion/Ioff ratio is increased to enable low frame frequency operation, then leakage current suppression improves, but achieving such a ratio in manufacturing is difficult
Solution Approach 1:
The patent introduces an intermediary element - the adjustable storage capacitance - that mediates between the TFT leakage characteristics and the required image holding performance. Instead of relying solely on achieving an extremely high Ion/Ioff ratio in the TFT (which is manufacturing-difficult), the storage capacitance acts as a buffer that can be pre-charged to higher voltages to compensate for leakage, thereby achieving reliable low frame frequency operation with more manufacturable TFT characteristics
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 allows for significant reduction in power consumption by adjusting capacitance levels based on frame frequency, maintaining image quality and extending battery life in mobile devices without noticeable flicker or image degradation.
Implementation Method 1
Each charging circuit includes an adjustable storage capacitance and is configured such that the storage capacitance is maintained at a first level over the first frame-frequency range, and at a second, lower level over the second frame-frequency range
Data Source
AI summary
An active matrix includes an array of pixels individually addressable over a first frame-frequency range and over a second, higher frame-frequency range. The active matrix also includes, for each pixel of the array, a charging circuit through which that pixel is addressed. Each charging circuit includes an adjustable storage capacitance and is configured such that the storage capacitance is maintained at a first level over the first frame-frequency range, and at a second, lower level over the second frame-frequency range.