Pre-Charging Circuit for LCD Data Line Power Reduction
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Solution Overview
Problem
Liquid crystal display devices face challenges with high power consumption and heat generation due to the substantial current flowing through output buffers, which affects driving reliability and requires further performance improvement in existing pre-charge methods.
Innovation Solution
A pre-charging circuit is implemented to selectively pre-charge data lines to voltage levels based on digital video data signals, using a combination of positive and negative pre-charge voltages and a charge share voltage, reducing the current through output buffers by optimizing voltage transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional output drivers are used to drive data lines in liquid crystal display devices, then the display function is achieved, but power consumption increases and heat generation occurs due to substantial current flow through the output buffers
Solution Approach 1:
The patent applies preliminary action by pre-charging data lines to specific voltage levels (ELVSS or ELVDD) before actual data writing occurs. The pre-charging circuit sets up the data line voltage in advance based on the video data value, so that when the output driver writes the actual data, the voltage transition required is minimized or eliminated, thereby reducing current flow and power consumption while maintaining reliable driving
2Reliability
If conventional output drivers are used to drive data lines in liquid crystal display devices, then the display function is achieved, but heat generation occurs due to substantial current flow through the output buffers
Solution Approach 1:
The pre-charging circuit performs preliminary voltage setup on data lines before data writing, eliminating large voltage transitions during actual data output. This preliminary action reduces current flow through the output buffer, thereby reducing I²R heat generation while maintaining stable and reliable data line driving for the liquid crystal display
3Use of energy by moving object
If existing pre-charge methods are used, then power consumption is reduced, but further performance improvement is needed to achieve optimal driving reliability
Solution Approach 1:
The patent applies parameter changes by dynamically selecting different pre-charge voltage levels (ELVSS or ELVDD) based on the actual video data value. When video data indicates a low level, the data line is pre-charged to ELVSS; when high, it is pre-charged to ELVDD. This adaptive parameter selection optimizes both power consumption reduction and driving reliability by matching the pre-charge state to the intended data state
Solution Approach 2:
The pre-charging circuit incorporates feedback by monitoring the video data signal and using it to control the pre-charging operation. The circuit responds to the video data input and adjusts the pre-charge voltage level accordingly, creating a closed-loop control system that optimizes power consumption while ensuring correct data line voltage states for reliable display driving
Data Source
AI summary
A liquid crystal display device is set forth that comprises a data line that is connected to drive a liquid crystal cell and an output driver connected to selectively provide a pixel drive signal to the data line. The pixel drive signal corresponds to a digital video data signal provided to the liquid crystal display device. A pre-charging circuit is used to reduce the power consumed by the output driver. To this end, the pre-charging circuit is connected to selectively pre-charge the data line to one or more of a plurality of voltage levels depending on the value of the digital video data signal. In one embodiment, the plurality of voltage levels comprises a positive pre-charge voltage, a negative pre-charge voltage, and a charge share voltage. The magnitudes of the positive pre-charge voltage and the negative pre-charge voltage may be chosen so that they are greater than the magnitude of the charge share voltage.