LCD Common Electrode Driving Circuit for Audible Noise Reduction
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Solution Overview
Problem
Liquid Crystal Displays (LCDs) driven in AC mode generate audible noise due to vibration of the common electrode, which becomes a problem in slim portable devices where the distance between the liquid crystal panel and the device is reduced, causing vibrations within the human audible bandwidth.
Innovation Solution
The LCD is designed to remove audible noise by setting the driving frequency of the common electrode to a wider range than the human audible bandwidth by supplying a DC voltage for a predetermined period and a common voltage for the remaining period of the first horizontal period, with the DC voltage being half the sum of the common and pixel voltage, effectively reducing the period when the common voltage is supplied.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the LCD is driven in AC mode with line inversion system, then the liquid crystal reliability is improved, but audible noise is generated due to substrate vibration
Solution Approach 1:
The patent applies periodic action by supplying DC voltage to the common electrode during specific periods (non-display periods) and alternating voltage during display periods. This periodic voltage supply pattern creates rhythmic substrate movement that shifts the vibration frequency beyond the human audible range, thereby eliminating audible noise while maintaining AC driving mode for liquid crystal reliability
Solution Approach 2:
The patent changes the voltage parameter supplied to the common electrode by introducing DC voltage components during specific time periods. This parameter change modifies the substrate vibration characteristics, shifting the vibration frequency from the audible range to the inaudible range, thus resolving the audible noise issue while preserving the AC driving benefits
2Object-generated harmful factors
If the driving frequency of common electrode is increased beyond audible bandwidth, then audible noise is removed, but power consumption increases
Solution Approach 1:
The patent uses periodic action by supplying DC voltage only during non-display periods (horizontal blanking intervals) rather than continuously. This periodic application of DC voltage achieves the noise reduction effect during critical periods while minimizing power consumption by not applying voltage during active display periods
Solution Approach 2:
The patent applies partial action by supplying DC voltage to the common electrode only during specific time intervals (non-display periods) rather than continuously throughout the entire frame period. This partial voltage application is sufficient to achieve noise reduction while significantly reducing overall power consumption compared to continuous voltage supply
Data Source
AI summary
A Liquid Crystal Display (LCD) includes: a liquid crystal panel having liquid crystal cells divided by scan lines and data lines and arranged in a matrix shape; a data driving circuit to supply an image signal to the liquid crystal cells via the data lines; a scan driving circuit to sequentially select and scan the scan lines and to control an on/off state of switching elements arranged in each of the liquid crystal cells; a timing controller to drive both the data driving circuit and the scan driving circuit, based on an externally inputted signal; and a common electrode driving circuit to drive a common electrode of the liquid crystal panel. The common electrode driving circuit supplies a common voltage to the common electrode, the common voltage including a DC voltage for a first period of a first horizontal period (1H) and another voltage for a second remaining period of the first horizontal period (1H).