Patent ID: 8054274

Claim:
A liquid crystal display device comprising: a liquid crystal panel configured for displaying images according to external image data, the liquid crystal panel comprising a plurality of sub-pixel regions arranged in a regular array, each of the sub-pixel regions having either a positive polarity or a negative polarity when displaying images; and a controlling circuit configured for adjusting a common voltage applied to the liquid crystal panel; wherein the controlling circuit is configured to adjust the common voltage applied to the liquid crystal panel according to a relationship between variations of the common voltage and polarity information of at least the plurality of the sub-pixel regions during operation of the liquid crystal display device, and comprises a receiving unit, an analyzing unit, and an adjusting unit connected in series, the receiving unit is configured for receiving the external digital image data and outputting corresponding voltage signals, the analyzing unit is configured for calculating out the polarity information of the sub-pixel regions in each row according to the voltage signals, the adjusting unit is configured for adjusting the common voltage applied to the common electrodes according to the polarity information, the receiving unit comprises a memory and a digital to analog converter connected to the memory, the memory is configured for receiving the external image data and the digital to analog converter is configured for converting the image signals to voltage signals, the analyzing unit comprises a subtracter, a comparator, and a calculator, the subtracter is configured for subtracting the value of the common voltage from the values of the voltage signals, respectively, the comparator is configured for comparing said subtracting results to a predetermined black image voltage which is defined as a voltage corresponding to a black image, and the calculator is configured for calculating the polarity information of the sub-pixels in each row according to comparing results that are output by the comparator.