A more complete appreciation of the present invention, and many of the attendant advantages thereof, will be readily apparent as the present invention becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein:
Hereinafter, an exemplary embodiment of the present invention is described with reference to the accompanying drawings.
Referring to
The liquid crystal panel 11 is driven to sequentially display an image of only one frame on the liquid crystal panel 11 by using the data driving circuit 12, the scan driving circuit 13, the timing controller 14, and the common electrode driving circuit 15.
The liquid crystal panel 11 is formed by facing a pair of transparent substrates and sealing a liquid crystal (a liquid crystal layer) between a pair of the substrates. Scan lines and data lines are arranged on a first substrate of the pair of the substrates, and a switching element such as TFT, and a pixel electrode are formed adjacent to intersection points of their signal lines.
A common electrode is formed in the second substrate facing the first substrate, and R (red), G (green) and B (blue) color filters are arranged in the second substrate, the color filters corresponding to each of the pixel electrodes.
The timing controller 14 receives a vertical synchronizing signal (Vsync), a horizontal synchronizing signal (Hsync), a clock signal (Clock), an enable signal (Enable), a RGB data signal (DATA), and generates a source start signal (SSP), a source clock signal (SCK), a latch signal (LS), a gate start signal (GSP) and a gate clock signal (GCK) in response to the inputted signals.
The data signal (DATA), the source start signal (SSP), the source clock signal (SCK) and the latch signal (LS) are outputted to the data driving circuit 12, and the gate start signal (GSP) and the gate clock signal (GCK) are outputted to the scan driving circuit 13.
The data signal (DATA), the source start signal (SSP), the source clock signal (SCK), the latch signal (LS), the gate start signal (GSP) and the gate clock signal (GCK) are all driving signals for driving the liquid crystal panel 11.
The common electrode driving circuit 15 is driven by reversing a polarity of the common voltage (Vcom), supplied to the common electrode, to be suitable for a reversed polarity (a polarity of the image signal) of the voltage supplied to the pixel electrode so that an effective value of the voltage supplied to the liquid crystal are identical if a polarity of the voltage supplied to each of the pixel electrodes is reversed when the liquid crystal display 10 is AC-driven in a line inversion system.
Hereinafter, the driving method of the liquid crystal display is described in more detail.
Generally, an enabling of the image signal in each of the liquid crystal cells carried out in the liquid crystal display is carried out by the AC driving. For example, a polarity of the image signal supplied to the pixel electrode is reversed in every scan signal line (every scan period) when the liquid crystal display is AC-driven in a line inversion system. If the liquid crystal display is driven in the AC driving, then an effective value of the voltage supplied to the liquid crystal is determined by the difference between the voltage supplied to the pixel electrode and the voltage supplied to the common electrode, namely a common voltage (Vcom).
For this purpose, the Vcom is supplied to the common electrode so that an effective value of the voltage supplied to the liquid crystal can be identical even though a polarity of the voltage supplied to each of the pixel electrodes is reversed when the liquid crystal display is driven in a line inversion system. Accordingly, a polarity of the common voltage (Vcom) is necessarily reversed to be suitable for the polarity (a polarity of the image signal) of the voltage supplied to the pixel electrode.
If the liquid crystal display is driven to reverse the polarity of the Vcom, then the second substrate in which the common electrode is formed vibrates when a voltage is supplied to the common electrode, and the vibration is recognized as audio noise in driving the liquid crystal display if a vibration frequency of the second substrate is within a human audible bandwidth, as described above.
In order to solve the problems, the liquid crystal display according to one embodiment of the present invention removes audio noise by setting a driving frequency of a common electrode to a wider range than a human audible bandwidth without an increase of the entire frame frequency since a period when a common voltage is actually supplied may be reduced by supplying a DC voltage for a predetermined period (first period) out of a first horizontal period (1H) of the voltage supplied to the common electrode and supplying a common voltage for the other remaining first horizontal period (second period), the DC voltage corresponding to a half of the sum of the common voltage and the pixel voltage supplied for the first horizontal period, as shown in
Generally, if the liquid crystal display is driven in a line inversion system, then the polarity of the common voltage (Vcom) is reversed in every first horizontal period (1H). Also, a driving frequency f(Hz) of the common electrode is represented by f(Hz)=½H period (herein, the 2H period means twice as much as an 1H) since a frequency is represented by the reciprocal of a period.
Accordingly, a driving frequency of the common electrode may be actually improved in the embodiment of the present invention, considering a period when a common voltage is actually supplied although a driving frequency of the common electrode is not changed, by supplying a DC voltage for a predetermined period, namely a first period, out of a first horizontal period (1H) and supplying a common voltage for the other remaining first horizontal period (second period), the DC voltage corresponding to a half of the sum of the common voltage and the pixel voltage that should be supplied for the first horizontal period, as described above.
For example, assume that a driving frequency of the common electrode is 10 KHz, a predetermined DC voltage is supplied during a period (a first period) corresponding to one half of the first horizontal period (1H), and a common voltage is supplied during a period (a second period) corresponding to the other half of the first horizontal period (1H).
A capacity of the DC voltage preferably corresponds to one half of the sum of the common voltage and the pixel voltage supplied during the first horizontal period.
The period when the common voltage is actually supplied is one half of the existing period since the common voltage is supplied only during the period corresponding to one half of the first horizontal period (1H), and therefore an actual driving frequency is 20 KHz (20,000 Hz).
However, the driving frequency of the common voltage is 10 kHz since it includes a period when the DC voltage is supplied. Accordingly, the driving frequency is represented by f(Hz)=10,000=½H period in the equation, and the 1H period is represented by 1H period=1/20,000 Hz=50 μs.
That is to say, when the 1H period is set to 50 μs as known in the art, an increase in the power consumption, required for driving the liquid crystal display, is prevented in this embodiment since the liquid crystal display is not driven at a high speed.
When a liquid crystal panel 11 having a resolution of QVGA (240×320 dot) is used for portable devices, etc., if the 1H period is set to 50 μs, then a period required for supplying a voltage to liquid crystal cells of only one frame is calculated by 50 μs×320 line=16 ms since the one frame has 320 scan signal lines. As a period required for displaying only on frame, a first vertical period (1V, a first frame period) is 1/60 s (about 16.7 ms) in the conventional liquid crystal display.
Accordingly, the increase of the power consumption required for driving the liquid crystal display is prevented by supplying a voltage to the liquid crystal cells of only one frame to be suitable for a conventional 1V period (about 16.7 ms) of only one frame since the driving frequency of the common electrode is not actually changed in this embodiment of the present invention.
The period when the common voltage is actually supplied is one half of the existing period since the common voltage is supplied only during the period corresponding to one half of the first horizontal period (1H), and therefore an actual driving frequency is 20 kHz (20,000 Hz), as described above. As a result, noise is removed by setting a driving frequency of a common electrode to a wider range than a human audible bandwidth without an increase of the entire frame frequency.
A polarity of the pixel voltage corresponding to the supplied common voltage is reversed and inputted during an 1H period in the same manner as described in the prior art, but the polarity of the pixel voltage is more preferably supplied to be suitable for a period when the common voltage is actually supplied, as shown in
That is to say, driving frequencies (frequencies of the driving voltages) of the pixel electrode and the common electrode may be set to 20 kHz or more by driving the liquid crystal display in a manner of reversing a polarity of the driving voltage supplied to each of the pixel electrode and the common electrode in every ½ period out of the 1H periods in this embodiment. Accordingly, a vibration of the substrate is not recognized as audio noise by humans since the vibration of the substrate exceeds 20 kHz, namely, exceeds a human audible bandwidth, if the vibration occurs in the substrate.
As described above, according to the present invention, audio noise is removed by setting a driving frequency of a common electrode to a wider range than a human audible bandwidth without an increase of the entire frame frequency, the noise being generated in driving the liquid crystal display.
Also, the driving method of the present invention is more suitable for slim portable devices using the liquid crystal display.
The description above refers to just a preferable example for the purpose of illustration only and is not intended to limit the scope of the present invention. It should therefore be understood that other equivalents and modifications could be made thereto without departing from the spirit and scope of the present invention as apparent to those skilled in the art. Therefore, it should be understood that the present invention is not defined within the scope of the detailed description but rather within the scope defined in the following claims.
Number | Date | Country | Kind |
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10-2006-0090130 | Sep 2006 | KR | national |