Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1997-06-04
2001-12-18
Shalwala, Bipin (Department: 2671)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S092000, C345S100000, C345S204000, C345S205000, C345S206000, C345S211000, C345S212000
Reexamination Certificate
active
06331844
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display apparatus whose power consumption is reduced.
In recent years, the power consumption of a liquid crystal display apparatus has been reduced by lowering the driving voltage or driving frequency. To further reduce the power consumption, a structure in which a memory is arranged for every pixel is proposed (Jpn. Pat. Appln. KOKAI Publication No. 58-196582 or 3-77922). With this technique employed for a still image, once display signals are transmitted to the respective pixels, the pixels may always be displayed with the signals held in the memories of the pixels. Theoretically, since only the power necessary for polarity inversion is consumed, the power consumption for the still image almost becomes “0”.
However, along with the progress in multimedia, display of moving images has been increasingly required recently. In a moving image, image information sequentially changes at a high speed. For this reason, even memories are provided in units of pixels, signals held in the memories must be frequently rewritten. To frequently rewrite the held signals (pixel signals), a large power is consumed, as in prior arts.
In the above-described LCD with pixel memories, display signals obtained through switches SW are held in the pixel memories, and an image is displayed using the contents held in the memories. When this technique is to be applied to still image display, pixel signals are temporarily stored in the pixel memories. Unless the image changes, the memory contents need not be rewritten. Therefore, the driving frequency or static power consumption is expected to lower. However, for a moving image, the memory contents must be rewritten so no power consumption reduction effect can be expected, unlike still image display.
A demand has arisen for a low-power liquid crystal display apparatus capable of reducing the power consumption even in case of moving image display, and for portable equipment using the liquid crystal display apparatus as an image display device, minimizing waste of the battery, i.e., the main power supply of the equipment to prolong the battery driving time.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a low power-consumption liquid crystal display apparatus capable of reducing the power consumption even in moving image display.
In order to achieve the above object, according to the first aspect of the present invention, there is provided a liquid crystal display apparatus comprising:
a substrate;
a plurality of scanning lines extending substantially in parallel with each other in a row direction on the substrate;
a plurality of signal lines extending substantially in parallel with each other in a column direction on the substrate;
a signal line driver for supplying a pixel signal of current variables to each of the plurality of signal lines;
a scanning line driver for selectively supplying a scanning signal to the plurality of scanning lines; and
a plurality of pixels arranged on the substrate at intersections of the plurality of scanning lines and the plurality of signal lines, each of the plurality of pixels including conversion means for receiving the pixel signal of current variables, which is supplied to the signal line, and converting the pixel signal into a voltage signal, and a liquid crystal cell to which the converted voltage signal is applied.
The conversion means may include one of a capacitor and a resistor.
Preferably, the pixel further comprises first switch means inserted between the conversion means and a corresponding one of the plurality of signal lines and ON/OFF-controlled in accordance with the scanning signal of a corresponding one of the plurality of scanning lines.
Preferably, the pixel further comprises second switch means inserted between the conversion means and the liquid crystal cell, and a driving period of the liquid crystal cell is determined by ON/OFF of the second switch means.
The signal line driver may receive a digital voltage image signal and output the pixel signal of current variables under a predetermined voltage.
An output stage of the signal line driver may be constituted by an operational amplifier.
The signal line driver may receive an image signal of current variables and output the pixel signal of current variables.
In the liquid crystal display apparatus having the above arrangement, the pixel signal for driving the liquid crystal cell is output as a current signal and converted into a voltage signal in the pixel. The voltage of the signal line need not be changed, unlike a case wherein the pixel signal is a voltage signal. Since the amplitude of the pixel signal voltage for driving the signal line can be made to almost zero, almost no power is consumed to drive the signal line. Therefore, the power consumption can be reduced even in moving image display.
According to the second aspect of the present invention, there is provided a liquid crystal display apparatus comprising:
a substrate;
a plurality of scanning lines extending substantially in parallel with each other in a row direction on the substrate;
a plurality of signal lines extending substantially in parallel with each other in a column direction on the substrate;
a signal line driver for supplying a pixel signal to each of the plurality of signal lines;
a scanning line driver for selectively supplying a scanning signal to the plurality of scanning lines; and
a plurality of pixels arranged on the substrate at intersections of the plurality of scanning lines and the plurality of signal lines, each of the plurality of pixels including holding means for holding the pixel signal supplied to the signal line, amplification means for amplifying the pixel signal, and a liquid crystal cell having a pixel electrode to which the amplified pixel signal is applied.
The amplification means may include an operational amplifier.
Preferably, the pixel further comprises first switch means for controlling energization to the operational amplifier in accordance with the scanning signal of a corresponding one of the plurality of scanning lines.
The amplification means may include a differential amplifier having two input terminals and two output terminals such that the pixel signals are input to the two input terminals from corresponding two of the plurality of signal lines.
Preferably, the pixel further comprises second switch means for selectively supplying two outputs from the differential amplifier to the pixel electrode of the liquid crystal cell.
Preferably, the pixel further comprises third switch means for controlling energization to the differential amplifier in accordance with the scanning signal of a corresponding one of the plurality of scanning lines.
Preferably, the pixel further comprises fourth switch means for selectively setting a potential of the pixel electrode of the liquid crystal cell at a reference potential.
Preferably, the pixel further comprises fifth switch means inserted between the amplification means and the pixel electrode of the liquid crystal cell and ON/OFF-controlled in accordance with the scanning signal of a corresponding one of this plurality of scanning lines.
Preferably, the pixel further comprises sixth switch means inserted between the amplification means and a corresponding one of the plurality of scanning lines and ON/OFF-controlled in accordance with the scanning signal of a corresponding one of the plurality of scanning lines.
According to this arrangement, each pixel has the amplification means for amplifying the pixel signal. The pixel signal is amplified by the amplification means and supplied to the liquid crystal cell to drive the liquid crystal cell. When the pixel signal is supplied as a voltage signal, the voltage of the pixel signal supplied to the signal line can be lowered. Therefore, the voltage for charging the signal line capacitor for transmitting the pixel signal lowers to result in a large reduction in power consumption for driving the signal line.
According to the third aspect of the present inv
Fujiwara Hisao
Itoh Goh
Kamiura Norihiko
Kinno Akira
Okumura Haruhiko
Frenel Vanel
Kabushiki Kaisha Toshiba
Shalwala Bipin
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