JP2008020769A - Display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce power consumption, in a display device having a precharge circuit for setting the display signal line to a precharge potential. <P>SOLUTION: The device comprises an arithmetic circuit 50 for performing arithmetic processing to video data R, G, and B prior to D/A conversion, and a second D/A converter DAC2 for converting the result of the arithmetic operation by the arithmetic circuit 50 so that the precharge potential Vdsd is generated by the second D/A converter DAC2. The arithmetic circuit 50 calculates the mean value of the video data R, G, and B, provided to a plurality of pixels 10 beforehand, in order to estimate the size of the video data R, G, and B. For example, the device calculates the mean value of the video data R, G, and B for a single horizontal period corresponding to a single horizontal line of a display part 1A. The mean value of the video data R, G, and B may be the mean value of all the bits, or the mean value of a part of the bits. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a display device, and more particularly to a display device including a precharge circuit that sets a display signal line to a precharge potential.

  In recent years, with the spread of portable electronic devices such as mobile phones and digital cameras, the demand for display devices such as liquid crystal display devices has been increasing. As one of liquid crystal display devices, an active matrix type liquid crystal display device is known.

  In this type of liquid crystal display device, a plurality of pixels having TFTs are arranged in a matrix, a scanning line to which a pixel selection signal is supplied is connected to the TFT gate of each pixel, and a display is provided to the drain of the TFT. The signal line is connected.

  Then, externally input video data is D / A converted by a D / A converter to generate a display signal, the display signal is amplified by an amplifier, and each pixel is passed through a display signal line having a capacitive load. To supply.

  Further, the display signal line is set to a constant precharge potential every horizontal period by the precharge circuit before the display signal is supplied. As a result, the load on the amplifier is reduced to reduce power consumption.

In addition, the following patent documents are mentioned as technical documents relevant to the present application.
JP 2006-154088 A

  However, in the conventional liquid crystal display device, the precharge potential is a constant DC potential. Therefore, depending on the size of the display signal, the difference between the display signal and the precharge potential becomes large, and the load on the amplifier becomes large, so that there is a problem that power consumption is not sufficiently reduced.

  Therefore, the present invention reduces the load on the display signal amplifier in a display device having a precharge circuit for setting the display signal line to the precharge potential so that the precharge potential can be optimally set according to the display signal. The power consumption is further reduced.

  That is, the display device of the present invention includes a plurality of pixels, a display signal line to which the plurality of pixels are connected, a first D / A converter that generates a display signal by D / A converting video data, And a precharge circuit that supplies a precharge potential to the display signal line and variably sets the precharge potential according to video data.

  According to the display device of the present invention, power consumption can be further reduced in a display device including a precharge circuit that sets a display signal line to a precharge potential.

  Embodiments of the present invention will be described. FIG. 1 is an equivalent circuit diagram of a liquid crystal display device according to an embodiment of the present invention.

  A plurality of pixels 10 are arranged in a matrix on a liquid crystal display unit (hereinafter, abbreviated as “display unit 1A”) on a display panel 1 made of a transparent substrate such as a glass substrate. Each pixel 10 is a pixel corresponding to display of red, green, blue, or other colors.

  In the display unit 1A, a pixel selection thin film transistor (10) of each pixel 10 is located in the vicinity of each intersection of the scanning lines GL1, GL2,... Extending in the row direction and the display signal lines DL1, DL2,. Thin Film Transistor (hereinafter abbreviated as “TFT”) 11 is disposed.

  The gate of the pixel selection TFT 11 is connected to each scanning line GL1, GL2,..., And its drain is connected to each display signal line DL1, DL2,. To the scanning lines GL1, GL2,..., Pixel selection signals Vg1, Vg2,... Output from the vertical drive circuit 20 are respectively applied, and pixel selection is performed according to the pixel selection signals Vg1, Vg2,. On / off of the TFT 11 is controlled.

  A pixel electrode 12 is connected to the drain of the pixel selection TFT 11. A liquid crystal layer 14 is provided between the pixel electrode 12 and the common electrode 13. A storage capacitor 15 that holds the display signal Vsig for one vertical period is connected to the pixel electrode 12.

  The video data R, G, B input from the outside is digital data corresponding to red, green, blue, etc., and these are D / A converted by the first D / A converter DAC1 to provide an analog display signal. Vsig is generated. The display signal Vsig is amplified by the amplifier 32. The amplified display signal Vsig is output to the display signal lines DL1, DL2,... Through the horizontal switch 31 of the horizontal drive circuit 30, and is applied to the pixel electrode 12 of each pixel through the pixel selection TFT 11 of each pixel.

  Further, the precharge circuit 40 is connected to the display signal lines DL1, DL2,..., And is switched according to the precharge control signal DSG, and the precharge potential Vdsd is supplied to the display signal lines DL1, DL2,. A precharge switch 41 for supplying to

  The precharge switch 41 is turned on in a horizontal blanking period before the display signal Vsig is output to the display signal lines DL1, DL2,..., And the display signal lines DL1, DL2,. And is controlled to turn off when the horizontal blanking period ends.

  The present invention pays attention to the fact that the load of the amplifier 32 changes depending on the difference between the display signal Vsig and the precharge potential Vdsd. The precharge potential Vdsd is switched according to the magnitude of the display signal Vsig, and the power consumption of the amplifier 32 is reduced. Reduced. That is, as shown in FIG. 2A, if the difference Vamp1 between the target potential of the display signal Vsig output from the amplifier 32 to the display signal lines DL1, DL2,... And the power consumption of the amplifier 32 is large. On the other hand, as shown in FIG. 2B, if the precharge potential Vdsd is brought close to the target potential of the display signal Vsig, that is, if the difference Vamp2 between the precharge potential Vdsd and the target potential of the display signal Vsig can be reduced, the amplifier The load of 32 is lightened, and the power consumption of the amplifier 32 is reduced.

  Therefore, an arithmetic circuit 50 that performs arithmetic processing on video data R, G, and B before D / A conversion, and a second D / A converter DAC2 that performs D / A conversion on the arithmetic result of the arithmetic circuit 50 are provided. And the precharge potential Vdsd is generated by the second D / A converter DAC2.

  The arithmetic circuit 50 calculates in advance the average value of the video data R, G, B supplied to the plurality of pixels 10 in order to estimate the size of the video data R, G, B. For example, an average value of video data R, G, B for one horizontal period corresponding to one horizontal line of the display unit 1A is calculated. The average value of the video data R, G, B may be an average value of all bits or an average value of some bits. Further, data sampled by an appropriate method from video data R, G, B for one horizontal period may be averaged.

  The most significant bit of the video data R, G, B determines about half of the display signal Vsig applied to the pixel electrode 12. Therefore, the circuit scale of the arithmetic circuit 50 can be reduced by calculating the average value of the most significant bits, not all the bits of the video data R, G, B.

  Therefore, the precharge potential Vdsd is switched every horizontal period so that the difference between the target potential of the display signal Vsig and the precharge potential Vdsd becomes small.

  Next, an operation example of the above-described liquid crystal display device will be described with reference to an operation timing chart of FIG. FIG. 3 shows the potential of the display signal line DL1 as an example from among the plurality of display signal lines DL1, DL2,. First, the arithmetic circuit 50 calculates the average value of the video data R, G, B for one horizontal period, and the precharge potential Vdsd is generated by the second D / A converter DAC2 accordingly.

  During the horizontal blanking period, when the precharge control signal DSG becomes high level and the precharge switch 41 is turned on, the display signal line DL1 is precharged to the precharge potential Vdsd. Thereafter, the precharge control signal DSG becomes low level, and the precharge switch 41 is turned off.

  When the horizontal blanking period ends and one horizontal period starts, the pixel selection signal Vg1 supplied to the scanning line GL1 in the first row becomes high level, and the pixel 10 in the first row is selected. The Then, the video data R, G, B are D / A converted by the first D / A converter DAC1, and the display signal Vsig is generated. The display signal Vsig is amplified by the amplifier 32 and then output to the display signal lines DL1, DL2,... Through the horizontal switch 31 of the horizontal drive circuit 30, and the pixel selection TFT 11 of each pixel 10 passes through the pixel selection TFT 11. Applied to the pixel electrode 12.

  At this time, the difference between the target potential of the display signal Vsig and the precharge potential Vdsd is small, and the power consumption of the amplifier 32 is reduced.

  In the next horizontal blanking period, the display signal lines DL1, DL2,... Are precharged to another precharge potential Vdsd. The arithmetic circuit 50 calculates the average value of the video data R, G, B for the next one horizontal period, and accordingly, the precharge potential Vdsd is generated by the second D / A converter DAC2. .

  Then, when the next one horizontal period starts, the pixel selection signal Vg2 supplied to the second row scanning line GL2 becomes high level, the second row pixels 10 are selected, and display is performed in the same manner. The signal Vsig is amplified by the amplifier 32 and then output to the display signal lines DL1, DL2,... Through the horizontal switch 31 of the horizontal drive circuit 30. Also at this time, the difference between the target potential of the display signal Vsig and the precharge potential Vdsd is small, and the power consumption of the amplifier 32 is reduced.

  In this way, according to the present invention, the precharge potential Vdsd is optimized for each horizontal period in accordance with the magnitude of the video data R, G, B, so that the power consumption of the amplifier 32 is reduced.

  In the above embodiment, the first D / A converter DAC1, the amplifier 32, the arithmetic circuit 50, the second D / A converter DAC2, and the buffer BF are connected to the display panel 1 by SOG (System on Glass) technology. If it is to be formed above, a large circuit area is required, and the size of the display panel 1 becomes large. Therefore, as another embodiment of the present invention, as shown in FIG. 4, the first D / A converter DAC1 and the amplifier 32 are configured as a semiconductor integrated circuit chip IC1, and the arithmetic circuit 50, the second D / A The converter DAC2 and the buffer BF may be configured as the semiconductor integrated circuit chip IC2, and the semiconductor integrated circuit chips IC1 and IC2 may be mounted on the display panel 1 by COG (Chip on Glass) technology.

  The present invention can be applied not only to a liquid crystal display device but also to other display devices such as an organic EL display device as long as the display device includes a precharge circuit for setting display signal lines to a precharge potential. Can do.

1 is an equivalent circuit diagram of a liquid crystal display device according to an embodiment of the present invention. It is a figure which shows the relationship between a display signal and a precharge electric potential. FIG. 5 is an operation timing chart of the liquid crystal display device according to the embodiment of the present invention. FIG. 6 is an equivalent circuit diagram of a liquid crystal display device according to another embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Display panel 1A Display part 10 Pixel 11 Pixel selection TFT 12 Pixel electrode 13 Common electrode 14 Liquid crystal layer 15 Retention capacity 20 Vertical drive circuit 30 Horizontal drive circuit 31 Horizontal switch 41 Precharge switch 32 Amplifier 40 Precharge circuit 50 Arithmetic circuit

Claims (5)

A plurality of pixels;
A display signal line to which the plurality of pixels are connected;
A first D / A converter that D / A converts video data to generate a display signal;
A display device comprising: a precharge circuit that supplies a precharge potential to the display signal line and variably sets the precharge potential according to the video data. The precharge circuit includes: an arithmetic circuit that performs arithmetic processing on the video data; and a second D / A converter that generates the precharge potential according to an arithmetic result of the arithmetic circuit. The display device according to claim 1, characterized in that: The display device according to claim 2, wherein the arithmetic circuit calculates an average value of the video data corresponding to the plurality of pixels. The display device according to claim 2, wherein the arithmetic circuit calculates an average value of the most significant bits of the video data corresponding to the plurality of pixels. 5. The display device according to claim 2, wherein the arithmetic circuit and the second D / A converter are configured as a semiconductor integrated circuit chip.

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