JPH1114967A - Display control method, liquid crystal display device, projection display device and electronic equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To emphasize the black display of a margin area by keeping ON a sampling switch element for transmitting an image signal to a column electrode line during scanning of the margin area on a screen longer than that during supplying of an image signal to a usual display area. SOLUTION: In a letter box display mode, a shift start signal has a pulse width equal to two cycles of a shift clock CLX, and when shifted by a shift register 12 based on the shift clock CLX, a selecting signal having a pulse width equal to two cycles of the shift clock CLX and overlapped parts of high- level periods is formed, sampling switches S1, S2,..., are provided, and these switches are successively turned ON. At this time, a black level signal is inputted to an image signal supply line 14, this black level signal is transferred to corresponding column electrode lines D1, D2,..., by the sampling switches S1, S2,..., taking longer time than that for original image displaying, and sufficient charging is provided for the load capacity of the column electrode line.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display control technique in a liquid crystal display device, for example, a display control in an active matrix liquid crystal display device when displaying an image signal having a smaller number of scanning lines than the number of row electrode lines on a display screen. The present invention relates to a technique suitable for use in a system.

[0002]

2. Description of the Related Art Conventionally, as a matrix type liquid crystal display device, pixel electrodes are formed in a matrix on a substrate such as glass or quartz, and a TFT (thin film transistor) element is formed corresponding to each pixel electrode. An active matrix type liquid crystal panel having a configuration in which a liquid crystal is driven by applying a voltage to each pixel electrode by a TFT has been put to practical use.

When such a matrix type liquid crystal display device is used as a television image display device, there are existing television systems having different numbers of scanning lines such as the NTSC system and the PAL system. Unless the driving circuit is devised to enable the display, the image may be shifted or displayed in a non-uniform manner. More specifically, an NTSC video signal having about 485 effective scanning lines is displayed on a liquid crystal panel having about 576 effective scanning lines of the PAL system or a row electrode line nearly half of the number of the scanning lines. 16: 9 on a display device with an aspect ratio of 4: 3
When trying to display a wide-format video signal such as 5: 3 or 5: 3, as shown in FIG.

Conventionally, when scanning such a blank area, an image signal of a black level is supplied to perform black display to improve the appearance. Hereinafter, in this specification, an operation mode in which the upper and lower margin areas of the screen are displayed in black is referred to as a letterbox display mode.

[0005] When a normal video signal is displayed on a wide-screen display device, there is also a technique for supplying an image signal of a predetermined gradation level to a margin area so that a video signal of any type can be displayed. Yes, such inventions include:
For example, there is JP-A-3-131182.

[0006]

When a liquid crystal display panel is driven by the above-mentioned conventional display method, a sufficient black display cannot be performed even if a black level signal is supplied as an image signal in a blank area. There is a point. Specifically, in a so-called normally white mode liquid crystal display panel in which white is displayed in a state where no voltage is applied to a pixel, a higher voltage must be applied to a pixel to be displayed in black than to other pixels. In the conventional method, however, the applied voltage level of the pixel is often the same in both the black display in the display area and the black display in the blank area. Further, even if the voltage applied to the pixels in the blank area is increased by only the applied voltage level, the transmittance of the liquid crystal on the black side is often already saturated. For this reason, particularly, it was not possible to display the blank area blacker than the black level in the display area to perform sharp display.

SUMMARY OF THE INVENTION It is an object of the present invention to display an image according to a display method having a smaller number of scanning lines on a liquid crystal panel having a predetermined number of row electrodes, or to provide a liquid crystal panel having an aspect ratio of 4: 3. It is an object of the present invention to provide a liquid crystal display control technique capable of displaying a blank area blacker when displaying an image on a wide screen and performing sharp display.

Another object of the present invention is to provide a liquid crystal display control technique capable of displaying a high-quality image by enhancing black display in a margin area formed above and below a screen without increasing the scale of a driving circuit. Is to do.

[0009]

In order to achieve the above object, the present invention provides a method for displaying an image signal of a display system in which the number of scanning lines in an effective display range is smaller than the number of row electrode lines of a liquid crystal panel. When scanning the blank area generated in the above, the switch element for transmitting the image signal to the column electrode line is turned on for a longer time than when the image signal is supplied to the normal display area.

More specifically, in a liquid crystal display device in which a column electrode line drive circuit includes a sampling switch element connected to each column electrode line and a shift register for forming a selection signal for sequentially turning on the switch elements. When scanning the upper and lower margin areas of the screen in the letterbox display mode, a black level image signal is supplied instead of the original image signal in accordance with the timing of scanning the margin area, and the column electrode line driving circuit A start signal having a longer pulse width than usual is supplied to the shift register.

Thus, when scanning the blank area, the sampling switch element is turned on for a longer period than usual, and the image signal (black level signal) is sufficiently transmitted to the column electrode line. The black display in the margin area can be emphasized by sufficiently applying the black level voltage to the corresponding pixel. At the same time, in a liquid crystal panel in which the drive circuit is provided on the same substrate as the liquid crystal display unit, only the externally applied start signal needs to be switched, and the circuit on the panel does not need to be changed at all, and the margin area is emphasized. Black display.

When display control is performed by a liquid crystal panel in which each pixel includes a pixel electrode and a switch element, as a method of enhancing black display in a margin area, a sampling switch for transmitting an image signal to a column electrode line is used. Instead, a switch element for transmitting the potential of the column electrode line to the pixel electrode may be turned on for a longer time than usual. Such control can be easily realized in the letterbox display mode in which a blank area is formed above and below the screen by making the selection period of the row electrode line serving as the blank area longer than the selection period of the row electrode line in the normal display area. can do.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of a liquid crystal display device to which the present invention is applied.

In FIG. 1, reference numeral 1 denotes an active matrix type liquid crystal panel having a liquid crystal display unit in which a plurality of pixels are arranged in a matrix, 2 denotes an image signal processing circuit for correcting and amplifying an input image signal VIDEO, 3, a polarity inversion circuit for inverting the polarity of the amplified image signal in accordance with a predetermined cycle to generate a signal Video having a level suitable for driving the liquid crystal; and 4, a display mode of the input image signal, that is, an image of any display standard. The mode determination circuit 5 determines whether the signal is a signal, and a PLL (Phase Locked Loop) for forming a reference clock signal OSC based on the horizontal synchronization signal HSYNC.
Loop) circuit 6, based on the reference clock signal OSC, the vertical synchronizing signal VSYNC and the horizontal synchronizing signal HSYNC, a shift start signal DX1, DX2, DY for the shift register included in the driving circuit of the liquid crystal panel 1, and a shift operation clock CLX, CLY, a mask control signal MASK for designating a blank area for black display, a timing control circuit FR for forming and outputting a timing signal FR for controlling switching of polarity reversal to the polarity reversing circuit 3, and the like. Black level image signal Vb
A switching circuit for switching between the black level signal Vb and the image signal Video from the polarity inversion circuit 3 based on the mask control signal MASK, and supplying the image signal Video to the liquid crystal panel 1. , 9 are shift start signals DX1, DX output from the timing control circuit 6 based on the mask control signal MASK.
2 is a switching circuit for switching and supplying to the liquid crystal panel 1. These 8, 9 switching circuits can be easily formed by analog switches, multiplexers using gates, and the like.

The image signal processing circuit 2, the polarity inverting circuit 3, the black level signal generating circuit 7, and the switching circuit 8 may be formed on a single semiconductor chip and configured as a semiconductor integrated circuit.

In this embodiment, the shift start signal DX1 has a pulse width of one cycle of the shift clock CLX, and the shift start signal DX2 is
The shift circuit 9 is formed so as to have a pulse width of two periods of X, and when scanning the blank area, the shift circuit 9 selects the shift start signal DX2. The configuration is such that a black level signal Vb is selected and supplied to the liquid crystal panel 1 instead of the image signal. Shift start signals DX1, DX2
Are signals synchronized with the horizontal synchronization signal HSYNC. However, the pulse width of the shift start signal DX2 need not be exactly two periods of the shift clock CLX. In short, if the X shift register 12 has a pulse width sufficient to capture the shift start signal DX2 twice by the shift clock CLX and output a selection signal having a pulse width of two cycles of the shift clock CLX. Good.

The black level signal Vb is a signal whose polarity is inverted about the same potential as the center potential of the original image signal (video center Vc). Specifically, as shown in FIG. 10, the video center potential Vc Is, for example, 6 V, each side is generated to have an amplitude of about 4.5 to 5.0 V with respect to the video center potential Vc. In FIG. 10,
LC-COM is a potential called a liquid crystal common potential applied to an electrode opposed to the pixel electrode with the liquid crystal interposed therebetween, and is a so-called push-down (substantial writing voltage is reduced by capacitive coupling due to capacitive coupling). This is the voltage shifted in advance by that amount in consideration of the phenomenon of shifting. VG is a signal of a row electrode line selection level output from the row electrode line drive circuit.

FIG. 2 shows an example of a substrate on the pixel electrode side of the liquid crystal panel 1 driven by the liquid crystal drive control circuit according to the present invention. Although there is no particular limitation, the liquid crystal panel of this embodiment can display m images (for example, m = 260) corresponding to the number of scanning lines so that the display can be performed by a standard PAL image signal. To Gm.

In FIG. 2, D1 to Dn denote column electrode lines arranged so as to intersect with the row electrode lines, and 11 denotes a row electrode line G1 to G1 which performs a shift operation by the shift start signal DY and a shift operation clock CLY. A Y shift register 12 as a row electrode line drive circuit for forming and outputting signals VG1 to VGm of a selected level with respect to Gm. X1 to Xn. The X shift register forms and outputs selection signals X1 to Xn for sequentially supplying image signals to Dn to Dn. Pixels 15 are provided at intersections of the row electrode lines G1 to Gm and the column electrode lines D1 to Dn. The display unit 22 is configured by arranging these pixels in a matrix.

Reference numeral 13 denotes a terminal to which the analog image signal Video or the black level signal Vb output from the switching circuit 8 is input. The image signal supply line 14 connected to the image signal input terminal 13 and the respective column electrode lines are provided. Switches S1 to Sn composed of MOSFETs are provided between D1 to Dn, and select signals X1 to Xn output from the X shift register 12 are connected to control terminals (gate terminals) of these switch MOSFETs S1 to Sn. Is applied and the switch S
1 to Sn are sequentially turned on, so that the image signal on the image signal supply line 14 is changed to the column electrode lines D1 to Dn.
Are sequentially applied. In this specification, a circuit combining the X shift register 12 and the switch MOSFETs S1 to Sn is referred to as a column electrode line drive circuit 16.

The row electrode lines G1 to Gm and the column electrode lines D1 to Dn
And a pixel 15 provided at each intersection with a TFT 15a serving as a switching element having a source connected to the column electrode line D and a gate connected to the row electrode line G1, as typically shown only two. And a pixel electrode 15b made of ITO or the like connected to the drain terminal of the TFT 15a. In a color liquid crystal panel,
The image signal input terminal 13 and the image signal supply line 14
Are provided for each of the three primary colors, and each of the column electrode lines is connected to the corresponding color image signal supply line 14 every other line.

Next, the operation of the liquid crystal display device of the embodiment will be described with reference to the timing charts of FIGS.

The timing control circuit 6 of the above embodiment
Indicates that when it is determined that the mode is the letterbox display mode, FIG.
As shown in FIG. 3, the Y shift register 11 synchronized with the vertical synchronization signal VSYNC included in the image signal.
When the shift operation is started by the start signal DY becoming high level and the row electrode lines are sequentially selected, the low level is maintained while the row electrode line corresponding to the pixel displaying the original image signal is selected. The mask control signal MASK for controlling the display of the blank area, which is set to the high level while the row electrode line corresponding to the pixel serving as the other blank area is selected.
Is formed and output. On the other hand, the timing control circuit 6
When it is determined that the normal full-screen display mode is not the letterbox display mode, the mask control signal MASK is continuously output at a low level.

Here, among the timing signals output from the timing control circuit 6, DX (DX1, DX2) is a start signal for giving a shift start timing of the X shift register 12, and is converted into an image signal with one horizontal scanning period as a cycle. HS formed based on the included horizontal synchronization signal
This signal has a relatively short pulse width synchronized with YNC. CLX is a shift operation clock of the X shift register 12, and the reference clock signal OSC from the PLL circuit 5 is provided so that at least two or more pulses of the X shift register 12 are provided between two pulses of the start signal DX.
It is formed based on. And the start signal DX
1 is formed as a signal having a pulse width of substantially one cycle of CLX. The signal OFH is the start signal DX.
Is a clock signal having the same cycle and a duty of approximately 50%, and is formed based on the horizontal synchronizing signal HSYNC similarly to DX.

In the timing signal supplied from the timing control circuit 6 to the liquid crystal panel 1, DY is a start signal for giving a shift start timing of the Y shift register 11, and has one vertical scanning period as a cycle and is included in the image signal. The signal is synchronized with VSYNC formed based on the vertical synchronization signal and is formed as a signal having a pulse width of about two cycles of the clock signal OFH. Also, C
LY is a shift operation clock of the Y shift register 11, and
Based on the clock signal OFH, it is formed as a signal having a frequency of 1/2 of OFH. Y shift register 11
Shifts one bit at a time in synchronization with the rising and falling edges of the clock CLY.

The operation in the letterbox display mode will be described below in comparison with the normal full screen display mode. FIG. 5 shows the timing in the normal full screen display mode, and FIG. 6 shows the timing in the letterbox display mode.

In the normal full-screen display mode, the timing control circuit 6 continuously outputs the low-level mask control signal MASK as described above. As a result, in the switching circuit 8, the original image signal V from the polarity inversion circuit 3 is output.
is selected and supplied to the liquid crystal panel 1, and the shift start signal D is continuously output by the switching circuit 9.
X1 is selected and supplied to the liquid crystal panel 1. The shift start signal DX1 is approximately 1 of the shift clock CLX.
Since the shift start signal DX1 is taken into the shift register 12 and shifted by the shift clock CLX because of having a pulse width of a cycle, as shown in FIG. Selection signals X1 having a width and high levels not overlapping each other
X2, X3,... Are formed, and the sampling switches S1, S2, S3,.

Therefore, in the normal full screen display mode,
Selection signals X1, X2, X3,... Having the same pulse width are supplied from the first row electrode line to the last row electrode line of the display unit 22. As a result, the image signal on the image signal supply line 14 is transmitted to each of the column electrode lines D1 to Dn under the same conditions, so that the image signal is uniformly displayed over one screen.

On the other hand, in the letterbox display mode, as shown in FIG. 3, the timing control circuit 6 sends a signal before and after the start signal DY of the Y shift register 11 (in this embodiment, from the first row electrode line to the fifteenth row electrode). A high-level mask control signal MASK is output over a period up to the line 246 and a period from the electrode line 246 to the electrode line 260. Thus, the switching circuit 8 selects the black level signal Vb instead of the original image signal and supplies it to the liquid crystal panel 1 only while the mask control signal MASK is at the high level, and the switching circuit 9 sets the MASK to the high level. The period is the shift start signal DX
DX2 is selected instead of 1 and supplied to the liquid crystal panel 1.

Since the shift start signal DX2 has a pulse width of two cycles of the shift clock CLX, when this shift start signal DX2 is taken into the shift register 12 and shifted by the shift clock CLX, it is shown in FIG. The shift clock CLX
Selection signals X1 ', X2', X3 ',... Having a pulse width of two periods
Are formed, and the sampling switches S1, S2,
S3 and ‥‥‥ are sequentially turned on. At this time, since the black level signal Vb is input to the image signal supply line 14, the black level signal is supplied to the corresponding column electrode line D1, D2 by the turned on sampling switches S1, S2, S3 #. D2, D3} are transferred over a longer time than when the original image is displayed, and the load capacity of the column electrode line is sufficiently charged.

As a result, as compared with the case where the sampling switches S1, S2, S3,... Are turned on by the narrow selection signals X1, X2, X3,. At that time, a voltage corresponding to the black level is sufficiently applied to the pixel selected by the row electrode line, and a black level stronger than the black level in the display area is displayed in the margin area.

Therefore, in the letterbox display mode,
Pixels corresponding to the 15 upper and lower row electrode lines on the screen are displayed in black, and a sharp image is obtained. In general, when it is desired to enhance the black display, it may be considered that the input black level voltage may be increased. However, the sampling switches S1, S2, S3,.
In the case of the ET configuration, when these elements are turned on, they operate in the saturation region. Therefore, even if the level of the input image signal is increased and the source-drain voltage is increased, the MOSFET is not turned on. Since the drain current does not increase due to the characteristics in the saturation region, the level of the column electrode line cannot be increased even if the black level voltage is increased. However,
In the above embodiment, the sampling switches S1, S2,
Since the time during which S3 and ‥‥‥ are turned on is lengthened, the column electrode lines D1, D2 and D3 can be used without increasing the black level voltage.
黒 can be transmitted sufficiently to enhance the black display.

In the above embodiment, it has been described that the selection signals X1, X2, X3,... For scanning the normal display area are formed so that their high levels do not overlap each other. When an image signal whose resolution does not matter so much is displayed, there is no problem even if the high levels of the selection signals slightly overlap. In the above embodiment, in the horizontal scanning period corresponding to the blank area, a signal DX2 having a pulse width of two cycles of the shift clock is used as a start signal instead of the signal DX1 having a pulse width of one cycle of the shift clock CLX. Although formed by the timing control circuit 6 and supplied to the liquid crystal panel 1, the pulse width of the start signal DX2 can be not less than two periods of the shift clock but three or more periods. Can be displayed even stronger black.

However, if the pulse width of the start signal DX2 is excessively widened, the image signal of the next row electrode line is output while the final stage of the X shift register 12 is still outputting the high-level selection signal Xn. Since the light enters the signal supply line 14, the pulse width may be set within a range in which this can be avoided. Usually, a television image signal includes a horizontal blanking period. Therefore, even if the pulse width of the start signal DX2 is set to two periods of the shift clock, the selection signal of the last stage of the X shift register 12 within the horizontal blanking period. Xn can be easily configured to be completely output.

In a liquid crystal panel, dummy pixels which do not contribute to display may be provided around the effective display section. In such a case, the shift register is configured to be longer by an amount corresponding to the dummy pixels. The shift operation may be terminated by resetting the shift register when the selection signal has shifted to the bit corresponding to the dummy pixel. As a result, it is possible to perform sufficient black display in the pixels which are in the blank area in the effective display section, and to prevent the display level from being lowered by the image signal of the next row electrode line.

Further, as a method of enhancing the black display in the margin area, the on-time of the sampling switch for transmitting the image signal to the column electrode line is lengthened in the above embodiment.
Instead or in combination therewith, for example, by devising the Y shift register 11 so that the selection signal of the row electrode line in the blank area is longer than the selection signal of the row electrode line in the display area, the signal on the column electrode line can be changed. The switch element 15a to be transmitted to the pixel electrode 15b may be turned on for a longer time than usual.

In the above embodiment, a row electrode line driving circuit including a Y shift register and a column electrode line driving circuit including an X shift register are applied to a display device using a liquid crystal panel in which a liquid crystal display portion is formed on the same substrate. However, the present invention is not limited thereto, and can be applied to a liquid crystal display device in which a driving circuit is configured separately from a liquid crystal panel. However, if at least the column electrode line drive circuit is applied to a circuit formed on a liquid crystal panel, the margin area of the screen can be sharpened without changing the drive circuit configuration and without increasing the circuit scale. Since a certain black display can be performed, in order to reduce the size of the liquid crystal panel, it is most effective to apply at least a column electrode line drive circuit formed on the liquid crystal panel.

In the above embodiment, the embodiment of the liquid crystal display device in which the image signal of the NTSC system can be displayed on the liquid crystal panel capable of displaying the image signal of the PAL system has been described. However, the present invention is not limited to this. 800 × 60
The present invention is also applied to a case where display is performed by a low-resolution image signal according to a 640 × 480 dot VGA (Video Graphics Array) standard on a high-resolution liquid crystal panel according to a 0-dot SVGA (Super Video Graphics Array) standard. be able to. Similarly, by devising the X shift register, the present invention is also applied to a display control for emphasizing black display in a margin area generated on the left and right sides of a screen when displaying an image having an aspect ratio of 4: 3 on a wide screen liquid crystal panel. Can be applied.

In the above embodiment, the case where the Y shift register 11 is provided only at one end of the row electrode line has been described. However, the Y shift register 11 is provided on the opposite side (the right side in the figure) of the row electrode lines G1 to Gm. A shift register similar to the Y shift register 11 may be provided so that the same voltage is applied to each row electrode line at the same timing, that is, one row electrode line 11 is simultaneously driven from both sides. . This can reduce a voltage level drop and a signal delay due to the parasitic resistance of the row electrode line 11.

Further, a precharge FET for applying a precharge level to each column electrode line is provided on the opposite side (lower side in the figure) of the column electrode lines D1 to Dn, and before applying an image signal to the column electrode lines. Alternatively, it may be configured to precharge to a predetermined level. Thus, the level of the column electrode line can be accurately transmitted to the pixel electrode within a short time. Further, the X and Y shift registers 11 and 12 may be configured as bidirectional shift registers so as to be able to shift in any direction.

The liquid crystal display device of the above embodiment can be applied to the case where either a transmissive liquid crystal panel or a reflective liquid crystal panel is used. However, the liquid crystal display device is configured so that each pixel has a TET and a storage capacitor. In a transmissive liquid crystal panel which needs to be covered with a light shielding film or a black matrix of a counter substrate so that light does not pass through, the aperture ratio cannot be made too high. On the other hand, in a reflective liquid crystal panel, the pixel electrodes are composed of reflective electrodes made of an aluminum layer or the like.
Even if a switching TET or a storage capacitor is formed below the pixel electrode, the aperture ratio does not decrease. Therefore, when it is desired to form a liquid crystal display device having a high aperture ratio, a reflective liquid crystal panel may be used. In the reflection type liquid crystal panel, the pixel electrode is formed of an electrode having a high reflectance such as aluminum. In the transmissive liquid crystal panel, the pixel electrode is formed of a transparent electrode such as ITO.

FIG. 7 is a schematic configuration diagram of a main part of a video projector (projection display device) as an example of an applied device to which the liquid crystal display device of the present invention is applied, as viewed in plan.

In FIG. 7, 370 is a light source such as a halogen lamp, 371 is a parabolic mirror, 372 is a heat ray cut filter, 373, 375 and 376 are blue reflections,
Green reflection, red reflection dichroic mirror, 374
377 is a reflection mirror, 378, 379 and 380 are light valves composed of liquid crystal panels, and 383 is a dichroic prism.

In the video projector of this embodiment, the white light emitted from the light source 370 is condensed by the parabolic mirror 371, passes through the heat ray cut filter 372, blocks the heat rays in the infrared region, and allows only visible light. The light enters the dichroic mirror system. First, the blue light (wavelength of about 50 nm or less) is reflected by the blue reflecting dichroic mirror 373, and the other light (yellow light) is transmitted. The reflected blue light changes its direction by the reflection mirror 374 and enters the blue modulation light valve 378.

On the other hand, the light transmitted through the blue reflection dichroic mirror 373 is reflected by the green reflection dichroic mirror 3.
75, the green light (wavelength of about 500 to 600 nm) is reflected, and the other light, red light (about 600 nm)
nm or more) is transmitted. Dichroic mirror 3
The green light reflected at 75 is a green modulated light valve 379
Incident on. The red light transmitted through the dichroic mirror 375 changes its direction by the reflection mirrors 376 and 377 and enters the red modulation light valve 380.

The light valves 378, 379, 380
The light, which is driven by the blue, green, and red primary color signals supplied from the image signal processing circuit, is incident on each light valve, is modulated by each light valve, and is synthesized by the dichroic prism 383. The dichroic prism 383 is formed such that the red reflection surface 381 and the blue reflection surface 382 are orthogonal to each other. Then, the color image synthesized by the dichroic prism 383 is enlarged and projected on the screen by the projection lens 384 and displayed. Reference numeral 385 denotes a control circuit including the timing control circuit 6, the black level signal generation circuit 7, and the switching circuits 8 and 9.

FIG. 8 shows a liquid crystal television and an information processing apparatus as another example of applied equipment to which the liquid crystal display device of the present invention is applied.

FIG. 8A shows a liquid crystal television. Reference numeral 1100 denotes a television main body, and 1101 denotes a liquid crystal display unit using a liquid crystal panel. In this liquid crystal television, a control circuit including the timing control circuit 6, the black level signal generation circuit 7, and the switching circuits 8 and 9 of the above embodiment is built in the television main body 1100 behind the liquid crystal panel 1101.

FIG. 8B shows a portable information processing apparatus such as a word processor or a personal computer. 1200 is an information processing device, 1202 is an input unit such as a keyboard, 1206 is a display unit using a liquid crystal panel, and 1204 is a main unit of the information processing device.

[0051]

As described above, according to the present invention, when displaying an image signal of a display method in which the number of scanning lines in the effective display range is smaller than the number of row electrodes of the liquid crystal panel, a blank area generated on the screen is reduced. When scanning, the sampling switch element for transmitting the image signal to the column electrode line is turned on for a longer time than when the image signal is supplied to the normal display area. Since the sampling switch element is turned on for a longer period than usual and the image signal (black level signal) is sufficiently transmitted to the column electrode line, the black level voltage is sufficiently applied to the corresponding pixel, and the blank area is formed. There is an effect that the black display can be emphasized.

Further, in the liquid crystal display device, the column electrode line drive circuit includes a sampling switch element connected to each column electrode line and a shift register for forming a selection signal for sequentially turning on the switch elements. When scanning the upper and lower margin areas of the screen in the display mode, a black level signal is supplied instead of the original image signal in accordance with the timing of scanning the margin area,
A start signal having a longer pulse width than usual is supplied to the shift register of the column electrode line drive circuit. Therefore, in a liquid crystal panel in which the drive circuit is provided on the same substrate as the liquid crystal display section, a start signal applied from outside is provided. Only the signal needs to be switched, and there is an effect that the black display with emphasis on the blank area can be performed without any change in the circuit on the panel.

In particular, in a liquid crystal display device which requires a high resolution, the higher the resolution, the narrower the pulse width of the selection signal output from the shift register. However, the on-time of the sampling switch element for transmitting the image signal to the column electrode line is shortened, and the black level in the marginal area tends to be further reduced. Even in the display device, the blank area can be displayed sufficiently black.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration example of a liquid crystal display device according to the present invention.

FIG. 2 is a circuit diagram showing an example of a substrate on a pixel electrode side of a liquid crystal panel used in the liquid crystal display device according to the present invention.

FIG. 3 is a timing chart showing a relationship among various timing signals in the liquid crystal display device of the embodiment.

FIG. 4 is a timing chart showing in detail the interrelationship of various timing signals within a shorter time than in FIG. 3 in the liquid crystal display device of the embodiment.

FIG. 5 is a timing chart showing a relationship between a start signal and a column electrode line selection signal in a normal full screen display mode in the liquid crystal display device of the embodiment.

FIG. 6 is a timing chart showing a relationship between a start signal of a blank area and a column electrode line selection signal in the letterbox display mode in the liquid crystal display device of the embodiment.

FIG. 7 is a schematic configuration diagram of a projector applied to a projection display device using a liquid crystal panel of the liquid crystal display device of the embodiment as a light valve.

FIG. 8 is a perspective view showing a schematic configuration example of a liquid crystal television and a portable personal computer to which the present invention is applied.

FIG. 9 is a diagram showing a screen displayed when a low-resolution image signal is displayed on a high-resolution liquid crystal panel or when a video signal such as 16: 9 or 5: 3 is displayed on a display device having an aspect ratio of 4: 3. Explanatory drawing which shows a state.

FIG. 10 is a waveform diagram showing an example of a black level signal used for displaying a blank area.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 liquid crystal panel 2 image signal processing circuit 3 polarity inversion circuit 4 display mode determination circuit 5 clock generation PLL circuit 6 timing control circuit 7 black level generation circuit 8 image signal switching circuit 9 start signal switching circuit G1 to Gm row electrode lines D1 to Dn Column electrode line 11 Row electrode line drive circuit (Y shift register) 12 Column electrode line drive circuit (X shift register) 13 Image signal input terminal 14 Image signal supply line 15 Pixel 15a Switching TFT 15b Pixel electrode 101, 102 Margin area 370 Lamp 373, 375, 376 Dichroic mirror 374, 377 Reflection mirror 378, 379, 380 Light valve 383 Dichroic prism 384 Projection lens

Claims (7)

[Claims] 1. A plurality of row electrode lines and a plurality of column electrode lines arranged in a grid, and a plurality of pixels arranged in a matrix corresponding to each intersection of the row electrode lines and the column electrode lines. A voltage based on an image signal is applied to the column electrode line via a switch element, and a pixel selected by the row electrode line is based on the image signal via the column electrode line. A display device that performs display by applying a voltage applied to the display unit, wherein when performing display based on an image signal of a display method in which the effective display range is smaller than the number of pixels of the display unit, the display unit Wherein the switch element for transmitting an image signal is turned on for a longer period of time than when an image is supplied to a normal display area when displaying a blank area which occurs in the display control method. A plurality of pixels arranged in a matrix, a plurality of row electrode lines and a plurality of column electrode lines arranged in a grid, and a pixel selected by the row electrode line is provided with a column electrode. A liquid crystal display unit for performing display by applying a voltage based on an image signal via a line;
A row electrode line driving circuit for sequentially selecting the row electrode lines according to the clock signal; a start signal synchronized with a horizontal synchronization signal; and a second clock signal having a shorter cycle than the first clock signal. A column electrode line driving circuit for outputting a signal based on an image signal, a first start signal synchronized with a horizontal synchronization signal, a second start signal having a pulse width longer than the first start signal, and a blank area A timing control circuit for forming and outputting a signal;
A first switching circuit for selecting either a first start signal or a second start signal according to the control signal supplied from the timing control circuit and supplying the selected signal to the column electrode line driving circuit; A black level signal generation circuit for generating a signal for causing the display means to perform black level display; and a black signal output from the black level signal generation circuit according to the control signal supplied from the timing control circuit. A second switching circuit for selecting any one of the level signals and supplying the selected signal to the liquid crystal display means. 3. The column electrode line drive circuit is started by a first start signal or a second start signal supplied from the first switching circuit, and is shifted and selected in synchronization with the second clock signal. A shift register that sequentially outputs signals, and an image signal or a black level signal supplied from the second switching circuit that is turned on and off by the selection signal output from the shift register and can be sequentially transmitted to the column electrode lines The liquid crystal display device according to claim 2, comprising a plurality of switch elements. 4. The row electrode line drive circuit and the column electrode line drive circuit are formed on the same substrate as a substrate constituting the display means.
3. The liquid crystal display device according to 1. 5. The pixel has a control terminal connected to the pixel electrode and the row electrode line, and is turned on and off by the row electrode line drive circuit to apply a voltage on a column electrode line to the corresponding pixel electrode. 5. The liquid crystal display device according to claim 2, comprising a switching element. 6. The liquid crystal display device according to claim 2, further comprising: a light source; and a liquid crystal panel that modulates and transmits or reflects light from the light source, and condenses the light modulated by the liquid crystal panel. A projection display device comprising: projection optical means for enlarging and projecting. 7. An electronic apparatus, comprising: a data output unit comprising the liquid crystal display device according to claim 1; and a data input unit.