JP2009163079A - Electrooptical device, driving method and projector thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrooptical device capable of reducing circuit load, thereby efficiently suppressing occurrence of scroll noise and reducing adverse effects to the service life of a light source. <P>SOLUTION: The electrooptical device comprises: a display panel having a plurality of pixels; a signal output circuit which outputs a timing signal with a presctibed period; a driving circuit which drives the display panel with the period of the outputting of the timing signal; the light source from which the display panel is irradiated with light rays through AC driving, according to a prescribed light source signal; and a frequency control circuit which changes a frequency of the light source control signal in the range of the prescribed frequency, with such a timing, as to have a prescribed relation to an output timing, in a period of time, until an integer-fold time of the prescribed period is elapsed, starting from the output timing of the timing signal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a technique for improving display quality in an electro-optical device such as a projector.

There is a projector that generates a reduced image using a light valve such as a liquid crystal panel, and enlarges and projects the reduced image using an optical system. As a light source used in such a projector, a high-pressure discharge lamp or the like is used, and AC driving using a pulse or a triangular wave is performed in order to extend its life (see Patent Document 1). As a result, since the light amount of the light source increases immediately after the polarity is switched, the light source blinks at a frequency twice the driving frequency. On the other hand, the liquid crystal panel is, for example, 50 Hz in the PAL system and 100 in the double speed driving system.
It is driven at a constant frequency such as Hz, and blinks according to the driving frequency.

Here, depending on the relationship between the driving frequency of the light source and the driving frequency of the liquid crystal panel, the flickering components may interfere with each other to generate a low-frequency component, resulting in flickering or scrolling bands (scrolling noise). Display quality may be deteriorated. In order to improve this, a technology is disclosed in which the driving frequency of the light source is set to a frequency at which scroll noise is difficult to see with respect to the driving frequency of the liquid crystal panel (see Patent Document 2). Further, a technique for changing the driving frequency of the light source is disclosed irrespective of driving of the liquid crystal panel so that the interference component does not have regularity (see Patent Document 3).
JP 2003-36992 A JP 2003-156798 A JP 2006-72196 A

Here, in the technique of Patent Document 2, depending on the driving frequency of the liquid crystal panel, the driving frequency of the light source for reducing scroll noise may be a frequency that adversely affects the lifetime. In the technique of Patent Document 3, depending on the mode of changing the driving frequency of the light source, scroll noise may occur if the changed driving pulse is similar for each video frame. In order to achieve this, it is necessary to frequently change the drive frequency, which increases the circuit load.

The present invention has been made in view of the above-described circumstances, and an electro-optical device that reduces the circuit load and efficiently suppresses the generation of scroll noise and reduces the adverse effect on the life of the light source,
An object is to provide a driving method and a projector.

In order to solve the above problems, the present invention drives a display panel having a plurality of pixels, a signal output circuit that outputs a timing signal at a predetermined period, and the display panel at a period at which the timing signal is output. A drive circuit that performs light source irradiation to the display panel by AC driving according to a predetermined light source control signal, and a period from the output timing of the timing signal to a time that is an integral multiple of the predetermined period And a frequency control circuit that changes the frequency of the light source control signal within a predetermined number range at a timing having a predetermined relationship with the output timing. According to this electro-optical device, since the driving frequency of the light source can be changed at any timing within one frame, the occurrence of scroll noise can be suppressed even if the frequency of changing the driving frequency of the light source is small. it can. Further, by changing the drive frequency within a predetermined number range, the light source can be driven in the vicinity of the frequency that does not adversely affect the life of the light source.

In another preferable aspect, the frequency control circuit changes the frequency of the light source control signal at any timing after the output timing of the timing signal and at which the light source control signal has a predetermined phase. You may do it. In this way, the timing at which the frequency of the light source control signal is changed is limited to a predetermined phase, so that the configuration for changing the frequency of the light source control signal can be simplified.

In another preferable aspect, the frequency control circuit may change the frequency of the light source control signal at the output timing of the timing signal. In this way, since the frequency of the light source control signal can be changed when the timing signal is output, the frequency of the light source control signal can be changed at intervals of one frame or more.

Note that the present invention can be conceptualized not only as an electro-optical device, but also as a driving method of the electro-optical device and a projector having the electro-optical device.

  Embodiments of the present invention will be described below with reference to the drawings.

<Embodiment>
FIG. 1 is a plan view showing a configuration of a projector to which an electro-optical device according to an embodiment of the invention is applied. As shown in FIG. 1, a projector 2100 is provided with a lamp 2102 made of a white light source such as a halogen lamp driven by alternating current.

The projection light emitted from the lamp 2102 is composed of three mirrors 2106 disposed inside.
And two dichroic mirrors 2108, 3 for R (red), G (green), and B (blue).
The light is separated into primary colors and led to display panels 100R, 100G, and 100B corresponding to the primary colors. Note that the B-color light has an incident lens 2122, a relay lens 2123, and an exit lens 21 in order to prevent loss due to a long optical path compared to other R colors and G colors.
It is guided through a relay lens system 2121 comprising 24.

As will be described later, the display panels 100R, 100G, and 100B are each driven by display data corresponding to each color of R, G, and B, whereby a reduced image of each color is formed.
Reduced images formed by the display panels 100R, 100G, and 100B, that is, modulated light, enters the dichroic prism 2112 from three directions. In the dichroic prism 2112, the R and B light is refracted at 90 degrees,
G light goes straight. Therefore, after the images of the respective colors are combined, a color image is projected onto the screen 2120 by the projection lens 2114.

The display panels 100R, 100G, and 100B include a dichroic mirror 21.
Since the light corresponding to the primary colors of R, G, and B is incident by 08, there is no need to provide a color filter. In addition, the transmission images of the display panels 100R and 100B are projected after being reflected by the dichroic prism 2112, whereas the transmission images of the display panel 100G are projected as they are, so that the reduced images formed by the display panels 100R and 100B. And the reduced image formed by the display panel 100G are in a horizontally reversed relationship.

Next, an electro-optical device with control of the display panels 100R, 100G, and 100B will be described.

FIG. 2 is a diagram illustrating a configuration of the electro-optical device 10. As shown in FIG. 2, the electro-optical device 1
0 includes the control circuit 12, the display panels 100R, 100G, 100B, and the like. Among these, the display panels 100R, 100G, and 100B are driven by the drive circuits 14R, 14G, and 14B, respectively, corresponding to the primary colors of R, G, and B, respectively.

FIG. 3 is a diagram showing the configuration of the display panel 100R and the drive circuit 14R. In FIG. 3, the display panel 100R is described as an example, but the display panels 100R, 100G, 1
The configurations of 00B are the same. Therefore, the following description of the display panel 100R is similarly applied to the display panels 100G and 100B.
, 100B and the reduced image formed by the display panel 100G are in a horizontally reversed relationship as described above.

As shown in FIG. 3, in the display panel 100R, 1080 scanning lines 112 are arranged in the horizontal direction (X
The data lines 114 of 1920 columns are extended in the vertical direction (Y direction).
Each of the plurality of pixels 110 forming the reduced image has these scanning lines 112 and data lines 114.
Are arranged corresponding to each intersection. As described above, in the present embodiment, the pixels 110 are arranged in a matrix of 1080 vertical rows by 1920 horizontal columns, but the present invention is not limited to this arrangement, and the intersection of a plurality of scanning lines and a plurality of data lines. Any arrangement may be used as long as it is provided corresponding to.

The pixel 110 includes a liquid crystal element and a switching transistor (hereinafter referred to as a TFT) that is turned on or off between one end of the liquid crystal element and the data line. this house,
The liquid crystal element is a kind of capacitance in which liquid crystal is sandwiched between one end and the other end maintained at a constant potential, and has a transmittance according to the effective value of the holding voltage. The TFT is turned on when the scanning line 112 is selected and connects one end of the liquid crystal element to the data line 114.

The drive circuit 14R is divided into a Y driver 142 that drives the scanning line 112 and an X driver 144 that drives the data line 114. Of these, the Y driver 142 is 1, 2, 3,.
Scan signals Y1, Y2, Y3,..., Y1080 are supplied to the scan line 112 in the 1080th row.
Specifically, in this embodiment, the Y driver 142 sets the scanning line 112 to 1, 2, 3,.
In the order of the 80th row, the scanning signal to the selected scanning line is set to a level for turning on the TFT, and the scanning signal to the other scanning line is set to a level for turning off the TFT. This is controlled by a scanning control signal Cry output from the control circuit 12 described later. On the other hand, the X driver 144 sends a data signal X to the data line 114 in the 1, 2, 3,.
1, X2, X3,..., X1920 are supplied. Specifically, the X driver 144 outputs a voltage data signal corresponding to the gradation value of the pixel (the gradation value specified by the display data Dr) to the pixel 110 located on the selected scanning line 112. The data line 114 is supplied. The display data Dr is R component display data supplied in synchronization with scanning of the display panel 100R, that is, in synchronization with a scanning control signal Cry described later. The display data Dg supplied to the drive circuit 14G and the display data Db supplied to the drive circuit 14B are:
The display data of the G component and B component, respectively. The display data Vd constituting the display data Dr, Dg, and Db is supplied from a higher-level device (not shown) in synchronization with the synchronization signal Sync.

As a result, the liquid crystal element in the pixel holds a voltage corresponding to the gradation and has a transmittance corresponding to the holding voltage. In addition, since a liquid crystal may be deteriorated when a direct current component is applied, the drive of the liquid crystal element is basically an alternating current drive. Therefore, X driver 14
4 supplies the voltage of the data signal supplied to the same liquid crystal element by alternately switching the voltage at the other end of the liquid crystal element between the high-order side (positive polarity) and the low-order side (negative polarity).

Returning to FIG. 2, the description will be continued. The control circuit 12 controls the operation of each part of the electro-optical device 10. The control circuit 12 controls the drive circuits 14R, 14G, and 14B with the scanning control signals Cry, Cgy, and Cby, respectively, so as to synchronize with the supply operation of the display data Dr, Dg, and Db of the display data Vd that is synchronized with the synchronization signal Sync. To do. Further, the control circuit 12 outputs a light source control signal Lf having a frequency fw corresponding to a frequency that is approximately twice the drive frequency of the light source drive signal Fla to the lighting circuit 20 described later. Here, of the configuration of the control circuit 12,
The configuration relating to the output of the scanning control signals Cry, Cgy, Cby and the light source control signal Lf will be described with reference to FIG.

FIG. 4 is a diagram illustrating a configuration of the control circuit 12. As shown in FIG. 4, the control circuit 12 outputs a timing signal DY at a period of one frame period corresponding to the input synchronization signal Sync, and generates a scanning control signal Cry corresponding to the timing signal DY. , Cgy, Cby
Is output. Further, when the timing signal is output, the control circuit 12 outputs a light source control signal Lf whose frequency fw is changed. Hereinafter, each configuration of the control circuit 12 will be described.

When the synchronization signal Sync is input, the signal output circuit 121 outputs the timing signal DY at a period of one frame period. In the present embodiment, the signal output circuit 121 has a PAL
The sync signal Sync of 50 Hz in the system is input, and 100H corresponding to the double speed drive
The timing signal DY is output every z period, that is, every 10 milliseconds. This timing signal DY is output to the scanning signal control circuit 122 and the frequency control circuit 123.

The scanning signal control circuit 122 is synchronized with the output timing signal DY and 1
Scan control signals Cry, Cgy, and Cby are generated so that the frame period is 10 milliseconds, and are output to the drive circuits 14R, 14G, and 14B, respectively. As a result, the drive circuit 14
R, 14G, and 14B are display panels 100R, 1 in a cycle in which the timing signal DY is output.
00G and 100B are driven. That is, the display panels 100R, 100G, and 100B are
Each frame is controlled so that the period of one frame is synchronized with each other in 10 milliseconds.

The frequency control circuit 123 controls the frequency fw of the light source control signal Lf output from the control signal output circuit 124 described later. This control is performed by changing the frequency fw from a frequency within a predetermined number range to a randomly selected frequency when the timing signal DY is output.

The frequency within the predetermined number range is determined as a range of about ± 1% around a frequency fc twice as long as a recommended drive frequency at which the life of the lamp 2102 is extended and a stable light quantity is obtained. The timing for changing the frequency fw is performed at a timing having a predetermined relationship with the output timing in a period from the output timing of the timing signal DY to a period before one frame period elapses. The frequency control circuit 123 may change the frequency fw when the timing signal DY is output a plurality of times. In this case, the frequency f
The timing for changing w is performed at a timing having a predetermined relationship with the output timing in the period from the output timing of the timing signal DY to the period before the period of the plurality of frames elapses.

The timing having the predetermined relationship is the timing at which the pulse signal related to the light source control signal Lf is first generated after the output timing of the timing signal DY. Note that the timing having the predetermined relationship may be a timing at which the pulse signal is generated a plurality of times, and may be any timing at which the light source control signal Lf has a predetermined phase. Further, the timing having the predetermined relationship may be the output timing of the timing signal DY, or may be the timing when a predetermined time has elapsed from this output timing.

The control signal output circuit 124 outputs the light source control signal Lf having the frequency fw to the lighting circuit 20. This frequency fw is changed by a frequency within a predetermined number range at a predetermined timing by the frequency control circuit 123 as described above. The above is the scanning control signal Cry of the control circuit 12.
, Cgy, Cby and the configuration relating to the output of the light source control signal Lf.

Returning to FIG. 2, the description will be continued. The lighting circuit 20 generates a drive signal Fl according to the light source control signal Lf.
The lamp 2102 is AC driven by outputting a. Specifically, the lighting circuit 20 performs a process of switching the polarity of the drive signal Fla at a timing at which a pulse signal related to the light source control signal Lf is generated. That is, the drive signal Fla that is an AC signal having a frequency that is half the frequency fw of the light source control signal Lf is output to the lamp 2102, and the lamp 2102 is AC driven. Here, when the polarity of the drive signal Fla is switched, the pulse shape of the drive signal Fla is adjusted (not shown) in order to increase the life of the lamp 2102. As a result, the lamp 2102 repeats blinking at the frequency fw because the amount of light increases immediately after the polarity is switched.

Next, the operation of the electro-optical device 10 according to the present embodiment will be described with reference to FIGS. 5 and 6 in comparison with the conventional technique in which the frequency fw of the light source control signal Lf is fixed to the frequency fc. .

FIG. 5 shows a timing signal DY, a light source control signal Lf, and a drive signal Fl in the prior art.
It is a figure which shows the relationship of a. The horizontal axis in FIG. 5 indicates the progress of time. In the prior art,
Since the frequency fw of the light source control signal Lf is fixed to the frequency fc, depending on the relationship between the period of one frame and the frequency fc, as shown in FIG. 5, the output timing of the timing signal DY and the control signal Lf The relative relationship (see the arrow in the figure) with the timing at which the pulse signal is generated shifts by a certain amount over time. As a result, the timing at which the light amount of the lamp 2102 increases and the position of the scanning line selected at that timing are gradually shifted and recognized as scroll noise. At this time, the closer the relationship between the period of one frame and the integral multiple of the period corresponding to the frequency fc is, the easier it is to be visually recognized because the relative relationship is shifted slowly. growing.

FIG. 6 is a diagram illustrating a relationship among the timing signal DY, the light source control signal Lf, and the drive signal Fla in the electro-optical device 10 according to the present embodiment. The horizontal axis of FIG. 6 shows the progress of time. As described above, when the timing signal DY is output, the frequency fw of the light source control signal Lf is changed by a frequency within a predetermined number range. For example, as shown in FIG.・ ・ It will be changed. As a result, the relative relationship between the output timing of the timing signal DY and the timing at which the pulse signal related to the light source control signal Lf is generated (see the arrow in the figure) shifts with the passage of time, but unlike the prior art, The mode of the deviation changes irregularly. As a result, even when the light amount of the lamp 2102 increases and the position of the scanning line selected at that timing changes, this shift mode is irregularly changed, so that it is not recognized as scroll noise.

Here, as the scroll noise moves from a predetermined frame to the next frame,
This occurs remarkably when the position of the scanning line selected at the timing when the light quantity of the lamp 2102 increases changes by a constant amount. Therefore, the light source control signal L within one frame period
Even if the frequency fw of f is changed a plurality of times, the effect of reducing the scroll noise is not improved, and is approximately 1
What is necessary is just to change the frequency of the light source control signal Lf for every timing more than a frame period. In the electro-optical device 10 according to the present embodiment, when the timing signal DY is output, the frequency f
Since w is changed, it is possible to prevent the frequency fw from being changed a plurality of times within the period of one frame, and the circuit load can be reduced. In addition, since the lamp 2102 can be driven at a frequency fw within a predetermined number range near the frequency fc, that is, near the recommended drive frequency, adverse effects on the life of the lamp 2102 can also be reduced.

As mentioned above, although embodiment of this invention was described, this invention can be implemented in various aspects as follows.

<Modification 1>
In the above-described embodiment, the frequency control circuit 123 changes the frequency fw from a frequency within a predetermined number range to a randomly selected frequency, but the frequency fw is changed to any frequency within the predetermined number range. If so, the mode of the change may be any way. For example, the frequency control circuit 123 stores a plurality of frequencies within a predetermined number range that are candidates for the frequency fw, selects the frequencies from the candidates at random or with a predetermined algorithm, and selects the frequency fw
May be changed. The predetermined algorithm may be any algorithm as long as it defines the order of candidate frequencies for changing the frequency fw.

<Modification 2>
In the embodiment described above, the control signal output circuit 124 may acquire a reference signal having a specific frequency within a predetermined number range from an external oscillator and output the reference signal as the light source control signal Lf. The frequency control circuit 123 may change the frequency fw of the light source control signal Lf output from the control signal output circuit 124 by modulating the frequency of the reference signal. here,
If the specific frequency is set to the frequency fc, the adverse effect on the life of the lamp 2102 is reduced, and the control signal output circuit 124 only modulates the reference signal from the outside by about ± 1%, and the light source control signal having the frequency fw. Lf can be output.

<Modification 3>
In the embodiment described above, the electro-optical device 10 includes the display panels 100R, 100G,
Although 100B uses a transmissive liquid crystal panel, it may be a reflective type. Also,
In the embodiment described above, the case where the electro-optical device 10 is applied to a projector has been described. However, the electro-optical device 10 may be used for a direct-view display having a backlight which is an AC-driven light source.

It is a top view which shows the structure of the projector which concerns on embodiment of this invention. 1 is a block diagram illustrating a configuration of an electro-optical device according to an embodiment of the invention. FIG. It is a figure which shows the structure of the display panel which concerns on embodiment of this invention. It is a block diagram which shows the structure of the control circuit which concerns on embodiment of this invention. It is a figure which shows operation | movement of the conventional electro-optical apparatus. FIG. 6 is a diagram illustrating an operation of the electro-optical device according to the embodiment of the invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Electro-optical apparatus, 12 ... Control circuit, 14R, 14G, 14B ... Drive circuit, 20 ... Lighting circuit, 100R, 100G, 100B ... Display panel, 110 ... Pixel, 121 ... Signal output circuit, 122 ... Scanning signal control circuit , 123 ... frequency control circuit, 124 ... control signal output circuit,
2100 ... Projector

Claims (5)

A display panel having a plurality of pixels;
A signal output circuit that outputs a timing signal at a predetermined period;
A drive circuit for driving the display panel in a cycle in which the timing signal is output;
A light source that irradiates light to the display panel by AC driving according to a predetermined light source control signal;
The frequency of the light source control signal is changed within a predetermined range at a timing having a predetermined relationship with the output timing in the period from the output timing of the timing signal to the time before the integral multiple of the predetermined period has elapsed. An electro-optical device comprising: a frequency control circuit that performs: The frequency control circuit changes the frequency of the light source control signal at any timing after the output timing of the timing signal and at which the light source control signal has a predetermined phase. The electro-optical device according to 1. The electro-optical device according to claim 1, wherein the frequency control circuit changes a frequency of the light source control signal at an output timing of the timing signal. An electro-optical device according to any one of claims 1 to 3,
A projector comprising: a projection lens that projects modulated light obtained by irradiating the display panel with light emitted from the light source. A display panel having a plurality of pixels;
A driving method of an electro-optical device comprising: a light source that irradiates light to the display panel by AC driving according to a predetermined light source control signal,
A timing signal is output at a predetermined cycle,
Driving the display panel in a cycle in which the timing signal is output;
The frequency of the light source control signal is changed within a predetermined range at a timing having a predetermined relationship with the output timing in the period from the output timing of the timing signal to the time before the integral multiple of the predetermined period has elapsed. A method for driving an electro-optical device.

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