JP4047333B2 - Display device - Google Patents

Description

  A color display device that displays a different color image for each display subfield and mixes colors by using the time axis composition of human eyes to obtain a multicolor display is called a field sequential type. The present invention relates to a display device having such a field sequential type multicolor display mode.

  One method of a field sequential display device is a display unit that emits light of a broadband wavelength that displays display information of light of a different wavelength for each subfield, and is specified for each subfield from the light of the broadband wavelength. It is a system which has a variable filter part which sorts out light of the wavelength range.

  In another method of the field sequential display device, a light source unit that can emit light of different wavelengths, a light source driving circuit that drives the light source unit, and light emitted from the light source unit are controlled based on display information. The light source unit emits a specific color for each subfield and controls the shutter unit corresponding to the shutter unit and a shutter unit control circuit that controls the shutter unit.

  The field frequency for rewriting display contents is normally set to 25 Hz to 30 Hz or more. In the case of 25 Hz or less, flicker is conspicuous and the display quality is lowered. In the case of field sequential color, one field is generally divided into three subfields corresponding to the three primary colors. Therefore, the subfield frequency is 75 Hz to 90 Hz or more.

  If the response speed of the shutter portion is defined as the sum of the rise time and fall time, and the respective rise time and fall time are defined as 90% saturation, the response speed must be somewhat faster than the subfield period. The subfield period is 1/75 sec to 1/90 sec = 11 msec to 13 msec, and the response speed of the shutter portion needs to be at least 10 msec or less.

  A typical device used for the shutter unit is a liquid crystal element. A liquid crystal element generally requires AC driving. Therefore, the subfield period is 1 / (75 × 2) seconds to 1 / (90 × 2) seconds = 1/150 seconds to 1/180 seconds = 5.6 msec to 6.7 msec. Therefore, when using a liquid crystal element for a shutter, it is necessary to be at least 5 msec or less.

  As described above, the shutter portion is required to have a high response speed.

  However, the liquid crystal element has a characteristic that the response speed varies depending on the environmental temperature, and the response speed is extremely slow particularly on the low temperature side.

  In STN (super twisted nematic) and TN (twisted nematic) type liquid crystal shutters, the response speed indicated by the sum of the rise time and fall time exceeds 10 msec at a low temperature such as 0 ° C., and the shutter function is lost. End up.

  Therefore, in order to guarantee the conventional field sequential color low temperature operation, it is impossible to use a liquid crystal element excellent in mass productivity such as STN for the shutter portion. There are liquid crystal modes that can operate at high speed, such as ferroelectric liquid crystals and anti-ferroelectric liquid crystals, but there are problems with mass production technology and mechanical strength. Even in the case of a ferroelectric liquid crystal or an antiferroelectric liquid crystal, the response speed is lowered at a low temperature of 0 degrees or less.

  As described above, the conventional field sequential color display device has a problem that it is difficult to use an element having a problem with low temperature characteristics such as a liquid crystal element in the shutter portion.

  Further, in the conventional field sequential color display device, each color light source of the light source section is turned on for about 1/3 of the entire time, and is about 1/3 of the maximum light quantity inherent to the light source. There is only it. Therefore, there was a problem that it was difficult to see in a bright environment.

  An object of the present invention is to solve the problems of the conventional example and provide a field sequential color display device capable of being displayed even in a low temperature or bright environment.

The present invention provides a light source unit composed of a plurality of color light sources that emit light of different wavelengths and can be controlled independently for each subfield , a light source drive circuit that drives the light source unit, and light emitted from the light source unit. a liquid crystal element for controlling, in a display device having a liquid crystal element control circuit for controlling the liquid crystal element, and the color display mode for performing color display, a monochrome display mode data write frequency is lower than the color display mode of the liquid crystal element , Characterized by having.

In the color display mode, a specific color light source emits light sequentially, and the liquid crystal element is controlled for the sequential light emission, thereby enabling color display. In the monochrome display mode, a plurality of color light sources emit light simultaneously. The data writing frequency may be lower than that in the color display mode by controlling the liquid crystal element corresponding to the simultaneous light emission.

In the color display mode, a specific color light source is sequentially emitted, and the liquid crystal element is controlled in response to the sequential light emission, thereby enabling color display. In the monochrome display mode, a specific color light source is used. The data writing frequency may be lower than that in the color display mode by sequentially emitting light and controlling the liquid crystal element without synchronizing with the sequential light emission.

The plurality of color light sources may be composed of three color light sources of red, green, and blue, and in the monochrome display mode, the number of colors to be displayed may be limited by simultaneously lighting two or three color light sources.

It is preferable that the color display mode and the monochrome display mode can be switched.

It is preferable to further have an environment detection function, and to switch between the color display mode and the monochrome display mode according to detection information obtained by the environment detection function.

Liquid crystal elements have different response speeds depending on the environmental temperature. At temperatures with a response speed that is difficult to control according to the light emitted from the color light source, the color display mode is changed from the color display mode to the monochrome display mode depending on the detection information from the environment detection function. You may have the function to switch to.

The liquid crystal element have a different characteristic response speed by the environmental temperature, the temperature is difficult response speed be controlled to correspond to the liquid crystal shutter for light emission of colored light sources, the color display mode by the detection information by the environment detection function May have a function of switching from the monochrome display mode to the monochrome display mode.

It has a function of detecting the peripheral light amount, and when the light amount is larger than a certain light amount, the color display mode may be switched to the monochrome display mode.

  As described above, since the display device of the present invention has two new display modes, it is difficult to use an element having a problem in low temperature characteristics such as a liquid crystal element in a shutter portion in a conventional field sequential color display device. It becomes possible to solve the problem of being.

  In addition, it is possible to greatly improve the problem that the conventional field sequential color display device is difficult to see in a bright environment.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same or corresponding elements are denoted by the same reference numerals, and redundant description is omitted.

  An embodiment of a field sequential display device of the present invention is shown in FIG. In the present invention, the light source unit includes a plurality of color light sources that emit light of different wavelengths and can be controlled independently. That is, it has the light source part 1 which consists of LED (light emitting diode) of three colors of red, green, and blue. The light source unit 1 includes an LED box 3 in which a plurality of three-color LEDs 4 are arranged and a diffusion plate 5. The light source unit 1 is driven by a light source driving circuit 8.

  In the present invention, a shutter unit for controlling light emitted from the light source unit 1 is provided. The embodiment shown in FIG. 2 has a liquid crystal shutter portion 2 made of a liquid crystal element. The liquid crystal shutter unit 2 has a display segment 6 capable of displaying letters and numbers. Of course, the liquid crystal shutter portion is not limited to the segment type but may be a matrix type. In this embodiment, the common electrode is used alone and static drive is used. The shutter unit 2 is controlled by a shutter control circuit 9.

  In this embodiment, the liquid crystal shutter is normally white, that is, an STN mode in which light is transmitted when an off voltage is applied and light is blocked when an on voltage is applied.

  The performance of the liquid crystal shutter was optimized and the following conditions were used. The liquid crystal molecules were twisted 240 degrees between the two substrates, and the polarization axis of the polarizing plate was arranged at an angle of about 45 degrees with respect to the liquid crystal molecules. When the thickness of the liquid crystal layer, that is, the cell gap is d and the birefringence of the liquid crystal is Δn, the retardation expressed by the product of Δn and d is set to about 800 nm.

  FIG. 3 shows a block diagram of the display device of the present invention. The light source unit 1 includes a red light source R, a green light source G, and a blue light source B, and is lit by a red light source lighting signal Lr, a green light source lighting signal Lg, and a blue light source lighting signal Lb supplied from the light source driving circuit 8. The shutter unit 2 is driven by a data signal D and a common signal C supplied from the shutter control circuit 9.

  FIG. 4 shows another block diagram of the embodiment of the display device of the present invention. The light source unit 1 includes a red light source R, a green light source G, and a blue light source B, and is lit by a red light source lighting signal Lr, a green light source lighting signal Lg, and a blue light source lighting signal Lb supplied from the light source driving circuit 8. The shutter unit 2 is driven by a data signal D and a common signal C supplied from the shutter control circuit 9. The difference from the embodiment shown in FIG. 3 is that the light source drive circuit 8 and the shutter control circuit 9 are controlled by the environment detection circuit 10.

  A feature of the present invention is that it has two display modes. In the first display mode, multi-color display is possible by turning on a specific color light source for each subfield and controlling the shutter unit corresponding to the subfield.

  FIG. 5 shows waveforms of signals in the first display mode in the embodiment of the present invention. Two fields f1 and f2 were used for AC driving of the liquid crystal shutter. Each field consists of three subfields fR, fG, and fB.

  The red light source lighting signal Lr is lit only in the subfield fR, and is not lit in the other subfields fG and fB. Similarly, the green light source lighting signal Lg is lit only in the subfield fG, is not lit in the other subfields fB and fR, and the blue light source lighting signal Lb is lit only in the subfield fB, and in the other subfields fR and fG. Not lit.

  The common signal C supplied to the liquid crystal shutter is c1 in the field f1 and c2 in the field f2.

  Since normally white STN liquid crystal is used in this embodiment, the data signal Dw during white display is in phase with the common signal C, and the data signal Dbl during black display is in reverse phase with the common signal C.

  The data signal for displaying a single primary color takes a potential such that the shutter is in a transmissive state (white) only in the subfield corresponding to that color. For example, the data signal Dr for displaying red is red. A potential is set such that the shutter is in a transmissive state only in the corresponding subfield fR. The data signal Dg for displaying green takes a potential such that the shutter is in a transmissive state only in the subfield fG corresponding to green. When displaying blue, the data signal Db takes such a potential that the shutter is in a transmissive state only in the subfield fG corresponding to blue.

  A data signal for displaying a plurality of primary colors takes a potential such that the shutter is in a transmissive state (white) only in the subfields corresponding to the respective colors. For example, the data signal Dc in the case of displaying blue-green takes a potential such that the shutter is in a transmission state in the subfields fG and fB corresponding to green and blue. The data signal Dm in the case of displaying purple is at a potential such that the shutter is in a transmission state in the subfields fB and fR corresponding to blue and red. The data signal Dy for displaying yellow takes a potential such that the shutter is in a transmissive state in the subfields fR and fG corresponding to red and green.

  In FIG. 5, the data signal always has only the potential of d1 or d2 in each subfield. However, in order to display multiple colors other than the primary colors, an intermediate value can be taken on the voltage axis or the time axis. The case where the voltage axis is multivalued corresponds to amplitude modulation, and the case where the time axis is multivalued corresponds to pulse width modulation.

  As described above, in the first display mode of the present invention, if a single primary color, a plurality of primary colors, or a drive waveform is devised, it is possible to display many colors corresponding to the intermediate colors.

  FIG. 1 shows waveforms of signals in the second display mode in the embodiment of the present invention. The two fields f1 and f2 include three subfields fR, fG, and fB. The red light source lighting signal Lr, the green light source lighting signal Lg, and the blue light source lighting signal Lb are in the lighting level in all the subfields. This is a feature of the second display mode.

  Since the light sources of the respective colors are turned on simultaneously, multicolor colors cannot be displayed, and the data signal has the same level in each subfield, such as the data signal Dbl at the time of display in FIG. 1 and the data signal Dw at the time of white display. Use the signal you have.

By using such a signal, it is not necessary to respond for each subfield in the second display mode of the present invention, and a so-called cumulative response of liquid crystal can be used. Therefore, it is possible to display even a liquid crystal with a slow response speed.

  The response speed of the STN liquid crystal used in this example is about 3 msec in total on / off at room temperature. Therefore, the field sequential color requirement of 5 msec or less is satisfied. However, the response speed at 0 ° C. is very slow and exceeds 10 msec, which does not satisfy the requirements for field sequential color.

  Therefore, even when a primary color display signal of a field sequential color such as the data signal Dr for red display, the data signal Dg for green display, and the data signal Db for blue display at FIG. Is possible. For example, in the case of a vehicle-mounted display, a state of 0 ° C. or lower may be sufficient, but cannot be displayed in the first display mode of FIG. In-vehicle displays, display is very important, such as speed information, and the fact that it does not function at low temperatures is a fatal problem.

  However, when the second display mode of the present invention is used, color information cannot be displayed even at such a low temperature, but sufficient information transmission is possible.

  In the embodiment of the present invention, the user performs switching between the first display mode and the second display mode as necessary. In another embodiment, an environment detection function such as an environmental temperature sensor is provided, and the first display mode and the second display mode are switched according to the detection information. In the embodiment of FIG. 4, the first display mode and the second display mode are switched by controlling the light source driving circuit 8 and the shutter control circuit 9 according to the information of the environment detection circuit 10.

  FIG. 6 is a waveform diagram of signals applied to the light source unit and the shutter unit in the second display mode according to another embodiment of the present invention. The difference from the embodiment of FIG. 1 is the light source lighting signal. In the embodiment of FIG. 1, the light source lighting signal of each color is in the lighting level in all the subfields. However, in FIG. 6, similarly to the first display mode in FIG. is there. That is, the red light source lighting signal Lr is in the lighting level only in the subfield fR, the green light source lighting signal Lg is in the lighting level only in the subfield fG, and the blue light source lighting signal Lb is in the lighting level only in the subfield fB.

  The embodiment of FIG. 6 is lower in brightness of the light source in the second display mode by about 1/3 than the embodiment of FIG. 1, but it is not necessary to respond to each subfield as in the embodiment of FIG. The so-called cumulative response of the liquid crystal can be used. Therefore, it is possible to display even a liquid crystal with a slow response speed. Accordingly, as in the embodiment of FIG. 1, color information cannot be displayed even at low temperatures, but sufficient information transmission is possible.

  FIG. 7 is a waveform diagram of signals applied to the light source unit and the shutter unit in the second display mode in another embodiment of the present invention. The difference from the embodiment of FIG. 1 is the light source lighting signal. In the embodiment of FIG. 1, the three color light sources are turned on simultaneously in the subfield, but in this embodiment, the two color light sources are turned on simultaneously.

  In this embodiment, the red light source lighting signal Lr is turned on in the subfield fR and the subfield fG, and is not turned on in the subfield fB. Similarly, the green light source lighting signal Lg is lit in the subfield fG and the subfield fB, is not lit in the subfield fR, the blue light source lighting signal Lb is lit in the subfield fB and the subfield fR, and is not lit in the subfield fG. It becomes.

In this embodiment, since a plurality of color light sources are turned on in each subfield, it is not possible to display a single primary color. However, it is possible to display a color composed of a plurality of primary colors. For example, the data signal Dm in the case of displaying purple takes a potential such that the shutter is in a transmissive state only in the subfield fR. The data signal Dy for displaying yellow takes a potential such that the shutter is in a transmissive state only in the subfield fG. The data signal Dc for displaying blue green takes a potential such that the shutter is in a transmissive state only in the subfield fG.

  Furthermore, although the saturation is low, it is possible to display pink, green and white, and blue and white. In this case, the data signal takes a potential such that the shutter is transmissive (white) in a plurality of subfields. For example, the data signal Dgw for displaying green and white takes a potential such that the shutter is in a transmissive state in the subfields fG and fB. The data signal Dbw for displaying blue and white takes such a potential that the shutter is in the transmissive state in the subfields fB and fR. The data signal Dp for displaying pink has a potential at which the shutter is in a transmissive state in the subfields fR and fG.

  The data signal Dbl for displaying black is a signal having a phase opposite to that of the common signal C since it is in a normally white mode. The data signal Dw for displaying white is a signal in phase with the common signal C.

  The data signals Dm, Dy, Dc, Dgw, Dbw, Dp in the second display mode of the embodiment of FIG. 7 are the same signals as the data signals Dr, Dg, Db, Dc, Dm, Dy in the first display mode. . Therefore, when liquid crystal is used for the shutter portion, it does not respond at low temperatures and cannot display color. Therefore, there is no big advantage even if it changes with environmental temperature.

  However, in the first display mode, one color light source is lit in each subfield, whereas in the second display mode, two color light sources are lit in each subfield. The brightness is realized. Therefore, even when it is difficult to recognize in the first display mode in a situation where the amount of environmental light is high, it is possible to sufficiently recognize in the second display mode.

  In the embodiment of the present invention, the user performs switching between the first display mode and the second display mode as necessary. However, another embodiment has an environment detection function such as an environmental temperature sensor, and switches between the first display mode and the second display mode according to the detection information. In FIG. 4, the first display mode and the second display mode are switched by controlling the light source driving circuit 8 and the shutter control circuit 9 based on the information of the environment detection circuit 10. A detection circuit that switches between the first display mode and the second display mode depending on the amount of light in the periphery.

  As described above, the embodiment of FIG. 7 is characterized in that the data signals Dm, Dy, Dc, Dgw, Dbw, Dp in the second display mode are the data signals Dr, Dg, Db, Dc, Dm, in the first display mode. It is the same signal as Dy. Therefore, although the colors are different, it is possible to display different colors that can be identified by the same signal. For example, when switching between the first display mode and the second display mode depending on the amount of peripheral light, it is possible to provide identifiable color information only by changing the light source signal and without changing the data signal.

  It is effective to use the second display mode shown in FIG. 1 even when the environmental variable is the peripheral light amount. In that case, since all three color light sources are turned on in each subfield, three times the brightness can be used as compared with the first display mode. However, color information cannot be provided as in the second display mode of FIG.

  In the embodiment of FIG. 2, the number of the three types of light sources red, green, and blue is the same. However, it is effective to change the number when the emission intensity of the light sources is different. For example, when the emission intensity of green LED is weaker than that of other blue and red LEDs, the color reproducibility and brightness can be changed by changing the number of green, blue and red LEDs to 2: 1: 1 etc. Can be improved.

It is a wave form diagram of the signal applied to the light source part and shutter part in the 2nd display mode of the display apparatus of the Example of this invention. It is explanatory drawing which shows the structure of the display apparatus of the Example of this invention. It is a block diagram of the display apparatus of the Example of this invention. It is a block diagram of the display apparatus of the other Example of this invention. It is a wave form diagram of the signal applied to the light source part and shutter part in the 1st display mode of the display apparatus of the Example of this invention. It is a wave form diagram of the signal applied to the light source part and shutter part in the 2nd display mode in the display apparatus of the other Example of this invention. It is a wave form diagram of the signal applied to the light source part and shutter part in the 2nd display mode in the display apparatus of the other Example of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Light source part, 2 ... Shutter part, 3 ... LED box, 4 ... 3 color LED, 5 ... Diffuser, 6 ... Display segment, 8 ... Light source drive circuit, 9 ... Shutter control circuit, 10 ... Environment detection circuit, D ... Data signal, C ... Common signal, R ... Red light source, G ... Green light source, B ... Blue light source, Lr ... Red light source lighting signal, Lg ... Green light source lighting signal, Lb ... Blue light source lighting signal, Dr ... Red display Dg: Data signal for green display, Db: Data signal for blue display, Dc: Data signal for blue green red display, Dm: Data signal for purple display, Dy ... Data signal for yellow display Dbl: black display data signal, Dw: white display data signal, fR: subfield, fB: subfield, fG: subfield.

Claims (9)

A light source unit composed of a plurality of color light sources that emit light of different wavelengths and can be controlled independently for each subfield , a light source drive circuit that drives the light source unit, and a liquid crystal element that controls the light emitted by the light source unit When, in a display device having a liquid crystal element control circuit for controlling the liquid crystal element,
Color display mode for color display,
A display device comprising: a monochrome display mode in which a data writing frequency to the liquid crystal element is lower than the color display mode. In the color display mode, the specific color light source is caused to emit light sequentially, and the liquid crystal element is controlled for the sequential emission, thereby enabling color display.
The monochrome display mode is characterized in that the data writing frequency is lower than that in the color display mode by simultaneously emitting light from a plurality of color light sources and controlling the liquid crystal element in response to the simultaneous light emission. The display device according to claim 1. In the color display mode, the specific color light source is caused to emit light sequentially, and the liquid crystal element is controlled in response to the sequential light emission, thereby enabling color display.
In the monochrome display mode, the data write frequency is lower than that in the color display mode by sequentially emitting the specific color light source and controlling the liquid crystal element without synchronizing with the sequential light emission. The display device according to claim 1, characterized in that:   The plurality of color light sources are composed of three color light sources of red, green, and blue, and the monochrome display mode has a limited number of colors to be displayed by simultaneously lighting two or three color light sources. The display device according to any one of claims 1 to 3.   The display device according to claim 1, wherein the color display mode and the monochrome display mode can be switched.   6. The display device according to claim 5, further comprising an environment detection function, wherein the color display mode and the monochrome display mode are switched according to detection information obtained by the environment detection function. The liquid crystal element has a characteristic in which a response speed varies depending on an environmental temperature, and the temperature of the response speed that is difficult to control corresponding to the light emission of the color light source is determined based on detection information by the environment detection function. The display device according to claim 6, wherein the display device has a function of switching to the monochrome display mode. The liquid crystal element have a different characteristic response speed by the environmental temperature, the temperature is difficult response speed be controlled to correspond to the liquid crystal element for light emission of the colored light sources, the information detected by the environment detection function The display device according to claim 6, wherein the display device has a function of switching from the color display mode to the monochrome display mode.   The display device according to claim 6, wherein the display device has a function of detecting a peripheral light amount, and switches from the color display mode to the monochrome display mode when the light amount is larger than a certain light amount.

Images