Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – Plural light emitting devices
Reexamination Certificate
1997-06-18
2001-04-24
Tran, Minh Loan (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
Plural light emitting devices
C257S089000, C257S090000, C257S103000
Reexamination Certificate
active
06222203
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of display devices, and, more particularly, the present invention relates to a selfluminous display device which has a plurality of light emission sources consisting of, for example, semiconductor lasers or light emitting diodes.
2. Description of the Related Art
Conventional display devices include stationary type Braun tube i.e. CRT (Cathode Ray Tube) devices and flat panel displays (FPD) which fulfil the requirements of portable uses and the realization of thin displays. Examples of flat panel displays include liquid crystal displays (LCD). In these display devices, the LCD itself does not emit light but employs backlighting for the display of information. In contrast, a CRT is a selfluminous display device which includes a luminescent substance that emits light itself.
Currently, in the audio field digital sound sources from which noise has been removed have been established for a long time, but in display devices they have not been established, and the demand for noiseless clear color reproduction, i.e. for digital reproduction is increasing. However, in a conventional selfluminous display device, it was difficult to make the digital reproducibility good. This point will be explained below.
FIG. 10
shows the range reproducible by a CRT based on the NTSC (National Television System Committee) format. As is clear also from this figure, with a CRT using luminescent substances it is only possible to reproduce the inside of the triangle (CRT) shown with single-dotted chain lines. The reason why the triangle (CRT) is primarily near the center is because the spectra of the luminescent substances are wide, the color purity is bad and approaches white. Also, the width is wide because in the luminescent substances there are many transition order levels of slightly different energies and there is a distribution in the transition energy. However, due to change over time and the like this transition order level distribution changes and the color reproducibility deteriorates. Also, there is a problem that because of this wide spectrum width the color purity deteriorates and also the reproduction range narrows. A triangle (LED) shown with solid lines shows the reproducible region of the present invention discussed later.
FIG. 11
shows the relationship between light emission wavelength (&lgr;) and light emission strength in conventional red (R), green (G) and blue (B) light emission sources for a CRT, and in this case, the display strength (F
NTSC
) of a selfluminous display device in which these light emission sources are used can be expressed with the following expression.
F
NTSC
=
∑
i
(
b
i
B
+
g
i
G
+
r
i
R
)
B, G, R light emission strength
b
i
, g
i
, r
i
coefficients
The spectra of the light emission strengths of these RGB light emission sources change due to deterioration of the respective light sources from the state shown with solid lines to the state shown with broken lines. Because as is clear also from this figure, the widths of the spectrum shapes are wide and also the changes thereof are not uniform, correcting the display strength (F
NTSC
) is difficult, and consequently as described above there has been the problem that the color reproducibility deteriorates.
Also in a flat panel display device in which a liquid crystal display (LCD) is used, in the transmission spectrum of the color filter there is a width for obtaining a limited strength, and consequently, the same problems exist as in the CRT case described above. In particular, there has been the problem that it is only possible to reproduce the inside of the triangle (LCD) shown with single-dotted chain lines in FIG.
10
and the reproducibility is bad. Conversely, there has been the problem that when a filter having a narrow transmission spectrum band is used in order to raise the color purity, the transmitted light strength falls significalty.
SUMMARY OF THE INVENTION
The present invention was made in view of these problem points, and an object of the invention is to make light emission strength a sole parameter and provide a selfluminous display device having a wider range of color reproducibility and also one in which it is possible to obtain a light emission strength having no change over time.
A selfluminous display device of the present invention comprises a plurality of light emission sources respectively having spectra of such levels that they do not mutually substantially overlap. The plurality of light emission sources, specifically, red, green and blue semiconductor light emitting devices (LED, LD) respectively have precursor delta function shaped spectra with a half band width 30 nm or less. Alternately, red, green and blue semiconductor lasers (LD) or light emitting diodes(LED) respectively having spectra in which the half band width of the envelope function is 30 nm or less are used. More specifically, gain guided wave type or refractive index guided wave type semiconductor lasers or light emitting diodes are used. These devices include on a substrate at least a clad layer and an active layer of a first conductivity type and a clad layer of a second conductivity type made from a group II-VI compound semiconductor or a group III-V compound semiconductor.
In a selfluminous display device of the present invention, because a plurality of light sources have spectra which do not mutually substantially overlap, i.e. light emission sources of extremely narrow limited widths, are used, the shape changes of the spectra are suppressed in the wavelength space and they can be seen as magnitude changes only. Thus, correction having only magnitude as a parameter becomes possible.
REFERENCES:
patent: 5650641 (1997-07-01), Sassa et al.
patent: 5739552 (1998-04-01), Kimura et al.
Ishibashi Akira
Nakayama Norikazu
Sonnenschein Nath & Rosenthal
Sony Corporation
Tran Minh Loan
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