JPH03220888A - Projection type color television receiver - Google Patents

Abstract

PURPOSE:To reduce saturation of blue color brightness at radiation of high density electron ray and to increase the white color brightness at a high current region by providing monochroic cathode ray tubes emitting three primary colors independently and applying horizontal scanning to only the blue cathode ray tube at a speed of an integral number of multiple of the scanning speed for the other 2 color cathode ray tubes. CONSTITUTION:A color difference signal B-Y obtained from a Y/C separation demodulation circuit 114 and a luminance signal Y obtained from a luminance signal processing circuit 113 are added by an adder circuit to obtain a blue primary color signal. The blue primary color signal is inputted to a double speed converter 112 together with horizontal synchronizing and vertical synchronizing signals and the blue primary color signal subject to double speed conversion and an horizontal synchronizing signal whose frequency is doubled (f=31.5kHz) are obtained as the outputs. A double speed deflection circuit 18 is operated by the horizontal synchronizing signal of 31.5kHz, its output is fed to a blue color horizontal deflection circuit 117 to apply horizontal scanning to the electron beam at a speed twice the speed of red and green colors. Moreover, the blue primary color signal subject to double speed conversion is fed to a blue projection tube 11 through a primary color signal processing circuit 17 and a blue cathode ray tube drive circuit 14.

Description

[Detailed description of the invention] [Industrial application field]

TECHNICAL FIELD The present invention relates to a projection type color television with high brightness and excellent white tone of highlights.

[Conventional technology]

Z n S : A g or Z rI S : C
Assume that a phosphor represented by u t A I is excited with an electron beam pulse and the time-integrated intensity of luminescence is measured. When the duty is kept constant and the pulse width is changed, the emission intensity increases more rapidly as the pulse width becomes shorter. This is a reverse phenomenon of the brightness saturation of the ZnS-based phosphor, and occurs because the brightness saturation is reduced as a whole by dividing this into a plurality of weak pulses rather than adding a strong pulse to -degrees. This phenomenon was reported in the Journal of the Electrochemical Society, Volume 116, Page 535, 1969 (Jou
rnal of the Electrochemica
l 5ociety 116535 (1969))
has been reported. A system in which an NTSC signal is frequency-converted by an image processor and sent to a picture tube at twice the frame frequency is included in the idea of HDTV, for example, as described in SMPT Vol. 93, No. 5, pp. 470-476. (1980) describes the concept.

[Problems to be Solved by the Invention] With the spread of high-definition, high-brightness image systems. There is a tendency for the input to the cathode ray tube to be significantly increased. As a result, the load on the fluorescent surface increases, causing various problems. For example, there is a phenomenon in which brightness is not proportional to an increase in current and tends to saturate (so-called brightness saturation). All phosphors have a tendency to cause brightness saturation as the electron beam current density increases, but this tendency is stronger for ZnS-based green and blue phosphors than for red, so the balance of the three primary colors is affected at high current densities. collapses, and white shifts toward red. The input power of a projection type cathode ray tube is two orders of magnitude higher than that of a direct view tube, so -
), the brightness saturation problem described above is particularly serious. A rare earth phosphor with low brightness saturation is used for the green color of projection type cathode ray tubes, so in this case, the blue phosphor Zn is used.
S: Ag, Al or Z n S: Ag. The biggest problem is the brightness saturation of C1. Blue phosphors with low brightness saturation have been developed, but none have been put into practical use due to drawbacks such as low efficiency and short lifespan. [Means for Solving the Problems] There are limits to how the problems can be solved by improving the phosphor material alone. Therefore, in the present invention, the horizontal scanning speed of the blue cathode ray tube is made higher than that of the red and green cathode ray tubes, so that the width of the electron beam pulse received by the blue phosphor is shortened. As a result, even if the time-averaged electron beam current value is the same,
Brightness saturation of the front wall light is reduced. As a means of implementing this method, the blue primary color signal is once recorded in a line memory, and then it is multiplied by an integer, for example, 2.
Read twice at twice the speed. A horizontal deflection circuit with twice the scanning speed was used to output the read primary color signals twice.

[Effect l Regarding phosphors that exhibit luminance saturation such as ZnS:Ag,
When the duty of the electron beam pulse is constant and the pulse width is shortened, the integrated intensity of light emission increases. This is because, as mentioned in the description of the prior art, the integrated intensity of a single pulse is relatively reduced. Looking at the emission intensity as a function of time after the pulse stops. Strong luminance saturation means that attenuation is rapid. When the pulse width is shortened by the duty, the peak height of each light emission decreases in accordance with the pulse width, but the attenuation becomes gentler and the total integrated intensity increases accordingly. Because the line memory sends the same image twice within one frame time, the width of the electron beam pulse received by the phosphor becomes 1/2. Therefore, only the brightness saturation of the front wall light body is significantly improved, and the imbalance between red and green is largely eliminated. Note that the output frequency from the line memory only needs to be an integral multiple of the input luminance signal frequency, and does not necessarily have to be twice. However, although the fluorescence output generally increases as the horizontal scanning speed increases, it stops increasing when the electron beam pulse interval becomes shorter than the fluorescence decay time. It usually takes 30 to 50 μs for the luminescence of ZnS:, Ag, and Al to decrease to 1% of the initial value.
From this point of view, the horizontal scanning speed is 20~
A frequency of about 30 kHz is desirable, and as the frequency exceeds 50 kHz, the advantages gradually decrease. Furthermore, the heat generation of the deflection coil increases almost in proportion to the horizontal scanning speed, which poses a major practical constraint. Current coil materials are thought to be able to withstand speeds up to about 8 times that of the NTSC system, but this comes at a big cost. Taking the above into consideration comprehensively, it is appropriate to set the horizontal scanning speed to two to three times, preferably twice, the current speed. [Example] Hereinafter, the present invention will be explained with reference to Examples. Example 1゜Composition formula Y, 0. : A red-emitting cathode ray tube coated with a red-emitting phosphor represented by Eu3+ and 1 composition formula Y. (Al, Ga) A green color obtained by mixing and coating a green-emitting phosphor represented by soxz:Tb3+ and a green-emitting phosphor represented by InB Oa:Tb3+ at a weight ratio of 8:2. Luminescent cathode ray tube and 1 composition formula7. nS:
A projection-type color television was created which has a blue-emitting cathode ray tube coated with a blue-emitting phosphor represented by A g eAl as a light source. The horizontal deflection output circuit of the blue cathode ray tube is made independent from the others, and this includes twice or three times the NTSC system.
A deflection frequency of 1.5 kHz was input. FIG. 1 is a block diagram showing one embodiment of the present invention. The operation will be specifically explained below. The NTSC video signal input to the synchronization separation circuit 115 is separated into H synchronization, ■ synchronization, and luminance (Y)+chroma (C) signals, respectively. The H and V synchronization signals are respectively sent to the horizontal deflection high voltage generation circuit 111. applied to vertical deflection circuit 110. The output of the vertical deflection circuit 110 is the R, G, B projection tube 1.
It is added to the vertical deflection coils 122 to 120 provided in the vertical deflection coils 3 to 11, and performs vertical scanning of each of the R, G, and B electron beams. On the other hand, the high voltage output of the horizontal deflection high voltage generation circuit 111 is sent to the R, G, and B projection tubes 13 to 11, and the horizontal deflection output is sent to the R, G, and B projection tubes 13-11.
Horizontal deflection coil 11 provided in projection tube 13.12 of G
9 and 118, and horizontal scanning of each RlG electron beam is performed. The signals that drive the projection tubes 13.12 of each R9G are sent to the Y/C separation demodulation circuit 114. Luminance signal processing circuit 113, color difference signal processing circuit 19. This is obtained by an R, G cathode ray tube drive circuit 16.15, which has a conventional general circuit configuration. Next, the circuit attached to the projection tube B will be explained. The color difference signal B-Y obtained from the Y/C separation and demodulation circuit 114 and the luminance signal Y obtained from the luminance signal processing circuit 113 are added by an adding circuit 123 to obtain a blue primary color signal. The blue primary color signal is sent to the double speed converter 1 along with the H and V synchronizing signals.
12, and its output is a blue primary color signal which has been converted to a double speed, and an H synchronization signal whose frequency has been doubled (f=
31.5kHz). The double-speed horizontal deflection circuit 18 is activated by the 31.5kHz H synchronization signal, and its output is B.
horizontal deflection circuit 117 for R and G electron beams.
Horizontal scanning is performed at twice the speed as compared to the horizontal scanning speed, and the converted blue primary color signal is applied to the B projection tube 11 through the primary color signal processing circuit 17 and the B cathode ray tube drive circuit 14. In this example, 15.75kHz and 31.5kHz
The Hz horizontal AFC circuit etc. is a well-known technology.
The explanation of the operation is omitted. Further, the double speed converter has a simple structure using an IH line memory and can be put to practical use, and its format is not particularly limited. Similarly, even if the high voltage generation circuit is configured to share the circuit with the double-speed horizontal deflection circuit 18,
It is well known that the two horizontal deflection circuits 111 and 118 may be completely separated from each other. When the brightness of a blue cathode ray tube operated with the circuit thus prepared is plotted against the cathode current, the result is a curve 24 in FIG. 2. On the other hand, the brightness of the same cathode ray tube operated in the conventional manner exhibited a characteristic as shown in the second curve 21. For example, with a current of 5 mA, the brightness of blue color increased by about 60%. The red luminance measured at the same time is curve 22. Green brightness curve 2
3. As a result, the white brightness has been greatly altered, and 1 m
In A, it improved by about 15%. At the same time, the blue luminance spreads well at high currents, resulting in a better balance of the three colors and less shift in white tone. [Effects of the Invention] According to the present invention, the blue luminance saturation during high-density electron beam irradiation can be reduced and the white luminance in the high current range can be increased by more than 10%. It is possible to improve the white tone in highlights.

[Brief explanation of drawings]

Figure 1 is a block diagram of a projection color television circuit that doubles the horizontal deflection frequency of a blue cathode ray tube, and Figure 2 shows the relationship between the brightness and cathode current of each color cathode ray tube operated by the circuit in Figure 1, and the conventional one. This figure shows the relationship between the brightness and cathode current of a blue cathode ray tube operated with an NTSC circuit. Explanation of symbols 11... Blue projection type cathode ray tube, 12... Green projection type cathode ray tube, 13... Red projection type cathode ray tube, 14
．． 15.16...Blue, green, and red cathode ray tube drive circuits, respectively, 17...Primary color signal processing circuit. 18...31.5kHz horizontal deflection circuit, 19...
Color difference signal processing circuit, 110... Vertical deflection circuit, 11
DESCRIPTION OF SYMBOLS 1... Horizontal deflection high voltage generation circuit, 112... Line memory, 113... Luminance signal processing circuit, 114... Y
/C separation demodulation circuit, 115... synchronous separation circuit, curve 2
1.22.23...Blue, red, driven by the circuit shown in Figure 1
Cathode current dependence of brightness of green cathode ray tube, 24...
・Cathode current dependence of blue brightness using conventional NTSC signal circuit

Claims (1)

[Scope of Claims] 1. A projection type color tube having independent monochrome cathode ray tubes that emit three primary colors, of which only the blue tube is horizontally scanned at an integral multiple of the speed of the other two color cathode ray tubes. television. 2. The projection color television set as claimed in claim 1, wherein only the blue tube is horizontally scanned at twice the speed of the cathode ray tubes for the other two colors. 3. The projection according to claim 1, characterized in that only the blue tube is equipped with a line memory capable of recording a luminance signal, converting it to a frequency twice or more, and outputting it to a horizontal deflection circuit. type color television.