CA2111422C - Brightness modulation circuit - Google Patents
Brightness modulation circuitInfo
- Publication number
- CA2111422C CA2111422C CA002111422A CA2111422A CA2111422C CA 2111422 C CA2111422 C CA 2111422C CA 002111422 A CA002111422 A CA 002111422A CA 2111422 A CA2111422 A CA 2111422A CA 2111422 C CA2111422 C CA 2111422C
- Authority
- CA
- Canada
- Prior art keywords
- horizontal
- parabolic wave
- vertical
- modulated
- brightness modulation
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N5/00—Details of television systems
- H04N5/44—Receiver circuitry for the reception of television signals according to analogue transmission standards
- H04N5/57—Control of contrast or brightness
Landscapes
- Engineering & Computer Science (AREA)
- Multimedia (AREA)
- Signal Processing (AREA)
- Video Image Reproduction Devices For Color Tv Systems (AREA)
- Television Receiver Circuits (AREA)
- Picture Signal Circuits (AREA)
- Transforming Electric Information Into Light Information (AREA)
Abstract
A brightness modulation circuit for a video display unit has a brightness level adjusting circuit including a memory (13) for storing data representing a suitable degree of brightness modulation corresponding to various types of uses of television systems, and a horizontal digital/analog converter (6) and a vertical digital/analog converter (7) issuing amplitude-modulated parabolic waves, which control the degree of the brightness modulation using the data read from the memory (13).
Description
TITLE OF T~E INVENTION
Brightness modulation circuit FIELD OF T~E INVENTION AND RELATED ART STATEMENT
1. FIELD OF T~E INVENTION
This invention relates to a brightness modulation circuit for a video display unit having a CRT(cathode-ray tube) which corresponds to various types of uses.
Brightness modulation circuit FIELD OF T~E INVENTION AND RELATED ART STATEMENT
1. FIELD OF T~E INVENTION
This invention relates to a brightness modulation circuit for a video display unit having a CRT(cathode-ray tube) which corresponds to various types of uses.
2. DESCRIPTION OF 1~ PRIOR ART
Conventionally, in a video display unit having a CRT, although a uniform brightness is required over the whole surface of the fluorescent screen, peripheral regions of the fluorescent screen do not generally have enough brightness compared to a center region of the fluorescent screen. The cause of the above-mentioned problem is explained as follows:
(1) With regard to the ordinary type, i.e.
direct observation type CRT (non-projection type) display:
In such ordinary type, it is necessary to decrease the generation of a mislanding between an electron beam landing positions and a fluorescent material dots, which should correspond to the electron beam landing positions of the same color, on the peripheral regions.
Therefore, in the peripheral regions, sizes of guard band or black matrix part, which separates neighboring different fluorescent material dots from each other must be made lager than those in the center region. As a result, in the peripheral regions, a size of the fluorescent material dots becomes smaller than those in the center region. Accordingly, brightnesses of the peripheral regions decrease compared to brightness of the center region. Furthermore, in the CRT for a high definition television system or the like, since an size of respective apertures on a shadow-mask is short so as to obtain a high resolution, the above-mentioned tendency of smaller brightnesses in the peripheral regions decreases compared to the brightness of the center region becomes more prominent. Similarly, in case a large deflection angle of the electron beam is adopted so as to decrease the depth of the CRT, namely achieve a shorter distance between the fluorescent screen and an electron gun, the above-mentioned tendency of brightness difference between the peripheral regions the center region becomes more evident.
(2) With regard to the projection type CRT
display:
In the CRT display using the projection systems, there is the following cause of producing the center VS.
peripheral brightness difference besides the above-mentioned causes for the ordinary direct observation type display. Since a raster, which is formed on the fluorescent screen, is magnified on a screen of the 2 1 ~ 1 ~ 2 2 projection display as a pictorial image with a projection lens, an efficiency for light utilization of the projection lens decreases at its peripheral parts in proportion to the distance from its center part.
Accordingly, brightnesses in the peripheral regions of the fluorescent screen decrease compared to the brightness of the center region.
In order to cope with the above-mentioned center VS. peripheral brightness-difference of the projection type display system, there have been proposed a modulation of an electron beam drive voltage of the CRT. That is, conventionally, the electron beam driving voltage of the CRT, is modulated higher in the peripheral regions than to the center region depending on distances from the center of the phosphor screen, or depending on deflection angles.
FIG.5 shows a circuit diagram of the conventional brightness modulation circuit for the CRT
using the projection display. In FIG.5, a horizontal synchronization signal 1 and a vertical synchronization signal 2 are input to a parabolic wave generation circuit 3. A horizontal parabolic wave 4, which is synchronized with a horizontal scanning frequency, is issued from the parabolic wave generation circuit 3 to three multiplying circuit 14, 15 and 16 for respective three video signals 8, 9 and 10 of different colors, through a buffer amplifier 33 and a horizontal level adjusting rheostat 31.
21~1q22 Similarly, a vertical parabolic wave 5, which is synchronized with a vertical scanning frequency, is issued from the parabolic wave generation circuit 3 to three multiplying circuit 14, 15 and 16 for respective three video signals 8, 9 and 10 of different colors, through a buffer amplifier 34 and a vertical level adjusting rheostat 32. R-video signal 8 for dots of red light-emitting fluorescent material (R) (hereinafter referred to as R-video signal 8 ) is input to the multiplying circuit (R) 14. Therefore, in the multiplying circuit (R) 14, a brightness modulation for R-video signal 8 is made to increase responding to the distance from the center region to the peripheral regions. Subsequently, R-video signal 8 is input to a CRT (R) 20, which is for red light-emitting, through an amplification circuit 17, which is for R-video signal 8. Similarly, G-video signal 9 for dots of green light-emitting fluorescent material (G) (hereinafter referred to as G-video signal 9 ) is input to the multiplying circuit (G) 15. Therefore, in the multiplying circuit (G) 15, a brightness modulation for G-video signal 9 is made to increase responding to the distance from the center region to the peripheral regions.
Subsequently, G-video signal 9 is input to a CRT (G) 21, which is for a green light-emitting, through an amplification circuit 18, which is for G-video signal 9.
Furthermore, B-video signal 10 for dots of blue light-emitting fluorescent material (B) (hereinafter referred toas B-video signal 10 ) is input to the multiplying circuit (B) 16. Therefore, in the multiplying circuit (B) 16, a brightness modulation for B-video signal 10 is made to increase responding to the distance from the center region to the peripheral regions. Subsequently, B-video signal 10 is input to a CRT (B) 22, which is for a blue light-emitting, through an amplification circuit 19, which is for B-video signal 10.
A degree of the brightness modulation is realized in a manner that the levels of the horizontal parabolic wave 4 and the vertical parabolic wave 5 are adjusted to the video signal, which is set to one of the various types of uses, by means of the two rheostats 31, 32 or alternatively by two fixed resistors. Since the above-mentioned modulation is realized, brightnesses of the peripheral regions is substantially equalized to brightness of the center region. Accordingly, in the whole surface of the fluorescent screen, the uniformity of brightness is achieved.
However, in the above-mentioned conventional brightness modulation circuit, another problem arises as followings:
In the conventional brightness modulation circuit, the degree of the brightness modulation is designed fixedly for the cause of improving the ordinary analog video signal only. And the modulation degree is fixed to the analog video signal use by means of the rheostats 31, 32 or two fixed resistors. Furthermore, since the rheostats 31, 32 are covered with a plastic cover and the adjustment of the rheostats 31, 32 requires a professional apparatuses, the rheostats 31, 32 are semipermanently fixed to the optimum positions for above-mentioned analog video signal in the factory. Therefore, in the conventional brightness modulation circuit, it is impossible that the degree of the brightness modulation is readjusted or modified for other mode of modulation responding to the type of the video signal to display.
Accordingly, in the conventional brightness modulation circuit, although a video display unit, which has been tuned to correspond to the ordinary analog video signal, is manufactured best for displaying the ordinary video signal, it is inadequate to be used as multiple source type display apparatus, which should realize the various degree of the brightness modulation. Furthermore, if an appropriate degree of the brightness modulation is not carried out, it is likely to cause the lowering of the resolution because of the below-mentioned reason.
FIG.6 shows a characteristic curve showing a relation of diameter of an electron beam spot and the driving voltage of the video signal. The diameter of the electron beam spot becomes lager responding to increase of the driving voltage as shown in FIG.6. Therefore, if the driving voltage is too large, the resolution of the fluorescent screen is lowered. Furthermore, it is to be noted that characteristic of the electron beam spot generally becomes poorer in the peripheral regions in comparison with the center region for the same driving voltage. Accordingly, a concrete example will be elucidated about the various types of uses usable for instance, for present color television systems including NTSC (national television system committee color television system), PAL (phase alternation by line color television system), and SECAM (sequential memoire color television system), a sequential color television system, the high definition television system, and a computer display system for an EWS (engineering work station).
In the high definition television system, number of scanning lines are more than two times of the present color television systems or the sequential color television system. Furthermore, band width of video frequency is expanded as compared with the present color television systems or the sequential color television system. Therefore, in the high definition television system, a fluorescent screen of a higher resolution is required as compared with the present color television systems or the sequential color television system.
Accordingly, it is impossible to realize the higher degree 2111~22 of the brightness modulation of peripheral VS. center regions than the present color television systems or the sequential color television system.
Now, differences between the computer display system for the EWS and other television systems will be elucidated in the following lines. FIG.7 shows an aspect ratio of respective television systems. An aspect ratios of the high definition system is 16:9, whereas an aspect ratios of the computer display system for the EWS is 4:3 as shown in FIG.7. Therefore, when the same CRT is used for EWS by switching from the high definition TV, it has a higher difficulty in achieving a good focus at the peripheral or corner regions as compared with the display for the high definition television system. However, in the computer display system for the EWS, the video signal mainly displays betters or characters, there is a strong requirement for a high resolution of the fluorescent screen as compared with the high definition television system, while requirement to uniform brightness is not so strong. Accordingly, it is not necessary that the degree of the brightness modulation for uniform brightness between the peripheral regions and the center region is not required so much.
OBJECT AND SUMMARY OF TE~E INVENTION
In order to solve the aforementioned problems on the video display unit for multiple usage display system, 21il422 a brightness modulation circuit in accordance with the present invention comprises:
a parabolic wave generation circuit for issuing a horizontal parabolic wave, which is synchronized with a horizontal scanning frequency, and a vertical parabolic wave, which is synchronized with a vertical scanning frequency, level adjusting means for controlling level of the horizontal parabolic wave and level of the vertical parabolic wave, the level adjusting means having a CPU, an address generator, and a memory part, the memory part storing data for a degree of the brightness modulation and issuing the data to the address generator upon receiving an address signal from the address generator, the address generator, being controlled by the CPU, issuing the data as a horizontal level control signal and a vertical level control signal, receiving selected one kind of the data from the memory part corresponding to kind of display usage, a horizontal digital/analog converter for issuing a horizontal amplitude-modulated parabolic wave by receiving horizontal parabolic signal from the parabolic wave generation circuit, which is modulated by the horizontal level control signal, a vertical digital/analog converter for issuing a vertical amplitude-modulated parabolic wave by receiving vertical parabolic signal from the parabolic wave generation circuit, which is modulated by the vertical level control signal, and at least three multiplying circuits for multiplying respective video signal with respective the horizontal amplitude-modulated parabolic wave and with the vertical amplitude-modulated parabolic wave to issue modulated driving voltage signals for respective cathode-ray tubes.
In the brightness modulation circuit of the present invention, the memory part of the level adjusting means stores the data of plural degree of the brightness modulation corresponding to the various types of uses.
Furthermore, the address generator of the adjusting means issues the data as the horizontal level control signal and the vertical level control signal to the horizontal digital/analog converter and the vertical digital/analog converter, respectively. Therefore, in the brightness modulation circuit of the present invention, it is possible that the degree of the brightness modulation according to the various types of uses accomplishes the realization of the suitable degree of the brightness modulation eliminating to reduce the resolution of the fluorescent screen. Although it is elucidated that the brightness modulation circuit of the present invention accomplishes the realization of the suitable degree of the 2111~22 brightness modulation against the various types of uses, it is possible that the degree of the brightness modulation accomplishes the realization of the degree of the brightness modulation against varied contents of the pictorial images in the same television system.
BRIEF DESCRIPTION OF T~E DRAWINGS
FIG.1 is a circuit diagram showing a brightness modulation circuit, which is a preferred embodiment of the present invention, for a CRT used for a projection display.
FIG.2 is a wave form chart showing waveforms (A), (B), (C) and (D), which are horizontal signals in a NTSC color television system, appearing points at A, B, C
and D in FIG.1, respectively.
FIG.3 is a wave form chart showing waveforms (A), (B), (C) and (D), which are horizontal signals in a high definition color television system, appearing points at A, B, C and D in FIG.1, respectively.
FIG.4 is a wave form chart showing waveforms (A), (B), (C) and (D), which are horizontal signals in a computer display system, appearing points at A, B, C and D
in FIG.1, respectively.
FIG.5 is a circuit diagram showing a prior art brightness modulation circuit, for a CRT using a projection display.
FIG.6 is a characteristic curve showing a 21~1422 relationship between a diameter of an electron beam spot and the driving voltage of the video signal.
FIG.7 is a top plan view of a fluorescent screen showing an aspect ratio with respect to various types of uses.
DESCRIPTION OF l~ PREFERRED EMBODIMENTS
One preferred embodiment of the present invention will be explained with reference to FIG.1, FIG.2, FIG.3 and FIG.4. FIG.1 is a circuit diagram showing a brightness modulation circuit of a preferred embodiment of the present invention, for a CRT using a projection display. In FIG.1, a horizontal synchronization signal 1 and a vertical synchronization signal 2 are input to a parabolic wave generation circuit 3. A horizontal parabolic wave 4, which is synchronized with a horizontal scanning frequency, is issued from the parabolic wave generation circuit 3 to a horizontal digital/analog converter 6. Furthermore, a horizontal level control signal, which is a digital signal of an eight bit data for a realization of an amplitude modulation, is issued from an address-generator 12 of a level adjusting circuit to the horizontal digital/analog converter 6. In the horizontal digital/analog converter 6, the horizontal level control signal is multiplied by the horizontal parabolic wave 4 after converting it from the digital signal to an analog signal. As a result, a horizontal amplitude-modulated parabolic wave is issued 21il422 from the horizontal digital/analog converter 6 and through a buffer amplifier 33 given to three multiplying circuits 14, 15 and 16 for respective three video signals 8, 9 and 10 of different colors. Similarly, a vertical parabolic wave 5, which is synchronized with a vertical scanning frequency, is issued from the parabolic wave generation circuit 3 to a vertical digital/analog converter 7.
Furthermore, a vertical level control signal, which is a digital signal of an eight bit data for a realization of an amplitude modulation, is issued from the address generator 12 of the level adjusting circuit to the vertical digital/analog converter 7. In the vertical digital/analog converter 7, the vertical level control signal is multiplied by a vertical parabolic wave 5 after converting it from the digital signal to the analog signal. As a result, a vertical amplitude-modulated parabolic wave is issued from the vertical digital/analog converter 7 and through a buffer amplifier 34 given to three multiplying circuits 14, 15 and 16 for respective three video signals 8, 9 and 10 of different colors. R-video signal 8 for dots of red light-emitting fluorescent material (R) (hereinafter referred to as R-video signal 8 ) is input to the multiplying circuit (R) 14. In the multiplying circuit (R) 14, R-video signal 8 is multiplied into respective of the horizontal amplitude-modulated parabolic wave and the vertical amplitude-modulated 21il422 parabolic wave. Subsequently, multiplied R-video signal is issued to a CRT 20 through an amplification circuit 17 for driving the CRT 20. Similarly, G-video signal 9 for dots of green light-emitting fluorescent material (G) (hereinafter referred to as G-video signal 9 ) is input to the multiplying circuit (G) 15. In the multiplying circuit (G) 15, G-video signal 9 is multiplied into respective of the horizontal amplitude-modulated parabolic wave and the vertical amplitude-modulated parabolic wave.
Subsequently, multiplied G-vi-deo signal is issued to a CRT
21 through an amplification circuit 18 for driving the CRT
21. Furthermore, B-video signal 10 for dots of blue light-emitting fluorescent material (B) (hereinafter referred to as B-video signal 10 ) is input to the multiplying circuit (B) 16. In the multiplying circuit (B) 16, B-video signal 10 is multiplied into respective of the horizontal amplitude-modulated parabolic wave and the vertical amplitude-modulated parabolic wave.
Subsequently, multiplied B-video signal is issued to a CRT
22 through an amplification circuit 19 for driving the CRT
22.
Hereafter, the level adjusting circuit of the present invention will be elucidated in the following.
The level adjusting circuit is consisted of a CPU 11, the address generator 12 and a memory part 13. The CPU 11 is controlled with an external electrical device, such as a 21;142~
remote controller. Firstly, one of various types of uses of the television systems is selected by the remote controller, and an address signal is issued from the address generator 12 to the memory part 13 in order to conduct a mode selection of the memory part 13 corresponding to the selected use of the television system. Secondary, the horizontal level control signal and the vertical level control signal are independently adjusted by the remote controller in a manner to confirm with a suitable pictorial image of a fluorescent screen and an appropriate degree of the brightness modulation is suitably decided. Thirdly, the decided levels of the horizontal level control signal and the vertical level control signal are stored in the selected mode of the memory part 13 as a data corresponding to the instruction of the remote controller. This procedure is repeated for other uses of the various types of uses. As a result, the suitable data for the degree of the brightness modulation are accumulated in the memory part 13. Therefore, it is possible to accomplish the realization of the suitable degree of the brightness modulation against the various types of uses. Furthermore, since the decision of the degree of the brightness modulation is conducted by watching the suitable pictorial image of the fluorescent screen, it is unlikely to reduce the resolution of the fluorescent screen.
Subsequently, a concrete example will be elucidated about differences of waveforms, which correspond to the various types of uses, in respective part of the brightness modulation circuit of the present invention with reference to FIG2, FIG.3 and FIG.4. In FIG.2, FIG.3 and FIG.4, "lH" indicates one period of a horizontal scanning and corresponds to a horizontal direction of the fluorescent screen.
FIG.2 is a wave form chart showing waveforms (A), (B), (C) and (D), which are horizontal signals in a NTSC color television system, appearing points at A, B, C
and D in FIG.1, respectively. In the NTSC color television system, since it is strictly required that brightness of peripheral regions of the fluorescent screen is nearly equal to one of center region of the fluorescent screen, the video signal is modulated so as to become larger as the distance from the center region to the peripheral regions increases. FIG.3 is a wave form chart showing waveforms (A), (B), (C) and (D), which are horizontal signals in a high definition color television system, appearing points at A, B, C and D in FIG.1, respectively. In the high definition color television system, since it is required that brightnesses in peripheral regions of the fluorescent screen is nearly equal to that center region of the fluorescent screen and that more excellent resolution is required as compared 21~1422 with the NTSC color television system, the degree of the brightness modulation is smaller than one of the NTSC
color television system. FIG.4 is a wave form chart showing waveforms (A), (B), (C) and (D), which are horizontal signals in a computer display system, appearing points at A, B, C and D in FIG.1, respectively. In the computer display system, since high resolutions of the fluorescent screen at all parts are required, a modulation of brightness are not carried out as shown in FIG.4 (B) and FIG.4 (D).
Although the present invention has been described in terms of the presently preferred embodiment, it is to be understood that such disclosure is not to be interpreted as limiting. Various alterations and modifications will no doubt become apparent to those skilled in the art after having read the above disclosure.
Accordingly, it is intended that the appended claims be interpreted as covering all alterations and modifications as fall within the true spirit and scope of the invention.
Conventionally, in a video display unit having a CRT, although a uniform brightness is required over the whole surface of the fluorescent screen, peripheral regions of the fluorescent screen do not generally have enough brightness compared to a center region of the fluorescent screen. The cause of the above-mentioned problem is explained as follows:
(1) With regard to the ordinary type, i.e.
direct observation type CRT (non-projection type) display:
In such ordinary type, it is necessary to decrease the generation of a mislanding between an electron beam landing positions and a fluorescent material dots, which should correspond to the electron beam landing positions of the same color, on the peripheral regions.
Therefore, in the peripheral regions, sizes of guard band or black matrix part, which separates neighboring different fluorescent material dots from each other must be made lager than those in the center region. As a result, in the peripheral regions, a size of the fluorescent material dots becomes smaller than those in the center region. Accordingly, brightnesses of the peripheral regions decrease compared to brightness of the center region. Furthermore, in the CRT for a high definition television system or the like, since an size of respective apertures on a shadow-mask is short so as to obtain a high resolution, the above-mentioned tendency of smaller brightnesses in the peripheral regions decreases compared to the brightness of the center region becomes more prominent. Similarly, in case a large deflection angle of the electron beam is adopted so as to decrease the depth of the CRT, namely achieve a shorter distance between the fluorescent screen and an electron gun, the above-mentioned tendency of brightness difference between the peripheral regions the center region becomes more evident.
(2) With regard to the projection type CRT
display:
In the CRT display using the projection systems, there is the following cause of producing the center VS.
peripheral brightness difference besides the above-mentioned causes for the ordinary direct observation type display. Since a raster, which is formed on the fluorescent screen, is magnified on a screen of the 2 1 ~ 1 ~ 2 2 projection display as a pictorial image with a projection lens, an efficiency for light utilization of the projection lens decreases at its peripheral parts in proportion to the distance from its center part.
Accordingly, brightnesses in the peripheral regions of the fluorescent screen decrease compared to the brightness of the center region.
In order to cope with the above-mentioned center VS. peripheral brightness-difference of the projection type display system, there have been proposed a modulation of an electron beam drive voltage of the CRT. That is, conventionally, the electron beam driving voltage of the CRT, is modulated higher in the peripheral regions than to the center region depending on distances from the center of the phosphor screen, or depending on deflection angles.
FIG.5 shows a circuit diagram of the conventional brightness modulation circuit for the CRT
using the projection display. In FIG.5, a horizontal synchronization signal 1 and a vertical synchronization signal 2 are input to a parabolic wave generation circuit 3. A horizontal parabolic wave 4, which is synchronized with a horizontal scanning frequency, is issued from the parabolic wave generation circuit 3 to three multiplying circuit 14, 15 and 16 for respective three video signals 8, 9 and 10 of different colors, through a buffer amplifier 33 and a horizontal level adjusting rheostat 31.
21~1q22 Similarly, a vertical parabolic wave 5, which is synchronized with a vertical scanning frequency, is issued from the parabolic wave generation circuit 3 to three multiplying circuit 14, 15 and 16 for respective three video signals 8, 9 and 10 of different colors, through a buffer amplifier 34 and a vertical level adjusting rheostat 32. R-video signal 8 for dots of red light-emitting fluorescent material (R) (hereinafter referred to as R-video signal 8 ) is input to the multiplying circuit (R) 14. Therefore, in the multiplying circuit (R) 14, a brightness modulation for R-video signal 8 is made to increase responding to the distance from the center region to the peripheral regions. Subsequently, R-video signal 8 is input to a CRT (R) 20, which is for red light-emitting, through an amplification circuit 17, which is for R-video signal 8. Similarly, G-video signal 9 for dots of green light-emitting fluorescent material (G) (hereinafter referred to as G-video signal 9 ) is input to the multiplying circuit (G) 15. Therefore, in the multiplying circuit (G) 15, a brightness modulation for G-video signal 9 is made to increase responding to the distance from the center region to the peripheral regions.
Subsequently, G-video signal 9 is input to a CRT (G) 21, which is for a green light-emitting, through an amplification circuit 18, which is for G-video signal 9.
Furthermore, B-video signal 10 for dots of blue light-emitting fluorescent material (B) (hereinafter referred toas B-video signal 10 ) is input to the multiplying circuit (B) 16. Therefore, in the multiplying circuit (B) 16, a brightness modulation for B-video signal 10 is made to increase responding to the distance from the center region to the peripheral regions. Subsequently, B-video signal 10 is input to a CRT (B) 22, which is for a blue light-emitting, through an amplification circuit 19, which is for B-video signal 10.
A degree of the brightness modulation is realized in a manner that the levels of the horizontal parabolic wave 4 and the vertical parabolic wave 5 are adjusted to the video signal, which is set to one of the various types of uses, by means of the two rheostats 31, 32 or alternatively by two fixed resistors. Since the above-mentioned modulation is realized, brightnesses of the peripheral regions is substantially equalized to brightness of the center region. Accordingly, in the whole surface of the fluorescent screen, the uniformity of brightness is achieved.
However, in the above-mentioned conventional brightness modulation circuit, another problem arises as followings:
In the conventional brightness modulation circuit, the degree of the brightness modulation is designed fixedly for the cause of improving the ordinary analog video signal only. And the modulation degree is fixed to the analog video signal use by means of the rheostats 31, 32 or two fixed resistors. Furthermore, since the rheostats 31, 32 are covered with a plastic cover and the adjustment of the rheostats 31, 32 requires a professional apparatuses, the rheostats 31, 32 are semipermanently fixed to the optimum positions for above-mentioned analog video signal in the factory. Therefore, in the conventional brightness modulation circuit, it is impossible that the degree of the brightness modulation is readjusted or modified for other mode of modulation responding to the type of the video signal to display.
Accordingly, in the conventional brightness modulation circuit, although a video display unit, which has been tuned to correspond to the ordinary analog video signal, is manufactured best for displaying the ordinary video signal, it is inadequate to be used as multiple source type display apparatus, which should realize the various degree of the brightness modulation. Furthermore, if an appropriate degree of the brightness modulation is not carried out, it is likely to cause the lowering of the resolution because of the below-mentioned reason.
FIG.6 shows a characteristic curve showing a relation of diameter of an electron beam spot and the driving voltage of the video signal. The diameter of the electron beam spot becomes lager responding to increase of the driving voltage as shown in FIG.6. Therefore, if the driving voltage is too large, the resolution of the fluorescent screen is lowered. Furthermore, it is to be noted that characteristic of the electron beam spot generally becomes poorer in the peripheral regions in comparison with the center region for the same driving voltage. Accordingly, a concrete example will be elucidated about the various types of uses usable for instance, for present color television systems including NTSC (national television system committee color television system), PAL (phase alternation by line color television system), and SECAM (sequential memoire color television system), a sequential color television system, the high definition television system, and a computer display system for an EWS (engineering work station).
In the high definition television system, number of scanning lines are more than two times of the present color television systems or the sequential color television system. Furthermore, band width of video frequency is expanded as compared with the present color television systems or the sequential color television system. Therefore, in the high definition television system, a fluorescent screen of a higher resolution is required as compared with the present color television systems or the sequential color television system.
Accordingly, it is impossible to realize the higher degree 2111~22 of the brightness modulation of peripheral VS. center regions than the present color television systems or the sequential color television system.
Now, differences between the computer display system for the EWS and other television systems will be elucidated in the following lines. FIG.7 shows an aspect ratio of respective television systems. An aspect ratios of the high definition system is 16:9, whereas an aspect ratios of the computer display system for the EWS is 4:3 as shown in FIG.7. Therefore, when the same CRT is used for EWS by switching from the high definition TV, it has a higher difficulty in achieving a good focus at the peripheral or corner regions as compared with the display for the high definition television system. However, in the computer display system for the EWS, the video signal mainly displays betters or characters, there is a strong requirement for a high resolution of the fluorescent screen as compared with the high definition television system, while requirement to uniform brightness is not so strong. Accordingly, it is not necessary that the degree of the brightness modulation for uniform brightness between the peripheral regions and the center region is not required so much.
OBJECT AND SUMMARY OF TE~E INVENTION
In order to solve the aforementioned problems on the video display unit for multiple usage display system, 21il422 a brightness modulation circuit in accordance with the present invention comprises:
a parabolic wave generation circuit for issuing a horizontal parabolic wave, which is synchronized with a horizontal scanning frequency, and a vertical parabolic wave, which is synchronized with a vertical scanning frequency, level adjusting means for controlling level of the horizontal parabolic wave and level of the vertical parabolic wave, the level adjusting means having a CPU, an address generator, and a memory part, the memory part storing data for a degree of the brightness modulation and issuing the data to the address generator upon receiving an address signal from the address generator, the address generator, being controlled by the CPU, issuing the data as a horizontal level control signal and a vertical level control signal, receiving selected one kind of the data from the memory part corresponding to kind of display usage, a horizontal digital/analog converter for issuing a horizontal amplitude-modulated parabolic wave by receiving horizontal parabolic signal from the parabolic wave generation circuit, which is modulated by the horizontal level control signal, a vertical digital/analog converter for issuing a vertical amplitude-modulated parabolic wave by receiving vertical parabolic signal from the parabolic wave generation circuit, which is modulated by the vertical level control signal, and at least three multiplying circuits for multiplying respective video signal with respective the horizontal amplitude-modulated parabolic wave and with the vertical amplitude-modulated parabolic wave to issue modulated driving voltage signals for respective cathode-ray tubes.
In the brightness modulation circuit of the present invention, the memory part of the level adjusting means stores the data of plural degree of the brightness modulation corresponding to the various types of uses.
Furthermore, the address generator of the adjusting means issues the data as the horizontal level control signal and the vertical level control signal to the horizontal digital/analog converter and the vertical digital/analog converter, respectively. Therefore, in the brightness modulation circuit of the present invention, it is possible that the degree of the brightness modulation according to the various types of uses accomplishes the realization of the suitable degree of the brightness modulation eliminating to reduce the resolution of the fluorescent screen. Although it is elucidated that the brightness modulation circuit of the present invention accomplishes the realization of the suitable degree of the 2111~22 brightness modulation against the various types of uses, it is possible that the degree of the brightness modulation accomplishes the realization of the degree of the brightness modulation against varied contents of the pictorial images in the same television system.
BRIEF DESCRIPTION OF T~E DRAWINGS
FIG.1 is a circuit diagram showing a brightness modulation circuit, which is a preferred embodiment of the present invention, for a CRT used for a projection display.
FIG.2 is a wave form chart showing waveforms (A), (B), (C) and (D), which are horizontal signals in a NTSC color television system, appearing points at A, B, C
and D in FIG.1, respectively.
FIG.3 is a wave form chart showing waveforms (A), (B), (C) and (D), which are horizontal signals in a high definition color television system, appearing points at A, B, C and D in FIG.1, respectively.
FIG.4 is a wave form chart showing waveforms (A), (B), (C) and (D), which are horizontal signals in a computer display system, appearing points at A, B, C and D
in FIG.1, respectively.
FIG.5 is a circuit diagram showing a prior art brightness modulation circuit, for a CRT using a projection display.
FIG.6 is a characteristic curve showing a 21~1422 relationship between a diameter of an electron beam spot and the driving voltage of the video signal.
FIG.7 is a top plan view of a fluorescent screen showing an aspect ratio with respect to various types of uses.
DESCRIPTION OF l~ PREFERRED EMBODIMENTS
One preferred embodiment of the present invention will be explained with reference to FIG.1, FIG.2, FIG.3 and FIG.4. FIG.1 is a circuit diagram showing a brightness modulation circuit of a preferred embodiment of the present invention, for a CRT using a projection display. In FIG.1, a horizontal synchronization signal 1 and a vertical synchronization signal 2 are input to a parabolic wave generation circuit 3. A horizontal parabolic wave 4, which is synchronized with a horizontal scanning frequency, is issued from the parabolic wave generation circuit 3 to a horizontal digital/analog converter 6. Furthermore, a horizontal level control signal, which is a digital signal of an eight bit data for a realization of an amplitude modulation, is issued from an address-generator 12 of a level adjusting circuit to the horizontal digital/analog converter 6. In the horizontal digital/analog converter 6, the horizontal level control signal is multiplied by the horizontal parabolic wave 4 after converting it from the digital signal to an analog signal. As a result, a horizontal amplitude-modulated parabolic wave is issued 21il422 from the horizontal digital/analog converter 6 and through a buffer amplifier 33 given to three multiplying circuits 14, 15 and 16 for respective three video signals 8, 9 and 10 of different colors. Similarly, a vertical parabolic wave 5, which is synchronized with a vertical scanning frequency, is issued from the parabolic wave generation circuit 3 to a vertical digital/analog converter 7.
Furthermore, a vertical level control signal, which is a digital signal of an eight bit data for a realization of an amplitude modulation, is issued from the address generator 12 of the level adjusting circuit to the vertical digital/analog converter 7. In the vertical digital/analog converter 7, the vertical level control signal is multiplied by a vertical parabolic wave 5 after converting it from the digital signal to the analog signal. As a result, a vertical amplitude-modulated parabolic wave is issued from the vertical digital/analog converter 7 and through a buffer amplifier 34 given to three multiplying circuits 14, 15 and 16 for respective three video signals 8, 9 and 10 of different colors. R-video signal 8 for dots of red light-emitting fluorescent material (R) (hereinafter referred to as R-video signal 8 ) is input to the multiplying circuit (R) 14. In the multiplying circuit (R) 14, R-video signal 8 is multiplied into respective of the horizontal amplitude-modulated parabolic wave and the vertical amplitude-modulated 21il422 parabolic wave. Subsequently, multiplied R-video signal is issued to a CRT 20 through an amplification circuit 17 for driving the CRT 20. Similarly, G-video signal 9 for dots of green light-emitting fluorescent material (G) (hereinafter referred to as G-video signal 9 ) is input to the multiplying circuit (G) 15. In the multiplying circuit (G) 15, G-video signal 9 is multiplied into respective of the horizontal amplitude-modulated parabolic wave and the vertical amplitude-modulated parabolic wave.
Subsequently, multiplied G-vi-deo signal is issued to a CRT
21 through an amplification circuit 18 for driving the CRT
21. Furthermore, B-video signal 10 for dots of blue light-emitting fluorescent material (B) (hereinafter referred to as B-video signal 10 ) is input to the multiplying circuit (B) 16. In the multiplying circuit (B) 16, B-video signal 10 is multiplied into respective of the horizontal amplitude-modulated parabolic wave and the vertical amplitude-modulated parabolic wave.
Subsequently, multiplied B-video signal is issued to a CRT
22 through an amplification circuit 19 for driving the CRT
22.
Hereafter, the level adjusting circuit of the present invention will be elucidated in the following.
The level adjusting circuit is consisted of a CPU 11, the address generator 12 and a memory part 13. The CPU 11 is controlled with an external electrical device, such as a 21;142~
remote controller. Firstly, one of various types of uses of the television systems is selected by the remote controller, and an address signal is issued from the address generator 12 to the memory part 13 in order to conduct a mode selection of the memory part 13 corresponding to the selected use of the television system. Secondary, the horizontal level control signal and the vertical level control signal are independently adjusted by the remote controller in a manner to confirm with a suitable pictorial image of a fluorescent screen and an appropriate degree of the brightness modulation is suitably decided. Thirdly, the decided levels of the horizontal level control signal and the vertical level control signal are stored in the selected mode of the memory part 13 as a data corresponding to the instruction of the remote controller. This procedure is repeated for other uses of the various types of uses. As a result, the suitable data for the degree of the brightness modulation are accumulated in the memory part 13. Therefore, it is possible to accomplish the realization of the suitable degree of the brightness modulation against the various types of uses. Furthermore, since the decision of the degree of the brightness modulation is conducted by watching the suitable pictorial image of the fluorescent screen, it is unlikely to reduce the resolution of the fluorescent screen.
Subsequently, a concrete example will be elucidated about differences of waveforms, which correspond to the various types of uses, in respective part of the brightness modulation circuit of the present invention with reference to FIG2, FIG.3 and FIG.4. In FIG.2, FIG.3 and FIG.4, "lH" indicates one period of a horizontal scanning and corresponds to a horizontal direction of the fluorescent screen.
FIG.2 is a wave form chart showing waveforms (A), (B), (C) and (D), which are horizontal signals in a NTSC color television system, appearing points at A, B, C
and D in FIG.1, respectively. In the NTSC color television system, since it is strictly required that brightness of peripheral regions of the fluorescent screen is nearly equal to one of center region of the fluorescent screen, the video signal is modulated so as to become larger as the distance from the center region to the peripheral regions increases. FIG.3 is a wave form chart showing waveforms (A), (B), (C) and (D), which are horizontal signals in a high definition color television system, appearing points at A, B, C and D in FIG.1, respectively. In the high definition color television system, since it is required that brightnesses in peripheral regions of the fluorescent screen is nearly equal to that center region of the fluorescent screen and that more excellent resolution is required as compared 21~1422 with the NTSC color television system, the degree of the brightness modulation is smaller than one of the NTSC
color television system. FIG.4 is a wave form chart showing waveforms (A), (B), (C) and (D), which are horizontal signals in a computer display system, appearing points at A, B, C and D in FIG.1, respectively. In the computer display system, since high resolutions of the fluorescent screen at all parts are required, a modulation of brightness are not carried out as shown in FIG.4 (B) and FIG.4 (D).
Although the present invention has been described in terms of the presently preferred embodiment, it is to be understood that such disclosure is not to be interpreted as limiting. Various alterations and modifications will no doubt become apparent to those skilled in the art after having read the above disclosure.
Accordingly, it is intended that the appended claims be interpreted as covering all alterations and modifications as fall within the true spirit and scope of the invention.
Claims
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A brightness modulation circuit for a video display unit, comprising:
a parabolic wave generation circuit for issuing a horizontal parabolic wave, which is synchronized with a horizontal scanning frequency of the unit, and a vertical parabolic wave, which is synchronized with a vertical scanning frequency of the unit;
level adjusting means for controlling a level of said horizontal parabolic wave and a level of said vertical parabolic wave, said level adjusting means including a CPU, an address generator, and a memory, said memory storing data for a degree of the brightness modulation and issuing the data to said address generator upon receiving an address signal from said address generator, said address generator being controlled by said CPU and, issuing said data as one of a horizontal level control signal and a vertical level control signal depending on the display usage, a horizontal digital/analog converter for issuing a horizontal amplitude-modulated parabolic wave by receiving a horizontal parabolic signal from said parabolic wave generation circuit, which is modulated by said horizontal level control signal, a vertical digital/analog converter for issuing a vertical amplitude-modulated parabolic wave by receiving the vertical parabolic wave signal from said parabolic wave generation circuit, which is modulated by said vertical level control signal, and at least three multiplying circuits for multiplying respective video signals with respective said horizontal amplitude-modulated parabolic wave and with said vertical amplitude-modulated parabolic wave to issue modulated driving voltage signals for respective cathode-ray tubes.
a parabolic wave generation circuit for issuing a horizontal parabolic wave, which is synchronized with a horizontal scanning frequency of the unit, and a vertical parabolic wave, which is synchronized with a vertical scanning frequency of the unit;
level adjusting means for controlling a level of said horizontal parabolic wave and a level of said vertical parabolic wave, said level adjusting means including a CPU, an address generator, and a memory, said memory storing data for a degree of the brightness modulation and issuing the data to said address generator upon receiving an address signal from said address generator, said address generator being controlled by said CPU and, issuing said data as one of a horizontal level control signal and a vertical level control signal depending on the display usage, a horizontal digital/analog converter for issuing a horizontal amplitude-modulated parabolic wave by receiving a horizontal parabolic signal from said parabolic wave generation circuit, which is modulated by said horizontal level control signal, a vertical digital/analog converter for issuing a vertical amplitude-modulated parabolic wave by receiving the vertical parabolic wave signal from said parabolic wave generation circuit, which is modulated by said vertical level control signal, and at least three multiplying circuits for multiplying respective video signals with respective said horizontal amplitude-modulated parabolic wave and with said vertical amplitude-modulated parabolic wave to issue modulated driving voltage signals for respective cathode-ray tubes.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002111422A CA2111422C (en) | 1993-12-14 | 1993-12-14 | Brightness modulation circuit |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002111422A CA2111422C (en) | 1993-12-14 | 1993-12-14 | Brightness modulation circuit |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2111422A1 CA2111422A1 (en) | 1995-06-15 |
| CA2111422C true CA2111422C (en) | 1997-05-13 |
Family
ID=4152621
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002111422A Expired - Fee Related CA2111422C (en) | 1993-12-14 | 1993-12-14 | Brightness modulation circuit |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2111422C (en) |
-
1993
- 1993-12-14 CA CA002111422A patent/CA2111422C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CA2111422A1 (en) | 1995-06-15 |
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| MKLA | Lapsed |