Television apparatus

Abstract: The television apparatus of the present invention is a apparatus which displays an image corresponding to a television signal, where an image signal is received and, by use of the received image signal, a first image signal and a second image signal are generated, between which time axis is deviated by n times (n is an integral number of 2 n 10) of horizontal scanning period, and by providing a cathod ray tube which simultaneously emits a first electron beam corresponding to the first image signal and a second electron beam corresponding to the second image signal, so that a high precision picture can be displayed and at the same time the brightness of display can be improved.

Description: The present invention is related to a television apparatus which displays an image corresponding to a television signal. Related Background Art In the conventional television apparatus, above all, in the projection type television device using the projection tube, high luminance can be usually obtained by raising the anode, voltage or beam current to the projection tube. However, in the case of the method to increase the anode voltage of the said projection tube, there is a limitation in increasing the said anode voltage, as X-ray generation amount is increased, and the pressure resistance of the glass at the projection tube, withstand voltage of inner electrode, etc. must be considered. In the case of electron beam amount increasing method by raising the beam current in the projection tube, where a single electron gun is used, the electron beam spot is enlarged at the high luminance time and, accordingly, the high precision degree is lowered, and such high precision television signals as EDTV, HDTV, etc. can not be reproduced sufficiently. In this connection, as shown in the Japanese Laid-Open Patent Application JP-A-62245792, an interference film filter is placed in front of red and green projection tube and such a blue projection tube is used, where 2 electron guns are provided, and the said blue projection tube is supplied with a television signal which is not delayed and also with a television signal which is delayed by one horizontal scanning period, so that the respective electron guns may be driven. In this way, the above problems are solved. However, since these electron guns are so arranged as to drive the television signal delayed by 1H (1 horizontal scanning period), it is necessary to make the afterglow time of fluorescent body of blue projection tube to be shorter than 30 µs, in the case of high precision television signals like EDTV or HDTV. On the other hand, the after-glow time of blue fluorescent substances (Zn: Ag·Al) for such a projection tube as is aimed, as explained above, to have high luminance, is as long as 65 µs (refer to Fig. 1A). This afterglow time is more than double in comparison with 1 horizontal scanning period (i.e., 30 µs) of such high precision television signal as EDTV or HDTV. The electron beam, supplied from the first electron gun to be driven by the television signal which is delayed by 1H, carries out the re-scanning, when the fluorescent body is still brightened by the scanning with the first electron gun and not yet sufficiently subdued. Hence, it cannot be so much expected that the luminance may be raised through the double scanning by the electron beam generated by 2 electron guns. (Refer to Fig. 1B) US-A-4807014 proposes a projection colour television system in which the red and green tubes have only one electron beam each, and the blue tube has two or three electron beams at one-line spacings. A ZnS:Ag phosphor is proposed, having a decay time of 10 µs. US-A-4668977 proposes a video projection system for interlace scan signals, in which each tube has two electron beams so that one beam scans even field lines while the other beam scans odd field lines in order to reduce field flicker. The two beams for the red and the green tubes receive the same signal and scan lines separated by half of a line interval. The two beams for the blue tube scan lines separated by 2½ line intervals and the signal applied to the trailing beam is delayed by 2 line periods. GB-A-2225686 shows a circuit for delaying a brightness signal in a multi-standard receiver. The amount of the delay is varied depending on the standard of the received signal. SUMMARY OF THE INVENTION The present invention provides a television apparatus as set out in claim 1. The remaining claims set out optional features. Embodiments of the present invention are described with reference to the following drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1A shows the comparison of afterglow time of fluorescent substances; Fig. 1B is a drawing to expand the luminescence action of the fluorescent substances when the double scanning is carried out with the electron beam generated by 2 electron guns; Fig. 2 shows the components of projection type television device an embodiment of this invention; Fig. 3 is the explanatory drawing on the electron beam scanning in the projection tube to display the blue image of the above Fig. 2; Fig. 4 is the explanatory drawing of the overscanning action in the projection tube of the above Fig. 2; Fig. 7 shows some components of the projection type television device in more detail. BRIEF DESCRIPTION OF PREFERRED EMBODIMENTS Following explanation on this invention is given in reference to the embodiment of the present invention. Fig. 2 shows the system of components of projections type television apparatus as an embodiment of this invention. In Fig. 2, 1 denotes a matrix circuit. 2, 3, 4 and 5 represent image output circuits which amplify respective colour image signals. 6 shows the delay element. 7 is the projection tube which displays a red colour image. 8 is a projection tube which displays a green colour image. 9 shows a projection tube which displays a blue colour image. The projection tube has 2 electron guns B1 and B2. The luminance signals received as input (Y in Fig. 2) and colour difference signals (I, Q in Fig. 2) are converted into the colour image signals of R (red), G (green) and B (blue). R and G signals are amplified in the image output circuits 2 and 3 respectively and drive the projection tubes 7 and 8 for red and green respectively. B signal is branched out into 2 lines, and one of them is directly amplified in the image output circuit 4 and drives the first electron gun B1 of the projection tube 9 for blue colour. Another B signal is delayed with the delay element 6 by the time T and then is amplified at the image output circuit 5 and thereafter drives the second electron gun B2 of the blue projection tube 9. Thus, the scanning in accordance with the same image signal is conducted twice and the fluorescent substance is brightened accordingly, and the apparent brightness of the scanning line is doubled in comparison with the case of one electron gun use. Fig. 7 shows some of the components of Fig. 2 in more detail. Meanwhile, the projection type television apparatus shown in Fig. 7 is of multi-system applicable model, which can receive the input of various kinds of television signal of NTSC system, PAL/SECAM system, ED/ADTV system, HDTV system, etc. as well as the video signal from personal computers (all of which are referred to herein as television standards), and can give the image picture display. In Fig. 7, 13 is the deflection yoke of projector tube 9 for blue colour. 14 is the control coil which deflects the beam emitted from the electron guns B1 and B2 to the vertical direction of the picture screen. 15 is the beam adjustment circuit which controls the beam deflecting action of the said control coil 14. 21 is the mode change-over circuit which changes over the display mode, depending on which display action is undertaken in response to the television signal from various kinds of the said television signals or the video signal output from personal computer. 22 is the change-over switch, which supplies the output signal by changing over from the delay elements 16 - 20 to be explained later in response to the instruction of the said mode change-over circuit 21, to the picture image output circuit 5. In Fig. 7, 16 - 20 are the delay elements respectively, and the delay time of the said delay elements is set at the least value among the time obtained by the following formulae in response to the image signal to be displayed respectively, in accordance with the after-glow time of the fluorescent substance shown in Fig. 1A and the overscanning amount in Fig. 4. Namely, the delay time TA of delay element 16 is set at 63.5 µs which corresponds to 1 horizontal scanning line period of NTSC system television signal. The delay time TB of delay element 17 is set at 64 µs which corresponds to 1 horizontal scanning line period of PAL/SECAM system television signal. The delay time TC of delay element 18 is set at 63.5 µs which corresponds to 2 horizontal scanning line periods of television signal of ED/ADTV television signal. The delay time TD of delay element 19 is set at 60 µs which corresponds to 2 horizontal scanning line periods of HDTV system television signal. The delay time TE of delay element 20 is set at 60 µs which corresponds to 4 horizontal scanning line periods of video signal output from the personal computer. In Fig. 7, the display mode is instructed by the operation section which is not shown in the drawing, and either one of the said plural kinds of television signals or video signal is received as input. Then, the said mode change-over circuit 21 regulates the said change-over switch 22 in response to the instructed display mode, and gives one of the signals supplied as output from the said delay elements 16 - 20, to the image output circuit 5. Then, the signal given via the above change-over switch 22 is amplified in the image output circuit 5 and is thereafter supplied to the electron gun B2 of projection tube 9 for blue colour. In the mode change-over circuit 21, 2 beams are emitted from the electron guns B1 and B2 of the said projection tube for blue colour by the beam adjustment circuit 15. The deflection action of 2 beams in the said deflection control coil 14 is controlled in such way that the distance relation to vertical direction of the said 2 beams may be 1H in the case of display mode corresponding to NTSC system or PAL/SECAM system, 2H in the case of ED/ADTV system or HDTV system, and 4H in the case of display mode to show the video signal given from the personal computer output. The display modes explained in this embodiment do not mean any restriction in mode but the same effect can be obtained by applying the present invention to the projection type television device having other combination display mode. As explained above, the projection tube for blue colour in the present embodiment is equipped with a plural number of electron guns. By driving a plural number of said electron guns with the image signals which are time-wise apart by such a period as corresponds to the integral number of horizontal scanning periods, a high precision image picture can be displayed, which has the same resolution degree with the case of single electron gun use, even when the beam current to the said projection tube for blue colour is increased by the number of electron guns. At the same time, the brightness can be raised and improved by the number of electron guns.

Claims: A television apparatus which displays an image corresponding to a television signal, comprising: (a) input means for receiving an image signal and providing a colour component signal for a colour component of the image signal; (b) delay means (6; 16, 17, 18, 19, 20, 22) for receiving and delaying the colour component signal; and (c) a cathode ray tube (9) which emits simultaneously first and second electron beams corresponding to the said colour component, the signal for the second electron beam being delayed relative to the signal for the first electron beam by said delay means, characterised in that the input means is for receiving an image signal according to any one of a plurality of different television standards and the delay means is operable to delay the signal for the second electron beam relative to the signal for the first electron beam by any of a plurality of delay amounts, and the delay amount is selected on the basis of the television standard of the received image signal. An apparatus according to claim 1, wherein said cathode ray tube (9) includes: (a) a first electron gun (B1) which is driven by the colour component signal and which emits said first electron beam; and (b) a second electron gun (B2) which is driven by the colour component signal delayed by said delay means and which emits said second electron beam. An apparatus according to claim 1 or claim 2, wherein the plurality of different television standards comprises the standards of the NTSC television system, the PAL/SECAM television system, the AD/ED television system, the HD television system and the image signal system of a personal computer. An apparatus according to claim 3 wherein said delay means comprises a plurality of delay elements (16, 17, 18, 19, 20), each for delaying the colour component signal by a respective delay period, and selection means (22) for selecting one of the delay elements on the basis of the television standard of the received image signal so that the delay means outputs the colour component signal after it has been delayed by the selected delay element. An apparatus according to claim 4 in which the delay period of the selected delay element is a first length of time in the case where the television standard is NTSC or ED/ADTV, a second length of time in the case where the television standard is PAL/SECAM, and a third length of time in the case where the television standard is HDTV or the image signal output system of a personal computer. An apparatus according to claim 5 in which the first length of time is 63.5 µs, the second length of time is 64 µs and the third length of time is 60 µs. An apparatus according to claim 4 in which the delay element selected for a first one of the plurality of television standards has a delay period of one horizontal scanning period in the respective television standard, the delay element selected for a second one of the plurality of television standards has a delay period of two horizontal scanning periods in the respective television standard, and the delay element selected for a third one of the plurality of television standards has a delay period of four horizontal scanning periods in the respective television standard. An apparatus according to any one of the preceding claims, further comprising deflection operation control means (15) for controlling deflection operations of the first electron beam and the second electron beam in the cathode ray tube (9) in such way that in the said cathode ray tube, said first electron beam and said second electron beam may arrive at positions being apart each other by a distance selected on the basis of the television standard of the image signal received by said input means. An apparatus according to claim 8, wherein said deflection operation control means (15) is so arranged that the first electron beam and the second electron beam arrive respectively at positions which are vertically apart by one horizontal scanning line to scanning line distance at the display screen of said cathode ray tube, if the image signal received by said input means conforms to NTSC television system or PAL/SECAM television system. An apparatus according to claim 8, wherein said deflection operation control means (15) is so arranged that the first electron beam and the second electron beam arrive respectively at positions which are vertically apart by two horizontal scanning line to scanning line distances at the display screen of said cathode ray tube, if the image signal received by said input means conforms to AD/ED television system or HD television system. An apparatus according to claim 8, wherein said deflection operation control means (15) is so arranged that the first electron beam and the second electron beam arrive respectively at positions which are vertically apart by four horizontal scanning line to scanning line distances at the display screen of the said cathode ray tube, if the image signal received by said input system conforms to the image signal output system of personal computer. An apparatus according to any one of the preceding claims comprising a further cathode ray tube (7, 8) which emits only one electron beam, corresponding to a further colour component signal for a further colour component of the image signal. An apparatus according to any one of the preceding claims, wherein said colour signal component is a blue colour component signal. An apparatus according to claim 13 comprising first and second further cathode ray tubes (7, 8) which respectively emit electron beams corresponding to colour component signals for a red colour component and a green colour component of the image signal.

Inventors: MINOURA NOBUO C O CANON KABUSH, MINOURA, NOBUO, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1991
Main classification: H04N5
IPC codes: H04N5, H04N9