The present invention relates to a reciprocative deflection type CRT display apparatus suited for displaying picture information with a superhigh definition.
Development and progress of computer techniques in recent years are really remarkable, being supported by digital circuit technology. By contrast, the display techniques for visualizing the information processed by the computer makes a very low progress. Even at the present time, there exists no other device than the CRT (cathode ray tube) device which is capable of reproducing motion pictures in natural colors in greatest detail or with a highest definition.
Unfortunately, however, the maximum horizontal frequency that can be realized at present in the CRT display dies not exceed about 130 kHz. Further, the number of the scanning lines is about 2000 lines at maximum. In most of the CRT display devices, the scanning line number remains less than about 1024 lines.
One of the reasons for such situations as mentioned above can be explained by the fact that attempt for realizing the horizontal scanning frequency greater than ca. 130 kHz is inevitably accompanied with excessively large power consumption in the electromagnetic type horizontal deflection output circuit, the reason for which in turn can be explained by the fact that because of necessity for generation of a flyback pulse of a high voltage on the order of 1 kV at the horizontal flyback or retrace interval, as well known in the art, a great difficulty is encountered in reducing the power loss involved in breaking or turning off the switching element which is designed to be capable of withstanding such high voltage as mentioned above.
FIG. 1 of the accompanying drawings shows a configuration of a horizontal deflection output circuit known heretofore. In this figure, reference numeral 1 designates a horizontal driving pulse input terminal, 2 denotes a horizontal output transistor, 3 denotes a damper diode, 4 denotes a horizontal deflecting coil, 5 denotes a power supplying choke coil, 6 denotes an electric power source, 7 denotes a horizontal retrace (flyback) interval resonance capacitor and 8 denotes an S-like distortion correcting capacitor.
Power loss brought about upon transition in turning off the horizontal output transistor 2 will be elucidated below by reference to waveform diagrams of FIGS. 2 and 3.
In FIG. 2, a curve 9 represents a waveform of a current flowing through the horizontal deflecting coil 4 and a curve 10 represents a waveform of a voltage appearing across the horizontal deflecting coil 4.
FIG. 3 shows exaggeratedly a waveform of a rise-up starting portion of a flyback (retrace) pulse. In this figure, a curve 11 represents a collector current of the horizontal output transistor 2 and a curve 12 represents a collector voltage thereof. These curves are depicted on the assumption that the breaking of the transistor current is started at a time point t=0 and terminated at a time point t=t.sub.f and that during this period, the current decreases linearly. Then, the power loss P accompanying the breaking of the transistor current can be determined in accordance with the expression (1) mentioned below. Further, because the horizontal retrace (or flyback) interval T.sub.ret is usually about 15% of the horizontal scanning period T.sub.H, the undermentioned expression (2) applies valid. Furthermore, from the expressions (1) and (2), the expression (3) mentioned below applies valid as well. ##EQU1## where T.sub.H represents a horizontal scanning period,
L represents inductance of the horizontal deflecting coil 4,
C represents capacitance of the resonance capacitor 7,
LI.sub.0.sup.2 /2 represents deflection energy which is, constant, and
t.sub.f represents the fall time.
As can be seen from the above expressions, the power loss is proportional to a square of the fall time t.sub.f and in inverse proportion to a cube of the horizontal scanning period T.sub.H.
A product of a current peak value I.sub.0 and a voltage peak value V.sub.0 required for the output transistor is in inverse proportion to the horizontal scanning period T.sub.H, as can be seen from the following expression: ##EQU2##
In the above expression (2), parenthesized number inserted underneath the equality sign represents the identification number of the expression from which the equality is derived. The same applies to those expressions which will be mentioned hereinafter.
It can be seen from the expressions (3) and (4) that the product of I.sub.0 V.sub.0 P is proportional to a square of the fall time t.sub.f and a biquadrate of the horizontal scanning frequency. For this reason, a great difficulty has heretofore been encountered in increasing the horizontal deflection frequency beyond a certain limit.
Besides, heat generation of the deflecting coil itself presents a problem remaining to be solved, because in a high frequency range, power loss ascribable to eddy currents increases in proportion to the frequency. More specifically, the eddy current loss becomes maximum at a center point of the flyback or retrace interval at which the rate of change of the deflecting magnetic field intensity becomes maximum.
As the hitherto known techniques which are directed to development of the reciprocative horizontal deflection systems for the CRT device as with the case of the present invention, there may be mentioned those disclosed in the specifications of U.S. Pat. Nos. 3,662,102, 2,717,329, 2,817,787 and 4,638,308. However, with these prior art techniques, the problem of zigzagged vertical line interference which will be described hereinafter is neither recognized nor tackled at all, much less the solution thereof.