Television – Video display – Cathode-ray tube
Reexamination Certificate
2000-01-21
2003-07-08
Miller, John (Department: 2614)
Television
Video display
Cathode-ray tube
C348S805000, C348S190000, C348S747000, C348S745000, C348S746000, C348S807000, C315S371000, C315S382000, C315S389000
Reexamination Certificate
active
06590620
ABSTRACT:
TECHNICAL FIELD
This invention relates to apparatuses for correcting a horizontal distortion of an image displayed on a CRT display apparatus and, more specifically, to a PLL circuit using a residual phase and a drive circuit of a CRT display apparatus using the PLL circuit.
BACKGROUND ART
In recent years, CRT display apparatuses for computers generally support various scanning frequencies. However, distortion due to assembly accuracy error is inevitable in an image displayed on the CRT display apparatus. Such distortion includes horizontal distortion causing an image to be deformed in the horizontal direction. The horizontal distortion includes center-displaced distortion, parallelogram distortion, and arcuate distortion. The phase of a horizontally-distorted image is shifted in the horizontal direction. To be properly displayed, the distorted image has to be corrected in the horizontal direction. Described briefly below are these horizontal distortions with reference to
FIGS. 31
,
32
,
33
, and
34
.
First,
FIG. 31
shows the relation between an undistorted image and various signals constructing video signals which generate the image. In the drawing, Hysnc denotes a horizontal synchronizing signal generating a pulse with a predetermined period. Ihd denotes a horizontal deflection current. Sv denotes a video signal for one frame. The horizontal deflection current Ihd synchronizes with the horizontal synchronizing signal Hsync, while the horizontal synchronizing signal Hsync and the video signal Sv have a constant temporal relation.
In one example shown in
FIG. 31
, the processing between time t
1
and time t
7
is repeated after the time t
7
. Therefore, described briefly below is the relation between the video signal and the image between the time t
1
and the time t
7
. As shown in the drawing, an H pulse Hp is a pulse signal rising at the time t
1
, falling at time t
3
, and rising at the time t
7
. The horizontal deflection current Ihd reaches its peak value at time t
2
in the H pulse Hp, and reaches its minimum value at time t
4
. The horizontal deflection current Ihd linearly increases from the time t
4
, and reaches its peak value at the time t
8
.
In response to the trailing edge of the horizontal deflection current Ihd at the time t
4
after a predetermined period (RiL) from the time (time t
3
) of the trailing edge of the pulse of the horizontal synchronizing signal Hsync, the video signal Sv starts rendering a raster image for one line. The raster image rendering ends at time t
6
preceding the time t
8
for a predetermined period (RiR). The interval between a raster frame Fr and a video frame Fv corresponding to the period RiL between the time t
4
and the time t
5
is herein called a left-retrace-line period RiL. Similarly, the interval between the raster frame Fr and the video frame Fv corresponding to the period RiR between the time t
6
and the time t
8
is herein called a right-retrace-line period RiR.
The image frames displayed on the CRT display apparatus upon receipt of these video signals are laid out as follows. Each image frame is cocentrically displayed with respect to a display frame Fc of a cabinet of the CRT display apparatus, allowing the user to feel quite normal in recognizing the image. For this purpose, the image displayed on the CRT display apparatus includes two types of images, which are distinguished as the raster frame Fr and the video frame Fv. The raster frame Fr is a frame displayed by a collection of scanning lines called raster, being scanned in a range larger than the cabinet display frame Fc.
That is, the raster frame Fr projected on the cabinet display frame Fc can be viewed as the raster frame Fr therethrough. The video frame Fv represents the actual image. In the figure, assuming that the scanning lines runs from the left end to the right, the left-retrace-line RiL from the left end of the raster frame Fr to the left end of the video frame Fv is generally constant. The left-retrace-line RiL is constant because the horizontal deflection current Ihd synchronizes with the horizontal synchronizing signal Hsync, and therefore the temporal relation between the horizontal synchronizing signal Hsync and the video signal Sv is constant. Similarly, the right-retrace-line RiR is also constant.
FIG. 32
shows a state of a distorted image with its center displaced. The raster frame Fr and the video frame Fv are displaced with respect to the cabinet display frame Fc in the horizontal direction, and as a result the video frame Fv is shifted from the center of the cabinet display frame Fc.
FIG. 33
shows a state of an image distorted in a parallelogram shape. The raster frame Fr is distorted to be a parallelogram shape with respect to the cabinet display frame Fc, and as a result the video frame Fv is also distorted in a parallelogram shape.
FIG. 34
shows distortion called arcuate distortion, in which the scan start position (the left end in the drawing) in the raster frame Fr is arcuately shifted, and therefore the video frame Fv is also viewed as arcuately distorted. These horizontal distortions as shown in
FIGS. 32
,
33
, and
34
do not necessarily occur independently, but may occur as combined.
These distortions in the horizontal direction are caused not by the divergence of the relation among the above described horizontal deflection current Ihd, video signal Sv, and horizontal synchronizing signal Hsync which is a start signal of the video signal Sv, but by mechanical mounting accuracy error of a deflection controller mainly including a deflection coil of the CRT, non-uniformity of the generated magnetic field, and other reasons.
Therefore, in recent years, to reduce distortion in the displayed image and maintain image quality, the CRT display apparatus is equipped with a distortion correcting circuit capable of adjusting the amount of correction of the image distortion according to scanning frequencies.
With reference to
FIGS. 35 and 36
, described below is an example of image distortion due to mechanical mounting accuracy error of the deflection controller. First,
FIG. 35
shows a state in which the deflection controller normally mounted on the CRT display apparatus scans the electron beam in the vertical direction. For viewability, the figure does not include components not required for description herein such as a glass tube of the CRT. In this example, the deflection controller is constructed of deflection magnetic poles
6
and their drive circuits (not shown).
An electron beam Eb emitted from an electronic gun
5
collides against a fluorescence surface of the CRT forming a screen, deflected and scanned in the vertical direction by the deflection magnetic poles
6
, and viewed as an emission line Lb on the screen. The emission line Lb is vertical with respect to a horizontal line Lh on the display screen of the CRT if the deflection controller is mounted on the CRT display apparatus correctly with respect to the CRT.
On the other hand,
FIG. 36
shows a state in which the deflection controller is mounted on the CRT display apparatus, being slightly inclined toward the CRT. In this example, compared with the case in
FIG. 35
, the deflection magnetic poles
6
are inclined an angle a (not shown) toward the CRT. Consequently, when the deflection magnetic poles
6
deflects the electron beam Eb for scanning in the vertical direction, the emission line Lb on the display screen of the CRT is not vertical but inclined to the horizontal line Lh. This is the main reason for the parallelogram distortion.
In other words, parallelogram distortion of the frame displayed on the CRT is caused not by the distortion of various video signals such as Hsync, Ihd, and Sv shown in
FIG. 31
, but by an assembly error of the CRT. Similarly, center-displaced distortion is caused also by an assembling error of the deflection controller. Although arcuate distortion is caused mainly by distortion of a deflection magnetic field or deflection electric field, this is caused not by an electric signal which controls the deflection magnetic field or de
Matsushita Electric - Industrial Co., Ltd.
Miller John
Natnael Paulos M.
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