Image distortion correcting device

Details Image distortion correcting device Image distortion correcting device

2000-11-01

2002-04-16

Barrera, Ramon M. (Department: 2832)

Electricity: magnetically operated switches, magnets, and electr

Magnets and electromagnets

Electron or ion beam deflecting type

C335S212000, C335S213000, C313S440000, C315S370000

Reexamination Certificate

active

06373360

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image distortion correcting device used in a CRT (Cathode-Ray Tube) display device.
2. Description of the Background Art
<Intermediate Pincushion Distortion of Vertical Lines>
FIG. 18
is a schematic diagram showing pincushion distortion of vertical lines in the intermediate areas (hereinafter referred to as “intermediate pincushion distortion”), which is often studied as a problem in CRT display devices used in current high-definition display monitors etc. In this diagram, vertical lines
23
are shown near the edges of the screen
20
and vertical lines
24
are shown in the intermediate areas of the screen (the intermediate areas between the central area and the marginal areas in the screen). When the vertical lines
23
in the marginal areas of the screen look approximately straight, the vertical lines
24
in the intermediate areas of the screen look distorted in a pincushion-like shape, which is called intermediate pincushion distortion.
It is difficult to solve such intermediate pincushion distortion only by controlling the magnetic field distribution of the deflection yoke.
Methods for correcting the intermediate pincushion distortion using circuitry include the well-known method of improved S-correction where the amount of S-correction is varied in the vertical scanning period (hereinafter simply referred to as vertical period).
<S-correction>
First, the S-correction is described. The S-correction is a correcting method in which the horizontal deflection current is modulated from a sawtooth form to an approximately S-shaped form to obtain appropriate linearity in the horizontal direction.
FIG. 19
is an explanation diagram showing display condition on the screen
20
with a horizontal deflection current IH having a sawtooth waveform. As shown in this diagram, when the sawtooth horizontal deflection current IH flows as shown in the graph G
11
, the amount of displacement, X, of the electron beam path
25
varies as shown in the graph G
12
in the horizontal section of the display, e.g. a CRT.
At this time, the marginal areas of the screen
20
(the screen is rotated counterclockwise by 90°) are more distant from the deflection center than the intermediate areas, so that, if the variation of the amount of deflection current is constant, the electron beam is deflected larger in the marginal areas than in the intermediate areas. Accordingly, the interval &Dgr;B between the vertical lines (horizontal lines in the diagram) in the marginal areas of the screen is larger than the interval &Dgr;A between the vertical lines in the intermediate areas of the screen (i.e. &Dgr;A<&Dgr;B).
FIG. 20
is an explanation diagram showing display condition on the screen
20
with a horizontal deflection current IH having an S-shape-corrected sawtooth waveform. In order to correct the horizontal linearity shown in
FIG. 19
, the sawtooth horizontal deflection current IH shown in the graph G
11
of
FIG. 19
is modulated into an approximately S-shaped form as shown in the graph G
21
in FIG.
20
.
When the horizontal deflection current IH is modulated into such approximately S-shaped form, the S-shaped current provides a larger amount of current than the sawtooth current in the intermediate areas and therefore the lack of deflection in the intermediate areas of the screen can be compensated for as shown in the graph G
22
of FIG.
20
. An at the ends of the Y axis. While the combined inductance Ls is determined by the difference between the amounts of variations of the two coils' inductances L
1
and L
2
from those at the ends of the Y axis, it is usually equal to or smaller than those at the ends of the Y axis.
As shown in
FIG. 10
, the condition in the display position TR (in the upper right corner of the screen) or the display position BR (in the lower right corner of the screen) can be regarded as overlap of the condition at the ends of the Y axis and that in the display position R. In this case, the horizontal correction coil L
1
becomes closer to the saturation state than at the ends of the Y axis, so that the inductance L
1
becomes smaller than at the ends of the Y axis; the saturation state of the horizontal correction coil L
2
is further canceled than at the ends of the Y axis so that the inductance L
2
becomes larger than at the ends of the Y axis. The combined inductance is equal to or smaller than those at the ends of the Y axis.
FIG. 11
is an explanation diagram showing the variations of the combined inductance of the horizontal correction coils with respect to the display positions on the screen. In this diagram, the vertical axis shows the combined inductance Ls and the horizontal axis shows the horizontal deflection current IH. In the two curves, the curve LC
1
shows the variation of the combined inductance Ls corresponding to a lateral line in the top and bottom of the screen and the curve LC
2
shows the variation of the combined inductance Ls corresponding to a lateral line in the middle area of the screen. The signs showing the display positions on the screen attached to the points on the graph are the same as those shown in FIG.
4
.
As can be seen from
FIG. 11
, in the top and bottom of the screen, the combined inductance Ls is the largest at the end of the Y axis and it becomes smaller as it approaches the corners of the screen. In the middle area of the screen, the combined inductance Ls is appropriate horizontal linearity (i.e. &Dgr;A=&Dgr;B) can thus be obtained as shown in the screen
20
of
FIG. 20
by appropriately controlling the approximately S-shaped waveform.
FIG. 21
is a circuit diagram showing an example of the circuit configuration of a horizontal deflection circuit having the S-correcting function. As shown in this diagram, the positive side of the power supply E
0
is connected to a fly-back transformer
41
and its negative side is connected to the emitter of a horizontal output transistor Q
1
. The collector of the horizontal output transistor Q
1
is connected to the primary side of the fly-back transformer
41
and its base receives a control pulse.
A diode D
20
, a capacitor C
20
, and a series connection of a horizontal deflection coil LH and an S-correction capacitor CS are connected in parallel to the horizontal output transistor Q
1
. A diode D
21
is connected to the secondary side of the fly-back transformer
41
and rectifies a signal transformed by the fly-back transformer
41
.
In this configuration, in order to modulate the horizontal deflection current into approximately S-shaped form, a pulse having the horizontal scanning periods (hereinafter simply referred to as “horizontal periods”) is supplied to the base of the horizontal output transistor Q
1
, and the horizontal deflection coil LH and the S-correction capacitor CS series-connected thereto are made to resonate at a resonant frequency determined by the horizontal deflection coil LH and the capacitor C
20
, and then a parabolic voltage as shown in
FIG. 22
appears at both ends of the S-correction capacitor CS. The amount of current becomes larger in the period where the voltage is high, i.e. in the scanning period in the intermediate part in the horizontal direction on the screen, and the sawtooth current is thus modulated into the approximately S-shaped horizontal deflection current IH.
<Intermediate Pincushion Distortion Correction with Vertical Modulation of S-correction>
For convenience of description, linearity where &Dgr;A<&Dgr;B as shown in
FIG. 19
is called outer-area expansion and linearity where &Dgr;A>&Dgr;B is called inner-area expansion.
Considering the intermediate pincushion distortion from the viewpoint of the horizontal linearity, it is seen that the inner-area expansion occurs in the top and bottom areas of the screen and the outer-area expansion occurs in the middle area of the screen. The inner-area expansion can be regarded as excess of S-correction and the outer-area expansion can be regarded as lack of S-correction. Hen

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