Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
2001-11-01
2004-01-27
Lee, Wilson (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
C315S371000
Reexamination Certificate
active
06683424
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a display apparatus and in particular to a circuit for correcting pincushion distortion and a display device comprising the circuit.
BACKGROUND OF THE INVENTION
In a cathode ray tube (termed “CRT”) of a Television receiver or display apparatus, as shown in
FIG. 16
a
, while a deflection radius of a uniform magnetic field for deflecting an electron beam
73
emitted from an electron gun (cathode electrode
72
) defines a spherical face, a screen (fluorescent surface)
74
is substantially planer so that the distance from the deflection center to the screen gets longer with the increase of the deflection angle and the projection size becomes larger as a raster image projected on the screen
74
moves toward the edges of the screen
74
. The raster image are extended most at the four corners where the deflection angle becomes the largest and are distorted in the form of a pincushion and hence this distortion is termed “pincushion distortion”. As shown in
FIG. 16
b
, the distortion in which the vertical line at opposing right and left edges on the screen are curved is referred to as “E-W Raster pincushion distortion” or “Side pincushion distortion” since it is the distortion at the right and left edges.
Correction of the left and right pincushion distortion has heretofore been achieved by causing a horizontal deflection current which is amplitude-modulated with a parabolic current in a vertical scanning period to flow through a horizontal deflection coil.
FIG. 17
is a block diagram showing an exemplary configuration of a CRT monitor in which a deflection distortion such as a side pincushion distortion is corrected. Referring to
FIG. 17
, the CRT monitor comprises a vertical sawtooth wave oscillating circuit
207
which receives a vertical synchronization signal Vsync output from a synchronization separating/synchronization input processing circuit
205
and generates a vertical sweeping sawtooth wave (termed vertical sawtooth wave) and a deflection distortion correcting circuit
208
which receives the vertical sawtooth wave output from the vertical sawtooth oscillating circuit
207
and generates a distortion correction signal Vo made up of a parabolic wave of one vertical sweeping period. The distortion correction signal Vo which is generated by the deflection distortion correcting circuit
208
is fed to a horizontal oscillating circuit
206
which receives a horizontal synchronization signal Hsync and generates a horizontal sweeping sawtooth wave (horizontal drive signal). The horizontal drive signal (the phase of which is controlled by the distortion correction signal) which is output from the horizontal oscillating circuit
206
is fed to a horizontal deflection output circuit
210
. The horizontal drive signal output from the horizontal oscillation circuit
206
and the distortion correction signal Vo output from the deflection distortion correction circuit
208
are fed to a +B power supply circuit
209
which boosts the +B voltage by a pulse amplification in a blanking period during which a high voltage is required. As is well known, one cycle of the sawtooth wave is made up of a scanning interval during which the electron beam is scanned at a constant rate and a blanking interval which is a period from the completion of the scanning in one direction to next scanning. The amplitude of the horizontal drive signal within one vertical period is corrected by correcting +B voltage with the distortion correction signal Vo, a frequency of which corresponds to one vertical period. The +B voltage is supplied by the +B power supply circuit
209
to the horizontal deflection output circuit
210
which provides a deflection current which flows into a horizontal deflection coil. The horizontal deflecting current in which the amplitude of the horizontal drive signal is changed in proportion with that of the distortion correction signal is output from the horizontal deflection output circuit
210
. The synchronization deflection circuit is configured as mentioned above. As an output circuit of a video signal (RGB signal), there exists an RGB preamplifier
201
which receives a input video signal (RGB input) and outputs pre-amplified signal to an RGB main amplifier
202
. The amplified output signal from the RGB main amplifier
202
is fed to an electron gun (not shown) of the CRT
203
. In the CRT
203
, deflection currents from horizontal and vertical deflection output circuits
210
and
211
are supplied to the horizontal and vertical deflection coils
204
, respectively and the electron beam which is emitted from the electron gun is deflected under the magnetic fields from deflection yokes (not shown) arranged on the neck of the CRT
203
.
A slight variation in a mounting angle of the deflection yoke on the neck of the CRT
203
in a vertical direction causes a difference in a distortion wave form of a pincushion distortion, trapezoidal distortion and the like between the upper and lower areas of the screen, and hence a vertically asymmetrical distortion is generated.
Although the raster images at the upper and lower areas of the screen of the CRT have been corrected by the same amount so that the distortions are not readily visible, implementation of a feature to independently correct the side pincushion distortion at upper and lower areas of the screen has been demanded with a recent increase in a size and a planar structure of the screen of CRT.
Apparatuses for correcting the side pincushion distortion or vertically asymmetric distortion are disclosed in, for example, Japanese Patent Kokai Publication JP-A-6-334887, JP-A-5-308538 and JP-A-11-313222.
Among of them, in JP-A-6-334887 is disclosed a configuration of a corner pincushion distortion correcting wave generating circuit which is capable of independently correcting the distortions at corners in the upper and lower levels of the screen. As shown in
FIG. 18
, the correcting wave generating circuit comprises a lower corner part extracting differential comparator circuit
102
which receives a sawtooth wave signal
101
(vertical sawtooth wave signal) having a period of one vertical interval and extracts (slices) a part of the waveform corresponding to the lower area of the screen in the sawtooth wave signal
101
; a multiplier circuit
105
for multiplying the extracted waveform; and an amplitude adjusting circuit (gain control circuit)
107
for adjusting the amplitude of the corrected wave, whereby the above-mentioned circuits correct the corner distortion in the lower area of the screen. The correction wave generating circuit further comprises an upper corner part extracting differential comparator circuit
103
which receives the sawtooth wave signal
101
and extracts a part of the waveform corresponding to the upper area of the screen in the sawtooth wave signal
101
; a multiplier circuit
106
for multiplying the extracted waveform; and an amplitude adjusting circuit (gain control circuit)
108
for adjusting the amplitude of the corrected wave, whereby the circuits correct the corner distortion at the upper area of the screen. The correcting wave generating circuit further includes an amplitude adjusting circuit (gain control circuit) for adjusting the amplitude of the signal after the lower corrected wave is added to the upper corrected wave in an adder
109
. A corner slice point bias circuit
104
provides reference bias voltages used in the lower and upper corner image extracting differential comparator circuits
102
and
103
respectively for extracting the lower and upper corner parts in images to the lower and upper corner extracting differential comparator circuits
102
and
103
, respectively.
In JP-A-5-308538 is disclosed a left and right side pincushion distortion correcting apparatus for correcting the side pincushion distortion wherein a current flowing through the horizontal deflection coil of a horizontal output circuit is modulated in a vertical period by a parabolic voltage generated by integrating the vertical sa
Lee Wilson
NEC Electronics Corporation
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