Electric lamp and discharge devices: systems – Cathode ray tube circuits
Reexamination Certificate
2001-06-25
2003-03-18
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
C315S371000
Reexamination Certificate
active
06534920
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a horizontal deflection circuit for performing bidirectional scanning with an electron beam in the horizontal direction of a display screen, and a bidirectional horizontal deflection apparatus including such a circuit.
2. Description of the Related Art
In the field of display devices such as a cathode ray tube (hereinafter simply as “CRT”), the use of a bidirectional horizontal deflection apparatus suitable for displaying high definition images has been suggested. The bidirectional horizontal deflection apparatus is used to perform bidirectional scanning with an electron beam using a horizontal deflection coil. In the bidirectional horizontal deflection apparatus, the horizontal deflection coil equivalently has an inductance component and a resistance component connected in series therewith, and therefore pixels which should be aligned vertically could be shifted in the horizontal direction between forward and retrace scanning.
FIGS. 11A and 11B
are charts for use in illustration of change with time in the horizontal deflection current passed across the horizontal deflection coil.
FIGS. 12A and 12B
are views for use in illustration of the state of a display screen corresponding to the current waveform of the horizontal deflection current shown in
FIGS. 11A and 11B
. Note that in
FIGS. 12A and 12B
, the coordinate in the horizontal direction is referred to as “x-coordinate”, and the coordinate in the vertical direction is referred to as “y-coordinate”.
FIG. 11A
shows an ideal current waveform for a horizontal deflection current. In the state in
FIG. 11A
, the length of a trace scanning period T
1
with an electron beam coincides with the length of a retrace scanning period T
2
, and time points t
1
and t
2
where current is zero during the forward and retrace scanning correspond to the midpoints of the scanning periods T
1
and T
2
, respectively. Therefore, as shown in
FIG. 12A
, pixels which should be aligned vertically are displayed on the same x-coordinate in froward and retrace scanning. In forward and retrace scanning, pixels e
1
and e
2
in the center of the horizontal direction of the screen in
FIG. 12A
for example are displayed at positions on the same x-coordinate.
FIG. 11B
shows a current waveform having a distortion caused by the resistance component of the horizontal deflection coil. In the state shown in
FIG. 11B
, the lengths of the forward and retrace scanning periods T
3
and T
4
coincide, while the midpoints t
4
and t
6
of forward and retrace scanning periods T
3
and T
4
do not coincide with time points t
3
and t
5
where the horizontal deflection current is zero. As a result, as shown in
FIG. 12B
, pixels which should be aligned vertically are shifted in a zigzag manner in forward and retrace scanning, in other words “zigzag vertical line interference” is caused. In forward and retrace scanning, pixels e
1
and e
2
for example in the center in the horizontal direction of the screen in
FIG. 12B
are displayed at different x-coordinates.
FIG. 13
is an equivalent circuit diagram of a configuration to prevent the zigzag vertical line interference by reducing the distortion in the horizontal deflection current. The circuit is used for example in a bidirectional horizontal deflection system disclosed by Japanese Patent Laid-Open No. 7-203238. In
FIG. 13
, since a horizontal deflection coil
212
and a negative resistance
218
are connected in series with each other. The negative resistance
218
cancels the resistance component R
H
of the horizontal deflection coil
212
.
FIG. 14
is a waveform chart showing the operation of the equivalent circuit in FIG.
13
. As shown in
FIG. 14
at (a), voltage V
1
applied to an input terminal
214
has a square waveform. Since the inductance L
H
of the horizontal deflection coil
212
is large, the horizontal deflection current passed across an output terminal
216
has a triangular waveform. The waveform of voltage V
R
generated with the negative resistance
218
is 90° out of phase from the triangular waveform shown in
FIG. 14
at (b). The voltage generated with the resistance component R
H
is cancelled by the voltage V
R
generated with the negative resistance
218
, so that the horizontal deflection current passed across the equivalent circuit in
FIG. 13
appears to have no loss by the resistance and no distortion. However, if the distortion of the current passed across the horizontal deflection coil
212
by the resistance component R
H
is cancelled with the negative resistance
218
, the power consumption increases.
In the horizontal deflection system, as means for preventing the zigzag vertical line interference with small power consumption, Japanese Patent Laid-Open No. 8-172543 discloses a reciprocating deflection type CRT display device. The CRT display device includes zigzag vertical line interference automatic cancellation means which modulates a reading clock signal used to read out data corresponding to each pixel, changes the amount of delay of a horizontal synchronizing signal used as a reference for the reading clock signal, and stabilizes the changing horizontal size to cancel the zigzag vertical line interference.
FIG. 15
is a waveform chart for use in illustration of the operation of the conventional zigzag vertical line interference automatic cancellation means. The voltage waveform
227
in
FIG. 15
at (a) is the waveform of pulse voltage V
P
applied to pass horizontal deflection current across the horizontal deflection coil. The voltage waveform
226
is the waveform of a voltage pulse obtained by frequency-dividing the reading clock signal into ½. The current waveform
228
in
FIG. 15
at (c) is the waveform of a horizontal scanning position signal in proportion to the waveform of the horizontal deflection current.
The zigzag vertical line interference automatic cancellation means compares the values I(A
1
) and I(B
1
), and values I(A
2
) and I(B
2
) of the horizontal scanning position signal having one-to-one correspondence with horizontal coordinates on a reproduced image at the starting point A
1
and the midpoint A
2
of the first trace scanning and at the ending point B
1
and the midpoint B
2
of retrace scanning following the trace scanning. The conventional zigzag vertical line interference automatic cancellation means detects the horizontal size based on the difference between the values I(A
1
) and I(A
3
) of the horizontal scanning position signal at the starting point A
1
and the ending point A
3
of the trace scanning.
FIG. 16
is a diagram showing the configuration of the conventional zigzag vertical line interference automatic cancellation means. The conventional zigzag vertical line interference automatic cancellation means shown in
FIG. 16
includes horizontal deflection current detection means
303
, decoder means
304
for sampling pulse generation, sample-hold means
305
to
309
, subtractors
310
to
312
, a comparison amplifier
313
, variable delay means
314
, a gain control circuit
315
, and a power supply voltage control circuit
316
.
The horizontal deflection current detection means
303
includes for example a resistor or/and a transformer, and is connected in series to a deflection coil
301
and an S distortion correction capacitor
302
.
An input terminal
326
is provided with a signal produced by frequency-dividing the horizontal synchronizing signal into ½. The decoder means
304
for sampling pulse generation is provided with a signal indicating the timing of reading out a pixel from a counter
317
forming a reading phase locked loop for generating a reading clock signal. The decoder means
304
for sampling pulse generation decodes the signal indicating the timing and outputs sampling signals
318
to
322
to the sample-hold means
305
to
309
depending on the signal at the input terminal
326
.
The sample-hold means
305
to
309
sample and hold a horizontal scanning position signal I output from the horizontal deflec
Tanaka Masanobu
Uwabata Hideyo
Armstrong Westerman & Hattori, LLP
Matsushita Electric - Industrial Co., Ltd.
Tran Chuc
Wong Don
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