Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
1999-04-12
2001-09-25
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
C315S382100
Reexamination Certificate
active
06294884
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vertical deflection circuit to be used in a color picture tube apparatus of a television or a display monitor.
2. Description of the Prior Art
In in-line color picture tubes used in televisions and display monitors, when there is a misalignment between the central axis of the vertical deflection magnetic field and the central axis of the color picture tube, or there is a rotational misalignment between the vertical deflection magnetic field and the color picture tube, mis-convergence occurs separately at the upper and lower portions of the color picture tube screen (fluorescent screen).
As means for separately correcting these kinds of mis-convergences at the upper portion and the lower portion of the color picture tube's screen, Publication of Unexamined Japanese Publication No. Hei 8-102270 discloses two auxiliary coils that are provided at a rear portion, i.e. on the electron gun side, of a deflection yoke. Those auxiliary coils are supplied with correction current by a convergence correction circuit that uses a diode bridge circuit.
FIG. 4
shows a conventional vertical deflection yoke circuit, and the curve (a) in
FIG. 5
shows the impedance characteristics of this conventional vertical deflection yoke.
As shown in
FIG. 4
, the vertical deflection yoke comprises vertical deflection coils
60
installed in a color picture tube
70
, a convergence correction circuit
2
that uses a diode switch, and vertical coma aberration correction coils
209
a,
209
b,
209
c,
209
d,
210
a,
and
210
b.
The convergence correction circuit
2
comprises a resistor
201
and a resistor
202
, which are connected in series. Connected in parallel thereto is a series circuit including a diode
203
, a variable resistor
205
, and a diode
204
disposed in the same direction as the diode
203
. Further, a series circuit, including a diode
206
which is disposed in the direction reverse to the diode
203
, a variable resistor
208
and a diode
207
disposed in the same direction as the diode
206
, is connected in parallel to the series circuit including the resistors
201
and
202
. The convergence correction circuit
2
is a part of a vertical deflection circuit.
However, if such a convergence correction circuit is added to correct mis-convergence the impedance characteristics of the vertical deflection yoke
3
change abruptly near the center of the vertical deflection period, or in other words, near a deflection current value of 0 A, as shown by curve (a) in the center of FIG.
5
. This is due to an impedance change of the convergence correction circuit
2
in response to the voltage-current characteristics of the diodes
203
,
204
,
206
and
207
in the convergence correction circuit
2
. For this reason, the vertical deflection voltage that is supplied to the vertical deflection yoke cannot follow an impedance change of the vertical deflection yoke with respect to the deflection current, and the rate of the vertical deflection decreases near the vertical center of the color picture tube screen. Therefore, the vertical density of scanning lines near the vertical center of the screen increases, causing the problem that a white horizontal belt-like area appears on the screen.
This type of white belt-like area also has appeared with convergence correction circuits other than that explained in this prior art example, for example, in circuits where a correction means using the switching characteristics of a diode were added to the vertical deflection circuit.
SUMMARY OF THE INVENTION
It is an object of the present invention to solve the above-mentioned problem, that is, to provide a vertical deflection circuit for a color picture tube apparatus that can reduce the white horizontal belt-like area appearing near the vertical center of a color picture tube screen, caused by an operation of a convergence correction circuit using switching characteristics of a diode.
A vertical deflection circuit in accordance with the invention comprises a vertical deflection yoke and a vertical linearity correction circuit connected to the vertical deflection yoke. The vertical deflection yoke has a vertical deflection coil, a convergence correction circuit using a diode as a switch, and a vertical coma aberration correction coil. The impedance of the vertical linearity correction circuit varies within a range where the vertical deflection current is in the vicinity of 0 (zero) A so as to reduce the impedance of the vertical deflection circuit.
With this configuration, the abrupt increase in the impedance of the vertical deflection circuit near the vertical center of the color picture tube display can be avoided. Consequently, the white horizontal belt-like area that appears near the vertical center of a color picture tube screen can be reduced to a level where it causes practically no problem.
It is preferable that the vertical linearity correction circuit is connected in parallel to the vertical deflection yoke and comprises a first diode; a second diode connected in parallel to the first diode and disposed in a direction reverse to the first diode a first resistor connected parallel to the first diode and the second diode; and a second resistor connected in series to the first diode and the second diode.
With this configuration, the impedance of the vertical deflection yoke near the vertical center of the color picture tube screen can be reduced with the switching function of the diodes, which operate under both polarities of the vertical deflection voltage. In other words, by adjusting the combined resistances of the first resistor and the second resistor, the impedance of the vertical deflection yoke easily can be adjusted, and the impedance change of the vertical deflection yoke near the vertical center of the color picture tube screen can be decreased.
It is preferable that the first diode and the second diode have substantially the same voltage-current characteristics as the diode in the convergence correction circuit. With this configuration, the diodes of the convergence correction circuit are switched on and off simultaneously with the diodes of the vertical linearity correction circuit. Consequently, the impedance of the vertical deflection yoke near the vertical center of the present color picture tube screen can be effectively decreased.
It is preferable that at least one of the first resistor and the second resistor is a variable resistor. With this configuration, the impedance of the vertical deflection yoke easily can be adjusted to an optimum value by adjusting the resistance of the variable resistor while observing the screen of the color picture tube.
In accordance with the present invention, a color picture tube apparatus having a color picture tube with a built-in inline electron gun, includes a vertical deflection circuit. The circuit comprises a vertical deflection yoke mounted on the color picture tube and a vertical linearity correction circuit connected to the vertical deflection yoke. The vertical deflection yoke has a vertical deflection coil, a convergence correction circuit using a diode as a switch, and a vertical coma aberration correction coil. An impedance of the vertical linearity correction circuit varies within a range where a vertical deflection current is in the vicinity of 0 A so as to reduce the impedance of said vertical deflection circuit.
It is preferable that the vertical linearity correction circuit is connected in parallel to the vertical deflection yoke and comprises a first diode; a second diode connected in parallel to the first diode and disposed in a direction reverse to the first diode; a first resistor connected in parallel to the first diode and the second diode; and a second resistor connected in series to the first diode and the second diode.
Thus, with the present invention, the white horizontal belt-like area that appears near the vertical center of the color picture tube screen can be effectively reduced by suppressing the increase of the impedance o
Iwamoto Tomoaki
Uchida Yukio
Dinh Trinh Vo
Matsushita Electronics Corporation
Merchant & Gould P.C.
Wong Don
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