Electric lamp and discharge devices: systems – Cathode ray tube circuits – Compensating for stray deflecting fields
Reexamination Certificate
2003-05-30
2004-12-14
Tran, Thuy V. (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Compensating for stray deflecting fields
C315S367000, C315S382000, C348S806000
Reexamination Certificate
active
06831415
ABSTRACT:
BACKGROUND OF THE INVENTION
This application claims the priority of Korean Patent Application No. 2002-36070, filed Jun. 26, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a circuit and method for controlling the vertical and horizontal sizes of a screen of a cathode ray tube (CRT) monitor, and more particularly, to a circuit for controlling the vertical and horizontal sizes of the screen of a CRT monitor in order to compensate for changes in the vertical and horizontal screen sizes of a CRT monitor due to variations in high voltage in the CRT monitor.
2. Description of the Related Art
CRT monitors are commonly receive a power supply voltage from a switched mode power supply (SMPS), which is a form of a power supply circuit.
Here, since the anode of the CRT monitor requires a high voltage, the highest voltage among power supply voltages output from the SMPS is usually stepped up by a flyback transformer (FBT) and the stepped-up voltage is applied to the anode.
However, when high voltage is generated using the FBT, if the level of the high voltage is decreased or fluctuates even slightly, the horizontal and vertical sizes of the screen of the monitor can become distorted. That is, a variation in the level of the high voltage directly affects the horizontal and vertical sizes of the screen of a monitor.
FIG. 1
is a block diagram of the internal structure of a typical CRT monitor. Referring to
FIG. 1
, a CRT monitor
100
includes a microcomputer (MICOM)
110
, a sync processor
120
, horizontal and vertical drivers
125
and
130
, a video amplifier (video amp)
165
, a video driver
170
, an electron gun
175
, vertical and horizontal deflection coils
185
and
190
, a CRT
180
, a deflection regulator
135
, a B+ voltage generator
140
, a switching power circuit
145
, a high voltage regulator
150
, a FBT
160
, and an anode
195
.
The sync processor
120
receives a vertical synchronization signal VIN and a horizontal synchronization signal HIN and generates a vertical output signal VOUT, a horizontal output signal HOUT, and an east-west correction signal EWOUT under the control of the MICOM
110
.
The horizontal driver
125
controls the horizontal deflection coil
190
in response to the horizontal output signal HOUT in order to control the horizontal size of the screen of a monitor
180
. The vertical driver
130
controls the vertical deflection coil
185
in response to the vertical output signal VOUT in order to control the vertical size of the screen of the monitor
180
.
A color signal RGB is applied to the electron gun
175
via the video amp
165
and the video driver
170
.
The deflection regulator
135
is controlled by the SMPS
145
and controls the B+ voltage generator
140
in response to the east-west correction signal EWOUT. The FBT
160
is controlled by the high voltage regulator
150
and applies high voltage to the anode
195
.
The CRT monitor
100
generates a high voltage to form a magnetic tunnel and projects electrons output from the electron gun
175
through the formed magnetic tunnel to the screen. If a change in the level of the high voltage occurs due to an overload or if a characteristic change due to a high temperature occurs when the high voltage is generated, the screen becomes distorted and the quality of an image is therefore deteriorated.
The sync processor
120
performs various operations to compensate for the anticipated distortion of the screen and the degradation of the image quality. In particular, when the screen is distorted due to a decrease in the DC voltage of the generated high voltage, the sync processor
120
performs extreme high transformer (EHT) compensation to compensate for such distortion.
Generally, the horizontal size of the screen is controlled based on the DC voltage of an east-west correction signal, and the vertical size of the screen is controlled based on the gain of the vertical output signal VOUT output from the sync processor
120
. EHT compensation controls the DC voltage of the east-west correction signal EWOUT and the gain of the vertical output signal VOUT.
To be more specific, the output of the high voltage regulator
150
is fed back as a DC voltage to the sync processor
120
. The sync processor
120
controls the level of the DC voltage of the east-west correction signal EWOUT using the fed-back DC voltage in order to compensate for the horizontal size of the monitor screen. Also, the sync processor
120
controls the vertical output signal VOUT in order to compensate for the vertical size of the monitor screen.
The horizontal size of the monitor screen is controlled using the DC voltage component of the east-west correction signal EWOUT, which is generally used to correct the geometry of the right and left sides of the screen. That is, the alternating current (AC) component of the east-west correction signal EWOUT is used for geometry correction.
The vertical size of the monitor screen is controlled based on the gain of the vertical output signal VOUT, and the DC voltage of the vertical output signal VOUT controls screen shifting.
During EHT compensation, the horizontal size of the screen is controlled according to a horizontal screen size correction signal HEHT, and the vertical size of the screen is controlled according to a vertical screen size correction signal VEHT.
However, since a typical CRT monitor pre-determines the degree of EHT compensation to be controlled, uniform compensation is applied for a variety of CRT monitors.
FIG. 2
is a graph showing the characteristics of conventional HEHT compensation. The horizontal size correction signal HEHT in the high voltage regulator
150
does not affect the CRT monitor system when the voltage value of the horizontal size correction signal HEHT is greater than or equal to the level of a horizontal reference voltage REFEHT that is set to be a threshold voltage.
As the voltage value of the horizontal size correction signal HEHT decreases below that of the horizontal reference voltage REFEHT, the amount of current of a horizontal current signal IO needed for compensating for the horizontal size of a monitor screen increases. When the voltage value of the horizontal size correction signal HEHT is 0V, the amount of current of the horizontal current signal IO is at a maximum.
In other words, the current value of the horizontal current signal IO increases in proportion to the difference between the voltage value of the horizontal size correction signal HEHT and the voltage value of the horizontal reference voltage REFEHT. The compensation characteristics of
FIG. 2
also apply to the characteristics of a vertical size correction signal VEHT.
However, as can be seen from the graph of
FIG. 2
, since the degree of EHT compensation (i.e., the slope of the straight line of
FIG. 2
) to be pre-set in a CRT monitor is fixed, uniform compensation is applied to a variety of CRT monitors. For this reason, CRT monitor manufactures are not able to apply compensation that depends on unique and specific requirements of each particular CRT unit.
SUMMARY OF THE INVENTION
The present invention provides a circuit for controlling the vertical and horizontal screen sizes of a cathode ray tube (CRT) monitor by variably adjusting the degree of extreme high transformer (EHT) compensation.
The present invention also provides a method of controlling the vertical and horizontal screen sizes of a CRT monitor by variably adjusting the degree of EHT compensation.
According to an aspect of the present invention, there is provided a circuit for controlling the horizontal and vertical sizes of a screen of a cathode ray tube (CRT) monitor, the circuit including a horizontal screen size compensation circuit, an east-west correction signal controller, a vertical screen size compensation circuit, and a vertical screen size correction signal controller.
The horizontal screen size compensation circuit compares the voltage value of a horizo
Mills & Onello LLP
Samsung Electronics Co,. Ltd.
Tran Thuy V.
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