Television – Video display – Cathode-ray tube
Reexamination Certificate
1998-04-14
2001-10-02
Hsia, Sherrie (Department: 2614)
Television
Video display
Cathode-ray tube
C348S746000
Reexamination Certificate
active
06297861
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image adjusting circuit of a display monitor and, more particularly, to such an image adjusting circuit which is to compensate for pin/barrel-shaped and trapezoid image distortions by integrating the PWM signal generated from a microcomputer of the display monitor and applying the output waveform to a horizontal size adjusting circuit.
2. Discussion of Related Art
Conventionally, in a display monitor, an electron beam generated from a cathode and passing through a shadow mask strikes phosphors in response to the picture signals supplied from a computer, thereby emitting light to form a projected image on the screen of the display monitor. An example of such a display monitor is shown in FIG.
1
.
In
FIG. 1
, a personal computer
100
is comprised of a CPU
110
for processing a keyboard signal and thereby generating output data, and a video card
120
for processing the data received from the CPU
110
into an RGB video signal and further generating horizontal and vertical sync signals which are to synchronize the RGB video signal.
Display monitor
200
receives the RGB video signal and the horizontal and vertical sync signals from the video card
120
in the computer
100
. The display monitor
200
is comprised of a microcomputer
210
receptive to the horizontal and vertical sync signals, and discriminating a resolution; a control button section
220
for generating a screen control signal; a horizontal and vertical output circuit section
230
receptive to the screen control signal and a reference oscillating signal generated from the microcomputer
210
, and synchronizing a raster; a video circuit section
240
for processing the RGB video signal received from the video card
120
through amplification and displaying them; and a power supplying circuit section
250
for supplying a driving power to the microcomputer
210
, the horizontal and vertical output circuit section
230
, and the video circuit section
240
.
Following is a detailed description of the respective blocks in the display monitor
200
constructed as above.
Microcomputer
210
which stores all sorts of screen control data is receptive to the horizontal and vertical sync signals from the video card
120
, and generates an image adjusting signal and a reference oscillating signal in response to the screen control signal applied from the control button section
220
.
Receiving the image adjusting signal and the reference oscillating signal from the microcomputer
210
, a horizontal and vertical oscillating signal processor
231
supplies a vertical pulse to a vertical drive circuit
232
. The vertical pulse is to control the switching rate of a sawtooth wave generating circuit in response to the horizontal and vertical sync signals received from the video card
120
.
As regards vertical drive circuit
232
receptive to the vertical pulse, most widely used are two types of them; one-stage vertical amplification type and emitter follower type. The emitter follower type vertical drive circuit has the base of the transistor therein used as an input with the emitter functioning as an output. Hence, the vertical drive circuit
232
normally performs an operation for the improvement of linear characteristic not of the gain.
The vertical drive circuit
232
, after amplification, supplies a current signal to a vertical output circuit
233
, which will generate a sawtooth current corresponding to the vertical synchronizing pulse flowing through a vertical deflection yoke (V-DY), determining a vertical scanning period in response to the sawtooth current. In addition, a horizontal drive circuit
234
receives a horizontal oscillating signal from the horizontal and vertical oscillating processor
231
, and accordingly, provides a current sufficient to switch the horizontal output circuit
235
. Horizontal drive circuit
234
is divided into two classes; in-phase type whose output is ON with the drive terminal ON, and out-of-phase type having the output if OFF with the drive terminal ON.
Upon receipt of the current from the horizontal drive circuit
234
, the horizontal output circuit
235
will generate a sawtooth current to the horizontal deflection yoke (H-DY), determining a horizontal scanning period depending on the sawtooth current.
In order to supply a stable DC voltage to the anode of a cathode ray tube (CRT)
244
, a high voltage is generated even with a weak collector voltage by use of the feedback collector via a fly-back transformed (FBT)
237
and the harmonic wave resulting from the leakage inductance and the distribution capacity of high-voltage circuit
236
.
Thus generated high voltage is applied to the anode terminal
244
a
of the CRT
244
, forming a high voltage across the anodic surface of the CRT
244
so as to adjust the luminance of the RGB picture signals which have been amplified in the video circuit section
240
. Simultaneously, the video circuit section
240
has an OSD section
241
receiving an on-screen display (OSD) data generated during the screen control of the microcomputer
210
to generate an OSD gain signal.
This OSD gain signal from the OSD section
241
is sent to a video pre-amplifier
242
together with the RGB video signal from the video card
120
. The video pre-amplifier
242
amplifies the RGB video signal to a limited voltage level via a low-voltage amplifier.
For example, a signal less than 1 V
PP
is subject to an amplification to the voltage of 4-6 V
PP
via the video pre-amplifier
242
. This picture signal is further amplified to 40-60 V
PP
through a video main amplifier
243
and sent to the cathode of the CRT
244
for displaying an image.
The OSD signal is also amplified via the video pre-amplifier
242
and the video main amplifier
243
to display an OSD data on the screen of the CRT
244
. This OSD data displayed on the screen provides the user with information relating to the display monitor
200
.
Power supplying circuit section
250
, which is to provide a driving voltage required for displaying the RGB picture signals on the screen of the display monitor, receives AC voltage through an AC input
251
. The AC level is applied to a degaussing coil
252
, which resumes the color blotted due to the influence of the earth magnetic field or external environment.
For this, degaussing coil
252
disperses the magnetic field formed across the shadow mask in CRT
244
in order to prevent the electron beams from being deflected unstably, while the AC voltage is applied to the degaussing coil
252
momentarily for 2-8 seconds.
The AC is normally rectified into a DC through a rectifier
253
and sent to a switching transformer
254
. The switching transformer
254
supplies all sorts of driving voltage required in the monitor
200
through a voltage regulator
255
. At this stage, where there is no vertical sync signal applied from the video card
120
, the microcomputer
210
will send a suspend mode signal to a voltage regulator
255
to interrupt the deflecting voltage.
Pulse-width-modulation (PWM) section
256
controls the switching operation of the switching transformer
254
, varying the conduction time through PWM so as to stabilize the output voltage of the transformer.
The microcomputer
210
sets up a power-off mode and a suspend mode depending on the presence of horizontal and vertical sync signals in order to save the power consumed in the display monitor
200
.
Normally, such a conventional display monitor
200
as described above compensates an image distortion caused by the structure of the CRT
244
. In displaying the RGB picture signals on the screen, CRT
244
has the cathode (not shown) generate thermoelectrons and deflects the electron beams in response to the horizontal and vertical sync signals H/V-SYNC.
Since the cathode is disposed in the center of the quadrilateral screen, however, thermoelectrons deflected towards the outer edge of the CRT
244
are projected to the inappropriate positions, which leads to an image distortion.
An embodiment of a convent
Bushnell Robert E.
Hsia Sherrie
Samsung Electronics Co,. Ltd.
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