Circuit and method for adjusting width of fly-back pulse in...

Television – Synchronization – Sync separation

Reexamination Certificate

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Details

C348S540000, C315S384000

Reexamination Certificate

active

06788351

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a video signal processing unit used for a monitor, and more particularly, to a circuit and method for adjusting the width of a fly-back pulse, the apparatus and method being applied to a video signal processing unit realized in one chip.
2. Description of the Related Art
In general, a horizontal blank signal used for the purpose of blocking an electron beam during a horizontal retrace period of a monitor system is generated by receiving a fly-back pulse from an external horizontal deflection transformer. Conventionally, a video amplifier, an on-screen display (OSD) using a horizontal blank signal, and a horizontal/vertical synchronous signal processing unit using a fly-back pulse have been manufactured as separate chips.
FIG. 1
is a schematic block diagram illustrating a video signal processing unit where a conventional circuit for adjusting the width of a fly-back pulse is applied. The video signal processing unit includes a horizontal deflection transformer
10
, a fly-back pulse width adjustment circuit
12
, a video amplifier
14
, an OSD unit
16
, and a horizontal/vertical synchronous signal processing unit
18
.
The fly-back pulse width adjustment circuit
12
illustrated in
FIG. 1
receives a fly-back pulse (AFC) from the horizontal deflection transformer
10
, adjusts the width of the fly-back pulse, and outputs the adjusted pulse as a horizontal blank signal (H_BLK). The pulse width of the horizontal blank signal must be adjusted to agree with a retrace period of a horizontal deflection yoke. In most cases, the fly-back pulse is applied after a predetermined time delay, and consequently, the fly-back pulse has a wider width as compared with a real horizontal retrace period. Therefore, a conventional video signal processing unit has used a fly-back pulse which is received from the fly-back pulse width adjustment circuit
12
, the width of which is adjusted to properties of a monitor, as a horizontal blank signal. If the width of the horizontal blank signal is greater than the horizontal retrace period, the horizontal blank signal can invade a video signal region. On the contrary if the width is less than the horizontal retrace period, there may be interference in the video signal region caused by electron emission from an electron gun of a cathode ray tube (CRT). Therefore, the width of the blank signal must be adjusted appropriately.
FIG. 2
is a detail circuit diagram illustrating the fly-back pulse width adjustment circuit
12
illustrated in FIG.
1
. In this figure, the fly-back pulse width adjustment circuit includes capacitors C
21
, C
22
, and C
23
, resistors R
21
, R
22
, and R
23
, a diode D
21
, and a transistor Q
21
.
With reference to
FIG. 2
, each of the capacitors C
21
, C
22
, and C
23
has a very large capacity, because the fly-back pulse (AFC) is applied with a high voltage of several kilovolts. Accordingly the capacitors C
21
, C
22
, and C
23
cannot be built as one chip and must be provided as external components. Moreover, in the case of the fly-back pulse width adjustment circuit
12
of
FIG. 2
, the capacitors C
21
, C
22
, and C
23
and the resistors R
21
, R
22
, and R
23
have been set to have fixed values, so that there is a disadvantage that the width of a pulse is fixed. Consequently, it is difficult to manufacture a printed circuit board (PCB) with use of the fly-back pulse width adjustment circuit
12
which is provided as external components, thereby causing an additional increase of the manufacturing cost. In addition, there is another disadvantage that the width of a fly-back pulse must be adjusted to accommodate properties of newly introduced monitors.
SUMMARY OF THE INVENTION
To solve the above problems, it is an object of the present invention to provide a circuit for adjusting the width of a fly-back pulse which is built into a video signal processing unit realized as one chip and which can adjust the width of a fly-back pulse easily.
It is another object of the present invention to provide a method for adjusting the width of a fly-back pulse which is performed in the fly-back pulse width adjustment circuit.
Accordingly, to achieve the first object of the invention, there is provided a circuit for adjusting the width of a fly-back pulse which is applied in a video signal processing unit realized in one chip according to the present invention. The fly-back pulse width adjustment circuit is built into a video signal processing unit including a video amplifier, and on-screen display, and a horizontal/vertical synchronous signal processing unit within the video signal processing unit realized as one chip. The fly-back pulse width adjustment circuit generates a horizontal blank signal by adjusting the width of an external fly-back pulse, and comprises a pulse standardization unit which shapes a fly-back pulse input from the outside via an input terminal and applies the shaped fly-back pulse to the horizontal/vertical synchronous signal processing unit. A pulse width adjustment unit adjusts the width of the shaped fly-back pulse in response to a predetermined control signal, generates a horizontal blank signal whose occurrence time can be varied from the result of the adjustment in response to a selection signal into a horizontal blank signal occurring at a different time, and then applies the horizontal blank signal to the video amplifier and the on-screen display unit.
To achieve the second object of the invention, there is provided a method of adjusting the width of a pulse which is applied to the video signal processing unit realized as one chip according to the present invention. Preferably, the method of adjusting the width of a pulse adjusts the width of an external fly-back pulse and subsequently generates a horizontal blank signal within the video signal processing unit where a video amplifier, an on-screen display unit and horizontal/vertical synchronous processing unit have been realized as one chip. The method of adjusting the width of a fly-back pulse includes the steps of shaping the fly-back pulse received from the outside, determining whether a mid-point of the shaped fly-back pulse is detected, generating a lamp signal by charge pumping performed corresponding to a section of the fly-back pulse if the mid-point of the shaped fly-back pulse is detected, comparing the lamp signal with a predetermined reference voltage, thereby generating an output signal from the result of the comparison, and combining the comparison output signal and the shaped fly-back pulse, thereby generating a horizontal blank signal.


REFERENCES:
patent: 4767971 (1988-08-01), Onozawa et al.
patent: 5561354 (1996-10-01), Simons et al.
patent: 5714849 (1998-02-01), Lee
patent: 5894203 (1999-04-01), Lee
patent: 5917292 (1999-06-01), Marsanne
patent: 5932977 (1999-08-01), Woo
patent: 6034736 (2000-03-01), Chen
patent: 6236436 (2001-05-01), Muchenberger et al.
patent: 0528176 (1997-01-01), None
patent: 0503806 (1999-06-01), None
patent: 06197234 (1994-07-01), None

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