Television – Synchronization – Sync generation
Reexamination Certificate
2000-09-21
2003-07-22
Miller, John (Department: 2614)
Television
Synchronization
Sync generation
C348S524000, C348S531000, C348S540000
Reexamination Certificate
active
06597403
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multi-scan compatible horizontal synchronizing signal generating system for making a horizontal synchronizing signal compatible with multi-scan by generating a predetermined horizontal deflection frequency in a television receiver, a monitor apparatus or the like.
2. Description of the Related Art
As television horizontal deflection frequency generating system, there have hitherto been known not only the television system such as the standard NTSC system and the PAL system but also an EDTV (Extended Definition TV) system for displaying a non-interlaced image by line-doubling an existing NTSC image and a line-doubling system which might be called a flicker-free system for removing a flicker in the PAL system, for example. Also, broadcasting based on a MUSE (Multiple Sub-Nyquist Sampling Encoding) has already been started. From such background, television receivers corresponding to both systems of the MUSE system and the NTSC system have been known.
Then, the above-mentioned systems have different horizontal deflection frequencies. The standard NTSC system has a horizontal deflection frequency of 15.734 kHz and the PAL system has a horizontal deflection frequency of 15.625 kHz. Moreover, since the EDTV system and the line-doubling system of the line-doubling or field-doubling system based on the NTSC, the PAL including the flicker-free system require a horizontal deflection frequency twice as high as those of the standard NTSC, PAL system, the line-doubling system based on the NTSC system (including the EDTV system) requires a horizontal deflection frequency of twice as high as that of the standard NTSC system, 15.734×2=31.468 kHz. Moreover, the line-doubling system based on the PAL system such as the flicker-free system requires a horizontal deflection frequency twice as high as that of the standard PAL system, 15.625×2=31.25 kHz. Furthermore, the MUSE system requires a horizontal deflection frequency of 33.75 kHz.
As described above, when various kinds of television systems become available, although different systems have different horizontal deflection frequencies, a horizontal deflection frequency generating apparatus should preferably be made common from a manufacturing cost standpoint. It was very difficult to form a horizontal deflection frequency generating circuit which may be made compatible with all of the above-mentioned horizontal deflection frequencies of various kinds of television system.
There have hitherto been known two methods of generating a horizontal deflection frequency in a television receiver compatible with a computer display or a point (fixed) frequency.
Initially, a first method is to generate a sawtooth signal by charging and discharging electric charges of a capacitor.
FIG. 1
shows its fundamental system diagram. Reference letter C denotes a capacitor to and from which electric charges are charged and discharged. Current sources I
0
, I
1
to which a current flows may be selected by a switch SW. When the current source I
1
is selected, a terminal voltage V increases.
When the terminal voltage V becomes higher than a voltage V
1
, a comparator
1
connects the switch SW to the opposite side to thereby select the current source I
1
. As a consequence, the terminal voltage V decreases. When the terminal voltage V becomes less than the voltage V
0
, a comparator V
0
connects the switch SW to the current source I
1
side again to thereby select the current source I
1
. After a series of operations were repeated, the terminal voltage V has a sawtooth wave shown in FIG.
1
B. The signal thus generated can be used as a fundamental signal of a horizontal deflection signal.
The sawtooth wave of
FIG. 1B
generated by the first method shown in
FIG. 1
is set to the same frequency as the horizontal deflection frequency or a multiplied frequency. In order to make the first method correspond to the multi-scan, if the current values of the charge and discharge current sources I
0
, I
1
increase, then an oscillation frequency increases. Therefore, if angles at which a sawtooth voltage increases or decreases are changed as shown in
FIGS. 2A
,
2
B, then a fundamental frequency is changed so that the first method can be made corresponding to the multi-scan.
However, according to the first method, a problem of jitter performance cannot be neglected. Since a noise is entered into the current sources I
0
, I
1
due to an action of thermal noise from an element, which may determine the reference potentials V
0
, V
1
and the oscillation frequency, it becomes very difficult to use such sawtooth wave signal as a horizontal deflection signal which may be sensitive to the jitter performance. Therefore, there have been adopted various countermeasures such that the values of the current sources I
0
, I
1
are increased considerably in order to make an apparent noise level become small and the capacitance of the capacitor C should be increased as well in order to prevent the oscillation frequency from increasing. However, as the capacitance of the capacitor C increases, the area of an integrated circuit increases, and a power consumption increases unavoidably. In practical design, it should be executed in such a manner that the capacitance of the capacitor C and the current values of the current sources I
0
, I
1
should be suppressed to be small to the extent that a jitter performance may not be degraded. However, since the capacitance of the capacitor and the current values of the current sources are designed to be as small as possible, in actual trial manufacturing, unavoidably, there invariably arises a problem that a jitter performance cannot be improved as it is expected.
Moreover, the biggest defect of this method is that this method requires an adjustment. The capacitance of the capacitor C and the current values of the reference potentials V
0
, V
1
and the current sources I
0
, I
1
should be constantly fluctuated because their components are assembled as integrated circuits. That is, some integrated circuits have a large capacity but other integrated circuit has a small capacity. Therefore, if the above-mentioned integrated circuits are oscillated according to the first method, then their frequencies are unavoidably fluctuated, and the integrated circuits are caused to output different oscillation frequencies. To solve this problem, when such integrated circuits are designed, it is customary that the oscillation frequencies should be adjusted. Thus, after such integrated circuit is mounted on the computer display or the television receiver, the oscillation frequency should be adjusted, which therefore leads to an increase in the manufacturing cost.
Next, a second method is such one in which an oscillator such as a ceramic is used to generate a clock having a reference oscillation frequency f
0
without fluctuations and this clock is counted in descending order such that this clock may become a horizontal deflection frequency.
FIG. 3
is a block diagram to which reference will be made in explaining this method. An oscillator
101
which oscillates a reference clock may include a ceramic or crystal piezoelectric transducer member having a high Q (a measure of sharpness of piezoelectric transducer system) as an oscillation element. A clock without fluctuations may be generated from the oscillator
101
. When a counter
102
counts this oscillation frequency f
0
by a value which results from dividing this oscillation frequency with a horizontal deflection frequency fh in a descending order, there can be generated a horizontal deflection clock. It is natural that this method need not adjust the oscillation frequency.
However, the arrangement of this method cannot be made compatible with multi-scan (synchronizing signal generating system compatible with a variety of frequencies if frequencies fall within a determined frequency range). For this reason, in order to make the second method become compatible with the multi-scan, there are further illus
Miura Satoshi
Nagamine Takatomo
Takahashi Shinji
Frommer William S.
Frommer & Lawrence & Haug LLP
Miller John
Sony Corporation
Tran Trang U.
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