Television – Synchronization
Reexamination Certificate
2000-01-04
2004-10-12
Harvey, David E. (Department: 2714)
Television
Synchronization
C348S542000
Reexamination Certificate
active
06803965
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to method of and apparatus for measuring horizontal frequency, and more particularly, is directed to an improvement in method of and apparatus for measuring horizontal frequency of a video signal, which is supplied to, for example, an image display equipment operative to display images based on video signals, with making use of a horizontal synchronous signal contained in the video signal.
2. Description of the Prior Art
An image display equipment provided with an image displaying screen portion on which images based on video signals are displayed, may be supplied selectively with various kinds of video signals which are different from one another in horizontal frequency, a ratio of a video signal period to a horizontal period and so on. Accordingly, there has been proposed such an image display equipment as possessing a user preset function with which a user can set the apparatus to display on its image displaying screen portion images at a size of display appropriate to the video signal supplied to the equipment.
When the user preset function accompanying the image display equipment is actually exhibited for attaining its purpose, it is necessary to measure the horizontal frequency of the video signal supplied to the image display equipment. Therefore, the image display equipment which possesses the user preset function is also provided with an apparatus for measuring the horizontal frequency of the video signal supplied thereto.
FIG. 1
shows a previously proposed apparatus for measuring the horizontal frequency of a video signal. The apparatus shown in
FIG. 1
comprises an 8-bit counter
11
to which a horizontal synchronous signal SH separated from a video signal is supplied and which is operative to count horizontal synchronous pulses PH constituting the horizontal synchronous signal SH, a 16-bit counter
12
to which clock pulses CLK having a predetermined frequency are supplied to be counted, a data latch
13
for latching count date DCU obtained from the 16-bit counter
12
at a predetermined periodic timing,and a control unit
15
to which an overflow signal SOF obtained from the 8-bit counter
11
, latch data DLA which are the count data DCU latched by the data latch
13
and a vertical synchronous signal SV separated from the video signal are supplied.
The control unit
15
is not provided only for constituting the apparatus for measuring the horizontal frequency of the video signal. Accordingly, an input/output device
16
, an external memory device
17
and a peripheral apparatus
18
, which are not related directly to the apparatus for measuring the horizontal frequency of the video signal, are connected with the control unit
15
. The control unit
15
communicates with the input/output device
16
, external memory device
17
and peripheral apparatus
18
.
The counting operation of the 16-bit counter
12
for counting the clock pulses CLK is reset whenever the count date DCU overflows so that the 16-bit counter
12
counts continuously the clock pulses CLK as far as the clock pulses CLK are supplied thereto. When the vertical synchronous signal SV as shown in
FIG. 2A
is supplied to the control unit
15
, the control unit
15
supplies the 8-bit counter
11
with a clear control signal CCL to reset the counting operation of the 8-bit counter
11
and supplies also the date latch
13
with a latch control signal CLA to cause the date latch
13
to latch anew the count data DCU obtained on that occasion from the 16-bit counter
12
at a time point t1 at which a predetermined waiting time T0 has passed after a time point t0 corresponding to the front edge of the vertical synchronous signal SV. The waiting time T0 is selected to correspond to a period which contains equalizing pulses and notching pulses appearing in the horizontal synchronous signal SH after the time point t0 as shown in FIG.
2
B.
At the time point t1, the 8-bit counter
11
starts to count anew the horizontal synchronous pulses PH appearing in the horizontal synchronous signal SH after the time point t1 as shown in
FIG. 2B
to form count data DCT of the horizontal synchronous pulses PH as shown in FIG.
2
C.
The data latch
13
latches the count data DCU obtained from the 16-bit counter
12
at the time point t1 and supplies the control unit
15
with the latch data DLA showing continuously a counted value Na represented by the count data DCU latched by the data latch
13
as shown in FIG.
2
E. The control unit
15
to which the latch data DLA is supplied from the data latch
13
is operative to store the latch data DLA in a memory device contained therein.
After that, the 8-bit counter
11
produces the overflow signal SOF having its front edge at a time point t2 as shown in
FIG. 2D
to be supplied to the control unit
15
when the counted value represented by the count data DCT has exceeded “255”.
The control unit
15
to which the overflow signal SFO is supplied from the 8-bit counter
11
supplies again the data latch
13
with the latch control signal CLA to cause the data latch
13
to latch anew the count data DCU obtained from the 16-bit counter
12
at a time point t3 at which a lag time &Dgr;T resulting from a time required for data processing in the control unit
15
has passed after the time point t2. The data latch
13
latches the count data DCU obtained on that occasion from the 16-bit counter
12
at the time point t3 and supplies the control unit
15
with the latch data DLA showing continuously a counted value Nb represented by the count data DCU latched by the data latch
13
as shown in FIG.
2
E. The control unit
15
to which the latch data DLA is supplied from the data latch
13
is operative to store the latch data DLA in the memory device contained therein.
After the latch data DLA showing continuously the counted value Nb are stored in the memory device contained in the control unit
15
, the control unit
15
calculates the difference between the counted value Nb and the counted value Na which is shown by the latch data DLA stored previously in the memory device contained in the control unit
15
, and detects a period corresponding to 256 times the horizontal period of the video signal. Then, the control unit
15
further calculates the horizontal frequency of the video signal by obtaining an inverse of {fraction (1/256)} the value representing the detected period corresponding to 256 times the horizontal period. In such a manner as described above, the horizontal frequency of the video signal is measured in the control unit
15
.
As for the aforementioned image display equipment accompanied with the user preset function, it is desired for sure exhibition of the user preset function that the horizontal frequency of the video signal used in the equipment is precisely measured in such a manner that an error in measurement is restrained to be, for example, less than ±0.2 KHz. However, in the previously proposed apparatus for measuring the horizontal frequency of a video signal as described above, it cannot be expected to measure precisely the horizontal frequency of the video signal supplied to the apparatus.
In the case of the previously proposed apparatus mentioned above, the difference between the counted value Nb and the counted value Na calculated in the control unit
15
includes theoretically a first error of one count arising in the 16-bit counter
12
which counts the clock pulses CLK, a second error of one count at the maximum arising in the 8-bit counter
11
which results from the fact that the count data DCU obtained from the 16-bit counter
12
are latched by the data latch
13
at the time point t1 at which the waiting time T0 has passed after the time point t0 corresponding to the front edge of the vertical synchronous signal SV, and a third error which corresponds to the lag time &Dgr;T from the time point t2 corresponding to the front edge of the overflow signal SOF obtained from the 8-bit counter
11
to the time point t3 at which the count data DC
Takegoshi Hirotaka
Yamazaki Nobuo
Frommer William S.
Frommer & Lawrence & Haug LLP
Harvey David E.
LandOfFree
Method of and apparatus for measuring horizontal frequency does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of and apparatus for measuring horizontal frequency, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of and apparatus for measuring horizontal frequency will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3260503